RU2297278C2 - Method of production and activation of poly-metallic zeolite catalysts, composition and application of catalyst for decomposition of n2o - Google Patents

Abstract

FIELD: production of poly-metallic catalysts.

SUBSTANCE: Fe is introduced into proposed catalyst by isomorphic substitution into zeolite lattice by hydro-thermal synthesis; then, zeolite is calcined and is transformed into H-form, after which Cu and /or Co is introduced by ion exchange in liquid or solid phase before calcination and activation of specimen at high temperature or by water steam and alkaline treatment. Zeolite has mole ratio Si/T 20-80, where T=Al, Ga, B or Ti. Method of decomposition or reduction of nitrous oxide in waste gases at temperature below 650 K with the use of obtained zeolite. Catalyst produced by this method possesses high conversion of N₂O at temperature <623 K and enhanced stability.

EFFECT: enhanced efficiency and stability of catalyst.

20 cl, 4 dwg, 4 tbl, 12 ex

Description

The invention relates to a method for the preparation and activation of polymetallic catalysts and their use to reduce the content of N ₂ O.

Technical field

The present invention relates to environmental systems for controlling emissions of pollutants and, in particular, to a catalytic method for reducing nitrous oxide in industrial gases (chemical production) and in combustion products. The characteristics of the exhaust gases are as follows: diluted flows of N ₂ O (in the range of 0.05-0.5 vol.%), Relatively low temperatures and in the presence of catalyst inhibitors.

Description of the Related Art

For a long time, nitrous oxide was considered as a relatively harmless compound, and it did not arouse the interest of scientists, engineers, and politicians. However, in the last decade, this interest has increased, since N ₂ O is a gas that causes a strong greenhouse effect (310 times more than CO ₂ ), and also participates in the destruction of the ozone layer. Emissions of N ₂ O, which can be quickly reduced, are associated with the chemical industry and with combustion processes. To reduce the content of N ₂ O in the exhaust gases, various options have been proposed, but so far there is no single technology. Despite the fact that there are many articles and patents on catalytic systems for the direct decomposition of N ₂ O and recovery using hydrocarbons, laboratory data often differ from the results of industrial practice, and tests on pilot plants are inaccessible. Moreover, stability tests in real conditions were often underestimated.

A new method for controlling the content of N ₂ O in the exhaust gases of plants producing adipic acid (concentration of N ₂ O 25-40 vol.%) Is to reuse N ₂ O as a selective oxidizing agent in the reaction of the conversion of benzene to phenol in the presence of zeolites Fe- MFI (U.S. Patents 5,672,777 and 5,110,995). However, this method is not applicable for "diluted" exhaust gases of other industries (with a concentration of N ₂ O in the range of 0.05-0.5 vol.%).

Recently, proposals have been made to add reducing agents (for example, light hydrocarbons and ammonia) to the initial mixture for the selective catalytic reduction of N ₂ O in the presence of Fe-MFI ion-exchange zeolites (patents WO 9949954 and WO 0151182). However, this proposal is not acceptable for stationary sources due to the high cost of the reducing agent and harmful emissions (slip or unwanted combustion products).

The direct catalytic decomposition of N ₂ O is a promising and cost-effective process for reducing N ₂ O emissions. However, none of the catalysts known in the literature has sufficient activity and stability in the conversion of N ₂ O in real conditions, which are determined by the composition of the initial mixture, temperature and space velocity (Centi et al. Chem. Tech . 29 (1999) 48, Kapteijn et al. Appl. Catal. B. , 9 (1996) 25). Catalysts based on transition (Cu, Co, Ni) and noble (Rh, Ru, Pd) metals on various supports (ZnO, CeO ₂ , Al ₂ O ₃ , TiO ₂ , ZrO ₂ or calcined hydrotalcites) are very active for the decomposition of N ₂ O in N ₂ O / He mixtures, but the presence of other gases in the feed stream (O ₂ , NO _x , H ₂ O, SO ₂ ) leads to a marked inhibition and / or deactivation of the catalyst.

Many metal-containing zeolites, including Cu- and Co-ZSM-5, as well as noble metal catalysts (Rh, Ru, and Pd), are much more active than Fe-ZSM-5 for the decomposition of N ₂ O in N ₂ mixtures O / He (F. Kapteijn et al., Stud. Surf. Sci. Catal. , 101 (1996) 641, Li and Armor, Appl. Catal. B. , 5 (1995) L257), but in the presence of O ₂ , NO and H ₂ O are best iron based systems (Perez-Ramirez et al., Chem. Commun. (2001) 693 and Appl. Catal. B. , 35 (2002) 227). This is due to (i) slightly pronounced hydrothermal properties of the first of these metals, (ii) the formation of stable nitrate or sulfate groups on the surface in the presence of NO or SO _2, respectively, and (iii) sintering of active centers under the reaction conditions (feed composition and temperature).

Interesting catalysts are Fe zeolites (mainly MFI, but also MOR, BEA, FER), since in the presence of these catalysts abnormal N ₂ O conversions (as part of typical exhaust gas components) are observed in comparison with other catalytic systems. WO 9934901 claims Fe ferrierite, highly active for the direct decomposition of N ₂ O in wet streams, but at relatively low space velocities (10,000 h ^-1 ), and no lengthy tests are reported in this application. In WO 0151415, ion-exchanged Fe zeolites are also used for direct decomposition of N ₂ O in the exhaust gases of nitric acid production. Perez-Ramirez et al., Catal. Today , 76 (2002) 53 it is concluded that the catalytic activity of Fe-ZSM-5 is determined by the method of its preparation. Steam-activated Fe-ZSM-5 is much more active in direct decomposition of N ₂ O than Fe-ZSM-5 catalysts obtained by other methods — ion exchange in liquid and solid phases and sublimation. The complete conversion of N ₂ O was achieved in simulated exhaust gases from the production of nitric acid (at 60,000 h ^-1 ) at a temperature of> 750 K. This temperature is too high to neutralize the flue gases, in particular flue gases from chemical plants. Adding C ₃ H ₆ lowers the operating temperature of the catalyst by 100K, but even this proposal remains economically disadvantageous.

The developed polymetallic zeolite systems can exhibit a synergy effect of metals, which affects the total activity and stability of the catalyst. In a previous patent (US 5110995), iron zeolites were highly active and selective in the selective oxidation of benzene to phenol using N ₂ O as an oxidizing agent. Fe-ZSM-5 was prepared by conventional hydrothermal synthesis and was calcined in the range 793-823K before the reaction. In some cases, iron zeolites also contained a second transition metal, for example, Co, V, Cr, Ni, Mo, introduced into the catalyst by conventional ion exchange or impregnation. Based on activity data, the patent authors concluded that in the presence of iron alone, activity and selectivity are higher, and the second metal does not have a positive effect (and even negatively affects) such important reaction parameters as benzene conversion and phenol selectivity. A later application by the same authors (US 5672777 and answer 36856) reported that a significant increase in activity during the conversion of benzene to phenol is achieved after hydrothermal treatment of Fe-MFI with a gas containing 3-100 vol.% H ₂ O in N ₂ at temperatures 773-1273K. Due to the lack of influence of the second transition metal, as described in the first patent, the second metal was excluded from the composition (and claims) of the last application.

The purpose of the invention

The main objective of the invention was the development of polymetallic zeolite catalysts for the direct decomposition of nitrous oxide (N ₂ O) to nitrogen (N ₂ ) and oxygen (O ₂ ).

Thus, the greatest attention is paid to the development of compositions that are highly active in the decomposition of N ₂ O at low temperature (<623K).

Another objective was the development of a stable catalyst that retains activity> 2000 hours under real conditions of the composition of the initial mixture (in the presence of inhibitors such as NO _x , H ₂ O, O ₂ and SO ₂ ).

The next task was to prepare catalytic systems that could be used at high space velocities> 50,000 h ^-1 .

Another significant task was the development of a method for reducing the amount of nitrous oxide in processes in which nitrous oxide is formed, for example, in chemical industries (production of nitric acid, adipic acid, caprolactam, acrylonitrile, glyoxal and processes using nitric acid as an oxidizing agent or involving the oxidation of ammonia ) and in combustion processes (coal, biomass and fluidized bed wastes), as well as in many reactions from which N ₂ O must be removed.

These and other objectives of the invention are achieved using the method described below, and the invention is further disclosed and characterized by the claims.

The invention is further explained with reference to the accompanying drawings in figures 1a, b-3.

FIG. 1 shows the temperature dependence of N ₂ O conversion in the presence of various mono- and polymetallic zeolites with the structure of MFI (a) and BEA (b).

FIG. 2 shows the conversion of N ₂ O on zeolites (Co) [Fe-T] MFI (c, s, a) with the MFI structure and different lattice composition (determined by the T atom); the designation (c, s, a) means the treatment of the catalyst before the reaction: c = calcination, s = steam treatment, a = alkaline treatment.

FIG. 3 shows the dependences of the N ₂ O conversion on the operating time in the presence of (Co) [Fe-Al] MFI (c, s, a) in experiments on a pilot plant.

The original idea of the invention was an attempt to combine the high activity of Cu and Co zeolites in the decomposition of N ₂ O in one polymetallic catalyst with pronounced stability and stability of Fe zeolites. The method of introducing metals into the structure of zeolite and its activation are crucial for obtaining active compounds operating at low temperature and stable in the processing of exhaust gases.

Thus, the invention relates to a method for producing a polymetallic zeolite in which Fe is isomorphically substituted in a zeolite lattice by hydrothermal synthesis. The zeolite in Na-form is calcined and exchanged with an ammonium salt, after which Cu and / or Co is introduced by ion exchange before calcination, activated at high temperature in vacuum or in air or by steam treatment and then subjected to alkaline treatment. In addition to Co and / or Cu, one or more elements of Mn, V, Ni or Cr can be introduced into the zeolite. For the introduction of a second, third or any additional metal, ion exchange can be used in both the liquid and solid phases. The zeolite catalyst may have a structure similar to MFI and / or BEA. It is preferable to use zeolites [Al] -ZSM-5, [Al] -BEA, [Ga] -ZSM-5, [B] -ZSM-5, [Ge, Al] -ZSM-5, silicalite or [Ti] -silikalite . Preferably, the molar ratio Si / T is 20-80, where T = Al, Ga, B, Ge or Ti.

The content of iron introduced into the substance varies from 0.1 to 1.0 wt.%. The content of Cu and / or Co varies in the range 0.1-1.0 wt.%. Preferred zeolite catalysts for these purposes are Fe-Co, Fe-Cu or Fe-Co-Cu zeolites. Preferably, the molar ratio of metals Fe / Co, Fe / Cu or Fe / Co + Cu is ~ 1. The zeolite is activated with water vapor at 623-1273K, 3-100 vol.% H ₂ O and an inert gas supply of 3-300 ml (normal conditions) min ^-1 for 0.5-6 hours. This treatment can be carried out in vacuum or in air at a temperature above 1073K. Alkaline treatment is carried out in an alkaline medium (NaOH, KOH or NH ₄ OH) at 298-363K, preferably for 10-60 minutes. Use solutions with a concentration in the range of 0.1-1.0 M.

The invention also provides a method for converting nitrous oxide (N ₂ O) to nitrogen (N ₂ ) and oxygen (O ₂ ) in the presence of polymetallic zeolites (MFI and BEA) containing transition metals. The invention also relates to a zeolite catalyst and a method for decomposing or reducing nitrous oxide at temperatures below 623K in exhaust gases using a zeolite of the general formula:

x T ₂ O _p - y Fe ₂ O ₃ - z M ₂ O _q -SiO ₂ ,

wherein

x = 0-0.065

y = 0.00002 - 0.02

z = 0.00002 - 0.02

T = Al, Ga, B, Ge or Ti

p = valence of the element T

M = Cu, Co, Mn, V, Ni, Cr

q = valency of element M

DETAILED DESCRIPTION OF THE INVENTION

At first, several iron-containing polymetallic zeolite catalysts were synthesized by various methods. Tests show that the combination of metals and the method of their introduction, as well as the method of incorporation of these metals into the zeolite significantly affect the activity of the final catalyst.

The following methods were used to introduce iron: hydrothermal synthesis, ion exchange in solid and liquid phases, and impregnation. The second (and third) metal was introduced by ion exchange (in liquid or solid phase) and impregnation. Used sequential or simultaneous methods of ion exchange or impregnation. To obtain good catalytic properties, the presence of iron, as well as the second, third or any additional transition metals, is mandatory. Zeolites with a combination of Fe with Co and / or Cu, prepared by a detailed procedure, found synergism in the catalytic decomposition of N ₂ O. This synergism leads to high activity at low temperature and stability during operation.

The activation of polymetallic zeolites, as synthesized, plays a crucial role in achieving the necessary catalytic properties. In the steam treatment, the temperature, the concentration of the vapor and the carrier gas were optimized. Compared to other processing methods (at higher temperatures in vacuum or in air), steam treatment in Ar at 873 K was recognized as the most effective. The final alkaline treatment is essential for increasing the activity of zeolites at low temperatures. This post-cooking treatment has also been optimized. Preferred is alkaline treatment in a 0.1 M NaOH solution at 333K for 30 minutes.

For the preparation of polymetallic zeolite catalysts, different schemes were used:

Scheme 1. Hydrothermal synthesis + ion exchange

1.a. Hydrothermal synthesis of zeolites without iron

Six series of molecular sieves with an MFI structure by hydrothermal synthesis were prepared by the procedure described below. The main difference between these series is the lattice composition, which can be varied by introducing different T-atoms instead of Si atoms: silicalite (pure silicate), Ti-silicalite, [Al] ZSM-5 (aluminosilicate), [Ga] ZSM-5 (gallosilicate ), [B] ZSM-5 (borosilicate) and [Ge, Al] ZSM-5 (germanoaluminosilicate). In each series (except for silicalites), samples were synthesized with different Si / T molar ratios (in the range from 20 to 80) (T = B, Al, Ga, Ti). The amount of Ge in the last sample varied from 0.1 to 1 wt.%.

The gel used in the synthesis contained tetraethylorthosilicate (TEOS), tetrapropylammonium hydroxide (TRAON), sodium hydroxide, aluminum nitrate nonahydrate (only for [Al] ZSM-5 and [Ge, Al] ZSM-5), germanium dioxide (only for [ Ge, Al] ZSM-5), gallium nitrate nonahydrate (only for [Ga] ZSM-5), tetraethylorthotitanate (TEOTi, only for Ti-silicalite) and boric acid or triethylorthoborate (only for [B] ZSM-5) in the following molar ratios: H ₂ O / Si = 45; TPAOH / Si = 0.1; NaOH / Si = 0.2; Si / T = 20-80 (T = Al, Ga, B, Ti); Ge = 0.1-1 wt.%.

Synthesis of zeolites . To obtain silicalite, a silica gel source (TEOS) was added to the organic template (TPAOH) and sodium hydroxide with stirring. The resulting gelatinous mixture was kept at 333K for 2 hours to remove excess ethanol resulting from TEOS hydrolysis. Then the gel was placed in a Teflon-lined autoclave and, for hydrothermal synthesis, was kept in an air thermostat at a constant temperature of 448 K for 5 days. After the synthesis was completed, the autoclave was cooled, the crystalline substance was filtered off and washed with distilled water. The white matter was dried at 373K overnight (indicated: freshly prepared sample (as synthesized)).

Zeolite [Al] beta was prepared according to the simple procedure described for zeolite [Al] ZSM-5. In this case, instead of TRAON, TEAON was used as a reference. Zeolite [Al] beta crystallized for 8 days at 415K. Details are specified in one example of a patent.

Zeolite activation or post-synthesis treatment . The dried sample was calcined in a stream of air at 823K for 10 hours to burn the standard. Samples were converted to proton form by three successive ion exchange operations with a solution of ammonium nitrate (0.1 M) overnight and subsequent calcination at 823K for 5 hours (designated as: calcined sample). The samples were then steam treated at high temperature (denoted as s: steam treated sample). This process was carried out at different temperatures (623-1273K), different water contents (3-100 vol.% H ₂ O), different flow rates (from about 3 to 300 ml of inert gas (normal conditions) min ^-1 ) and during different time periods (0.5-6 hours). Finally, the samples were treated in an alkaline medium (preferably NaOH, but also KOH and NH ₄ OH) with a concentration of 0.1-1.0 M at 310-370K for 10-60 minutes (preferred conditions: 0.1 M solution, 353K, 30 min). Then the suspension was cooled immediately in an ice bath, filtered, washed at 353K with distilled water and dried at 383K (designated as a: sample after alkaline treatment).

Ti-silicalite was similarly prepared. In this case, TEOTi was added dropwise to the TEOS solution with stirring. The resulting yellow solution of silicon and titanium alkoxides was kept at room temperature for 2 hours. This solution was added to a solution of TRAON and NaOH with continuous stirring. Samples of freshly prepared, calcined, steamed and alkali-treated samples of Ti-silicalite were prepared according to the general procedure described above.

To prepare [T] ZSM-5 samples (T = B, Al, Ga), a solution containing TEOS, TPAOH, and NaOH (solution A) was added dropwise to the corresponding solution of boron, aluminum, or gallium compound (solution B). The resulting solution was kept at 333K for 2 hours to remove excess ethanol. To obtain freshly prepared, calcined, steamed and alkali treated [T] ZSM-5 zeolites, the general procedure described for silicalites was used. To obtain samples with different Si / T molar ratios (T = B, Al, Ga), the amounts of boric acid or triethylorthoborate, aluminum nitrate, and gallium nitrate were chosen so that these ratios were in the range of 20-80.

Zeolites containing Ge and Al were prepared analogously to the method described for [Al] ZSM-5. The required amount of GeO _{2 was} added to the TEOS / TPAOH / NaOH solution. The resulting gelatinous mixture was added dropwise to solution B (aluminum nitrate), and a freshly prepared, calcined, steamed and alkaline sample was prepared according to the general procedure. Samples were prepared with a molar ratio of Si / Al in the range from 20 to 80, containing from 0.1 to 2 wt.% Ge.

1.b. Hydrothermal synthesis of zeolites with iron

In order to introduce iron into zeolites, the authors used the same method as described in section 1.a. To obtain each sample from the six series described in section 1.a, the corresponding iron-containing molecular sieves were prepared. For this, it is preferable to use iron (III) nitrate nonahydrate as an iron source (but you can also use acetate, chloride, carbonate and ferrous sulfate). In all cases, a salt, for example, iron nitrate, was dissolved in solution B, and solution A was added dropwise to solution B. The above method of activation of freshly prepared zeolites (calcination, treatment with steam and alkali) was applied.

1.s The introduction of the second, third or any additional transition metal in iron-containing zeolites

To prepare iron-containing molecular sieves modified by introducing a second transition metal by ion exchange, a method similar to that described in section 1.b. was used. In this case, after exchange with the ammonium salt (and before calcination to decompose the ammonium salt and convert to the proton form), the samples were exchanged with the second transition metal. All iron-containing samples of ([Fe] -siliconite, [Fe, Ti] -silicalite, [Fe, Al] ZSM-5, [Fe, Ga] ZSM-5, [Fe, B] ZSM-5 and [Fe, Ge, Al] ZSM-5) were exchanged in order to obtain different contents of the second transition metal (Co, Cu, Ni, Mn, Cr and V).

The second transition metal ion was introduced by exchange in liquid or solid phases. When exchanging in the liquid phase, a 0.1 M aqueous solution of the corresponding salt (nitrate, sulfate, chloride, carbonate and acetate) was used to obtain a concentration of the second transition metal in the range from about 0.1 to 1 wt.%.

Solid state ion exchange was also used to introduce a second transition metal into the zeolite. To this end, calcined iron-containing molecular sieves were mechanically mixed with appropriate amounts of a metal precursor (preferably chloride).

The products of ion exchange were calcined, activated by steam and alkali, as described in section 1.a.

Since most of the metals used can be in different degrees of oxidation, in cases where it was possible, the authors carried out ion exchange with salts of transition metals in different degrees of oxidation.

Scheme 2. Simultaneous or sequential ion exchange

Samples obtained as described in section 1.a were subjected to simultaneous or sequential ion exchange in a liquid or solid phase. In simultaneous ion exchange, iron and the second, third, or any additional transition metal ion were introduced simultaneously by exchange in a liquid or solid phase, while in the sequential method, ion exchange with a second, third, or any additional transition metal was followed by ion exchange with an iron salt . All samples in a series of six catalysts (silicalite, [Ti] -silicalite, [Al] ZSM-5, [Ga] ZSM-5, [B] ZSM-5 and [Ge, Al] ZSM-5) were subjected to ion exchange.

After ion exchange with the ammonium salt and before calcination, the samples were exchanged with a mixture of an iron salt (nitrate, sulfate, chloride, carbonate or acetate) and a second transition metal (cobalt, copper, chromium, vanadium, manganese, and nickel) to decompose the ammonium ion and obtain the proton form )

In ion exchange in the liquid phase, a 0.1 M (for all metals) aqueous solution of the corresponding salts (nitrates, sulfates, chlorides, carbonates and acetates) was used to obtain a concentration of each transition metal in the range from 0.1 to 1 wt.% Metal in final sample. In ion exchange in the solid phase, an appropriate amount of each salt was used to obtain a metal concentration in the final sample in the range from 0.1 to 1.0 wt.% Of each metal. If possible, metal salts in different oxidation states were used.

As described in section 1.a, the ion-exchange samples were calcined, activated with steam, and finally with alkali.

Scheme 3. Hydrothermal synthesis + impregnation

In order to introduce a second transition metal, the samples prepared according to the procedure described in section 1.b were treated with impregnation. After ion exchange and before calcination, the samples were impregnated with a solution of the second transition metal to decompose the ammonium ion and obtain the proton form. Each iron-containing sample from six series of ([Fe] -siliconite, [Fe, Ti] -silicalite, [Fe, Al] ZSM-5, [Fe, Ga] ZSM-5, [Fe, B] ZSM-5 and [Fe , Ge, Al] ZSM-5) was impregnated with a solution of the second transition metal (cobalt, copper, chromium, vanadium, manganese and nickel).

The second transition metal was introduced by impregnation in moisture capacity, each time using an aqueous solution of the corresponding salt (nitrate, sulfate, chloride, carbonate or acetate). These solutions were prepared from the volume of water needed to fill the pore volume in the sample and the required amount of metal salt to obtain the desired metal concentration (from about 0.1 to 1 wt.%). As noted in Section 1.c, in all cases when it was possible, salts of transition metals in various oxidation states were used for impregnation.

As described in section 1.a, the impregnated samples were calcined, activated with steam, and finally with alkali.

Scheme 4. Simultaneous or sequential impregnation

Samples prepared as described in section 1.a were impregnated either simultaneously or sequentially (by moisture capacity). In the simultaneous method, iron and the second, third or any additional transition metal were introduced simultaneously, while in the sequential method, the impregnation with an iron salt was followed by the impregnation with a second, third or any additional transition metal.

After exchange with an ammonium salt and before calcination to decompose the ammonium ion and obtain the proton form, the samples were impregnated with a mixed solution of an iron salt (nitrate, sulfate, chloride, carbonate or acetate) and a salt (nitrate, sulfate, chloride, carbonate and acetate) of the second transition metal ( cobalt, copper, chromium, vanadium, manganese and nickel). Each sample was impregnated from six series (silicalite, [Ti] -silicalite, [Al] ZSM-5, [Ga] ZSM-5, [B] ZSM-5, or [Ge, Al] ZSM-5).

Transition metal ions were introduced by impregnation (in terms of moisture capacity) using each time an aqueous solution of the corresponding salts. To prepare these solutions, the volume of water needed to fill the pore volume in the sample and the required amount of metal salt to obtain the desired metal concentration (from about 0.1 to 1 wt.%) Were used. As noted in section 1.c, in all cases when it was possible, the impregnation was carried out with transition metal salts of varying degrees of oxidation.

As described in section 1.a, the impregnated samples were calcined, activated with steam, and finally with alkali.

The prepared samples were tested both in the laboratory and in the pilot plant.

Laboratory Activity Tests

The activity and stability of the samples was studied in a reactor with parallel flows and a weighed portion of the catalyst of 50 mg (300-400 μm) at a space velocity (GHSV) of 60,000 h ^-1 and a total pressure of 5 bar. Catalytic activity was measured in various starting mixtures. The partial pressures of the reagents were 6.5 mbar N ₂ O, 150 mbar O ₂ , 10 mbar NO _x , 75 mbar H ₂ O, 0.25 mbar CO, 0.25 mbar SO ₂ , 6.5 mbar C ₃ H ₆ ; the rest is helium. Before the reaction, the catalysts were heated in the corresponding initial mixture at 723 K for 1 hour and cooled in the flow of this gas to the initial reaction temperature. The reaction products were analyzed on a gas chromatograph (N ₂ O, N ₂ , O ₂ , C ₃ H ₆ , CO, CO ₂ ) and a chemiluminescent analyzer (NO, NO ₂ , NO _x ).

Preparation and activity of monolithic catalysts

Laboratory searches are performed on catalyst tablets. Fine particles are usually not used in traditional fixed bed industrial reactors due to the large pressure drop. In practice, the form of the catalyst is critical to obtaining reliable data for the full application of the process. Therefore, a structurally monolithic reactor coated with a bimetallic zeolite catalyst was created and tested in a pilot installation.

The deposition of zeolite crystals by immersion leads to a coating consisting of randomly oriented layers of zeolite crystals involved in the processes of adsorption and catalysis. The carrier is soaked in a suspension of zeolite crystals in a solvent containing a binder and other additives, and then the solvent is removed by evaporation, drying and calcination.

The invention will now be illustrated by examples detailing the preparation and catalytic testing of samples.

Example 1 - Obtaining [Fe-Al] MFI

To obtain [Fe-Al] MFI with a Si / Al molar ratio of 50 and 0.5 wt.% Fe, TEOS was used as a source of Si, aluminum and iron nitrates as sources of Al and Fe, respectively, and TPAOH as a reference. With stirring, TEOS (20.83 g, 0.1 mol) was added dropwise to a mixture of NaOH (0.8 g, 0.02 mol), 10.169 g TPAOH (20% aqueous solution) and 67.115 g of distilled water. Solution A was added dropwise with stirring to a solution of iron and aluminum nitrates (solution B) prepared by dissolving 0.750 g of Al (NO ₃ ) ₃ · 9H ₂ O (2.0 mmol) and 0.235 g of Fe (NO ₃ ) ₃ · 9H ₂ O (0.58 mmol) in 12.95 g of water. The final solution was kept at 333K for 2 hours to remove excess ethanol resulting from TEOS hydrolysis. Then the gel was placed in a Teflon-lined autoclave and kept in an air thermostat at a constant temperature of 448 K for 5 days to carry out hydrothermal synthesis. At the end of the synthesis, the autoclave was cooled, the crystalline substance was filtered off and thoroughly washed with distilled water. Freshly prepared zeolite was dried at 373K overnight.

Example 2 - Obtaining [Fe-Al] BEA

To obtain [Fe-Al] BEA with a Si / Al molar ratio of 50 and 0.5 wt.% Fe, TEOS was used as a source of Si, aluminum and iron nitrates as sources of Al and Fe, respectively, and TEAOH as a reference. 20.83 g of TEOS (0.1 mol) was added dropwise with stirring to a mixture of 0.4 g of NaOH (0.01 mol), 29.4 g of TEAOH (20% aqueous solution) and 9.68 g of distilled water. Solution A was added dropwise with stirring to a solution of iron and aluminum nitrates (solution B) prepared by dissolving 0.750 g of Al (NO ₃ ) ₃ · 9H ₂ O (2.0 mmol) and 0.235 g of Fe (NO ₃ ) ₃ · 9H ₂ O (0.58 mmol) in 1.0 g of water. The final solution was kept at 333K for 2 hours to remove excess ethanol resulting from TEOS hydrolysis. Then the gel was placed in a Teflon-lined autoclave and kept in an air thermostat at a constant temperature of 415 K for 8 days to carry out hydrothermal synthesis. At the end of the synthesis, the autoclave was cooled, the crystalline substance was filtered off and thoroughly washed with distilled water. Freshly prepared zeolite was dried at 348K overnight.

Example 3 - Preparation of zeolites with different composition of the lattice

Zeolites with lattices of various compositions were prepared mainly by the method of Example 1. The nature of the T atom in the composition of [Fe, T] MFI was varied. In Examples 1 and 2, T = Al, but it can also be Ga, B, Ti, Ge or without a T atom in the structure. To obtain a Si / T molar ratio of 50, the following amounts of T precursors were added to the synthesis gel (solution B):

[Fe-Ga] MFI: 0.835 g of Ga (NO ₃ ) ₃ · 9H ₂ O (2 mmol)

[Fe-B] MFI: 0.124 g of boric acid (2 mmol)

0.292 g of triethylorthoborate (2 mmol)

[Fe-Ti] MFI: 0.456 g of tetraethylorthotitanate (2 mmol) or

[Fe] MFI: the T atom precursor was not introduced into the synthesis gel.

Example 4 - Activation of Fe-Zeolite Catalysts

The activation of the dried samples obtained in Examples 1, 2 and 3, began with calcination in a stream of air at 823 K for 10 hours to burn the standard. Then, the sample was converted to the H form by three successive operations of ion exchange in the liquid phase with a solution of ammonium nitrate (0.1 M) overnight and subsequent calcination in air at 823 K for 5 hours. Then the samples were processed:

in vacuum at temperatures 1073-1173K for 5 hours or

water vapor at temperatures of 623-1273K, water vapor concentration of 3-100 vol.% and inert gas flow rate of 3-300 ml (normal conditions) min ^-1 for 0.5-6 hours.

Finally, the samples activated by these operations were treated with an alkaline solution at temperatures of 298-363K for 10-60 minutes in 0.1-1.0 M aqueous solutions of NaOH, KOH, NH ₄ OH. Then the suspension was cooled immediately in an ice bath, filtered, washed at 353K with distilled water and dried at 383K.

Example 5 - Obtaining polymetallic zeolites Fe-Co, Fe-Cu and Fe-Co-Cu

The catalysts obtained by the methods of Examples 1, 2 and 3, after exchanging with an ammonium salt, were subjected to ion exchange in the liquid phase with Co (CH ₃ CO ₂ ) ₂ · 4H ₂ O and / or CuSO ₄ (separately, simultaneously or sequentially) before calcination . Ion exchange was carried out with 0.1 M solutions. During ion exchange, a constant pH of ~ 4 was maintained prior to calcination by the addition of dilute nitric acid. The ion exchange process was repeated until a sample was obtained with about 0.5 wt.% Co or Cu or about 0.25 wt.% Co and Cu (simultaneously, i.e. in one solution, or sequentially). After exchange, the samples were activated as described in Example 4, i.e. calcined, treated in vacuum or steam at high temperature, and finally subjected to alkaline treatment.

Example 6 - Laboratory testing of zeolite catalysts for the conversion of N ₂ O

Laboratory tests for the conversion of N ₂ O were carried out in the presence of various mono- and polymetallic zeolites MFI and BEA. Data for various zeolites are shown in figures 1A and b. The experimental conditions were as follows: 6.5 mbar N ₂ O, 150 mbar O ₂ , the rest He; total pressure = 5 bar, GHSV = 64000 hour ^-1 .

Samples were prepared and activated as described in Examples 1, 2, 3 and 4. The temperature dependence of the N ₂ O conversion on the MFI and BEA zeolites is shown in figures 1a and b, respectively. Designations of the studied zeolites: c = calcined at 823K for 10 hours, s = steam treated with a concentration of 30 vol.% H ₂ O in N ₂ at 873K for 5 hours and a = after alkaline treatment with an aqueous solution of ammonium hydroxide (0, 2 M) at 353K for 0.5 hour. The molar ratio of Si / Al in zeolites is 50. The concentration of metals in the catalysts: 0.5 wt.% Each metal. The brackets [] denote the metal introduced by isomorphic substitution (during hydrothermal synthesis), and the brackets () indicate the metal introduced by ion exchange in the liquid phase.

In the case of the most active catalysts containing Fe and Co and / or Cu, the complete conversion of the initial mixture of N ₂ O + O ₂ / He was reached between 625 and 650 K. The conversion of N ₂ O in the presence of polymetallic zeolites is higher than in the presence of monometallic zeolites. For example, in the case of MFI, the combination of Co and Fe allows one to obtain the same activity in the decomposition of N ₂ O at temperatures 60 and 80 K lower than on monometallic Co and Fe zeolites, respectively. From the indicated noticeable shift in the working range towards lower temperatures, we can conclude that the synergism between Co and Fe is more pronounced than between Cu and Fe. In the presence of a physical mixture of monometallic Co- and Fe-zeolites, the conversion is close to the value obtained on the most active of both zeolites — Co-zeolite, which indicates the role of the chemical nature of promotion. Similar trends were observed on BEA zeolites, and complete N ₂ O conversion was achieved at the same temperatures (625-650K). This indicates a positive (synergistic) effect from the combination of these metals in different types of zeolites. Other catalysts prepared in the same way in which iron is present in combination with metals other than Co and / or Cu (for example, transition metals such as Ni, Cr, Mn and V or noble metals such as Rh, Pd) did not show a synergistic effect , i.e. the activity was equal to or less than the activity of the corresponding monometallic zeolites. An example of this is the Ni-Fe system shown in figa.

Example 7 - Laboratory testing of zeolites with different lattice compositions in the reaction of the conversion of N ₂ O

Zeolites with lattices of various compositions were also tested in the N ₂ O conversion reaction. The synergy effect in the combination of Fe with Co and / or Cu was established not only in the case of zeolites of different types, as shown in Example 6, but also for zeolites of the same type with different compositions. The experimental conditions were as follows: 6.5 mbar N ₂ O, 150 mbar O ₂ , the rest He; temperature = 623K; total pressure = 5 bar, flow rate (GHSV) = 64000 hour ^-1 .

In FIG. 2 shows the conversion of N ₂ O on bimetallic Co-Fe MFI zeolites with different lattice compositions obtained as described in Example 3. The data of the tested zeolites: c = calcined at 823K in air for 10 hours, s = treated with water vapor at a concentration of 45 vol.% N ₂ About in N ₂ at various temperatures (see figure) for 5 hours and a = after alkaline treatment with aqueous solutions of ammonium hydroxide (0.2 M) at 353 K for 0.5 hour. The molar ratio Si / T in the initial zeolites was 50. The concentration of metal in the catalysts: 0.5 wt.% Each metal (Co and Fe).

As follows from figure 2, close activity can be obtained by optimizing the temperature during the activation of the catalysts with water vapor. On zeolite matrices with Brandsted acidity (Si-Al, Si-Ga), higher activity is achieved at a lower temperature than on zeolites with low acidity (Si-B, Si-Al-Ge) or neutral zeolites (Si, Si-Ti ) A similar trend is observed for a bimetallic catalyst containing copper, and for polymetallic systems containing Fe, Co, and Cu.

Example 8 - Dependence of catalytic activity on the method of obtaining

Various zeolites with the MFI and BEA structure were obtained in different ways and their catalytic activity was studied. The effect of synergism upon decomposition of N ₂ O depends on the preparation method. Tables 1 and 2 show data on all zeolites obtained by different methods and their activity in the decomposition of N ₂ O. First of all, it is clear that the activation of the prepared iron-containing zeolites is essential to achieve high activity in the decomposition of N ₂ O. Apparently, the treatment with water vapor is more effective than the treatment in vacuum. Alkaline treatment further enhances the activity of the catalysts. To obtain a positive effect from the metals contained in the final catalyst, iron should first be introduced into the zeolite lattice by hydrothermal synthesis, and the second metal (Co and / or Cu) should be introduced by ion exchange in the liquid phase. The introduction of metals into zeolite should be followed by activation in a vacuum or in steam and then alkaline treatment. If you follow this optimal production scheme, you can achieve the conversion of N ₂ O in wet exhaust gases> 80% at ~ 600K. When iron is introduced by ion exchange in liquid or solid phases or by impregnation in terms of moisture capacity, the activity is low and temperatures> 700 K are needed to achieve high N ₂ O conversions. With the introduction of the second metal (Co and Cu) by ion exchange in the solid phase or by impregnation by moisture capacity, the activity is also low. The optimal method described above for MFI zeolites has been applied to BEA zeolites. This structure gives a slightly higher activity than the MFI structure.

Table 1
The influence of the preparation method on the catalytic activity (N ₂ O conversion) of various zeolites with the MFI structure. Experimental conditions: 6.5 mbar N ₂ O, 150 mbar O ₂ , 1.0 mbar NO _x , 75 mbar H ₂ O, the rest is He; total pressure = 5 bar; GHSV = 64000 hour ^-1 . Catalyst T / K X (N ₂ O) / - [Fe-AI] MFI (c) ¹ 800 0.32 [Fe-AI] MFI (c, v) ² 700 0.68 [Fe-AI] MFI (c, s) ³ 725 0.76 [Fe-AI] MFI (c, s, a) ⁴ 715 0.83 (Fe) [AI] MFI (c, s, a) ⁵ 735 0.59 / Fe / [AI] MFI (c, s, a) ⁷ 750 0.36 (Co) [Fe-AI] MFI (c) 690 0.72 (Co) [Fe-AI] MFI (c, s) 600 0.85 (Cu) [Fe-AI] MFI (c, s, a) 602 0.94 (Co) (Cu) [Fe-AI] MFI (c, s, a)) 610 0.81 (Co, Cu) [Fe-AI] MFI (c, s, a) 608 0.77 (Co, Cu-Fe) [AI] MFI (c, s, a) 720 0.56 {Co} [Fe-AI] MFI (c, s, a) 660 0.70 {Cu} [Fe-AI] MFI (c, s, a) 650 0.62 / Co / Cu / [Fe-AI] MFI (c, s, a) 745 0.70 / Co, Cu, Fe / [AI] MFI (c, s, a) 750 0.40 / Co / [Fe-AI] MFI (c, s, a) 740 0.62 / Cu / [Fe-AI] MFI (c, s, a) 735 0.66 / Co-Cu-Fe / [AI] MFI (c, s, a) 750 0.45 1. [] = metal introduced by hydrothermal synthesis (isomorphically substituted), and c = calcined at 823K for 10 hours.
2. v = activated in vacuum, 1173K, 5 hours.
3. s = activated by water vapor, 450 mbar H ₂ O in N ₂ , 873K; 5 hours
4. a = activated alkaline solution, NaOH, 0.1 M, 333K; 30 minutes.
5. (,) or () () = metal introduced by ion exchange in the liquid phase (simultaneously or sequentially).
6. {,} or {} {} = metal introduced by ion exchange in the solid phase (simultaneously or sequentially).
7. /, / //// = metal introduced by impregnation by moisture capacity (simultaneously or sequentially). table 2
The effect of the production method on the catalytic activity (N ₂ O conversion) of various zeolites with a BEA structure. Experimental conditions: 6.5 mbar N ₂ O, 150 mbar O ₂ , 1.0 mbar NO _x , 75 mbar H ₂ O, the rest is He; total pressure = 5 bar; GHSV = 64000 hour ^-1 Catalyst T / K X (N ₂ O) / - [Fe-AI] BEA (c) 800 0.25 [Fe-AI] BEA (c, v) 700 0.70 [Fe-AI] BEA (c, s) 725 0.83 (Co) [Fe-AI] BEA (c) 650 0.60 (Co) [Fe-AI] BEA (c, s) 605 0.91 (Cu) [Fe-AI] BEA (c, s, a) 590 0.75 (Co) (Cu) [Fe-AI] 610 0.83 BEA (c, s, a)
(Co, Cu) [Fe-AI]
615
0.95 BEA (c, s, a)
(Co, Cu-Fe) [AI]
BEA (c, s, a)
705
0.59

Example 9 - Dependence of catalytic activity on chemical composition

The observed activity is affected not only by the production method, but also by the chemical composition of the catalysts. Table 3 shows the N ₂ O conversion data at a given temperature on zeolite samples with different chemical composition and metal content. Lower Si / Al ratios as well as iron / (cobalt + copper) molar ratios close to 1 are preferred. In particular, samples with a Si / Al molar ratio of 50 in freshly prepared materials containing 0.5 wt.% Fe and 0.5 wt.% Co (or 0.5 wt.% Cu) exhibit maximum activity.

Table 3

Conversion of N ₂ O in the presence of mono- and polymetallic zeolites with different compositions (Si / Al ratios) and metal content. Experimental conditions: 6.5 mbar N ₂ O, 150 mbar O ₂ , 1.0 mbar NO _x , 75 mbar H ₂ O, the rest is He; total pressure = 5 bar; GHSV = 64000 hour ^-1 .

Example 10 The activity of polymetallic zeolites in various source gas mixtures

The activity of the most promising catalyst was determined in the initial mixtures of different compositions simulating its use for the treatment of exhaust gases of various nature. The results are summarized in table 4. The effect of additives of propylene, carbon monoxide and sulfur dioxide on the activity of promising bimetallic catalysts was studied. When reducing agents are added (C ₃ H ₆ , CO), the working temperature of the samples decreases (cf. columns B and C with A). A typical waste gas component of SO ₂ combustion processes, in contrast, raises the operating temperature. Highly active systems operate in the range of 600-800K, depending on the intended use. The activity of a bimetallic catalyst containing Cu and Fe decreases slightly in the presence of propylene, while a bimetallic catalyst containing Co and Fe allows it to operate at a lower temperature. A similar positive effect is achieved by adding CO. The presence of SO ₂ shifts the decomposition reaction to higher temperatures.

Table 4
The activity of polymetallic zeolites under various experimental conditions (see footnote) Catalyst A B C D T / K X (N ₂ O) /
- T / K X (N ₂ O) /
- T / K X (N ₂ O) /
- T / K X (N ₂ O) /
- (Co) [Fe-
AI] MFI (c, s, a) 610 0.95 562 0.90 551 0.88 685 0.83 (Co) [Fe-
AI] BEA (c, s, a) 598 0.92 543 0.95 540 0.80 660 0.80 (Cu) [Fe-
AI] MFI (c, s, a) 632 0.95 663 0.90 589 0.86 695 0.72 (Cu) [Fe-
AI] BEA (c, s, a) 638 0.91 658 0.92 594 0.90 703 0.78 Experimental conditions:
A: 6.5 mbar N ₂ O, 150 mbar O ₂ , 1.0 mbar NO _x , 75 mbar H ₂ O, the rest is He.
B: 6.5 mbar N ₂ O, 150 mbar O ₂ , 1.0 mbar NO _x , 75 mbar H ₂ O, 6.5 mbar C ₃ H ₆ , the rest He.
C: 6.5 mbar N ₂ O, 150 mbar O ₂ , 1.0 mbar NO _x , 75 mbar H ₂ O, 0.25 mbar CO, the rest He.
D: 6.5 mbar N ₂ O, 150 mbar O ₂ , 1.0 mbar NO _x , 75 mbar H ₂ O, 0.25 mbar SO ₂ , the rest is He.
In all cases: total pressure = 5 bar;
Volumetric speed = 75,000 hour ^-1 .

Example 11 - Obtaining monolithic catalysts for testing in a pilot installation

Monolithic catalysts for testing in a pilot installation were obtained by immersion. Cordierite (2Al ₂ O ₃ · 5SiO ₂ · 2MgO) was used as a carrier. The diameter and length of the monoliths used in the experiments on the deposition of the active component were 25 cm and 10 cm, respectively. Monolithic structures had a density of 200 cubic feet per square meter. inch (cpsi) (wall thickness 0.3 mm and channel diameter 1.49 mm). The preliminary treatment of cordierite was its calcination at 1273K for 3 hours to remove contaminants from the carrier. The application of (Co) [Fe-Al] MFI (c, s, a) was carried out by immersion of monoliths based on a mixture of catalyst powder, solvent (butyl acetate, 10-20 wt.%), A binder (colloidal silicon dioxide Ludox AS-40, 40 wt.% Suspension of colloidal silicon dioxide in water) and a surfactant (Teepol). To bind zeolite crystals, before calcination, 1.2 g of nitrocellulose moistened with 35% ethanol was added to the mixture as a temporary binder. To obtain a homogeneous dispersed mixture, the suspension was mixed in a mixer for 1 min at a speed of 13000 rpm. Then the monoliths were immersed in the mixture for 3 minutes. Excess liquid was removed using compressed air. After drying the monoliths coated with zeolite overnight at room temperature and rotating horizontally, the monoliths were dried in air, raising the temperature at a speed of 1K per minute to 473K, and calcined at 673K (heating rate 10K per minute).

Example 12 - Tests in a pilot installation

The activity of monolithic catalysts was studied in a pilot installation. The conversion in exhaust gases containing N ₂ O, O ₂ , NO, and H ₂ O in the presence of (Co) [Fe-Al] MFI (c, s, a) remained stable over time for> 2000 h, as can be seen in FIG. 3.

Experimental conditions: 6.5 mbar N ₂ O, 150 mbar O ₂ , 1.0 mbar NO _x , 75 mbar H ₂ O, the rest is He; temperature = 630K; total pressure = 5 bar; pilot installation: total space velocity = 220 m ³ per hour; reactor volume = 5.9 l. Designations of the studied catalysts: c = calcined at 823K in air for 10 hours, s = steam treated with a concentration of 45 vol.% H ₂ O at various temperatures (see figure) and a = after alkaline treatment with aqueous solutions of ammonium hydroxide (0 , 2 M) at 353K for 0.5 hour. The molar ratio Si / Al in the initial zeolite was 50. The concentration of metal in the catalysts: 0.5 wt.% Each metal (Co and Fe).

It was found that the production method has a significant effect on the activity of the final catalyst. The optimal inclusion of metals in the zeolite is achieved as a result of isomorphic substitution of iron in the zeolite lattice and ion exchange in liquid or solid phases with other metals. Other methods tested by the authors led to catalysts with lower activity in the studied reaction.

The experiments showed that the polymetallic Co-Fe, Cu-Fe and Co-Cu-Fe zeolite catalysts exhibit a synergistic effect in the catalyzed decomposition of N ₂ O, which is expressed in a decrease in the operating temperature in comparison with the corresponding monometallic zeolites. The increased activity is due to the presence of nanoscale Fe-Co and Fe-Cu oxoclusters in zeolite channels. The specific structure and concentration of these clusters, in which both metals are close to each other and are connected by oxygen bridges, is determined by the new production method described in the invention. Other catalysts with a combination of Fe — Ni and Fe — Mn do not exhibit synergism, which is explained by the high affinity of Cu or Co for Fe.

Activation of the catalysts by steam and alkaline treatment is essential for the formation of these specific clusters and thus leads to active and stable catalytic systems for the decomposition of N ₂ O in the exhaust gases of various processes. This new aspect is very important for practical purposes.

Claims (19)

1. A method for producing polymetallic zeolite catalysts in which Fe is introduced by isomorphic substitution into a zeolite lattice by hydrothermal synthesis, then the zeolite is calcined and converted to the H-form, after which Cu and / or Co are introduced by ion exchange in liquid or solid phases before the sample calcined, activated at high temperature (> 1073 K) or water vapor, and subjected to alkaline treatment. 2. The method according to claim 1, in which the zeolite catalyst has a structure similar to MFI and / or BEA. 3. The method according to claim 1, in which the zeolite used is [Al] -ZSM-5, [Al] -BEA, [Ga] -ZSM-5, [B] -ZSM-5, [Al, Ge] - ZSM-5, silicalite or [Ti] silicalite. 4. The method according to claim 3, in which the molar ratio Si / T is 20-80 and T = Al, Ga, B, Ge or Ti. 5. The method according to claim 1, in which the content of iron introduced into zeolites is in the range of 0.1-1.0 wt.% Fe. 6. The method according to claim 1, in which the content of the introduced Cu and / or Co is in the range of 0.1-1.0 wt.%. 7. The method according to claim 1, in which the obtained zeolite is Fe-Co, Fe-Cu or Fe-Co-Cu zeolite. 8. The method according to any one of claims 1 to 7, in which the ratio of Fe / Co, Fe / Cu or Fe / Co + Cu≈1. 9. The method according to any one of claims 1 to 7, in which one or more Mn, V, Ni or Cr elements are introduced into the composition of the zeolite along with Co and / or Cu. 10. The method according to claim 8, in which one or more elements Mn, V, Ni or Cr are introduced into the composition of the zeolite along with Co and / or Cu. 11. The method according to claim 1, in which Cu or Co is introduced by ion exchange in liquid or solid phases. 12. The method according to claim 1, in which the zeolite is activated with steam at 623-1273 K, 3-100 vol.% N ₂ About at an inert gas feed rate of 3-300 ml (normal conditions) per minute for 0.5- 6 hours 13. The method according to claim 1, in which the zeolite is activated in vacuum or in air at temperatures above 1073 K. 14. The method according to claim 1, in which the alkaline treatment is carried out in alkaline environments (NaOH, KOH or NH ₄ OH) for 0.5-3 hours 15. The use of polymetallic zeolite obtained according to claims 1 to 14, for direct catalytic decomposition of N ₂ O. 16. The method of decomposition or reduction of nitrous oxide in the exhaust gases at temperatures below 650 ° K using a zeolite of the General formula xT ₂ O _r- y Fe ₂ O ₃ -z M ₂ O _q -SiO ₂ , in which x = 0-0.065; y = 0.00002-0.02; z = 0.00002-0.02; T = Al, Ga, B, Ge or Ti; p = valency of the element T; M = Cu, Co, Mn, V, Ni, Cr; q = valency of element M. 17. The method according to clause 16, where zeolite is used, in which M = Cu and / or Co. 18. Zeolite catalyst of the General formula xT ₂ O _r y Fe ₂ O ₃ -z M ₂ O _q -SiO ₂ , in which x = 0-0.065; y = 0.00002-0.02; z = 0.00002-0.02; T = Al, Ga, B, Ge or Ti; p = valency of the element T; M = Cu, Co, Mn, V, Ni, Cr; q = valency of element M. 19. The zeolite catalyst according to claim 18, wherein M = Cu and / or Co.

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