SYNTHESIS OF A CATALYST COMPRISING AN IZM-10 ZEOLITE OF AEI STRUCTURAL TYPE AND AT LEAST ONE TRANSITION METAL FOR THE SELECTIVE REDUCTION OF NOx

Abstract

The invention relates to a catalyst for the selective reduction of NOx, based on an IZM-10 zeolite of AEI structural type and at least one transition metal and its preparation process comprising at least the mixing in aqueous medium of a zeolite of FAU structural type having a SiO2 (FAU) / Al2O3 (FAU) molar ratio of between 10 and 60, limits included and a mass percentage of sodium in cationic form of less than 0.005%, of a nitrogenous organic compound R, R being (6R,10S)-6,10-dimethyl-5-azoniaspiro[4,5]decane in its hydroxide form and optionally sodium hydroxide, until a homogeneous precursor gel is obtained; ii) a hydrothermal treatment iii) at least one ion exchange with a solution comprising at least one species capable of releasing a transition metal iv) a heat treatment by drying and calcination. Figure to be published: Figure 2

Description

Title of the invention: SYNTHESIS OF A CATALYST COMPRISING AN IZM-10 ZEOLITE OF AEI STRUCTURAL TYPE AND AT LEAST ONE TRANSITION METAL FOR THE SELECTIVE REDUCTION OF NOx Technical field

[0001] The subject of the invention is a process for preparing a catalyst based on an IZM-10 zeolite of structural type AEI and at least one transition metal, the catalyst prepared or capable of being prepared by the process, and its use for the selective catalytic reduction of NOx in the presence of a reducing agent, in particular for the combustion gases of internal combustion engines. Prior art

[0002] Nitrogen oxide (NOx) emissions resulting from combustion are a major concern for society as they are responsible for health problems, tropospheric ozone, acid rain and smog (which can be translated as smoke or haze). Increasingly stringent standards are being put in place by government bodies to limit the impact on the environment and on health. Highly efficient pollution control systems such as three-way catalysts or selective catalytic reduction catalysts, designated by the English acronym "SCR" for "Selective Catalytic Reduction", have therefore been developed to equip means of transport in order to achieve these objectives. Selective catalytic reduction is carried out using a reducing agent, generally ammonia, and can therefore be designated by NH3-SCR.Ammonia (NH3) involved in the SCR process is typically generated via the decomposition of an aqueous urea solution (e.g., a commercial AdBlue or DEF-type solution), and produces N2 and H2O upon reaction with NOx.

[0003] Zeolites exchanged with transition metals are used in particular as catalysts for NH3-SCR applications in transport. Small-pore zeolites, in particular of the AEI and CHA structural type exchanged with copper, are particularly suitable.

[0004] Zeolites of structural type AEI include in particular zeolite SSZ-39 (Wagner, P et al., J. Am. Chem. Soc., 122, 263-273 (2000)), and zeotypes ALPO-18 (Simmen, A. et al., Zeolites, 11, 654-661 (1991)) and SAPO-18 (Chen, JS et al., Catalysis Letters, 28, 241-248 (1994)). The structural type "AEI" is defined by the "Structure Commission" of the International Zeolite Association (IZA).

[0005] Zeolites of structural type AEI have a three-dimensional system of pores delimited by eight TO4 tetrahedra and obtained by the three-dimensional connection of double cycles of atoms T (D6R) or T can be silicon, aluminum or phosphorus. Many methods for synthesizing zeolites of structural type AEI are known. They require the simultaneous use of an organic structuring agent and an inorganic base (sodium or potassium hydroxide). To obtain the protonated form of the zeolite, it is necessary to carry out an ion exchange step with NH4NO3, NH4CI, ammonium acetate or any other aqueous source of ammonium cations.

[0006] Patent application CN112758954 presents the synthesis of a core-layer SSZ-39 zeolite where the core contains copper. The synthesis is carried out in the presence of sodium or potassium hydroxide in the presence of an organic structuring agent chosen from the ions of: N,N-diethyl-2,6-dimethylpiperidine, 1,1,3,5-tetramethylpiperidine, 2,6-dimethyl-5-azoniumspiro-[4,5]-decane, N,N-diethyl-2-ethylpiperidine, N-ethyl-N-propane-2,6-dimethylpiperidine, N-methyl-N-ethyl-2,6-dimethylpiperidine, N-methyl-N-ethyl-2-ethylpiperidine, 2,5-dimethyl-N,N-diethylpyrrole, 2,6-dimethyl-N,N-dimethylpiperidine, 3,5-dimethyl-N,N-dimethylpi peridine, 2-Ethyl-N,N-dimethylpiperidine, 2,2,6,6-Tetramethyl-N-methyl-N-ethylpiperidine, N-cyclooctyl-pyridine, 2,2,6,6-tetramethyl-N,N-dimethylpiperidine and N,N-dimethyl-N,N-bicyclononane, preferably the organic structuring agent is chosen from: N,N-diethyl-2,6-dimethylpiperidine and / or 3,5-dimethyl-N,N-dimethylpiperidine.The molar ratio Na2O(NaOH) / SiO2 in the synthesis mixture is between 0.05 and 0.25. To obtain the protonated form of the zeolite, it is necessary to carry out an ion exchange step with NH4NO3.

[0007] Patent application US2022106192 presents the synthesis of a zeolite of structural type AEI in the presence of an organic structuring agent of N,N-dialkyl-dialkylpiperidinium cation type of N,N-(Cl-C3)-dialkyl-(Cl-C3)-dialkylpiperldinium cation, preferably an N,N-(Cl-C2)-dialkyl-(Cl-C3)-dialkylpiperidinium cation, preferably the N,N-diethyl-2.6-dimethylpiperidinium cation, more preferably the N,N-diethyl-cis-2.6-dimethylpiperidinium cation. The synthesis of the zeolite is carried out in the presence of sodium hydroxide in addition to any other source of Na cations. The molar ratio Na2O(NaOH) / SiO2 in the synthesis mixture is between 0.25 and 1. Preferably, the synthesis gel does not contain a zeolite of the FAU structural type. To obtain the protonated form of the zeolite, it is necessary to carry out an ion exchange step with NH4NO3.

[0008] The article “Hydrothermal Conversion of Titanated FAU to AEI Zeolite and Its Enhanced Catalytic Performance for NOx Reduction” (Adv. Porous Mater. 2016, VOL 4, No. 1, 62) presents the synthesis of an AEI zeolite using [Al, Ti] FAU zeolite as a source of silicon and aluminum in the presence of sodium hydroxide and the organic structuring agent: 1,1-diethyl-2,6-dimethylpiperidinium hydroxide (DEDMPOH). The molar ratio Na2O(NaoH) / SiO2 in the synthesis mixture is 0.1. To obtain the protonated form of the zeolite, it is necessary to carry out an ion exchange step with NH4NO3.

[0009] Patent application CN105314646A presents the synthesis of a zeolite of structural type AEI in the presence of an organic structuring agent chosen from the cations: 1-methyl-2,6-dimethyl-piperidine, l-ethyl-2,6-dimethyl-piperidine, l-methyl-3,5-dimethyl-piperidine, l-ethyl-3,5-dimethyl-piperidine, l,l-dimethyl-2,6-dimethyl-pipe ridine, l,l-diethyl-2,6-dimethyl-piperidine, l,l-dimethyl-3,5-dimethyl-piperidine, 1-ethyl-3,5-dimethyl-piperidine, l,l-bis-ethyl-2,6-dimethyl-piperidine, l,l-diethyl-3,5-dimethyl-piperidine. The synthesis of AEI structural type zeolite is carried out in the presence of sodium or potassium hydroxide. The molar ratio Na2O(NaOH) / SiO2 in the synthesis mixture is between 0.1 and 0.5. To obtain the protonated form of the zeolite, an ion exchange step with NH4 NO3 is necessary.

[0010] Patent application CN107285333A presents the synthesis of a zeolite of structural type AEI using microwaves and in the presence of an organic structuring agent chosen from the cations: 1,1,2,2,6,6-hexamethylpiperidinium, 1,1,2,2,6,6-hexamethyl-4-oxo-piperidinium, 1,1,3,5-tetramethyl-4-oxo-piperidine, 1 -hydroxy-1,1,2,2,6,6-hexamethylpiperidinium, 1,1 -dimethyl-4,4-propoxypiperidinium, 3,5-dimethoxy-l,l-dimethyl piperidinium, 3,5-dihydroxy-l,l-dimethyl piperidinium, 4-ethyl-l,l-dimethyl-3,5-dioxo-pyridinium, l-ethyl-l-methyl-2,2,6-methyl-piperidine, l-epoxy-propyl-l-methyl-2,2,6,6-hexamethylpiperidinium. The synthesis of the AEI structural type zeolite is carried out in the presence of sodium or potassium hydroxide. The molar ratio Na2O(NaOH) / SiO2 in the synthesis mixture is between 0.1 and 0.5.

[0011] Patent application CN107308980A presents the use of a zeolite of structural type AEI containing copper in NH3-SCR. The synthesis of zeolite of structural type AEI is carried out in the presence of sodium hydroxide and an organic structuring agent chosen from the cations: 1,1,2,2,6,6-hexamethylpiperidinium, 1,1,2,2,6,6-hexamethyl-4-oxo-piperidinium, 1,1,3,5-tetramethyl-4-oxo-piperidine, 1-hydroxy-1,1,2,2,6,6-hexamethylpiperidinium, 1,1-dimethyl-4,4-propoxypiperidinium, 3,5-dimethoxy-l,l-dimethyl piperidinium, 3,5-dihydroxy-l,l-dimethyl piperidinium, 4-ethyl-l,l-dimethyl-3,5-dioxo-pyridinium, l-ethyl-l-methyl-2,2,6-methyl-piperidine, l-epoxy-propyl-l-methyl-2,2,6,6-hexamethylpiperidinium. The molar ratio of Na2O (NaOH) / SiO2 in the synthesis mixture is between 0.1 and 0.5.

[0012] Patent US5958370 presents the synthesis of a SSZ-39 zeolite of structural type AEI in the presence of sodium hydroxide and an organic structuring agent chosen from the cations: N,N-Diethyl-2,6-dimethylpiperidinium, N,N-Dimethyl-9-azoniabicyclo[3. 3. l]nonane, N,N-Dimethyl-2,6-dimethylpiperidinium, N-Ethyl-N-methyl-2,6-dimethylpiperidinium, N,N-Diethyl-2-ethylpiperidinium, N,N-Dimethyl-2-(2-hydroxyethyl)piperidinium, N,N-Dimethyl-2-ethylpiperidinium, N,N-Dimethyl-3,5-dimethylpiperidinium, N-Ethyl-N-methyl-2-ethylpiperidinium, 2,6-Dimethyl-1-Azonium[5.4]decane, N-Ethyl-N-propyl-2,6-dimethylpiperidinium, 2,2,4,6,6-Pentamethyl-2-azoniabicyclo[3.2.1]octane, N,N-Diethyl-2,5-dimethyl-2,5-dihydr opyrrolium. The molar ratio Na2O(NaOH) / SiO2 in the synthesis mixture is between 0.3 and 1. The synthesis times are greater than 6 days. According to this patent the structuring agents: N,N-Dimethyl-2-ethylpiperidinium, N-Ethyl-N-methyl-2-ethylpiperidinium, 2,6-Dimethyl-1-Azonium[5.4]decane and N-Ethyl-N-propyl-2,6-dimethylpiperidinium do not allow to obtain a pure SSZ-39 zeolite of AEI structural type, analcime impurities are present. To obtain the protonated form of the zeolite it is necessary to carry out an ion exchange step with NH4 NO3.

[0013] Patent application US2017128921 presents the synthesis of a zeolite of structural type AEI in the presence of sodium hydroxide and an organic structuring agent chosen from the cations: N,N-dimethyl-3,5-dimethylpiperidinium, N,N-dimethyl-2-(2-hydroxyethyl)piperidinium, N,N-dimethyl-2-ethylpiperidinium and 2,2,4,6,6-pentamethyl-2-azoniabycyclo[3.2.1]octane. The molar ratio Na2O(NaOH) / SiO2 in the synthesis mixture is between 0.2 and 1. To obtain the protonated form of the zeolite, it is necessary to carry out an ion exchange step with ammonium acetate.

[0014] The article “Transformation synthesis of aluminosilicate SSZ-39 zeolite from ZSM-5 and beta zeolite” (J. Mater. Chem. A, 2019, 7, 4420) presents the synthesis of an SSZ-39 zeolite of structural type AEI by interzeolitic transformation in the presence of the organic structuring agent N,N-diethyl-cis-2,6-dimethylpiperidine hydroxide and sodium hydroxide. The molar ratio Na2O(NaOH) / SiO2 in the synthesis mixture is 0.17. To obtain the protonated form of the zeolite, it is necessary to carry out an ion exchange step with NH4NO3.

[0015] The article “Synthesis of high-silica AEI zeolites with enhanced thermal stability by hydrothermal conversion of FAU zeolites, and their activity in the selective catalytic reduction of NOx with NH3 (J. Mater. Chem. A, 2015, 3, 857) presents the synthesis of a zeolite of structural type AEI by interzeolite transformation in the presence of the organic structuring agent tetraethylphosphonium in a fluoride medium. This synthesis makes it possible to obtain a zeolite of structural type AEI more stable at high temperature than that obtained with the organic structuring agent N,N-diethyl-2,6-dimethylpiperidinium in a basic medium. The molar ratio Na2O(NaOH) / SiO2 in the synthesis mixture is 0.05. To obtain the protonated form of the zeolite, it is necessary to carry out an ion exchange step with NH4C1.

[0016] Patent application US2018093257 presents the synthesis of a JMZ-8 zeolite of structural type AEI in the presence of sodium hydroxide and an organic structuring agent R chosen from N,N-diethyl-cis-2,6-dimethylpiperidinium or NN-Dimethyl-3.5-dimethylpiperidinium. The molar ratio Na2O(NaOH) / Al2O3 in the synthesis mixture is between 0.5 and 2. The purity of the AEI zeolite obtained is greater than 90%. To obtain the protonated form of the zeolite, it is necessary to carry out an ion exchange step with NH4NO3.

[0017] Patent application US2018093256 presents the synthesis of a JMZ-9 zeolite of structural type AEI in the presence of an organic structuring agent R chosen from N,N-diethyl-cis-2,6-dimethylpiperidinium or NN-Dimethyl-3.5-dimethylpiperidinium or the mixture of the two. The molar ratios claimed are: (SiO2)) / (Al2O3) between 20 and 50, H2O / SiO2 between 10 and 40, R / SiO2 between 0.25 and 1, HO / SiO2 between 0.25 and 1,

[0018] Patent application US2020-0360906A1 presents the synthesis of a JMZ-8 zeolite of structural type AEI in the presence of sodium hydroxide and an organic structuring agent R chosen from N,N-diethyl-cis-2,6-dimethylpiperidinium or NN-Dimethyl-3.5-dimethylpiperidinium. The molar ratio Na2O(NaoH) / Al2O3 in the synthesis mixture is between 0.5 and 2. The purity of the AEI zeolite obtained is greater than 90%. To obtain the protonated form of the zeolite, it is necessary to carry out an ion exchange step with NH4NO3.

[0019] Patent application WO2016 / 166245 presents the synthesis of a zeolite of structural type AEI in the presence of sodium hydroxide and an organic structuring agent chosen from: NN-Dimethyl-3.5-dimethylpiperidinium, N,N-diethyl-2,6-dimethylpiperidinium (DEDMP), N,N-dimethyl-2,6-dimethylpiperidinium, N-ethyl-N-methyl-2,6-dimethylpiperidinium alone or in a mixture. The molar ratio Na2O(NaOH) / A12O3 in the synthesis mixture is between 0.001 and 2. To obtain the protonated form of the zeolite, it is necessary to carry out an ion exchange step with NH4 NO3. Summary of the invention

[0020] The applicant has discovered that it is possible to directly prepare a catalyst based on an IZM-10 zeolite of AEI structural type obtained directly in at least partially protonated form and that a catalyst based on an IZM-10 zeolite of AEI structural type prepared according to a particular synthesis method and at least one transition metal, in particular copper, has interesting NOx conversion performance. For the purposes of the present invention, the term "partially protonated" means an AEI zeolite comprising an Al2O3 / Na2O molar ratio of between 100 and 400, and "fully protonated" means an AEI zeolite comprising an Al2O3 / Na2O molar ratio of greater than 400. The process for synthesizing the catalyst according to the invention thus makes it possible to dispense with the additional step of ion exchange with ammonium nitrate while guaranteeing better exchange with the transition metal.The NOx conversion performances are improved, in particular the initiation temperatures are notably lower than those obtained with prior art catalysts, such as catalysts based on zeolite of the CHA or AEI structural type exchanged with copper, while presenting lower nitrous oxide N2O emissions. This catalyst also presents a high thermal and hydrothermal stability.

[0021] The invention relates to a process for preparing a catalyst based on an IZM-10 zeolite of AEI structural type and at least one transition metal comprising at least the following steps:

[0022] i) the mixture in aqueous medium of a zeolite of structural type FAU having a molar ratio SiO2 (FAu) / A12O3 (FAu) of between 10 and 60, limits included and a mass percentage of sodium in cationic form of less than 0.005%, of an organic nitrogen compound R, R being (6R,10S)-6,10-dimethyl-5-azoniaspiro[4,5]decane in its hydroxide form and optionally sodium hydroxide, the reaction mixture having the following molar composition:

[0023] -(SiO2 (fau)) / (A12O3 (fau)) between 10 and 60, preferably between 30 and 50

[0024] -H2O / (SiO2 (fau)) between 20 and 60, preferably between 30 and 50

[0025] -R / (SiO2 (fau)) between 0.05 and 0.70, preferably between 0.15 and 0.60

[0026] -Na2O (NaoH) / (SiO2 (FAu)) between 0 and 0.20, preferably between 0 and 0.15

[0027] -Na2O (FAU) / (SiO2(FAU)) between 3.5*105 and 7*105, preferably between 4* 105 and 6*105

[0028] in which Na2O (Fau) denotes the quantity of Na2O provided by the FAU zeolite, Na2O (NaoH) denotes the quantity of Na2O provided by the soda, SiO2(pAu) denotes the quantity of SiO2 provided by the FAU zeolite, and A12O3 (Fau) denotes the quantity of Al2 O3 provided by the FAU zeolite, until a homogeneous precursor gel is obtained;

[0029] ii) the hydrothermal treatment of said precursor gel obtained at the end of step i) at a temperature between 120°C and 220°C, for a period between 12 hours and 7 days until an AEI zeolite is obtained;

[0030] iii) 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 a transition metal, in solution in reactive form with stirring at room temperature for a period of between 1 hour and 2 days;

[0031] iv) a heat treatment by drying the solid obtained at the end of the previous step at a temperature between 20 and 150°C followed by at least one calcination under air flow at a temperature between 400 and 700°C for a duration between 8 and 24 hours.

[0032] Steps iii) and iv) may be repeated.

[0033] Said transition metal released in the exchange solution of step iii) can be selected from the group formed by the following elements: Ti, V, Mn, Mo, Fe, Co, Cu, Cr, Zn, Nb, Ce, Zr, Rh, Pd, Pt, Au, W, Ag, preferably from the group formed by the following elements: Fe, Cu, Nb, Ce or Mn, more preferably from Fe, Ce or Cu, alone or in a mixture and even more preferably said transition metal is Cu.

[0034] The SiO2 / Al2O3 molar ratio of the AEI zeolite is advantageously between 10 and 60, preferably between 12 and 50, limits included, and the Al2O3 / Na2 O molar ratio of the AEI zeolite is advantageously greater than 100 and preferably greater than 400,

[0035] The FAU structural type zeolite may have a SiO2 / Al2O3 molar ratio of between 20 and 50, inclusive, and a mass percentage of Na2O of less than 0.0048%.

[0036] In one embodiment, no sodium hydroxide is added to the reaction mixture of step i) (Na2O(NaoH / (SiO2(FAU)) = 0).

[0037] Crystalline seeds of a zeolite of structural type AEI can 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 Al2O3.

[0038] 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.

[0039] The hydrothermal treatment of step ii) can be carried out under autogenous pressure at a temperature between 120°C and 220°C, preferably between 150°C and 200°C, even more preferably between 160°C and 195°C, for a period of between 12 hours and 7 days, preferably between 12 hours and 6 days.

[0040] The solid phase obtained at the end of step ii) can be filtered, washed, and dried at a temperature between 20 and 150°C, preferably between 60 and 100°C, for a period of between 5 and 24 hours to obtain a dried zeolite.

[0041] The dried zeolite can then be calcined at a temperature between 450 and 700°C for a period of between 2 and 20 hours, the calcination possibly being preceded by a gradual increase in temperature.

[0042] The content of transition metal(s) introduced by the ion exchange step iii) 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.

[0043] The invention also relates to a catalyst for the selective reduction of NOx capable of being obtained by the preparation process according to any one of its variants comprising:

[0044] -a zeolite of structural type AEI with a SiO2 / Al2O3 molar ratio of between 10 and 60, inclusive, and a purity greater than or equal to 98% by weight, preferably greater than or equal to 99% by weight;

[0045] -and 0.5 to 6% of a transition metal, preferably copper,

[0046] The invention also relates to a process for the selective reduction of NOX by a reducing agent such as NH3 or H2 using the catalyst previously described or the catalyst directly obtained by the preparation process according to any one of its variants for the selective reduction of NOX by a reducing agent such as NH3 or H2.

[0047] The catalyst may be formed by deposition in the form of 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.

[0048] The honeycomb structure may be formed of parallel channels open at both ends or comprise porous filtering walls for which the adjacent parallel channels are alternately blocked on either side of the channels.

[0049] The quantity of catalyst deposited on said structure can be between 40 and 250 g / L for filter structures and between 60 and 300 g / L for structures with open channels.

[0050] 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 pollutant adsorption capacities in particular of NOx, reduction of pollutants in particular NOx or promoting the oxidation of pollutants.

[0051] Said catalyst can be integrated:

[0052] - in an exhaust line of an internal combustion engine operating at from carbon-based or non-carbon fuels, or

[0053] - in a reactor for treating industrial fumes. LIST OF FIGURES [Fig 1]

[0054] [Fig. 1] represents the chemical formula of the organic nitrogen compound (6R,10S)-6,10-dimethyl-5-azoniaspiro[4,5]decane in its hydroxide form used in the synthesis process according to the invention. [Fig 2]

[0055] [Fig.2] represents the conversion C in % obtained during a catalytic test for the reduction of nitrogen oxides (NOx) by ammonia (NH3) in the presence of oxygen (O2) as a function of the temperature T in °C, for the catalysts synthesized according to examples 2, 3 and 4, CuIZM-10 curve symbolized by the triangles, CuCHA, comparative, curve symbolized by the circles and CuAEI, comparative, curve symbolized by the squares.

[0056] Other characteristics and advantages of the synthesis process according to the invention, of the catalyst according to the invention and of the use 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. Description of the embodiments Preparation process

[0057] The invention relates to a process for preparing a catalyst based on an IZM-10 zeolite of AEI structural type and at least one transition metal comprising at least the following steps:

[0058] Step i) of mixing:

[0059] Step i) comprises mixing in an aqueous medium, a zeolite of structural type FAU having a molar ratio SiO2 (fau) / A12O3 (Fau) of between 10 and 60, limits included and a mass percentage of sodium in cationic form of less than 0.005%, of an organic nitrogen compound R, R being (6R,10S)-6,10-dimethyl-5-azoniaspiro[4,5]decane in its hydroxide form and optionally sodium hydroxide, the reaction mixture having the following molar composition:

[0060] (SiO2 (fau)) / (A12O3 (fau)) between 10 and 60, preferably between 30 and 50

[0061] H2O / (SiO2 (fau)) between 20 and 60, preferably between 30 and 50

[0062] R / (SiO2 (fau)) between 0.05 and 0.70, preferably between 0.15 and 0.60

[0063] Na2O(NaoH) / (SiO2(FAU)) between 0 and 0.20, preferably between 0 and 0.15

[0064] Na2O (fau / (SiO2 (FAu)) between 3.5*105 and 7*10\ preferably between 4*105 and 6*105

[0065] in which Na2O (FAu) denotes the quantity of Na2O provided by the FAU zeolite, Na2O (NaoH) denotes the quantity of Na2O provided by the soda, SiO2(FAU) denotes the quantity of SiO2 provided by the FAU zeolite, and A12O3 (FAu) denotes the quantity of Al2 O3 provided by the FAU zeolite, until a homogeneous precursor gel is obtained.

[0066] Advantageously, the SiO2 / Al2O3 molar ratio of the AEI zeolite obtained can be between 10 and 60, preferably between 12 and 50, limits included.

[0067] The zeolite of structural type FAU used in the reaction mixture of step i) has a SiO2 / Al2O3 molar ratio of between 10 and 60, preferably of between 20 and 50, limits included, and a mass percentage of Na2O of less than 0.005%, preferably less than 0.048%.

[0068] The low amount of sodium in the starting FAU zeolite helps to minimize the sodium content in the synthesis reaction mixture while facilitating zeolitization towards a zeolite of AEI structural type, and the AEI zeolite is thus obtained in at least partially protonated form.

[0069] For the purposes of the present invention, the term “partially protonated” means an AEI zeolite comprising an Al2O3 / Na2O molar ratio of between 100 and 400, and “fully protonated” means an AEI zeolite comprising an Al2O3 / Na2O molar ratio of greater than 400.

[0070] A ratio Na2O(NaoH) / (SiO2(FAU)) = 0 means that there is no sodium hydroxide added to the synthesis gel, which makes it possible to obtain the AEI zeolite in protonated form directly.

[0071] Crystalline seeds of a zeolite of structural type AEI can 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 Al2O3.

[0072] 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.

[0073] Step ii) of hydrothermal treatment:

[0074] A hydrothermal treatment of said precursor gel obtained at the end of step i) is carried out at a temperature of between 120°C and 220°C, for a period of between 12 hours and 7 days.

[0075] The hydrothermal treatment of step ii) can be carried out under autogenous pressure at a temperature between 120°C and 220°C, preferably between 150°C and 200°C, even more preferably between 160°C and 195°C, for a period of between 12 hours and 7 days, preferably between 12 hours and 6 days.

[0076] The solid phase obtained at the end of step ii) can be filtered, washed, and dried at a temperature between 20 and 150°C, preferably between 60 and 100°C, for a period of between 5 and 24 hours to obtain a dried zeolite.

[0077] The dried zeolite can then be calcined at a temperature of between 450 and 700°C for a period of between 2 and 20 hours, the calcination possibly being preceded by a gradual increase in temperature.

[0078] The zeolite of structural type AEI with a SiO2 / Al2O3 molar ratio of between 10 and 60, inclusive, obtained by the preparation process described above, advantageously exhibits the following significant X-ray diffraction lines:

[0079] [Tables 1] 2 Ma O 2 theta n tel 9.530 9.241 FF 25.371 3.508 ff. 10.690 8.268 f 26.066 3.416 ff. 13.000 6.805 n 26.47 3.365 f 13.554 6.528 n. 27.317 3.262 ff. 14.019 6.312 a .28.002 3.184 t 14.811 5.976 a 29.481 3.027 n 16.179 5.474 f 29.841 2.992 ff. 17,019 5,206 te 30,19 2,958 ff 17,313 5,118 te 30,605 2.919 H 19,179 4,624 ff 31,033 2,879 El 19,762 4,489 ff 31,335 2,852 F 20,158 4,402 ff 31,869 2,806 Et 20,78 4,271 f 32,409 2,760 F 21,472 4,135 f 32,924 2.718 a 22,103 4,018 ff 33,206 2,696 a 22,609 3,930 S 33.986 2.636 M 23.288 3.817 ff 34.514 2.597 M 24.078 3.693 te 34.994 2.562 And

[0080] where FF = very strong; F = strong; m = medium; mf = medium weak; f = weak; ff = very low. 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 in the X-ray diffraction pattern: ff <15; 15 <f <30 ; 30 < mf <50 ; 50 <m < 65 ; 65 <F < 85 ; FF >85;

[0081] and a purity greater than or equal to 98%, preferably greater than or equal to 99% by weight, as well as an Al2O3 / Na2O molar ratio greater than 100 and preferably greater than 400.

[0082] Step iii) of ion exchange:

[0083] Step iii) includes 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 a transition metal, in particular copper, in solution in reactive form with stirring at room temperature for a period of between 1 hour and 2 days.

[0084] Said transition metal released in the exchange solution of step iii) can be selected from the group formed by the following elements: Ti, V, Mn, Mo, Fe, Co, Cu, Cr, Zn, Nb, Ce, Zr, Rh, Pd, Pt, Au, W, Ag, preferably from the group formed by the following elements: Fe, Cu, Nb, Ce or Mn, more preferably from Fe, Ce or Cu, alone or in a mixture and even more preferably said transition metal is Cu.

[0085] The content of transition metal(s) introduced by the ion exchange step iii) 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.

[0086] Step iv) of heat treatment:

[0087] Step iv) comprises a heat treatment by drying the solid obtained at the end of the previous step at a temperature between 20 and 150°C followed by at least one calcination under air flow at a temperature between 400 and 700°C for a duration between 8 and 24 hours.

[0088] Steps iii) and iv) may optionally be repeated, for example to increase the metal content. The catalyst

[0089] The catalyst according to the invention comprises at least one IZM-10 zeolite of AEI type, and at least one additional transition metal, preferably copper.

[0090] According to the invention, the transition metal or metals included in the catalyst is (are) selected from the elements from the group formed by the elements of groups 3 to 12 of the periodic table of elements including the lanthanides.

[0091] In particular, the transition metal or metals included in the catalyst is (are) selected from the group formed by the following elements: Ti, V, Mn, Mo, Fe, Co, Cu, Cr, Zn, Nb, Ce, Zr, Rh, Pd, Pt, Au, W, Ag, preferably from the group formed by the following elements: Fe, Cu, Nb, Ce or Mn, more preferably from Fe, Ce or Cu alone or in mixture and even more preferably said transition metal is Cu.

[0092] In the catalyst according to the invention, the content of transition metal(s), in particular copper, is between 0.5 and 6% by mass, preferably between 0.5 and 5% by mass, more preferably between 1 and 4% relative to the total mass of the final anhydrous catalyst.

[0093] Characterization of the catalyst prepared according to the invention

[0094] X-ray diffraction makes it possible to verify that the solid obtained by the process according to the invention is indeed a zeolite of structural type AEI. The purity obtained is advantageously greater than 98% and preferably greater than or equal to 99% by weight, even more preferably greater than or equal to 99.8% by weight.

[0095] This diffraction diagram is obtained by radiocrystallographic analysis using a diffractometer using the classical powder method with Ka 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(dhld) on dhk 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 in Angstroms (Â). Each of these values ​​must be assigned the measurement error A(dhki) between ± 0.6Â and ± 0.01Â.

[0096] X-ray fluorescence (FX) spectrometry 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 accurate and reproducible results. X-rays are used to excite the atoms in the sample, causing them to emit X-rays with an 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.

[0097] 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 5 and 25% 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.

[0098] Process for the selective reduction of NOx by a reducing agent such as NH 3 using 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 selective reduction of NOx by a reducing agent such as NH3 or H2, 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 particularly found for stationary applications. The invention can also be shaped in the form of extrudates or beads.

[0100] The honeycomb structure is formed of parallel channels open at both ends (flow-through in English) or comprises 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, FeCrAl type steel.

[0101] The quantity of catalyst according to the invention deposited on said structure can be between 40 and 250 g / L for filtering structures and between 60 and 300 g / L for structures with open channels.

[0102] The coating itself ("washcoat") comprises the catalyst according to the invention, advantageously associated 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, 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.

[0103] 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 particularly NOx or promoting the oxidation of pollutants, particularly that of ammonia.

[0104] Another possibility is to put the catalyst in extruded form. In this case, the structure obtained can contain up to 100% of catalyst according to the invention.

[0105] Said structure coated with the catalyst according to the invention can advantageously be integrated into an exhaust line of an internal combustion engine operating mainly in a lean mixture, that is to say in excess air compared to the stoichiometry of the combustion reaction as is the case for Diesel engines or H2 combustion engines for example. Under these operating conditions of the Diesel engine, the exhaust gases contain in particular the following pollutants: soot, unburned hydrocarbons (HC), carbon monoxide (CO), nitrogen oxides (NOx). In the case of H2 combustion, the soot, HC and CO contents are very low because they come only from the lubricant, but nitrogen oxides are always present and the water content (H2O) is much higher than in the case of Diesel combustion.Upstream of said structure coated with the catalyst according to the invention, an oxidation catalyst may be placed whose function is to oxidize HC and CO as well as a filter to remove soot from the exhaust gases, the function of said coated structure being to remove NOx, its operating range being between 100 and 900°C and preferably between 150°C and 500°C. Advantages of the invention

[0106] The catalyst according to the invention, based on an IZM-10 zeolite of AEI structural type and at least one transition metal, in particular copper, exhibits a notable gain in initiation compared to the catalysts of the prior art, such as catalysts based on zeolite of CHA or AEI structural type exchanged with copper. In particular, the use of the catalyst according to the invention makes it possible to obtain lower initiation temperatures for the NOx conversion reaction when the water content is high in the gases to be treated while ensuring very good selectivity for N2O. EXAMPLES

[0107] The invention is illustrated by the following examples which are in no way limiting.

[0108] Example 1: preparation of (6R,10S)-6,10-dimethyl-5-azoniaspiro[4,5]decane in its hydroxide form (structuring R).

[0109] In a 500 mL two-necked flask containing 140 mL of water, 5.68 g (0.142 mol) of sodium hydroxide and 30.66 g (0.142 mol, 16.82 mL) of 1,4-dibromobutane are added with stirring. The mixture is heated to reflux and 16.07 g (0.142 mol, 19.13 mL) of (2R,6S)-2,6-dimethylpiperidine are added dropwise over half an hour using a dropping funnel. After twelve hours of reflux, the mixture is cooled to 0°C and 70 mL of cold 40% NaOH solution is added. The precipitate formed is extracted three times with 200 mL of chloroform. The extracted organic fractions are evaporated to a volume of 100 mL and the amine, in its bromide form, is precipitated with ether. The reaction yield is approximately 80-85%.

[0110] Molecular formula: CnH22NBr

[0111] Molar mass: 248 g / mol

[0112] 1H NMR (D2O, 400MHz, 25°C, δppm) for (6R,10S)-6,10-dimethyl-5-azoniaspiro [4,5]decane (cis-trans mixture): 1.30 (d, 6H, CH3); 1.55 (m, 4H, CH2); 1.70 (m, 2H, CH2); 2.10 (m, 4H,CH2); 3.28 (t, 2H, CH2-N); 3.50 (t, 2H, CH2-N); 3.64 (m, 2H, CH-N).

[0113] 18.9 g of Ag2O (0.08 mol, 99%, Aldrich) are added to a Teflon beaker of 250 mL containing 20 g of (6R,10S)-6,10-dimethyl-5-azonias piro[4,5]decane bromide (0.08 mol) and 100 mL of deionized water. The reaction medium is stirred away from light for 12 hours. The mixture is then filtered and part of the water is evaporated using a rotary evaporator. The filtrate obtained is composed of an aqueous solution of (6R,10S)-6,10-dimethyl-5-azoniaspiro[4,5]decane in its hydroxide form (29.06% by weight). The determination of this species is carried out by proton NMR using formic acid as a standard.

[0114] Example 2: preparation of an IZM-10 zeolite of AEI structural type according to the invention (with seeds).

[0115] 1.25 g of a zeolite of structural type FAU (CBV720, SiO2 / Al2O3= 33.34, Zeolyst, PAF = 14.34%, percentage of sodium in cationic form = 0.0045%) were mixed with 6.22 g of an aqueous solution of (6R,10S)-6,10-dimethyl-5-azo niaspiro[4,5]decane in its hydroxide form (29.06% by weight) prepared according to Example 1. 7.54 g of deionized water are added to the previous mixture, the preparation obtained is kept stirring for 10 minutes. In order to promote the formation of an IZM-10 zeolite of structural type AEI, 54 mg of seeds (5% relative to the mass of the CBV720 zeolite) of an IZM-10 zeolite of structural type AEI prepared according to Example 2 are added to the synthesis mixture and kept stirring for 5 minutes. The molar composition of the precursor gel is as follows: 1 SiO2: 0.03 Al2O3: 0.58 R: 40 H2O, i.e. a SiO2 / Al2O3 ratio of 33.3. The precursor gel is then transferred, after homogenization, into an autoclave.The autoclave is closed and then heated for 140 hours at 180°C with stirring at 35 rpm using a rotating spit system. The solid obtained is filtered, washed with deionized water and then dried overnight at 100°C. The loss on ignition of the dried solid is 10%. 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 temperature rise of 1°C / min up to 550°C followed by a hold at 550°C maintained for 8 hours and then a return to room temperature.

[0116] The calcined solid product was analyzed by X-ray diffraction and identified as consisting of an IZM-10 zeolite of structural type AEI with a purity greater than 99% by weight. X-ray fluorescence analysis gives a molar ratio SiO2 / A12O3 = 29.20 and a molar ratio Al2O3 / Na2O = 460.

[0117] Ion exchange with Cu

[0118] 1g of calcined IZM-10 zeolite is suspended in 30 mL of a 0.016 M [Cu(NH3)4](NO3)2 solution for 1 day with stirring at room temperature. The final solid is separated, washed and dried and calcined under a flow of dry air at 550°C for 8 hours.

[0119] Chemical analysis by X-ray fluorescence (FX) gave a SiO2 / Al2O3 molar ratio of 29.20 and a mass percentage of Cu of 2.78%.

[0120] The catalyst obtained is denoted CuIZM-10.

[0121] Example 3 (comparative): preparation of a Cu-CHA catalyst based on a commercial zeolite

[0122] 1g of commercial CHA type zeolite is suspended in 30 mL of a 0.016 M [Cu(NH3)4](NO3)2 solution for 1 day with stirring at room temperature. The final solid is separated, washed and dried and calcined under a flow of dry air at 550°C for 8 hours.

[0123] Chemical analysis by X-ray fluorescence (FX) gives a SiO2 / Al2O3 molar ratio of 17.8 and a mass percentage of Cu of 2.92%.

[0124] The catalyst obtained is denoted CuCHA.

[0125] Example 4 (comparative): preparation of a Cu-AEI catalyst based on a commercial zeolite

[0126] 1g of commercial AEI type zeolite is suspended in 30 mL of a 0.016 M [Cu(NH3)4](NO3)2 solution for 1 day with stirring at room temperature. The final solid is separated, washed and dried and calcined under a flow of dry air at 550°C for 8 hours.

[0127] Chemical analysis by X-ray fluorescence (FX) gives a SiO2 / Al2O3 molar ratio of 19.2 and a mass percentage of Cu of 2.85%.

[0128] The catalyst obtained is noted CuAEI.

[0129] Example 5: Conversion of NOx: comparison of copper catalysts according to the invention with the prior art

[0130] A catalytic test for the reduction of nitrogen oxides (NOx) by ammonia (NH3) in the presence of oxygen (O2) under Standard SCR conditions is carried out at different operating temperatures for the catalysts prepared according to Example 2 (CuIZM-10), Example 3 (CuCHA) and Example 4 (CuAEI).

[0131] For the testing of each sample, 200 mg of catalyst in powder form is placed in a quartz reactor. 145 L / h of a load representative of an exhaust gas mixture from an H2 engine is fed into the reactor.

[0132] This charge has the following molar composition: 450 ppm NO, 150 ppm NO2, 660 ppm NH3, 15% O2, 15% H2O, qpc N2.

[0133] An FTIR analyzer makes it possible to measure the concentration of the species NO, NO2, NH3, N2O, CO, CO2, H2O, O2 at the reactor outlet. The NOx conversions are calculated as follows:

[0134] Conversion = (NOx input -NOx output) / NOx input

[0135] The NOx conversion results are shown in [Fig.2], the curves marked by triangles, circles and squares corresponding respectively to the tests carried out with the catalysts synthesized according to Example 2 (CuIZM-10), Example 3 (CuCHA) and Example 4 (CuAEI). The catalyst according to the invention offers an optimized initiation temperature and therefore makes it possible to convert NOx at a lower temperature than the catalyst synthesized according to the prior art.

[0136] The CuIZM-10 catalyst synthesized according to the invention is particularly effective at low temperatures with 53% NOx conversion at 190°C while the CuAEI and CuCHA catalysts only offer 35% and 28% NOx conversion at this same temperature.

[0137] The ignition temperatures of catalysts containing 3% copper are given in Table 2 below for Standard-SCR conditions:

[0138] [Tables2] T50 T80 T90 CuIZM-10 188 °C 217 °C 231 °C CuCHA 207 °C 231 °C 242 °C CuAEI 202 °C 226 °C 238 °C

[0139] T50 corresponds to the temperature at which 50% of the NOx in the gas mixture are converted by the catalyst. T80 corresponds to the temperature at which 80% of the NOx in the gas mixture is converted by the catalyst. T90 corresponds to the temperature at which 90% of the NOx in the gas mixture is converted by the catalyst.

[0140] The CuIZM-10 catalyst synthesized according to the invention gives superior performances to the CuAEI and CuCHA catalysts synthesized according to the prior art. in terms of ignition temperatures and NOx conversion at low temperatures (T<300°C) under Standard SCR conditions. Indeed, at the same conversion rate (50% or 80%), the ignition temperatures obtained with the catalyst according to the invention CuIZM-10 are lower compared to those obtained with the CuAEI and CuCHA catalysts.

[0141] The maximum nitrous oxide (N2O) emissions are given in the following Table 3:

[0142] [Tables3] N2O max CuIZM-10 10 ppm CuCHA 17 ppm CuAEI 22 ppm

[0143] The CuIZM-10 catalyst synthesized according to the invention gives lower N2O emissions than the CuAEI and CuCHA catalysts synthesized according to the prior art.

Claims

1. Claims Process for preparing a catalyst based on an IZM-10 zeolite of AEI structural type and at least one transition metal comprising at least the following steps: i) the mixture in aqueous medium of a zeolite of structural type FAU having a molar ratio SiO2(FAU) / Al2O3(FAU) of between 10 and 60, limits included and a mass percentage of sodium in cationic form of less than 0.005%, of an organic nitrogen compound R, R being (6R,10S)-6,10-dimethyl-5-azoniaspiro[4,5]decane in its hydroxide form and optionally sodium hydroxide, the reaction mixture having the following molar composition: -(SiO2 (fau)) / (A12O3 (fau)) between 10 and 60, preferably between 30 and 50 -H2O / (SiO2 (fau)) between 20 and 60, preferably between 30 and 50 -R / (SiO2 (fau)) between 0.05 and 0.70, preferably between 0.15 and 0.60 -Na2O (NaOH) / (SiO2 (fau)) between 0 and 0.20, preferably between 0 and 0.15 -Na2O (FAU) / (SiO2 (fau)) between 3.5*105 and 7*105, preferably between 4*105 and 6*10 5 in which Na2O (FAu) denotes the quantity of Na2O provided by the FAU zeolite, Na2O (NaOH) denotes the quantity of Na2O provided by the soda, SiO2 (FAu) denotes the quantity of SiO2 provided by the FAU zeolite, and A12O3 (FAu) denotes the quantity of A12O3 provided by the FAU zeolite, until a homogeneous precursor gel is obtained; ii) the hydrothermal treatment of said precursor gel obtained at the end of step i) at a temperature of between 120°C and 220°C, for a period of between 12 hours and 7 days until an AEI zeolite is obtained; iü) 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 a transition metal, in solution in reactive form with stirring at room temperature for a period of between 1 hour and 2 days; iv) heat treatment by drying the solid obtained at the end of the previous step at a temperature between 20 and 150°C followed by at least one calcination under air flow at a temperature between 400 and 700°C for a duration between 8 and 24 hours.

2. A preparation process according to claim 1 wherein steps iii) and iv) are repeated.

3. Preparation process according to one of claims 1 or 2 wherein said transition metal released in the exchange solution of step iii) is selected from the group formed by the following elements: Ti, V, Mn, Mo, Fe, Co, Cu, Cr, Zn, Nb, Ce, Zr, Rh, Pd, Pt, Au, W, Ag, preferably from the group formed by the following elements: Fe, Cu, Nb, Ce or Mn, more preferably from Fe, Ce or Cu, alone or in a mixture and even more preferably said transition metal is Cu.

4. Process for preparing a catalyst according to one of claims 1 to 3 in which the SiO2 / Al2O3 molar ratio of the AEI zeolite is between 10 and 60, preferably between 12 and 50, limits included and the Al2O3 / Na2O molar ratio of the AEI zeolite is greater than 100 and preferably greater than 400.

5. Process for preparing a catalyst according to one of claims 1 to 4 in which the zeolite of structural type FAU has a SiO2 / Al2O3 molar ratio of between 20 and 50, limits included, and a mass percentage of Na2O of less than 0.0048%.

6. Process for preparing a catalyst according to one of claims 1 to 5 in which no sodium hydroxide is added to the reaction mixture of step i) (Na2O(NaoH) / (SiO2(FAu)) = 0).

7. Process for preparing a catalyst according to one of the preceding claims, in which crystalline seeds of a zeolite of structural type AEI are 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 Al2O3.

8. Process for preparing a catalyst according to one of the preceding claims in which step i) comprises a step of maturing 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.

9. Process for preparing a catalyst according to one of the preceding claims, in which the hydrothermal treatment of step ii) is carried out under autogenous pressure at a temperature of between 120°C and 220°C, preferably between 150°C and 200°C, even more preferably between 160°C and 195°C, for a period of between 12 hours and 7 days, preferably between 12 hours and 6 days.

10. Process for preparing a catalyst according to one of the preceding claims, in which the solid phase obtained at the end of step ii) is filtered, washed, and dried at a temperature between 20 and 150°C, preferably between 60 and 100°C, for a period of between 5 and 24 hours to obtain a dried zeolite.

11. Process for preparing a catalyst according to claim 10 in which the dried zeolite is then calcined at a temperature of between 450 and 700°C for a period of between 2 and 20 hours, the calcination possibly being preceded by a gradual increase in temperature.

12. Process for preparing a catalyst according to one of the preceding claims in which the content of transition metal(s) introduced by the ion exchange step iii) 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.

13. Catalyst for the selective reduction of NOx comprising a zeolite of structural type AEI with a SiO2 / Al2O3 molar ratio of between 10 and 60, limits included, and with a purity greater than or equal to 98% by weight, preferably greater than or equal to 99% by weight; and 0.5 to 6% of a transition metal, preferably copper, obtained by the preparation process according to one of claims 1 to 12.

14. Process for the selective reduction of NOX by a reducing agent such as NH3 or H2 using the catalyst directly obtained by the preparation process according to one of claims 1 to 12 for the selective reduction of NOX by a reducing agent such as NH3 or H2.

15. A method for selectively reducing NOX by a reductant such as NH3 or H2 according to claim 14 wherein the catalyst is formed by deposition in the form of 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.

16. A method for selectively reducing NOX by a reducer such as NH3 or H2 according to claim 15 in which the honeycomb structure is formed of parallel channels open at both ends or comprises porous filtering walls for which the adjacent parallel channels are alternately blocked on either side of the channels.

17. Method for selective reduction of NOX by a reducer such as NH3 or H2 according to one of claims 15 or 16 in which the quantity of catalyst deposited on said structure is between 40 and 250 g / L for filter structures and between 60 and 300 g / L for structures with open channels.

18. Method for selective reduction of NOX by a reducing agent such as NH3 or H2 according to one of claims 15 to 17 in which the catalyst is associated 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 associated with another coating having capacities for adsorbing pollutants, in particular NOx, for reducing pollutants, in particular NOx, or promoting the oxidation of pollutants.

19. Method for selectively reducing NOX by a reducer such as NH3 or H2 according to one of claims 14 to 18 in which said catalyst is integrated: - in an exhaust line of an internal combustion engine operating from carbonaceous or non-carbonaceous fuels, or - in a reactor for treating industrial fumes.

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