Synthesis of a catalyst comprising a high-purity nu-86 zeolite and iron for the converson of NOX and n2o

Abstract

The invention relates to a method for preparing a catalyst based on high-purity Nu-86 zeolite and on iron, the method comprising at least the steps of: i) mixing, in an aqueous medium, at least one source of silicon (Si) in oxide form SiO2, at least one source of aluminium (Al) in oxide form AI2O3, a nitrogenous organic compound R, R being octamethonium bromide (OctBr2), and at least two sources of sodium including sodium bromide (NaBr), until a homogenous precursor gel is obtained; ii) curing the gel in order to direct the zeolite to form free of impurities; iii) hydrothermally treating the precursor gel to obtain a crystallised solid phase; iv) carrying out at least one ion-exchange with iron; v) carrying out a heat treatment. The invention also relates to the catalyst capable of being obtained or directly obtained by the method and to the use of the catalyst for the conversion of NOx and / or N2O.

Description

[0001] SYNTHESIS OF CATALYST COMPRISING HIGH PURITY ZEOLITE Nu-86 AND IRON FOR THE CONVERSION OF NOX AND N2O

[0002] TECHNICAL FIELD OF THE INVENTION

[0003] The subject of the invention is 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 in combustion and industrial processes such as the production of nitric and adipic acid.

[0004] PRIOR ART

[0005] Nitrogen oxide (NOx) emissions resulting from combustion are a major concern for society as they are responsible for health problems, ground-level ozone, acid rain, and smog. Governments are implementing increasingly stringent standards to limit the impact on the environment and health. Highly efficient pollution control systems such as three-way catalysts or selective catalytic reduction (SCR) catalysts have been developed to equip transportation systems to achieve these objectives. However, the selectivity of these systems often leads to 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 4. ème IPCC report.

[0006] Ammonia is considered an important fuel for decarbonization. However, the combustion of ammonia (or an H2 / NH3 mixture) presents potentially significant exhaust emissions of N2O, NOx, and NH3.

[0007] Other sectors are responsible for high NOx and N2O emissions, the nitric acid industry is one of the main sources of nitrous oxide (N2O) emissions. N2O is formed as a by-product of ammonia oxidation over a Pt / Rh catalyst. The NOx, which is the main product at the outlet of the Pt / Rh catalyst, is then absorbed in water to form nitric acid. The absorption step is not 100% efficient and results in NOx emissions at the outlet (100 to 500 ppm).

[0008] NOx and N2O treatment for applications related to decarbonization and industrial fumes is therefore necessary. NOx treatment has already been the subject of numerous studies, whether in industry or transport. For N2O treatment, several types of catalysts have been studied depending on the temperature at which they are effective. Precious metals have good efficiency around 250°C, but are expensive and very often deactivated in the presence of inhibitors (CO, H2O, NOx, O2, etc.), which is not compatible with the constraints of nitric or adipic acid production. Zeolites, on the other hand, have a relatively low cost and a very large developed surface area, which makes it possible to obtain a good catalytic system by incorporating a transition metal, particularly iron. Sàdovskà et al. (Sàdovskà, G., Bernauer, M., Bernauer, B., Tabor, E., Vondrovà, A., & Sobalik, 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-ferrous FER-type zeolites exhibited very high performance in N2O decomposition and that there was a positive effect of NO for decomposition even at 600-900°C. The FER structure that presents AI pairs resists high-temperature DeN2O conditions 900°C (Tabor, E., Mlekodaj, K., Sàdovskà, G., Bernauer, M., Klein, P., Sazama, P., ... & Sobalik, Z. (2019). Structural stability of metal containing ferrierite under the conditions of HT-N2O decomposition. Microporous and Mesoporous Materials, 281 , 15-22.).

[0009] The presence of cation, especially iron, promotes decomposition but increasing the content beyond 1% does not seem to promote the activity for 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 N2O decomposition and NH3-SCR of NOx was analyzed by Sazama et al. (Sazama, P., Wichterlovà, B., Tàbor, E., St'astnÿ, P., Sathu, NK, Sobalik, Z., ... & Vondrovà, 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.).

[0010] It is possible to combine NOx and N2O reduction 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, associated with an NH3-SCR stage; a DeNOx stage followed by N2O reduction with ammonia or hydrocarbons (methane or propane). 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.

[0011] SUMMARY OF THE INVENTION

[0012] The applicant has discovered that a catalyst based on a Nu-86 type zeolite prepared according to a particular synthesis method and iron as transition metal, exhibited interesting performances for the simultaneous conversion of NOx and N2O. The performances for the conversion of NOx and N2O with a reducing agent, in particular over the temperature range from 300 to 500°C, are notably superior to those obtained with catalysts of the prior art, such as catalysts based on zeolite of the FER structural type exchanged with iron. The properties of direct decomposition of N2O using this catalyst are also particularly interesting from 450°C.

[0013] The invention relates to a process for preparing a catalyst based on a zeolite of structural type Nu-86 and iron comprising at least the following steps: i) mixing in an aqueous medium, at least one source of silicon (Si) in the form of SiO2 oxide, at least one source of aluminum (Al) in the form of AI2Oa oxide, an organic nitrogen compound R, R being octamethonium bromide (OctBr2), at least two sources of sodium, one of them being sodium bromide (NaBr), the reaction mixture having the following molar composition:

[0014] SiO2 / AI2C>3 between 8 and 20

[0015] H2O / SiO2 between 15 and 60

[0016] R / SiO2 between 0.05 and 0.35

[0017] Na2O / SiO2 between 0.05 and 0.3,

[0018] NaBr / SiO2 between 0.01 and 0.1, limits included, 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 maturing of the precursor gel of said step i) at a temperature between 20 and 100°C with or without stirring, 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 dried 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 with 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 air flow at a temperature between 400 and 700°C for a period of between 2 and 20 hours.;

[0019] Steps iv) and v) can be reversed, and possibly repeated.

[0020] 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 step iv) of ion exchange with iron.

[0021] Crystalline seeds of a zeolite of structural type Nu-86 can be added to the reaction mixture of step i), in an amount of between 0.01 and 10% of the total mass of the sources of the tetravalent (Si) and trivalent (Al) elements in their oxide form (SiO2 and AI2O3) in anhydrous form used in the reaction mixture, said crystalline seeds not being taken into account in the total mass of the sources of the tetravalent and trivalent elements.

[0022] 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.

[0023] 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 capable of being obtained or directly obtained by the preparation process according to any of its variants.

[0024] The iron content of the catalyst may 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. 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.

[0025] The catalyst may be formed by deposition as a coating, on a honeycomb structure or a plate structure or said catalyst may be in extrudate or bead form, containing up to 100% of said catalyst.

[0026] 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.

[0027] 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.

[0028] The catalyst may be combined with a binder such as ceria, zirconium oxide, alumina, non-zeolitic silica-alumina, titanium oxide, a mixed oxide of ceria-zirconia type, a tungsten oxide and / or a spinel to be shaped by deposition in the form of a coating, said coating preferably being able to be combined with another coating having capacities for adsorbing pollutants, in particular NOx, for reducing pollutants, in particular NOx, or promoting the oxidation of pollutants.

[0029] Said catalyst can be integrated:

[0030] - in an exhaust line of an internal combustion engine operating on carbonaceous or non-carbonaceous fuels, or

[0031] - in a reactor to treat industrial fumes.

[0032] LIST OF FIGURES

[0033] Other characteristics and advantages of the process for preparing the catalyst according to the invention will appear on reading the following description of non-limiting examples of embodiments, with reference to the figures appended and described below.

[0034] Figure 1 shows the X-ray diffraction (XRD) patterns of the Nu-86 zeolite-based catalyst containing iron, Fe-Nu-86, obtained according to Example 1. DESCRIPTION OF THE EMBODIMENTS

[0035] The invention relates to a process for preparing a catalyst based on Nu-86 zeolite and iron comprising at least the following steps: i) mixing in an aqueous medium, at least one source of silicon (Si) in the form of SiO2 oxide, at least one source of aluminum (Al) in the form of AI2O3 oxide, an organic nitrogen compound R, R being octamethonium bromide (OctBr2), at least two sources of sodium, one of them being sodium bromide (NaBr), the reaction mixture having the following molar composition:

[0036] SiCh / AhCh between 8 and 20

[0037] LLO / SiCh between 15 and 60

[0038] R / SiCh between 0.05 and 0.35

[0039] Na2O / SiC>2 between 0.05 and 0.3,

[0040] NaBr / SiCh between 0.01 and 0.1, limits included,

[0041] 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 of between 20 and 100°C with or without stirring, 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 of between 120°C and 220°C, for a period of between 12 hours and 35 days until said Nu-86 zeolite is formed;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 with stirring at a temperature of 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 said Nu-86 zeolite obtained at the end of the previous step at a temperature of between 20 and 150°C followed by at least one calcination under air flow at a temperature of between 400 and 700°C.;

[0042] Steps iv) and v) may be reversed, and possibly repeated. The Nu-86 zeolite obtained in step iii) may in this case directly undergo step v) of heat treatment, then an ion exchange with an acid, or a compound such as ammonium chloride, sulfate or nitrate to obtain a calcined Nu-86 zeolite in protonated form, before step iv) of ion exchange with iron.

[0043] Crystalline seeds of a Nu-86 zeolite may be added to the reaction mixture of step i), preferably in an amount of between 0.01 and 10% by 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 ALOa.

[0044] Step i) may comprise a step of maturing the reaction mixture at a temperature of between 20 and 100°C, with or without stirring, for a period of between 30 minutes and 48 hours.

[0045] The hydrothermal treatment of step iii) may 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.

[0046] 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 between 5 and 24 hours to obtain a dried Nu-86 zeolite.

[0047] 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 successively bringing the solid into contact with different solutions each comprising at least one, preferably a single, species capable of releasing a transition metal, which is iron.

[0048] 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.

[0049] Advantageously, step v) of heat treatment comprises drying the solid at a temperature of 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 in air, optionally dry, at a temperature of 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 optionally dry air 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.

[0050] The invention also relates to the catalyst based on a Nu-86 zeolite and iron, capable of being obtained or directly obtained by the preparation process.

[0051] 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.

[0052] The invention also relates to the use of the catalyst according to any of its variants or of the catalyst capable of being obtained or directly obtained by the preparation process, for the selective reduction of NO X by a reducing agent such as NH3 or H2.

[0053] The invention also relates to the use of the catalyst described above or the use of the catalyst obtainable or directly obtainable 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.

[0054] The catalyst can be shaped directly by extrusion in the form of pellets or by deposition in the form of a coating, on a honeycomb structure or a plate structure.

[0055] The honeycomb structure may be formed of parallel channels open at both ends or may have porous filtering walls in which adjacent parallel channels are alternately blocked on either side of the channels.

[0056] The quantity of catalyst deposited on said structure can advantageously be between 50 and 200 g / L for filter structures and between 80 and 300 g / L for structures with open channels.

[0057] The catalyst may be combined with a binder such as ceria, zirconia, alumina, non-zeolitic silica-alumina, titanium oxide, a mixed oxide of the ceria-zirconia type, a tungsten oxide and / or a spinel to be formed by deposition in the form of a coating.

[0058] Said coating may be combined with another coating having pollutant adsorption capacities, in particular nitrogen oxides, pollutant reduction capacities, in particular NOx, or promoting the oxidation of pollutants, such as CO or hydrocarbons. Said catalyst may be in the form of an extrudate or bead or any other form known to those skilled in the art, containing up to 100% of said catalyst.

[0059] 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. The shaping can advantageously be carried out, for example, by extrusion, by pelletizing, by the oil-drop method, by granulation on a rotating plate or by any other method well known to those skilled in the art. The supports thus obtained can be in different shapes and sizes. Advantageously, the different constituents of the support or of the catalyst can be shaped by a mixing step to form a paste followed by extrusion of the paste obtained, or by mixing powders followed by pelletizing, or by any other known method of agglomerating a powder containing alumina. The supports thus obtained can be in different shapes and sizes. Preferably, the shaping is carried out by mixing and extrusion.

[0060] Furthermore, the use of additives can advantageously be implemented to facilitate shaping and / or improve the final mechanical properties of the supports as is well known to those skilled in the art. Examples of additives include cellulose, carboxymethylcellulose, carboxyethylcellulose, tall oil, xanthan gums, surfactants, flocculating agents such as polyacrylamides, carbon black, starches, stearic acid, polyacrylic alcohol, polyvinyl alcohol, biopolymers, glucose, polyethylene glycols, etc.

[0061] Water can be advantageously 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.

[0062] 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. A hydrate is preferably used, and even more preferably an aluminum hydrate. The loss on ignition of this hydrate is advantageously greater than 15%.

[0063] The extrusion of the paste resulting from the kneading step can advantageously be carried out by any conventional, commercially available tool. The paste resulting from the kneading is advantageously extruded through a die, for example using a piston or a single-screw or twin-screw extrusion machine. The extrusion can advantageously be carried out by any method known to those skilled in the art.

[0064] The catalyst supports according to the invention are generally in the form of cylindrical or polylobed extrudates such as bilobed, trilobed, polylobed of straight or twisted shape, but can optionally be manufactured and used in the form of crushed powders, tablets, rings, balls and / or wheels. Preferably, the catalyst supports according to the invention can have the form of spheres or extrudates. Advantageously, the support can be 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 can be hollow or not) and / or twisted cylindrical and / or multilobed (2, 3, 4 or 5 lobes for example) and / or annular. The multilobed shape is advantageously used in a preferred manner.

[0065] The structure coated by said catalyst or obtained by extrusion of said catalyst can be integrated:

[0066] - in an exhaust line of an internal combustion engine operating on carbon-based or non-carbon fuels, such as NH3, H2, etc. (non-exhaustive list)

[0067] - in a reactor to treat industrial fumes. In a nitric acid plant, it can be integrated in the tertiary stage, either to sequentially eliminate N2O by decomposition and NOx with the addition of a reducing agent such as NH3 or to concomitantly eliminate NOx and N2O with the addition of a reducing agent.

[0068] The catalyst

[0069] The catalyst according to the invention comprises at least one Nu-86 zeolite, and iron.

[0070] 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.

[0071] The catalyst according to the invention may also comprise other elements, such as for example alkali and / or alkaline earth metals, for example sodium, originating in particular from the synthesis, in particular of the compounds of the reaction medium of step i) of the process for preparing said catalyst.

[0072] Process for preparing the catalyst

[0073] Step i) of mixing

[0074] Step i) implements: i) the mixing in aqueous medium of at least one source of silicon (Si) in the form of SiC>2 oxide, at least one source of aluminum (Al) in the form of AI2O3 oxide, of an organic nitrogen 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:

[0075] SiO2 / AhO3 between 8 and 20

[0076] LLO / SiCh between 15 and 60

[0077] R / SiCh between 0.05 and 0.35

[0078] Na2O / SiC>2 between 0.05 and 0.3,

[0079] NaBr / SiCh between 0.01 and 0.1, limits included, in which H2O corresponds to the molar quantity of water present in the reaction mixture, R the molar quantity of said organic nitrogen compound, Na2O the molar quantity expressed in the form of sodium oxide, step i) being carried out for a time allowing 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.

[0080] The silicon source may be any of the said sources commonly used for the synthesis of zeolites, for example powdered silica, silicic acid, colloidal silica, dissolved silica or tetraethoxysilane (TEOS). Among the 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 having different particle sizes, for example with an average equivalent diameter of 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.

[0081] According to the invention, the source of aluminum is preferably aluminum hydroxide or an aluminum salt, for example chloride, nitrate, or sulfate, sodium aluminate, aluminum alkoxide, or alumina itself, preferably in hydrated or hydratable form, such as for example colloidal alumina, pseudoboehmite, gamma alumina or alpha or beta trihydrate. Mixtures of the above-mentioned sources can also be used.

[0082] Step (i) of the process according to the invention consists in preparing an aqueous reaction mixture containing at least one source of silicon, at least one source of aluminum, at least one organic nitrogen compound R, R being octamethonium bromide (OctBr2), in the presence of at least two sources of sodium, 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 indicated previously so as to give this gel a composition allowing the crystallization of a Nu-86 zeolite.

[0083] It may be advantageous to add seeds of a Nu-86 zeolite 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 crystals of a Nu-86 zeolite and / or the total crystallization time. Said crystal seeds also promote the formation of said Nu-86 zeolite to the detriment of impurities. Such seeds comprise crystallized solids, in particular crystals of a Nu-86 zeolite. The crystal seeds 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 crystal seeds not being taken into account in the total mass of the sources of the tetravalent and trivalent elements.Said germs are also not taken into account for determining the composition of the reaction mixture and / or the gel, defined further, that is to say in the determination of the different molar ratios of the composition of the reaction mixture.

[0084] Step i) of mixing is carried out until a homogeneous mixture is obtained, preferably for a period of between 5 and 15 minutes, preferably with stirring by any system known to those skilled in the art with low or high shear rate.

[0085] At the end of step i), a homogeneous precursor gel is obtained.

[0086] Step ii) ripening of the precursor gel

[0087] Step ii) involves maturing the reaction mixture before hydrothermal crystallization in order to promote the formation of said Nu-86 zeolite to the detriment of impurities. The maturing of the reaction mixture during said step ii) of the process of the invention may be carried out at room temperature or at a temperature between 20 and 100°C with or without stirring, for a period advantageously between 10 minutes and 48 hours, preferably between 18 and 24 hours.

[0088] Step iii) of hydrothermal treatment

[0089] 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 a 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 “crystalline solid”) is formed.

[0090] The precursor gel is advantageously placed under hydrothermal conditions under autogenous 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.

[0091] The time required to achieve crystallization varies between 12 hours and 35 days, preferably between 12 hours and 33 days.

[0092] The reaction is generally carried out with or without stirring, preferably with stirring. Any stirring system known to those skilled in the art can be used as the stirring system, for example, inclined blades with counterblades, stirring turbines, Archimedes screws.

[0093] Very advantageously, the process of the invention leads to the formation of a Nu-86 zeolite, free from any other crystallized or amorphous phase.

[0094] The hydrothermal treatment of step iii) may be followed by filtration, washing and drying of the Nu-86 zeolite obtained, advantageously at a temperature of 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).

[0095] 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.

[0096] In this embodiment, the zeolite of structural type Nu-86 obtained at the end of step iii) directly undergoes a heat treatment (step v) comprising drying at a temperature of between 20 and 150°C, preferably between 60 and 100°C, for a duration of between 2 and 24 hours, followed by at least one calcination, in air, optionally dry, at a temperature of between 400 and 700°C, preferably between 500 and 600°C for a duration of between 2 and 20 hours, preferably between 5 and 10 hours, more preferably between 6 and 9 hours, the flow rate of optionally dry air 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. 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 ammonium chloride, sulfate or nitrate to obtain a calcined Nu-86 zeolite in protonated form, before step iv) of ion exchange with iron. Step iv) of ion exchange.

[0097] The process for preparing the catalyst according to the invention comprises at least one ion exchange step comprising bringing the crystallized solid obtained at the end of the previous 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, into contact with at least one solution comprising at least one species capable of releasing a transition metal, here iron, in solution in reactive form, with stirring at room temperature for a period of between 1 hour and 2 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 it is desired to incorporate into said crystallized solid.

[0098] The transition metal released into the exchange solution is iron.

[0099] According to the invention, by "species capable of releasing a transition metal" is meant a species capable of dissociating in an aqueous medium, such as for example sulfates, nitrates, chlorides, oxalates, organometallic complexes of a transition metal or their mixtures. Preferably, the species capable of releasing a transition metal is a sulfate or a nitrate of said transition metal.

[0100] 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.

[0101] Advantageously, the process for preparing the catalyst according to the invention may comprise a step iv) of ion exchanges by bringing the crystallized solid into contact with a solution comprising a species capable of releasing a transition metal or by successively bringing the solid into contact with several solutions each comprising a species capable of releasing a transition metal, said metal being iron.

[0102] 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.

[0103] 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.

[0104] According to one embodiment, the catalyst according to the invention is prepared by a process comprising a step iv) of ion exchange, the solid or the dried and calcined solid being brought into contact with a solution comprising a species capable of releasing iron in solution in 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.

[0105] Step v) heat treatment

[0106] The preparation process according to the invention comprises a heat treatment step v) carried out at the end of the previous step, i.e. at the end of hydrothermal treatment step iii) or at the end of ion exchange step iv), preferably at the end of ion exchange step iv). Step v) of the preparation process can advantageously be interchanged with step iv). Each of the two steps iv) and v) can also optionally be repeated.

[0107] Said heat treatment step v) comprises drying the solid at a temperature of 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, in air, optionally dry, at a temperature advantageously of 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 optionally dry air 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 increase in temperature.

[0108] The catalyst obtained at the end of heat treatment step v) is free of any organic species, in particular free of the organic structuring agent R.

[0109] In particular, the catalyst obtained by a process comprising at least steps i), ii), iii), iv) and v) previously described has improved properties for the conversion of N2O.

[0110] Characterization of the catalyst prepared according to the invention

[0111] The catalyst comprises a zeolite with the Nu-86 structure. This structure is characterized by X-ray diffraction (XRD).

[0112] The X-ray diffraction pattern (XRD) is obtained by radiocrystallographic analysis using a diffractometer using the classical powder method with the Kai radiation of copper (X = 1.5406Â). From the position of the diffraction peaks represented by the angle 20, the characteristic reticular equidistances dhki of the sample are calculated using the Bragg relation. The measurement error A(dhki) on dhki is calculated using the Bragg relation as a function of the absolute error A(20) assigned to the measurement of 20. An absolute error A(20) equal to + 0.02° is commonly accepted. The relative intensity l rei assigned to each value of dhki 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 comprises at least the lines at the values ​​of d h ki data in Table 1 (Mean values ​​of d hki and relative intensities measured on an X-ray diffraction pattern of the zeolite catalyst of structural type Nu-86 calcined according to the invention). In the dhki column, the average values ​​of the inter-reticular distances in Angstroms (Â) are indicated. Each of these values ​​must be affected by the measurement error A(dhki) between + 0.6Â and + 0.01Â.

[0113] Table 1 where FF = very strong; F = strong; m = medium; mf = medium weak; f = weak; ff = very weak. The relative intensity l rei is given in relation to a relative intensity scale where a value of 100 is assigned to the most intense line in the X-ray diffraction pattern: ff < 15; 15 <f <30 ; 30 < mf <50 ; 50 < m < 65 ; 65 <F < 85 ; FF >85.

[0114] The qualitative and quantitative analysis of the chemical species present in the materials obtained is carried out by X-ray fluorescence (FX) spectrometry. This is a chemical analysis technique using a physical property of matter, X-ray fluorescence. It allows the analysis of the majority of chemical elements from 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 the energy 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.

[0115] The loss on ignition (LAI) 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 LAI, corresponds to the difference in mass of the sample before and after a heat treatment at 1000°C for 2 hours. It is expressed in % corresponding to the percentage loss of mass. 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 mineral solid constituents.

[0116] Use of the catalyst according to the invention

[0117] 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 in the form of a coating ("washcoat" according to English terminology) on a honeycomb structure mainly for mobile applications or a plate structure which is found particularly for stationary applications. The invention can also be shaped in the form of extrudates or beads. Preferably, the supports of the catalyst according to the invention have 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 can be hollow or not) 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 used in a preferred manner.

[0118] The honeycomb structure is formed of parallel channels open at both ends (flow-through in English) or has porous filtering walls and in this case the adjacent parallel channels are alternately blocked on either side of the channels in order to force the gas flow to pass through the wall (wall-flow monolith in English). Said honeycomb structure thus coated constitutes a catalytic bread. Said structure can be composed of cordierite, silicon carbide (SiC), aluminum titanate (AITi), alpha alumina, mullite or any other material whose porosity is between 30 and 70%. Said structure can be made of metal sheet, stainless steel containing chromium and aluminum, FeCrAI type steel.

[0119] The quantity of catalyst according to the invention 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.

[0120] The coating itself ("washcoat") comprises the catalyst according to the invention, advantageously combined with a binder such as ceria, zirconium oxide, alumina, non-zeolitic silica-alumina, titanium oxide, a mixed oxide of the ceria-zirconia type, a tungsten oxide, a spinel. Said coating is advantageously applied to said structure by a deposition method (washcoating in English) which consists of dipping the monolith in a suspension (slurry in English) 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 quantity of coating is reached. In certain cases the slurry can also be sprayed within the monolith. Once the coating is deposited, the monolith is calcined at a temperature of 300 to 600°C for 1 to 10 hours.

[0121] Said structure may be coated with one or more coatings. The coating comprising the catalyst according to the invention is advantageously associated with, i.e. covers one or is covered by, another coating having capacities for adsorbing pollutants, in particular NOx, for reducing pollutants, in particular NOx, or promoting the oxidation of pollutants, in particular that of ammonia.

[0122] Another possibility is to put the catalyst in the form of an extrudate or a bead or any other form 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.

[0123] 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. The shaping can advantageously be carried out, for example, by extrusion, by pelletizing, by the oil-drop method, by granulation on a rotating plate or by any other method well known to those skilled in the art. The supports thus obtained can be in different shapes and sizes. Advantageously, the different constituents of the support or of the catalyst can be shaped by a mixing step to form a paste followed by extrusion of the paste obtained, or by mixing powders followed by pelletizing, or by any other known method of agglomerating a powder containing alumina. The supports thus obtained can be in different shapes and sizes. Preferably, the shaping is carried out by mixing and extrusion.

[0124] Furthermore, the use of additives can advantageously be implemented to facilitate shaping and / or improve the final mechanical properties of the supports as is well known to those skilled in the art. Examples of additives include cellulose, carboxymethylcellulose, carboxyethylcellulose, tall oil, xanthan gums, surfactants, flocculating agents such as polyacrylamides, carbon black, starches, stearic acid, polyacrylic alcohol, polyvinyl alcohol, biopolymers, glucose, polyethylene glycols, etc.

[0125] Water can be advantageously 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.

[0126] 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. A hydrate is preferably used, and even more preferably an aluminum hydrate. The loss on ignition of this hydrate is advantageously greater than 15%.

[0127] The extrusion of the paste resulting from the kneading step can advantageously be carried out by any conventional, commercially available tool. The paste resulting from the kneading is advantageously extruded through a die, for example using a piston or a single-screw or twin-screw extrusion machine. The extrusion can advantageously be carried out by any method known to those skilled in the art.

[0128] The catalyst supports according to the invention are generally in the form of cylindrical or polylobed extrudates such as bilobed, trilobed, polylobed of straight or twisted shape, but can optionally be manufactured and used in the form of crushed powders, tablets, rings, balls and / or wheels. Preferably, the catalyst supports according to the invention have 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 can be hollow or not) and / or twisted cylindrical and / or multilobed (2, 3, 4 or 5 lobes for example) and / or rings. The multilobed shape is advantageously used in a preferred manner.

[0129] ADVANTAGES OF THE INVENTION

[0130] The catalyst according to the invention, based on a Nu-86 zeolite and iron, has improved deNOx and deN2O properties compared to the catalysts of the prior art. In a stream with a high N2O concentration, the NOx and N2O conversion performances with a reducing agent such as NH3 are notably superior to those obtained with catalysts based on FER structural type zeolite, in particular over the temperature range from 300 to 500°C. The direct decomposition properties of N2O using this catalyst are also particularly interesting from 450°C.

[0131] EXAMPLES

[0132] Example 1: Preparation of a catalyst containing a Nu-86 zeolite and iron according to the invention Fe-Nu-86

[0133] 271.72 g of an aqueous solution of octamethonium bromide (25% by weight, SACHEM) are mixed with 280.71 g of deionized water, while stirring and at room temperature. 8.89 g of sodium hydroxide (98% by weight, Aldrich) are dissolved in the previous mixture while stirring and at room temperature. Subsequently 2.39 g of sodium bromide (NaBr, Prolabo) are added while stirring and at room temperature. 4.13 g of sodium aluminate (NaAIC>2 Carlo Erba) then 140.4 g of deionized water are incorporated into the synthesis mixture, which is kept stirring for half an hour at room temperature. As soon as the suspension obtained is homogeneous, 41.8 g of fumed silica (Aerosil 200, Degussa) are poured in and the suspension obtained is kept under vigorous stirring for 10 minutes at room temperature. The molar composition of the precursor gel is as follows: 1 SiCh: 0.031 AI2O3: 0.255 OctaBr2: 0.2 Na2O: 0.033 NaBr: 50 H2O, i.e. a SiCh / AhCh ratio of 32.4.The precursor gel is then transferred, after homogenization, into a 1000 mL stainless steel reactor equipped with a four-blade inclined stirring system to follow a ripening step at room temperature for 24 hours with stirring at 180 rpm. After the ripening step, the reactor is heated for 32 days with a temperature increase of 0.4°C / min up to 155°C with stirring at 300 rpm to allow the crystallization of a 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 rise of 1.5°C / min up to 200°C, a hold at 200°C maintained for 2 hours, a rise of 1°C / min up to 550°C followed by a hold at 550°C maintained for 12 hours and then a return to room temperature.

[0134] After calcination, the zeolite is brought into contact with a 1 M aqueous solution of NH4NO3 for 1 hour with stirring at 80°C. The ratio between volume of solution and mass of zeolite is equal to 19 (V / P). The solid obtained is filtered and washed and the exchange procedure is repeated once again under the same conditions. The material obtained is named NH4-NU-86 and is treated under a flow of dry air at 550°C for 4 hours with a temperature rise ramp of 1°C / min. The material obtained is a Nu-86 zeolite in protonated form (H-Nu-86).

[0135] The H-Nu-86 zeolite is then brought into contact with an aqueous solution of Fe(NO3)3'9H2O at 80°C for 17 hours with stirring and a volume of solution to mass of zeolite ratio equal to 200 (V / P). The final solid is centrifuged and dried overnight at 100°C.

[0136] The solid obtained after contact with the Fe(NC>3)3 solution is then calcined under air flow at 550°C for 8 hours with a temperature rise ramp of 1°C / min. The material obtained is named Fe-Nu-86.

[0137] The Fe-Nu-86 catalyst thus prepared comprises 2.6% by weight of iron relative to the total weight of catalyst.

[0138] The Fe-Nu-86 catalyst was analyzed by X-ray diffraction and identified as consisting predominantly of a Nu-86 zeolite with a purity greater than 99% by weight. The X-ray diffraction pattern performed on the Fe-Nu-86 catalyst is given in Figure 1. The product has a SiO2 / AI2O3 molar ratio of 30 as determined by FX.

[0139] Example 2: Commercial Fe-ferrierite (Fe-FER)

[0140] A commercial Fe-FER DeNOx / DeN2O catalyst was sourced. The product has a SiO^AfeOs molar ratio of 17.5 and a Fe mass percentage of 2% as determined by FX. The resulting catalyst is denoted Fe-FER.

[0141] Example 3: Conversion of NOx and N2O: comparison of the catalysts according to the invention with the prior art

[0142] A catalytic test for 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).

[0143] 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 with 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. An FTIR analyzer is used to measure the concentration of NO, NO2, NH3, N2O, CO, CO2, H2O, O2 species at the reactor outlet. The NOx conversions are calculated as follows: NOx conversion = (NOx inlet -NOx out) / NOx inlet N2O conversion = (N2O inlet -N2O out) / N2O inlet

[0144] In these formulas, the input and output indices indicate the content before and after catalytic reduction respectively.

[0145] The NOx conversion results are shown in the following Table 2:

[0146] Table 2

[0147] The N3O conversion results are shown in the following Table 3:

[0148] Table 3

[0149] 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 performance to the Fe-FER catalyst, or even slightly superior.

[0150] Example 4: Conversion of NOx and N2O: comparison of the catalysts according to the invention with the prior art

[0151] A catalytic test for 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).

[0152] 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 with 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. An FTIR analyzer is used to measure the concentration of NO, NO2, NH3, N2O, CO, CO2, H2O, O2 species at the reactor outlet. The NOx conversions are calculated as follows: NOx conversion = (NOx in -NOx out) / NOx in N2O conversion = (N2O in -N2O out) / N2O in In these formulas, the inlet and outlet indices indicate the content before and after catalytic reduction, respectively.

[0153] The NOx conversion results are shown in the following Table 4:

[0154] Table 4

[0155] The N2O conversion results are shown in the following table: Table 5

[0156] The Fe-Nu-86 catalyst synthesized according to the invention provides superior DeN2O performance to the Fe-FER catalyst with lower temperature initiation. It also provides almost similar performance 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, 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 / AhO3 between 8 and 20 IW / SiCh between 15 and 60 R / SiC>2 Between 0.05 and 0.35 Na2O / SiC>2 between 0.05 and 0.3, NaBr / SiCh between 0.01 and 0.1 inclusive, step i) being conducted for a period of between 5 and 15 minutes until a homogeneous mixture called precursor gel is obtained; ii) The maturation of the precursor gel from 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 20 hours. A process according to claim 1 wherein steps iv) and v) are reversed, and optionally repeated. A preparation process according to claim 2, wherein the Nu-86 zeolite obtained in step iii) directly undergoes a heat treatment step v), then at least one ion exchange with an acid, or a compound such as ammonium chloride, sulfate or nitrate to obtain a calcined Nu-86 zeolite in protonated form, before the ion exchange step iv) with iron.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 of between 0.01 and 10% of the total mass of the tetravalent (Si) and trivalent (Al) element sources in their oxide form (SiC2 and Al2O3) in anhydrous form used in the reaction mixture, said crystal seeds not being included in the total mass of the tetravalent and trivalent element sources. A preparation method 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.A 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 is directly obtained by the preparation process according to any one of claims 1 to 5. A catalyst according to claim 6, 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. 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, wherein the gas to be treated is contacted with a catalyst according to any one of claims 6 to 7.A process for the decomposition of N2O or the reduction of N2O or the simultaneous reduction of NOx and N2O according to claim 8, wherein said catalyst is formed by deposition as a coating on a honeycomb structure or a plate structure, or said catalyst is in the form of an extrudate or a bead, containing up to 100% of said catalyst.

10. A method for decomposing N2O or reducing N2O or simultaneously reducing NOx and N2O according to claim 9, 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.

11. A process for the decomposition of N2O or the reduction of N2O or the simultaneous reduction of NOx and N2O according to claim 10, wherein the quantity 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.

12. 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 9 to 11, 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.

13. A process for decomposing N2O or reducing N2O or simultaneously reducing NOx and N2O according to any one of claims 8 to 12, wherein 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.

Images