CATALYST SYNTHESIS COMPRISING HIGH-PURITY Nu-86 ZEOLITH AND IRON FOR NOX AND N2O CONVERSION

Abstract

The invention relates to a process for preparing a catalyst based on high-purity Nu-86 zeolite and iron, comprising at least the following steps: i) mixing in aqueous medium, of at least one source of silicon (Si) in the form of SiO2 oxide, at least one source of aluminum (Al) in the form of Al2O3 oxide, of a nitrogenous organic compound R, R being octamethonium bromide (OctBr2), of at least two sources of sodium, one of them being sodium bromide (NaBr), until a homogeneous precursor gel is obtained; ii) a maturation of the gel in order to promote the formation of said zeolite at the expense of impurities; iii) hydrothermal treatment of said precursor gel to obtain a crystallized solid phase; iv) at least one ion exchange with iron; v) heat treatment. The invention also relates to the catalyst that can be obtained or is directly obtained by the process and its use for the conversion of NOx and / or N2O. Figure to be published: Figure 1

Description

Title of the invention: SYNTHESIS OF A CATALYST COMPRISING A HIGH-PURITY Nu-86 ZEOLITH AND IRON FOR THE CONVERSION OF NOX AND N2O. TECHNICAL FIELD OF THE INVENTION

[0001] The invention relates to a process for preparing a catalyst based on a Nu-86 zeolite and at least one transition metal, in particular iron, the catalyst prepared or capable of being prepared by the process, and its use for the simultaneous reduction of nitrogen oxides (NOx) and nitrous oxide (N2O), in particular on combustions and industrial processes such as the production of nitric and adipic acid. PREVIOUS ART

[0002] Nitrogen oxide (NOx) emissions from combustion are a major concern for society, as they are responsible for health problems, tropospheric ozone depletion, acid rain, and smog. Increasingly stringent standards are being implemented by government agencies to limit the impact on the environment and health. Highly efficient pollution control systems, such as three-way catalytic converters or selective catalytic reduction (SCR) catalysts, have therefore been developed for use in transportation vehicles to achieve these objectives. However, it is not uncommon for the selectivity of these systems to induce nitrous oxide (N2O) emissions. Nitrous oxide is the third largest contributor to radiative forcing after carbon dioxide (CO2) and methane (CH4).In addition to affecting stratospheric ozone, a given amount of N2O in the atmosphere has 298 times more effect over 100 years on global warming than the same amount of CO2, according to the IPCC's 4th report.

[0003] Ammonia is considered an important fuel for decarbonization. However, the combustion of ammonia (or an H2 / NH3 mixture) presents potentially significant emissions of N2O, NOx, NH3 in the exhaust.

[0004] Other sectors are also responsible for significant NOx and N2O emissions; the nitric acid industry is one of the main sources of nitrous oxide (N2O) emissions. N2O is formed as a byproduct of ammonia oxidation on a Pt / Rh catalyst. The NOx, which is the main output product of the Pt / Rh catalyst, is then absorbed from water to form nitric acid. The absorption step is not 100% efficient and results in NOx emissions (100 to 500 ppm).

[0005] A treatment of NOx and N2O for applications related to decarbonization and Industrial fumes are therefore necessary.

[0006] NOx treatment has already been the subject of numerous studies, both in industry and transportation. For N2O treatment, several types of catalysts have been studied according to the temperature at which they are effective. Precious metals show good efficiency around 250°C, but are expensive and very often deactivated in the presence of inhibitors (CO, H2O, NOx, O2, etc.), which is incompatible with the production requirements of nitric or adipic acid. Zeolites, on the other hand, have a relatively low cost and a very large surface area, which makes it possible to obtain a good catalytic system by incorporating a transition metal, particularly iron. Sâdovskâ et al. (Sâdovskâ, G., Bernauer, M., Bemauer, B., Tabor, E., Vondrovâ, A., & Sobalfk, Z. (2018). On the mechanism of high-temperature N2O decomposition over Fe-FER in the presence of NO.Catalysis Communications, 112, 58-62) showed that iron-bearing FER-type zeolites exhibited very high performance in N2O decomposition and that there was a positive effect of NO on decomposition even at 600-900°C. The FER structure, which has Al pairs, resists high-temperature DeN2O conditions up to 900°C (Tabor, E., Mlekodaj, K., Sâdovskâ, G., Bemauer, M., Klein, P., Sazama, P.,... & Sobalfk, Z. (2019). Structural stability of metal containing ferrierite under the conditions of HT-N2O decomposition. Microporous and Mesoporous Materials, 281, 15-22.).

[0007] The presence of cations, particularly iron, promotes decomposition, but increasing the content beyond 1% does not appear to promote activity for an Fe-BEA zeolite. (Chen, B., Liu, N., Liu, X., Zhang, R., Li, Y., Li, Y., & Sun, X. (2011). Study on the direct decomposition of nitrous oxide over Fe-beta zeolites: From experiment to theory. Catalysis today, 175(1), 245-255). The redox behavior of Fe species in Fe-ZSM-5 catalysts for the decomposition of N2O and NH3-SCR of NOx was analyzed by Sazama et al. (Sazama, P., Wichterlovâ, B., Tâbor, E., Sfastnÿ, P., Sathu, NK, Sobalfk, Z.,... & Vondrovâ, A. (2014). Tailoring of the structure of Fe-cationic species in Fe-ZSM-5 by distribution of Al atoms in the framework for N2O decomposition and NH3-SCR-NOx. Journal of catalysis, 312, 123-138.).

[0008] It is possible to combine the reduction of NOx and N2O in a single reactor. In the case of a nitric acid plant, Groves et al. (Michael CE Groves & Alexander Sasonow (2010) Uhde EnviNOx® technology for NOX and N2O abatement: a contribution to reducing emissions from nitric acid plants, Journal of Integrative Environmental Sciences, 7:S1, 211-222) tested different configurations: an N2O decomposition stage, combined with an NH3-SCR stage; a DeNOx stage followed by N2O reduction with ammonia or with hydrocarbons (methane or propane).

[0009] The use of Nu-86 type zeolites for NH3-SCR applications is known (US6126912), but no work has evaluated the efficiency of catalysts in DeN2O or simultaneous DeNOx / DeN2O operation. Summary of the invention

[0010] The applicant discovered that a catalyst based on a Nu-86 type zeolite prepared according to a specific synthesis method and iron as a transition metal exhibited promising simultaneous conversion performance of NOx and N2O. The NOx and N2O conversion performance with a reducing agent, particularly in the temperature range of 300 to 500°C, is notably superior to that obtained with prior art catalysts, such as catalysts based on iron-exchanged structural FER zeolites. The direct decomposition properties of N2O using this catalyst are also particularly promising from 450°C.

[0011] The invention relates to a process for preparing a catalyst based on a Nu-86 structural type zeolite and iron comprising at least the following steps: (i) mixture in aqueous medium, of at least one source of silicon (Si) in the form of SiO2 oxide, of at least one source of aluminium (Al) in the form of Al2O3 oxide, of a nitrogenous organic compound R, R being octamethonium bromide (OctBr2), of at least two sources of sodium, one of them being sodium bromide (NaBr), the reaction mixture having the following molar composition: SiO2 / Al2O3 between 8 and 20 H2O / SiO2 between 15 and 60 R / SiO2 between 0.05 and 0.35 Na2O / SiO2 between 0.05 and 0.3, NaBr / SiO2 between 0.01 and 0.1, inclusive, step i) being carried out for a period of between 5 and 15 minutes until a homogeneous mixture called precursor gel is obtained; ii) the ripening of the precursor gel of said step i) at a temperature between 20 and 100°C with or without agitation, for a period of between 10 minutes and 48 hours, preferably between 18 and 24 hours; iii) the hydrothermal treatment of said precursor gel obtained at the end of step ii) at a temperature between 120°C and 220°C, preferably between 140 and 195°C, for a period of between 12 hours and 35 days, preferably between 12 hours and 33 days, until said Nu-86 zeolite is formed; (iv) at least one ion exchange comprising contacting said zeolite dried obtained at the end of the previous step, with a solution comprising at least one species capable of releasing iron, in solution in reactive form under stirring at a temperature between 20 and 95 °C preferably between 40 and 90 °C for a period of between 1 hour and 2 days; (v) heat treatment by drying the Nu-86 zeolite obtained at the end of the previous step at a temperature between 20 and 150°C for a period of between 2 and 24 hours followed by at least one calcination under airflow at a temperature between 400 and 700°C for a period of between 2 and 20 hours.

[0012] Steps iv) and v) can be reversed, and possibly repeated.

[0013] In this case, the Nu-86 zeolite obtained in step iii) can directly undergo a step v) of heat treatment, then at least one ion exchange with an acid, or a compound such as chloride, sulfate or ammonium nitrate to obtain a calcined Nu-86 zeolite in protonated form, before the step iv) of ion exchange with iron.

[0014] Crystalline seeds of a Nu-86 structural type zeolite can be added to the reaction mixture of step i), in an amount between 0.01 and 10% of the total mass of the sources of tetravalent (Si) and trivalent (Al) elements in their oxide form (SiO2 and Al2O3) in anhydrous form used in the reaction mixture, said crystalline seeds not being taken into account in the total mass of the sources of tetravalent and trivalent elements.

[0015] The iron content introduced by the ion exchange step iv) is between 0.5 and 6% by mass, preferably between 0.5 and 5% by mass, more preferably between 1 and 4% by mass relative to the total mass of the final anhydrous catalyst.

[0016] The invention also relates to a catalyst based on a Nu-86 zeolite and iron for the decomposition of N2O or the reduction of N2O or the simultaneous reduction of NOx and N2O by a reducing agent such as NH3 or H2 which can be obtained or directly obtained by the preparation process according to any one of its variants.

[0017] The iron content of the catalyst can be between 0.5 and 6% by mass, preferably between 0.5 and 5% by mass, more preferably between 1 and 4% by mass relative to the total mass of the final anhydrous catalyst.

[0018] The invention also relates to a process for decomposing N2O or reducing N2O or for simultaneously reducing NOx and N2O by a reducing agent such as NH3 or H2 in which the gas to be treated is brought into contact with a catalyst according to any one of the variants described.

[0019] The catalyst can be shaped by deposition as a coating on a honeycomb structure or a plate structure, or said catalyst can be under extruded or bead form, containing up to 100% of said catalyst.

[0020] Said honeycomb structure may be formed of parallel channels open at both ends or may comprise porous filtering walls for which the adjacent parallel channels are alternately blocked on either side of the channels.

[0021] The quantity of catalyst deposited on said structure can be between 50 and 250 g / L for filter structures and between 80 and 300 g / L for structures with open channels.

[0022] The catalyst can be associated with a binder such as cerine, zirconium oxide, alumina, non-zeolitic silica-alumina, titanium oxide, a mixed oxide of the cerine-zirconia type, a tungsten oxide and / or a spinel to be shaped by deposition in the form of a coating, said coating preferably being associated with another coating having the capacity to adsorb pollutants in particular NOx, to reduce pollutants in particular NOx or to promote the oxidation of pollutants.

[0023] Said catalyst can be integrated: - in the exhaust system of an internal combustion engine running on carbon-based or non-carbon fuels, or - in a reactor to treat industrial fumes. LIST OF FIGURES

[0024] Other features and advantages of the catalyst preparation process according to the invention will become apparent from the following description of non-limiting examples of embodiments, with reference to the figures attached and described below. [Fig 1]

[0025] Figure 1 shows the X-ray diffraction (XRD) patterns of the iron-containing, Nu-86 zeolite-based catalyst, Fe-Nu-86, obtained according to Example 1. Description of embodiments

[0026] The invention relates to a process for preparing a catalyst based on Nu-86 zeolite and iron comprising at least the following steps:

[0027] i) mixture in aqueous medium, of at least one source of silicon (Si) in the form of SiO2 oxide, at least one source of aluminium (Al) in the form of Al2O3 oxide, of a nitrogenous organic compound R, R being octamethonium bromide (OctBr2), of at least two sources of sodium, one of them being sodium bromide (NaBr), the reaction mixture having the following molar composition: SiO2 / Al2O3 between 8 and 20 H2O / SiO2 between 15 and 60, R / SiO2 between 0.05 and 0.35, Na2O / SiO2 between 0.05 and 0.3 NaBr / SiO2 between 0.01 and 0.1, inclusive,

[0028] Step i) being carried out for a period of between 5 and 15 minutes until a homogeneous mixture called precursor gel is obtained;

[0029] ii) The ripening of the precursor gel of said step i) at a temperature between 20 and 100°C with or without agitation, for a period of between 10 minutes and 48 hours, preferably between 18 and 24 hours;

[0030] iii) the hydrothermal treatment of said precursor gel obtained at the end of step ii) at a temperature between 120°C and 220°C, for a period of between 12 hours and 35 days until said Nu-86 zeolite is formed;

[0031] iv) at least one ion exchange comprising bringing said Nu-86 zeolite obtained at the end of the previous step into contact with a solution comprising at least one species capable of releasing a transition metal, in particular iron, in solution in reactive form under stirring at a temperature between 20 and 95 °C preferably between 40 and 90 °C for a period of between 1 hour and 2 days;

[0032] v) heat treatment by drying of said Nu-86 zeolite obtained at the end of the previous step at a temperature between 20 and 150°C followed by at least one calcination under airflow at a temperature between 400 and 700°C.

[0033] Steps iv) and v) can be reversed, and possibly repeated.

[0034] The Nu-86 zeolite obtained in step iii) can in this case directly undergo step v) of heat treatment, then an ion exchange with an acid, or a compound such as chloride, sulfate or ammonium nitrate to obtain a calcined Nu-86 zeolite in protonated form, before step iv) of ion exchange with iron.

[0035] Crystalline seeds of a Nu-86 zeolite can be added to the reaction mixture of step i), preferably in an amount between 0.01 and 10% weight relative to the total mass of the sources of tetravalent and trivalent elements in anhydrous form present in said mixture, said crystalline seeds not being taken into account in the total mass of the sources of SiO2 and Al2O3.

[0036] Step i) may include a maturation step of the reaction mixture at a temperature between 20 and 100°C, with or without stirring, for a period of between 30 minutes and 48 hours.

[0037] The hydrothermal treatment of step iii) can be carried out under autogenous pressure at a temperature between 120°C and 220°C, preferably between 140°C and 195°C, for a period of between 12 hours and 35 days, preferably between 12 hours and 33 days.

[0038] The Nu-86 zeolite obtained at the end of step iii) is advantageously filtered, washed, and dried at a temperature between 60 and 120°C, for a period of between 5 and 24 hours to obtain a dried Nu-86 zeolite.

[0039] Step iv) of ion exchange can be carried out by bringing the solid into contact with a solution comprising a single species capable of releasing a transition metal or by successive contacting of the solid with different solutions each comprising at least one, preferably only one, species capable of releasing a transition metal, which is iron.

[0040] The iron content introduced by the ion exchange step iv) is advantageously between 0.5 and 6% by mass, preferably between 0.5 and 5% by mass, more preferably between 1 and 4% by mass relative to the total mass of the final anhydrous catalyst.

[0041] Advantageously, heat treatment step v) comprises drying the solid at a temperature between 20 and 150°C, preferably between 60 and 100°C, for a period of between 2 and 24 hours, followed by at least one calcination under air, possibly dry, at a temperature between 400 and 700°C, preferably between 500 and 600°C, for a period of between 2 and 8 p.m., preferably between 5 and 10 a.m., most preferably between 6 and 9 hours, the flow rate of possibly dry air preferably being between 0.5 and 1.5 L / h / g of solid to be treated, more preferably between 0.7 and 1.2 L / h / g of solid to be treated.

[0042] The invention also relates to the catalyst based on a Nu-86 zeolite and iron, which can be obtained or directly obtained by the preparation process.

[0043] The iron content of the catalyst obtained is advantageously between 0.5 and 6% by mass, preferably between 0.5 and 5% by mass relative to the total mass of the final anhydrous catalyst.

[0044] The invention also relates to the use of the catalyst according to any of its variants or of the catalyst that can be obtained or directly obtained by the preparation process, for the selective reduction of NOX by a reducing agent such as NH3 or H2.

[0045] The invention also relates to the use of the catalyst described above or the use of the catalyst that can be obtained or directly obtained by the preparation process for the direct decomposition of N2O or the simultaneous reduction of NOx and N2O by a reducing agent such as NH3 or H2.

[0046] The catalyst can be shaped directly by extrusion in pellet form or by deposition in coating form, on a honeycomb structure or a plate structure.

[0047] The honeycomb structure can be formed of parallel channels open at both ends or can include porous filtering walls for which the adjacent parallel channels are alternately blocked on either side of the channels.

[0048] The quantity of catalyst deposited on said structure may advantageously be between 50 and 200 g / L for filter structures and between 80 and 300 g / L for the structures with open channels.

[0049] The catalyst can be associated with a binder such as cerine, zirconium oxide, alumina, non-zeolitic silica-alumina, titanium oxide, a mixed oxide of the cerine-zirconia type, a tungsten oxide and / or a spinel to be shaped by deposition in the form of a coating.

[0050] Said coating can be associated with another coating having the capacity to adsorb pollutants in particular nitrogen oxides, to reduce pollutants in particular NOx or to promote the oxidation of pollutants, such as CO or hydrocarbons.

[0051] Said catalyst may be in the form of an extrudate or ball or any other form known to those skilled in the art, containing up to 100% of said catalyst.

[0052] The catalyst support used in the process according to the invention can advantageously be shaped by any technique known to those skilled in the art. Shaping can advantageously be carried out, for example, by extrusion, pelletizing, the oil-drop coagulation method, rotary plate granulation, or any other method well known to those skilled in the art. The supports thus obtained can be in various shapes and sizes. Advantageously, the various constituents of the support or catalyst can be shaped by mixing to form a paste and then extruding the resulting paste, or by mixing powders and then pelletizing, or by any other known process for agglomerating a powder containing alumina. The supports thus obtained can be in various shapes and sizes. Preferably, shaping is carried out by mixing and extrusion.

[0053] Furthermore, the use of additives can advantageously be implemented to facilitate shaping and / or improve the final mechanical properties of the substrates, as is well known to those skilled in the art. Examples of additives include cellulose, carboxymethyl cellulose, carboxyethyl cellulose, tall oil, xanthan gums, surfactants, flocculating agents such as polyacrylamides, carbon black, starches, stearic acid, polyacrylic alcohol, polyvinyl alcohol, biopolymers, glucose, polyethylene glycols, etc.

[0054] Water can advantageously be added or removed to adjust the viscosity of the paste to be extruded. This step can advantageously be carried out at any stage of the mixing step.

[0055] To adjust the solids content of the paste to be extruded in order to make it extrudable, a predominantly solid compound, preferably an oxide or a hydrate, can also be added. Preferably, an aluminum hydrate is used, and even more preferably, an aluminum hydrate. The loss on ignition of this hydrate is advantageously greater than 15%.

[0056] The extrusion of the paste from the mixing step can advantageously be carried out using any commercially available conventional tool. The paste from the mixing process is advantageously extruded through a die, for example, using a piston or a single or double screw extrusion die. The extrusion can advantageously be carried out by any method known to those skilled in the art.

[0057] The catalyst supports according to the invention are generally in the form of cylindrical or multilobed extrudates such as bilobed, trilobed, or multilobed, with a straight or twisted shape, but may optionally be manufactured and used in the form of crushed powders, tablets, rings, beads, and / or wheels. Preferably, the catalyst supports according to the invention may be in the form of spheres or extrudates. Advantageously, the support may be in the form of extrudates with a diameter between 0.5 and 5 mm, and more particularly between 0.7 and 2.5 mm. The shapes may be cylindrical (which may be hollow or solid) and / or twisted cylindrical and / or multilobed (2, 3, 4, or 5 lobes, for example) and / or annular. The multilobed shape is advantageously preferred.

[0058] The structure coated by said catalyst or obtained by extrusion of said catalyst can be integrated: - in the exhaust system of an internal combustion engine operating on carbonaceous or non-carbonaceous fuels, such as NH3, H2... (non-exhaustive list) - in a reactor for treating industrial fumes. In a nitric acid plant, it can be integrated in a tertiary stage, either to sequentially remove N2O by decomposition and NOx with the addition of a reducing agent such as NH3, or to simultaneously remove NOx and N2O with the addition of a reducing agent. The catalyst

[0059] The catalyst according to the invention comprises at least one Nu-86 zeolite, and iron.

[0060] The total iron content is between 0.5 and 6% by mass, preferably between 0.5 and 5% by mass relative to the total mass of the final catalyst, in its anhydrous form.

[0061] The catalyst according to the invention may also include other elements, such as alkali and / or alkaline earth metals, for example sodium, obtained in particular from the synthesis, in particular from the compounds of the reaction medium of step i) of the process of preparing said catalyst. Catalyst preparation process Step i) of mixing

[0062] Step i) implements:

[0063] i) the mixture in aqueous medium of at least one source of silicon (Si) in the form SiO2 oxide, at least one source of aluminium (Al) in the form of Al2O3 oxide, of a nitrogenous organic compound R, R being octamethonium bromide (OctBr2), of at least two sources of sodium, at least one of them being sodium bromide (NaBr), the reaction mixture having the following molar composition: SiO2 / Al2O3 between 8 and 20, H2O / SiO2 between 15 and 60, R / SiO2 between 0.05 and 0.35, Na2O / SiO2 between 0.05 and 0.3, NaBr / SiO2 between 0.01 and 0.1, inclusive,

[0064] in which H2O corresponds to the molar quantity of water present in the reaction mixture, R the molar quantity of said nitrogenous organic compound, Na2O the molar quantity expressed as sodium oxide, step i) being carried out for a period enabling the obtaining of a homogeneous mixture called precursor gel, generally from 5 to 15 minutes, once all the components are introduced into the reaction mixture.

[0065] The silicon source may be any one of the sources commonly used for the synthesis of zeolites, for example, powdered silica, silicic acid, colloidal silica, dissolved silica, or tetraethoxysilane (TEOS). Among powdered silicas, precipitated silicas may be used, in particular those obtained by precipitation from an alkali metal silicate solution, fumed silicas, for example, "CAB-O-SIL," and silica gels. Colloidal silicas with different particle sizes may be used, for example, with an average equivalent diameter between 10 and 15 nm or between 40 and 50 nm, such as those marketed under registered trademarks such as "LUDOX." Preferably, the silicon source is Arerosil 200.

[0066] According to the invention, the aluminum source is preferably aluminum hydroxide or an aluminum salt, for example, aluminum chloride, nitrate, or sulfate, sodium aluminate, aluminum alkoxide, or alumina itself, preferably in hydrated or hydratable form, such as colloidal alumina, pseudoboehmite, gamma alumina, or alpha or beta trihydrate. Mixtures of the sources mentioned above may also be used.

[0067] Step (i) of the process according to the invention consists of preparing an aqueous reaction mixture containing at least one silicon source, at least one aluminum source, at least one nitrogenous organic compound R, R being octamethonium bromide (OctBr2), in the presence of at least two sodium sources, one of them being sodium bromide (NaBr), to obtain a precursor gel of a Nu-86 zeolite. The quantities of said reagents are adjusted as previously indicated so as to give this gel a composition allowing the crystallization of a Nu-86 zeolite.

[0068] It may be advantageous to add Nu-86 zeolite nuclei to the reaction mixture during said step i) of the process of the invention in order to reduce the time required for the formation of Nu-86 zeolite crystals and / or the total crystallization time. Said nuclei also promote the formation of said Nu-86 zeolite at the expense of impurities. Such nuclei include crystalline solids, in particular Nu-86 zeolite crystals. The nuclei are generally added in a proportion of between 0.01 and 10% of the total anhydrous mass of the sources of said tetravalent (Si) and trivalent (Al) element(s) used in the reaction mixture, said nuclei not being included in the total mass of the sources of the tetravalent and trivalent elements.These germs are also not taken into account when determining the composition of the reaction mixture and / or the gel, as defined further on, i.e., in determining the different molar ratios of the composition of the reaction mixture.

[0069] Step i) of mixing is carried out until a homogeneous mixture is obtained, preferably for a period of between 5 and 15 minutes, preferably under agitation by any system known to the person skilled in the art with low or high shear rate.

[0070] At the end of step i) a homogeneous precursor gel is obtained. Step ii) maturation of the precursor gel

[0071] Step ii) involves maturing the reaction mixture before hydrothermal crystallization to promote the formation of said Nu-86 zeolite at the expense of impurities. The maturation of the reaction mixture during said step ii) of the process of the invention can be carried out at room temperature or at a temperature between 20 and 100°C with or without stirring, for a duration advantageously between 10 minutes and 48 hours, preferably between 18 and 24 hours. Step iii) of hydrothermal treatment

[0072] In accordance with step iii) of the process according to the invention, the precursor gel obtained at the end of step ii) is subjected to hydrothermal treatment, preferably carried out at a temperature between 120°C and 220°C for a period of between 12 hours and 35 days, until said Nu-86 zeolite (or "crystallized solid") is formed.

[0073] The precursor gel is advantageously placed under hydrothermal conditions under an autogenic reaction pressure, optionally by adding gas, for example nitrogen, at a temperature preferably between 120°C and 220°C, preferably between 140°C and 195°C, until complete crystallization of a Nu-86 zeolite.

[0074] The time required to obtain crystallization varies between 12 hours and 35 days, preferably between 12 hours and 33 days.

[0075] The reaction is generally carried out under agitation or in the absence of agitation, preferably under agitation. As an agitation system, any system known to those skilled in the art may be used, for example, inclined blades with counter-blades, agitation turbines, Archimedes screws.

[0076] In a very advantageous manner, the process of the invention leads to the formation of a Nu-86 zeolite, free from any other crystallized or amorphous phase.

[0077] The hydrothermal treatment of step iii) can be followed by filtration, washing and drying of the Nu-86 zeolite obtained, advantageously at a temperature between 60 and 120°C, for a period of between 5 and 24 hours to obtain a dried Nu-86 zeolite before the ion exchange step iv).

[0078] It is also advantageous to obtain the protonated form of the Nu-86 type zeolite after step iii). In this embodiment, said protonated form can be obtained by carrying out an ion exchange with an acid, in particular a strong mineral acid such as hydrochloric, sulfuric or nitric acid, or with a compound such as ammonium chloride, sulfate or nitrate, before the ion exchange iv) with iron.

[0079] In this embodiment, the Nu-86 structural type zeolite obtained at the end of step iii) directly undergoes a heat treatment (step v) comprising drying at a temperature between 20 and 150°C, preferably between 60 and 100°C, for a period of between 2 and 24 hours, followed by at least one calcination, under air, possibly dry, at a temperature between 400 and 700°C, preferably between 500 and 600°C for a period of between 2 and 20 hours, preferably between 5 and 10 hours, more preferably between 6 and 9 hours, the flow rate of air, possibly dry, preferably being between 0.5 and 1.5 L / h / g of solid to be treated, more preferably between 0.7 and 1.2 L / h / g of solid to be treated. Calcination may be preceded by a gradual increase in temperature.The dried and calcined Nu-86 zeolite then undergoes at least one ion exchange with an acid, or a compound such as chloride, sulfate or ammonium nitrate to obtain a calcined Nu-86 zeolite in protonated form, before step iv) of ion exchange with iron. Step iv) of ion exchange

[0080] The catalyst preparation process according to the invention comprises at least one ion exchange step comprising contacting the crystalline solid obtained at the end of the preceding step, i.e., the Nu-86 zeolite obtained at the end of step iii) or the dried and calcined Nu-86 zeolite obtained at the end of step v) in the preferred case where steps iv) and v) are reversed, or the dried, calcined and protonated Nu-86 zeolite, with at least one solution comprising at least one species capable of releasing a transition metal, here iron, in solution in reactive form, under stirring at room temperature for a period of between 1 and 2 hours. days, advantageously for a period of between 0.5 days and 1.5 days, the concentration of said species capable of releasing iron in said solution being a function of the quantity of iron that one wishes to incorporate into said crystallized solid.

[0081] The transition metal released into the exchange solution is iron.

[0082] According to the invention, by "species capable of releasing a transition metal" is meant a A species capable of dissociating in aqueous media, such as sulfates, nitrates, chlorides, oxalates, organometallic complexes of a transition metal, or mixtures thereof. Preferably, the species capable of releasing a transition metal is a sulfate or nitrate of said transition metal.

[0083] According to the invention, the solution with which the crystallized solid or dried and calcined crystallized solid is brought into contact, comprises at least one species capable of releasing a transition metal, preferably a single species capable of releasing a transition metal, in this case iron.

[0084] Advantageously, the process for preparing the catalyst according to the invention may include a step iv) of ion exchange by contacting the crystallized solid with a solution comprising a species capable of releasing a transition metal or by successively contacting the solid with several solutions each comprising a species capable of releasing a transition metal, said metal being iron.

[0085] At the end of the ion exchange, the solid obtained can advantageously be filtered, washed and then dried to obtain said catalyst in powder form.

[0086] The total quantity of iron contained in said final catalyst is between 0.5 and 6% by mass relative to the total mass of the catalyst in its anhydrous form.

[0087] According to one embodiment, the catalyst according to the invention is prepared by a process comprising an ion exchange step (iv), the solid or the dried and calcined solid being contacted with a solution comprising a species capable of releasing iron in solution in a reactive form. Advantageously, the total amount of iron contained in said final catalyst, i.e., at the end of the preparation process according to the invention, is between 0.5 and 6%, preferably between 0.5 and 5% by mass, all percentages being mass percentages relative to the total mass of the final catalyst according to the invention in its anhydrous form, obtained at the end of the preparation process. Step v) of heat treatment

[0088] The preparation process according to the invention comprises a heat treatment step (v) carried out after the preceding step, i.e., after hydrothermal treatment step (iii) or after ion exchange step (iv), preferably after ion exchange step (iv). Step (v) of the preparation process may advantageously be interchanged with step (iv). Each of the two steps (iv) and (v) may also optionally be repeated.

[0089] Said heat treatment step v) comprises drying the solid at a temperature between 20 and 150°C, preferably between 60 and 100°C, advantageously for a period of between 2 and 24 hours, followed by at least one calcination, under air, possibly dry, at a temperature advantageously between 400 and 700°C, preferably between 500 and 600°C, for a period of between 2 and 20 hours, preferably between 5 and 10 hours, more preferably between 6 and 9 hours, the flow rate of the air, possibly dry, being preferably between 0.5 and 1.5 L / h / g of solid to be treated, more preferably between 0.7 and 1.2 L / h / g of solid to be treated. The calcination may be preceded by a gradual temperature increase.

[0090] The catalyst obtained at the end of step v) of heat treatment is free of any organic species, in particular free of the organic structuring agent R.

[0091] In particular, the catalyst obtained by a process comprising at least the steps i), ii), iii), iv) and v) previously described exhibits improved properties for the conversion of N2O.

[0092] Characterization of the catalyst prepared according to the invention

[0093] The catalyst comprises a zeolite of Nu-86 structure. This structure is characterized by X-ray diffraction (XRD).

[0094] The X-ray diffraction (XRD) pattern is obtained by X-ray crystallographic analysis using a diffractometer with the classical powder method and copper Kα radiation (X = 1.5406 Å). From the position of the diffraction peaks represented by the angle 20°, the characteristic interplanar spacings dhki of the sample are calculated using Bragg's law. The measurement error A(d hki) on dhki is calculated using Bragg's law as a function of the absolute error A(20°) assigned to the measurement of 20°. An absolute error A(20°) of +0.02° is commonly accepted. The relative intensity Irei assigned to each value of dαi is measured from the height of the corresponding diffraction peak.The X-ray diffraction pattern of the crystallized solid obtained at the end of step iii) of the process according to the invention includes at least the lines with the dhki values ​​given in Table 1 (Average dδ values ​​and relative intensities measured on an X-ray diffraction pattern of the Nu-86 structural-type zeolite catalyst calcined according to the invention). In the dδ column, the average values ​​of the interplanar spacings in Angstroms (Å) are indicated. Each of these values ​​must be adjusted by the measurement error A(dhki) of between +0.6Å and +0.01Å.

[0095] [Tables 1] 2 theta (°) dhkl (Â) Irel 2 theta (°) dhkl (Â) Irel 6.566 13.45 f 20.973 4.23 ff 7.847 11.26 F 21.448 4.14 f 7.535 11.72 F 22.177 4.01 f 7.953 11.11 M 22.501 3.95 F 9.013 9.80 f 22.631 3.93 FF 10.363 8.53 ff 22.783 3.90 FF 12.487 7.08 ff 25.152 3.54 ff 14.143 6.26 ff 26.956 3.30 ff 14,629 6.05 ff 28.75 3.10 ff 15,519 5.71 ff

[0096] where FF = very strong; F = strong; m = medium; mf = medium weak; f = weak; ff = very weak. The relative intensity Irei is given in relation to a relative intensity scale where a value of 100 is assigned to the most intense line of the X-ray diffraction pattern: ff < 15; 15 <f <30 ; 30 < mf <50 ; 50 < m < 65 ; 65 <F < 85 ; FF >85.

[0097] The qualitative and quantitative analysis of the chemical species present in the materials obtained is performed by X-ray fluorescence (XRF) spectrometry. This is a chemical analysis technique that uses a physical property of matter, X-ray fluorescence. It allows the analysis of the majority of chemical elements, starting with Beryllium (Be), in concentration ranges from a few ppm to 100%, with precise and reproducible results. X-rays are used to excite the atoms in the sample, causing them to emit X-rays with energies characteristic of each element present. The intensity and energy of these X-rays are then measured to determine the concentration of the elements in the material.

[0098] The loss on ignition (LOI) of the catalyst obtained after the drying step (and before calcination) or after the calcination step of step iv) of the process according to the invention is generally between 4 and 15% by weight. The loss on ignition of a sample, designated by the acronym LOI, corresponds to the difference in mass of the sample before and after heat treatment at 1000°C for 2 hours. It is expressed as a percentage corresponding to the percentage of mass loss. The loss on ignition generally corresponds to the loss of solvent (such as water) contained in the solid, but also to the elimination of organic compounds contained in the solid mineral constituents. Use of the catalyst according to the invention

[0099] The invention also relates to the use of the catalyst according to the invention, directly prepared or capable of being prepared by the process described above, for the direct decomposition of N2O or the reduction of NOx and N2O by a reducing agent such as NH3 or a hydrocarbon, advantageously shaped by deposition as a coating (a "washcoat" in Anglo-Saxon terminology) on a honeycomb structure, primarily for mobile applications, or on a plate structure, which is particularly common for stationary applications. The invention can also be shaped into extrudates or beads. Preferably, the supports for the catalyst according to the invention are in the form of spheres or extrudates. Advantageously, the support is in the form of extrudates with a diameter of between 0.5 and 5 mm, and more particularly between 0.7 and 2.5 mm.The shapes can be cylindrical (which may or may not be hollow) and / or twisted cylindrical and / or multi-lobed (2, 3, 4 or 5 lobes for example) and / or annular. The multi-lobed shape is advantageously and preferentially used.

[0100] The honeycomb structure is formed of parallel channels open at both ends (flow-through) or comprises porous filtering walls, in which case the adjacent parallel channels are alternately blocked on either side of the channels to force the gas flow through the wall (wall-flow monolith). This coated honeycomb structure constitutes a catalytic block. The structure may be composed of cordierite, silicon carbide (SiC), aluminum titanate (AITi), alpha alumina, mullite, or any other material with a porosity between 30 and 70%. The structure may be made of sheet metal, stainless steel containing chromium and aluminum, or FeCrAl steel.

[0101] The quantity of catalyst according to the invention deposited on said structure is between 50 and 250 g / L for filtering structures and between 80 and 300 g / L for structures with open channels.

[0102] The coating itself (“washcoat”) comprises the catalyst according to the invention, advantageously combined with a binder such as cerine, zirconium oxide, alumina, non-zeolitic silica-alumina, titanium oxide, a cerine-zirconia mixed oxide, tungsten oxide, or spinel. This coating is advantageously applied to the structure by a deposition method (washcoating) which consists of dipping the monolith into a slurry of catalyst powder according to the invention in a solvent, preferably water, and potentially binders, metal oxides, stabilizers, or other promoters. This dipping step can be repeated until the desired amount of coating is achieved. In some cases, the slurry can also be sprayed into the monolith. Once the coating is applied, the monolith is calcined at a temperature of 300 to 600°C for 1 to 10 hours.

[0103] Said structure can be coated with one or more coatings. The coating comprising the catalyst according to the invention is advantageously associated with, that is to say covers or is covered by, another coating having capacities for adsorption of pollutants in particular of NOx, for reduction of pollutants in particular of NOx or promoting the oxidation of pollutants, in particular that of ammonia.

[0104] Another possibility is to put the catalyst in the form of an extrudate or a bead or any other shape known to those skilled in the art. In this case, the shaped structure can contain up to 100% of the catalyst according to the invention.

[0105] The catalyst support used in the process according to the invention can advantageously be shaped by any technique known to those skilled in the art. Shaping can advantageously be carried out, for example, by extrusion, pelletizing, the oil-drop coagulation method, rotary plate granulation, or any other method well known to those skilled in the art. The supports thus obtained can be in various shapes and sizes. Advantageously, the various constituents of the support or catalyst can be shaped by mixing to form a paste and then extruding the resulting paste, or by mixing powders and then pelletizing, or by any other known process for agglomerating a powder containing alumina. The supports thus obtained can be in various shapes and sizes. Preferably, shaping is carried out by mixing and extrusion.

[0106] Furthermore, the use of additives can advantageously be implemented to facilitate shaping and / or improve the final mechanical properties of the substrates, as is well known to those skilled in the art. Examples of additives include cellulose, carboxymethyl cellulose, carboxyethyl cellulose, tall oil, xanthan gums, surfactants, flocculating agents such as polyacrylamides, carbon black, starches, stearic acid, polyacrylic alcohol, polyvinyl alcohol, biopolymers, glucose, polyethylene glycols, etc.

[0107] Water can advantageously be added or removed to adjust the viscosity of the paste to be extruded. This step can advantageously be carried out at any stage of the mixing step.

[0108] To adjust the solids content of the extrusion paste to make it extrudable, a predominantly solid compound, preferably an oxide or a hydrate, can also be added. Preferably, an aluminum hydrate is used, and even more preferably, an aluminum hydrate. The loss on ignition of this hydrate is advantageously greater than 15%.

[0109] The extrusion of the paste from the mixing step can advantageously be carried out using any commercially available conventional tool. The paste from the mixing process is advantageously extruded through a die, for example, using a piston or a single or double screw extrusion die. The extrusion can advantageously be carried out by any method known to those skilled in the art.

[0110] The catalyst supports according to the invention are generally in the form of cylindrical or multilobed extrudates such as bilobed, trilobed, or multilobed, with a straight or twisted shape, but may optionally be manufactured and used in the form of crushed powders, tablets, rings, beads, and / or wheels. Preferably, the catalyst supports according to the invention are in the form of spheres or extrudates. Advantageously, the support is in the form of extrudates with a diameter between 0.5 and 5 mm, and more particularly between 0.7 and 2.5 mm. The shapes may be cylindrical (which may or may not be hollow) and / or twisted cylindrical and / or multilobed (2, 3, 4, or 5 lobes, for example) and / or rings. The multilobed shape is advantageously preferred. ADVANTAGES OF THE INVENTION

[0111] The catalyst according to the invention, based on Nu-86 zeolite and iron, exhibits improved deNOx and deN2O properties compared to prior art catalysts. In a stream with a high N2O concentration, the NOx and N2O conversion performance with a reducing agent such as NH3 is notably superior to that obtained with FER structural zeolite-based catalysts, particularly in the temperature range of 300 to 500°C. The direct N2O decomposition properties using this catalyst are also particularly advantageous from 450°C. EXAMPLES

[0112] Example 1: preparation of a catalyst containing a Nu-86 zeolite and iron according to the invention Fe-Nu-86

[0113] 271.72 g of an aqueous solution of octamethonium bromide (25% by weight, SACHEM) are mixed with 280.71 g of deionized water, with stirring and at room temperature. 8.89 g of sodium hydroxide (98% by weight, Aldrich) are dissolved in the previous mixture with stirring and at room temperature. Subsequently, 2.39 g of sodium bromide (NaBr, Prolabo) are added with stirring and at room temperature. 4.13 g of sodium aluminate (NaAlO2, Carlo Erba) and then 140.4 g of deionized water are incorporated into the synthesis mixture, which is kept under stirring for half an hour at room temperature. As soon as the resulting suspension is homogeneous, 41.8 g of fumed silica (Aerosil 200, Degussa) are added, and the resulting suspension is kept under vigorous stirring for 10 minutes. at room temperature. The molar composition of the precursor gel is as follows: 1 SiO2: 0.031 Al2O3: 0.255 OctaBr2: 0.2 Na2O: 0.033 NaBr: 50 H2O, resulting in a SiO2 / Al2O3 ratio of 32.4. After homogenization, the precursor gel is transferred to a 1000 mL stainless steel reactor equipped with a four-bladed stirring system for a 24-hour maturation step at room temperature with stirring at 180 rpm. Following this maturation step, the reactor is heated for 32 days at a rate of 0.4°C / min up to 155°C with stirring at 300 rpm to allow the crystallization of Nu-86 zeolite. The crystallized product obtained is filtered, washed with deionized water, then dried for 12 hours at 100°C.The solid is then introduced into a muffle furnace where a calcination step is carried out: the calcination cycle includes a temperature increase of 1.5°C / min up to 200°C, a plateau at 200°C maintained for 2 hours, a rise of 1°C / min up to 550°C followed by a plateau at 550°C maintained for 12 hours and then a return to ambient temperature.

[0114] After calcination, the zeolite is contacted with an aqueous IM solution of NH4NO3 for 1 hour under stirring at 80°C. The ratio of the volume of solution to the mass of zeolite is 19 (V / W). The resulting solid is filtered and washed, and the exchange procedure is repeated once more under the same conditions.

[0115] The material obtained is named NH4-Nu-86 and is treated under a dry air stream at 550°C for 4 hours with a temperature ramp of 1°C / min. The material obtained is a Nu-86 zeolite in protonated form (H-Nu-86).

[0116] The H-Nu-86 zeolite is then contacted with an aqueous solution of Fe(NO3)3·9H2O at 80°C for 17 hours with stirring and a volume-to-mass ratio of 200 (V / W) of solution to zeolite. The final solid is centrifuged and dried overnight at 100°C.

[0117] The solid obtained after contact with the Fe(NO3)3 solution is then calcined under an air stream at 550°C for 8 hours with a temperature ramp of 1°C / min. The resulting material is named Fe-Nu-86.

[0118] The Fe-Nu-86 catalyst thus prepared comprises 2.6% by weight of iron relative to the total weight of catalyst.

[0119] The Fe-Nu-86 catalyst was analyzed by X-ray diffraction and identified as consisting mainly of Nu-86 zeolite with a purity greater than 99 wt%. The X-ray diffraction pattern obtained for the Fe-Nu-86 catalyst is shown in [Fig. 1]. The product has a SiO2 / Al2O3 molar ratio of 30 as determined by X-ray diffraction.

[0120] Example 2: Commercial Fe-ferrierite (Fe-FER)

[0121] A commercial Fe-FER DeNOx / DeN2O catalyst has been procured. The product has a SiO2 / Al2O3 molar ratio of 17.5 and a mass percentage of Fe of 2% as determined by FX. The resulting catalyst is denoted Fe-FER.

[0122] Example 3: Conversion of NOx and N2O: comparison of the catalysts according to the invention with the prior art

[0123] A catalytic test of the reduction of nitrogen oxides (NOx) and nitrous oxide (N2O) by ammonia (NH3) in the presence of oxygen (O2) is carried out at different operating temperatures for the catalysts synthesized according to example 1 (Fe-Nu-86) and example 2 (Fe-FER).

[0124] For the test of each sample, 200 mg of catalyst in powder form is placed in a quartz reactor. 145 L / h of a gas mixture having the following molar composition is fed into the reactor: 200 ppm NO, 200 ppm NO2, 200 ppm N2O, 800 ppm NH3, 8.5% O2, 9% CO2, 10% H2O, qpc N2.

[0125] An FTIR analyzer allows the concentration of the species NO, NO2, NH3, N2O, CO, CO2, H2O, and O2 to be measured at the reactor outlet. The NOx conversions are calculated as follows: NOx conversion = (NOx input - NOx output) / NOx input N2O conversion = (N2O input - N2O output) / N2O input

[0126] In these formulas, the input and output indices respectively indicate the content before and after catalytic reduction.

[0127] The NOx conversion results are presented in the following table 2: [Tables2] 300°C 400°C 450°C 500°C Fe-Nu-86 100% 100% 100% 100% Fe-FER 94% 100% 100% 100%

[0128] The results of the conversion of N2O are presented in the following table 3: [Tables3] 300°C 400°C 450°C 500°C Fe-Nu-86 0% 10% 31% 70% Fe-FER 0% 10% 31% 66%

[0129] The Fe-Nu-86 catalyst synthesized according to the invention provides superior performance to the Fe-FER catalyst in terms of NOx conversion, particularly at low temperatures (300°C). For N2O conversion, the Fe-Nu-86 catalyst exhibits similar, or even slightly superior, performance to the Fe-FER catalyst.

[0130] Example 4: Conversion of NOx and N2O: comparison of the catalysts according to the invention with the prior art

[0131] A catalytic test of the reduction of nitrogen oxides (NOx) and nitrous oxide (N2O) by ammonia (NH3) in the presence of oxygen (O2) is carried out at different operating temperatures for the catalysts synthesized according to example 1 (Fe-Nu-86) and example 2 (FeFER).

[0132] For the test of each sample, 200 mg of catalyst in powder form is placed in a quartz reactor. 145 L / h of a gas mixture having the following molar composition is fed into the reactor: 200 ppm NO, 50 ppm NO2, 1000 ppm N2O, 1250 ppm NH3, 2.5% O2, 8% H2O, qpc N2.

[0133] An FTIR analyzer allows the concentration of the species NO, NO2, NH3, N2O, CO, CO2, H2O, and O2 to be measured at the reactor outlet. The NOx conversions are calculated as follows: NOx conversion = (NOx input - NOx output) / NOx input N2O conversion = (N2O input - N2O output) / N2O input

[0134] In these formulas, the input and output indices respectively indicate the content before and after catalytic reduction.

[0135] The NOx conversion results are presented in the following Table 4: [Tables4] 300°C 400°C 450°C 500°C 600°C Fe-Nu-86 54% 88% 100% 100% 100% Fe-FER 58% 92% 100% 100% 100%

[0136] The results of the conversion of N2O are presented in the following table: [Tables5] 300°C 400°C 450°C 500°C 600°C Fe-Nu-86 0% 15% 56% 86% 100% Fe-FER 0% 5% 35% 80% 97%

[0137] The Fe-Nu-86 catalyst synthesized according to the invention provides DeN2O performance superior to the Fe-FER catalyst with a lower initiation temperature. It also offers performance almost identical to the Fe-FER catalyst in terms of NOx conversion.

Claims

Demands

1. A process for preparing a catalyst based on a Nu-86 structural-type zeolite and iron comprising at least the following steps: i) mixing in aqueous medium, at least one silicon (Si) source in the form of SiO2 oxide, at least one aluminum (Al) source in the form of Al2O3 oxide, a nitrogenous organic compound R, R being octamethonium bromide (OctBr2), at least two sodium sources, one of them being sodium bromide (NaBr), the reaction mixture having the following molar composition: SiO2 / Al2O3 from 8 to 20, H2O / SiO2 from 15 to 60, R / SiO2 from 0.05 to 0.35, Na2O / SiO2 from 0.05 to 0.3, NaBr / SiO2 from 0.01 to 0.1, inclusive, step i) being carried out for a period of between 5 and 15 minutes until a homogeneous mixture called precursor gel is obtained; ii) The ripening of the precursor gel of said step i) at a temperature between 20 and 100°C with or without agitation, for a period of between 10 minutes and 48 hours, preferably between 18 and 24 hours; iii) the hydrothermal treatment of said precursor gel obtained at the end of step ii) at a temperature between 120°C and 220°C, preferably between 140 and 195°C, for a period of between 12 hours and 35 days, preferably between 12 hours and 33 days, until said Nu-86 zeolite is formed; (iv) at least one ion exchange comprising bringing said zeolite obtained at the end of the previous step into contact with a solution comprising at least one species capable of releasing iron, in solution in reactive form under stirring at a temperature between 20 and 95°C, preferably between 40 and 90°C for a period of between 1 hour and 2 days; (v) Heat treatment by drying the Nu-86 zeolite obtained at the end of the previous step at a temperature between 20 and 150°C for a period of between 2 and 24 hours followed by at least one calcination under airflow at a temperature between 400 and 700°C for a period of between 2 and 8 p.m.

2. A method according to claim 1 in which steps iv) and v) are reversed, and optionally repeated.

3. A preparation method according to claim 2, wherein the Nu-86 zeolite obtained in step iii) directly undergoes a step v) of heat treatment, then at least one ion exchange with an acid, or a compound such as chloride, sulfate or ammonium nitrate to obtain a calcined Nu-86 zeolite in protonated form, before the step iv) of ion exchange with iron.

4. A preparation method according to any one of the preceding claims, wherein crystal seeds of a Nu-86 structural type zeolite are added to the reaction mixture of step i), in an amount between 0.01 and 10% of the total mass of the sources of tetravalent (Si) and trivalent (Al) elements in their oxide form (SiO2 and Al2O3) in anhydrous form used in the reaction mixture, said crystal seeds not being taken into account in the total mass of the sources of tetravalent and trivalent elements.

5. A preparation process according to any one of the preceding claims wherein the iron content introduced by the ion exchange step iv) is between 0.5 and 6% by mass, preferably between 0.5 and 5% by mass, more preferably between 1 and 4% by mass relative to the total mass of the final anhydrous catalyst.

6. Catalyst based on Nu-86 zeolite and iron for the decomposition of N2O or the reduction of N2O or the simultaneous reduction of Nox and N2O by a reducing agent such as NH3 or H2 which can be obtained or directly obtained by the preparation process according to any one of claims 1 to 5 wherein the total iron content is between 0.5 and 6% by mass, preferably between 0.5 and 5% by mass, more preferably between 1 and 4% by mass relative to the total mass of the final anhydrous catalyst.

7. A process for the decomposition of N2O or the reduction of N2O or the simultaneous reduction of NOx and N2O by a reducing agent such as NH3 or H2 in which the gas to be treated is brought into contact with a catalyst according to claim 6.

8. A process for the decomposition of N2O or the reduction of N2O or the simultaneous reduction of NOx and N2O according to claim 7, wherein said catalyst is shaped by deposition as a coating on a honeycomb structure or a plate structure, or said catalyst is in extruded or bead form, containing up to 100% of said catalyst.

9. A method for decomposing N2O or reducing N2O or for simultaneously reducing NOx and N2O according to claim 8, wherein the honeycomb structure is formed of parallel channels open at both ends or comprises filtering porous walls for which the adjacent parallel channels are alternately blocked on either side of the channels.

10. A process for decomposing N2O or reducing N2O or simultaneously reducing NOx and N2O according to claim 9 wherein the amount of catalyst deposited on said structure is between 50 and 250 g / L for filter structures and between 80 and 300 g / L for structures with open channels.

11. A process for the decomposition of N2O or the reduction of N2O or the simultaneous reduction of NOx and N2O according to any one of claims 8 to 10 wherein the catalyst is associated with a binder such as cerine, zirconium oxide, alumina, non-zeolitic silica-alumina, titanium oxide, a mixed oxide of the cerine-zirconia type, a tungsten oxide and / or a spinel for being shaped by deposition as a coating, said coating preferably being associated with another coating having the capacity to adsorb pollutants in particular NOx, to reduce pollutants in particular NOx or to promote the oxidation of pollutants.

12. A process for decomposing N2O or reducing N2O or simultaneously reducing NOx and N2O according to any one of claims 7 to 11 in which said catalyst is integrated: - in an exhaust line of an internal combustion engine operating from carbon or non-carbon fuels, or - in a reactor for treating industrial fumes.