WO2019224086A1

WO2019224086A1 - Catalyst comprising an afx-structure zeolite of very high purity and at least one transition metal for selective reduction of nox

Info

Publication number: WO2019224086A1
Application number: PCT/EP2019/062558
Authority: WO
Inventors: David BERTHOUT; Bogdan Harbuzaru
Original assignee: IFP Energies Nouvelles
Priority date: 2018-05-24
Filing date: 2019-05-16
Publication date: 2019-11-28
Also published as: FR3081348A1; EP3801840A1; FR3081348B1; JP2021524373A

Abstract

The invention relates to a method for preparing a catalyst containing an AFX-structure zeolite of very high purity and at least one transition metal, said method comprising at least the following steps: i) in an aqueous medium, mixing of an FAU-structure zeolite having a molar ratio SiO₂ _(FAU)/Al₂O₃ (FAU) of between 6.00 and 200 inclusive, an organic nitrogen-containing compound R, at least one source of at least one alkali and/or alkaline-earth metal M, until a homogeneous precursor gel is obtained; ii) hydrothermal treatment of said precursor gel in order to obtain a crystallized solid phase, known as the "solid" phase; iii) at least one ion exchange with a transition metal; and iv) thermal treatment. The invention also relates to the catalyst that can be obtained or obtained directly by the method and to the use thereof for the selective reduction of NOx.

Description

CATALYST COMPRISING A VERY HIGH-PURITY AFX STRUCTURAL TYPE ZEOLITE AND AT LEAST ONE TRANSITION METAL FOR

SELECTIVE REDUCTION OF NO _x

TECHNICAL FIELD OF THE INVENTION

The invention relates to a process for the preparation of a catalyst based on a zeolite of structural type AFX 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 on internal combustion engines.

PRIOR ART

The emissions of nitrogen oxides (NOx) that result from the burning of fossil fuels are a major concern for society. Increasingly stringent standards are being put in place by government authorities to limit the impact of emissions from combustion on the environment and on health. For light vehicles in Europe under the Euro 6c regulation, NOx and particulate emissions must reach a very low level for all operating conditions. The new Worldwide Harmonized Light Vehicles Test Cycle (WLTC) and compliance-related real-driving emissions (RDE) require the development of a highly effective pollution control system to achieve these objectives. The selective catalytic reduction, designated by the acronym "SCR" for "Selective Catalytic Reduction", appears as an efficient technology to eliminate nitrogen oxides in the oxygen-rich exhaust gas, typical of diesel engines and with positive ignition in lean mixture. The selective catalytic reduction is achieved by a reducing agent, generally ammonia, and can thus be designated NH ₃ -SCR. The ammonia (NH ₃ ) involved in the SCR process is usually generated via the decomposition of a aqueous solution of urea (AdBlue or DEF), and product N ₂ and H ₂ O during the reaction with NOx.

Zeolites exchanged with transition metals are used in particular as catalysts for NH ₃ -SCR applications in transport. Small-pore zeolites, particularly copper-exchanged chabazites, are particularly suitable. They exist commercially in the form of silico-aluminophosphate Cu-SAPO-34 and aluminosilicates Cu-SSZ-13 (or Cu-SSZ-62). Their hydrothermal behavior and their NOx conversion efficiency make them the current references. However, the standards being more and more constraining, the performance of the catalysts still needs to be improved.

The use of zeolites AFX structural type for NH ₃ -SCR applications is known, but few studies evaluate the effectiveness of catalysts implementing this zeolite.

Fickel et al. (Fickel, DW, & Lobo, RF (2009), The Journal of Physical Chemistry C, 114 (3), 1633-1640) studies the use of a copper-exchanged SSZ-16 (structural type AFX) for the NOx removal. This zeolite is synthesized according to US Pat. No. 5,194,235, wherein the copper is introduced by exchange using copper (II) sulfate at 80 ° C for 1 h. Recent results (Fickel, D.W. D'Addio, E. Lauterbach, JA, & Lobo, RF (2011), 102 (3), 441-448) show excellent conversion and good hydrothermal stability for 3.78% copper weight.

Work on the synthesis of AFX structural zeolites has been carried out with various structural agents (Lobo, RF, Zones, SI, & Medrud, RC (1996), Chemistry of Materials, 8 (10), 2409-2411) as well as synthesis optimization work (Hrabanek, P., Zikanova, A., Supinkova, T., Drahokoupil, J., Fila, V., Lhotka, M., Bernauer, B. (2016), Microporous and Mesoporous Materials, 228, 107-115).

Wang et al. (Wang, D. et al., CrystEngComm., (2016), 18 (6), 1000-1008) studied the replacement of the TMHD structuring agent with a TEA-TMA mixture for the SAPO-56 training and get unwanted SAPO-34 and SAPO-20 phases. The incorporation of transition metals is not discussed.

The application US 2016/0137518 describes a quasi-pure zeolite AFX, its synthesis from sources of silica and alumina in the presence of a structuring agent of type 1, 3-Bis (1-adamantyl) imidazolium hydroxide, the preparation a transition metal-exchanged zeolite AFX catalyst and its use for NFI3-SCR applications. No particular form of AFX zeolite is mentioned.

More recently, application US 2018/0093259 discloses the synthesis of zeolites with small pores, such as the zeolite of the structural type AFX, from zeolite of FAU type in the presence of a structurant, such as 1,3-bis (1 - adamantyl) imidazolium hydroxide and an alkaline earth metal source. It also presents applications of the zeolite of AFX structural type obtained, in particular the use of this zeolite as a NOx reduction catalyst, after exchange with a metal such as iron. Meanwhile, the application US 2016/0096169A1 discloses the use in the NOx conversion of a catalyst based on a zeolite AFX structural type having a Si / Al ratio of 15 to 50 exchanged with a metal, the zeolite AFX being obtained from a structuring agent of type 1, 3-Bis (1-adamantyl) imidazolium hydroxide. The results obtained, in the conversion of NOx, show in particular a selectivity of the catalysts prepared according to US 2018/0093259 and US 2016/0096169 to nitrous oxide not exceeding 20 ppm.

JP 2014-148441 describes the synthesis of a solid related to an AFX zeolite, in particular an SAPO-56 comprising copper usable for the reduction of NO _x . The solid is synthesized and then added to a mixture comprising an alcohol and a copper salt, the whole being calcined. The copper is therefore added after the formation of the SAPO solid which is related to the AFX structural type zeolite. This traded solid appears to have increased resistance to the presence of water. Ogura et al. (Bull Chemical Co., 2018, 91, 355-361) show the very good activity of a copper-exchanged zeolite SSZ-16 relative to other zeolite structures, even after hydrothermal aging.

WO 2017/080722 discloses a direct synthesis of a zeolite comprising copper. This synthesis requires starting from a zeolite of structural type FAU and using a complexing agent TEPA and an element M (OFI) _x to result in different types of zeolites, mainly of the CFIA type. Zeolites of the ANA, ABW, PHI and GME type are also produced.

The Applicant has discovered that a catalyst based on a zeolite of AFX structural type prepared according to a particular mode of synthesis and of at least one transition metal, in particular copper, exhibited interesting performances of conversion of NO _x and of selectivity towards N ₂ 0. The NOx conversion performances, in particular at low temperature (T <250 ° C.), are in particular greater than those obtained with prior art catalysts, such as catalysts based on zeolite of the AFX structural type exchanged with copper, while maintaining a good selectivity towards nitrous oxide N ₂ 0.

SUMMARY OF THE INVENTION

The invention relates to a method for preparing a zeolite catalyst of structural type AFX and of at least one transition metal comprising at least the following steps:

i) mixing in an aqueous medium, a zeolite of structural type FAU having a molar ratio S102 _(FAU Al2O3 (FAUJ between 6.00 and 200, inclusive limits, of a nitrogenous organic compound R, R being chosen from dihydroxide of 1,5-bis (methylpiperidinium) pentane, the dihydroxide of

1.6-bis (methylpiperidinium) hexane or dihydroxide

1.7-bis (methylpiperidinium) heptane, of at least one source of at least one alkali metal and / or alkaline earth metal M of valence n, n being an integer greater than or equal to 1, selected from lithium, potassium, sodium, magnesium and calcium and the mixture of at least two of these metals,

the reaction mixture having the following molar composition:

(SiO 2 _(FAU) ) / (Al 2 O 3 _(FAU) ) between 6.00 and 200, preferably between 6.00 and 100

H ₂ O / (SiO ₂ (FAU)) of between 1, 00 and 100, preferably between 5 and 60

R / (Si0 _{2 (FAU)} ) of between 0.01 to 0.60, preferably between 0.05 and 0.50

M _{2 /} n0 / (Si0 ₂ (FAU)) of between 0.005 to 0.45, preferably between 0.05 and 0.25, limits included,

wherein S1O2 (FAU) refers to the amount of S1O ₂ provided by the FAU zeolite, and Al2O3 (FAU) refers to the amount of AI ₂ O ₃ provided by the FAU zeolite, until a homogeneous precursor gel is obtained;

ii) hydrothermal treatment of said precursor gel obtained at the end of stage i) at a temperature of between 120 ° C. and 220 ° C., for a period of between 12 hours and 15 days to obtain a crystallized solid phase, called " solid ";

iii) at least one ion exchange comprising contacting said solid obtained at the end of the preceding step with a solution comprising at least one species capable of releasing a transition metal, in particular copper, in solution in the form of reactive with stirring at room temperature for a period of between 1 hour and 2 days; iv) heat treatment by drying of the solid obtained at the end of the preceding step at a temperature of between 20 and 150 ° C. followed by at least calcining under an air stream at a temperature of between 400 and 700 ° C. .

Steps iii) and iv) can be reversed, and possibly repeated.

The reaction mixture of step i) may comprise at least one additional source of an oxide XO ₂ , X being one or more tetravalent element (s) chosen from the group formed by the following elements: silicon , germanium, titanium, so that the molar ratio XO2 / S102 (FAU) is between 0.001 and 1, preferably between 0.001 and 0.9 and more preferably between 0.001 and 0.01, terminals inclusive, the content of Si0 ₂ (FAUJ in said ratio being the content provided by the zeolite of structural type FAU.

The reaction mixture of stage i) advantageously has the following molar composition:

(X0 ₂ + SO2 (FAU)) / AI203 (FAU) between 6.00 and 200, preferably between 6.00 and 100

H ₂ 0 / (X0 ₂ + S1O ₂ (FAU)) of between 1 and 100, preferably between 5 and 60

R / (X0 ₂ + SiO _{2 (} FAU ₎ ) of between 0.01 to 0.6, preferably of between 0.05 and 0.5 M _{2 / n} 0 / (X0 ₂ + S ₁₀ O ₂ (FAU)) of between 0.005 at 0.45, preferably between 0.05 and 0.25 inclusive.

Preferably, X is silicon.

The reaction mixture of step i) may comprise at least one additional source of an oxide Y ₂ O ₃ , Y being one or more trivalent element (s) chosen from the group formed by the following elements. : aluminum, boron, gallium, so that the molar ratio Y ₂ O ₃ / Al ₂ O ₃ (FAU) is between 0.001 and 10, and preferably between 0.001 and 8, limits included, the content of Al ₂ O _{3 (FAU)} in said ratio being the content provided by the zeolite of structural type FAU.

The reaction mixture of stage i) then advantageously has the following molar composition:

S1O ₂ (FAU (AI203 (FAU) + Y ₂ O ₃ ) of between 6.00 and 200, preferably between 6.00 and 100

HI ₂ 0 / 5ί0 _{2 (FAU)} between 1 and 100, preferably between 5 and 60

R / S1O2 (FAU) between 0.01 to 0.6, preferably between 0.05 and 0.5

M _{2 / n} 0 / SiO ₂ (FAU) of between 0.005 to 0.45, preferably between 0.05 and 0.25, limits included,

Si0 ₂ (FAU) being the amount of Si0 ₂ provided by the zeolite FAU, and Al ₂ 0 ₃ (FAU) being the amount of Al ₂ O ₃ provided by the zeolite FAU. Preferably, Y is aluminum.

The reaction mixture of stage i) may contain:

at least one additional source of an oxide XO2

and at least one additional source of a Y ₂ O ₃ oxide,

the FAU zeolite representing between 5 and 95% by weight, preferably between 50 and 95% by weight, very preferably between 60 and 90% by weight, and even more preferably between 65 and 85% by weight relative to the total amount of trivalent and tetravalent elements SiO ₂ (FAU), XO ₂ , Al ₂ O ₃ (FAUJ and Y ₂ O ₃ of the reaction mixture, and the reaction mixture having the following molar composition:

(XO2 + S1O2 _(FAU) ) / (AI ₂ 0 _{3 (FAU)} + Y ₂ 0 ₃ ) between 6.00 and 200, preferably between 6.00 and 100

H ₂ O / (XO ₂ + SiO ₂ (FAU)) of between 1 and 100, preferably between 5 and 60

R / (X0 ₂ + S1O2 (FAU)) of between 0.01 to 0.6, preferably of between 0.05 and 0.5 M _{2 / n} 0 / (X0 ₂ + S 10 O 2 (FAU)) of between 0.005 at 0.45, preferably between 0.05 and 0.25 inclusive.

The precursor gel obtained at the end of stage i) advantageously has a molar ratio of the total amount expressed as tetravalent element oxides to the total amount expressed as trivalent element oxides of between 6.00 and 100. included.

Preferably, the zeolite of structural type FAU has a molar ratio Si0 ₂ / Al ₂ O ₃ of between 6.00 and 100 inclusive.

Crystalline seeds of an AFX structural zeolite 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 the tetravalent and trivalent elements. in anhydrous form present in said mixture, said seed crystals not being taken into account in the total mass of the sources of the tetravalent and trivalent elements. Step i) may comprise 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.

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 195 ° C, for a period of between 12 hours and 12 days, preferably between 12 hours and 10 days.

The ion exchange step iii) may be carried out by bringing the solid into contact with a solution comprising a single species capable of releasing a transition metal or by bringing the solid into contact successively with different solutions each comprising at least one of preferably a single species capable of releasing a transition metal, preferably the transition metals of the different solutions being different from each other.

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

The transition metal content (aux) introduced by the ion exchange step iii) is advantageously between 0.5 and 6% by weight, preferably between 0.5 and 5% by weight, more preferably between 1 and 4% by weight, based on the total mass of the anhydrous final catalyst.

Advantageously, the heat treatment step iv) comprises drying the solid 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 a calcination in air, optionally dry, at a temperature of between 450 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 optionally dry air flow 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 invention also relates to the catalyst based on an AFX zeolite and at least one transition metal obtainable or obtained directly by the preparation process.

The metal or transition metals may or may be selected from the group consisting of: Ti, V, Mn, Mo, Fe, Co, Cu, Cr, Zn, Nb, Ce, Zr, Rh, Pd , Pt, Au, W, Ag, preferably in the group consisting of Fe, Cu, Nb, Ce or Mn, more preferably from Fe or Cu and even more preferably said transition metal is Cu.

The total content of the transition metals is advantageously between 0.5 and 6 wt%, preferably between 0.5 and 5 wt%, more preferably between 1 and 4 wt%, relative to the total mass of the final catalyst. anhydrous.

In one embodiment, the catalyst comprises copper alone at a content of between 0.5 and 6%, preferably between 0.5 and 5%, more preferably between 1 and 4% by weight relative to total mass of the anhydrous final catalyst.

In another embodiment, the catalyst comprises copper in combination with at least one other transition metal selected from the group consisting of Fe, Nb, Ce, Mn, the copper content of the catalyst being between 0.05 and 2 % by weight, preferably 0.5 and 2% by weight, the content of said at least one other transition metal being between 1 and 4% by weight relative to the total weight of the anhydrous final catalyst.

In yet another embodiment, the catalyst comprises iron in combination with another metal selected from the group consisting of Cu, Nb, Ce, Mn, iron content being between 0.05 and 2% by weight, preferably between 0.5 and 2% by weight, the content of said other transition metal being between 1 and 4% by mass, relative to the total mass of the final catalyst; anhydrous.

The invention also relates to the use of the above catalyst or of the catalyst obtainable or directly obtained by the preparation process, for the selective reduction of NO _x by a reducing agent such as NH ₃ or H ₂ .

The catalyst may be shaped by coating deposition, on a honeycomb structure or a plate structure.

The 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 plugged on either side of the channels.

The amount of catalyst deposited on said structure is advantageously between 50 to 180 g / l for the filtering structures and between 80 and 200 g / l for structures with open channels.

The catalyst may be combined with a binder such as ceria, zirconium oxide, alumina, non-zeolitic silica-alumina, titanium oxide, a mixed ceria-zirconia type oxide, a tungsten oxide and or spinel to be shaped by coating deposition.

Said coating may be associated with another coating having pollutant adsorption capacities, in particular NOx, reduction of pollutants in particular NOx or promoting the oxidation of pollutants.

Said catalyst may be in extruded form, containing up to 100% of said catalyst. The structure coated by said catalyst or obtained by extrusion of said catalyst can be integrated into an exhaust line of an internal combustion engine.

LIST OF FIGURES

FIG. 1 represents the chemical formulas of the nitrogenous organic compounds that may be chosen as structuring agent used in the synthesis process according to the invention.

FIG. 2 represents the X-ray diffraction pattern of the AFX zeolite obtained according to Example 2.

FIG. 3 represents the conversion C in% obtained during a catalytic test for the reduction of nitrogen oxides (NOx) by ammonia (NH ₃ ) in the presence of oxygen (O 2) under Standard SCR conditions as a function of the temperature T in ° C for the catalysts synthesized according to Example 2 (CuAFX3, according to the invention, curve symbolized by squares), Example 3 (CuAFXI, according to the invention, curve symbolized by circles) and Example 4 (CuSSZ16, comparative, curve symbolized by triangles).

FIG. 4 represents the conversion C in% obtained during a catalytic test for the reduction of nitrogen oxides (NOx) by ammonia (NH ₃ ) in the presence of oxygen (O ₂ ) under Fast SCR conditions in function of the temperature T in ° C for the catalysts synthesized according to Example 2 (CuAFX3, according to the invention, curve symbolized by squares) Example 3 (CuAFXI, according to the invention, curve symbolized by circles) and the Example 4 (CuSSZ16, comparative, curve symbolized by triangles).

FIG. 5 represents the conversion C in% obtained during a catalytic test for the reduction of oxides of nitrogen (NOx) by ammonia (NH ₃ ) in the presence of oxygen (O ₂ ) under Standard SCR conditions in function temperature T in ° C, after hydrothermal aging for the catalysts synthesized according to Examples 2 and 4, then aged according to the procedure described in Example 5 (CuAFX3 aged, according to the invention, curve symbolized by the triangles and aged CuSSZ16, comparative, curve symbolized by the circles)

Other features and advantages of the synthesis process according to the invention, the catalyst according to the invention and the use according to the invention will become apparent on reading the following description of nonlimiting examples of embodiments, in particular Referring to the accompanying figures and described below.

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to a process for preparing a catalyst comprising an AFX structural zeolite and at least one transition metal, comprising at least the following steps:

i) mixing in an aqueous medium, a zeolite of FAU structural type having a molar ratio S102 _(FAU AI2O3 (FAUJ between 6 and 200, inclusive limits, of a nitrogenous organic compound R, also called specific structurant, chosen from 1,5-bis (methylpiperidinium) pentane dihydroxide, the dihydroxide of

1.6-bis (methylpiperidinium) hexane, or the dihydroxide of

1.7-bis (methylpiperidinium) heptane, at least one alkali metal and / or alkaline earth metal M of valence n, n being an integer greater than or equal to 1, the mixture having the following molar composition:

(S02 _(FAU) ) / (AI203 _(FAU) ) between 6.00 and 200, preferably between 6.00 and 100

Fl ₂ 0 / (Si0 ₂ (FAU)) of between 1 and 100, preferably between 5 and 60

R / (Si0 _{2 (FAU)} ) of from 0.01 to 0.6, preferably of from 0.05 to 0.5

M _{2 / n} 0 / (SiO ₂ (FAU)) between 0.005 to 0.45, preferably between 0.05 and 0.25 in which Si0 _{2 (FAU)} is the amount of SiO ₂ provided by the FAU zeolite, and Al 2 O 3 (FAU) being the amount of Al ₂ O 3 provided by the FAU zeolite, HI the molar amount of water present in the reaction mixture, R the molar amount of said organic nitrogen compound, M _{2 / n} 0 the molar amount expressed as oxide form of M _{2 / n} O provided by the source of alkali metal and / or alkaline earth metal, and M is one or more alkali metal (s) and / or alkaline earth metal (s) selected from lithium, sodium, potassium, calcium, magnesium and a mixture of at least two of these metals very preferably M is sodium, step i) being conducted for a time to obtain a homogeneous mixture called precursor gel.

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 duration of between 12 hours and 15 days to obtain a crystallized solid phase, so-called "Solid";

iii) at least one ion exchange comprising contacting said solid obtained at the end of the preceding step with a solution comprising at least one species capable of releasing a transition metal, in particular copper, in solution in the form of reactive with stirring at room temperature for a period of between 1 hour and 2 days; iv) the heat treatment by drying of the solid obtained at the end of the preceding step at a temperature of between 20 and 150 ° C. followed by at least calcining under an air stream at a temperature of between 400 and 700 ° C. C; steps iii) and iv) can advantageously be inverted, and possibly repeated if necessary.

The present invention also relates to the catalyst comprising a zeolite AFX structural type and at least one transition metal obtainable or obtained directly by the process described above.

The invention finally relates to the use of a catalyst according to the invention for the selective catalytic reduction of NOx in the presence of a reducing agent.

The catalyst

The catalyst according to the invention comprises at least one zeolite AFX type, and at least one additional transition metal, preferably copper. According to the invention, the metal or transition metals included in the catalyst is (are) selected from among the elements from the group formed by the elements of groups 3 to 12 of the periodic table of the elements including the lanthanides.

In particular, the metal or transition metals included in the catalyst are (are) selected from the group consisting of the following elements: Ti, V, Mn, Mo, Fe, Co, Cu, Cr, Zn, Nb, Ce, Zr, Rh, Pd, Pt, Au, W, Ag.

Preferably, the catalyst according to the invention comprises copper, alone or in combination with at least one other transition metal, chosen from the group of elements listed above; in particular Fe, Nb, Ce, Mn. The total content of the transition metals is between 0.5 and 6 wt%, preferably between 0.5 and 5 wt%, and even more preferably between 1 and 4 wt%, relative to the total mass of the catalyst. final, in its anhydrous form.

For catalysts which contain only copper as the transition metal, the content is between 0.5 and 6% by weight, preferably between 0.5 and 5% by weight, more preferably between 1 and 4% with respect to the total mass of the anhydrous final catalyst.

For catalysts comprising copper and another element such as, preferably, Fe, Nb, Ce, Mn, the copper content of the catalyst is between 0.05 and 2% by weight, preferably 0.5 and 2% by weight, whereas that of the other transition metal is preferably between 1 and 4% by weight, the contents of transition metals being given as a percentage by weight relative to the total mass of the final dry catalyst.

For catalysts which contain only iron as the transition metal, the content is between 0.5 and 4% and more preferably between 1.5 and 3.5% relative to the total weight of the anhydrous final catalyst.

For catalysts comprising iron and another element such as, preferably Cu, Nb, Ce, Mn, the iron content of the catalyst is between 0.05 and 2% by weight, preferably between 0.5 and 2% by weight, whereas that of the other transition metal is preferably between 1 and 4% by weight, the contents of transition metals being given as a percentage by weight relative to the total mass of the final dry catalyst.

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 especially from synthesis, in particular from the compounds of the reaction medium of step i ) of the process for preparing said catalyst.

Process for preparing the catalyst

Step i) of mixing Step i) implements:

i) mixing in an aqueous medium, a zeolite of FAU structural type having a molar ratio S102 _(FAU AI2O3 (FAUJ between 6 and 200, inclusive limits, of a nitrogenous organic compound R, also called specific structurant, chosen from 1,5-bis (methylpiperidinium) pentane dihydroxide, 1,6-bis (methylpiperidinium) hexane dihydroxide, or dihydroxide of

1, 7-bis (methylpiperidinium) heptane, at least one alkali metal and / or alkaline earth metal M of valence n, n being an integer greater than or equal to 1, the mixture having the following molar composition:

H ₂ 0 / (SiO ₂ (FAU)) of between 1 and 100, preferably between 5 and 60

R / (SiO ₂ (FAU)) of from 0.01 to 0.6, preferably from 0.05 to 0.5

M _{2 / n} 0 / (SiO ₂ (FAU)) between 0.005 to 0.45, preferably between 0.05 and 0.25 in which S102 (FAU) is the amount of S102 provided by the FAU zeolite, and Al2O3 (FAU) being the amount of Al ₂ O 3 provided by the FAU zeolite, H ₂ 0 the molar amount of water present in the reaction mixture, R the molar amount of said nitrogenous organic compound, M _{2 / n} 0 the molar amount expressed in oxide form M _{2 / n} 0 by the source of alkali metal and / or alkaline earth metal, and M is one or more alkali metal (s) and / or alkaline earth metal (s) selected from lithium, sodium, potassium, calcium, magnesium and a mixture of at least two of these metals very preferably M is sodium, step i) being conducted for a time to obtain a homogeneous mixture called precursor gel.

The starting structural type zeolite FAU having a molar ratio S10 ₂ / Al ₂ O ₃ of between 6 and 200, inclusive limits can be obtained by any method known to those skilled in the art, for example by treatment with the Steaming and acid washings on a zeolite of structural type FAU of molar ratio S1O ₂ / Al ₂ O _{3 of} less than 6.00. Among the sources of FAU with a SiO ₂ / Al ₂ O ₃ ratio greater than or equal to 6.00, the commercial zeolites CBV712, CBV720, CBV760 and CBV780 produced by Zeolyst, the commercial zeolites HSZ-350HUA, HSZ- 360HUA and HSZ-385HUA produced by TOSOH.

The preparation process according to the invention therefore allows to adjust the ratio S1O ₂ / Al ₂ O ₃ precursor gel containing a zeolite with structure type FAU depending on the zeolite chosen FAU structural type and the additional input or not within the reaction mixture of at least one source of at least one tetravalent element XO ₂ and / or at least one source of at least one trivalent element Y ₂ O ₃ .

Step i) comprises the mixing in an aqueous medium of a zeolite of FAU structural type having an SiO ₂ molar ratio ₍ F _AU AI ₂ O ₃ (FAUJ between 6 and 200, inclusive limits), of a nitrogenous organic compound R, R being the dihydroxide of

1.5-bis (methylpiperidinium) pentane, the dihydroxide of

1.6-bis (methylpiperidinium) hexane, or the dihydroxide of

1.7-bis (methylpiperidinium) heptane, used alone or in admixture, at least one alkali metal and / or alkaline earth metal M of valence n, n being an integer greater than or equal to 1, the reaction mixture having the following molar composition :

(Si0 _{2 (FAU)} ) / (Al ₂ _O 3 _(FAU) ) between 6.00 and 200, preferably between 6.00 and 100

H ₂ 0 / (SiO ₂ (FAU)) of between 1 and 100, preferably between 5 and 60

R / (Si0 _{2 (FAU)} ) of from 0.01 to 0.6, preferably of from 0.05 to 0.5 M _{2 / n} 0 / (SiO _{2 (FAU)} ) between 0.005 to 0.45, preferably between 0.05 and 0.25 in which Si0 _{2 (FAU} J is the amount of SiO ₂ provided by the FAU zeolite, and Al ₂ 0 ₃ _(FAU) is the amount of Al ₂ O ₃ provided by the FAU zeolite, and M is one or more alkali metal (s) and / or alkaline earth metal (s) chosen from lithium, sodium, potassium, calcium, magnesium and the mixture of at least two of these metals, very preferably M is sodium.

In a preferred embodiment, the reaction mixture of step i) also comprises at least one additional source of an oxide X0 ₂ so that the molar ratio X0 ₂ / Si0 _{2 (FAU} J is between 0.001 and 1, the mixture advantageously having the following molar composition:

(X0 ₂ + SI0 ₂ (FAU)) / AI ₂ 0 ₃ (FAU) between 6.00 and 200, preferably between 6.00 and 100

Fl ₂ 0 / (X0 ₂ + SiO _{2 (FAU)} ) between 1 and 100, preferably between 5 and 60

R / (X0 ₂ + Si0 ₂ (FAU)) between 0.01 to 0.6, preferably between 0.05 and 0.5 M _{2 / n} 0 / (X0 ₂ + Si0 _{2 (FAU)} ) between 0.005 to 0.45, preferably between 0.05 and 0.25

wherein X is one or more tetravalent element (s) selected from the group consisting of silicon, germanium, titanium, preferably X is silicon, SiO _{2 (FAU)} being the amount of Si0 ₂ provided by the zeolite FAU, and Al ₂ 0 ₃ _(FAU) being the amount of Al ₂ O ₃ provided by the zeolite FAU, R being the dihydroxide of 1,5-bis (methylpiperidinium) pentane, the dihydroxide of

1.6-bis (methylpiperidinium) hexane or dihydroxide

1.7-bis (methylpiperidinium) heptane, and M is one or more alkali metal (s) and / or alkaline earth metal (s) selected from lithium, sodium, potassium, calcium, magnesium and the mixture at least two of these metals, very preferably M is sodium.

In another preferred embodiment, the reaction mixture of step i) also comprises at least one additional source of an oxide Y ₂ 0 ₃ so that the molar ratio Y ₂ O ₃ / Al ₂ O ₃ (FAU) is between 0.001 and 10, the mixture advantageously having the following molar composition: Si0 _{2 (FAU} (AI ₂ 0 _{3 (FAU)} + Y ₂ O ₃ ) of between 6.00 and 200, preferably between 6.00 and 100

H ₂ O / SiO ₂ (FAU) of between 1 and 100, preferably between 5 and 60

R / SiO _{2 (FAU)} of from 0.01 to 0.6, preferably from 0.05 to 0.5

M _{2 / n} 0 / SiO _{2 (FAU)} between 0.005 to 0.45, preferably between 0.05 and 0.25 in which Y is one or more trivalent element (s) chosen from group formed by the following elements: aluminum, boron, gallium, preferably Y is aluminum, Si0 _{2 (FAU)} being the amount of SiO ₂ provided by the zeolite FAU, and Al ₂ 0 ₃ (FAU) being the amount of Al ₂ 0 ₃ provided by the zeolite FAU, R being the dihydroxide of 1,5-bis (methylpiperidinium) pentane, the dihydroxide of

1.6-bis (methylpiperidinium) hexane or dihydroxide

In another preferred embodiment, the reaction mixture of step i) contains a percentage between 5 and 95% by weight, preferably between 50 and 95% by weight, very preferably between 60 and 90% by weight and still more preferred between 65 and 85% by weight of a zeolite of structural type FAU with respect to the total amount of the sources of the trivalent and tetravalent elements of the mixture and also comprises at least one additional source of an oxide X0 ₂ and at least one source addition of an oxide Y ₂ O ₃ , the reaction mixture having the following molar composition:

(X0 ₂ + Si0 _{2 (FAU)} ) / (AI ₂ 0 ₃ (FAU) + Y ₂ 0 ₃ ) between 6.00 and 200, preferably between 6.00 and 100

in which X is one or more tetravalent element (s) chosen from the group formed by the following elements: silicon, germanium, titanium, preferably X is silicon, Y is one or more trivalent element (s) chosen from the group formed by the following elements: aluminum, boron, gallium, preferably aluminum, S1O ₂ (FAUJ being the amount of S1O ₂ provided by the zeolite FAU, and Al ₂ O ₃ _(FAU) being the amount of Al ₂ O ₃ provided by the zeolite FAU, R being the dihydroxide of 1,5-bis (methylpiperidinium) pentane, the dihydroxide of

1.6-bis (methylpiperidinium) hexane or dihydroxide

Step i) makes it possible to obtain a homogeneous precursor gel.

According to the invention, a zeolite of structural type FAU having a molar ratio S102 _(FAU Al2O3 (FAUJ between 6 and 200 inclusive, preferably between 6.00 and 100 inclusive) is incorporated into the reaction mixture. for the implementation of step (i) as a source of silicon and aluminum elements.

According to the invention, R is a nitrogenous organic compound chosen from 1,5-bis (methylpiperidinium) pentane dihydroxide, the dihydroxide of

1.6-bis (methylpiperidinium) hexane or dihydroxide

1.7-bis (methylpiperidinium) heptane, said compound being incorporated in the reaction mixture for carrying out step (i), as organic structuring agent. The anion associated with the quaternary ammonium cations present in the structuring organic species for the synthesis of an AFX structural zeolite according to the invention is the hydroxide anion.

According to the invention, at least one source of at least one alkali metal and / or alkaline earth metal M of valence n is used in the reaction mixture of step i), not being a higher integer or equal to 1, M being preferably selected from lithium, potassium, sodium, magnesium and calcium and the mixture of at least two of these metals. Most preferably, M is sodium.

Preferably, the source of at least one alkali metal and / or alkaline earth metal M is sodium hydroxide.

According to the invention, at least one additional source of an oxide XO 2, X being one or more tetravalent element (s) chosen from the group formed by the following elements: silicon, germanium, titanium, and preferably X is silicon, so that the molar ratio X0 ₂ / Si0 ₂ (FAUJ is between 0.001 and 1, preferably between 0.001 and 0.9 and more preferably between 0.001 and 0.01, the content of Si0 ₂ _(FAU) in said ratio being the content provided by the zeolite of structural type FAU, is advantageously implemented in the reaction mixture of step i).

The addition of at least one additional source of an oxide X0 ₂ makes it possible in particular to adjust the ratio X0 ₂ / Y ₂ C> ₃ of the precursor gel of a zeolite of structural type AFX obtained at the end of the step i).

The source (s) of said tetravalent element (s) may be any compound comprising element X and capable of releasing this element in aqueous solution in reactive form.

When X is titanium, Ti (EtO) ₄ is advantageously used as a source of titanium. In the preferred case where X is silicon, the silicon source may be any of the 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, it is possible to use precipitated silicas, especially those obtained by precipitation from an alkali metal silicate solution, pyrogenic silicas, for example "CAB-O-SIL" and silica gels. Colloidal silicas having different particle sizes, for example having a mean equivalent diameter of between 10 and 15 nm or between 40 and 50 nm, such as those sold under registered trademarks such as "LUDOX", may be used. Preferably, the silicon source is CAB-O-SIL. According to the invention, at least one additional source of an oxide Y 2 O 3, Y being one or more trivalent element (s) chosen from the group formed by the following elements: aluminum, boron, gallium, is advantageously implemented in the mixture of step i). Preferably Y is aluminum, so that the molar ratio Y 2 O 3 / Al 2 O 3 (FAUJ is between 0.001 and 10, and preferably between 0.001 and 8, the content of Al 2 O 3 (FAU) in said ratio being the content provided by the zeolite of structural type F AU.

The addition of at least one additional source of a Y2O3 oxide thus makes it possible to adjust the XO2 / Y2O3 ratio of the precursor gel of an AFX structural type zeolite obtained at the end of step i).

The source (s) of said trivalent element (s) Y may be any compound comprising element Y and capable of releasing this element in aqueous solution in reactive form. Element Y may be incorporated into the mixture in an oxidized form YO _b with 1 <b <3 (b being an integer or a rational number) or in any other form. In the preferred case where Y is aluminum, the aluminum source is preferably aluminum hydroxide or an aluminum salt, for example chloride, nitrate, or sulphate, sodium aluminate, an aluminum alkoxide, or alumina proper, preferably in hydrated or hydratable form, such as for example colloidal alumina, pseudoboehmite, gamma alumina or alpha or beta trihydrate. It is also possible to use mixtures of the sources mentioned above.

Step (i) of the process according to the invention consists in preparing an aqueous reaction mixture containing a zeolite of structural type FAU, optionally a source of an oxide X0 ₂ or a source of a oxide Y2O3, at least one nitrogen-containing organic compound R, R being chosen from 1,5-bis (methylpiperidinium) pentane dihydroxide, 1,6-bis (methylpiperidinium) hexane dihydroxide or 1,7-bis (methylpiperidinium) dihydroxide heptane in the presence of at least one source of one or more alkali metal (s) and / or alkaline earth metal, to obtain a precursor gel of an AFX structural type zeolite. The amounts of said reagents are adjusted as indicated previously so as to confer on this gel a composition allowing the crystallization of a zeolite of structural type AFX.

It may be advantageous to add seeds of an AFX structural 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 zeolite of the type structural AFX and / or the total crystallization time. Said crystal seeds also promote the formation of said zeolite AFX structural type at the expense of impurities. Such seeds comprise crystalline solids, in particular crystals of an AFX structural zeolite. The crystalline seeds are generally added in a proportion of between 0.01 and 10% of the total anhydrous mass of the sources of said tetravalent (s) and trivalent (s) element (s) used in the reaction mixture, said crystalline seeds not being not taken into account in the total mass of the sources of the tetravalent and trivalent elements. Said seeds are also not taken into account to determine the composition of the reaction mixture and / or gel, defined further, that is to say in the determination of the different molar ratios of the composition of the reaction mixture.

The mixing step i) is carried out until a homogeneous mixture is obtained, preferably for a period greater than or equal to 15 minutes, preferably with stirring by any system known to those skilled in the art at low or high shear rate.

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

It may be advantageous to carry out a ripening of the reaction mixture before the hydrothermal crystallization during said step i) of the process of the invention in order to control the crystal size of an AFX structural type zeolite. Said ripening also promotes the formation of said zeolite AFX structural type at the expense of impurities. The ripening of the reaction mixture during said step i) of the process of the invention can be carried out at room temperature. ambient temperature or at a temperature between 20 and 100 ° C with or without stirring, for a period advantageously between 30 min and 48 hours.

Step ii) hydrothermal treatment

According to step ii) of the process according to the invention, the precursor gel obtained at the end of step i) is subjected to a hydrothermal treatment, preferably carried out at a temperature of between 120.degree. C. and 220.degree. a duration of between 12 hours and 15 days, until said zeolite of structural type AFX (or "crystallized solid") is formed.

The precursor gel is advantageously placed under hydrothermal conditions under an autogenous reaction pressure, optionally by adding gas, for example nitrogen, at a temperature of preferably between 120 ° C. and 220 ° C., preferably between 150 ° C. and 195 ° C, until the complete crystallization of a zeolite AFX structural type.

The time required to obtain the crystallization varies between 12 hours and 15 days, preferably between 12 hours and 12 days, and more preferably between 12 hours and 10 days.

The reaction is generally carried out with stirring or without stirring, preferably with stirring. As stirring system can be used any system known to those skilled in the art, for example, blades inclined with counterpanes, stirring turbines, screws Archimedes.

Very advantageously, the process of the invention leads to the formation of a zeolite of AFX structural type, free from any other crystallized or amorphous phase.

Step iii) exchange

The process for preparing the catalyst according to the invention comprises at least one ion exchange step comprising contacting the crystallized solid obtained with the result of the preceding step, that is to say of the AFX zeolite obtained at the end of step ii) or of the dried and calcined zeolite AFX obtained at the end of step iv) in the preferred case where the steps iii) and iv) are inverted, with at least one solution comprising at least one species capable of releasing a transition metal, preferably copper, 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 able to release the transition metal in said solution being a function of the amount of transition metal that it is desired to incorporate in said crystallized solid. It is also advantageous to obtain the protonated form of the structural type zeolite AFX after step ii). Said hydrogen 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, sulphate or nitrate before ion exchange with the transition metal (s).

The transition metal released in the exchange solution is selected from the group consisting of: Ti, V, Mn, Mo, Fe, Co, Cu, Cr, Zn, Nb, Ce, Zr, Rh, Pd, Pt , Au, W, Ag. Preferably the transition metal is Fe, Cu, Nb, Ce or Mn, preferably Cu. According to the invention, the term "species capable of releasing a transition metal" means a species capable of dissociating in an aqueous medium, such as, for example, sulphates, nitrates, chlorides, oxalates or organometallic complexes of a transition metal or mixtures thereof. Preferably, the species capable of releasing a transition metal is a sulphate or a nitrate of said transition metal. According to the invention, the solution with which the crystallized solid or crystallized solid dried and calcined 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, of preferably iron or copper, preferably copper. Advantageously, the process for preparing the catalyst according to the invention comprises a step iii) ion exchange by bringing the crystallized solid into contact with a solution comprising a species capable of releasing a transition metal or by bringing the solid into contact successively with several solutions each comprising a species capable of releasing a transition metal, the different solutions comprising species capable of releasing a different transition metal.

At the end of the exchange, the solid obtained is advantageously filtered, washed and then dried in order to obtain said catalyst in powder form.

The total amount of transition metal, preferably copper, contained in said final catalyst is between 0.5 and 6% by weight relative to the total weight of the catalyst in its anhydrous form.

According to one embodiment, the catalyst according to the invention is prepared by a process comprising an ion exchange step iii), the solid or the dried and calcined solid being brought into contact with a solution comprising a species capable of releasing copper. in solution in reactive form. Advantageously, the total amount of copper contained in said final catalyst, that is to say at the end of the preparation process according to the invention, is between 0.5 and 6%, preferably between 1 and 6% by weight, all percentages being percentages by weight relative to the total mass of the final catalyst according to the invention in its anhydrous form, obtained at the end of the preparation process.

Step iv) heat treatment

The preparation process according to the invention comprises a step iv) of heat treatment carried out at the end of the preceding step, that is to say at the end of the hydrothermal treatment step ii) or at the end of resulting from the ion exchange step iii), preferably at the end of the ion exchange step iii). Step iii) of the preparation process can advantageously be interchanged with step iv). Each of the two steps iii) and iv) can also optionally be repeated. Said heat treating step iv) comprises drying the solid at a temperature of between 20 and 150 ° C., preferably between 60 and 100 ° C., advantageously for a duration of between 2 and 24 hours, followed by at least one calcination in air, optionally dry, at a temperature advantageously between 450 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 optionally dry air flow 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 rise in temperature.

The catalyst obtained at the end of step iv) of heat treatment is devoid of any organic species, in particular devoid of the organic template R.

In particular, the catalyst obtained by a process comprising at least steps i), ii), iii), and iv) previously described has improved properties for the conversion of NO _x .

Characterization of the catalyst prepared according to the invention

The catalyst comprises a zeolite AFX structure according to the classification of the International Zeolite Association (IZA), exchanged with at least one transition metal. This structure is characterized by X-ray diffraction (XRD). The X-ray diffraction pattern (XRD) is obtained by radiocrystallographic analysis using a diffractometer using the conventional powder method with copper Kai radiation (l = 1.5406). From the position of the diffraction peaks represented by the angle θ2, the Bragg relation is used to _{calculate the} characteristic reticular equidistance of the sample. The measurement error A (d _hki ) on d _hki is calculated using the Bragg relation as a function of the absolute error D (2Q) assigned to the measurement of 2Q. An absolute error D (2Q) equal to ± 0.02 ° is commonly accepted. The relative intensity I _rei assigned to each d _hki value is measured from the height of the corresponding diffraction peak. Comparison of the diffractogram with the records of the database International Center for Diffraction Data (ICDD) data using software such as DIFFRACT. SUITE also allows us to identify the crystalline phases present in the material obtained.

A zeolite of pure AFX structural type is used as a reference.

The qualitative and quantitative analysis of the chemical species present in the materials obtained is made by X-ray fluorescence spectrometry (FX). This is a technique of chemical analysis using a physical property of matter, the fluorescence of X-rays. The spectrum of X-rays emitted by the material is characteristic of the composition of the sample, by analyzing this spectrum, one can deduce the elemental composition, that is to say the mass concentrations in elements.

The loss on ignition (PAF) of the catalyst obtained after the drying step (and before calcination) or after the calcining 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, referred to as PAF, corresponds to the mass difference of the sample before and after heat treatment at 1000 ° C for 2 hours. It is expressed in% corresponding to the percentage of 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.

Use of the catalyst according to the invention

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 NO _x by a reducing agent such as NH ₃ or H ₂ , advantageously shaped by deposition as a coating ("washcoat" according to the English terminology) on a honeycomb structure mainly for mobile applications or a plate structure that is found particularly for stationary applications. 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 plugged on either side of the channels in order to force the flow of gas through the wall (wall-flow monolith in English). Said honeycomb structure thus coated constitutes a catalytic bread. Said structure may 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 may be made of sheet metal, stainless steel containing chromium and aluminum, FeCrAI type steel.

The quantity of catalyst according to the invention deposited on said structure is between 50 to 180 g / l for the filtering structures and between 80 and 200 g / l for structures with open channels.

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 the cerine-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 the catalyst powder according to the invention in a solvent, preferably water and potentially binders, metal oxides, stabilizers or other promoters. This quenching step can be repeated until the desired amount of coating is reached. In some cases the slurry can also be sprayed within the monolith. The coating once deposited, the monolith is calcined at a temperature of 300 to 600 ° C for 1 to 10 hours.

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

Another possibility is to put the catalyst in the form of extruded. In this case, the structure obtained can contain up to 100% of catalyst according to the invention. Said structure coated with the catalyst according to the invention is advantageously integrated in an exhaust line of an internal combustion engine operating mainly in lean mixture, that is to say in excess of air relative to the stoichiometry of the combustion reaction as is the case for diesel engines for example. Under these operating conditions of the engine, the exhaust gases contain in particular the following pollutants: soot, unburned hydrocarbons (HC), carbon monoxide (CO), nitrogen oxides (NOx). Upstream of said structure coated with the catalyst according to the invention can be placed an oxidation catalyst whose function is to oxidize the HC and the CO and a filter for removing 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 200 ° C and 500 ° C.

ADVANTAGES OF THE INVENTION

The catalyst according to the invention, based on an AFX structural zeolite and at least one transition metal, in particular copper, has improved properties compared to the catalysts of the prior art. In particular, the use of the catalyst according to the invention makes it possible to obtain lower priming temperatures for the NOx conversion reaction and a better NO _x conversion over the entire operating temperature range (150.degree. ° C - 600 ° C), while maintaining good selectivity in N ₂ 0. It also has a better resistance to hydrothermal aging, guaranteeing high performance even after aging. EXAMPLES

Example 1: Preparation of 1,6-bis (methylpiperidinium) hexane dihydroxide (structuring R).

50 g of 1,6-dibromohexane (0.20 mol, 99%, Alfa Aesar) are added to a 1 L flask containing 50 g of N-methylpiperidine (0.51 mol, 99%, Alfa Aesar) and 200 ml. ethanol. The reaction medium is stirred and refluxed for 5 hours. The mixture is then cooled to room temperature and filtered. The mixture is poured into 300 ml of cold diethyl ether and the precipitate formed is filtered off and washed with 100 ml of diethyl ether. The solid obtained is recrystallized from an ethanol / ether mixture. The solid obtained is dried under vacuum for 12 hours. 71 g of a white solid are obtained (ie a yield of 80%).

The product has the expected ¹ H NMR spectrum. ¹ H NMR (D ₂ O, ppm / TMS): 1.27 (4H, m); 1.48 (4H, m); 1.61 (4H, m); 1.70 (8H, m); 2.85 (6H, s); 3.16 (12H, m).

18.9 g of Ag ₂ 0 (0.08 mol, 99% Aldrich) are added into a 250 mL Teflon beaker containing 30 g of structuring dibromide 1, 6-bis (methylpiperidinium) hexane (0.07 mole) and 100 mL of deionized water. The reaction medium is stirred in the dark for 12 hours. The mixture is then filtered. The filtrate obtained is composed of an aqueous solution of 1,6-bis (methylpiperidinium) hexane dihydroxide. The assay of this species is carried out by proton NMR using formic acid as a standard.

EXAMPLE 2 Preparation of a zeolite of structural type AFX according to the invention 3%

Cu

Preparation of AFX zeolite

1645 g of a zeolite of structural type FAU (CBV780, SiO ₂ / Al ₂ O ₃ = 95.97, Zeolyst, PAF = 9.30%) were mixed with 6424 g of an aqueous dihydroxide solution of 1, 6-bis (methylpiperidinium) hexane (18.36% by weight) prepared according to Example 1. 9114 g of deionized water are added to the above mixture, the resulting preparation is stirred for 10 minutes. 164 g of sodium hydroxide (98% by weight, Aldrich) were incorporated into the synthesis mixture and stirred for 15 minutes. Subsequently, 153.85 g of amorphous gel of aluminum hydroxide (Al (OH) ₃ amorphous gel, 58.55% by weight of Al ₂ O ₃ , Merck), corresponding to a molar ratio (Al ₂ 0 ₃ (amorphous gel) / Al ₂ O ₃ ( FAU) of 6.49 are incorporated and the synthesis gel is stirred for 15 minutes The molar composition of the precursor gel is as follows: 1 SiO ₂ : 0.05 Al ₂ O ₃ : 0.167 R: 0.093 Na ₂ 0: 36.7 H ₂ O, ie a Si0 ₂ / Al ₂ O ₃ ratio of 20. The precursor gel is then transferred, after homogenization, into a 25-liter stainless steel reactor, the reactor is closed and then heated for 23 hours. at 170 ° C. under autogenous pressure and with stirring at 200 rpm with a system equipped with 4 inclined blades The crystalline solid product obtained is filtered, washed with deionized water and then dried overnight at 100 ° C. The PAF of dried solid is 9.7%.

The solid is then introduced into a muffle furnace where a calcination step is carried out: the calcining cycle comprises a rise of 1.5 ° C./min in temperature up to 200 ° C., a plateau at 200 ° C. maintained during 2 hours, a rise of 1 ° C / min in temperature up to 550 ° C followed by a bearing at 550 ° C maintained for 8 hours, then a return to room temperature.

The calcined solid product was analyzed by X-ray diffraction and identified as consisting of a zeolite of AFX structural type, with a purity greater than 99%. The product has an SiO ₂ / Al ₂ O ₃ molar ratio of 14.8 as determined by X-ray fluorescence.

The calcined AFX zeolite is brought into contact with a solution of molar NH ₄ NO ₃ for 1 hour with stirring at 80 ° C. for ionic exchange with NH ₄ ⁺ . The ratio of the volume of NH ₄ NO ₃ solution to the mass of solid is 10. The solid obtained is filtered and washed and the exchange procedure is repeated two more times under the same conditions. The final solid is separated, washed and dried for 12 hours at 100 ° C. A DRX analysis shows that the product obtained is a zeolite in ammoniacal form of pure AFX structural type.

The AFX zeolite in ammoniacal form is then treated under an air stream at 550 ° C. for 8 hours with a temperature rise ramp of 1 ° C./min. The loss at fire (PAF) is 4% weight. The product obtained is an AFX zeolite in protonated form.

Ionic ion exchange

The AFX zeolite calcined in protonated form is brought into contact with a solution of [Cu (NFl ₃ ) ₄ ] (NO ₃ ) ₂ for 1 day with stirring at room temperature. The final solid is separated, washed and dried for 12 hours at 100 ° C.

The Cu-AFX exchanged solid obtained after being placed in contact with the [Cu (NFl ₃ ) ₄ ] (NO ₃ ) _{2 solution} is calcined under a stream of air at 550 ° C. for 8 hours.

The calcined solid product is analyzed by X-ray diffraction and identified as an AFX structural zeolite.

The product has an SiO ₂ / Al ₂ O ₃ molar ratio of 14.8 and a mass percentage of Cu of 3% as determined by X-ray fluorescence.

The catalyst obtained is noted CuAFX3.

EXAMPLE 3 Preparation of a zeolite of AFX structural type according to the invention at 1% Cu

Preparation of AFX zeolite

1645 g of a zeolite of structural type FAU (CBV780, SiO ₂ / Al ₂ O ₃ = 95.97, Zeolyst, PAF = 9.30%) were mixed with 6424 g of an aqueous dihydroxide solution of 1, 6-bis (methylpiperidinium) hexane (18.36% by weight) prepared according to Example 1. 9114 g of deionized water are added to the above mixture, the resulting preparation is stirred for 10 minutes. 164 g of sodium hydroxide (98% by weight, Aldrich) were incorporated into the synthesis mixture and stirred for 15 minutes. Subsequently, 153.85 g of amorphous gel of aluminum hydroxide (Al (OH) ₃ amorphous gel, 58.55% by weight of Al ₂ O ₃ , Merck), corresponding to a molar ratio (Al ₂ O 3 ₃ (amorphous gel) / Al ₂ O ₃ (FAU) of 6.49 are incorporated and the synthesis gel is stirred for 15 minutes The molar composition of the precursor gel is as follows: 1 Si0 ₂ : 0.05 AI ₂ Ü ₃ : 0.167 R: 0.093 Na ₂ 0: 36.7 Fl ₂ 0, a ratio Si0 ₂ / Al ₂ 0 ₃ of 20. The precursor gel is then transferred, after homogenization, into a 25 liter stainless steel reactor. The reactor is closed and then heated for 23 hours at 170 ° C. under autogenous pressure and with stirring at 200 rpm with a system provided with 4 inclined blades. The crystallized product obtained is filtered, washed with deionized water and then dried overnight at 100 ° C. PAF of the dried solid is 9.7%.

The calcined solid product was analyzed by X-ray diffraction and identified as consisting of an AFX structural zeolite, with a purity greater than 99%. The product has a molar ratio S102 / Al2O3 of 14.8 as determined by X-ray fluorescence.

The calcined AFX zeolite is brought into contact with a solution of 3 molar NHI ₄ NO ₃ for 1 hour with stirring at 80 ° C. for ion exchange with NFI ₄ ⁺ . The ratio between the volume of NFI ₄ N0 _{3 solution} and the mass of solid is 10. The solid obtained is filtered and washed and the exchange procedure is repeated two more times under the same conditions. The final solid is separated, washed and dried for 12 hours at 100 ° C. A DRX analysis shows that the product obtained is a zeolite in ammoniacal form of pure AFX structural type. The AFX zeolite in ammoniacal form is treated under a stream of air at 550 ° C. for 8 hours with a temperature rise ramp of 1 ° C./min. The loss on ignition (PAF) is 4% by weight. The product obtained is an AFX zeolite in protonated form. Ionic ion exchange

The burned zeolite AFX in protonated form is brought into contact with a solution of [CU (NH ₃ ) ₄ ] (NO ₃ ) ₂ for 1 day with stirring at room temperature. The final solid is separated, washed and dried for 12 hours at 100 ° C.

The Cu-AFX exchanged solid obtained after being placed in contact with the solution of [CU (NH ₃ ) ₄ ] (NO ₃ ) ₂ is calcined under a stream of air at 550 ° C. for 8 hours.

The product has an SiO ₂ / Al ₂ O ₃ molar ratio of 14.8 and a mass percentage of Cu of 1% as determined by X-ray fluorescence.

The catalyst obtained is noted CuAFXI.

Example 4: In this example, a zeolite SSZ-16 exchanged with Cu is synthesized according to the prior art. In this example, the copper is introduced by ion exchange.

Preparation of zeolite SSZ-16

17.32 g of sodium hydroxide are dissolved in 582.30 g of deionized water, with stirring (300 rpm) and at room temperature. 197.10 g of sodium silicate are added to this solution and the mixture is homogenized with stirring (300 rpm at room temperature, 9.95 g of NaY CBV100 zeolite are then added with stirring (300 rpm) and The solution is then continued until the zeolite is dissolved, 43.67 g of the DABCO-C4 structurant are dissolved in the solution obtained, and the mixture is then homogenized with stirring (450 rpm) for 30 minutes at room temperature.

The reaction mixture has the following molar composition: 100 SiO ₂ : 1, 67 Al ₂ O ₃ : 50 Na ₂ O: 10 DABCO-C 4: 4000 H ₂ O

The reaction mixture obtained in the mixing step is kept at room temperature with stirring for 24 hours.

The gel obtained is left in an autoclave at a temperature of 150 ° C. for 6 days with stirring (200 rpm). The crystals obtained are separated and washed with water permutated until a wash water pH of less than 8 is obtained. The washed crystalline solid is dried for 12 hours at 100 ° C.

A DRX analysis shows that the product obtained is a zeolite SSZ-16 synthetic and pure raw AFX structural type (ICDD sheet, PDF 04-03-1370).

The synthetic SSZ-16 zeolite is treated under a flow of N ₂ dry at 550 ° C for 8 h, and then calcined under a stream of dry air at 550 ° C for 8 hours. The loss on ignition (PAF) is 18% by weight.

The calcined zeolite SSZ-16 is brought into contact with a solution of 3 molar NH ₄ NO ₃ for 5 hours with stirring at room temperature for ion exchange with NH ₄ ⁺ . The ratio between the volume of NFI ₄ N0 _{3 solution} and the solid mass is 10. The solid obtained is filtered and washed and the exchange procedure is repeated again under the same conditions. The final solid is separated, washed and dried for 12 hours at 100 ° C.

The zeolite SSZ-16 in ammoniacal form (NFI ₄ -SSZ-16) is treated under a stream of dry air at 550 ° C. for 8 hours with a temperature rise ramp of 1 ° C./min. The loss on ignition (PAF) is 4% by weight. The product obtained is a zeolite SSZ-16 in protonated form (FI-SSZ-16).

Cu ion exchange on the H-SSZ-16

The FI-SSZ-16 zeolite is brought into contact with a solution of [Cu (NH ₃ ) ₄ ] (NO ₃ ) ₂ for 1 day with stirring at room temperature. The final solid is separated, washed and dried and calcined under a stream of dry air at 550 ° C. for 8 hours. A DRX analysis shows that the product obtained is a zeolite SSZ-16 of pure AFX structural type (ICDD file, PDF 04-03-1370).

X-ray fluorescence (FX) chemical analysis gave an Si0 ₂ / Al ₂ O ₃ molar ratio of 13 and a mass percentage of Cu of 3%.

The catalyst obtained is noted CuSSZ16. Example 5 Hydrothermal Aging Step

200 mg of each of the samples synthesized according to Example 2 (CuAFX3), Example 3 (CuAFXI) and Example 4 (CuSSZ16) are placed in powder form in a quartz reactor. They are traversed by a flow rate of 150 L / h of a mixture of the following molar composition: 10% H ₂ 0, 20% 0 ₂ and N ₂ in addition.

The samples are subjected to these conditions for 4 hours at a temperature of 800 ° C.

They are then cooled to room temperature under a stream of N ₂ .

Example 6

The sample synthesized according to Example 2 and aged under the conditions of Example 5 is named CuAFX3vieilli.

The sample synthesized according to Example 3 and aged under the conditions of Example 5 is called CuAFXI aged.

The sample synthesized according to Example 4 and aged under the conditions of Example 5 is named CuSSZ16vieilli.

Example 7 Conversion of NOx into SCR Standard: Comparison of catalysts according to the invention with the prior art

A catalytic test for the reduction of oxides of nitrogen (NOx) by ammonia (NH ₃ ) in the presence of oxygen (O ₂ ) under Standard SCR conditions is carried out at different operating temperatures for the catalysts synthesized according to the example 2 (CuAFX3), Example 3 (CuAFXI) and Example 4 (CuSSZ16).

For the test of each sample, 200 mg of catalyst in powder form is placed in a quartz reactor. 145 L / h of a representative load of a mixture of exhaust gas of a diesel engine are fed into the reactor. This feed has the following molar composition: 400 ppm NO, 400 ppm NH ₃ , 8.5% 0 ₂ , 9% C0 ₂ , 10% H ₂ 0, qpc N ₂ .

An FTIR analyzer makes it possible to measure the concentration of NO, NO ₂ , NH ₃ , N ₂ O, CO, CO ₂ , H ₂ O, O ₂ species at the outlet of the reactor. The NOx conversions calculated as following:

Conversion = (NOx input -NOx output) / NOx input The NOx conversion results are shown in FIG. 3, the curves marked by squares, circles and triangles respectively corresponding to the tests carried out with the catalysts synthesized according to Example 2 (CuAFX3) Example 3 (CuAFXI) and Example 4 (CuSSZ16). It appears that the catalysts according to the invention make it possible to convert NOx.

The CuAFXI catalyst synthesized according to the invention is particularly effective at high temperatures with 100% conversion of NOx from 350 ° C. and a maintained efficiency greater than 95% up to 550 ° C. The catalyst CuAFX3 synthesized according to the invention gives much higher performance to the catalyst synthesized according to the prior art in terms of NOx conversion over the entire temperature range tested. A maximum conversion of 100% is reached between 270 and 410 ° C for the CuAFX3 catalyst while the CuSSZ16 catalyst synthesized according to the prior art achieves only 89% conversion between 340 and 400 ° C. The initiation temperatures of the catalysts containing 3% copper are given below for Standard-SCR conditions:

T50 is the temperature at which 50% of the NOx in the gas mixture is converted by the catalyst. T80 is the temperature at which 80% of the NOx in the gas mixture is converted by the catalyst. T90 is the temperature at which 90% of the NOx in the gas mixture is converted by the catalyst. T100 is the temperature at which 100% NOx of the gas mixture is converted by the catalyst.

The catalyst CuAFX3 synthesized according to the invention gives much superior performance to the catalyst CuSSZ16 synthesized according to the prior art in terms of initiation temperatures and NOx conversion over the entire temperature range tested in Standard SCR condition. Indeed, at the same conversion rate (50% or 80%), the priming temperatures obtained with the catalyst according to the invention CuAFX3 are lower compared to those obtained with the catalyst CuSSZI 6.

Example 8: Conversion of NOx into Fast SCR:

A catalytic test for the reduction of nitrogen oxides (NOx) by ammonia (NH ₃ ) in the presence of oxygen (O 2) under Fast SCR conditions is carried out at different operating temperatures for the catalyst synthesized according to the invention. 4 and the sample CuSSZI 6 synthesized according to the prior art (example 5)

200 mg of catalyst in powder form is placed in a quartz reactor. 218 L / h of a representative load of a mixture of exhaust gas of a diesel engine are fed into the reactor. This feed has the following molar composition: 200 ppm NO, 200 ppm NO 2, 400 ppm NH ₃ , 8.5% O 2, 9% CO 2, 10% H ₂ 0, qpc N ₂ for Fast SCR conditions.

An FTIR analyzer makes it possible to measure the concentration of NO, NO 2, NH ₃ , N ₂ O, CO ₂ , CO ₂ , H ₂ O, O ₂ species at the outlet of the reactor. The NOx conversions calculated as following:

Conversion = (NOx input -NOx output) / NOx input

The NOx conversion results are shown in FIG. 4, the curves marked by squares, circles and triangles respectively corresponding to the tests carried out with the catalysts synthesized according to Example 2 (CuAFX3) Example 3 (CuAFXI) and Example 4 (CuSSZI 6).

Catalyst initiation temperatures are given below for Fast-SCR conditions

T50 is the temperature at which 50% of the NOx in the gas mixture is converted by the catalyst. T80 is the temperature at which 80% of NOx of the gaseous mixture are converted by the catalyst. T90 is the temperature at which 90% of the NOx in the gas mixture is converted by the catalyst. T100 is the temperature at which 100% NOx of the gas mixture is converted by the catalyst.

The catalysts CuAFXI and CuAFX3 synthesized according to the invention give superior performance to the catalyst CuSSZ16 synthesized according to the prior art in terms of initiation temperatures and NOx conversion over the entire temperature range tested under Fast SCR conditions. Indeed, at the same conversion rate (50%, 80%, 90% or 100%), the initiation temperatures obtained with the catalysts according to the invention CuAFXI and CuAFX3 are lower compared with those obtained with the catalyst CuSSZ16 .

In addition, nitrous oxide (N ₂ 0) emissions, in the case of CuAFXI and CuAFX3 catalysts according to the invention, remain low over the entire temperature range tested (<15 ppm between 150 and 550 ° C.).

Example 9 Conversion of NOx into Standard and Fast SCR After Hydrothermal Aging

A catalytic test for the reduction of nitrogen oxides (NOx) by ammonia (NH ₃ ) in the presence of oxygen (O ₂ ) under Standard SCR and Fast SCR conditions is carried out at different operating temperatures for the catalysts synthesized according to Examples 2 and 4 then aged according to the procedure described in Example 5, noted CuAFX3vieilli and CuSSZ16vieilli.

200 mg of catalyst in the form of a powder is placed in a quartz reactor. 145 l / h of a representative charge of an exhaust gas mixture are fed into the reactor. This feed has the following molar composition: 400 ppm NO, 400 ppm NH ₃ , 8.5% 0 ₂ , 9% CO ₂ , 10% H ₂ 0, qpc N ₂ for Standard SCR conditions and the following molar composition: 200 ppm NO, 200 ppm N0 ₂ , 400 ppm NH ₃ , 8.5% 0 ₂ , 9% C0 ₂ , 10% H ₂ 0, qpc N ₂ for Fast SCR conditions. An FTIR analyzer makes it possible to measure the concentration of NO, NO ₂ , NH ₃ , N ₂ O, CO, CO ₂ , H ₂ O, O ₂ species at the outlet of the reactor. The NOx conversions calculated as following:

Conversion = (NOx input -NOx output) / NOx input

Figure 5 shows the NOx conversion of aged CuAFX3 and aged CuSSZ16 catalysts as a function of temperature under Standard SCR conditions.

Catalyst initiation temperatures are given below for Standard-SCR conditions:

Catalyst initiation temperatures are given below for Fast-SCR conditions

The catalyst CuAFX3 synthesized according to the invention gives a much higher performance than the catalyst CuSSZ16 synthesized according to the prior art in terms of initiation temperatures and NOx conversion over the entire range of temperature tested under Standard SCR conditions after hydrothermal aging. Indeed, at the same conversion rate (50%), the initiation temperatures obtained with the catalyst according to the invention CuAFX 3 are lower compared with those obtained with the catalyst CuSSZ16. A conversion of 100% is reached between 275 and 330 ° C for the CuAFX3 catalyst while the CuSSZ16 catalyst achieves only 66% conversion at 330 ° C.

The performance under Fast SCR conditions is also higher for the aged CuAFX3 catalyst synthesized according to the invention; the maximum conversion is 100% and is reached between 225 and 360 ° C while the aged CuSSZ16 catalyst reaches only 78% at most between 305 and 360 ° C.

The nitrous oxide (N ₂ O) emissions are comparable for the two catalysts tested (<15 ppm between 150 and 550 ° C).

Claims

A process for preparing a zeolite catalyst of structural type AFX and at least one transition metal comprising at least the following steps: i) mixing in an aqueous medium, a zeolite of structural type FAU having a molar ratio Si0 ₂ (FAU AI2O3 (FAUJ between 6.00 and 200, inclusive limits, of a nitrogenous organic compound R, R being chosen from dihydroxide of

1.5-bis (methylpiperidinium) pentane, the dihydroxide of

1.6-bis (methylpiperidinium) hexane or dihydroxide

1.7-bis (methylpiperidinium) heptane, of at least one source of at least one alkali metal and / or alkaline earth metal M of valence n, n being an integer greater than or equal to 1, chosen from lithium, potassium, sodium, magnesium and calcium and the mixture of at least two of these metals,

the reaction mixture having the following molar composition:

(SiO 2 _(FAU) ) / (Al 2 O 3 _(FAU) ) of between 6.00 and 200, preferably between 6.00 and 100 μF ₂ O / (SiO ₂ (FAU)) of between 1.00 and 100, preferably between 5 and 60

R / (Si0 _{2 (FAU)} ) of between 0.01 to 0.60, preferably between 0.05 and 0.50 M _{2 / n} 0 / (Si0 ₂ (FAU)) of between 0.005 and 0.45, preferably between 0.05 and 0.25, limits included,

in which S1O ₂ (FAU) designates the amount of S1O ₂ provided by the FAU zeolite, and AI ₂ O ₃ (FAU) designates the quantity of AI ₂ O ₃ supplied by the FAU zeolite, until obtaining a homogeneous precursor gel;

2. The method of claim 1, wherein steps iii) and iv) are inverted, and optionally repeated.

3. Method according to one of claims 1 or 2 wherein the reaction mixture of step i) comprises at least one additional source of an oxide XO2, X being one or more tetravalent element (s) selected ( s) in the group formed by the following elements: silicon, germanium, titanium, so that the molar ratio XO2 / S102 (FAU) is between 0.001 and 1, preferably between 0.001 and 0.9 and more preferably between 0.001 and 0.01, limits included, the content of S102 (FAU) in said ratio being the content provided by the zeolite of structural type FAU.

The process according to claim 3 wherein the reaction mixture of step i) has the following molar composition:

(XO2 + S1O2 (FAU)) / AI203 (FAU) between 6.00 and 200, preferably between 6.00 and 100

R / (X0 ₂ + S1O2 (FAU)) of between 0.01 to 0.6, preferably of between 0.05 and 0.5 M _{2 / n} 0 / (X0 ₂ + SiO _{2 (FAU)} ) of between 0.005 at 0.45, preferably between 0.05 and 0.25 inclusive.

5. Method according to one of claims 3 to 4 wherein X is silicon.

6. Method according to one of the preceding claims wherein the reaction mixture of step i) comprises at least one additional source of an oxide Y2O3, Y being one or more trivalent element (s) chosen in the group formed by the following elements: aluminum, boron, gallium, so that the molar ratio Y 2 O 3 / Al 2 O 3 (FAU) is between 0.001 and 10, and preferably between 0.001 and 8, inclusive, the content of Al 2 O 3 _{( FAU)} in said ratio being the content provided by the zeolite of structural type FAU.

The process of claim 6 wherein the reaction mixture of step i) has the following molar composition:

S1O ₂ (FAU) / (AI203 (FAU) + Y ₂ O ₃ ) between 6.00 and 200, preferably between 6.00 and 100

H ₂ O / SiO _{2 (FAU)} of between 1 and 100, preferably between 5 and 60

R / S1O ₂ (FAU) between 0.01 to 0.6, preferably between 0.05 and 0.5

M _{2 / n} 0 / SiO _{2 (FAU)} of between 0.005 to 0.45, preferably between 0.05 and 0.25, limits included,

Si0 _{2 (FAU)} being the amount of Si0 ₂ provided by the zeolite FAU, and Al ₂ 0 _{3 (FAU)} being the amount of Al ₂ O ₃ provided by the zeolite FAU.

8. Method according to one of claims 6 to 7 wherein Y is aluminum.

9. Method according to one of the preceding claims wherein the reaction mixture of step i) contains:

at least one additional source of an oxide XO ₂

and at least one additional source of a Y ₂ O ₃ oxide,

the FAU zeolite representing between 5 and 95% by weight, preferably between 50 and 95% by weight, very preferably between 60 and 90% by weight, and even more preferably between 65 and 85% by weight relative to the total amount of trivalent and tetravalent elements S10 ₂ (FAU), XO ₂ , Al ₂ O ₃ (FAU) and Y ₂ O ₃ of the reaction mixture, and the reaction mixture having the following molar composition:

(X0 ₂ + Si0 _{2 (FAU)} ) / (AI ₂ 0 _{3 (FAU)} + Y ₂ O ₃ ) from 6.00 to 200, preferably from 6.00 to 100

FI ₂ 0 / (X0 ₂ + S1O ₂ (FAU)) of between 1 and 100, preferably between 5 and 60 R / (X0 ₂ + S10 ₂ (FAU)) of between 0.01 and 0.6, preferably between 0.05 and 0.5

M _{2 / n} 0 / (X0 ₂ + Si0 ₂ (FAU)) between 0.005 to 0.45, preferably between 0.05 and 0.25, inclusive.

10. Method according to one of the preceding claims wherein the precursor gel obtained at the end of step i) has a molar ratio of the total amount expressed as tetravalent element oxides on the total amount expressed as oxides of trivalent elements between 6.00 and 100 inclusive.

11. Method according to one of the preceding claims wherein the zeolite of structural type FAU has a molar ratio S102 / Al2O3 of between 6.00 and 100 inclusive.

12. Process according to one of the preceding claims, in which crystalline seeds of a zeolite of structural type AFX are added to the reaction mixture of stage i), preferably in an amount of between 0.01 and 10% by weight relative to to the total mass of the sources of the tetravalent and trivalent elements in anhydrous form present in said mixture, said seed crystals not being taken into account in the total mass of the sources of the tetravalent and trivalent elements.

13. Method according to one of the preceding claims wherein 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 minutes. hours.

14. Method according to one of claims 1 to 13 wherein the hydrothermal treatment of step ii) is carried out under autogenous pressure at a temperature between 120 ° C and 220 ° C, preferably between 150 ° C and 195 ° C, for a period of between 12 hours and 12 days, preferably between 12 hours and 10 days.

15. Method according to one of claims 1 to 14, wherein the step iii) ion exchange is carried out by contacting the solid with a solution comprising a single species capable of releasing a transition metal or by setting successive contacts of the solid with different solutions each comprising at least one, preferably only one species capable of releasing a transition metal, preferably the transition metals of the different solutions being different from each other.

The method of claim 15 wherein said at least one transition metal released in the exchange solution of step iii) is selected from the group consisting of: Ti, V, Mn, Mo, Fe, Co , Cu, Cr, Zn, Nb, Ce, Zr, Rh, Pd, Pt, Au, W, Ag, preferably in the group consisting of Fe, Cu, Nb, Ce or Mn, more preferably Fe or Cu and even more preferably said transition metal is Cu.

17. Method according to one of the preceding claims wherein the transition metal content (aux) introduced by the ion exchange step iii) is between 0.5 to 6% by weight, preferably between 0.5 and 6%. 5% by weight, more preferably between 1 and 4% by weight, based on the total weight of the anhydrous final catalyst.

18. Method according to one of the preceding claims, wherein the step iv) heat treatment comprises drying the solid at a temperature between 20 and 150 ° C, preferably between 60 and 100 ° C for a period of time between 2 and 24 hours, followed by at least one calcination in air, possibly dry, at a temperature of between 450 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 optionally dry air flow being preferably between 0.5 and 1.5 L / h / g of solid to be treated, more preferably preferred between 0.7 and 1.2 L / h / g of solid to be treated.

19. Catalyst based on an AFX zeolite and at least one transition metal obtained by the process according to one of claims 1 to 18.

The catalyst of claim 19 wherein the transition metal or metals is (are) selected from the group consisting of: Ti, V, Mn, Mo, Fe, Co, Cu, Cr, Zn, Nb, Ce, Zr, Rh, Pd, Pt, Au, W, Ag, preferably in the group formed by the following elements: Fe, Cu, Nb, Ce or Mn, more preferably from Fe or Cu and still more preferably said transition metal is Cu.

21. Catalyst according to one of claims 19 to 20 wherein the total content of the transition metals is between 0.5 to 6% by weight, preferably between 0.5 and 5% by weight, more preferably between 1 and 4% by weight, based on the total mass of the anhydrous final catalyst.

22. Catalyst according to claim 21 comprising copper, alone, at a content between 0.5 and 6% by weight, preferably between 0.5 and 5% by weight, more preferably between 1 and 4% by weight relative to the total mass of the anhydrous final catalyst.

The catalyst of claim 21 comprising copper in combination with at least one other transition metal selected from the group consisting of Fe, Nb, Ce, Mn, the copper content of the catalyst being between 0.05 and 2% by mass. , preferably 0.5 and 2% by weight, the content of said at least one other transition metal being between 1 and 4% by weight relative to the total weight of the anhydrous final catalyst.

24. Catalyst according to claim 21 comprising iron in combination with another metal selected from the group formed by Cu, Nb, Ce, Mn, the iron content being between 0.05 and 2% by weight, preferably between 0, 5 and 2% by weight, the content of said other transition metal being between 1 and 4% by weight, relative to the total weight of the anhydrous final catalyst.

25. Use of the catalyst according to one of claims 19 to 24 or obtained by the process according to any one of claims 1 to 18, for the selective reduction of NO _x by a reducing agent such as NH ₃ or H ₂ .

26. Use according to claim 25, wherein the catalyst is shaped by coating deposition on a honeycomb structure or a plate structure.

27. Use according to claim 26, wherein the honeycomb structure is formed of parallel channels open at both ends or has porous filter walls for which the adjacent parallel channels are alternately blocked on either side of the channels.

28. Use according to claim 27, wherein the amount of catalyst deposited on said structure is between 50 to 180 g / L for the filter structures and between 80 and 200 g / L for structures with open channels.

29. Use according to one of claims 25 to 28, for which the catalyst is associated with a binder such as ceria, zirconium oxide, alumina, non-zeolitic silica-alumina, titanium oxide, a mixed ceria-zirconia type oxide, a tungsten oxide and / or spinel to be shaped by coating deposition.

30. Use according to one of claims 26 to 29, wherein said coating is associated with another coating having pollutant adsorption capabilities in particular of NOx, pollutants reduction especially NOx or promoting oxidation of pollutants.

31. Use according to claim 25, wherein said catalyst is in extruded form, containing up to 100% of said catalyst.

32. Use according to one of claims 25 to 31, wherein the structure coated by said catalyst or obtained by extrusion of said catalyst is integrated in an exhaust line of an internal combustion engine.