EP3664935A1

EP3664935A1 - Iron supported catalyst comprising a ca-deficient hydroxyapatite for waste gas treatment

Info

Publication number: EP3664935A1
Application number: EP18752485.5A
Authority: EP
Inventors: Thierry Delplanche; Antonella Gervasini
Original assignee: Solvay SA
Current assignee: Solvay SA
Priority date: 2017-08-09
Filing date: 2018-08-08
Publication date: 2020-06-17
Also published as: WO2019030278A1

Abstract

A catalyst composition for catalytic reduction of NOx compounds, comprising Fe deposited on a porous support comprising at least 60 wt % of a calcium-deficient hydroxyapatite having a Ca/P molar ratio of less than 1.67. The support preferably has a specific BET surface area of at least 110 m2/g and a pore volume of at least 0.5 cm3/g, both measured after heat treatment at 200°C. The catalyst composition may be brought into contact in a fixed or fluidized bed or by injection with a NOx-containing waste gas stream at a temperature of at least 100°C and preferably at most 600°C to carry out, in the presence of 02, a reduction by NH3 of at least a portion of the NOx. The process may further include injecting an alkali sorbent into the waste gas stream to remove other contaminants such as heavy metals and/or acid gases with the alkali sorbent. A blend comprising the alkali sorbent and the deNOx catalyst may be formed to treat the waste gas stream. The ammonia may be injected into the waste gas or may be included in the alkali sorbent and/or the deNOx catalyst.

Description

Iron Supported Catalyst comprising a Ca-Deficient Hydroxyapatite for Waste

Gas Treatment

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to U.S. provisional application No.

62/543099 filed August 9, 2017, the whole content of this application being incorporated herein by reference for all purposes.

TECHNICAL FIELD

The invention pertains to the field of selective catalytic reduction catalysts. Particularly, embodiments of the invention relate to an iron-containing supported catalyst on a support material comprising hydroxyapatite having high BET surface area and pore volume and to methods to using such catalyst in a process for waste gas purification treatment. More particularly, embodiments of the invention relate to a DeNOx catalyst for the removal of nitrogen oxides (NOx) from a waste gas effluent generated by a combustion process, for example from a flue gas stream originating from a stationary combustion source.

BACKGROUND

When burning fossil fuels to produce energy, one typically uses a high temperature combustion process in the presence of air. Unfortunately, this type of process produces both nitrogen oxides (NOx), which are well-known pollutants, and other components that are harmful to health or the environment, such as carbon monoxide, sulfur oxides (SOx), volatile heavy metals, and unburned hydrocarbons. Thus, it is important to remove these materials prior to their release into the environment.

There have been many investigations into methods that allow for the removal of these substances. Combustion modifications and adsorption techniques can be used for this removal, but may suffer from limited maximum removal of pollutants such as NOx and limited capacity. A method for addressing the problem of noxious exhaust gases is catalytic removal, which by comparison, is extremely effective in removing large proportions of unwanted exhaust components and is capable of treating very large volumes of exit gases for long periods of time.

Selective catalytic reduction (SCR) has been one of the most effective technologies for removing NO (the main nitrogen oxide formed at high temperature) from a waste gas effluent originating from a stationary or mobile combustion source. Stationary combustion sources are mainly utility boilers, industrial boilers, incinerators, and cogeneration turbines. Mobile combustion sources are mainly vehicles such as automobiles, trucks.

The SCR process is widely used for example in the U.S., Japan, and Europe to reduce emissions of large utility boilers and other commercial applications. Increasingly, SCR processes are being used to reduce emissions in mobile applications such as in large diesel engines like those found on ships, diesel locomotives, automobiles and the like.

In order to effect the reduction of NOx in waste combustion gases through catalytic reduction processes, it is necessary either to introduce a reducing agent, such as ammonia, and/or to use the unburned hydrocarbons present in the waste gas effluent. The SCR process generally provides the reduction of NOx, (NO, N₂0 and NO₂) species using the reducing agent (e.g., ammonia) in the presence of oxygen and a catalyst to produce molecular nitrogen and water.

Selective catalytic reduction (SCR) of NO by NH₃ as reducing agent in the presence of O₂, that causes the formation of NO₂ (from the parent NO) in the gas reagent mixture, is a complex reaction can be schematized with the following series of main reactions (I) and (II):

4 NO + 4 NH₃ + 0₂→ 4 N₂ + 6 H₂0 (I)

2 N0₂ + 4 NH₃ + 0₂→ 3 N₂ + 6H₂0 (II)

Other common reactions that could be taken into account when low 02 concentration is present in the gas mixture are the following reactions (III) and (IV):

NO + N0₂ + 2NH₃→ 2 N₂ + 3 H₂0 (III)

6 N0₂ + 8 NH₃→ 7N₂ + 12 H₂0 (IV).

At temperatures around 300-350°C, competition between the reaction of NO reduction by NH₃ and the reaction of NH3 oxidation by oxygen forming NO and/or N₂ and/or N₂O can occur, according to the following reactions (V) to (VII):

4 NH₃ + 5 0₂→ 4 NO + 6 H₂0 (V)

2 NH₃ + 2 0₂→ N₂0 + 3 H₂0 (VI)

4 NH₃ + 3 0₂→ 2 N₂ + 6 H₂0 (VII).

These last reactions (V) to (VII) sequestrate NH₃, the reducing agent, to the SCR process: they are in competition with the previous reactions of NOx reduction. The occurrence of these reactions (V) to (VII) is responsible for the observation of a maximum of the conversion curve of the NOx species as a function of reaction temperature; that is to say, the rate of NOx (NO+N0₂) reduction is not continuously increasing with temperature because, staring from a defined temperature, the concentration of the reducing agent (NH₃) decreases due to its oxidation by oxygen.

The SCR process is a competitive reaction scheme constituted by series of parallel reactions, the kinetics of each reaction and its dependence on

temperature has to be exploited in order to selectively obtain NO reduction by ammonia and to avoid ammonia oxidation by oxygen. Finding a catalytic system to selectively obtain NO reduction by ammonia in a large temperature interval is thus challenging.

Various catalysts have been used in the SCR processes. Catalysts, including various metals, transition metal oxides, and mixed metal oxides have been employed for NO reduction. Initial catalysts, which employed platinum or platinum group metals, were found unsatisfactory because of the need to operate in a temperature range in which explosive ammonium nitrate forms. In response to environmental regulations in Japan, the first vanadium/titanium SCR catalyst was developed, which has proven to be highly successful. Further development has resulted in the development of vanadium catalyst deposited on titanium oxide/tungsten oxide support material.

Metal-promoted zeolite catalysts including, among others, iron-promoted and iron-promoted zeolite catalysts, for the selective catalytic reduction of nitrogen oxides with ammonia are known.

Zeolites are aluminosilicate crystalline materials having rather uniform pore sizes which, depending upon the type of zeolite and the type and amount of cations included in the zeolite lattice, range from about 3 to 10 Angstroms in diameter.

Iron-promoted zeolite beta (US 4961917) has been an effective commercial catalyst for the selective reduction of nitrogen oxides with ammonia.

Unfortunately, it has been found that under harsh hydrothermal conditions, for example exhibited during regeneration of a soot filter with temperatures locally exceeding 700° C, the activity of many metal-promoted zeolites begins to decline. This decline is often attributed to dealumination of the zeolite and the consequent loss of metal-containing active centers within the zeolite.

The catalysts employed in the SCR process ideally should be able to retain good catalytic activity over the wide range of temperature conditions of use, for example, from 200 °C to 600 °C or higher, preferably under hydrothermal conditions since water is generated during NOx reduction (see reactions (I) and (II) above). Hydrothermal conditions are also encountered in practice, such as during the regeneration of a soot filter, a component of the exhaust gas treatment system used for the removal of particles.

Despite the various catalysts being developed such as the zeolite supported catalysts, there exists a need for lower cost catalysts that provide and maintain high catalytic activity in the SCR reaction, especially for once-through applications in which the catalyst is injected into a waste gas stream and where the contact time between the supported catalyst and NOx may be short in the order of a second to a few minutes.

SUMMARY OF INVENTION

An embodiment of the present invention relates to a catalyst composition for catalytic reduction of NO_x compounds, comprising an active catalyst component deposited on a porous support;

wherein said active catalyst component comprises iron; and

wherein said porous support comprises at least 60 wt % of a calcium- deficient hydroxyapatite having a calcium to phosphate molar ratio (Ca/P) of less than 1.67, preferably more than 1.5 and less than 1.67;

said porous support having a specific BET surface area of at least 110 m²/g and a pore volume of at least 0.5 cm³/g both measured after heat treatment at 200°C.

In preferred embodiment of the present invention, the porous support in the catalyst composition may further comprise calcium carbonate in an amount of less than 20 wt%, preferably from 1 wt% to 19 wt%, more preferably from 2 wt% to 18 wt%, even more preferably from 5 wt% to 15 wt%, yet even more preferably from 7 wt% to 13 wt%, most preferably from 8 wt% to 12 wt%.

In preferred embodiment of the present invention, the porous support in the catalyst composition may further comprise less than 1 wt% of calcium

dihydroxide Ca(OH)₂, preferably less than 0.5 wt% calcium dihydroxide Ca(OH)₂, more preferably less than 0.3 wt% calcium dihydroxide Ca(OH)₂, even more preferably less than 0.2 wt% calcium dihydroxide Ca(OH)₂, most preferably being substantially free of calcium dihydroxide Ca(OH)₂.

In preferred embodiment of the present invention, the porous support in the catalyst composition before deposition of the active catalyst component on its surface may further comprise water in an amount of less than 20 wt%, preferably from 1 wt% to 18 wt%, more preferably from 2 wt% to 15 wt%, even more preferably from 4 wt% to 12 wt%, yet even more preferably from 5 wt% to 11 wt% most preferably from 6 wt% to 11 wt%.

In some preferred embodiments, the porous support in the catalyst composition is substantially free of carbon, i.e., less than 0.5 wt% of carbon.

In some other embodiments, the porous support in the catalyst composition may comprise carbon for example in an amount of at least 0.5 wt% carbon but in an amount of less than 7 wt% carbon, preferably less than 6 wt% carbon, more preferably less than 5 wt% carbon or less than 4 wt% carbon.

In some preferred embodiments, the porous support in the catalyst composition is substantially free of bone char. "Bone char" (also called "bone charcoal") refers to a porous, black, granular material produced by charring animal bones. Its composition varies depending on how it is made. Bones (especially cow bones) are heated in a sealed vessel at up to 700 °C (1,292 °F); a low concentration of oxygen is maintained during heating, as oxygen content affects the quality of the bone char product, particularly its adsorption capacity. Most of the organic material in the bones is driven off by heat. Bone char generally contains 7-10% carbon.

In some embodiment of the present invention, the porous support in the catalyst composition may comprise a Ca/P molar ratio of 1.60 or more, preferably of 1.65 or more, preferably of 1.67 or more, more preferably of 1.68 or more.

The porous support in the catalyst composition may comprise a Ca/P molar ratio greater than the Ca/P molar ratio of the calcium-deficient hydroxyapatite.

The porous support in the catalyst composition may comprise at least 65 wt%, preferably at least 70 wt%, more preferably at least 75 wt%, yet more preferably at least 80 wt%, yet most preferably at least 85 wt%, of the calcium- deficient hydroxyapatite,

and/or

- at most 99 wt%, preferably at most 98 wt%, more preferably at most 97 wt%, yet more preferably at most 95 wt%, even more preferably at most 93 wt%, most preferably at most 91 wt% of the calcium-deficient hydroxyapatite.

The porous support in the catalyst composition may have a BET specific surface area measured after heat treatment at 200°C of at least 120 m²/g and/or at most 160 m²/g. In some preferred embodiments, the porous support in the catalyst composition contains less than 1 wt% of magnesium.

The porous support in the catalyst composition may have a BET specific surface area measured after heat treatment at 400°C of at least 60 m²/g and/or at most 100 m²/g.

The porous support in the catalyst composition may have a pore volume measured after heat treatment at 200°C of at least 0.55 cm³/g, preferably of at least 0.55 cm³/g and/or at most 1.0 cm³/g, preferably of at most 0.95 cm³/g.

The porous support in the catalyst composition may have a pore volume measured after heat treatment at 400°C of at least 0.50 cm³/g, preferably of at least 0.60 cm³/g and/or of at most 1 cm³/g.

The active catalyst component may comprise

- at least 0.5 wt%, preferably at least 0.7 wt%, more preferably at least 1.0 wt%, most preferably at least 1.5 wt%, of iron;

and/or

- at most 15 wt%, preferably at most 13 wt%, more preferably at most 12 wt%, most preferably at most 11 wt%, of iron.

The active catalyst component may be deposited on the porous support by ion exchange or impregnation, preferably by ion exchange.

The active catalyst component may be deposited on the porous support using an iron precursor selected from the group consisting of iron nitrate, iron chloride, iron perchlorate, iron sulfate, iron fluorosilicate, any hydrated form thereof, and any mixture thereof. The iron precursor may include Fe³⁺ or Fe²⁺, preferably Fe³⁺. The iron precursor is preferably selected from the group consisting of iron (III) nitrate, iron (III) chloride, iron (III) sulfate, iron (III) perchlorate, any hydrated form thereof, and any mixture thereof.

If a solution containing the iron precursor is used, the solution preferably uses a solvent such as water. The iron precursor is preferably selected to be soluble in that solvent. For example, when the solvent is water, the solution pH may be adjusted in order to increase the solubility of the iron precursor.

The catalyst may be subjected to a heat treatment using a temperature from 105°C up to 500°C, prior to being used as a catalyst.

The catalyst composition may have a BET specific surface area measured after being calcined at 400°C of at least 65 m²/g and/or at most 100 m²/g.

The catalyst composition may have a pore volume measured after being calcined at 400°C of: - at least 0.3 cm³/g, preferably of at least 0.41 cm³/g, and/or

- at most 1.1 cm³/g, preferably of at most 1.0 cm³/g, more preferably of at most 0.9 cm³/g. most preferably of at most 0.8 cm³/g.

Another aspect of the present invention relates to a process for treating a waste gas stream containing nitrogen oxides (NOx), said gas stream originating from a combustion process, in which an ammonia source is injected into the waste gas stream; and in which the catalyst composition according to any embodiments of the present invention is brought into contact with the waste gas stream containing ammonia at a temperature of at least 100°C and preferably at most 600°C to carry out, in the presence of 0₂, a reduction by NH₃ of at least a portion of the NOx to N₂ and water.

In the process, the waste gas stream temperature is at least 105 °C, or at least 120 °C, or at least 150 °C, or at least 180 °C, or at least 200 °C, or at least 250 °C, or at least 300 °C; and/or at most 550 °C, or at most 500 °C, or at most 450 °C, or at most 400 °C.

In some embodiment of the process for treating a waste gas stream containing NOx, the catalyst composition may be injected into the waste gas stream in the form of a dry powder injection or a semi-dry injection of a slurry of the catalyst to provide contact of the catalyst with the waste gas.

In some embodiment of the process for treating a waste gas stream containing NOx, the catalyst composition may be packed into a fixed bed in order for the waste gas stream passes through the bed of the catalyst to provide contact of the catalyst with the waste gas.

In some embodiment of the process for treating a waste gas stream containing NOx, the catalyst composition may be fluidized in a fluidized bed to provide contact of the catalyst with the waste gas. The fluidization gas to maintain the catalyst particles suspended in the fluidized bed may comprise or consist of the waste gas stream to be treated.

Another aspect of the present invention relates to a multi-pollutant treatment process for treating a waste gas stream containing nitrogen oxides (NOx) and contaminants selected from the group consisting of heavy metals, acid gases (such as S0₂, S0₃, H₃P0₄, HC1, HI, HBr, and/or HF) HI, H₃P0₄, and/or heavy metals like an element selected from the group consisting of : Al, Ag, As, Ba, Be, Bi, Ce, Co, Cd, Cu, Cr, Fe, Hf, Hg, La, Li, Mg, Mn, Mo, Ni, Pb, Pd, Rb, Sb, Se, Sn, Sr, Th, Ti, U, V, Y, Zn, and Zr, and combinations thereof, said waste gas stream originating from a combustion process. Such multi-pollutant treatment process may comprise:

injecting an alkali sorbent into the waste gas stream, said alkali sorbent comprising a compound selected from the group consisting of sodium

bicarbonate, sodium carbonate, sodium sesquicarbonate (trona), quick lime, hydrated lime, limestone, and combinations thereof, preferably selected from the group consisting of sodium bicarbonate, sodium carbonate, sodium

sesquicarbonate (trona), and combinations thereof;

contacting at least a portion of the contaminants with the alkali sorbent to remove at least a portion of the contaminants from the waste gas stream,

injecting an ammonia source into the waste gas stream;

injecting a catalyst into the waste gas stream; and

converting, in the presence of 0₂, by reduction with NH₃ of at least a portion of the NOx in the waste gas stream to N₂ and water at a temperature of at least 100°C and preferably at most 600°C,

wherein the catalyst comprises an active catalyst component deposited on the porous support (as described in any of the embodiments herein);

wherein said active catalyst component comprises iron; and

wherein said porous support comprises at least 60 wt % of a calcium- deficient hydroxyapatite having a calcium to phosphate molar ratio (Ca/P) of less than 1.67, preferably more than 1.5 and less than 1.67.

Another embodiment of the present invention relates to a blend comprising the catalyst and an alkali sorbent, wherein the alkali sorbent comprises a compound selected from the group consisting of sodium bicarbonate, sodium carbonate, sodium sesquicarbonate (trona), quick lime, hydrated lime, limestone, and combinations thereof, preferably selected from the group consisting of sodium bicarbonate, sodium carbonate, sodium sesquicarbonate (trona), and combinations thereof; more preferably selected from the group consisting of sodium bicarbonate, sodium sesquicarbonate (trona), and combinations thereof.

The blend may comprise

- at least 0. 1 wt%, or at least 0.2 wt%, or at least 0.5 wt%, or at least I wt%, or at least 3 wt%, or at least 5 wt%, of the catalyst, and or

- at most 20 wt%, or at most 15 wt%, or at most 12 wt%, or at most 10 wt%, of the catalyst.

Another aspect of the present invention relates to the use of the blend in a process for treating a waste gas stream containing nitrogen oxides (NOx) and optionally other contaminants selected from the group consisting of heavy metals, acid gases (such as S0₂, S0₃, H₃PO₄, HC1, HI, HBr, and/or HF), and combinations thereof, said waste gas stream originating from a combustion process.

Such treating process may comprise:

injecting the blend comprising the alkali sorbent and the catalyst into the waste gas stream;

removing at least a portion of the contaminants from the waste gas stream with the alkali sorbent, and

converting with the catalyst, in the presence of 0₂, by reduction with NH₃ of at least a portion of the NOx in the waste gas stream to N₂ and water at a temperature of at least 100°C and preferably at most 600°C.

In any of the embodiments of the process according to the various aspects of use of the catalyst with an alkali sorbent, the alkali sorbent preferably comprises a sodium- based sorbent selected from the group consisting of sodium bicarbonate, sodium carbonate, sodium sesquicarbonate (trona), and

combinations thereof, more preferably comprises a sodium- based sorbent selected from the group consisting of sodium bicarbonate, sodium

sesquicarbonate (trona) , and combinations thereof. Sodium- based sorbents are generally more efficient at removing sulfur oxides (SOx) from a waste gas than calcium-based sorbents (such as quick lime, hydrated lime, limestone, or combinations thereof). Since sulfur oxides can interfere with the efficiency for denitrification (deNOx) activity of the catalyst, using a sodium-based .sorbent (particularly sodium bicarbonate and. or trona) with the present catalyst prov ides an advantage over the calcium-based sorbents.

In any embodiments of the various aspects of use of the catalyst (treatment process), the temperature of the waste gas stream to be treated may be:

- at least 105°C, or at least 120°C, or at least 150°C, or at least 180°C, or at least 200°C, or at least 250°C, or at least 300°C; and/or

- at most 550°C, or at most 500°C, or at most 450°C, or at most 400°C. The catalyst used in any embodiments referring to the treatment processes or to blend or to the use of blend in a treatment process according to the invention may have a BET specific surface area measured after being calcined at 400°C of at least 65 m²/g and/or at most 100 m²/g.

The catalyst used in the process or in the blend according to the invention may have a pore volume measured after being calcined at 400°C of:

- at least 0.3 cmVg, preferably of at least 0.41 enr /g, and/or - at most 1 . 1 cnr /g, preferably of at most 1 .0 cnr /g, more preferably of at most 0.9 cffiVg. most preferably of at most 0.8 cnr <g.

The porous support disclosed herein comprises a Ca-deficient

hydroxyapatite useful for the deposition of the active metallic component(s) of the catalytic composition.

The porous support generally comprises or at least 60 percent by weight (wt%), or at least 65 wt%, or at least 70 wt%, or at least 75 wt% percent by weight of the calcium-deficient hydroxyapatite.

The porous support may consist of or consist essentially of at least one calcium-deficient hydroxyapatite, as described herein.

The calcium-deficient hydroxyapatite is generally in the present invention in crystalline form or in vitreous form.

In preferred embodiments, the porous support may further include one or more additional components different from the calcium-deficient hydroxyapatite.

In an advantageous embodiment of the invention, the porous support is obtained or may be obtainable by the process of any items 1 to 16 of this patent application described herein below.

The porous support may be a material according to any items 17 to 30 of this patent application described herein below.

The porous support is advantageously a material according to any items 31 to 44 of this patent application described herein below.

The catalyst containing the active metallic component on the porous support is advantageously a material according to any items 45 to 53 of this patent application described herein below.

In another embodiment of the invention, it is particularly advantageous that the catalyst according to any of the embodiments presented herein comprising iron is brought into contact with a waste gas stream containing nitrogen oxides (NOx) according to any items 54 to 115 of this patent application described herein below.

The porous support may be used in the form of a wet solid (D'), or a pulverulent solid (D"), preferably a pulverulent solid (D"), when the support particles are loaded with iron.

An advantage of the present invention is that the support used in the catalyst according to the invention, presents when in dried powder (as pulverulent solid) an improved flowability and dispersion ability in gas streams compared to previous calcium phosphate material of prior art (in particular the ones described in WO 2008/095921 from SOL V AY, using a gel step during the manufacture of the support).

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 illustrates the conversion of NO and Ν¾ over a hydroxyapatite- based support over the range of temperature 120-450°C in a NH₃-SCR reaction test.

FIG. 2 illustrates the conversion of NO and NH₃ and the percent of production of N₂ over the range of temperature in a NH₃-SCR reaction test 120- 400°C for a hydroxyapatite-based Fe-exchanged catalyst with about 2 wt% Fe.

FIG. 3 illustrates the conversion of NO and NH₃ and the percent of production of N₂ over the range of temperature 120-400°C in a NH₃-SCR reaction test for a hydroxyapatite-based Fe-exchanged catalyst with about 6 wt% Fe.

FIG. 4 is a schematic of a treatment process according to an embodiment of the present invention, wherein an ammonia source, an alkaline compound 2 and a particulate reactant containing apatite 3 are injected separately into a flue gas stream.

FIG. 5 is a schematic of a treatment process according to an embodiment of the present invention, wherein an ammonia source and a particulate catalyst 3 containing hydroxyapatite are injected together and an alkaline compound 2 is injected separately into a flue gas stream.

FIG. 6 is a schematic of a treatment process according to an embodiment of the present invention, wherein an ammonia source and an alkaline compound 2 are injected together and a particulate catalyst 3 containing hydroxyapatite is injected separately into a flue gas stream.

FIG. 7 is a schematic of a treatment process according to an embodiment of the present invention, wherein an ammonia source, an alkaline compound 2 and a particulate catalyst 3 containing hydroxyapatite are injected together into a flue gas stream.

FIG. 8 is a schematic of a treatment process according to an embodiment of the present invention, wherein an alkaline compound 2 and a particulate catalyst 3 containing hydroxyapatite are injected together and an ammonia source is injected separately into a flue gas stream.

DEFINITIONS

Unless otherwise specified, all reference to percentage (%) herein refers to percent by weight. The terms "catalyst support," "support particles," or "porous support" are intended to have their standard meaning in the art and refer to particles comprising a hydroxyapatite structure on the surface of which an active metal component is deposited.

The terms "active metal catalyst" or "active component" refer to the active component deposited on support material that catalyzes the reduction of NOx compounds.

The term "catalyst" (or "catalyst composition") is intended to have its standard meaning in the art and refers to the combination of the active metal catalyst supported on the catalyst support particles

"Fresh" catalyst denotes a material which has not been in contact with NOx, whereas "spent" catalyst denotes a material which has already been in contact with NOx.

The term "trona" is intended to mean a mineral containing at least 60 %, preferably at least 80 %, more preferably at least 90 %, even more preferably at least 95 % by weight of sodium sesquicarbonate (NaHCO₃.Na₂CO₃.2H₂O). The remainder of the mineral generally consists of clays, or carbonate of calcium or magnesium.

As used herein, the term "upstream" refers to a position situated in the opposite direction from that in which the gas stream to be treated flows.

As used herein, the term "downstream" refers to a position situated in the same direction from that in which the gas stream to be treated flows.

As used herein, the terms "% by weight", "wt%", "wt. %", "weight percentage", or "percentage by weight" are used interchangeably.

In the present specification, the choice of an element from a group of elements also explicitly describes :

- the choice of two or the choice of several elements from the group,

- the choice of an element from a subgroup of elements consisting of the group of elements from which one or more elements have been removed.

In addition, it should be understood that the elements and/or the characteristics of a composition, a method, a process or a use, described in the present specification, can be combined in all ways possible with the other elements and/or characteristics of the composition, method, process, or use, explicitly or implicitly, this being without departing from the context of the present specification.

In the passages of the present specification that will follow, various embodiments or items of implementation are defined in greater detail. Each embodiment or item of implementation thus defined can be combined with another embodiment or with another item of implementation, this being for each mode or item unless otherwise indicated or clearly incompatible when the range of the same parameter of value is not connected. In particular, any variant indicated as being preferred or advantageous can be combined with another variant or with the other variants indicated as being preferred or advantageous.

In the present specification, the description of a range of values for a variable, defined by a bottom limit, or a top limit, or by a bottom limit and a top limit, also comprises the embodiments in which the variable is chosen, respectively, within the value range : excluding the bottom limit, or excluding the top limit, or excluding the bottom limit and the top limit.

In the present specification, the description of several successive ranges of values for the same variable also comprises the description of embodiments where the variable is chosen in any other intermediate range included in the successive ranges. Thus, for example, when it is indicated that "the magnitude X is generally at least 10, advantageously at least 15", the present description also describes the embodiment where : "the magnitude X is at least 11", or also the embodiment where : "the magnitude X is at least 13.74", etc.; 11 or 13.74 being values included between 10 and 15.

The term "comprising" includes "consisting essentially of and also "consisting of.

In the present specification, the use of "a" in the singular also comprises the plural ("some"), and vice versa, unless the context clearly indicates the contrary. By way of example, "a mineral" denotes one mineral or more than one mineral.

If the term "approximately" is used before a quantitative value, this corresponds to a variation of ± 10 % of the nominal quantitative value, unless otherwise indicated.

DETAILED DESCRIPTION OF INVENTION

Porous Support

In the text of the application, the "porous support" may be referred to as the "calcium phosphate porous support"; these terms can be used

interchangeably.

The porous support used in the catalyst of the present invention preferably consists of particles. In some embodiments, the mean diameter D50 of the porous support is greater than 10 μηι, in general greater than 20 μηι, or even greater than 50 μηι. However, this mean diameter of the porous support is in general preferably less than 200 μιη, or even less than 150 μιη. This makes it possible to limit the stirring powers to prevent the particles of the porous support from needing high velocities of waste gases to be treated at the injection points of the catalyst for the treatment of the waste gases. Alternatively, the mean diameter of the porous support may be at least 150 μιη, or at least 200 μιη, or at least 250 μιη, and/or up to 1,500 μιη, or up to 1,000 μιη, or up to 750 μιη, or up to 600 μιη, or up to 500 μιη. This mean diameter would allow for the resulting particles supported on the porous support to be used in a flow-through system, for example where the waste gas to be treated is passed through a bed of catalyst particles.

Moreover the porous support may have a particularly high BET specific surface area (at least 110 mVg) measured after treatment of the porous support at 120°C.

The porous support may have a particularly high pore volume (at least 0.41 cm³/g) measured after heat treatment of the porous support at 120°C.

Particularly, the porous support may have a high adsorption capacity of metals, in particular of iron.

In particular embodiments, the porous support has a BET specific surface area measured after heat treatment at 200°C of at least 120 m²/g and/or at most 160 m²/g.

In particular embodiments, the porous support has a BET specific surface area measured after heat treatment at 600°C of at least 20 m²/g and/or at most 40 m²/g.

In particular embodiments, the porous support has a pore volume measured after heat treatment at 200°C of at least 0.55 cm³/g, preferably of at least 0.55 cm³/g and/or at most 1.0 cm³/g, preferably of at most 0.95 cm³/g.

In particular embodiments, the porous support has a pore volume measured after heat treatment at 600°C of at least 0.42 cm³/g, preferably of at least 0.44 cm³/g and/or at most 0.8 cm³/g, preferably of at most 0.75 cm³/g.

For comparison, natural apatites found in Moroco for instance have specific surface areas of about 16 mVg. Synthetic hydroxyapatites made by Dalahay's group at the Ecole Nationale Superieure de Montpellier, France, have specific BET surface areas of - about 26 m²/g (Tounsi et al, Applied Catalysis B: Environmental, 2011, vol. 107, pages 158-163); and

- about 44 m²/g (Jemal et al, Reac. Kinet. Mech. Cat, 2013, vol. 109, pages 159-165).

In Jemal et al, Reac. Kinet. Mech. Cat, 2013, vol. 109, pages 159-165, a synthetic hydroxyapatite made using an aqueous medium had a BET about 35 m²/g and a pore volume of 0.4 cm³/g, while another synthetic hydroxyapatite made using an ethanol- water medium had a BET about 72 m²/g and a pore volume of 0.34 cm³/g.

The porous support should comprise at least 60 wt % of a calcium- deficient hydroxyapatite having a calcium to phosphate molar ratio (Ca/P) of less than 1.67.

It is preferred that the calcium-deficient hydroxyapatite has a calcium to phosphate molar ratio (Ca/P) of more than 1.5 and less than 1.67.

In particular embodiments, the porous support comprises at least 65 wt%, preferably at least 70 wt%, more preferably at least 75 wt%, yet more preferably at least 80 wt%, yet most preferably at least 85 wt%, of the calcium-deficient hydroxyapatite.

In particular embodiments, the porous support comprises at most 99 wt%, preferably at most 98 wt%, more preferably at most 97 wt%, yet more preferably at most 95 wt%, even more preferably at most 93 wt%, most preferably at most 91 wt% of the calcium-deficient hydroxyapatite.

In particular embodiments, the porous support may comprise a Ca/P molar ratio of 1.60 or more, preferably more than 1.62, more preferably more than 1.65.

In some embodiments, the porous support may comprise a Ca/P molar ratio of 1.60 or more, preferably of 1.62 or more, more preferably of 1.65 or more, even more preferably of 1.67 or more, most preferably of 1.68 or more.

The porous support particles are preferably composed of calcium phosphate, the structure of which is intermediate between tricalcium phosphate and calcium phosphate hydroxyapatite. These particles then evolve very rapidly towards an apatite structure. The porous support particles preferably contain a calcium-deficient hydroxyapatite structure having a calcium to phosphate molar ratio (Ca/P) of less than 1.67. It is preferred that the calcium-deficient hydroxyapatite has a calcium to phosphate molar ratio (Ca/P) of more than 1.5 and less than 1.67. Such porous support particles are composed on their surface of plate-like crystallites, of thickness of a few nano-meters (nm).

Particles of calcium phosphate porous support may be covered with platelike crystallites, having a thickness of at most 25 nm, preferably of at most 20 nm, more preferably of at most 10 nm. The thickness of plate-like crystallites may be at least 1 nm, preferably at least 2 nm, more preferably at least 4 nm.

The porous support used in the present invention may further have a remarkably low solubility of the phosphates contained in the porous support particles.

The particles of the calcium phosphate porous support used in the catalyst of the present invention in general comprise at least 60 wt% calcium phosphate and advantageously still at least 65 wt% calcium phosphate.

The particles of the calcium phosphate porous support may further comprise : water, of the order of from 0 to 20 wt%, advantageously from 3 % to 20 wt%, more advantageously from 5 wt% to 20 wt%; calcium carbonate from 0 to 20 wt%, advantageously from 1 wt% to 25 wt% , more advantageously from

5 wt% to 20 wt%.

In some embodiments, the particles of the calcium phosphate porous support may further comprises calcium carbonate in an amount of less than 20 wt%, preferably from 1 wt% to 19 wt%, more preferably from 2 wt% to 18 wt%, even preferably from 5 wt% to 15 wt%, yet even more preferably from 7 wt% to

13 wt%, most preferably from 8 wt% to 12 wt%.

5 wt% to 20 wt%.

The particles of the calcium phosphate porous support may further comprise calcium dihydroxide from 0 to 20 %, advantageously from 0 % to 4 %, or more advantageously from 0 to 1 wt%. In some embodiments, the porous support may comprise less than 1 wt% of calcium dihydroxide Ca(OH)₂, preferably less than 0.5 wt% calcium dihydroxide, more preferably less than 0.3 wt% calcium dihydroxide, even more preferably less than 0.2 wt% calcium dihydroxide. In some embodiments, the porous support is substantially free of calcium dihydroxide (i.e., less tha 0.1 wt% Ca(OH)₂). In some embodiments, the porous support may comprise at least 2 wt%, preferably at least 2.5 wt% or at least 3 wt%, more preferably at least 5 wt%, and yet more preferably at least 6 wt% of hydroxide ions.

In some embodiments, the porous support may comprise from 2 wt% to 6 wt% of hydroxide ions, preferably from 2.5 wt% to 5 wt% of hydroxide ions.

The particles of calcium phosphate porous support may additionally contain residual compounds originating from the use of the raw materials in the method of making it, such as : CaCl₂, Ca(N03)₂, sands or clays; these constituents are in general less than 5 wt%, advantageously less than 2 wt%.

Although it is possible that the calcium phosphate porous support may contain iron in its structure, the calcium phosphate porous support on which iron is deposited is preferably substantially free of iron, that is to say, the iron content of the calcium phosphate porous support should be less than 0.5 wt%, preferably less than 0.3 wt%, more preferably less than 0.1 wt%. Any iron present in the calcium phosphate porous support structure generally originates from one or more raw materials from which the support is made.

The term "apatite" denotes a family of mineral compounds, the chemical formula of which can be written in the following general form :

In this formula, Me generally represents a divalent cation (Me²⁺), X0₄ a trivalent anionic group (X0₄ ^3~) and Y a monovalent anion (Y ).

Calcium phosphate hydroxyapatite Caio (P0₄)6(OH)₂ crystallizes in the space group of the hexagonal system. This structure consists of a close-packed quasi- hexagonal stack of X0₄ groups, forming two types of parallel tunnels.

The existence of these tunnels gives apatites chemical properties akin to those of zeolites. Vacancies may also be created either by the departure of anions and cations, or by the presence of cations or anions of different valency. Apatites therefore appear to be particularly stable structures which may tolerate large gaps in their composition.

Hydroxyapatite should not be confused with tricalcium phosphate (TCP), which has a similar weight composition : Ca₃(P0₄)₂. The Ca/P molar ratio of TCP is 1.5 whereas the Ca/P molar ratio is 1.67 for hydroxyapatite. Industrial apatites sold as food additives or mineral fillers are, as a general rule, variable mixtures of TCP and hydroxyapatite.

The present hydroxyapatite in the porous support is deficient in calcium compared to a hydroxyapatite with a Ca/P molar ratio of 1.67. The Ca/P molar ratio of the calcium-deficient hydroxyapatite is preferably more than 1.5 and less than 1.67.

Calcium may be and is preferably present in another form (other than the calcium-deficient hydroxyapatite) in the porous support. Calcium carbonate is generally present in the porous support. The weight ratio of the calcium-deficient hydroxyapatite to calcium carbonate is generally equal to or greater than 3, preferably equal to or greater than 4, more preferably equal to or greater than 5, yet more preferably greater than 7, most preferably equal to or greater than 9.

Generally, because of that other form of Ca in the porous support, the porous support generally has a higher Ca/P molar ratio than the calcium-deficient hydroxyapatite present in the porous support. For that reason, even though the calcium-deficient hydroxyapatite in the porous support may have a Ca/P molar ratio less than 1.67, the entire porous support may have a Ca/P molar ratio equal to or more than 1.67. In preferred embodiments, the calcium-deficient hydroxyapatite in the porous support may have a Ca/P molar ratio of about 1.55- 1.59, while the porous support may have a Ca/P molar ratio of about 1.60-1.67.

Other salts of calcium and phosphate, including TCP, do not have the same properties as hydroxyapatite or a hydroxyapatite like structure. Although TCP can also react with metals, a hydroxyapatite of Ca/P=1.67 as well as a calcium- deficient hydroxyapatite (Ca/P < 1.67) are more advantageous as they can enclose metals in the form of an insoluble, and therefore relatively inert, matrix.

In some preferred embodiments, the calcium phosphate porous support is substantially free of carbon, i.e., less than 0.5 wt% of carbon.

In some other embodiments, the calcium phosphate porous support may comprise carbon for example in an amount of at least 0.5 wt% carbon but in an amount of less than 7 wt% carbon, preferably less than 6 wt% carbon, more preferably less than 5 wt% carbon or less than 4 wt% carbon.

In some preferred embodiments, the calcium phosphate porous support is substantially free of bone char..

In preferred embodiments, the calcium phosphate porous support excludes bone char.

Method for making the porous support

The process for producing the calcium phosphate porous support may comprise :

- in a first step, use is made of a source of calcium and a source of phosphate ions in water, in a molar ratio that is adjusted so as to obtain a Ca/P molar ratio of between 0.5 and 1.6, and the source of calcium is reacted with the phosphate ions at a pH of between 2 and 8, in order to obtain a suspension (A) of calcium phosphate, and

- in a second step, added to the suspension (A) are an alkaline compound comprising hydroxide ions in order to set a pH of more than 8, preferably of at least 8.5, and an additional source of calcium in order to obtain a suspension (B) of calcium phosphate porous support having a Ca/P molar ratio of more than 1.6.

In the process of manufacture, the source of calcium to make the support advantageously comprises calcium carbonate, or calcium oxide, or calcium hydroxide, or calcium chloride, or calcium nitrate, or calcium acetate. The source of calcium is more advantageously a limestone, or a mixture of limestone and calcium oxide or hydroxide. More advantageously, the source of calcium is in the form of powder or aqueous suspension of powder and the powder is selected from the group consisting of: calcium carbonate, calcium oxide, calcium hydroxide, and a mixture thereof, and the powder for the source of calcium has a mean particle size of less than 300 μιη.

It is advantageous for the source of calcium selected from the group consisting of: calcium carbonate, calcium oxide, calcium hydroxide, and mixtures thereof to be in the form of a powder or aqueous suspension of powder, and to have a small particle size. In one recommended variant, the mean diameter of the particles of the powder for the calcium source is less than 300 μιη, advantageously less than 200 μιη and preferably less than 100 μιη. The mean diameter in question is the D50, that is to say the diameter such that 50 % by weight of the particles have a diameter less than said value.

In the process of manufacture, various sources of phosphate ions to make the support may be used, in particular :

- phosphoric acid,

- or a dihydrogen phosphate salt such as a sodium, potassium or

ammonium dihydrogen phosphate salt, preferably a sodium dihydrogen phosphate salt,

- or a monohydrogen phosphate salt such as a sodium, potassium or ammonium monohydrogen phosphate salt, preferably a sodium monohydrogen phosphate salt. In the process of manufacture to make the porous support, phosphoric acid is preferred due to its greater availability and lower cost compared to dihydrogen and monohydrogen phosphate salts.

In the process of manufacture to make the porous support, in the first step the Ca/P molar ratio is in particular :

- between 0.50 and 1.35, preferably between 0.70 and 1.30,

- or : between 1.4 and 1.6, preferably between 1.4 and 1.5.

During the first step where calcium and phosphate are used in a Ca/P molar ratio of between 0.5 and 1.6 and where they are reacted at a pH between 2 and 8, the compounds formed in the suspension (A) are a mixture of monocalcium phosphate (MCP) having the weight formula Ca(H₂P0₄)2, of dicalcium phosphate (DCP) having the weight formula CaHP0₄, or the hydrate thereof, brushite, having the weight formula CaHP0₄.2H₂0, and of octacalcium having the weight formula Ca₈H₂(P0₄)6.6.5H₂0. The Ca/P molar ratios are respectively for these compounds : 0.5 (MCP), 1.0 (DCP and brushite), 1.33 (octacalcium).

In order to promote, in the first step, the formation of MCP and DCP, a Ca/P ratio of between 0.50 and 1.35, preferably between 0.7 and 1.30, is favored. This Ca/P molar ratio is particularly advantageous when the source of calcium from the first step comprises calcium carbonate, and the source of phosphate is phosphoric acid (H₃P0₄) or is a dihydrogen phosphate salt such as a sodium or potassium or ammonium salt. Specifically, this makes it possible to obtain a rapid attack of the calcium carbonate and a rapid degassing of the C0₂. In addition to calcium carbonate, the source of calcium may comprise calcium oxide, or calcium hydroxide, or calcium chloride, or calcium nitrate, or calcium acetate.

In order to promote, in the first step, the formation of DCP and

octacalcium, a Ca/P ratio of between 1.4 and 1.6, preferably between 1.4 and 1.5, is favored. This molar ratio is advantageous when use is made of a source of calcium having less than 30 % by weight of carbonate, such as preferably :

calcium oxide, or calcium hydroxide, or calcium chloride, or calcium nitrate, or calcium acetate.

In the method of manufacture to make the porous support, in the first step, the source of calcium and the phosphate ions are in general reacted for at least 0.1 hour, preferably at least 0.5 hour. It is not useful to react them over excessively long periods of time. Advantageously, the source of calcium and the phosphate ions are reacted for at most 4 hours, more advantageously at most 2 hours, or even at most 1 hour. For example, a time period of 1 hour at pH=5 already enables a good reaction of the calcium and the phosphate ions, and makes it possible to sufficiently release the C0₂ when a source of calcium comprising calcium carbonate is used, before moving on to the second step.

In the method of manufacture to make the porous support, in the second step, the suspension (B) of calcium phosphate porous support in general has a Ca/P molar ratio of at most 5, preferably of at most 3, more preferably still of at most 2.

In the method of manufacture to make the porous support, it is

advantageous, in the second step, for the alkaline compound used, that comprises hydroxide ions, to be sodium hydroxide and/or calcium hydroxide.

In the method of manufacture to make the porous support, it is particularly advantageous for the additional source of calcium to be selected from the group consisting of calcium chloride, calcium nitrate, and calcium acetate, preferably calcium chloride, and for this additional source of calcium to be added to the alkaline compound, in order to finely adjust the Ca/P molar ratio and in order to limit the concentration of phosphorus element in the aqueous solution (C) of the suspension (B) to at most 5 mmol, advantageously to at most 0.5 mmol, more advantageously to at most 0.05 mmol of phosphorus element per liter of the aqueous solution (C). Specifically, this makes it possible, coupled with the use of hydroxide ions for setting the pH of the second step, to limit the losses of phosphates in the process water.

In the method of manufacture to make the support, in general, the stirring speed rate and the density of the suspension, in the second step and

advantageously also in the first step, are adjusted in order to avoid the appearance of a calcium phosphate gel having a viscosity of at least 200 cps. The viscosity of the porous support suspension (B) in the second step of the process of the present invention is typically about 10 cps (mPa.s). Specifically, the production of a gel, even in the presence of the second step, results in making porous support particles of small particle size, with weight-mean D50 values of less than 10 μιη, which may be a disadvantage for certain applications.

The suspended solids density of the suspension (A) in the first step is in general at most 20 wt%. The suspended solids density of the suspension (B) in the second step is in general at most 15 wt%. The suspended solids density of the suspension (A) and/or of the suspension (B) is advantageously at least 5 wt%, more advantageously at least 7 wt%, most advantageously at least 10 wt%. It has been indeed observed that a too low density of the suspension decreases the efficacy of the produced porous support particles in metal adsorption (in particular on Fe). Moreover a too low density of the suspension induces longer time of water separation when decantation or filtration is used in the method of making the support.

In the method of manufacture to make the support, the stirring speed of the suspension during the first and second steps corresponds generally to a stirring dissipated energy in the reactors volume of at least 0.2 kW/m³ and at most 1.5 kW/m³, preferably at least 0.5 kW/m³ and at most 1.0 kW/m³.

In a first embodiment of the method of manufacturing the support, the first step is carried out at a temperature of less than 50°C, preferably at most 45°C, or at most 40°C. This low-temperature first step makes it possible to obtain a calcium phosphate porous support at the end of the second step in the form of particles of large to medium particle size and having a high specific surface area. The method may manufacture in particular particles of porous support by this first embodiment, comprising at least 60 % by weight of hydroxyapatite or hydroxyapatite-like structure, and having a mean size of at least 30 μιη, preferably of at least 50 μιη and having a specific BET surface area and/or pore volume as described above. In some embodiments, the specific BET surface area measured after heat treatment at 200°C is at least 110 mVg.

In some embodiments, the porous support may comprise at least 2 wt%, preferably at least 2.5 wt% or at least 3 wt%, more preferably at least 5 wt%, and yet more preferably at least 6 wt% of hydroxide ions.

In a second embodiment of the method for manufacturing the support, the first step is carried out at a temperature of at least 50°C, preferably of at least 55°C, or of at least 60°C. This makes it possible to obtain a porous support in the second step in the form of particles of small particle size and having a lower specific surface area. The process may manufacture in particular particles of porous support obtained by the method according to this second embodiment, comprising at least 60 % by weight of hydroxyapatite, and having a mean size of at most 30 μιη, preferably of at most 20 μιη. In some embodiments, particles of porous support have a specific BET surface area of at least 15 m²/g, preferably of at least 50 mVg, and having a content of hydroxide ions of greater than 2 % by weight, preferably greater than 3.5 % by weight, and more preferably greater than 4 % by weight.

In the first or second embodiment of the method of manufacture, it is advantageous for the second step to be carried out at a temperature of at least 45°C, preferably of at least 55°C, or of at least 60°C, or of at least 80°C.

Specifically, this makes it possible to rapidly convert the calcium phosphate compounds from the first step into the calcium phosphate porous support, with a good fixation of the hydroxide ions at the core and at the surface of the calcium phosphate porous support, and to more rapidly consume the phosphates from the solution of the suspension (B). Advantageously, the second step of the manufacture method is carried out at a temperature of at least 45°C, preferably of at least 55°C, or of at least 60°C, or of at least 80°C, for a time period of at least 0.1 to 0.5 hour. In general, the addition of the alkaline compound comprising hydroxide ions in order to set the pH of the second step, and of the additional source of calcium in order to obtain a suspension (B) of calcium phosphate porous support having a Ca/P molar ratio of greater than 1.6 last no more than 4 hours, advantageously no more than 2.5 hours : at higher temperature such as at 50°C or at 60°C generally one hour is sufficient, as at 40°C the alkaline compound addition to set the pH of the second step is generally longer : and about 2.5 hours are needed. Preferably, the alkaline compound addition is stopped when the pH remains at the set value for at least 15 minutes.

Advantageously, once the additions of hydroxide ions for setting the pH of the second step, and the addition of the additional source of calcium are completed, the suspension (B) is left to cool for 1 to 24 hours, preferably at least 10 hours, down to ambient temperature. This makes it possible to mature the calcium phosphate porous support and to reduce the residues of MCP/DCP or brushite, or of octacalcium (precipitated during the first step), into a hydroxyapatite structure and into calcium phosphate and calcium hydroxide complexes, within the suspension (B).

Optionally, in the manufacture method, at the end of the second step, the suspension (B) comprises an aqueous solution (C) and calcium phosphate porous support particles, and

- in a third step, a portion of the aqueous solution (C) is separated from the suspension (B) in order to obtain an aqueous suspension (D) comprising at least 18 % and at most 50 % of calcium phosphate porous support particles, or in order to obtain a wet solid (D') comprising at least 50 % and at most 80 % of calcium phosphate porous support particles, or a pulverulent solid (D") comprising at least 80 % and at most 95 % of calcium phosphate porous support particles and at least 5 % and at most 20 % of water.

In some embodiments, the porous support material is not isolated from the aqueous solution in which it is suspended prior to deposition of the active catalyst component.

In alternate embodiment, the porous support material may be isolated prior to deposition of the active catalyst component. Preferably in this instance, greater than 90% or 95% by weight of the solvent or dispersion medium is removed.

More preferably, greater than 98% of the medium is removed. The isolation may comprise any type of solid/liquid separation; filtration is a preferred isolation technique.

In some embodiments, the porous support material may not be subjected to drying prior to deposition of the active catalyst component.

In alternate embodiment, the porous support material may be dried prior to deposition of the active catalyst component. Drying is preferably carried out after the porous support material has been isolated. When water is the dispersion medium, a suitable drying temperature is about 80° C to about 120° C. However, it will be apparent to one of skill in the art that lower or higher drying

temperatures may be used. For example, drying temperatures of less than 80° C may be used if the drying time is increased or the drying pressure is decreased. A preferred drying temperature is from about 100° C to about 120° C.

Iron-containing supported catalyst

The calcium phosphate porous support obtained by the manufacture method described herein may be effective for use as a support for a catalyst for treating a waste gas contaminated by nitrogen oxides, in particular a flue gas contaminated by NOx and originating from a combustion process.

One or more embodiments of the present invention pertain to a catalyst supported on the calcium phosphate porous support as described previously.

A particular embodiment of the present invention pertains to a catalyst composition for catalytic reduction of NO_x compounds, comprising an active catalyst component deposited on the porous support; wherein the active catalyst component comprises iron.

Although it is possible that the calcium phosphate porous support may contain iron in its structure, the calcium phosphate porous support on which iron is deposited is preferably substantially free of iron, that is to say, the iron content of the calcium phosphate porous support should be less than 0.5 wt%, preferably less than 0.3 wt%, more preferably less than 0.1 wt%.

The active catalyst component may comprise at least 0.5 wt%, preferably at least 0.7 wt%, more preferably at least 1.0 wt%, most preferably at least 1.5 wt%, of iron; and/or may comprise at most 15 wt%, preferably at most 13 wt%, more preferably at most 12 wt%, most preferably at most 11 wt%, of iron. A range of from 1.5 wt% to 12 wt% of Fe is particularly suitable. A range of from 2 wt% to 8 wt% of Fe is also particularly suitable.

In particular embodiments, the catalyst composition has a BET specific surface area measured after being calcined at 400 °C of at least 65 m²/g and/or at most 100 m²/g.

In particular embodiments, the catalyst composition has a pore volume measured after being calcined at 400 °C of at least 0.3 cm³/g, preferably of at least 0.41 cm³/g, and/or at most 1.1 cm³/g, preferably of at most 1.0 cm³/g, more preferably of at most 0.9 cm³/g. most preferably of at most 0.8 cm³/g.

In particular embodiments, the catalyst composition has an average pore radius measured after being calcined at 400°C of at least 5 nm, preferably at least 7 nm, and/or at most 30 nm, preferably at most 25 nm. The average pore radius is preferably determined from Gurvich rule : rp (nm) = 2 (Vp/SBET) 10³, where Vp is the pore volume in cm³/g, SBET is the BET surface area in m²/g, and the pore radius is in nm.

In particular embodiments, the catalyst composition has a microporous and mesoporous morphology.

In some embodiments, the catalyst composition contains not more than

10%, preferably not more than 5%, more preferably not more than 3%, yet more preferably not more than 1%, of the iron species in the oxide form (Fe₂C"3).

In preferred embodiments, the catalyst composition is in the form of particles. The mean diameter D50 of the catalyst composition is greater than 10 μιη, in general greater than 20 μιη, or even greater than 50 μιη. However, this mean diameter of the catalyst composition is in general preferably less than 200 μιη, or even less than 150 μιη. This makes it possible to limit the stirring powers to prevent the particles from needing high velocities of waste gases to be treated at the injection points of the catalyst for the treatment of the waste gases.

Alternatively, the mean diameter of the catalyst composition may be at least 150 μιη, or at least 200 μιη, or at least 250 μιη, and/or up to 1500 μιη, or up to 1000 μηι, or up to 750 μηι, or up to 600 μηι, or up to 500 μηι. This mean diameter would allow for the resulting catalyst particles to be used in a flow-through system where the waste gas to be treated is passed through a bed of catalyst particles.

Method of making the iron-containing supported catalyst

The active catalyst component may be deposited on the porous support using a solution of an iron precursor. The iron precursor may include Fe³⁺ or Fe²⁺, preferably Fe³⁺. A preferred iron precursor may be selected from the group consisting of iron nitrate, iron chloride, iron perchlorate (Fe(C10₄) ₂), iron sulfate (Fe₂(S04)3), iron fluorosilicate (FeSiF₆), any hydrated form thereof, and any mixture thereof. The iron nitrate may be selected from Fe(N03)₂.6H₂0 or Fe(N03)₃.9H₂0. The iron chloride may be selected from FeCl₂ or FeCi3. The iron precursor is more preferably selected from the group consisting of iron (III) nitrate, iron (III) chloride, iron (III) sulfate, iron (III) perchlorate, any hydrated form thereof, and any mixture thereof.

The active catalyst component may be deposited on the porous support by wet impregnation or ion-exchange, preferably by ion-exchange.

Wet impregnation (with small amount of excess water solution) is a catalyst preparation technique that does not require an iron precursor with ionic character. Therefore, an iron precursor which is not water soluble may be used for the catalyst preparation via impregnation.

Impregnation is a technique in which a new phase is added on the external surface and in the pores of the porous support (if the pore dimensions allow the entrance of the used Fe precursor). In the case of the hydroxyapatite containing porous support, Fe besides Ca will be present in the final catalyst composition.

Ionic exchange (or ion-exchange or ion exchange, used interchangeably) is a technique for modifying the surface composition of materials that have metal cations bound to the framework with electrostatic bonds. This preparation technique necessitates a Fe precursor with ionic character. Therefore, iron sulfate, iron chloride, iron perchlorate, and iron nitrate can be selected as iron precursor to provide iron cations. Iron (III) chloride, iron (III) sulfate, and iron (III) nitrate are particularly suitable as iron precursor with the ion exchange method.

The new iron cations are introduced in the sample composition and they substitute the original cations of the sample (in this case iron cations substitute Ca²⁺ cations of the hydroxyapatite which enter into solution). Ionic exchange is a method that exploits the electrostatic interaction between the added cations and the negative framework of the starting material (hydroxyapatite).

Concerning the possibility to load the support material with a given desired amount of the added metal, there are differences among the two preparation methods.

By impregnation, it is possible to load the support with a given amount of impregnating phase which has been chosen "a priori". The preparation technique does not employ any filtration or separation step of the impregnated support sample from the solution that contains the metal precursor of the loading phase. So, all the desired amount of metal precursor can effectively be loaded on the support.

By ion exchange, it is not possible to load the support exactly with a desired amount of any cation. Once the exchange reaction has finished, filtration has to be performed to separate the exchanged solid from the iron precursor solution that may contain some residual amount of the iron cations.

After depositing the active catalyst component on the porous support, the particles may be washed to remove the non-exchanged or excess active component species. Washing medium may comprise water (such as deionized water) or a solvent similar to the one used to dissolve or disperse the iron precursor(s).

After the deposition of the active catalyst component on the porous support and the optional washing, the particles may be isolated by any suitable means, such as filtration, to remove the medium/solvent into which the iron precursor is dissolved or suspended or to remove the washing medium at the end of the washing step. Preferably, greater than 90% or 95% of the medium is removed. More preferably, greater than 98% of the medium is removed.

In some embodiments, after the deposition of the iron precursor onto the support, the (isolated) catalyst particles may be subjected to a heat treatment. The heat treatment may use a temperature from 105°C to 500°C, preferably from 200°C to 400°C.

In some embodiments, after the deposition of the iron precursor onto the support, the resulting (isolated) catalyst particles may be subjected to a heat treatment (drying). The temperature at which the particles are dried is dependent on the solvent medium and the pressure which is used to dry the particles.

Drying typically uses a temperature of 180 °C or less. Drying is typically carried out in air or in an 0₂-containing atmosphere which may comprise another gaseous component such as nitrogen gas (N₂), helium or combination thereof. Drying may be carried out in a vacuum or not.

Typically, the same drying temperatures and times described above for drying the porous support will be useful for drying the supported catalyst after the active metal component has been deposited. The moisture level of the dried supported catalyst can be measured by standard methods known in the art to determine if the material has been dried for a sufficient amount of time at the particular temperature. When water is the medium into which the iron precursor is dissolved or suspended, a suitable drying temperature is about 80° C to about 120° C. However, it will be apparent to one of skill in the art that lower or higher drying temperatures may be used. For example, drying temperatures of less than 80° C may be used if the drying time is increased or the drying pressure is decreased. A preferred drying temperature is from about 100 °C to about 120 °C. Usually, the catalyst is dried for at least 10 hours at 100-120 °C to ensure that the solvent is adequately removed. More typically, the catalyst may be dried for at least 12, 14 or 16 hours at 100-120 °C to ensure that the solvent is removed to a sufficient level.

In some embodiments, after the deposition of the iron precursor onto the support, the catalyst is subjected to a heat treatment (calcining) using a temperature more than 180 °C and up to 500 °C. Preferably, calcining is performed after a drying step, but not necessarily.

In some embodiments, after the deposition of the iron precursor, the catalyst is not subjected to a heat treatment using a temperature greater than 180 °C (no calcination), prior to being used as a catalyst.

Alkali Sorbent

The alkali sorbent may comprise a sodium-containing compound or a calcium-containing compound. A preferred alkali sorbent may comprise sodium bicarbonate, sodium carbonate, sodium sesquicarbonate (trona), quick lime, hydrated lime, limestone or any mixture thereof. The more preferred alkali sorbent may comprise sodium bicarbonate, sodium carbonate, sodium

sesquicarbonate (trona), or any mixture thereof. The yet more preferred alkali sorbent may comprise sodium bicarbonate, sodium sesquicarbonate (trona), or any mixture thereof. The most preferred alkali sorbent may comprise or consist of sodium bicarbonate.

The alkali sorbent may comprise a sodium-containing compound and in addition an ammonia source. For example the alkali sorbent may contain between 60 % and 98 %, preferably between 80 and 98 %, by weight of sodium bicarbonate, but may additionally contain up to 2 wt%, preferably between 0.02 % and 2.0 % by weight of ammonia, expressed in the form of ammonium ions NH₄ ⁺.

The sodium bicarbonate material described in WO2015/118165 and

WO2015/118166 both from SOLVAY SA are suitable to be used in this process.

A suitable alkali sorbent in this process may include or consist of the reactive composition disclosed in WO2015/118165. This reactive composition comprises between 60 % and 98 %, preferably between 80 and 98 %, by weight of sodium bicarbonate, between 1 % and 40 %, preferably between 1 % and

12 % by weight of sodium carbonate and between 0.02 % and 2.0 % by weight of ammonia, expressed in the form of ammonium ions NH₄ ⁺, characterized in that the composition comprises less than 1.0 %, preferably less than 0.9 %, more preferably less than 0.8 % by weight of water.

Another suitable alkali sorbent in this process may include or consist of the reactive composition disclosed in WO2015/118166. This reactive composition comprises between 60 % and 98 %, preferably between 80 and 98 %, by weight of sodium bicarbonate, between 1 % and 40 %, preferably between 1 % and 12 % by weight of sodium carbonate and between 0.02 % and 2.0 % by weight of ammonia, expressed in the form of ammonium ions NH₄ ⁺, and comprising from 0.01 to 5 % by weight of a compound selected from hydrocarbons, fatty alcohols, fatty acids, or fatty acid salts , preferably fatty acids having 12 to 20 carbon atoms per molecule or a salt thereof.

The alkali sorbent is preferably in the form of particles having a diameter D90 of less than 50 μιη and a diameter D50 of less than 35 μιη, preferably a diameter D90 of less than 35 μιη and a diameter D50 of less than 20 μιη, more preferably a diameter D90 of less than 30 μιη and a diameter D50 of less than 15 μιη, measured by laser diffractometry.

Ammonia Source

The ammonia source may include urea, N¾, and/or an ammonium containing salt or solution (such as ammonium bicarbonate).

The ammonia source may be in the form of a gas (a gas comprising or consisting of NH₃), a liquid (e.g., solution of ammonium salt such as ammonium bicarbonate, solution of urea, solution of N¾, or any mixtures thereof), or a solid (powder comprising an ammonium salt and/or urea). The ammonia source may be included in the alkali sorbent and/or in the catalyst.

Blend of supported catalyst and alkali sorbent

Consequently, the present invention also relates to a blend comprising the supported deNOx catalyst and an alkali sorbent. This blend may be used for the multi-pollutant purification of a waste gas. In particular, this blend may be used for the removal of NOx and acid gases like SOx, HC1, and/or HF through an injection of this blend into a waste gas stream contaminated by these pollutants.

The blend may comprise:

- at least 0.1 wt%, or at least 0.2 wt%, or at least 0.5 wt%, or at least 1 wt%, or at least 3 wt%, or at least 5 wt%, of the deNOx catalyst based on total weight of the blend, and. or

- at most 20 wt%, or at most 15 wt%, or at most 12 wt%, or at most 10 wt%, of the deNOx catalyst based on total weight of the blend.

The weight ratio of the deNOx catalyst to the alkaline sorbent in the blend may be at least 0.001, or at least 0.005, or at least 0.010, or at least 0.020, or at least 0.030, or at least 0.045. The weight ratio of the deNOx catalyst to the alkaline sorbent in the blend may be at most 1.00, or at most 0.50, or at most 0.40, or at most 0.30.

In some embodiments, the blend may further comprise an ammonia source.

The ammonia source may include urea, an ammo ium, salt, and, or Nl

In some embodiments, the alkali sorbent in the blend may further contain an ammonia source. The ammonia source may include urea, an ammonium salt, and. or NH₃.

The preferred alkali sorbent in the blend may comprise a compound selected from the group consisting of sodium scsquicarbonate (trona), sodium bicarbonate, and mixture thereof.

In some embodiments, the alkali sorbent in the blend may comprise sodium bicarbonate and an ammonia source.

In some embodiments, the alkali sorbent in the blend may comprise at least

60 wt% sodium bicarbonate and from 0.02 wt% to 2 wt% of ammonia expressed in the form of ammonium ions NH₄ ⁺.

In a particular embodiment, the alkali sorbent in the blend may comprise between 60 % and 98 %, preferably between 80 and 98 %, by weight of sodium bicarbonate, between 1 % and 40 %, preferably between 1 % and 12 % by weight of sodium carbonate and between 0.02 % and 2.0 % by weight of ammonia, expressed in the form of ammonium ions NH₄ , characterized in that the alkali sorbent comprises less than 1 .0 %, preferably less than 0.9 %, more preferably less than 0.8 % by weight of water.

In a particular embodiment, the alkali sorbent in the blend may comprise between 60 % and 98 %, preferably between 80 and 98 %, by weight of sodium bicarbonate, between 1 % and 40 %, preferably between 1 % and 12 % by weight of sodium carbonate and between 0.02 % and 2.0 % by weight of ammonia, expressed in the form of ammonium ions NH₄ ⁺, and comprising from 0.01 to 5 % by weight of a compound selected from hydrocarbons, fatty alcohols, fatty acids, or fatty acid salts , preferably fatty acids having 12 to 20 carbon atoms per molecule or a salt thereof.

In some embodiments, the alkali sorbent in the blend is in the form of particles having a diameter D90 of less than 50 μιη and a diameter D50 of less than 35 μιη, preferably a diameter D90 of less than 35 μιη and a diameter D50 of less than 20 μιη, more preferably a diameter D90 of less than 30 μιη and a diameter D50 of less than 15 μιη, measured by laser diffractometry.

In some embodiments, the catalyst in the blend is in the form of particles having a diameter D90 of less than 50 μιη and a diameter D50 of less than 35 μιη, preferably a diameter D90 of less than 35 μιη and a diameter D50 of less than 20 μιη, more preferably a diameter D90 of less than 30 μιη and a diameter D50 of less than 15 μιη, measured by laser diffractometry.

Use of the supported catalyst

Consequently, another aspect of the present invention also relates to the use of the supported catalyst for the purification of a waste gas. In particular, the supported catalyst may be used for the removal of NOx by contacting the supported catalyst with a waste gas stream contaminated by the NOx pollutants. Since the catalyst is active for the removal of NOx and hence has deNOx activity, the catalyst may be referred to as a "deNOx catalyst".

An embodiment of the present invention also relates to the use of the supported catalyst and the alkali sorbent for the purification of a waste gas.

In particular, the supported deNOx catalyst and the alkali sorbent may be used for the removal of pollutants: NOx and acid gases like SOx, HF, HCl, HBr, HI, and/or H₃PO₄ by contacting the supported deNOx catalyst and the alkali sorbent with a waste gas stream contaminated by these NOx and acid gas (e.g., SOx) pollutants. Purification process for the removal of NOx from waste gas

A particular embodiment of the present invention relates to a deNOx process according to which an ammonia source is injected into a combustion waste gas stream containing NOx; and according to which the catalyst composition is brought into contact with the waste gas stream at a temperature of at least 100°C and preferably at most 600°C to carry out, in the presence of 0₂, a reduction by N¾ of at least a portion of the NOx.

In the treatment process according to the invention, the catalyst particles are contacted with the waste gas stream for a sufficient time so that the catalyst converts by reduction by N¾ at least a portion of the NOx.

Preferably, the particulate catalyst is used with the waste gas stream in a contact reactor such as packed in a fixed bed or fluidized in a fiuidized bed, or is injected in a duct/pipe/conduit through which the waste gas stream flows. The fiuidization gas to maintain the catalyst particles suspended in the fluidized bed may comprise or consist of the waste gas stream to be treated.

In some embodiment of the process for treating a waste gas stream containing NOx, if the catalyst is dispersed into the waste gas to be treated, the catalyst may be injected into the waste gas stream in the form of a dry powder injection or a semi-dry injection of a slurry of the catalyst.

If the catalyst is dispersed into the waste gas to be treated, the resulting mixture is subjected to a separation in order to produce a treated gas which is partially purified of NOx and a spent catalyst that is removed from the treated gas.

In the treatment process according to the invention, the waste gas stream may be a flue gas stream containing at least NOx. The catalyst supported on the porous support particles may be contacted with the flue gas stream, the flue gas stream being at a temperature of at least 100°C, or of at least 150°C, or of at least 180°C, or of at least 200°C, the resulting mixture then being subjected to a separation in order to obtain a resulting solid and a flue gas stream partially purified of NOx. The flue gas stream may be at a temperature of at most 800°C, or of at most 600°C, of at most 550°C, or of at most 500°C.

In some embodiment of the process for treating a waste gas stream containing NOx, the catalyst composition may be packed into a fixed bed in order for the waste gas stream passes through the bed of the catalyst to provide contact of the catalyst with the waste gas. In some embodiment of the process for treating a waste gas stream containing NOx, the catalyst composition may be fluidized in a fluidized bed to provide contact of the catalyst with the waste gas. The fluidization gas to maintain the catalyst particles suspended in the fluidized bed may comprise or consist of the waste gas stream to be treated.

When the catalyst is injected as a powder into a flue gas stream flowing through a flue duct, its use may be once-through - that is to say, the catalyst is not used again. The contact time between the particulate catalyst and the flue gas stream to be treated may be very short in the order of millisecond(s) to seconds, such as at least one millisecond (ms), advantageously at least 5 ms, more advantageously at least 10 ms and/or at most 5 seconds, even more

advantageously at most 4 seconds, yet even more advantageously at most 3 seconds.

When the catalyst is packed or fluidized in a contact reactor, its use may be more long term - that is to say, the catalyst bed, whether fixed or fluidized, is used for a period of time greater than one week or even several months. The contact time between the particulate catalyst and the waste gas effluent to be treated may be in the order of millisecond(s) to seconds, such as at least one millisecond (ms), advantageously at least 5 ms, more advantageously at least 10 ms and/or at most 3 seconds, even more advantageously at most 2 seconds, yet even more advantageously at most 1 second.

The effectiveness of the treatment of NOx may be monitored by comparing the concentrations of NOx upstream (in the waste gas stream) and downstream of the treatment (in the partially treated gas stream), for example by an automatic analyser or by sampling and analysis.

For a deNOx application which is not once-through, the supported catalyst charge of a SCR contact reactor may be in general regularly renewed in portions, for example, by partial purging of the spent catalyst which has been in contact with NOx, and by adding fresh supported catalyst to the contact reactor. "Fresh" catalyst denotes a material which has not been in contact with NOx, whereas

"spent" catalyst denotes a material which has already been in contact with NOx. Such a process thus may ensure a replenishment of the catalyst activity when the catalyst may suffer from some catalytic deactivation after contact with the waste gas stream and reaction with NOx. Purification process for the removal of several pollutants from waste gas

Consequently, the present invention also relates to the use of the supported catalyst and the alkali sorbent for the purification of a waste gas.

In particular, the supported deNOx catalyst and the alkali sorbent may be used for the removal of several pollutants including NOx and acid gases like SOx, HF, HCl, HBr, HI, and/or H₃PO₄ by their injection into a waste gas stream contaminated by these NOx and acid gas (e.g., SOx) pollutants.

The supported deNOx catalyst and the alkali sorbent may be injected together by first forming a blend and then injecting the blend, or by injecting the two materials at the same time and same location into the gas stream for effectively mixing them in situ.

A particular embodiment of the present invention relates to a purification process for the removal of pollutants, such as NOx, acid gas such as SOx (S0₂ & SO₃), HF, HCl, HBr, HI, H₃PO₄, and/or heavy metals like an element selected from the group consisting of : Al, Ag, As, Ba, Be, Bi, Ce, Co, Cd, Cu, Cr, Fe, Hf, Hg, La, Li, Mg, Mn, Mo, Ni, Pb, Pd, Rb, Sb, Se, Sn, Sr, Th, Ti, U, V, Y, Zn, and Zr, from a combustion waste gas stream.

In a particular embodiment, the process comprises the steps:

- an ammonia source is injected into the combustion waste gas stream; - the deNOx catalyst as described herein is brought into contact with the waste gas stream at a temperature of at least 100°C and preferably at most 600°C to carry out, in the presence of 0₂, a reduction by NH₃ of at least a portion of the NOx, and

- the alkali sorbent is brought into contact with the same waste gas stream at a temperature of at least 100°C and preferably at most 600°C to remove at least a portion of the acid gas(es) like SOx, HF, HCl, HBr, HI, and/or H₃PO₄ and/or at least a portion of the heavy metals.

In the process according to the invention, the catalyst particles are contacted with the waste gas stream for a sufficient time so that the catalyst converts by reduction by N¾ at least a portion of the NOx.

In the process according to the invention, the alkali sorbent is contacted with the waste gas stream for a sufficient time so that the alkali sorbent adsorbs/reacts with at least a portion of the acid gas (SOx, HF, HCl, HBr, HI, and/or H₃PO₄) and/or heavy metals.

The deNOx catalyst, the alkali sorbent, and the ammonium source used in the process has been described previously. The deNOx catalyst and/or the alkali sorbent is preferably in the form of particles having a diameter D90 of less than 50 μιη and a diameter D50 of less than 35 μιη, preferably a diameter D90 of less than 35 μιη and a diameter D50 of less than 20 μιη, more preferably a diameter D90 of less than 30 μιη and a diameter D50 of less than 15 μιη, measured by laser diffractometry.

The weight ratio of the DeNOx catalyst to said alkaline sorbent brought into contact with the waste gas stream to be treated may be at least 0.001, or at least 0.005, or at least 0.010, or at least 0.020, or at least 0.030, or at least 0.045. The weight ratio of the deNOx catalyst to said alkaline sorbent brought into contact with the waste gas stream to be treated may be at most 1.00, or at most 0.50, or at most 0.40, or at most 0.30.

Preferably, the particulate catalyst (solid), the sorbent (solid) and the ammonia source (in liquid, gas or solid form) are injected in a duct/pipe/conduit through which the waste gas stream flows.

When the catalyst is dispersed into the waste gas to be treated, the catalyst may be injected into the waste gas stream in the form of a dry powder injection or a semi-dry injection of a slurry of the catalyst.

When the sorbent is dispersed into the waste gas to be treated, the sorbent may be injected into the waste gas stream in the form of a dry powder injection or a semi-dry injection of a slurry of the catalyst.

When the ammonia source is dispersed into the waste gas to be treated, the ammonia source may be injected into the waste gas stream in the form of a gas (NH₃ gas), in the form of a liquid (solution of ammonium bicarbonate and/or solution of urea, solution of ammonia, or combinations thereof), in the form of a powder (urea).

Alternatively or additionally, the ammonia source may be present in the catalyst composition or in the alkali sorbent.

In the treatment process according to the invention, the waste gas stream may be a flue gas stream containing at least NOx and SOx.

The injection in the treatment process may proceed as follows:

- an alkaline sorbent is injected in the flue gas stream,

- an ammonia source is injected in the flue gas stream downstream of the point of injection where the alkaline sorbent is injected;

- a particulate deNOx catalyst (as described herein) containing a Ca- deficient hydroxyapatite is injected into the flue gas stream downstream of the point of injection where the alkaline sorbent and the ammonia source is injected.

The injection in the treatment process may proceed as follows:

- an alkaline sorbent is injected in the flue gas stream,

- an ammonia source and a particulate deNOx catalyst (as described herein) are injected simultaneously in the flue gas stream downstream of the point of injection where the alkaline sorbent is injected.

The injection in the treatment process may proceed as follows:

- an alkaline sorbent and the ammonia source are injected simultaneously injected in the flue gas stream,

- the particulate deNOx catalyst is injected separately in the flue gas stream downstream of the point of injection where the alkaline sorbent and the ammonia source are injected.

The injection in the treatment process may proceed as follows:

- the alkali sorbent, the ammonia source , and the deNOx catalyst are injected simultaneously into the flue gas stream.

The injection in the treatment process may proceed as follows:

- the ammonia source is injected into the flue gas stream;

- the alkali sorbent and the particulate deNOx catalyst are injected simultaneously in the flue gas stream downstream of the point of injection where the ammonia source is injected.

If the catalyst and the sorbent both in solid form (powder) are dispersed into the waste gas stream to be treated, the resulting mixture is subjected to a gas/solid separation in order to produce a treated gas which is partially purified of NOx and SOx and solids comprising spent catalyst and sorbent in order for the solids to be removed from the treated gas. The separation preferably comprises a bag filter or an electrostatic precipitator (ESP), preferably a bag filter.

The supported catalyst and the sorbent may be dispersed in the flue gas stream, the flue gas stream being at a temperature of at least 100°C, or of at least 150°C, or of at least 180°C, or of at least 200°C.

The supported catalyst and the sorbent may be dispersed in the flue gas stream, the flue gas stream being at a temperature of at most 800°C, or of at most 600°C, of at most 550°C, or of at most 500°C, of at most 450°C, of at most 400°C. When the catalyst and sorbent are injected as powder into a flue gas stream flowing through a flue duct, their use may be once-through - that is to say, the catalyst and the sorbent are not used again. The contact time between the solid particles (catalyst and sorbent) and the waste gas stream to be treated may be very short in the order of millisecond(s) to seconds, such as at least one millisecond (ms), advantageously at least 5 ms, more advantageously at least 10 ms and/or at most 5 seconds, even more advantageously at most 4 seconds, yet even more advantageously at most 3 seconds.

The effectiveness of the treatment of NOx and SOx may be monitored by comparing the concentrations of NOx and SOx upstream (in the waste gas stream) and downstream of the treatment (in the partially treated gas stream), for example by an automatic analyser or by sampling and analysis.

FIG. 4 is a schematic of a treatment process according to an embodiment of the present invention, in which a flue gas stream (dashed line in the figure) containing NOx and SOx and optionally heavy metals, is treated, and in which an alkali sorbent, an ammonia source, and the deNOx catalyst are injected separately into the flue gas. The process proceeds as follows:

FIG. 5 is a schematic of a treatment process according to another embodiment of the present invention, in which a flue gas stream (dashed line in the figure) containing NOx and SOx and optionally heavy metals, is treated and an alkali sorbent is injected into the flue gas stream and separately the ammonia source and the deNOx catalyst are injected simultaneously downstream into the flue gas stream. The process proceeds as follows:

- an alkaline sorbent 2 is injected in the flue gas stream,

- an ammonia source 1 and the particulate deNOx catalyst 3 (as described herein) containing a Ca-deficient hydroxyapatite are injected simultaneously in the flue gas stream downstream of the point of injection where the alkaline sorbent 2 is injected; and

- the rest of the process downstream of these injections is the same as described for FIG. 4.

In this embodiment, the ammonia source may be injected at the same time and at the same location as the catalyst 3 is, but the N¾ source and catalyst are not blended before they are injected.

In another embodiment, the N¾ source and catalyst are blended before they are injected together into the flue gas. FIG. 6 is a schematic of a treatment process according to yet another embodiment of the present invention, in which a flue gas stream (dashed line in the figure) containing NOx and SOx and optionally heavy metals, is treated and an alkali sorbent and the ammonia source are injected simultaneously into the flue gas stream and separately the deNOx catalyst is injected downstream into the flue gas stream. The process proceeds as follows:

- an alkaline sorbent 2 and the ammonia source 1 are injected

simultaneously injected in the flue gas stream,

- the particulate deNOx catalyst 3 (as described herein) containing a Ca- deficient hydroxyapatite is injected separately in the flue gas stream downstream of the point of injection where the alkaline sorbent 2 and the ammonia source 1 are injected; and

In this embodiment, the ammonia source may be injected at the same time and at the same location as the alkali sorbent is, but the NH₃ source and catalyst are not blended before they are injected.

In preferred embodiment, the NH₃ source and the alkali sorbent are blended before they are injected together into the flue gas.

In more preferred embodiment, the alkali sorbent is manufactured so that its composition includes a suitable NH₃ source.

FIG. 7 is a schematic of a treatment process according to a preferred embodiment of the present invention, in which a flue gas stream (dashed line in the figure) containing NOx and SOx and optionally heavy metals, is treated, and the alkali sorbent 2, the ammonia source 1, and the deNOx catalyst 3 are injected simultaneously into the flue gas stream and the rest of the process downstream of this injection is the same as described for FIG. 4.

In this embodiment, the ammonia source and the catalyst may be injected at the same time and at the same location as the alkali sorbent is, but the NH₃ source, the alkali sorbent and the catalyst are not blended together before they are injected at the same time and at the same location in a flue gas duct.

In preferred embodiment, the NH₃ source and the alkali sorbent are blended before they are injected together into the flue gas, and the deNOx catalyst is injected at the same time and at the same location where the blend is injected. In more preferred embodiment, the alkali sorbent is manufactured so that its composition includes a suitable NH₃ source, and the deNOx catalyst is injected at the same time and at the same location where the NH₃ source- containing sorbent is injected.

In most preferred embodiment, the NH₃ source, the alkali sorbent and the catalyst are comprised in a blend, and this blend is injected into the flue gas stream.

FIG. 8 is a schematic of a treatment process according to yet another preferred embodiment of the present invention, in which a flue gas stream (dashed line in the figure) containing NOx and SOx and optionally heavy metals, is treated and the alkali sorbent and the deNOx catalyst are injected

simultaneously into the flue gas stream and separately the NH₃ source is injected upstream into the flue gas stream. The process proceeds as follows:

- the ammonia source 1 is injected into the flue gas stream;

- an alkaline sorbent 2 and the particulate deNOx catalyst 3 (as described herein) containing a Ca-deficient hydroxyapatite are injected simultaneously in the flue gas stream downstream of the point of injection where the ammonia source 1 is injected; and

In this embodiment, the deNOx catalyst may be injected at the same time and at the same location as the alkali sorbent is, but the alkali sorbent and deNOx catalyst are not blended before they are injected.

In preferred embodiment, the deNOx catalyst and the alkali sorbent are blended before they are injected together into the flue gas.

In particular, the present invention relates to the following embodiments : Item 1. Process for producing a calcium phosphate porous support, according to which :

in a first step, use is made of a source of calcium and a source of phosphate ions in water, in a molar ratio that is adjusted so as to obtain a Ca/P molar ratio of between 0.5 and 1.6, and the source of calcium is reacted with the phosphate ions at a pH of between 2 and 8, in order to obtain a suspension (A) of calcium phosphate, and

- in a second step, added to the suspension (A) are an alkaline compound comprising hydroxide ions in order to set a pH of more than 8, preferably of more than 8.5, preferably of at least 9, or of at least 10, and an additional source of calcium in order to obtain a suspension (B) of calcium phosphate porous support having a Ca/P molar ratio of more than 1.6.

Item 2. Process according to the preceding item, in which in the second step the pH is set between 8 and 10.5, preferably between 8.5 and 10.

Item 3. Process according to any one of the preceding items, in which the source of calcium comprises calcium carbonate, or calcium oxide, or calcium hydroxide, or calcium chloride, or calcium nitrate, or calcium acetate.

Item 4. Process according to any one of the preceding items, in which the source of phosphate ions is phosphoric acid.

Item 5. Process according to any one of items 1 to 3, in which the source of phosphate ions is a dihydrogen phosphate salt such as a sodium, potassium or ammonium dihydrogen phosphate salt, preferably a sodium dihydrogen phosphate salt.

Item 6. Process according to any one of items 1 to 3, in which the source of phosphate ions is a monohydrogen phosphate salt such as a sodium, potassium or ammonium monohydrogen phosphate salt, preferably a sodium

monohydrogen phosphate.

Item 7. Process according to any one of the preceding items, wherein in the second step, the suspension (B) of calcium phosphate porous support has a Ca/P molar ratio of at most 5, preferably of at most 3, more preferably still of at most 2.

Item 8. Process according to any one of the preceding items, in which, in the first step, the Ca/P molar ratio is :

- between 0.50 and 1.35, preferably between 0.70 to 1.30,

- or : between 1.4 and 1.6, preferably between 1.4 and 1.5.

Item 9. Process according to any one of the preceding items, wherein the source of calcium is in the form of powder or aqueous suspension of powder and the powder is selected from : calcium carbonate, calcium oxide, calcium hydroxide, or a mixture thereof, and the powder has a mean particle size of less than 300 μιη.

Item 10. Process according to any one of the preceding items, in which the stirring speed and the density of suspension, in the second step and

advantageously also in the first step, are adjusted in order to avoid the appearance of a calcium phosphate gel having a viscosity of at least 100 cps or at least 200 cps. Item 11. Process according to any one of the preceding items, in which, in the second step, the alkaline compound used that comprises hydroxide ions is sodium hydroxide and/or calcium hydroxide and/or magnesium hydroxide.

Item 12. Process according to any one of the preceding items, in which, in the second step, the additional source of calcium is selected from calcium chloride, calcium nitrate, or calcium acetate, preferably calcium chloride, and is added in addition to the alkaline compound, in order to finely adjust the Ca/P molar ratio and limit the concentration of phosphorus element in the aqueous solution (C) of the suspension (B) to at most 5 mmol, advantageously to at most 0.5 mmol, more advantageously to at most 0.05 mmol of phosphorus element per litre of aqueous solution (C).

Item 13. Process according to any one of the preceding items, in which the first step is carried out at a temperature of less than 50°C, preferably of at most 45°C, more preferably of at most 40°C.

Item 14. Process according to any one of items 1 to 12, in which the first step is carried out at a temperature of at least 50°C, preferably of at least 55°C, more preferably of at least 60°C.

Item 15. Process according to any one of the preceding items, in which the second step is carried out at a temperature of at least 40°C, preferably of at least 45°C, more preferably of at least 55°C, even more preferably of at least 60°C, or of at least 80°C.

Item 16. Process according to any one of the preceding items wherein at the end of the second step, the suspension (B) comprises an aqueous solution (C) and calcium phosphate porous support particles, and

- in a third step, a portion of the aqueous solution (C) is separated from the suspension (B) in order to obtain an aqueous suspension (D) comprising at least 18 % and at most 50 % of calcium phosphate porous support particles, or to obtain a wet solid (D') comprising at least 50 % and at most 80 % of calcium phosphate porous support particles, or to obtain a pulverulent solid (D") comprising at least 80 % and at most

95 % of calcium phosphate porous support particles and at least 5 % and at most 20 % of water.

Item 17. Particles of calcium phosphate porous support obtainable by the process according to item 13, comprising at least 60 % by weight of

hydroxyapatite, and having a mean size of at least 30 μιη. Item 18. Particles of calcium phosphate porous support according to the preceding item comprising at least 70 %, preferably at least 75 %, more preferably at least 80 % by weight of hydroxyapatite.

Item 19. Particles of calcium phosphate porous support according to Items 17 or 18 having a mean size of at least 50 μιη.

Item 20. Particles of calcium phosphate porous support according to items 17 to 19 having a specific surface area of at least 50 m²/g, more preferably of at least 110 m²/g, even more preferably of at least 120 m²/g, or of at least 140 m²/g, or at least 160 m²/g.

Item 21. Particles of calcium phosphate porous support according to Items

17 or 19 having a mean size of at most 200 μιη, preferably of at most 100 μιη, more preferably of at most 70 μιη.

Item 22. Particles of calcium phosphate porous support according to items 17 to 21 comprising at least 2 %, preferably at least 2.5 wt% or at least 3 wt%, more preferably at least 5 %, and yet more preferably at least 6 % by weight of hydroxide ions, or comprising from 2 wt% to 6 wt% of hydroxide ions, preferably from 2.5 wt% to 5 wt% of hydroxide ions.

Item 23. Particles of calcium phosphate porous support according to items 17 to 22 covered with plate-like crystallites, and wherein the plate-like crystallites have a thickness of at most 25 nm, preferably of at most 20 nm, more preferably of at most 10 nm.

Item 24. Particles of calcium phosphate porous support according to item 23 wherein the thickness of plate-like crystallites is at least 1 nm, preferably at least 2 nm, more preferably at least 4 nm.

Item 25. Particles of calcium phosphate porous support according to Items

17 to 24 and having a mean size of at least 50 μιη.

Item 26. Particles of calcium phosphate porous support according to Items 17 to 25 wherein the solubilized phosphate of 10 g of such particles stirred in 90 mL of water during 24 hours with a lab magnetic barrel, then filtrated on a 0.45 μιη nitrocellulose membrane, is less than 10 mg P0₄/ L of water.

Item 27. Aqueous suspension (D) comprising at least 25 % and at most 50 % by weight of calcium phosphate porous support particles according to item 17 to 26, preferably obtainable from the process of item 16.

Item 28. A pulverulent solid (D") comprising at least 80 wt% and at most 95 wt% of the calcium phosphate porous support particles according to item 17 to 26 and comprising at least 5 wt%, preferably at least 6 wt%, more preferably at least 10 wt%, even more preferably at least 15 wt% of water, advantageously obtainable from the process of item 16.

Item 29. A pulverulent solid (D") according to item 28 comprising at most 20 wt% of water.

Item 30. Particles of calcium phosphate porous support obtainable by the process according to item 14, comprising at least 60 % by weight of

hydroxyapatite, and having a mean size of at most 30 μιη, preferably of at most 20 μιη and having a specific surface area of at least 15 m²/g, preferably of at least 50 m²/g, and having a content of hydroxide ions of greater than 2 % by weight, preferably greater than 3.5 % by weight, and more preferably greater than 4 % by weight.

Item 31. A porous support comprises at least 60 wt % of a calcium- deficient hydroxyapatite having a calcium to phosphate molar ratio (Ca/P) of less than 1.67, preferably more than 1.5 and less than 1.67; the porous support having a specific BET surface area measured after heat treatment at 200°C of at least 110 m2/g and a pore volume measured after heat treatment at 200°C of at least 0.5 cm3/g.

Item 32. The porous support according to Item 31 further comprising calcium carbonate in an amount of less than 20 wt%, preferably from 1 wt% to 19 wt%, more preferably from 2 wt% to 18 wt%, even more preferably from 5 wt% to 15 wt%, yet even more preferably from 7 wt% to 13 wt%, most preferably from 8 wt% to 12 wt%.

Item 33.- The porous support according to Item 31 or 32, comprising less than 1 wt% of calcium dihydroxide Ca(OH)₂, preferably less than 0.5 wt% calcium dihydroxide Ca(OH)₂, more preferably less than 0.3 wt% calcium dihydroxide Ca(OH)₂, even more preferably less than 0.2 wt% calcium dihydroxide Ca(OH)₂, most preferably being substantially free of calcium dihydroxide Ca(OH)₂.

Item 34 - The porous support according to any of the items 31 to 33, further comprising water in an amount of less than 20 wt%, preferably from 1 wt% to 18 wt%, more preferably from 2 wt% to 15 wt%, even more preferably from 4 wt% to 12 wt%, yet even more preferably from 5 wt% to 11 wt% most preferably from 6 wt% to 11 wt%.

Item 35 - The porous support according to any of the Items 31 to 34, comprising a Ca/P molar ratio of 1.60 or more, preferably of 1.65 or more, preferably of 1.67 or more, more preferably of 1.68 or more. Item 36 - The porous support according to any of the Items 31 to 35, comprising a Ca/P molar ratio greater than the Ca/P molar ratio of the calcium- deficient hydroxyapatite.

Item 37 - The porous support according to any of the Items 31 to 36, comprising at least 65 wt%, preferably at least 70 wt%, more preferably at least 75 wt%, yet more preferably at least 80 wt%, yet most preferably at least 85 wt%, of the calcium-deficient hydroxyapatite.

Item 38 - The porous support according to any of the Items 31 to 37, comprising at most 99 wt%, preferably at most 98 wt%, more preferably at most 97 wt%, yet more preferably at most 95 wt%, even more preferably at most 93 wt%, most preferably at most 91 wt% of the calcium-deficient hydroxyapatite.

Item 39 - The porous support according to any of the Items 31 to 38, having a BET specific surface area measured after heat treatment at 200°C of at least 120 m²/g and/or at most 160 m²/g.

Item 40 - The porous support according to any of the Items 31 to 39, having a BET specific surface area measured after heat treatment at 400°C of at least 60 m²/g and/or at most 100 m²/g.

Item 41 - The porous support according to any of the Items 31 to 40, having a BET specific surface area measured after heat treatment at 600°C of at least 20 m²/g and/or at most 40 m²/g.

Item 42 - The porous support according to any of the Items 31 to 41 , having a pore volume measured after heat treatment at 200°C of at least 0.55 cm³/g, preferably of at least 0.55 cm³/g and/or at most 1.0 cm³/g, preferably of at most 0.95 cm³/g.

Item 43 - The porous support according to any of the Items 31 to 42, having a pore volume measured after heat treatment at 400°C of at least 0.50 cm³/g, preferably of at least 0.60 cm³/g and/or at most 1 cm³/g.

Item 44 - The porous support according to any of the Items 31 to 43, having a pore volume measured after heat treatment at 600°C of at least 0.42 cm³/g, preferably of at least 0.44 cm³/g and/or at most 0.8 cm³/g, preferably of at most 0.75 cm³/g.

Item 45- A catalyst composition for catalytic reduction of NO_x compounds, comprising an active catalyst component deposited on the porous support of any of the Items 31 to 44, wherein said active catalyst component comprises iron. Item 46- The catalyst composition for catalytic reduction of NO_x compounds according to any of the preceding Item 45, according to which the active catalyst component comprises

- at least 0.1 wt%, preferably at least 0.5 wt%, more preferably at least 1.0 wt%, most preferably at least 1.5 wt%, of iron;

and/or

- at most 15 wt%, preferably at most, more preferably at most 13 wt%,yet more preferably at most 12 wt%, most preferably at most 11 wt%, of iron.

Item 47- The catalyst composition for catalytic reduction of NO_x compounds according to any of the Items 45-46, according to which the active catalyst component is deposited on the porous support by ion exchange.

Item 48- The catalyst composition for catalytic reduction of NO_x compounds according to any of the Items 45-47, according to which the active catalyst component is deposited on the porous support using an iron precursor selected from the group consisting of iron nitrate, iron chloride, iron perchlorate, iron sulfate, iron fluorosilicate, any hydrated form thereof, and any mixture thereof; preferably using an iron precursor selected from the group consisting of iron (III) nitrate, iron (III) chloride, iron (III) sulfate, iron (III) perchlorate, any hydrated form thereof, and any mixture thereof.

Item 49- The catalyst composition for catalytic reduction of NO_x compounds according to any of the Items 45-48, which is subjected to a heat treatment using a temperature from 105°C up to 500°C, preferably from 200°C to 400°C, prior to being used as a catalyst.

Item 50- The catalyst composition for catalytic reduction of NO_x compounds according to any of the Items 45-49, which is not subjected to a heat treatment using a temperature greater than 200°C, prior to being used as a catalyst for catalytic reduction of NO_x compounds.

Item 51 - The catalyst composition for catalytic reduction of NO_x compounds according to any of the Items 45-50, in which the catalyst composition has a BET specific surface area measured after being calcined at 400°C of at least 65 m²/g and/or at most 100 m²/g, and /or in which the catalyst composition has a pore volume measured after being calcined at 400°C of :

- at least 0.3 cm³/g, preferably of at least 0.41 cm³/g, and/or

- at most 1.1 cm³/g, preferably of at most 1.0 cm³/g, more preferably of at most 0.9 cm³/g. most preferably of at most 0.8 cm³/g. Item 52- The catalyst composition for catalytic reduction of NO_x compounds according to any of the Items 45-51, having a microporous and mesoporous morphology, and/or in which the catalyst composition has an average pore radius measured after being calcined at 400°C of at least 5 nm, or at least 7 nm, and/or at most 30 nm, or at most 25 nm, preferably wherein the average pore radius is determined from Gurvitch rule : rp = 2 (Vp/SBET) 10³, where Vp is the pore volume in cm³/g, SBET is the BET surface area in m²/g, and the pore radius is in nm.

Item 53- A catalyst composition for catalytic reduction of NO_x compounds, comprising an active catalyst component deposited on the particles of the calcium phosphate porous support according to any of the Items 17 to 26 or Item 30, or of the pulverulent solid (D") according to Item 28 or 29, wherein the active catalyst component comprises iron.

Item 54 - Process for treating a waste gas stream containing nitrogen oxides (NOx), said gas stream originating from a combustion process, in which an ammonia source is injected into the waste gas stream; and in which the catalyst composition according to any of the Items 45-53 is brought into contact with the waste gas stream containing ammonia at a temperature of at least 100°C and preferably at most 600°C to carry out, in the presence of 0₂, a reduction by NH₃ of at least a portion of the NOx to N₂ and water.

Item 55 - Process according to item 54 in which the waste gas stream temperature is :

- at least 105°C, or at least 120°C, or at least 150°C, or at least 180°C, or at least 200 °C, or at least 250°C, or at least 300°C; and/or

- at most 550°C, or at most 500°C, or at most 450°C, or at most 400°C.

Item 56 - Process according to Item 54 or 55 in which the catalyst composition is injected into the waste gas stream in the form of a dry powder injection or a semi-dry injection of a slurry of the catalyst.

Item 57 - Process for treating a waste gas stream containing nitrogen oxides (NOx) and contaminants selected from the group consisting of heavy metals, acid gases (such as S0₂, SO₃, HC1, and/or HF) and combinations thereof, said waste gas stream originating from a combustion process, said treating process comprising:

injecting an alkali sorbent into the waste gas stream, said alkali sorbent comprising a compound selected from the group consisting of sodium bicarbonate, sodium carbonate, sodium sesquicarbonate (trona), quick lime, hydrated lime, limestone, and combinations thereof;

contacting at least a portion of the contaminants with the alkali sorbent to remove at least a portion of the contaminants from the waster gas stream,

injecting an ammonia source into the waste gas stream;

injecting a catalyst into the waste gas stream; and

converting, in the presence of 0₂, by reduction with N¾ of at least a portion of the NOx in the waste gas stream to N₂ and water at a temperature of at least 100°C and preferably at most 600°C,

the catalyst comprises an active catalyst component deposited on a porous support;

wherein said active catalyst component comprises iron; and

Item 58 -Process according to Item 57 wherein the porous support of the catalyst further comprises calcium carbonate in an amount of less than 20 wt%, preferably from 1 wt% to 19 wt%, more preferably from 2 wt% to 18 wt%, even more preferably from 5 wt% to 15 wt%, yet even more preferably from 7 wt% to 13 wt%, most preferably from 8 wt% to 12 wt%.

Item 59 -Process according to Item 57 or 58, wherein the porous support of the catalyst comprises less than 1 wt% of calcium dihydroxide Ca(OH)₂, preferably less than 0.5 wt% calcium dihydroxide Ca(OH)₂, more preferably less than 0.3 wt% calcium, dihydroxide Ca(OH)₂, even more preferably less than 0.2 wt% calcium dihydroxide Ca(OH)₂, most preferably being substantially free of calcium dihydroxide Ca(OH)₂.

Item 60 -Process according to any of Items 57-59, wherein the porous support of the catalyst further comprises water in an amount of less than 20 wt%, preferably from 1 wt% to 18 wt%, more preferably from 2 wt% to 15 wt%, even more preferably from 4 wt% to 12 wt%, yet even more preferably from 5 wt% to 11 wt% most preferably from 6 wt% to 1 1 wt%.

Item 61 -Process according to any of Items 57-60, wherein the porous support of the catalyst comprises a Ca/P molar ratio greater than the Ca/P molar ratio of the calcium-deficient hydroxyapatite. Item 62 -Process according to any of Items 57-61 , wherein the porous support of the catalyst comprises a Ca/P molar ratio of 1.60 or more, preferably of 1.65 or more, preferably of 3 .67 or more, more preferably of 1.68 or more.

Item 63 -Process according to any of Items 57-62, wherein the porous support of the catalyst compri ses :

- at least 65 wt%, preferably at least 70 wt%, more preferably at least 75 wt%, yet more preferably at least 80 wt%, yet most preferably at least 85 wt%, of the calcium-deficient hydroxyapatite,

and/or comprises

Item 64 -Process according to any of Items 57-63, wherei the porous support has a specific BET surface area of at least 1 10 nr/g and a pore v olume of at least 0.5 cm³/g after a heat treatment at 200°C

Item 65 -Process according to any of Items 57-64, wherein the catalyst has a BET specific surface area measured after being calcined at 400°C of at least 65 m²/g and/or at most 100 nr/g.

Item 66 -Process according to any of Items 57-65, wherein the catalyst has a pore volume measured after being calcined at 400 °C of:

- at least 0.3 cm Vg, preferably of at least 0.41 cm³/g, and or

- at most 1 . 1 cm³/g, preferably of at most 1 .0 cffiVg, more preferably of at most 0.9 cmVg. most preferably of at most 0.8 cm³/g.

Item 67 -Process according to any of Items 57-66, wherein the activ e catalyst component comprises :

- at least 0. 1 wt%, preferably at least 0.5 wt%, more preferably at least 1 .0 wt%, most preferably at least 1 .5 wt%, of iron;

and/or

- at most 1 5 wt%, preferably at most, more preferably at most 13 wt%,yet more preferably at most 1 2 wt%, most preferably at most 1 1 wt%, of iron.

Item 68 -Process according to any of Items 57-67, wherein the active catalyst component is deposited on the porous support by ion exchange or impregnation using an iron precursor selected from the group consisting of iron nitrate, iron chloride, iron perchlorate. iron sulfate, iron fluorosilicate, any hydrated form thereof, and any mixture thereof: preferably using an iron precursor selected from the group consisting of iron (III) nitrate, iron (III) chloride, iron ( 111 ) pcrchlorate, iron ( II I ) sulfate, any hydrated form thereof, and any mixture thereof

Item 69 -Process according to any of Items 57-68, wherein the alkali sorbent comprises or consists of a compound selected from the group consisting of trona, sodium bicarbonate, and mixture thereof.

Item 70 -Process according to any of Items 57-69, wherein the alkali sorbent contains an ammonia source.

Item 71 -Process according to any of Items 57-70, wherein the weight ratio of the catalyst to said alkali sorbent is

- at least 0.001, or at least 0.005, or at least 0.010, or at least 0.020, or at least 0.030, or at least 0.045; and/or

- at most 1.00, or at most 0.50, or at most 0.40, or at most 0.30.

Item 72 -Process according to any of Items 57-71 , wherein the alkali sorbent and the catalyst are mixed to form a blend to be injected together into the waste gas stream.

Item 73 -Process according to Item 72, wherein the blend comprises

- at least 0. 1 wt%, or at least 0.2 wt%, or at least 0.5 wt%, or at least 1 wt%, or at least 3 wt%, or at least 5 wt%, of the catalyst, and/or

- at most 20 wt%, or at most 1 5 wt%, or at most 12 wt%, or at most 10 wt%, of the catalyst.

Item 74 - Process according to any of Items 57-73, wherein the alkali sorbent and the catalyst are injected sequentially into the waste gas stream flowing through a duct, and wherein the alkali sorbent is injected in a duct at a location upstream of where the catalyst is injected.

Item 75 -Process according to any of Items 57-74, wherein the ammonia source and the catalyst are injected simultaneously into the waste gas stream.

Item 76 - Process according to any of Items 57-75, wherein the temperature is at least 105 °C, or at least 120 °C, or at least 150 °C, or at least 180 °C, or at least 200 °C, or at least 250 °C, or at least 300 °C; and/or at most 550 °C, or at most 500 °C, or at most 450 °C, or at most 400 °C.

Item 77 - Process according to any of Items 57-76, wherein the alkali sorbent is selected from the group consisting of trona, sodium bicarbonate, and mixture thereof. Item 78 - Process according to any of Items 57-77, wherein the alkali sorbent contains an ammonia source.

Item 79 - Process according to any of Items 57-78, wherein the weight ratio of the catalyst to said alkali sorbent is

- at most 1.00, or at most 0.50, or at most 0.40, or at most 0.30.

Item 80 - Process according to any of Items 57-79, wherein the catalyst further comprises an ammonia source.

Item 81 - Process according to any of Items 57-80, wherein the alkali sorbent further comprises an ammonia source.

Item 82 - Process according to Item 81 , wherein the alkali sorbent comprises sodium bicarbonate and an ammonia source.

Item 83 - Process according to any of Items 57-82, wherein the ammonia source is urea, an ammonium salt, and/or NH3.

Item 84 - Process according to Item 82, wherein the alkali sorbent comprises at least 60 wt% sodium bicarbonate and from 0.02 wt% to 2 wt% of ammonia expressed in the form of ammonium ions NH .

Item 85 - Process according to Item 84, wherein the alkali sorbent comprises between 60 % and 98 %, preferably between 80 and 98 %, by weight of sodium bicarbonate, between 1 % and 40 %, preferably between 1 % and 12 % by weight of sodium carbonate and between 0.02 % and 2.0 % by weight of ammonia, expressed in the form of ammonium ions NH₄ ⁺, characterized in that the alkali sorbent comprises less than 1 .0 %, preferably less than 0.9 %, more preferably less than 0.8 % by weight of water.

Item 86 - Process according to Item 84, wherein the alkali sorbent comprises comprises between 60 % and 98 %, preferably between 80 and 98 %, by weight of sodium bicarbonate, between 1 % and 40 %, preferably between 1 % and 12 % by weight of sodium carbonate and between 0.02 % and 2.0 % by weight of ammonia, expressed in the form of ammonium ions NH₄ ⁺, and comprising from 0.01 to 5 % by weight of a compound selected from

hydrocarbons, fatty alcohols, fatty acids, or fatty acid salts , preferably fatty acids having 12 to 20 carbon atoms per molecule or a salt thereof.

Item 87 - Process according to any of Items 57-86, wherein the alkali sorbent is in the form of particles having a diameter D90 of less than 50 μιη and a diameter D50 of less than 35 μιη, preferably a diameter D90 of less than 35 μιη and a diameter D50 of less than 20 μιη, more preferably a diameter D90 of less than 30 μιη and a diameter D50 of less than 15 μιη, measured by laser

diffractometry.

Item 88 - Process according to any of Items 57-87, wherein the catalyst is in the form of particles having a diameter D90 of less than 50 μιη and a diameter D50 of less than 35 μιη, preferably a diameter D90 of less than 35 μιη and a diameter D50 of less than 20 μιη, more preferably a diameter D90 of less than 30 μιη and a diameter D50 of less than 15 μιη, measured by laser diffractometry.

Item 89 - A blend comprising or consisting of an alkali sorbent and a catalyst,

said alkali sorbent being selected from the group consisting of limestone, lime, trona, sodium bicarbonate, and combinations thereof,

said catalyst comprising an active catalyst component deposited on a porous support; wherein said active catalyst component comprises iron;

wherein said porous support comprises at least 60 wt % of a calcium- deficient hydroxy apatite having a calcium to phosphate molar ratio (Ca/P) of less than 1.67, preferably more than 1 .5 and less than 1.67.

Item 90 - Blend according to Item 89, comprising

- at least 0. 1 wt%, or at least 0.2 wt%, or at least 0.5 wt%, or at least 1 wt%, or at least 3 wt%, o at least 5 wt%, of the catalyst, and/or

- at most 20 wt%, or at most 1 5 wt%, or at most 12 wt%, or at most 10 wt%, of the catalyst;

Item 91 - Blend according to Item 89 or 90, wherein the porous support of the catalyst further comprises calcium carbonate in an amount of less tha 20 wt%, preferably from 1 wt% to 19 wt%, more preferably from 2 wt% to 18 wt%, even more preferably from 5 wt% to 15 wt%, yet even more preferably from 7 wt% to 13 wt%, most preferably from 8 wt% to 12 wt%.

Item 92 - Blend according to any of Items 89-91 , wherein the porous support of the catalyst comprises less than I wt% of calcium dihydroxide Ca(OH)₂, preferably less than 0.5 wt% calcium dihydroxide Ca(OH)₂, more preferably less than 0.3 wt% calcium dihydroxide Ca(OH)₂, ev en more preferably less than 0.2 wt% calcium dihydroxide Ca(OH)₂, most preferably being substantially free of calcium dihydroxide Ca(OH)₂.

Item 93 - Blend according to any of Items 89-91 , wherein the porous support of the catalyst further comprises water in an amount of less than 20 wt%, preferably from 1 wt% to 18 wt%, more preferably from 2 wt% to 15 wt%, even more preferably from 4 wt% to 1 2 wt%, yet even more preferably from 5 wt% to 1 1 wt% most preferably from 6 wt% to 1 1 wt%.

Item 94 - Blend according to any of Items 89-92, wherein the porous support of the catalyst comprises a Ca/P molar ratio greater than the Ca/P molar ratio of the calcium-deficient hydroxyapatite.

Item 94 - Blend according to any of Items 89-93, wherein the porous support of the catalyst comprises a Ca/P molar ratio of 1.60 or more, preferably of 1.65 or more, preferably of 1.67 or more, more preferably of 1.68 or more.

Item 95 - Blend according to any of Items 89-94, wherein the porous support of the catalyst comprises :

and/or comprises

- at most 99 wt%, preferably at most 98 wt%, more preferably at most 97 wt%, yet more preferably at most 95 wt%, even more preferably at most 93 wt%, most preferably at most 91 wt% of the calcium-deficient hydroxyapat ite.

Item 96 - Blend according to any of Items 89-95, wherein the porous support has a specific BET surface area of at least 1 10 m²/g and a pore volume of at least 0.5 env /g after a heat treatment at 200°C

Item 97 - Blend according to any of Items 89-96, wherein the catalyst has a BET specific surface area measured after being calcined at 400°C of at least 65 m²/g and/or at most 1 00 m²/g.

Item 98 - Blend according to any of Items 89-97, wherein the catalyst has a pore volume measured after being calcined at 400°C of:

- at least 0.3 cmVg, preferably of at least 0.4 1 env /g, and/or

- at most 1 . 1 cm³/g, preferably of at most 1 .0 cm³/g, more preferably of at most 0.9 cm³/g. most preferably of at most 0.8 cmVg.

Item 99 - Blend according to any of Items 89-98, wherein the active catalyst component comprises :

- at least 0. 1 wt%, preferably at least 0.5 wt%, more preferably at least 1 .0 wt%, most preferably at least 1 .5 wt%, of i on;

and/or

- at most 1 5 wt%, preferably at most, more preferably at most 13 wt%,yet more preferably at most 12 wt%, most preferably at most 1 1 wt%, of iron. Item 100 - Blend according to any of Items 89-99, wherein the active catalyst component is deposited on the porous support by ion exchange or impregnation using an iron precursor selected from the group consist ing of iron nitrate, iron chloride, iron perchlorate. iron sulfate, iron fluorosilicate, any hydrated form thereof, and any mixture thereof; preferably using an iron precursor selected from the group consisting of iron (III) nitrate, iron (III) chloride, iron (III) sulfate, iron (III) perchlorate, any hydrated form thereof, and any mixture thereof.

Item 101 - Blend according to any of Items 89- 100, wherein the alkali sorbent comprises a compound selected from the group consist ing of trona, sodium bicarbonate, and mixture thereof.

Item 102 - Blend according to any of Items 89- 101 , wherein the alkali sorbent contains an ammonia source.

Item 103 - Blend according to any of Items 89- 102, wherein the weight ratio of the catalyst to said alkali sorbent is

- at least 0.001 , or at least 0.005, or at least 0.010, or at least 0.020, or at least 0.030, or at least 0.045; and/or

- at most 1.00, or at most 0.50, or at most 0.40, or at most 0.30.

Item 103 - Blend according to any of Items 89- 102, further comprising an ammonia source.

Item 104 - Blend according to Item 103, w herein the ammonia source is urea, an ammonium salt, and or NH3.

Item 105 - Blend according to Item 103 or 104, wherein the alkali sorbent comprises sodium bicarbonate and an ammonia source.

Item 106 - Blend according to any of Items 103- 105, wherein the alkali sorbent comprises at least 60 wt% sodium bicarbonate and from 0.02 wt% to 2 wt % of ammonia expressed in the form of ammonium ions NH .

Item 107 - Blend according to any of Items 103- 106, wherein the alkali sorbent comprises between 60 % and 98 %, preferably between 80 and 98 %, by weight of sodium bicarbonate, between 1 % and 40 %, preferably between 1 % and 12 % by weight of sodium carbonate and between 0.02 % and 2.0 % by weight of ammonia, expressed in the form of ammonium ions NH₄ ⁺, characterized in that the alkali sorbent comprises less than 1 .0 %, preferably less than 0.9 %, more preferably less than 0.8 % by weight of water.

Item 108 - Blend according to any of Items 103- 107, w herein the alkali sorbent comprises comprises between 60 % and 98 %, preferably between 80 and 98 %, by weight of sodium bicarbonate, between 1 % and 40 %, preferably between 1 % and 12 % by weight of sodium carbonate and between 0.02 % and 2.0 % by weight of ammonia, expressed in the form of ammonium ions N¾⁺, and comprising from 0.01 to 5 % by weight of a compound selected from hydrocarbons, fatty alcohols, fatty acids, or fatty acid salts , preferably fatty acids having 12 to 20 carbon atoms per molecule or a salt thereof.

Item 109 - Blend according to any of Items 103-108, wherein the alkali sorbent is in the form of particles having a diameter D90 of less than 50 μιη and a diameter D50 of less than 35 μιη, preferably a diameter D90 of less than 35 μιη and a diameter D50 of less than 20 μιη, more preferably a diameter D90 of less than 30 μιη and a diameter D50 of less than 15 μιη, measured by laser

diffractometry.

Item 1 10 - Blend according to any of Items 103- 109, wherein the catalyst is in the form of particles having a diameter D90 of less than 50 μιη and a diameter D50 of less than 35 μιη, preferably a diameter D90 of less than 35 μιη and a diameter D50 of less than 20 μιη, more preferably a diameter D90 of less than 30 μιη and a diameter D50 of less than 15 μιη, measured by laser

diffractometry.

Item 111 - Process for treating a waste gas stream containing nitrogen oxides (NOx) and contaminants selected from the group consisting of heavy metals, acid gases (such as S0₂, SO₃, H₃PO₄, HC1, HI, HBr, and/or HF) and combinations thereof, said waste gas stream originating from a combustion process, said treating process comprising:

injecting the blend according to any of Items 89-110 into the waste gas stream;

removing at least a portion of the contaminants from the waste gas stream with the alkali sorbent,

converting, in the presence of 0₂, by reduction with NH₃ of at least a portion of the NOx in the waste gas stream to N₂ and water at a temperature of at least 100°C and preferably at most 600°C.

Item 1 12 - The process according to Item 1 1 1 , wherein the temperature is at least 105°C and at most 500°C; preferably at least 105°C, or at least 120°C, or at least 150°C, or at least 180°C, or at least 200°C, or at least 250°C, or at least 300°C; and/or at most 550°C, or at most 500°C, or at most 450°C, or at most 400°C. Item 113 - The process according to any Items 1-16, or the particles according to any Items 17-26 or 30, or the aqueous suspension according to Item 27, or the pulverulent solid (D") of Item 28 or 29, or the support according to any Items 31-44, or the catalyst according to any Items 45-53, or the process according to any Items 54-88, or the blend according to any Items 89-110, or the process according to Item 111 or 112, wherein the support is substantially free of carbon, i.e., less than 0.5 wt% of carbon.

Item 114 - The process according to any Items 1-16, or the particles according to any Items 17-26 or 30, or the aqueous suspension according to Item 27, or the pulverulent solid (D") of Item 28 or 29, or the support according to any Items 31-44, or the catalyst according to any Items 45-53, or the process according to any Items 54-88, or the blend according to any Items 89-110, or the process according to Item 111 or 112, wherein the support comprises at least 0.5 wt% but less than 7 wt%, preferably less than 6 wt%, more preferably less than 5 wt% or less than 4 wt% carbon.

Item 115 - The process according to any Items 1-16, or the particles according to any Items 17-26 or 30, or the aqueous suspension according to Item 27, or the pulverulent solid (D") of Item 28 or 29, or the support according to any Items 31-44, or the catalyst according to any Items 45-53, or the process according to any Items 54-88, or the blend according to any Items 89-110, or the process according to Item 111 or 112, wherein the support is substantially free of bone char.

Many modifications and variations of this invention can be made without departing from its spirit and scope, as will be apparent to those skilled in the art. The specific embodiments described herein are offered by way of example only, and the invention is to be limited only by the terms of the appended claims, along with the full scope of equivalents to which such claims are entitled.

The present invention having been generally described, the following Examples are given as particular embodiments of the invention and to demonstrate the practice and advantages thereof. It is understood that the examples are given by way of illustration and are not intended to limit the specification or the claims to follow in any manner.

EXAMPLES

Example 1 - Preparation of Catalyst Support

In this example, three calcium phosphate (Ca/P) supports labelled S12,

S14, S16 were made under similar conditions as those described in example 1 (particularly in examples lb and lc) of WO2015/173437 patent application. The differences in conditions are explained below. After synthesis, the support samples were filtered and these wet samples were subjected to several analysis.

The calcium phosphate (Ca/P) support S12 was prepared in similar conditions as the ones of example lb of WO2015/173437. Limestone was dispersed in water at 20-25°C in a baffled 200-liter reactor. For the first step, H₃PO₄ (75%) was then added to this suspension and the mixture was stirred at 390 rpm using a double 4-blade impeller. At the end of the addition of acid, the mixture was heated up to about 50°C, and a 25 wt% suspension of Ca(OH)₂ was added to maintain the pH of the suspension at 8-8.8 for the second step. The reaction time was 140 minutes. After the reaction time, the suspension is continually stirred at half the stirring speed than was used in the first step to allow it to cool down to 20-25°C. The final density of solid suspension in aqueous suspension (B) was 18% by weight (solid weight reported to total weight of the aqueous suspension).

The calcium phosphate (Ca/P) support S14 was prepared in similar conditions as the ones of example lc of WO2015/173437. Limestone was dispersed in water at 20-25°C in a 5-liter reactor (without baffle). For the first step, H₃PO₄ (75%)) was then added to this suspension and the mixture was stirred at 700 rpm using a 4-blade impeller. At the end of the addition of acid, the mixture was heated up to about 50°C, and a 25 wt% suspension of Ca(OH)₂ was added to maintain the pH of the suspension at 8.2-8.7 for the second step. The reaction time was 145 minutes. After the reaction time, the suspension is continually stirred at half the stirring speed than was used in the first step to allow it to cool down to 20-25°C. The final density of solid suspension in aqueous suspension (B) was 5% by weight (solid weight reported to total weight of the aqueous suspension).

The calcium phosphate (Ca/P) support S16 was prepared in similar conditions as the ones of example lb of WO2015/173437. Limestone was dispersed in water at 20-25°C in a 5-liter reactor (without baffle). For the first step, H₃PO₄ (75%)) was then added to this suspension and the mixture was stirred at 320 rpm using a double 4-blade impeller. At the end of the addition of acid, the mixture was heated up to about 50°C, and a 25 wt% suspension of Ca(OH)₂ was added to maintain the pH of the suspension at 8.1-8.9 for the second step. The reaction time was 175 minutes. After the reaction time, the suspension is continually stirred at half the stirring speed than was used in the first step to allow it to cool down to 20-25°C. The final density of solid suspension in aqueous suspension (B) was 18% by weight (solid weight reported to total weight of the aqueous suspension).

la. Porosity and particle size after drying of the support samples S12, S14, S16

The porosity characteristics were determined after a heat treatment at 110 °C under vacuum overnight (about 16 hours). The BET specific surface area was determined by gas adsorption on a Micro meritics ASAP2020 machine. Before the analysis, the samples (0.7 to 1 g) are pretreated under vacuum at 110°C until a stable vacuum of 4-5 μbar has been achieved. The measurements were carried out using nitrogen as adsorbent gas at 77°K via the volumetric method, according to the ISO 9277 : 2010 standard (Determination of the specific surface area of solids by gas adsorption - BET method). The BET specific surface area was calculated in a relative pressure (P/P0) range varying from around 0.05 to 0.20.

The mean particles size D50 was also measured. The mean diameter D50 is the diameter such that 50 % by weight of the particles have a diameter less than said value. The particle size measurement was carried out on a Beckman Coulter LS 230 laser diffraction particle size analyser (laser of wavelength 750 nm) on particles suspended in water and using a size distribution calculation based on Fraunhofer diffraction theory (particles greater than 10 μιη) and on Mie scattering theory (particles less than 10 μιη), the particles being considered to be spherical.

The results can be found in TABLE 1.

TABLE 1

* after thermal treatment at 110°C under vacuum overnight lb. Thermal treatment (200-600° C) of the support samples SI 2, SI 4, SI 6

Ageing of the 3 support samples at several temperatures (from 200°C up to 600°C) for 8 hours was carried out, in order to observe morphological changes of the samples as a function of temperature to check their thermal stability. The supports containing the hydroxyapatite will need to work in a wide temperature range (up to 600°C) to be effective support for a deNOx catalyst.

Description of Method:

Around 10 g of the support samples (S12, S14, and S16) were put in ceramic crucibles and put in the electrical oven (Nabertherm, Germany, with temperature/time controller B-180). The thermal treatments were done in an air atmosphere under the following temperature program: from room temperature to the final temperature at l°C/min and maintenance of the final temperature for a defined time of 8 hours. The resulting samples have been labelled with a code, which indicates the Temperature and time of the treatment (SXX/Temp./time): S12/200/8, S12/400/8, S12/600/8; S14/200/8, S14/400/8, S14/600/8, and S16/200/8, S16/400/8, S16/600/8.

The specific surface area (computed by the linear BET equation) and porosity (pore volume, pore size and pore size distribution) have been determined by N2 adsorption/desorption isotherms collected at -196 °C using an automatic analyzer of surface area on a Sorptomatic 1900 instrument, Italy. From the Slope and Intercept of the obtained line, the volume of N2 adsorbed on the surface in a monolayer (VM) and CBET constant have been calculated.

Pore size distribution (PSD) was computed by Barrett- Joyner-Halenda (BJH) model equation from the desorption branch of the collected isotherms and average pore size (rav,p, pore radius in nm or in A) was calculated by the classical Gurvitch's rule:

rav,p (A) = (2 Vp/SBET ) 10⁴

rav,p (nm) = (2 Vp/SBET ) 10³

where Vp is the pore volume in cm³/g, SBET is the BET surface area in m²/g, and the pore radius is in A or nm (1 A = 0.1 nm).

Prior to the analysis, the wet hydroxyapatite samples and the thermally treated samples (from 0.15 to 0.30 g) have been outgassed at 150°C for 4 hours under vacuum.

From the results obtained (adsorption-desorption isotherms and pore-size distribution), the morphology of both the S 12 and S14 samples changed with temperature. This is an expected phenomenon: sintering of solids with temperature is observed on (almost) all the solids.

Sintering causes loss of surface, decrease of pore volume and of pore size. In particular, the small pores disappear and large porosity appeared. The new porosity can be also associated with inter-particle voids. This is due to the decrease of the pore volume that results in the formation of larger volume (void) among the solid particles.

Concerning S12 and S14 support samples, surface area values started from an average value of surface area around 100 m²/g and then decrease down to values of 20 m²/g following thermal treatment at 600°C. Pore Size Distribution of the two samples was centered around 2-3 nm of pore radius (for low temperature of treatment) and it increased and became very broader for high temperatures of treatment.

Concerning S16 support sample, starting from an average value of surface area of 120 m²/g, values of 30 m²/g have been observed following thermal treatment at 600°C. PSD of the sample is centered around 2 nm of pore radius (for low temperature of treatment) and it increases and become very broader for high temperatures of treatment.

Almost linear decreasing trend can be observed starting from 200°C of thermal treatment for S 12 and S14, while S16 follows a different trend. In the temperature range from 200°C to 400°C, the decrease of surface area in S16 is limited, as well as the loss of pore volume (see TABLE 2).

TABLE 2

a: determined after heat treatment at 110 °C under vacuum overnight (see Section 1 a) b: determined from 2-parameters BET equation

c: determined at P/P°= 0.999

d: observed from PSD (by BJH model from desorption branch of the isotherm) e: determined from Gurvich-rule: rp (nm)= (2 Vp/SBET)- 10³ with Vp in cm³/g and

SBET in m²/g lc. Evaluation of the water content

The wet support samples (S12, S14, and S16) have been weighed in ceramic crucibles (ca. 10 g with precision on an analytical scale). The crucibles were put into an oven (Heraeus Instruments, Germany, vacutherm.) overnight (ca. 16 h) at 120°C in static dry air atmosphere. After cooling to room

temperature in a dryer, the crucibles were weighed again on an analytical scale.

The following losses of mass, corresponding to water desorption, were obtained and are shown in TABLE 3.

Id. Temperature Programmed Desorption of water by TGA/DTGA

The wet samples (S12, S14, and S16) were put on the plate of the thermobalance (ca. 15 mg). The following three-step program on a TGA 7 PerkinElmer thermal analyzer was applied entirely done under N2 flowing: i) isothermal step at 35°C for 2 min; ii) heating from 35°C to 800°C, at controlled rate (10°C/min); Hi) cooling from 800°C to 50°C. A calibration of the temperature was performed by measuring the Curie transitions (TC) of high- purity reference materials (alumel, nickel, perkalloy, and iron: TC of 163°, 354°, 596°, and 780°C, respectively) at the same heating rate (b) employed for this analysis. For each sample, three analyses were carried out to check the reproducibility of the obtained results.

Total amount of water desorbed in the temperature interval 35°C-800°C are shown in TABLE 3. The determined values are in agreement with those evaluated from the simple mass determinations after treatment at 120°C (see paragraph: lc. Evaluation of water content). This indicates that the samples did not contain any impurity derived from the synthetic method.

le. Temperature of water desorption:

The water desorption began almost at room temperature or little higher (at the starting of the TGA analysis, 35°C) and it ended at the following

temperatures: 105°C, 112°C, and 103°C for S12, S14, and S16, respectively (evaluated by computing the end of the desorption process on the DTGA curve). The maximum rate of water desorption was observed at the following temperatures (Tmax) are shown in TABLE 3. After the phenomenon of water loss, any other desorption events at higher temperature could not be observed from the recorded thermogravimetric profiles. TABLE 3

Example 2 - Characterization of support composition

In this example a calcium phosphate (Ca/P) support labelled S97 was made under similar conditions as those described in example 1 of WO2015/173437 patent application. The sample was dried for 48 h at 105 °C in a drying oven. All analyses below have been carried on the dried sample.

The composition of the support was determined.

The calcium carbonate (CaC0₃) concentration was calculated from the following technique. An Orsat gas analyzer is an apparatus in which various gases, in this case C0₂, can be selectively absorbed by passing them through a series of preselected chemical solutions. The apparatus mainly consists of a calibrated water-jacketed gas burette, containing slightly acidified NaCl brine with a trace of a colour indicator (methyl orange). The burette is connected by glass capillary tubing to an absorption bottle containing a 4 M sodium hydroxide solution, which absorbs the C0₂ gas. By acidification and heating of the sample, carbonate is liberated as C0₂ gas. The volume of gas in the burette is read before and after absorption in the NaOH solution. The difference in volume

corresponds to the C0₂ liberated from the sample. The quantity of carbonate is calculated from the volume of C0₂, taking the temperature of the water in the water-jacket of the burette into account as well as the atmospheric pressure.

The total calcium concentration was determined by potentiometric titration with EDTA solution using an indicative calcium electrode (ion selective electrode Ca²⁺ electrode Metrohm 6.0508.110) and an Ag/AgCl reference electrode (Metrohm 6.0726.100). During titration an electronic voltmeter can be used to detect the change in potential between the two electrodes. The equivalence point of the titration corresponds to the jump in voltage observed when all the Ca is complexed by EDTA. The indicative calcium electrode detects the disappearance of free (uncomplexed) calcium. The titrator was Metrohm 799 GPT Titrino. Inductively coupled plasma optical emission spectrometry (ICP-OES) was used to determine P and the minor elements Mg and Si. The magnesium carbonate (MgC0₃) concentration was calculated from the Mg concentration (measured by ICP-OES). The silicon dioxide (Si0₂) concentration was calculated from the Si concentration (measured by ICP-OES).

The water content was determined by colometric Karl-Fisher titration after thermal desorption at 300 °C. The sample was heated in a dedicated tubular furnace for KF analysis and the desorbed water was swept by means of a dry argon gas flow into the colometric titration cell, containing the colometric Karl Fischer reagent (methanol, diethanolamine, sulfur dioxide, imidazole and imidazolium iodide).

The hydroxyapatite concentration was calculated from the Ca and P concentrations in the following way:

• The molar Ca concentration to be assigned to hydroyxylapatite was calculated from the total % Ca concentration (determined by

potentiometric titration with EDTA solution) minus the calcium already assigned to CaC0₃: 8.22 mol/kg

• The molar P concentration assigned to hydroxyapatite was calculated from the total % P concentration (measured by ICP-OES): 5.19 mol/kg

• Then the molar Ca/P ratio in the hydroxyapatite was calculated from these molar Ca and P concentrations assigned to hydroxyapatite. The estimated molar Ca/P ratio of the hydroxyapatite was 1.58, whereas the theoretical Ca/P of hydroxyapatite (Cai₀(PO₄)6(OH)₂) is 1.67. Hydroxyapatites with a molar Ca/P ratio between 1.50 and 1.67 are calcium-deficient

hydroxyapatite (CDA) with the chemical formula

Ca₁₀-_x(HPO₄)_x(PO₄)6-_x(OH)₂__x.

• x has been calculated from the molar Ca/P ratio: x = 10 - 6*Ca/P = 0.503.

• Thus, the exact chemical formula of the calcium-deficient hydroxylapatite was slightly different from the theoretical hydroxylapatite chemical formula: Ca₄.₄9₇(HPO₄)₀.₅₀3(PO₄)₅.₄9₇(OH)₁.₄9₇ with a molar mass of 976.41 g/mol.

The following TABLE 4 summarizes the estimated composition in wt% of the support sample S97. The sum of the compounds in this table is slightly below 100 % due to the experimental uncertainty associated with each of the analytical methods applied. The support contains no carbon. TABLE 4

Absence of calcium dihydroxide (Ca(OH)₂) demonstrated by pH determination:

The support did not contain calcium dihydroxide (Ca(OH)₂). This absence of soluble hydroxide from calcium dihydroxide (Ca(OH)₂) was demonstrated by preparing a diluted sample suspension and by measuring the pH of the supernatant solution. Hydroxylapatite being extremely insoluble in water (K_sp= 6.8^X 10 ³⁷), the OH^" from the apatite molecule does not contribute to the pH.

Calcium carbonate is also very insoluble (13 mg/1 a 25 °C), whereas Ca(OH)₂ is soluble until 1.6-1.7 g/1 at 20 °C. If the pH of the sample solution is lower than 7, then the sample cannot contain any Ca(OH)₂. In order to demonstrate what the pH would be if the sample contained 0.1 % calcium dihydroxide, the pH was also measured in a solution of a sample spiked with 0.1 % calcium dihydroxide. The pH electrode was a calibrated Aquatrode Plus with Pt 1000 temperature sensor (Metrohm 6.0257.000).

o Sample solution: 5 g of sample were brought into contact with degassed ultrapure water at about 20 °C during 10 min while stirring the liquid. The suspension was then centrifuged. At this concentration of sample in the solution, up to 1.6 % of Ca(OH)₂ in the original solid sample would still be soluble. An aliquot of the supernatant was then diluted about 3 times and the pH was measured.

o Solution of a sample spiked with 0.1 % Ca(OH)₂: 5 g of sample + 0.005 g Ca(OH)₂ were brought into contact with degassed ultrapure water during 10 min while stirring the liquid. The suspension was then centrifuged. An aliquot of the supernatant was then diluted about 3 times and the pH was measured.

The pH of the sample solution was 6.3. Since there is no alkalinity, there was no calcium dihydroxide in the sample. The pH of the sample spiked with 0.1 % of calcium dihydroxide was 7.5. It was concluded that the support material did not contain calcium dihydroxide.

Example 3 - Preparation of catalysts

The catalyst samples prepared were identified by a code; in the code there were the Fe wt.% (X) and the support sample HAP (= S16 as used in Example 1). The preparation method used was ion exchange, and the Fe-precursor used was iron nitrate.

Example of catalyst preparation by ion exchange

Catalyst Fe6/HAP

Support HAP= S16 dried at 120°C, 16 h = 5 g

Fe(N0₃)3. H₂0 from Sigma Aldrich was dissolved in water to reach a molar concentration of 10^"2 M. Fe-nitrate water solution was put at pH of about 5 to increase Fe stabilization and avoid aggregation.

1° step: Addition of HAP powder into the clear solution of Fe(N0₃)₃ under vigorous magnetic stirring at 40°C (pH=7), the suspension operation lasted 20 h.

2° step: Separation of the solid from the solution by filtration on a buckner under moderate vacuum (ca. 15 mbar).

3° step: washing cycles with hot water (40°C) up to the obtainment of clear water without any amount of Fe(N0₃)₃ - via spectrophotometric control) were carried out.

The first 3 steps were carried out two times in order to obtain a total Fe loading of 6 w% on HAP support. The Fe deposition was done twice via ion exchange, because the solubility of Fe(N0₃)₃ is not high (KS= 10^"36), and the ion exchange method requires complete solubilisation of the Fe precursor used. Finally after the second round of the first 3 steps, two final steps were carried out:

4° step: drying of the exchanged powder in an oven at atmospheric pressure at 120°C for 16 hours

5° step: calcination, l°C/min up to 450°C, maintained for 4 hours.

Catalyst sample obtained = 5.48 wt% Fe on HAP Catalyst Fe2HAP

One more catalyst was prepared by ion exchange in a similar manner as the one prepared with 6 wt% using Fe(N0₃)₃ as Fe precursor except that only one ion exchange was carried out (steps 1-3 were performed only once), and identified as Fe2/HAP (with an actual loading of 2 wt% Fe).

In order to evaluate the effective Fe-loading on S16 support, the filtrate water solution at the end of each exchange procedure and all the washing waters have been analyzed by spectrophotometric analysis (in the interval 200-800 nm). Because of the low solubility of Fe³⁺ in aqueous solution (Fe(OH)₃, KS= 10-36), for the quantitative analysis of the water solutions of Fe nitrate, it is advisable to complex the Fe³⁺ with a reagent acting as ligand in FiN0₃ solution. Potassium thiocyanate (KSCN) has been used as ligant species. In acidic solution, Fe³⁺ reacts with KSCN to give a series of intensely blood-red complexes, all highly soluble in water:

Fe³⁺ + 3 SCN-→ Fe(SCN)₃

Once known the initial Fe concentration of the solutions used for the exchange (Fe solution put in contact with S16 support sample) and the final Fe concentration (filtrate Fe-solution after the exchange procedure and washing waters) measured at 460 nm, it was possible, by difference, to evaluate the amount of Fe3+ left behind on the SI 6 support during the exchange procedure (Fe-loading). For such quantitative analysis, the Lambert-Beer equation has to be known for Fe³⁺ aqueous solutions prepared from Fe(N03)₃ and complexed by KSCN in HN0₃ acid:

= ε I [Fe(III)]solution

where ε = molar extinction coefficient and I = light path (1 cm)

At fixed wavelength (460 nm), absorbance values were determined for standard solutions of Fe(N0₃) ₃ in 0.0001- 0.00045 M interval to be :

ε =7884± 1.048.

Example 4 - XRD analysis of support (dried or calcined) and catalyst

Experimental and Method:

Structural properties of the samples were performed by X-ray powder diffractometer equipped with a PW 1830 generator, monochromator in graphite, copper pipe, Cu Ka radiation at 40 kV x 40 mA.

Analyses were carried out with the following method: type of scan:

continuous; start angle: 10° 2Θ; end angle: 60° 2Θ; step size: 0.05° 2Θ; time for step: 5 sec; scan speed: 0.010 29/sec; number of step: 1000; total time: lh 23 min.

Hydroxyapatite (HAP) is a crystalline material with a typical XRD pattern that can be found in JCPDS: 00-009- 0432 (see relevant TABLE 5).

TABLE 5 : XRD pattern of Hydroxyapatite

The dried support sample S16 (dried at 120°C, labelled "SI 6- 120") and calcined support sample S16 samples treated at higher temperatures: 400°C and 600°C for 8 hours (labelled "SI 6-400-8" and "SI 6-600-8") had all the same structure that corresponds to the hydroxyapatite XRD pattern JCPDS: 00-009- 0432. The crystallinity degree became higher with the temperature increasing of S16 treatment (see relevant XRD patterns in TABLES 6 A, 6B, 6C).

TABLE 6A TABLE 6B TABLE 6C

S16-120 SI 6-400-8 S16-600-8

2 theta counts 1/10 counts 1/10 counts 1/10

25.975 615 0.538529 740 0.574088 924 0.592308

28.425 282 0.246935 237 0.183863 174 0.111538

29.025 320 0.28021 289 0.224205 317 0.203205

32.125 1142 1 1289 1 1560 1

39.775 250 0.218914 262 0.203258 388 0.248718

46.825 328 0.287215 299 0.231963 475 0.304487

49.625 380 0.33275 449 0.348332 576 0.369231

53.325 303 0.265324 250 0.193949 313 0.200641 The structure of Fe6/HAP catalyst (see Example 3) has been analyzed by the same XRD method. This catalyst sample presents the typical crystalline structure of hydroxyapatite (09- 0432) without any line for the presence of some structures of iron oxide (as hematite, F₂O₃, pattern 40-1139) - see XRD pattern in TABLE 7. This finding suggests the absence of structured Fe-oxide aggregates in the catalyst and indicates a good dispersion of Fe in and on the hydroxyapatite support structure.

TABLE 7 : XRD pattern of catalyst Fe6/HAP

Example 5 - SCR testing of catalysts

5a. Preparation of catalyst loading into SCR reactor.

A continuous flow reactor was part of the Selective Catalytic Reaction system. When using such a flow reactor, the catalyst sample has to be put inside as grains of given size; placing solids in powder form would result in high pressure loss, with consequences of having non-correct fluid dynamics when feeding gaseous mixture. The dimension of the grains has to be selected so as to guarantee the absence of diffusional limits (external and internal diffusion) and a suitable fluid dynamics of the gaseous mixture.

For that reason, the catalyst samples to be tested were pressed, crushed, and sieved as particles of 45-60 mesh (0.354 mm - 0.250 mm, respectively) in size. The procedure to realize such particles was not straightforward as the correct pressure had to be found experimentally in order to obtain catalyst grain sizes stable to mechanical shocks; the grains should not lose powder with time during the reaction. For hydroxyapatite-based Fe catalyst samples tested for SCR reaction, the grains were obtained by pressing each powder sample put between two steel disks under 3 tons for 30 seconds. The resulting sample in form of compacted disk (of few mm thickness) was then crushed and sieved between two sieves of 45 and 60 mesh (0.354 mm - 0.250 mm, respectively) of size.

5b. NH₃-SCR reaction experimental procedure.

Tests of the SCR reaction were performed in a continuous reaction line equipped with a set of mass flow controllers (Bronkhorst, Hi-Tec and Brooks Instruments), a tubular vertical electric oven (maximum temperature of 1000°C), a glass tubular catalytic micro reactor (with 5 mm i.d.), and an on-line FTIR spectrophotometer (Bio-Rad with DTGS detector) for the qualitative and quantitative determination of the fed and vented gaseous species.

A catalyst sample (ca. 0.20 g), sieved as particles of 0.35-0.25 mm of size and dried at 120°C in an oven overnight, was pre-treated in situ under an 0₂/He flow (20% v/v) at 120 °C for 30 min.

Typically, when the catalyst activity was studied for a given temperature selected to be in the 120-400°C range, the concentration of the feeding gas mixture and total flow rate were maintained constant via a Eurotherm Controller- Programmer type 818, and the temperature at which the reaction was being studied was maintained at least for 60 minutes in order to allow reaching steady- state conditions.

Typically, the fed gas mixture was prepared mixing ca. 500 ppm of NO, 500 ppm of NH3, and 10,000 ppm of 0₂. After the mixing, the effective gas mixture being fed to the catalyst bed also contained N0₂ (because N0₂ is formed from the reaction in gas phase between NO and 0₂): ca. 450 ppm of NO, 50 ppm of N02, 500 ppm of NH₃, and ca. 10,000 ppm of 0₂. The total flow of the gaseous mixture was kept constant at 6 NL/h (corresponding to 0.12 s of contact time).

The mixture exiting from the reactor was monitored each 180 seconds by FT-IR equipped with a multiple reflection gas cell with 2.4 m path length;

resolution, 2 cm^"1; sensibility, 1.5, 92 scans per 180 seconds) for quantified the reagent species. The total absorbance of all the IR active species {Gram- Schmidt) flowing from the reactor was continuously monitored as a function of time, while the reaction temperature was changing. The NO, N0₂, and NH₃ and other formed species (if any) were quantified from the peak height of a selected absorbance lines, on the basis of the measured calibration factors. The following TABLE 8 provides the working wavelengths (cm ¹) for the IR active species NO, N0₂, N₂0, NH₃, H₂0:

TABLE 8

5c. NH₃-SCR catalytic tests: experimental results with Support S16/400/8 (HAP support)

As a control, the NH₃- SCR reaction on the hydroxyapatite-based support (SI 6/400/8, calcined at 400°C for 8 h) was studied over the range of temperature 120-450°C while the concentration of the feeding mixture and flow rate were maintained the same (that is to say the contact time remained the same). The sample was prepared as explained in the Section 4. a. The sample was pre-treated under a flow of 0₂ in He (20 %) at 3 NL/h for 30 min at 120°C. The feeding mixture contained NO, NH₃, 0₂, as well as N0₂ formed in gas phase from NO+0₂.

TABLE 9

Conditions for the reaction test:

Flow 6 (NL/h)

Surface Area 92.76 (m²/g)

Cat. Density 1 (g/ml)

Cat. Mass dry 0.198 (g)

GHSV 30272 (h^"1)

Contact Time (tl) 3.303E-05 (h)

Contact Time (t2) 119 (g*s/NL)

Contact Time (t3) 2.665 (g*s/mmol)

From the concentration values of all the species involved in the SCR reaction, the catalytic data can be computed. FIG. 1 illustrates the conversion of NO and NH₃ over the hydroxyapatite-based support SI 6/400/8 over the range of temperature 120-450°C. Conversion of NO was around 15-20% and that of N0₂ was much higher (ca. 60-70%); the reactivity of N0₂ is much higher than that of NO. Ammonia, after being adsorbed at low temperature (120°C), had conversion around 20-30%) in the temperature range 200-450°C. These observations showed that SI 6/400/8 support sample was inert in the NH₃-SCR reaction. 5d. NH₃-SCR catalytic tests: experimental results with two Fe catalysts over temperature range

The NH₃-SCR reaction was studied on two catalysts prepared by ion- exchange on the same support S16 with iron nitrate as a precursor (Fe2/HAP and Fe6/HAP) over the range of temperature 120-400°C while the concentration of the feeding mixture and flow rate were maintained the same (that is to say the contact time remained the same). The catalyst samples were made as explained in the Section 3; their actual Fe contents were 2 wt% Fe and 5.48 wt% Fe. The catalyst samples were prepared and loaded in the SCR reactor as explained in the Section 5a. The catalyst sample was pre-treated under a flow of 0₂ in He (20 % v/v) at 3 NL/h for 30 min at 120°C. The conditions for reaction are provided in the TABLES 10a and 10b.

TABLE 10a

Conditions for the reaction test with Fe2/HAP:

Flow 6.01 (NL/h)

Cat. Density 1 (g/ml)

Cat. Mass 0.116 (g)

GHSV 51635 (h ¹)

Contact Time (tl) 1.937E-05 (h)

Contact Time (t2) 70 (g*s/NL)

Contact Time (t3) 1.563 (g*s/mmol)

% Fe 2

TABLE 10b

Conditions for the reaction test with Fe6/HAP:

Flow 6 (NL/h)

Cat. Density 1 (g/ml)

Cat. Mass 0.206 (g)

GHSV 29169 (h ¹)

Contact Time (tl) 3.428E-05 (h)

Contact Time (t2) 123 (g*s/NL)

Contact Time (t3) 2.766 (g*s/mmol)

% Fe 5.479

The collected results at each temperature (after the attainment of the steady state of the catalyst) are reported as Peak Height of the selected line of Absorbance for each species, then the Peak Height values are converted in concentrations by applying the Calibration Factor (see TABLE 11). TABLE 11 : Calibration Factor for the IR species evaluated by FT-IR spectrometry

From the concentration profiles of reagent and products collected at various temperatures, the following catalytic results have been computed. The percent conversion of NO and NH3 and the percent of production of N₂ as a function of the reaction temperature are provided in FIG. 2 and 3 over the hydroxyapatite-based Fe catalysts: Fe2/HAP and Fe6/HAP, respectively, over the range of temperature 120-400°C.

For Fe2/HAP: The NO concentration and also N0₂ concentration (this species if formed in homogeneous phase from the reaction of NO with oxygen) on Fe2/HAP catalyst had a clear decreasing trend starting from 250°C; at lower temperatures no significant modification of NO concentration was observed. Ammonia concentration followed the same trend as NO species.

In the explored temperature interval, the reaction of NH₃ oxidation to form

NO_x (besides N₂) was not observed. The catalyst was very selective and it could reduce NOx by using NH₃ as reducing species. The competitive oxidation reaction (NH₃ to N₂ and NO_x) cannot take place.

The N₂0 species were not detected among the formed products (this species can be formed from NH₃ oxidation by 0₂). It is worth noticing that the conversion of NO, N0₂, and NOx starts to be observed at 250°C. At higher temperatures, NOx conversion increases attaining a value of about 70% (at 400°C). Ammonia conversion follows the trend of the NO species (maximum conversion observed at 400°C is around 60%>).

Formation of N₂ is computed by difference between the total NO_x fed and the total NO_x present at given temperature. N₂ can be formed from NO_x reduction and NH₃ oxidation. The (little) superior amount of N₂ formed in comparison with NO_x converted is likely to an experimental error or a (little) oxidation of ammonia to N₂.

For Fe6/HAP: The NO concentration on Fe6/HAP catalyst had a clear and regular decreasing trend as a function of temperature up to 300°C, then it remained low. For temperatures higher than 300°C, the NO and N0₂ conversion remained low while the concentration of N₂0 increased slightly, likely due to the parallel undesired reaction of oxidation of ammonia by 0₂. The N0₂ species followed a similar trend as the NO; The N0₂ content decreased with temperature (up to 225°C) and them it remained quite low.

Concerning NH₃, its concentration was decreasing regularly from 120°C up to 400°C. The sample was unable to absorb/transform all the fed ammonia.

Results indicate that a low Fe concentration to the HAP support was sufficient in order to observe SCR activity. The activity on Fe2/HAP started at higher temperatures in comparison with the activity observed on Fe-catalyst at higher Fe-concentration (Fe6/HAP). A lower NOx conversion was obtained on Fe2/HAP than on Fe6/HAP.

Without wishing to be bound to this theory, it is likely that the addition of higher Fe concentration would increase the acidity of the catalyst (since Fe can act as Lewis acid sites) and therefore higher amount of NH₃ can be adsorbed on the catalyst surface (on Fe-sites). SCR needs ammonia in the adsorbed state to take place.

It was noted that the conversion of NO and NOx remain stable around values of ca. 95% in the high temperature range (from 200-400°C) without suffering the undesired reaction of NH₃ oxidation that subtracted ammonia to the deNOx reaction. The NO curve remained stable with low values (<40 ppm) in the interval of temperatures from 275 to 400°C corresponding to conversion higher than 90-95 wt%.

The Fe catalyst had poor deNOx activity at low temperature (150-250°C). However the Fe-based catalyst seems very promising for actual applications due to its high selectivity to the deNOx reaction. This catalyst was able to utilize ammonia to reduce NOx and this action was maintained at high temperatures.

From further laboratory testing, it was observed that it is possible to load higher amount of Fe on a given support with positive outcome on NOx conversions at low temperatures and maintenance of the deNOx selectivity at high temperature.

The disclosure of all patent applications, and publications cited herein are hereby incorporated by reference, to the extent that they provide exemplary, procedural or other details supplementary to those set forth herein.

Should the disclosure of any of the patents, patent applications, and publications that are incorporated herein by reference conflict with the present specification to the extent that it might render a term unclear, the present specification shall take precedence. In the present application, where an element or component is said to be included in and/or selected from a list of recited elements or components, it should be understood that in related embodiments explicitly contemplated here, the element or component can also be any one of the individual recited elements or components, or can also be selected from a group consisting of any two or more of the explicitly listed elements or components. Any element or component recited in a list of elements or components may be omitted from such list. Further, it should be understood that elements, embodiments, and/or features of processes or methods described herein can be combined in a variety of ways without departing from the scope and disclosure of the present teaching, whether explicit or implicit herein.

Accordingly, the scope of protection is not limited by the description set out above, but is only limited by the claims which follow, that scope including all equivalents of the subject matter of the claims. Each and every claim is incorporated into the specification as an embodiment of the present invention. Thus, the claims are a further description and are an addition to the preferred embodiments of the present invention.

While preferred embodiments of this invention have been shown and described, modifications thereof can be made by one skilled in the art without departing from the spirit or teaching of this invention. The embodiments described herein are exemplary only and are not limiting. Many variations and modifications of systems and methods are possible and are within the scope of the invention.

Claims

C L A I M S

Claim 1 - A catalyst composition for catalytic reduction of NO_x compounds, comprising an active catalyst component deposited on a porous support; wherein said active catalyst component comprises iron; and wherein said porous support comprises at least 60 wt % of a calcium- deficient hydroxyapatite having a calcium to phosphate molar ratio (Ca/P) of less than 1.67, preferably more than 1.5 and less than 1.67; said porous support having a specific BET surface area of at least 110 m²/g and a pore volume of at least 0.5 cm³/g both measured after heat treatment at 200°C.

Claim 2 - The catalyst composition according to claim 1, in which the porous support further comprises calcium carbonate in an amount of less than 20 wt%, preferably from 1 wt% to 19 wt%, more preferably from 2 wt% to 18 wt%, even more preferably from 5 wt% to 15 wt%, yet even more preferably from 7 wt% to 13 wt%, most preferably from 8 wt% to 12 wt%; and/or comprises water in an amount of less than 20 wt%, preferably from 1 wt% to 18 wt%, more preferably from 2 wt% to 15 wt%, even more preferably from 4 wt% to 12 wt%, yet even more preferably from 5 wt% to 11 wt% most preferably from 6 wt% to 11 wt%; and/or comprises less than 1 wt% of calcium dihydroxide Ca(OH)₂, preferably less than 0.5 wt% calcium dihydroxide Ca(OH)₂, more preferably less than 0.3 wt% calcium dihydroxide Ca(OH)₂, even more preferably less than 0.2 wt% calcium dihydroxide Ca(OH)₂, most preferably being substantially free of calcium dihydroxide Ca(OH)₂.

Claim 3 - The catalyst composition according to any of the preceding claims, in which the porous support comprises a Ca/P molar ratio of 1.60 or more, preferably of 1.65 or more, preferably of 1.67 or more, more preferably of 1.68 or more. Claim 4 - The catalyst composition according to any of the preceding claims, in which the porous support comprises a Ca/P molar ratio greater than the Ca/P molar ratio of the calcium-deficient hydroxyapatite. Claim 5 - The catalyst composition according to any of the preceding claims, in which the porous support comprises

- at least 65 wt%, preferably at least 70 wt%, more preferably at least 75 wt%, yet more preferably at least 80 wt%, yet most preferably at least 85 wt%, of the calcium-deficient hydroxyapatite, and/or comprises

Claim 6 - The catalyst composition according to any of the preceding claims, in which the porous support has a BET specific surface area measured after heat treatment at 200°C of at least 120 m²/g and/or at most 160 m²/g and/or a pore volume measured after heat treatment at 200°C of at least 0.55 cm³/g, preferably of at least 0.55 cm³/g and/or at most 1.0 cm³/g, preferably of at most 0.95 cm³/g. Claim 7 - The catalyst composition according to any of the preceding claims, in which the porous support has a BET specific surface area measured after heat treatment at 400°C of at least 60 m²/g and/or at most 100 m²/g and/or a pore volume measured after heat treatment at 400°C of at least 0.50 cm³/g, preferably of at least 0.60 cm³/g and/or of at most 1 cm³/g. Claim 8 - The catalyst composition according to any of the preceding claims, in which the active catalyst component comprises

- at least 0.5 wt%, preferably at least 1.0 wt%, more preferably at least 1.5 wt%, of iron; and/or - at most 15 wt%, preferably at most 13 wt%, yet more preferably at most 12 wt%, most preferably at most 11 wt%, of iron.

Claim 9 - The catalyst composition according to any of the preceding claims, in which iron is deposited on the porous support by ion exchange.

Claim 10 - The catalyst composition according to any of the preceding claims, in which the active catalyst component is deposited on the porous support using an iron precursor selected from the group consisting of iron nitrate, iron chloride, iron perchlorate, iron sulfate, iron fluorosilicate, any hydrated form thereof, and any mixture thereof, preferably using an iron precursor selected from the group consisting of iron (III) nitrate, iron (III) chloride, iron (III) sulfate, iron (III) perchlorate, any hydrated form thereof, and any mixture thereof.

Claim 11 - The catalyst composition according to any of the preceding claims, in which the catalyst is subjected to a heat treatment using a temperature from 105°C up to 500°C, prior to being used as a catalyst.

Claim 12. - The catalyst composition for catalytic reduction of NO_x compounds according to any of the preceding claims, in which the catalyst composition has a BET specific surface area measured after being calcined at 400°C of at least 65 m²/g and/or at most 100 m²/g.

Claim 13. - The catalyst composition for catalytic reduction of NO_x compounds according to any of the preceding claims, in which the catalyst composition has a pore volume measured after being calcined at 400°C of:

- at least 0.3 cm³/g, preferably of at least 0.41 cm³/g, and/or

Claim 14. - Process for treating a waste gas stream containing nitrogen oxides (NOx), said gas stream originating from a combustion process, in which an ammonia source is injected into the waste gas stream; and in which the catalyst composition according to any of the preceding claims is brought into contact with the waste gas stream containing ammonia at a temperature of at least 100°C and preferably at most 600°C to carry out, in the presence of 0₂, a reduction by NH₃ of at least a portion of the NOx to N₂ and water.

Claim 15. - Process according to claim 14, in which the waste gas stream temperature is at least 105°C, or at least 120°C, or at least 150°C, or at least 180°C, or at least 200°C, or at least 300°C; and/or at most 550°C, or at most 500°C, or at most 450°C, or at most 400°C.

Claim 16. - Process according to claim 14, in which the catalyst composition is injected into the waste gas stream in the form of a dry powder injection or a semi-dry injection of a slurry of the catalyst. Claim 17.- Process for treating a waste gas stream containing nitrogen oxides (NOx) and contaminants selected from the group consisting of heavy metals, acid gases (such as S0₂, S0₃, H₃P0₄, HCl, HI, HBr, and/or HF) and combinations thereof, said waste gas stream originating from a combustion process, said treating process comprising: injecting an alkali sorbent comprising a compound selected from the group consisting of sodium bicarbonate, sodium carbonate, sodium sesquicarbonate (trona), quick lime, hydrated lime, limestone, and combinations thereof; contacting at least a portion of the contaminants with the alkali sorbent to remove at least a portion of the contaminants from the waster gas stream, injecting an ammonia source into the waste gas stream; injecting a catalyst into the waste gas stream; and converting, in the presence of 0₂, by reduction with NH₃ of at least a portion of the NOx in the waste gas stream to N₂ and water at a temperature of at least 100°C and preferably at most 600°C, wherein the catalyst comprises an active catalyst component deposited on a porous support; wherein said active catalyst component comprises iron; and wherein said porous support comprises at least 60 wt % of a calcium- deficient hydroxyapatite having a calcium to phosphate molar ratio (Ca/P) of less than 1.67, preferably more than 1.5 and less than 1.67.

Claim 18 - A blend comprising an alkali sorbent and a catalyst, said alkali sorbent comprising a compound selected from the group consisting of sodium bicarbonate, sodium carbonate, sodium sesquicarbonate (trona), quick lime, hydrated lime, limestone, and combinations thereof, preferably selected from the group consisting of sodium bicarbonate, sodium carbonate, sodium sesquicarbonate (trona), and combinations thereof, more preferably selected from the group consisting of sodium bicarbonate, sodium sesquicarbonate (trona), and combinations thereof; wherein the blend comprises

- at least 0. 1 wt%, or at least 0.2 wt%, or at least 0.5 wt%, or at least 1 wt%, or at least 3 wt%, or at least 5 wt%, of the catalyst, and or

- at most 20 wt%, or at most 15 wt%, or at most 1 2 wt%, or at most 10 wt%, of the catalyst; said catalyst comprising an active catalyst component deposited on a porous support; wherein said active catalyst component comprises iron; wherein said porous support comprises at least 60 wt % of a calcium- deficient hydroxyapatite having a calcium, to phosphate molar ratio (Ca/P) of less than 1.67, preferably more than 1.5 and less than 1.67.

Claim 19. - The process according to claim 17 or blend according to claim 18, wherein the catalyst has a BET specific surface area measured after being calcined at 400°C of at least 65 m²/g and/or at most 100 trf/g, and/or a pore volume measured after being calcined at 400°C of:

- at least 0.3 cm Vg, preferably of at least 0.41 cm³/g, and/or

- at most 1 . 1 cm Vg, preferably of at most 1 .0 cm³/g, more preferably of at most 0.9 cm Vg. most preferably of at most 0.8 cm³/g. Claim 20 - The process according to claim 1 7 o blend according to claim 18, wherein the active catalyst component comprises :

- at least 0. 1 wt%, preferably at least 0.5 wt%, more preferably at least 1 .0 wt%, most preferably at least 1 .5 wt%, of iron; and/or

- at most 1 5 wt%, preferably at most, more preferably at most 13 wt%, yet more preferably at most 12 wt%, most preferably at most 1 1 wt%, of iron.

Claim 21 - The process according to claim 17 or blend according to claim 18, wherein the active catalyst component is deposited on the porous support by ion exchange or impregnation using an iron precursor selected from, the group consisting of iron nitrate, iron chloride, iron perch lorate, iron sulfate, iron fluorosilicate, any hydrated form thereof, and any mixture thereof; preferably using an iron precursor selected from the group consisting of iron (III) nitrate, iron (III) chloride, iron (III) sulfate, iron (III) perchlorate, any hydrated form thereof, and any mixture thereof.

Claim. 22 - The process according to any of claims 17 and 19-21 or blend according to any of claims 18-21 , wherein the alkali sorbent comprises or consists of a compound selected from the group consisting of trona, sodium bicarbonate, and mixture thereof. Claim 23 - The process according to any of claims 17 and 19-22 or blend according to any of claims 18-22, wherein the alkal i sorbent contains an ammonia source.

Claim 24 - The process according to any of claims 17 and 19-23, wherein the alkali sorbent and the catalyst are mixed to form, a blend to be injected simultaneously into the waste gas stream, and wherein the blend comprises

- at least 0.1 wt%, or at least 0.2 wt%, or at least 0.5 wt%, or at least 1 wt%, or at least 3 wt%, or at least 5 wt%, of the catalyst, and or

- at most 20 wt%, or at most 15 wt%, or at most 12 wt%, or at most 10 wt%, of the catalyst. Claim 25 - The process according to any o f claims 17 and 19-24, wherein the alkali sorbent and the catalyst are injected sequentially into the waste gas stream flowing through a duct, and wherein the alkali sorbent is injected in a duct at a location upstream of where the catalyst is injected. Claim 26 - The process according to claims 17 and 19-25, wherein, the ammonia source and the catalyst are injected simultaneously into the waste gas stream.

Claim 27 - Process for treating a waste gas stream containing nitrogen oxides (NOx) and contaminants selected from the group consisting of heavy metals, acid gases (such as S0₂, S0₃, H₃P0₄, HCl, HI, HBr, and/or HF) and combinations thereof, said waste gas stream originating from a combustion process, said treating process comprising: injecting the blend according to any of claims 18-23 into the waste gas stream; removing at least a portion of the contaminants from the waste gas stream with the alkali sorbent, and converting, in the presence of 0₂, by reduction with NH₃ of at least a portion of the NOx in the waste gas stream to N₂ and water at a temperature of at least 100°C and preferably at most 600°C.