RU2673344C2 - Exhaust gas treatment catalysts - Google Patents

Abstract

FIELD: technological processes.SUBSTANCE: invention relates to a catalyst for treating an exhaust gas from a diesel engine comprising: (a) 0.1 to 10 wt.% of a group 8 to 11 transition metal; and (b) 90 to 99.9 wt.% of a support. Wherein the support comprises at least 90 wt.% of cerium dioxide and 0.1 to 10 wt.% of a dopant doped on the cerium dioxide, wherein the dopant comprises niobium (Nb) or tantalum (Ta). Invention also relates to a process for preparing said catalyst comprising: (a) impregnating cerium dioxide with an aqueous solution comprising a water-soluble niobium (Nb) or tantalum (Ta) salt; (b) calcining the impregnated cerium at a temperature within the range of 600 °C to 1,000 °C to obtain a support; (c) impregnating the support with a solution comprising a platinum group transition metal. Invention also relates to an exhaust gas after-treatment system comprising a catalyst and optionally a SCR catalyst, a diesel particulate filter, a catalyzed soot filter, an ammonia slip catalyst, or a combination thereof, and to a method for oxidizing a gaseous flow of diesel exhaust gas comprising carbon monoxide, unsaturated hydrocarbons, or both, in the presence of said catalyst.EFFECT: improved ability to oxidize NO, CO and a reduced tendency to oxidize ammonia, improved resistance to sulfur poisoning.20 cl, 12 dwg, 6 ex

Description

FIELD OF THE INVENTION

The present invention relates to catalysts that use doped cerium dioxide supports. Catalysts are used to clean exhaust gas.

BACKGROUND OF THE INVENTION

The combustion of hydrocarbons in diesel engines, stationary gas turbines and other systems leads to the formation of exhaust gas, which must be cleaned to remove nitrogen oxides (NO _x ), carbon monoxide (CO), hydrocarbons (HCs) and particulate matter ((PM) (PM) )). The exhaust gas generated in lean combustion engines is usually oxidative, and NO _x can be selectively reduced using a heterogeneous catalyst and a reducing agent, which is usually ammonia or short chain hydrocarbon. This method is known as selective catalytic reduction ((SCR) (SCR)).

As the requirements are becoming more stringent, especially for motor engines, the purification of diesel exhaust gas should be a target for each of the pollutants identified above. Modern after-treatment systems for engines include a diesel oxidation catalyst (DOC) for converting hydrocarbons and carbon monoxide to carbon dioxide and water, an SCR catalyst for converting NO _x to N ₂ and a catalyzed soot filter, or a diesel solid filter particles (see, for example, US2007 / 0028604, US2011 / 0138776 and WO2012 / 166833). Post-treatment systems may also include an NO _x adsorber-catalyst that chemically binds nitrogen oxides during lean operation of the engine. After the capacity of the adsorber is saturated, the system is regenerated during the period of engine operation in the enriched mode, and the released NO _{x is} catalytically reduced to nitrogen.

Diesel oxidation catalysts typically include a platinum group metal (e.g., Pd, Pt, Rh, Ru, Ir) and a support. The carrier may be an inorganic oxide, a mixed oxide, a zeolite (see US8263032 and US2012 / 0308439), clay or the like. It is also common to apply metal with or without a carrier to a ceramic monolith, honeycomb structure or other high surface area structure, flow carrier or “block”.

Cerium dioxide, aluminum dioxide, or combinations thereof are used as supports for diesel oxidation catalysts (see US2012 / 030843, US2013 / 0089481, US5462907 and EP0960649). Cerium dioxide is also combined with Group 5 metals in the absence of a platinum group metal for use as SCR catalysts and other catalytic methods. For example, see Le Gal et al., J. Phys. Chem. C116 (2012) 13516 (tantalum doped cerium dioxide used as a catalyst for the conversion of water during the solar thermomechanical generation of hydrogen), S. Zhao et al., Appl. Catal., A 248 (2003), 9 (Nb- or Ta doped cerium dioxide as a catalyst for the oxidation of butane), K. Yashiro et al., Solid State Ionics, 175 (2004), 341 (cerium dioxide obtained in the presence of preformed niobium dioxide and the effect on electrical conductivity) and E. Ramirez- Cabrera et al., Solid State Ionics, 136-137 (2000), 825 (cerium dioxide doped with niobium dioxide and their use for conversion conversion of methane into synthesis gas). M. Casapu et al., Appl. Catal., B103 (2011), 79 show diesel oxidation catalysts as part of a complete post-treatment system that includes ATP, SCR catalyst, and DPF. Doped cerium dioxide is described for use in SLE and soot oxidation. The tested catalysts contained 10% wt. Nb ₂ O ₅ on a mixed carrier (cerium dioxide) - (zirconia) or 30% wt. Nb ₂ O ₅ on cerium dioxide.

The patents and published patent applications also discuss combinations of niobium dioxide and cerium dioxide, again in the absence of a platinum group metal and not for diesel oxidation catalysts. See, for example, EP2368628 (catalysts containing at least 10% by weight of cerium dioxide and at least 10% by weight of niobium dioxide and their use for the SCR method) and US2013 / 0121902 (mixed oxides of cerium dioxide , zirconia, niobium dioxide and rare earth sesquioxide as catalysts for the SCR method).

SCR catalysts containing niobium dioxide and cerium dioxide are discussed in WO2012 / 041921, WO2012 / 004263 and WO2013 / 037507. The catalysts in WO2012 / 004263 contain 2-20% wt. niobium oxide. It was shown that catalysts having <50% Zr have a greater ability to reduce hydrogen compared to a similar catalyst made with 77.6% Zr. In two examples (examples 9 and 10), 3.2% wt. or 8.6% wt. Nb ₂ O ₅ , zirconia is not present, and the rest is up to 100% wt. makes up cerium dioxide. However, these catalysts are essentially niobium dioxide encapsulated in cerium dioxide, to a greater extent, and not niobium dioxide “doping” cerium dioxide. As shown in the examples, the catalysts are prepared by molding cerium dioxide in the presence of a small proportion of preformed niobium dioxide. Own work of the inventors (described here) shows that, with identical proportions of niobium dioxide and cerium dioxide, these catalysts are less effective for reducing NO _x than compositions in which niobium dioxide doping cerium dioxide. In addition, as shown in WO2012 / 041921 (table 5, examples 9 and 10), it turns out that these catalysts deactivate during hydrothermal aging (750 ° C., 16 hours).

WO2012 / 004263 describes that niobium dioxide encapsulated in cerium dioxide can be used as a carrier for a noble metal such as platinum, palladium, silver, gold or iridium (see pages 13-14), and possible applications for noble metals on carriers include their use as oxidation catalysts. However, there are no specific examples showing diesel diesel oxidation catalysts. As noted above, the inventors have determined that the niobium dioxide encapsulated in cerium dioxide described in WO2012 / 004263 is different from the cerium dioxide doped with niobium dioxide described herein.

EP0960649 describes an exhaust gas purification catalyst containing a platinum group metal deposited on a 50:50 mixture (cerium dioxide) :( aluminum dioxide), where the mixture (cerium dioxide) :( aluminum dioxide) is coated with 2.3% niobium (see example 2) . The catalysts show a high ability to purify saturated hydrocarbons, in particular propane.

Known diesel oxidation catalysts with cerium dioxide as a carrier are susceptible to sulfur poisoning. NO _{x scavengers} are also susceptible to sulfur poisoning. Since diesel fuels can have a high sulfur content, this is an important limitation. Catalysts that have too much tendency to adsorb sulfur dioxide quickly lose their effectiveness for oxidation.

Improved diesel oxidation catalysts are required. In particular, industry will benefit from the availability of catalysts with improved ability to convert carbon monoxide and hydrocarbons to carbon dioxide and water at relatively low temperatures (for example, <200 ° C and, preferably, <150 ° C). Also of interest are diesel oxidation catalysts having an improved ability to oxidize NO and a reduced tendency to oxidize ammonia at temperatures below 300 ° C. In theory, catalysts should be able to withstand long-term exposure to sulfur-containing gases, such as SO ₂ , without undue poisoning.

SUMMARY OF THE INVENTION

It has been unexpectedly found that cerium oxide doped with niobium (Nb) and tantalum (Ta) having low ligand levels (1-10% by weight) is an excellent support for catalysts containing a transition metal of groups 8-11, such as diesel oxidation catalysts . In particular, the catalysts have improved ability to convert carbon monoxide and hydrocarbons to carbon dioxide and water at relatively low temperatures compared to similar catalysts in which the transition metal of groups 8-11 is applied to undoped cerium dioxide. In addition, the catalysts have an improved ability to oxidize NO and a reduced tendency to oxidize ammonia, so that the catalyst can work more efficiently in connection with an SCR catalyst. The catalysts of the invention also show improved resistance to sulfur poisoning.

The present invention provides a catalyst containing a transition metal of groups 8-11 and a carrier. In particular, the catalyst contains 0.1-10% wt. transition metal of groups 8-11 and 90-99.9% wt. carrier. The media contains at least 90% wt. cerium oxide and 0.1-10% wt. cerium dioxide dopant, where the additive contains niobium (Nb) or tantalum (Ta). The reference to "cerium dioxide dopant" refers to cerium dioxide doped with an additive. Typically, the additive is niobium dioxide or tantalum dioxide.

The carrier may be a calcined carrier, such as a calcined carrier, obtained by calcining the carrier at a temperature in the range of 600-1000 ° C. The catalyst may be a calcined catalyst obtained by calcining the catalyst at a temperature in the range of 600-1000 ° C.

The catalyst of the present invention is usually suitable for purification of the exhaust gas of a diesel engine or is a diesel oxidation catalyst.

Another aspect of the invention relates to a method for producing a catalyst. The method comprises: (a) impregnating cerium oxide with an aqueous solution containing a water-soluble salt of niobium (Nb) or tantalum (Ta) (for example, to obtain an impregnated cerium oxide), (b) calcining the impregnated cerium oxide to obtain a carrier (for example, a carrier containing at least 90% by weight of cerium oxide and 0.1-10% by weight of an additive doping cerium dioxide in which the additive contains niobium (Nb) or tantalum (Ta); (c) impregnating the support with a solution containing a transition metal groups 8-11.

Typically, the method of the invention further comprises: (d) calcining the product (e.g., catalyst) from step (c) at a temperature in the range of 600-1000 ° C (for example, to obtain a calcined catalyst, where the calcined catalyst contains 0.1-10% wt. transition metal groups 8-11).

The present invention also relates to a catalyst for purifying an exhaust gas of a diesel engine. The catalyst is obtained or it can be obtained by the method according to the invention.

The present invention further provides an exhaust gas aftertreatment system. The exhaust gas after-treatment system comprises a catalyst of the invention and, optionally, an SCR catalyst, a diesel particulate filter, a catalyzed carbon black filter, an ammonia conversion catalyst, or a combination thereof.

Another aspect of the invention relates to a method which comprises oxidizing a gaseous stream of diesel exhaust gas containing carbon monoxide, unsaturated hydrocarbons, or both, in the presence of a catalyst according to the invention.

Brief Description of the Drawings

The figure 1 presents a graph of the lattice parameter in relation to% wt. Nb₂O₅, for cerium dioxide doped with niobium dioxide, used for diesel oxidation catalysts of the invention, and for comparative compositions prepared according to WO 2012/004263.

The figure 2 shows the dependence of the conversion of NO_x temperature for cerium dioxide doped with niobium dioxide, used to produce diesel oxidation catalysts of the invention, and for comparative compositions prepared according to WO 2012/004263.

The figure 3 presents graphs of the consumption of sulfur dioxide for a catalyst with 2% palladium on ceria, doped with niobium dioxide (catalyst B), and comparative Pd / CeO ₂ catalysts (catalysts A and C).

The figure 4 presents graphs of the release of sulfur dioxide from temperature for a catalyst with 2% palladium on cerium dioxide doped with niobium dioxide (catalyst B), and comparative Pd / CeO ₂ catalysts (catalysts A and C), where the catalysts are pre-aged in sulfur dioxide .

The figure 5 presents a graph of the conversion of carbon monoxide from temperature for a catalyst with 2% palladium on cerium dioxide doped with niobium dioxide (catalyst B), and comparative Pd / CeO ₂ catalysts (catalysts A and C), where the catalysts either matured at 750 ° C, or aged at 750 ° C and subjected to cyclic sulfonation / desulfurization.

Figure 6 shows a graph of propylene conversion versus temperature for a catalyst with 2% palladium on niobium doped ceria (catalyst B) and comparative Pd / CeO ₂ catalysts (catalysts A and C), where the catalysts either matured at 750 ° C C, or aged at 750 ° C and subjected to cyclic sulfonation / desulfurization.

Figure 7 shows a graph of the% conversion of propylene or ammonia versus temperature for a catalyst with 2% palladium on tantalum doped cerium dioxide and for a comparative Pd / CeO ₂ catalyst.

Figure 8 shows a graph of% carbon monoxide conversion versus temperature and shows the effect of tantalum dioxide for 2% palladium on tantalum doped cerium dioxide and for the comparative Pd / CeO ₂ catalyst.

Figure 9 shows a graph of% propylene conversion versus temperature and shows the effect of tantalum dioxide for 2% palladium on tantalum doped cerium dioxide and for the comparative Pd / CeO ₂ catalyst.

Figure 10 shows the effect of tantalum dioxide content on NO oxidation temperature requirements for 2% palladium on tantalum doped cerium dioxide and for the comparative Pd / CeO ₂ catalyst.

Figure 11 shows graphs of sulfur dioxide consumption for a catalyst with 2% palladium on tantalum doped cerium dioxide and for a comparative Pd / CeO ₂ catalyst.

Figure 12 shows graphs of the temperature of sulfur dioxide release for a catalyst with 2% palladium on tantalum doped cerium dioxide and for a comparative Pd / CeO ₂ catalyst, where the catalysts were preliminarily supported in sulfur dioxide.

DETAILED DESCRIPTION OF THE INVENTION

The catalyst of the invention is typically a diesel oxidation catalyst or NO _x scavenger.

The catalyst typically contains a carrier (for example, a macroscopic carrier), such as a metal plate or a monolith carrier (for example, cordierite honeycombs). Typically, a catalyst composition (e.g., transition metal of groups 8-11 and a support) is coupled to the support. Such placement is particularly preferred in heterogeneous catalysts.

Typically, the transition metal of groups 8-11 is dispersed and / or distributed over the surface of the carrier.

Transition metals suitable for use are in groups 8-11 of the periodic system of elements. Suitable metals include, for example, Fe, Ru, Os, Co, Rh, Ir, Ni, Pd, Pt, Cu, Ag, and Au. Preferred metals of Groups 8-11 include Pt, Ru, Rh and Ag, preferably Pt. The catalyst may comprise a mixture or combination of any of the transition metals of Groups 8-11. Particularly preferred are combinations of Pd with one or more of Cu, Ag, Au, Pt, Co, Rh and Ir, and in particular Pd with Pt.

It may be preferable that the transition metal of groups 8-11 is a transition metal, more preferably, the metal of groups 8-11 is copper (Cu).

The transition metal of groups 8-11 is preferably a noble metal. More preferably, the transition metal of groups 8-11 is a platinum group metal. Even more preferably, the transition metal of groups 8-11 is palladium.

The catalyst of the invention contains 0.1-10% wt., Preferably 1-5% wt., Most preferably 1.5-3% wt. a transition metal of groups 8-11 with respect to the total mass of a transition metal of groups 8-11 plus a carrier.

The transition metal of groups 8-11 can be deposited on the carrier in any way. For example, an aqueous solution containing a soluble transition metal salt of groups 8-11 (e.g., palladium-II) nitrate, palladium (II) chloride, platinum (II) chloride, palladium- (II) acetate, rhodium (II) acetate dimer or the like ), can be applied to obtain an aqueous suspension, which is then dried and calcined. An initial wettability method may also be used in which the solution is slowly introduced into the carrier in an amount similar to the pore volume of the carrier, followed by drying and calcination.

The catalyst of the invention contains 90-99.9% wt., Preferably 95-99% wt. carrier in relation to the total mass of the transition metal of groups 8-11 plus the carrier.

The carrier may comprise cerium dioxide doped with niobium dioxide (Nb ₂ O ₅ ) or cerium dioxide doped with tantalum dioxide (Ta ₂ O ₅ ). Preferably, the support and / or catalyst does not or substantially does not contain vanadium or any oxide thereof. Thus, the carrier and / or catalyst does not contain vanadium.

Typically, the carrier contains at least 90% wt. cerium dioxide and 0.1-10% wt. niobium dioxide or tantalum dioxide as its ligand. Preferably, the carrier contains 90-99.5% wt. cerium dioxide and 0.5-10% wt. niobium dioxide or tantalum dioxide. More preferably, the carrier contains 92-99% wt. cerium dioxide and 1-8% wt. niobium dioxide or tantalum dioxide. Most preferably, the carrier contains at least 95% wt. cerium dioxide, preferably 95-99% wt. cerium dioxide, and 1-5% wt. niobium dioxide or tantalum dioxide. The above ranges in% wt. carrier compositions relate to the total weight of the carrier.

A carrier containing cerium dioxide doped with niobium dioxide is particularly preferred.

Cerium dioxide has a surface area of more than 50 m ² / g, more preferably more than 100 m ² / g (as measured using the BET method). Such suitable high surface area cerium dioxide are commercially available. Examples include Rhodia HAS cerium dioxide, high surface area cerium oxides available from MolyCorp, HEFA Rare Earth, NanoOxides or other suppliers, and the like. Suitable cerium dioxide with a high surface area can also be synthesized, as described, for example, in US7094383, US5063193, US4859432 and US4661330, the descriptions of which are incorporated herein by reference, as well as in WO2001 / 036332 and EP0444470.

Doped cerium dioxide can be identified as having a reduced lattice parameter when compared with undoped cerium dioxide, when the ligand (e.g., Nb or Ta) usually has a smaller ionic radius compared to cerium. Niobium or tantalum can either be uniformly distributed in the lattice, or be in a higher concentration in the layer on or near the surface of the lattice of cerium dioxide. Here, cerium dioxide is either formed before the introduction of niobium, or cerium dioxide and niobium dioxide are formed essentially simultaneously, as in the coprecipitation method. Thus, “doped cerium dioxide” differs from physical oxide mixtures and excludes compositions in which cerium dioxide is formed in the presence of preformed particles of niobium dioxide or tantalum dioxide. Such preformed compositions are described, for example, in WO2012 / 004263 in Examples 9 and 10.

The catalyst of the invention may or may not contain a physical coating of niobium dioxide or tantalum dioxide on cerium dioxide, and / or the catalyst of the invention may not or substantially not contain a physical coating of ceria on niobium dioxide or tantalum dioxide.

In preferred cerium dioxide doped with niobium dioxide or tantalum dioxide, the lattice parameter is significantly reduced compared to undoped cerium dioxide. Such a contraction of the lattice may indicate that niobium dioxide or tantalum dioxide have become part of the lattice framework. Preferably, the lattice parameter of cerium dioxide doped with niobium dioxide or tantalum dioxide is at least 0.02% less, more preferably at least 0.04% less than the lattice parameter of undoped cerium dioxide. It has been unexpectedly found that such a contraction of the lattice can be observed even when the support is calcined under relatively mild (e.g., 500 ° C) conditions. As shown in FIG. 1, a reduction in the lattice appears with increasing levels of niobium dioxide, when the ceria doped with niobium dioxide is obtained by the impregnation method described in Examples 1-3 below. On the contrary, this degree of lattice reduction is not observed when cerium dioxide is formed in the presence of niobium dioxide, as described in WO2012 / 004263 and repeated in comparative examples 4-6 below.

The carrier can be prepared by impregnating cerium dioxide with a solution of a niobium or tantalum salt, followed by calcination.

In one suitable synthetic approach, doped cerium dioxide is prepared by impregnating cerium dioxide with an aqueous solution containing a soluble salt of niobium or tantalum, usually acetate, nitrate, halide, oxalate or the like, such as niobium (V) chloride, niobium (III) nitrate, ammonium niobate (V ) oxalate or tantalum (V) chloride. If desired, even water can be used to form a suspension. Alternatively, the amount of water can be minimized, as in the initial wettability process. Wet mechanical mixing may also be used (see EP2368628). In any case, the water is then usually removed by drying, and the product is calcined to obtain cerium dioxide doped with niobium dioxide or tantalum dioxide. For an example of an impregnation approach, see US2013 / 0121902, the description of which is incorporated herein by reference.

Ligand-doped cerium dioxide can also be obtained by coprecipitation of cerium dioxide and niobium dioxide or tantalum dioxide from an aqueous medium. In this case, an aqueous solution containing dissolved salts of cerium and niobium or tantalum is combined with aqueous ammonia, ammonium carbonate, or another basic compound. Hydrogen peroxide can be added to further maintain deposition. The product is separated, washed, dried and calcined to obtain cerium dioxide doped with niobium dioxide or tantalum dioxide. Since some sources of niobium hydrolyze more rapidly than the corresponding cerium compounds, coprecipitation can result in a carrier having depressions of niobium dioxide with cerium dioxide incorporated. For a coprecipitation approach, see US6605264, the description of which is incorporated by reference, and EP2368628.

The carrier and / or catalyst can usually be calcined at a temperature in the range of 600-1000 ° C, preferably 700-950 ° C, more preferably 750-900 ° C. Calcination can be carried out briefly (for example, less than an hour), or it can be longer (for example, up to 24 hours).

The carrier and / or catalyst is preferably calcined in air. If desired, however, the support and / or catalyst may be hydrothermally treated. That is, the carrier and / or catalyst can mature in the presence of both heat and moisture. Typical hydrothermal ripening conditions include a temperature of 500-900 ° C in the presence of introduced water vapor.

Calcination (and / or hydrothermal maturation) can facilitate the migration of niobium dioxide or tantalum dioxide to the surface of the carrier. The degree of migration can be determined using x-ray photoelectron spectroscopy or other suitable methods.

Typically, cerium dioxide doped with a ligand has on its surface (for example, as determined by X-ray photoelectron spectroscopy) a molar ratio of niobium or tantalum to cerium, which at least doubles upon calcination.

Ligand-doped cerium dioxide usually has on its surface (for example, as determined by X-ray photoelectron spectroscopy) a molar ratio of niobium or tantalum to cerium of more than 0.2, preferably more than 0.3.

The proportion of niobium dioxide or tantalum dioxide on the surface of the carrier (for example, by migration) can be expressed in terms of the distribution coefficient Q, which is given by the expression

Q = (E _surface / Ge _surface) / (E _v / Ge _v)

In this expression, the E _surface / Ce _surface is the molar ratio of niobium or tantalum to cerium determined on the surface of the support by X-ray photoelectron spectroscopy, and the E _volume / Ce _volume is the molar ratio of niobium or tantalum to cerium in the bulk sample of the carrier. For cerium dioxide doped with a ligand, in the catalyst of the invention, Q is preferably more than 1.5, and more preferably has a value in the range of 2-10.

The catalyst may further comprise additional support material. An additional carrier may be zeolite, clay, aluminum dioxide, (silicon dioxide) - (aluminum dioxide), zirconia, titanium dioxide, or a mixture or a combination of any two or more of them. More preferably, the additional carrier is zeolite, aluminum dioxide, (silicon dioxide) - (aluminum dioxide), zirconia, titanium dioxide, or a mixture or combination of any two or more of them. If the catalyst contains an additional carrier material, then the carrier contains at least 90% wt. cerium dioxide and 0.1-10% wt. cerium dioxide doping ligand.

It may be preferred that the support or catalyst is free or substantially free of zirconia. It may be preferred that the support or catalyst is free or substantially free of alumina and / or (silica) - (alumina). It may be preferred that the support or catalyst is free or substantially free of titanium dioxide. It may be preferred that the support or catalyst is free or substantially free of zeolite. It may be preferable that the support or catalyst is free or substantially free of clay.

It has been unexpectedly found that cerium dioxide doped with niobium dioxide and tantalum dioxide having low ligand levels (1-10% by weight) are excellent carriers of oxidation catalysts containing a transition metal of groups 8-11, in particular, diesel oxidation catalysts (ATP) ) and mercury oxidation catalysts. For such embodiments, platinum group metals are particularly preferred, for example, Pd and / or Pt. Compared to similar catalysts in which the transition metal of groups 8-11 is supported on undoped cerium dioxide, the catalyst of the invention has an improved ability to convert carbon monoxide and hydrocarbons at low temperatures, a reduced tendency to oxidize ammonia, a greater tendency to oxidize NO, and an improved resistance to sulfur poisoning.

Preferably, the catalyst of the invention (e.g., a diesel oxidation catalyst (DCO)) absorbs under oxidation conditions in a diesel engine in the presence of sulfur dioxide by at least 10%, more preferably at least 20% and, most preferably, at least 50% less sulfur than a similar catalyst (for example, supported on undoped cerium dioxide). By “oxidation conditions in a diesel engine” are meant conditions in which CO or hydrocarbons are burned in the exhaust gas system under normal operating conditions, i.e. in the presence of an air mixture containing NO _x , carbon dioxide, water and oxygen at temperatures in the range of 100-400 ° C, preferably 100-300 ° C. In figures 3-6, 11 and 12 shows the ability of the catalysts of the invention to absorb less sulfur than a comparative catalyst using undoped cerium dioxide as a carrier.

Preferably, the catalyst of the invention (e.g., ATP) has an improved ability, under oxidation conditions in a diesel engine, to convert carbon monoxide, unsaturated hydrocarbons or both at temperatures below 250 ° C, preferably below 200 ° C, with respect to such a catalyst (e.g. , with undoped cerium dioxide as a carrier). Preferably, the relatively improved ability is maintained by prolonged exposure to the sulfur catalyst. In figures 5-9 shows these characteristics of the catalysts of the invention.

Preferably, the catalyst of the invention (eg, ATP) can convert under oxidation conditions in a diesel engine at temperatures below 300 ° C. at least 10% less ammonia, more preferably at least 20% less ammonia, and most preferably at least 50% less ammonia than a similar catalyst (for example, supported on undoped cerium dioxide). Figure 7 shows this characteristic.

Preferably, the catalyst of the invention (e.g., ATP) can convert under oxidation conditions in a diesel engine at temperatures below 400 ° C. at least 10% more NO, more preferably at least 20% more NO, most preferably at least 50% more NO than a similar catalyst (for example, supported on undoped cerium dioxide). Figure 10 shows this characteristic.

The above reference to “a similar catalyst” refers to a catalyst that has the same composition, except that cerium dioxide is undoped (i.e., undoped cerium dioxide).

The present invention also provides a catalytic primer layer. The catalytic primer is preferably a solution, suspension or suspension. The catalyst of the invention can be obtained or obtained by applying a catalytic primer layer to a carrier.

The catalytic primer layer may contain a non-catalytic component, such as a filler, a binder, a stabilizer, a viscosity modifier and / or another additive, including one or more of aluminum dioxide, silicon dioxide, non-zeolite (silicon dioxide) - (aluminum dioxide), titanium dioxide, dioxide zirconium, cerium dioxide.

The catalytic primer layer may contain a blowing agent, such as graphite, cellulose, starch, polyacrylate and / or polyethylene and the like.

The non-catalytic component and / or pore former should not catalyze the desired reaction, but instead improve the efficiency of the catalytic material, for example, by increasing its operating temperature range, increasing the contact surface area of the catalyst, increasing the adhesion of the catalyst to the carrier, etc.

Typically, the content of the catalytic primer is> 0.3 g / in ³ (0.018 g / cm ³ ), such as> 1.2 g / in ³ (0.072 g / cm ³ ),> 1.5 g / in ³ (0.090 g / cm ³ ),> 1.7 g / in ³ (0.102 g / cm ³ ) or> 2.00 g / in ³ (0.120 g / cm ³ ).

Typically, the content of the catalytic primer is <3.5 g / in ³ (0.210 g / cm ³ ), such as <2.5 g / in ³ (0.150 g / cm ³ ).

Preferably, the catalytic primer is applied to the carrier in an amount of about 0.8-1.0 g / in ³ (0.048-0.060 g / cm ³ ), such as 1.0-1.5 g / in ³ (0.060-0.090 g / cm ³ ) or, more preferably, 1.5-2.5 g / in ³ (0.090-0.150 g / cm ³ ).

Suitable catalytic primers may include a surface coating, a coating that impregnates part of the carrier, a coating that penetrates the carrier, and some combination thereof. Two of the most common carrier designs are plate and honeycomb.

Preferably, the carrier (i.e., especially for mobile applications) is a flowing monolith. The flow monolith may have a honeycomb structure that contains a plurality (for example, a plurality of adjacent) parallel channels, where each channel is open at both ends (i.e., open on the inlet side and open on the outlet side), and each channel goes from the inlet side to the outlet side of the media. This arrangement results in a high surface area to volume ratio.

For some applications, the cellular flow monolith preferably has a high cell density, for example, 600-800 cells per inch ² (93-124 cells / cm ² ), and / or an average inner wall thickness of about 0.18-0.35 mm, preferably about 0.20-0.25 mm.

For some other applications, the cellular flow monolith preferably has a low cell density of about 150-600 cells per inch ² (23-93 cells / cm ² ), more preferably about 200-400 cells / inch ² (31-62 cells / cm ³ ).

Preferably, the honeycomb monolith is porous.

Typically, the support is made of cordierite, silicon carbide, silicon nitride, ceramic, metal, aluminum nitride, silicon nitride, aluminum titanate, гли-alumina, mullite, for example, needle mullite, pollucite, termite, such as Al ₂ OsZFe, Al ₂ O ₃ / Ni or B ₄ CZFe, or composites containing segments of any two or more of them. Preferred materials include cordierite, silicon carbide and aluminum titanate.

Plate type catalysts have a low pressure drop and are less susceptible to clogging and clogging than honeycomb types, which is preferred in highly efficient stationary applications, but plate designs can be much larger and more expensive. The honeycomb structure is usually smaller than the plate type, which is preferred in mobile applications, but has a higher pressure drop and clogs more easily. In some embodiments, the plate carrier is constructed of metal, preferably corrugated metal.

The catalytic primer layer may be located on a carrier, such as a flowing monolith, in the zone. The area of the catalytic primer layer may be located on the carrier in the front zone extending from the inlet end (i.e., inlet side) of the carrier to 5-60% of the carrier length. Alternatively, the area of the catalytic primer layer may be located on the carrier in the rear zone, such as the rear zone extending from the outlet end (i.e., outlet side) of the carrier to 5-60% of the length of the carrier.

The carrier may be a filter with a flowing wall. When the carrier is a flow-through filter, the catalytic primer layer may be located on the inlet or outlet side of the flow-through filter.

Typically, a catalyst is prepared or obtained by a process comprising the step of (i) applying a catalytic composition, preferably a catalytic primer, to the carrier as a layer (for example, either before or after applying at least one additional layer of another composition for purifying the exhaust gas to media). When there are many layers on a carrier, including a catalyst composition layer or a primer layer, the layers are arranged in successive layers.

The catalyst of the invention may comprise a catalyst composition or a primer layer located on the carrier as a first layer, and another composition, such as an SCR catalyst, is located on the carrier as a second layer. Alternatively, the catalyst composition or primer layer may be located on the carrier as a second layer, and another composition, such as an SCR catalyst, is located on the carrier as the first layer.

Typically, a second layer is applied to a carrier (e.g., an inert carrier) as a lower layer, and the first layer is an upper layer that is applied over a second layer (i.e., as a series of layers). In this arrangement, the exhaust gas penetrates (and then contacts) into the first layer, before contacting with the second layer, and then returns through the first layer to the exit of the catalytic component.

The first layer may be a first zone located on (for example, a part upstream) of the carrier, and the second layer may be a second zone located on the carrier, where the second zone is downstream of the first zone.

The catalyst can be obtained or obtained by a method that comprises the step of (i) applying the catalyst composition, preferably as a catalytic primer, to the carrier as a first zone and (ii) applying (for example, sequentially) at least one additional composition or a primer layer for cleaning the exhaust gas onto the carrier as a second zone, where at least a portion of the first zone is downstream of the second zone. Alternatively, the catalyst composition or catalytic primer layer may be applied to the carrier in a second zone, which is located downstream of the first zone containing the additional composition or primer layer. Examples of additional compositions include SCR catalysts and refined components (e.g., sulfur, water, etc.).

To reduce the amount of space required for the exhaust system, individual components of the exhaust system are designed to carry out more than one function. For example, applying a catalyst to a filter carrier with flow walls instead of a flow carrier serves to reduce the overall size of the exhaust gas purification system while allowing one carrier to serve two functions, namely, the catalytic purification of unwanted components from the exhaust gas and the mechanical removal of soot from the exhaust gas.

Accordingly, the carrier may be a filter with flow walls or a filter with a partial flow. Filters with flow walls are similar to flow media in that they contain many adjacent parallel channels. However, the channels of flowing cell carriers are open at both ends, while the channels of carriers with flow walls have one end clogged, where clogging occurs at opposite ends of adjacent channels in an alternating pattern. Clogging the alternating ends of the channels prevents the gas entering the inlet side of the carrier from directly passing through and being located. Instead, the exhaust gas enters the front of the carrier and moves about half of the channels, where it is pumped through the walls of the channels before entering the second half of the channels and being on the back of the carrier.

The wall of the carrier has porosity and pore size, which is gas permeable, but traps the main part of solid particles, such as soot, from gas when gas passes through the wall. Preferred flow wall media are high performance filters. Flow wall filters for use with the present invention preferably have an efficiency of at least 70%, at least about 75%, at least about 80%, or at least about 90%. In some embodiments, the effectiveness is from about 75 to about 99%, about 75-90%, about 80-90%, or about 85-95%. Here, efficiency is given relative to soot and other similar particles of a certain size, and particulate concentrations are usually found in a traditional diesel exhaust gas. For example, particulate matter in diesel exhaust gas may be in the size range from 0.05 μm to 2.5 μm. Thus, the effectiveness can be based on a given interval or sub-interval, such as 0.1-0.25 microns, 0.25-1.25 microns or 1.25-2.5 microns.

Porosity is a measure of the percentage of empty space in a porous carrier and refers to backpressure in the exhaust system: usually the lower the porosity, the higher the backpressure. Preferably, the porous carrier has a porosity of about 30-80%, for example, about 40-75%, about 40-65%, or about 50-60%.

Pore interconnection, measured as a percentage of the total pore volume of a carrier, is the degree to which the pores, voids, and / or channels are connected to form continuous paths through the porous carrier, i.e. from inlet side to outlet side. In contrast to the interconnectedness of pores, there is a sum of the volume of closed pores and the volume of pores that have a passage to only one of the surfaces of the carrier. Preferably, the porous carrier has an interconnected pore volume of at least about 30%, more preferably at least about 40%.

The average pore size of the porous support is also important for filtration. The average pore size can be determined by any suitable method, including mercury porosimetry. The average pore size of the porous support must be sufficiently high to promote low backpressure while ensuring adequate performance by any support as such, when promoting a layer of caked soot on the surface of the support or a combination of both. A preferred porous support has an average pore size of about 10-40 microns, for example, about 20-30 microns, about 10-25 microns, about 10-20 microns, about 20-25 microns, about 10-15 microns and about 15-20 microns .

Typically, the preparation of an extruded continuous body containing a catalyst involves mixing the catalyst, a binder, optional organic viscosity, an improving compound into a homogeneous paste, which is then introduced into the binder / matrix component or their precursor, and optionally one or more of the stabilized cerium dioxide and inorganic fibers. The mixture is sealed in a mixing or plasticizing device or in an extruder. The mixtures contain organic additives, such as binders, blowing agents, plasticizers, surfactants, lubricants, dispersants, as processing aids to improve wetting and result in a uniform batch. The resulting plastic material is then molded, in particular using an extrusion press or extruder, including an extrusion die, and the resulting moldings are dried and calcined. Organic additives “burn out” during the calcination of the extruded solid. A separate catalyst may also be applied as a primer or otherwise applied to an extruded continuous body as one or more sublayers that remain on the surface or penetrate fully or partially into the catalytic extruded continuous body.

Extruded solid bodies containing the catalysts of the present invention typically have a honeycomb structure having equally sized and parallel channels extending from their first end to the second end. The walls of the channels defining the channels are porous. Typically, the outer "sheath" surrounds many of the channels of the extruded solid. The extruded solid can be molded to any desired cross section, such as round, square or oval. Individual channels in a plurality of channels may be square, triangular, hexagonal, round, etc. The channels at the first upstream end can be blocked, for example, with suitable ceramic cement, and the channels that are not blocked at the first upstream end can also be blocked at the second downstream end to form a filter with flow walls. Typically, the arrangement of the blocked channels at the first upstream end coincides with the staggered arrangement of a similar arrangement of the blocked and open ends of the channels downstream.

The binder / matrix component is preferably selected from the group consisting of cordierite, nitrides, carbides, borides, intermetallic compounds, lithium aluminum silicate, spinel, optionally doped aluminum dioxide, a source of silicon dioxide, titanium dioxide, zirconia, - (titania) zirconium), zircon and mixtures of any two or more of them. The paste may optionally contain reinforcing inorganic fibers selected from the group consisting of carbon fibers, glass fibers, metal fibers, boron fibers, alumina fibers, silica fibers, (silica) - (alumina) fibers, silicon carbide fibers, potassium titanate fibers, aluminum borate fibers and ceramic fibers.

The alumina binder / matrix component is preferably gamma alumina, but may be any other transitional alumina, i.e. alpha-alumina, beta-alumina, chi-alumina, eta-alumina, ro-alumina, kappa-alumina, theta-alumina, delta-alumina, lanthanum-alumina, and mixtures of any two or more of these transitional alumina. Preferably, the alumina is doped with at least one non-aluminum element to increase the heat resistance of alumina. Suitable alumina ligands include silicon, zirconium, barium, lanthanides, and mixtures of any two or more of them. Suitable lanthanide ligands include La, Ce, Nd, Pr, Gd, and mixtures of any two or more of them.

Sources of silica may include silica sol, quartz, fused or amorphous silica, sodium silicate, amorphous aluminosilicate, alkoxysilane, a silicone resin binder such as methyl phenyl silicone resin, clay, talc, or a mixture of any two or more thereof. From this list, silicon dioxide can be SiO ₂ per se, feldspar, mullite, silica-alumina, silica-magnesia, (silicon dioxide) - (zirconium dioxide), (silicon dioxide) - (thorium dioxide), (silicon dioxide) - (beryllium dioxide), (silicon dioxide) - (titanium dioxide), triple (silicon dioxide) - (aluminum dioxide) - (zirconium dioxide), triple (silicon dioxide) - (aluminum dioxide) - (magnesia), triple (silicon dioxide ) _- magnesia- (zirconium dioxide), triple (silicon dioxide) - (aluminum dioxide) - (thorium dioxide) and a mixture of any two or more of them.

Preferably, the catalyst is dispersed throughout and, preferably, uniformly throughout, throughout the extruded body of the catalyst.

When any of the above extruded solid bodies is configured as a filter with flow walls, the porosity of the filter with flow walls can be 30-80%, such as 40-70%. Porosity and pore volume and pore radius can be measured, for example, using mercury intrusion porosimetry.

The catalyst of the present invention can also promote the oxidation of ammonia. Thus, the catalyst can be formulated to favor the oxidation of ammonia with oxygen, in particular at ammonia concentrations found downstream of the SCR catalyst (e.g., ammonia oxidation catalyst (AMOX), such as ammonia conversion catalyst (ASC).

The catalyst may be located as the lower layer under the upper SCR layer. Preferably, the CKV catalyst is a metal-promoted zeolite (e.g., a Cu- or Fe-promoted aluminosilicate zeolite selected from BEA, CHA, AEI, AFX, ZSM-5, ZSM-34, MFI, KFI, LEV or the like) or metal-promoted vanadium dioxide (e.g., Fe- or W-promoted vanadium dioxide).

The catalyst may be an ammonia conversion catalyst, which is located downstream of the selective catalytic reduction catalyst (SCR). The ammonia conversion catalyst oxidizes at least a portion of any nitrogen reducing agent that is not consumed by the selective catalytic reduction method. For example, the ammonia conversion catalyst may be located on the outside of the filter with flow walls, and the SCR catalyst may be located on the side upstream of the filter. Alternatively, the ammonia conversion catalyst may be located at the end downstream of the flow carrier, and the SCR catalyst may be located at the end upstream of the flow carrier. In another embodiment, the ammonia conversion catalyst and the SCR catalyst each have a separate carrier (i.e., they are each located on separate blocks) in the exhaust system. These individual carriers, or blocks, can be adjacent and in contact with each other or separated by a certain distance, provided that they are in fluid communication with each other, and provided that the carrier, or block, of the SCR catalyst is located upstream from a carrier, or block, ammonia conversion catalyst.

The catalytic oxidation process is usually carried out at a temperature of at least 100 ° C, such as from about 150 ° C to about 750 ° C, in particular from about 175 ° C to about 550 ° C (e.g. 175-400 ° C ) The catalytic oxidation method can be carried out at a temperature of 450-900 ° C, preferably 500-750 ° C, 500-650 ° C, 450-550 ° C or 650-850 ° C. Options using temperatures above 450 ° C are used in particular to clean exhaust gas from a heavy and light-duty diesel engine that is equipped with an exhaust system that contains (optionally catalyzed) diesel particulate filters that are actively regenerated, for example, by introducing a hydrocarbon into the exhaust system upstream of the filter, where the zeolite catalyst for use in the present invention is located downstream of the filter.

Typically, all or at least part of a nitrogen-containing reducing agent, in particular NH ₃ , for consumption in the SCR method can be supplied by the catalyst of the present invention, acting as a NO _x scavenger catalyst (NAC), depleted NO _x trap (LNT) or NO _x storage / reduction catalyst (NSRC) located upstream of an SCR catalyst, for example, an SCR catalyst of the present invention, located on a flow-walled filter. The NAC components used in the present invention comprise a combination of a base material (such as an alkali metal, alkaline earth metal or rare earth metal, including alkali metal oxides, alkaline earth metal oxides and combinations thereof) and a noble metal (such as platinum) and optionally a component of a reduction catalyst such as rhodium. Certain types of base material used in NAC include cesium oxide, potassium oxide, magnesium oxide, sodium oxide, calcium oxide, strontium oxide, barium oxide, and combinations thereof. The noble metal is preferably present in an amount of about 10-200 g / ft ³ (333-6660 g / m ³ ), such as 20-60 g / ft ³ (666-2000 g / m ³ ). Alternatively, the noble metal of the catalyst is characterized by an average concentration, which may be from about 40 to about 100 g / ft ³ (from about 1332 to about 3330 g / m ³ ).

Under certain conditions, in cases of periodic enrichment regeneration, NH ₃ can be generated using a NO _x absorbent catalyst. An SCR catalyst downstream of the NO _x scavenger catalyst can improve the overall NO _x reduction efficiency of the system. In an integrated system, an SCR catalyst is able to accumulate NH ₃ released from the NAC catalyst during enrichment regeneration and uses the accumulated NH ₃ to selectively recover part or all of the NO _x that is converted using the NAC catalyst under normal lean operating conditions.

The exhaust gas purification method, as described herein, can be carried out on exhaust gas obtained from a combustion method, such as an internal combustion engine (either mobile or stationary), a gas turbine, and coal or oil power plants. The method can also be used for gas purification from industrial methods, such as oil refining, oil refining heaters and boilers, furnaces, chemical processing industry, coke ovens, municipal waste processing plants and incinerators, etc. In a particular embodiment, the method is used to purify exhaust gas from an internal combustion engine with incomplete combustion of a vehicle, such as a diesel engine, incomplete gasoline engine, or a petroleum gas or natural gas engine.

In some aspects, the subject of the invention is a system for purifying exhaust gas generated by a combustion method, such as from an internal combustion engine (either mobile or stationary), a gas turbine, power plants operating on coal or oil, and the like. Such systems comprise a catalytic product containing the catalyst described herein and at least one additional component for purifying exhaust gas, where the catalytic product and at least one additional component are intended to function as a linked unit. The system may comprise a diesel oxidation catalyst, an NO _x scavenger and / or a mercury oxidation catalyst, as described herein, and optionally one or more of an SCR catalyst, a diesel particulate filter, a catalyzed carbon black filter, an ammonia conversion catalyst, or a combination thereof. Such systems optionally include one or more sections of an exhaust gas passage from the engine to the end of the after-treatment and / or recirculation system of at least a portion of the partially purified exhaust gas to the after-treatment system.

The system may comprise an oxidation catalyst (e.g., a diesel oxidation catalyst (DCO)) for oxidizing nitrogen monoxide in the exhaust gas to nitrogen dioxide, located upstream of the dosing point of the nitrogenous reducing agent in the exhaust gas. The oxidation catalyst may be designed to produce a gas stream introducing a zeolite SCR catalyst having a ratio of NO to NO ₂ from about 4: 1 to about 1: 3 by volume, for example, at an exhaust gas temperature at the inlet of the oxidation catalyst from 250 ° C to 450 ° C.

The present invention includes an oxidation process. The method may comprise a gaseous stream of diesel exhaust gas containing carbon monoxide, unsaturated hydrocarbons, or both in the presence of a diesel oxidation catalyst, as described herein. The method is preferably carried out under “oxidation conditions in a diesel engine” as described above, i.e. in an exhaust system under normal operating conditions, where normal operating conditions comprise the presence of a mixture containing NO _x , carbon dioxide, water and oxygen at temperatures ranging from 100 ° C to 400 ° C, preferably 100-300 ° C.

The invention may include a method for oxidizing mercury. The invention may include a method for adsorbing NO _x , in particular when used in combination with an SCR method downstream.

The present invention also relates to a privately prepared catalyst. The method contains four stages. Firstly, cerium dioxide is impregnated with an aqueous solution containing a water-soluble niobium, or tantalum salt. The water-soluble niobium or tantalum salt is usually acetate, nitrate, halide, oxalate or the like, such as niobium (V) chloride, niobium (III) nitrate, ammonium niobate (V) oxalate or tantalum (V) chloride. Secondly, the impregnated cerium dioxide is calcined at a temperature in the range from 600 ° C to 1000 ° C, preferably 700-950 ° C, more preferably 750-900 ° C, to obtain a carrier. The media contains at least 90% wt. cerium dioxide and 0.1-10% wt. niobium dioxide or tantalum dioxide as a cerium dioxide ligand. Preferably, the carrier contains 91-95% wt. cerium dioxide and 0.5-9% wt. niobium dioxide or tantalum dioxide. Thirdly, cerium dioxide doped with niobium dioxide or tantalum dioxide is impregnated with a solution containing a transition metal of groups 8-11. Finally, the product is calcined at a temperature in the range of 600 ° C. to 1000 ° C. to obtain a catalyst. The catalyst contains 0.1-10% wt. transition metal of groups 8-11.

Definitions

As used here, the term "catalyst" means any substance that modifies the rate of a chemical reaction without spending the reaction, including (but not limited to) adsorbents.

As used here, the term "carrier" in relation to the metal catalyst of groups 8-11 means a solid material, usually having a high surface area, with which the catalyst is bonded (for example, by impregnation).

By “doped” is meant that niobium or tantalum is integrated into the lattice structure of cerium dioxide, usually as a mixed oxide (for example, niobium dioxide and cerium dioxide or tantalum dioxide and cerium dioxide).

As used here, the term "essentially does not contain" component, usually used in relation to the carrier or catalyst, refers to less than 0.1% wt. or even less than 0.01% wt. component. More preferably, the carrier or catalyst does not contain a component.

As used here, the term "consistent" with respect to the catalyst layers on the carrier means that each layer is in contact with its adjacent layer (s), and that the catalyst layers as a whole are located one on top of the other on the carrier.

As used here, the terms “first layer” and “second layer” are used to describe the relative positions of the catalytic layers in the catalyst product with respect to the normal direction of the exhaust gas through, passing and / or over the catalyst product. Under normal exhaust gas passage conditions, the exhaust gas is contacted with the first layer before being contacted with the second layer.

Examples

The following examples only illustrate the invention; one skilled in the art will identify many variations that are within the spirit of the invention and are within the scope of the claims.

Example 1

Obtaining cerium dioxide doped with niobium dioxide (3.2% wt. Nb ₂ O ₅ )

Ammonium niobate (V) oxalate (21% Nb, 1.06 g, 2.4 mmol Nb, equivalent to 0.32 g Nb ₂ O ₅ ) is dissolved in water (6 ml) with stirring and gentle heating. High surface area cerium dioxide (9.68 g) was added and the mixture was stirred. The pore volume of cerium dioxide is slightly excessive, so that the sample is mixed and slightly heated to dryness on a hot plate. The sample is additionally dried in an oven at 105 ° C. Portions of the sample are calcined (“burned”) at 500 ° C for 2 hours or at 800 ° C for 4 hours (linear temperature increase rate of 10 ° C / min).

Example 2

Obtaining cerium dioxide doped with niobium dioxide (5.0% wt. Nb ₂ O ₅ )

The basic procedure of Example 1 was followed using ammonium niobate (V) oxalate (3.33 g, 7.52 mmol Nb, equivalent to 1.00 g Nb ₂ O ₅ ), cerium dioxide (19 g) and water (12 ml).

Example 3

Obtaining cerium dioxide doped with niobium dioxide (8.6% wt. Nb ₂ O ₅ )

The basic procedure of Example 1 was followed using ammonium niobate (V) oxalate (2.86 g, 6.47 mmol Nb, equivalent to 0.86 g Nb ₂ O ₅ ), cerium dioxide (9.14 g) and water (6 ml) .

In comparative examples 4-6, the main procedure from WO2012 / 004263 is followed to obtain catalysts in which cerium dioxide is formed in the presence of niobium dioxide. Based on the production method, the catalysts have a niobium dioxide core surrounded by a cerium dioxide shell.

Reference Example 4

Obtaining sol niobium dioxide

Ethanol (100 ml) was dried for 20 hours on 3A molecular sieves (18 g). The sieves are preliminarily fired at 400 ° C. for 1 hour to remove water. Anhydrous ethanol (40 ml) and a small magnetic stir bar are charged into a round bottom flask. Ethanol is stirred and niobium (V) chloride (10 g, 0.037 mol) is added using a plastic spatula. When the introduction is complete, the result is a pale yellow solution. More ethanol (21 ml) was introduced, stirring was stopped, and the flask was closed with a stopper and stood for 2 hours. The stopper was replaced with a reflux condenser.

and the solution is heated to about 70 ° C for 1 hour. After heating, the solution loses color and is left to stand until morning at room temperature.

Concentrated (35%) ammonia (25.1 g) was stirred with a magnetic stirrer in a beaker. The niobium (V) chloride / ethanol solution obtained above was poured into stirred ammonia simultaneously with water (76 ml). A white precipitate forms immediately and the mixture is exothermic. After stirring for 0.5 h, the mixture is filtered and the solid material is washed with water until the filtrate has a thermal conductivity of about 1 mS. The mixture is slowly filtered and washed.

The precipitate was stirred in nitric acid (81 ml of 1M aq. HNO ₃ ) for 4 days (96 hours). A white suspension of Nb ₂ O _{5 is} obtained (pH: 0.55; suspension yield: 122.6 g). Preventing losses, the sol of niobium dioxide contains 0.037 mol of Nb (0.0001508 mol of Nb ₂ / g).

Obtaining niobium dioxide encapsulated by cerium dioxide

Water (50 ml), a magnetic stirrer and a pH probe are loaded into a beaker. The pH is adjusted to about 9.0 with a pair of drops of ammonia solution (obtained by diluting 24 ml of concentrated (35%) ammonia to 100 ml).

Separately, cerium (III) nitrate hexahydrate (24.4 g, 0.0562 mol, equivalent to 9.68 g of CeO ₂ ) is dissolved in water (180 ml). A portion of the niobium dioxide sol is introduced (7.95 g, equivalent to 0.32 g of Nb ₂ O ₅ , 0.0012 mol of Nb ₂ ) followed by 30% hydrogen peroxide (6.37 g, 0.0562 mol). With the introduction of peroxide, the suspension becomes yellow.

The suspension is pumped (16 ml / min) into a well-mixed ammonia solution prepared previously, and an additional ammonia solution is added dropwise manually by maintaining the pH at about 9.0. When the addition is complete, the mixture is stirred for 0.5 hours and then filtered. The resulting yellow-orange precipitate was washed with water (3x500 ml) and then dried (105 ° C) to obtain a solid product (10.4 g). Portions of the sample are calcined at 500 ° C for 2 hours or at 800 ° C for 4 hours (linear temperature increase rate of 10 ° C / min). The final product contains 3.2% wt. Nb ₂ O ₅ .

Reference Example 5

The whole procedure of comparative example 4 is followed using a niobium dioxide sol (12.47 g, equivalent to 0.5 g Nb ₂ O ₅ , 0.00188 mol Nb ₂ ), cerium (III) nitrate hexahydrate (23.97 g, 0.0552 mol, equivalent to 9.5 g of CeO ₂ ), a solution of ammonia and 30% hydrogen peroxide (6.26 g, 0.0552 mol). Yield: 10.47 g. Portions of the sample are calcined at 500 ° C for 2 h or at 800 ° C for 4 h (linear temperature increase rate of 10 ° C / min). The final product contains 5.0% wt. Nb ₂ O ₅ .

Reference Example 6

The whole procedure of comparative example 4 is followed using a niobium dioxide sol (21.44 g, equivalent to 0.86 g of Nb ₂ O ₅ , 0.00324 mol of Nb ₂ ), cerium (III) nitrate hexahydrate (23.06 g, 0.0531 mol, equivalent to 9.14 g of CeO ₂ ), a solution of ammonia and 30% hydrogen peroxide (6.02 g, 0.0531 mol). Yield: 10.34 g. Portions of the sample are calcined at 500 ° C for 2 h or at 800 ° C for 4 h (linear temperature increase rate of 10 ° C / min). The final product contains 8.6% wt. Nb ₂ O ₅ .

Determination of the lattice parameter

A Bruker AXS D8 X-ray diffractometer was used with a device for changing 90 positions of the sample. The lattice parameter is determined by Reitveld analysis (L Vol-IB method) using a method for obtaining a diffraction x-ray of a completely powdery sample.

Test conditions for NH ₃ -SCR activity

Powdered samples of the catalysts are obtained by tabletting the starting samples, crushing the tablets and then passing the resulting powder through a 255-350 micron sieve. The sieved powders are loaded into a catalyst synthetic activity test reactor (SCAT) and tested using the following synthetic diesel exhaust gas mixture (inlet), including ammonia as reducing agent: 500 ppm NO, 500 ppm NH ₃ , 9% O ₂ , 5% CO ₂ , 5% H ₂ O, 300 ppm CO, the rest up to 100% - N ₂ at a spatial speed of 30,000 h ^-1 .

Samples are gradually heated from 150 ° C to 550 ° C at 5 ° C / min, and the composition of the exhaust gases is analyzed using Fourier transform infrared spectroscopy ((IRSFP) (FTIR)) to determine the% conversion of NO _x gases. The test results of the catalysts of examples 2 and 3 and comparative examples 5 and 6 are shown in figure 2.

Catalyst B: 2% Pd on niobium doped cerium dioxide

The solution is prepared by dissolving ammonium niobium oxalate (0.66 g, 21% wt. Nb, 1.5 mmol) in 912 ml of water. The solution is used to impregnate cerium dioxide (19.8 g) with a high surface area. The mixture is dried, calcined at 500 ° C and further calcined at 750 ° C for 2 hours to obtain a product that contains 1% wt. Nb ₂ O ₅ . Then, cerium dioxide doped with niobium dioxide was combined with aqueous palladium nitrate (2.6 g of a 15% aqueous solution, 3.7 mmol), and the mixture was dried at 100 ° C and calcined at 500 ° C. The catalyst, which contains 2.0% wt. Pd additionally matures at 750 ° C. for 10 hours before use.

Comparative Catalyst A: 2% Pd on Cerium Dioxide

Cerium dioxide (20 g) was combined with aqueous palladium nitrate (2.6 g of a 15% aqueous solution, 3.7 mmol), and the mixture was dried at 100 ° C and calcined at 500 ° C. The catalyst, which contains 2.0% wt. Pd additionally matures at 750 ° C. for 10 hours before use.

Comparative Catalyst C: 2% Pd on Cerium Dioxide

Cerium dioxide (20 g) is calcined at 750 ° C, then combined with aqueous palladium nitrate, dried and calcined, as described in the preparation of comparative catalyst A. The catalyst, which contains 2.0% wt. Pd additionally matures at 750 ° C. for 10 hours before use.

Sulfur dioxide adsorption and temperature-programmed oxidation

For the sulfur dioxide adsorption step, catalyst B and comparative catalysts A and C are aged in sulfur dioxide (60 ppm, 9 mg S / g) for 30 minutes at 300 ° C. under 10% oxygen, and consumption is measured (in hours / million) SO ₂ . The results are shown in figures 3 and 11. For temperature-programmed oxidation, sulfur-treated catalysts are heated from room temperature to 1000 ° C at a rate of 10 ° C / min under 10% oxygen, and the concentration of sulfur dioxide released is determined as a function of temperature. The results are shown in figures 4 and 12.

Cyclic sulfonation-desulfurization for catalyst conditioning

Catalyst B and comparative catalysts A and C undergo six sulfonation-desulfurization cycles to investigate the effects of sulfur poisoning on the ability of the catalyst to oxidize hydrocarbons and carbon monoxide.

Sulfonation is carried out by holding the catalyst in a mixture of propylene (300 ppm), NO (200 ppm), O ₂ (10%), CO ₂ (4.5%) and SO ₂ (60 ppm) for 20 min at 300 ° C (total about 9 mg S / g of catalyst).

The catalyst is then desulfurized by introducing propylene (7500 ppm) and CO (5000 ppm) into the gaseous mixture. After 4 minutes, an exotherm of about 518 ° C. (up to 818 ° C.) was calculated.

The sulfonation-desulfurization cycle is then repeated more than five times (a total of approximately 54 mg S / g of catalyst). The ability of the treated catalyst to oxidize carbon monoxide or propylene is then determined as described below.

Diesel Oxidation Test Conditions

Powdered samples of catalysts AC, which were either subjected to ripening at 750 ° C or aging and then subjected to cyclic sulfonation-desulfurization, are obtained by tabletting the initial samples, crushing the tablets and then passing the resulting powder through a 255-350 micron sieve. The sifted powders are loaded into a catalyst synthetic activity test reactor (SCAT) and tested for their ability to oxidize CO or propylene using the following synthetic mixture of diesel exhaust gas (inlet) at a spatial speed of 30,000 h ^-1 : 1500 ppm CO, 150 ppm NO _x, 40 ppm propylene, 16 ppm toluene, 30 ppm decane, 40 ppm methane, 4.5% CO ₂ , 4.5% H ₂ O , 12% O ₂ , the rest up to 100% - N ₂ .

Samples are heated gradually from 100 ° C to 300 ° C at 5 ° C / min, and the composition of the exhaust gases is analyzed using infrared spectroscopy with Fourier transform (IKSFP) to determine the% conversion of carbon monoxide or propylene. The results are shown in figures 5 and 6.

The preparation of catalysts with Pd on cerium dioxide doped with tantalum dioxide

Obtaining carriers of cerium dioxide doped with tantalum dioxide (1%, 5% and 10% Ta ₂ O ₅ )

Ta oxalate colloid

Tantalum (V) chloride (5.0 g, 0.014 mol) was dissolved in concentrated hydrochloric acid (25 ml, about 0.3 mol) and then water (10 ml) was added. The solution is cooled to a temperature below 10 ° C in an ice bath. Concentrated ammonia (25 ml) is diluted to 50 ml and carefully added dropwise to an acid solution, not allowing the temperature to go above 20 ° C until a pH of 7.5 is reached. Then the addition of ammonia is stopped. The resulting precipitate was recovered by filtration and washed well with water.

Separately, oxalic acid dihydrate (3.53 g, 0.028 mol) was dissolved in water (15 ml) with gentle heating. The temperature is maintained below 70 ° C, and precipitated washed titanium oxide is slowly added. The mixture was stirred under mild heating for about 1 hour and then stirred overnight without further heating. A stable colloid is obtained. The mass of the obtained sol: 38.2 g. Preventing losses, the sol should contain 3 g of Ta ₂ O ₅ .

1% wt. Ta ₂ O ₅ on cerium dioxide

A portion of the Ta oxalate colloid obtained as described above (2.55 g, equivalent to 0.2 g Ta ₂ O ₅ ) is weighed in a small beaker and water is added to obtain a total mass of 12 g. Cerium dioxide is added (19.8 d) with a high surface area, and the mixture is thoroughly mixed. The sample was dried in an oven at 105 ° C, then calcined at 500 ° C in air for 2 hours (linear temperature increase rate of 10 ° C / min).

5% wt. Ta ₂ O ₅ on cerium dioxide

A portion of Ta colloid of oxalate (12.73 g, equivalent to 1.0 g of Ta ₂ O ₅ ) is weighed in a small beaker and water is added to obtain a total mass of 12 g. Cerium dioxide (19.0 g) is added and the mixture is thoroughly mixed . The sample was dried in an oven at 105 ° C, then calcined at 500 ° C in air for 2 hours.

10% wt. Ta ₂ O ₅ on cerium dioxide

A portion of the Ta oxalate colloid (12.73 g, equivalent to 1.0 g Ta ₂ O ₅ ) is weighed in a small beaker and water is added to obtain a total mass of 12 g. Cerium dioxide (9.0 g) is added and the mixture is thoroughly mixed . The sample was dried in an oven at 105 ° C, then calcined at 500 ° C in air for 2 hours.

Impregnation of tantalum doped cerium dioxide using 2% Pd

A solution of palladium (II) nitrate (1.98 g, 15.14% Pd, equivalent to 0.3 g Pd) is weighed in a small beaker and diluted with water (7.0 ml). A tantalum doped cerium dioxide sample prepared as described above (1.0% wt. Ta ₂ O ₅ / cerium dioxide, 14.7 g) was added and the mixture was thoroughly mixed before drying at 105 ° C. The sample is calcined at 500 ° C in air for 2 hours (linear temperature increase rate of 10 ° C / min).

An identical technique is used to obtain 2% palladium on cerium dioxide doped with 5% wt. and 10% wt. Ta ₂ O ₅ / cerium dioxide.

The catalysts are calcined at 750 ° C. before being tested as diesel oxidation catalysts. The results are presented in figures 7-10.

Catalysts of palladium on cerium dioxide and palladium on cerium dioxide doped with tantalum dioxide are studied for the oxidation of propylene and ammonia in a SCAT reactor under the following conditions: 335 ppm propylene, 50 ppm NH ₃ , 8% CO ₂ , 5 % H ₂ O. Temperature: 150 ° C-400 ° C (rate of linear increase in temperature 5 ° C / min). The oxidation of NO is determined as described above in the diesel oxidation test.

results

The lattice parameter (in Angstroms) for each of the materials obtained in examples 1-3 and comparative examples 4-6 is determined as described above. Figure 1 shows that cerium dioxides doped with niobium dioxide used as supports for the diesel oxidation catalysts of the invention (obtained in Examples 1-3) undergo a significant reduction in the lattice with increasing levels of niobium dioxide.

This is confirmed by the large negative slope of the best aligned line. The results suggest that these materials introduce niobium into the lattice frame. In contrast, when the procedure of WO2012 / 004263 is used to prepare catalysts having the same Nb ₂ O ₅ content (comparative examples 4-6), a slight or no lattice reduction is confirmed. This shows that the procedure for obtaining from document WO2012 / 004263 gives a different product from the products obtained in examples 1-3, even if the content of Nb ₂ O ₅ is the same. The result is noticeable since the procedure from WO2012 / 004263 first obtains niobium dioxide, then forms cerium dioxide in the presence of niobium dioxide. In contrast, niobium dioxide doped with preformed cerium dioxide in examples 1-3.

Further confirmation that the cerium dioxide doped with niobium dioxide of examples 1-3 is different from the products of comparative examples 4-6, is shown in figure 2. Figure 2 shows the graphs of the conversion of NO _x depending on temperature for doped with niobium dioxide cerium dioxide and for comparative compositions obtained according to WO2012 / 004263. As shown in figure 2, doped with niobium dioxide cerium dioxide converts a much higher percentage of NO _x at temperatures in the range from 150 ° C to 550 ° C, when the content of niobium dioxide is 5.0% wt. or 8.6% wt.

Since the compositions of examples 1-3 differ from the compositions obtained in comparative examples 4-6 (as confirmed by both measurements of the reduction of the lattice and the characteristic of the reduction of NO _{x of} these materials), any diesel oxidation catalyst obtained by applying a transition metal of groups 8-11 to the doped ceria, niobium dioxide should also be different.

The figure 3 presents graphs of the consumption of sulfur dioxide for a catalyst with 2% palladium doped with niobium dioxide cerium dioxide (catalyst B) and comparative catalysts Pd / CeO ₂ (catalysts A and C). The methods for the preparation of catalysts AC are presented above. Each catalyst is sulfonated at 300 ° C. using 60 ppm SO ₂ and 10% O ₂ in N ₂ to 42 mg S / g of catalyst. As shown in FIG. 3, comparative catalysts A and C adsorb SO ₂ almost quantitatively over a much longer period of time compared to catalyst B. Calcination of the support impairs the consumption of sulfur (A against C), while doping with niobium sharply reduces it. Catalyst B is much less prone to adsorbing SO ₂ and departs from the maximum level in minutes in this experiment.

After an experiment on the consumption of sulfur dioxide (Figure 3), the same catalysts undergo temperature-programmed oxidation (TPO). The supply of sulfur dioxide is stopped, and the temperature gradually increases. The concentration of SO ₂ released from the catalyst is controlled. As shown in FIG. 4, each of the catalysts releases SO ₂ at approximately the same temperature, but catalyst B releases much less SO ₂ . This confirms that Pd on niobium doped ceria (Catalyst B) adsorbs less SO ₂ than the comparative Pd / CeO ₂ catalysts during the consumption phase.

Figure 5 shows the conversion of carbon monoxide as a function of temperature for a catalyst with 2% palladium doped with niobium dioxide cerium dioxide (catalyst B) and comparative Pd / CeO ₂ catalysts (catalysts A and C), where the catalysts either mature at 750 ° C. or age at 750 ° C and undergo cyclic sulfonation / desulfurization. As the results with matured catalysts show, doping with niobium dioxide allows the catalyst to oxidize CO more efficiently at temperatures below 200 ° C and reduce the temperature at which the conversion becomes close to quantitative. Annealing cerium dioxide alone (C vs. A) improves oxidation efficiency, but not as much as doping. The repeated exposure to sulfur poisoning (during cyclic sulfonation / desulfurization) reduces the oxidation efficiency of all three catalysts. However, a catalyst with doped niobium dioxide cerium dioxide as a carrier retains more of its effectiveness. Compare the results at 210 ° C, where the conversion of CO by catalyst B is about 60% compared to about 30% or less with catalyst A or C. Furthermore, any advantage of catalyst C over catalyst A obtained by calcining cerium dioxide is lost when processing sulfur.

In figure 6, the conversion of propylene versus temperature is compared for catalysts AC in the same diesel oxidation experiment used to create figure 5. The trends are basically the same as those observed for CO oxidation. Pd, supported on niobium doped with ceria (catalyst B), oxidizes propylene more efficiently at temperatures below 200 ° C and achieves a "clarification" of propylene (defined as the temperature at which 50% conversion is achieved) at a lower temperature. When exposed to sulfur, catalyst B shows a better propylene conversion compared to catalyst A or C at temperatures below about 250 ° C.

Doped with tantalum dioxide, cerium dioxide is an effective support for transition metal catalysts of groups 8-11 for oxidation in a diesel engine. Valuable catalysts have the ability to oxidize hydrocarbons and NO while also inhibiting the oxidation of ammonia. This allows the oxidation catalyst and the SCR catalyst to work together. Figure 7 shows a graph of the% conversion of propylene and ammonia versus temperature for a catalyst with 2% palladium doped with tantalum dioxide cerium dioxide and a comparative catalyst Pd / CeO ₂ . As shown in figure 7, doping of cerium dioxide in a small amount up to 1% wt. Ta ₂ O ₅ reduces the clarification temperature of propylene and inhibits the conversion of ammonia. Although the clarification of propylene is manifested in the best way below 5% wt. Ta ₂ O ₅ , more tantalum dioxide is better for promoting the conversion of ammonia to higher temperatures.

Figure 8 shows a graph of% carbon monoxide conversion versus temperature, and shows the effect of tantalum dioxide for a catalyst with 2% palladium on tantalum doped cerium dioxide and a comparative Pd / CeO ₂ catalyst. The figure shows a significant improvement in activity in the oxidation of CO for doped with tantalum dioxide catalyst, in particular, at 10% wt. Ta ₂ O ₅ . The same trends observed in figure 8 are confirmed in figure 9, which shows the results of the conversion of propylene with the same catalysts. The clarification temperature of propylene decreases sharply when doping a cerium dioxide support with 10% tantalum dioxide. Figure 10 shows the effect of tantalum dioxide on NO oxidation temperature requirements for a catalyst with 2% palladium doped with tantalum dioxide cerium dioxide and a comparative Pd / CeO ₂ catalyst. The shift of the curves to the left (to lower temperatures) with the introduction of a small amount of up to 1% wt. tantalum dioxide shows easier oxidation of NO when Ta-doped cerium dioxide is used as a transition metal carrier of groups 8-11.

Oxidation catalysts using cerium dioxide doped with tantalum dioxide as a carrier have a reduced tendency to accumulate sulfur compared to Pd / CeO ₂ . As shown in figure 11, the consumption of sulfur dioxide on a catalyst with 2% palladium on doped tantalum dioxide cerium dioxide stops the adsorption of the introduced SO ₂ more quickly than the comparative catalyst without doping the carrier with tantalum dioxide. The results presented in FIG. 12 confirm that Pd on Ta ₂ O ₅ -doped cerium dioxide is less prone to sulfur accumulation. Temperature-programmed oxidation produces a reduced amount of sulfur dioxide released from a catalyst with doped tantalum dioxide cerium dioxide as a carrier after exposure to sulfur dioxide.

The preceding examples are for illustration only; the following claims define the scope of the invention.

Claims (27)

1. A catalyst for cleaning an exhaust gas of a diesel engine, comprising: (a) 0.1-10% wt. a transition metal of a platinum group and (b) 90-99.9% wt. carrier where the carrier contains at least 90% wt. cerium dioxide and 0.1-10% wt. cerium dioxide dopant, where the additive contains niobium (Nb) or tantalum (Ta). 2. The catalyst according to claim 1, wherein the additive is niobium dioxide or tantalum dioxide. 3. The catalyst according to claim 1 or 2, in which the transition metal of the platinum group is palladium. 4. The catalyst according to claim 1, which contains 1-5% wt. transition metal platinum group. 5. The catalyst according to claim 1, in which the carrier contains at least 95% wt. cerium dioxide. 6. The catalyst according to claim 1, in which the carrier contains cerium dioxide having a surface area of more than 100 m ² / g. 7. The catalyst according to claim 1, in which the carrier contains 1-5% wt. additives. 8. The catalyst according to claim 1, in which the carrier is a calcined carrier and, optionally, where this calcined carrier is obtained by calcination at a temperature in the range from 600 ° C to 1000 ° C. 9. The catalyst according to claim 1, which is obtained by calcination at a temperature in the range from 600 ° C to 1000 ° C. 10. The catalyst according to claim 1, wherein the catalyst is a diesel oxidation catalyst. 11. The catalyst according to claim 1, wherein the catalyst is an NO _x scavenger. 12. The catalyst according to claim 1, where the catalyst is a catalyst for the oxidation of mercury. 13. A method of obtaining a catalyst for purification of exhaust gas of a diesel engine, defined according to any one of paragraphs. 1-9, including: (a) impregnating cerium dioxide with an aqueous solution containing a water-soluble salt of niobium (Nb) or tantalum (Ta); (b) calcining the impregnated cerium dioxide at a temperature in the range of 600 ° C to 1000 ° C to obtain a carrier; (c) impregnating the support with a solution containing a transition metal of a platinum group. 14. The method of claim 13, further comprising: (d) calcining the product from step (c) at a temperature in the range of 600 ° C. to 1000 ° C. to obtain a calcined catalyst, wherein the calcined catalyst contains 0.1-10% by weight. transition metal platinum group. 15. The catalyst for cleaning the exhaust gas of a diesel engine, obtained by the method according to p. 13 or 14. 16. An exhaust gas aftertreatment system comprising a catalyst according to any one of claims. 1-9 or 15, and optionally an SCR catalyst, a diesel particulate filter, a catalyzed carbon black filter, an ammonia conversion catalyst, or a combination thereof. 17. The exhaust gas aftertreatment system according to claim 16, wherein the catalyst is a diesel oxidation catalyst. 18. The exhaust gas aftertreatment system of claim 16, wherein the catalyst is an NO _x scavenger. 19. An exhaust gas aftertreatment system according to claim 16, wherein the catalyst is a mercury oxidation catalyst. 20. The method of oxidizing a gaseous stream of diesel exhaust gas containing carbon monoxide, unsaturated hydrocarbons, or both, in the presence of a catalyst according to any one of paragraphs. 1-12 or 15.

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