Synthesis of palladium-containing composite AFX-BEA zeolite catalysts for NOx adsorption

Abstract

The present invention relates to the preparation of a zeolite composite catalyst comprising a mixture of AFX- and BEA-structure-type zeolites and palladium, comprising at least the following steps: i) In aqueous media, a total SiO 2(FAU) / AlO 3(FAU) mixing a zeolite or a mixture of zeolites of FAU structure type having a molar ratio, an organic nitrogen compound MPC6 (MPC6 is 1,6-bis(methylpiperidinium)hexane dihydroxide), and at least one sodium cation source until a homogeneous precursor gel is obtained; ii) Hydrothermal treatment. iii) filtering, washing, and drying, and then calcining the material; iv) at least one step of ion exchange to obtain the calcined material in ammonium form, followed by drying again at a temperature between 60°C and 120°C; v) Depositing the palladium solution. The invention also relates to the catalyst obtained and to its use for the selective reduction of NOx.

Description

[Technical field]

[0001] Technical Field The present invention relates to a method for producing a palladium-containing zeolite composite catalyst composed of a mixture of AFX- and BEA-structure-type zeolites, to catalysts produced or capable of being produced according to any one of its variants, and to their use, in particular as passive NOx adsorbents in internal combustion engines. [Background technology]

[0002] Prior Art Emissions of nitrogen oxides (NOx) from the combustion of fossil fuels are a serious problem for society. Increasingly stringent standards are being set by government authorities to limit the environmental and health impacts of combustion emissions. Selective catalytic reduction (SCR) has emerged as an effective technology for removing nitrogen oxides from the oxygen-rich exhaust gases typical of lean-mix diesel and spark-ignition engines. Selective catalytic reduction is performed using a reducing agent, usually ammonia, and therefore reduces the amount of NH 3 Transition metal exchanged zeolites are particularly effective in reducing the amount of NH 3 -Used as a catalyst in SCR applications. Small pore zeolites, especially copper exchanged chabazite, are particularly suitable. For spark ignition engines operating stoichiometrically, three-way catalysts (TWCs), if properly formulated, are very effective at reducing NOx.

[0003] However, neither system can effectively treat NOx emissions during cold starts, or more generally when exhaust temperatures are below 180-200°C. Specifically, the decomposition of aqueous urea solutions requires temperatures in excess of 180°C, which results in the formation of NH 3 -SCR efficiency is limited and, for TWC catalysts, optimization of low temperature activity, while still possible, is still considered very difficult to achieve.

[0004] Devices capable of storing and thermally releasing NOx at low temperatures offer the potential to address the efficiency shortfalls of SCR and TWC systems at low temperatures. The concept is not new, having been proposed in the late 1990s by Ford Global Technologies LLC (U.S. Patent No. 6,182,443) and BASF Catalysts LCC (U.S. Patent No. 6,471,924), but recent studies have shown it to be one of the most promising technologies for cold-start NOx emission control. These systems are often referred to as passive NOx adsorbers, or PNAs. In recent years, various materials have been evaluated for NOx adsorption and desorption.

[0005] Related to the cold start concept, Johnson Matthey has proposed a thermally regenerable adsorbent based on palladium dispersed in cerium oxide, mixed oxides, or composite oxides based on cerium (U.S. Pat. No. 8,105,559).

[0006] US 2015 / 01580 19 A1 describes the use of zeolites with platinum group metals as adsorbents, in particular zeolites of the CHA or AEI type. Various zeolite structures have been studied. Passive NOx adsorbents consist of precious metals and molecular sieves of the OFF type (US 2019 / 0217269 A1), MAZ type (WO 2016135465 A1), LTL type (WO 2017 / 001828) or STI type (WO 2019 / 186163 A1) structure. WO 2020039015 A1 describes passive NOx adsorbents consisting of 12MR and 8MR zeolites, such as zeolites of the MOZ structure (ZSM-10), containing palladium.

[0007] US 2020 / 0061595A1 presents a passive NOx adsorbent based on small pore zeolite materials with transition metals dispersed at atomic level within the micropores. The high loading of metals dispersed at atomic level within the micropores of small pore zeolites, especially of the SSZ-13 (CHA) type, provides important adsorption properties.

[0008] Zeolites of the AFX structure type are mentioned in the list of small pore zeolites that can be used for the adsorption of NOx in WO 2015 / 085303 A1 and WO 016135465 A1, but none of these patent applications highlights the advantages offered by this structure, especially depending on its synthesis mode.

[0009] In Catal Lett 146, 1706-1711 (2016), the performance of the Pd / BEA catalyst was evaluated, showing that the NOx storage capacity was good at 100°C, but deteriorated rapidly as the temperature increased. NOx desorption was observed from 200°C.

[0010] WO 19224091 of the applicant company presents a method for the synthesis of a zeolite composite material consisting of a mixture of AFX and BEA structure-type zeolites.

[0011] The applicant has discovered that a novel zeolite composite catalyst, consisting of an intimate mixture of AFX- and BEA-structure-type zeolites, prepared according to a specific synthesis scheme, containing palladium (Pd), not only exhibits an increased total NOx storage capacity compared to the prior art, but also a higher NOx desorption temperature, which can be adjusted as a function of the relative ratio of BEA and AFX zeolites in the composite. Furthermore, the catalyst has a high hydrothermal stability, allowing it to be used under harsh conditions such as those of automobile exhaust gases. [Prior art documents] [Patent documents]

[0012] [Patent Document 1] U.S. Patent No. 6,182,443 [Patent Document 2] U.S. Patent No. 6,471,924 [Patent Document 3] U.S. Patent No. 8,105,559 [Patent Document 4] U.S. Patent Publication No. 2015 / 0158019A1 [Patent Document 5] U.S. Patent Publication No. 2019 / 0217269A1 [Patent Document 6] International Publication No. 2016 / 135465A1 [Patent Document 7] International Publication No. 2017 / 001828A1 [Patent Document 8] International Publication No. 2019 / 186163A1 [Patent Document 9] International Publication No. 2020039015A1 [Patent Document 10] US Patent No. 2020 / 0061595A1 [Patent Document 11] International Publication No. 2015 / 085303A1 [Patent Document 12] International Publication No. 2016 / 135465A1 [Patent Document 13] International Publication No. 19224091 Summary of the Invention [Problem to be solved by the invention]

[0013] Summary of the Invention The present invention relates to a method for preparing a zeolite composite catalyst consisting of a mixture of AFX-type and BEA-type zeolites and palladium, the method comprising at least the following steps: Step i) In an aqueous medium, a total SiO 2(FAU) / Al 2 O 3(FAU)Mixing a zeolite or a mixture of zeolites of FAU structure type having a molar ratio, an organic nitrogen compound MPC6 (MPC6 is 1,6-bis(methylpiperidinium)hexane dihydroxide), and at least one source of sodium cations until a homogeneous precursor gel is obtained, the reaction mixture having the following molar composition: (SiO 2(FAU) ) / (Al 2 O 3(FAU) ) is 20-60, H 2 O / (SiO 2(FAU) ) is 5 to 60, MPC6 / (SiO 2(FAU) ) 0.10 to 0.50, Na 2 O / (SiO 2(FAU) ) 0.05 to 0.11 (including limits), SiO 2(FAU) SiO supplied by FAU Zeolite 2 indicates the amount of Al 2 O 3(FAU) Al supplied by FAU Zeolite 2 O 3 Indicates the amount of; step ii) hydrothermally treating the precursor gel obtained at the end of step i) at a temperature between 160° C. and 220° C. for 12 to 150 hours in order to obtain an AFX-BEA zeolite composite material; step iii) filtering, washing and drying of the AFX-BEA zeolite composite material obtained at the end of step ii), said drying being carried out at a temperature of 60-120° C. for 5-24 hours to obtain a dried AFX-BEA zeolite composite material, followed by calcination of said dried AFX-BEA zeolite composite material at a temperature of 500-700° C. for 2-20 hours to obtain a calcined AFX-BEA zeolite composite material, said calcination optionally being carried out at a gradually increasing temperature; step iv) at least one step of ion exchange of the calcined AFX-BEA zeolite composite material obtained in step iii), in order to obtain the calcined material in ammonium form, by contacting the calcined AFX-BEA zeolite composite material obtained in step iii) with a solution containing ammonium cations, preferably ammonium nitrate, at a temperature between 20 and 95°C, preferably between 60 and 85°C, for a period between 1 hour and 2 days, with stirring, and then redrying at a temperature between 60°C and 120°C; Step v) Depositing a palladium solution onto the calcined and dried AFX-BEA zeolite composite material in ammonium form.

[0014] In step v), the palladium solution can be deposited by dry impregnation or via a colloidal route.

[0015] The reaction mixture of step i) is 2 O 3(C) and wherein the reaction mixture of step i) has the following molar composition: SiO 2(FAU) / (Al 2 O 3(FAU) +Al 2 O 3(C) ) is between 20 and 60 (including the limit value), H 2 O / SiO 2(FAU) is 5 to 60, MPC6 / SiO 2(FAU) is 0.10 to 0.50, Na 2 O / SiO 2(FAU) is 0.05 to 0.11 (including the limit value), and SiO 2(FAU) is SiO provided by FAU Zeolite 2 is the amount of Al 2 O 3(FAU) Al provided by FAU Zeolite 2 O 3 is the amount of Al 2 O 3(C) is the Al provided by the additional aluminum source, considered to be in oxide form. 2 O3 and MPC6 is the dihydroxide form of the organic nitrogen compound 1,6-bis(methylpiperidinium)hexane.

[0016] The additional aluminum source is selected from aluminum hydroxide or aluminum salts, sodium aluminate, aluminum alkoxides, or alumina, either alone or in mixture, and preferably the conventional aluminum source is aluminum hydroxide.

[0017] The source of sodium cations is sodium hydroxide.

[0018] Seed crystals of zeolite of AFX structure type or zeolite of BEA structure type or a mixture of the two are added to the anhydrous form of SiO 2 present in the mixture. 2 and Al 2 O 3 The seed crystals are added to the reaction mixture of step i) in an amount of 0.01% by weight to 10% by weight based on the total mass of the source, and the seed crystals are SiO 2 and Al 2 O 3 It is not taken into account in the total mass of the source.

[0019] The step i) may include a step of aging the reaction mixture at a temperature of 20 to 100° C., with or without stirring, for 30 minutes to 48 hours.

[0020] The content of palladium introduced by deposition step v) can be between 0.5% and 5% by weight, preferably between 0.8% and 3% by weight, more preferably between 0.9% and 2% by weight and very advantageously about 1% by weight relative to the total weight of said anhydrous composite catalyst.

[0021] The present invention also relates to a palladium-containing AFX-BEA zeolite composite catalyst obtained by the preparation process according to any one of its variants.

[0022] Advantageously, the AFX-BEA zeolite composite catalyst according to the invention comprises SiO 2 / Al 2 O3 The ratio is 6 to 80 (limits included), preferably 10 to 40 (limits included).

[0023] The mass ratio of the amount of the AFX-structure-type zeolite to the amount of the BEA-structured zeolite in the catalyst is 0.9 to 5.7.

[0024] The palladium content is 0.5% to 5% by mass, preferably 0.8% to 3% by mass, more preferably 0.9% to 2% by mass, and even more advantageously about 1% by mass, based on the total mass of the anhydrous final catalyst, and the metal dispersion of palladium, measured by CO chemisorption, is 40% to 100%, preferably 50% to 100%.

[0025] The present invention also relates to a method for producing a compound comprising the steps of: 3 Or H 2 The present invention relates to the use of a catalyst according to any one of the described variants or a catalyst obtained by a method according to any one of the described variants for the selective reduction of NOx with a reducing agent such as

[0026] The catalyst may be formed by deposition in the form of a coating on a honeycomb or plate structure.

[0027] The honeycomb structure may be formed by parallel channels that are open at both ends, or may consist of porous filtering walls in which adjacent parallel channels are alternately blocked at both ends of the channels.

[0028] The amount of catalyst deposited on the structure can be between 50 and 240 g / L for filtering structures and between 50 and 320 g / L for structures with open channels.

[0029] To be formed by deposition in the form of a coating, the catalyst may be combined with a binder such as ceria, zirconium oxide, alumina, non-zeolitic silica-alumina, titanium oxide, mixed oxides of the ceria-zirconia type, tungsten oxide and / or spinel.

[0030] The coating may be combined with another coating capable of adsorbing pollutants, particularly NOx, reducing pollutants, particularly NOx, or promoting the oxidation of pollutants.

[0031] In another embodiment, the catalyst may be in the form of an extrudate comprising up to 100% of the catalyst.

[0032] A structure coated with the catalyst or obtained by extrusion of the catalyst can be incorporated into the exhaust line of an internal combustion engine.

[0033] List of Figures Other characteristics and advantages of the process for preparing a catalyst according to the invention will become apparent on reading the following description of non-limiting exemplary embodiments, with reference to the attached figures, which are described below. [Brief description of the drawings]

[0034] [Figure 1] FIG. 1 represents the X-ray diffraction (XRD) pattern of the zeolite composite material Pd / AFX-BEA1, obtained according to Example 2, consisting of a mixture of AFX- and BEA-structure-type zeolites containing Pd. [Diagram 2] FIG. 2 represents the X-ray diffraction (XRD) pattern of the zeolite composite Pd / AFX-BEA2, obtained according to Example 3, composed of a mixture of AFX- and BEA-structure-type zeolites containing Pd. [Diagram 3] FIG. 3 represents the X-ray diffraction (XRD) pattern of the Pd-containing zeolite of AFX structure type obtained according to Example 5. [Figure 4] FIG. 4 represents the X-ray diffraction (XRD) pattern of the Pd-containing BEA zeolite (CP814E) used according to Example 4. [Diagram 5] FIG. 5 represents the X-ray diffraction (XRD) pattern of Pd / AFX-BEA-mecal, a mixture of AFX-structure-type zeolite and BEA-structure-type zeolite (CP814E), obtained according to Example 5. [Figure 6] FIG. 6 shows the NOx concentrations desorbed by the catalysts synthesized according to Example 2 (Pd / AFX-BEA1 according to the present invention), Example 3 (Pd / AFX-BEA2 according to the present invention), Example 4 (Pd / BEA, comparative example), Example 5 (Pd / AFX-BEA-meca1, comparative example) and Example 6 (Pd / AFX-BEA-meca2, comparative example). [Figure 7] FIG. 7 shows the concentrations of NOx desorbed by the Pd / AFX-BEA1-aged catalyst, the Pd / AFX-BEA2-aged catalyst, the Pd / BEA-aged catalyst, the Pd / AFX-BEA-meca1-aged catalyst, and the Pd / AFX-BEA-meca2-aged catalyst. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0035] Description of the embodiments Throughout the description, ranges of values ​​are understood to be inclusive of the limits, unless otherwise specified.

[0036] The present invention more particularly relates to a process for the preparation of a palladium-containing zeolite composite catalyst consisting of an intimate mixture of AFX-structure-type and BEA-structure-type zeolites, the process comprising at least the following steps: Step i): In an aqueous medium, a total SiO 2(FAU) / Al 2 O 3(FAU) Mixing a zeolite or a mixture of zeolites of FAU structure type having a molar ratio, an organic nitrogen compound MPC6 (MPC6 is 1,6-bis(methylpiperidinium)hexane dihydroxide), and at least one source of sodium cations until a homogeneous precursor gel is obtained, the reaction mixture having the following molar composition: (SiO 2(FAU) ) / (Al 2 O 3(FAU) ) is 20-60, H 2 O / (SiO 2(FAU) ) is 5 to 60, MPC6 / (SiO 2(FAU)) 0.10 to 0.50, Na 2 O / (SiO 2(FAU) ) 0.05 to 0.11 (including limits), SiO 2(FAU) SiO supplied by FAU Zeolite 2 indicates the amount of Al 2 O 3(FAU) Al supplied by FAU Zeolite 2 O 3 Indicates the amount of.

[0037] The source of sodium cations is preferably sodium hydroxide.

[0038] In another embodiment, the reaction mixture of step i) contains at least one conventional, i.e., additional source of aluminum considered in its oxide form, not obtained from an already formed zeolite (Al 2 O 3(C) ) may be included.

[0039] In this case, the reaction mixture of step i) preferably has the following molar composition: SiO 2(FAU) / (Al 2 O 3(FAU) +Al 2 O 3(C) ) 20 to 60 (including limits) H 2 O / SiO 2(FAU) is 5 to 60, MPC6 / SiO 2(FAU) 0.10 to 0.50, Na 2 O / SiO 2(FAU) 0.05 to 0.11 (including limits) SiO 2(FAU) SiO provided by FAU Zeolite 2 is the amount of Al 2 O 3(FAU) Al provided by FAU Zeolite 2 O 3 is the amount of Al 2 O 3(C)Al is provided by additional aluminum sources considered in their oxide form. 2 O 3 and MPC6 is an organic nitrogen compound, 1,6-bis(methylpiperidinium)hexane.

[0040] The source of sodium cations is preferably in the form of sodium hydroxide dihydroxide.

[0041] Seed crystals of zeolite of AFX or BEA structure type or a mixture of the two can be added to the reaction mixture of step i), said seed crystals preferably being present in the mixture in anhydrous form, SiO 2 and Al 2 O 3 and the seed crystals are introduced in an amount of 0.01% to 10% by weight relative to the total mass of the source of SiO 2 and Al 2 O 3 is not taken into account in the total mass of the source.

[0042] The zeolite or mixture of zeolites of the FAU structural type used in synthesis step i) is preferably SiO 2 / Al 2 O 3 The molar ratio is 20 to 60 (limits included).

[0043] SiO2 from 20 to 60 (including the limit value) 2 / Al 2 O 3 A mixture of zeolites of the FAU structure type having a molar ratio of, for example, SiO 2 (FAU) / Al 2 O 3(FAU) By any method known to those skilled in the art, such as steaming and acid washing over a zeolite of the FAU structure type having a molar ratio of less than 6.00, or by SiO 2(FAU) / Al 2 O 3(FAU) SiO with a molar ratio of 20 to 60 (including the limit value) 2(FAU) / Al 2 O 3(FAU) To obtain the molar ratio of different SiO 2(FAU) / Al 2O 3(FAU) The starting zeolite of FAU structure type can be obtained by mixing zeolites of the FAU structure type in the ratio of 1:1 to 1:1. Among the sources of FAU, mention may be made of the commercial zeolites CBV712, CBV720, CBV760 and CBV780 from Zeolyst, and the commercial zeolites HSZ-350HUA, HSZ-360HUA and HSZ-385HUA from Tosoh. The starting zeolite of FAU structure type can be used in its sodium form or in other forms, or can be obtained after partial or complete exchange of sodium cations with ammonium cations, optionally after a calcination step.

[0044] Al 2 O 3 Additional sources of oxides are preferably aluminium hydroxide or aluminium salts such as chloride, nitrate or sulphate, sodium aluminate, sodium aluminate or alumina itself, preferably in a hydrated or hydratable form such as colloidal alumina, perseudocboehmite, gamma-alumina or alpha or beta alumina trihydrate. Mixtures of the above mentioned sources can also be used. Preferably, Al 2 O 3 An additional source of oxide is aluminum hydroxide.

[0045] Step i) may include maturing the reaction mixture at a temperature between 20 and 100° C., with or without stirring, for a time between 30 minutes and 48 hours.

[0046] Step ii): The precursor gel obtained at the end of step i) is subjected to a hydrothermal treatment at a temperature of 160° C. to 220° C. for a time period of 12 hours to 150 hours.

[0047] Advantageously, the SiO 2 content of the resulting AFX-BEA zeolite composite material is 2 / Al 2 O 3 The molar ratio is between 6 and 80 (limits included), preferably between 10 and 40 (limits included).

[0048] Filtration, washing, drying and calcination process iii). In this step, the AFX-BEA zeolite composite material obtained at the end of step ii) is filtered, washed and dried at a temperature of 60-120°C for 5-24 hours to obtain a dried AFX-BEA zeolite composite material, which is then calcined at a temperature of 500-700°C for a time period between 2-20 hours, optionally with a gradual increase in temperature.

[0049] Ion exchange step iv): At least one ion exchange is carried out on the calcined AFX-BEA zeolite composite material obtained in step iii) in order to obtain a calcined material in ammonium form, which consists in contacting the calcined AFX-BEA zeolite composite material obtained in step iii) with a solution containing ammonium cations, preferably ammonium nitrate, under stirring, at a temperature between 20 and 95°C, preferably between 60 and 85°C, for a time period between 1 hour and 2 days. At the end of the ion exchange step, the calcined AFX-BEA zeolite composite material in ammonium form is dried again at a temperature between 60 and 120°C, preferably for a time period between 5 and 24 hours. This ion exchange step can be repeated several times in order to obtain a solid containing less than 0.01% by weight of Na.

[0050] Palladium Deposition Step v): The deposition of the palladium solution onto the calcined and dried AFX-BEA zeolite composite material in ammonium form can be carried out according to any technique known to the person skilled in the art.

[0051] The palladium solution is preferably deposited by dry impregnation or by a colloidal route.

[0052] The content of palladium introduced by the deposition step v) is advantageously between 0.5% and 5% by weight, preferably between 0.8% and 3% by weight, more preferably between 0.9% and 2% by weight and very advantageously about 1% by weight, relative to the total weight of the anhydrous composite catalyst.

[0053] Dry impregnation In one embodiment according to the invention, the palladium solution is deposited by dry impregnation. More specifically, the method for preparing the catalyst comprises the following steps: a) Preparing an aqueous solution containing at least one palladium precursor salt. b) The dry AFX-BEA zeolite composite material in ammonium form obtained in step iv) of the preparation process according to the invention is impregnated, at ambient temperature, with the aqueous solution obtained in step a). c) The catalyst precursor obtained at the end of step b) is dried to obtain a dried catalyst precursor; the catalyst precursor is generally dried at a temperature of preferably 50°C to 250°C, more preferably 70°C to 200°C, in order to remove all or part of the water introduced during impregnation. Drying times of 0.5 to 20 hours are preferred. Longer times are not excluded, but are not necessarily an improvement. Drying is generally carried out under combustion air of a hydrocarbon, preferably methane, or under heated air consisting of 0 to 80 g of water per kg of combustion air, an oxygen content of 5% to 25% by volume and a carbon dioxide content of 0% to 10% by volume. d) Optionally, the dried catalyst precursor obtained in step c) is calcined at a temperature between 250 and 900° C. to obtain a calcined catalyst precursor. After drying, the catalyst is mixed with air, preferably combustion air, more preferably 40-80 g water per kg air, with an oxygen content of 5% to 15% by volume and 4% to 10% by volume of CO 2 The calcination can be performed under combustion air containing methane. The calcination temperature is generally 250°C to 900°C, preferably about 350°C to about 550°C. The calcination time is generally 0.5 to 5 hours. The calcination time is generally 0.5 to 5 hours. e) Optionally, the reduction treatment is carried out by contacting with a reducing gas.

[0054] Impregnation via colloidal route In another embodiment of the present invention, the palladium solution is deposited by a colloidal method. More specifically, the method of preparing the catalyst comprises the following steps: a) Preparation of an aqueous solution comprising at least one palladium precursor salt. In step a), an aqueous solution is prepared comprising at least one palladium precursor salt, preferably selected from sodium chloropalladium salt and palladium nitrate. b) Preparation of the impregnated support: The deposition of palladium on the calcined and dried AFX-BEA zeolite composite material in ammonium form obtained in step iv) of the preparation method according to the invention is carried out by dry impregnation of the calcined and dried AFX-BEA zeolite composite material in ammonium form with the aqueous solution obtained in step a), the volume of said aqueous solution being generally 0.9-1.1 times the pore volume of the calcined and dried AFX-BEA zeolite composite material in ammonium form. c) Aging of the support impregnated in step b). After impregnation, the ammonium form calcined and dried AFX-BEA zeolite composite material is aged in a wet state for 0.5 to 40 hours, preferably 1 to 30 hours. Longer times are not construed as being undesirable, but may not necessarily provide an improvement. d) Drying of the catalyst precursor obtained in step b) or step c) The catalyst precursor is generally dried at a temperature of preferably 50° C. to 250° C., more preferably 70° C. to 200° C., in order to remove all or part of the water introduced during impregnation. The drying time is preferably 0.5 to 20 hours. Although longer drying times are not necessarily rejected, they do not necessarily provide an improvement. Drying is generally carried out under combustion air of a hydrocarbon, preferably methane, or under heated air containing 0 to 80 g of water per kg of combustion air, an oxygen content of 5 to 25% by volume, and a carbon dioxide content of 0% to 10% by volume. e) Calcining the dried catalyst obtained in step d) under combusted air (optional step).

[0055] After drying, the catalyst is mixed with air, preferably combustion air, more preferably 40-80 g water per kg air, with an oxygen content of 5% to 15% by volume and 4% to 10% by volume of CO 2 The calcination can be performed under combustion air containing methane. The calcination temperature is generally 250°C to 900°C, preferably about 350°C to about 550°C. The calcination time is generally 0.5 to 5 hours. The calcination time is generally 0.5 to 5 hours.

[0056] The present invention also relates to a composite catalyst in the form of a palladium-containing zeolitic material composed of a mixture of AFX-type zeolite and BEA-type zeolite, which can be prepared by a method according to an embodiment of the present invention, said composite catalyst having a mass ratio of the amount of AFX-type zeolite to the amount of BEA-type zeolite of 0.9 to 5.7.

[0057] The content of palladium in the zeolite composite catalyst according to the invention is advantageously between 0.5% and 5% by weight, preferably between 0.8% and 3% by weight, very preferably between 0.9% and 2% by weight, very advantageously about 1% by weight, relative to the total mass of the anhydrous catalyst.

[0058] In the zeolite composite catalyst according to the invention, the dispersion of palladium, measured by CO chemisorption, is advantageously between 40% and 100%, preferably between 50% and 100%.

[0059] Characterization of the catalyst according to the present invention At the end of steps ii), iii), iv) or v) of the preparation of the catalyst according to the invention, it is possible to verify by X-ray diffraction that the solid obtained in the process according to the invention is in fact an AFX-BEA zeolite composite comprising zeolites of the AFX and BEA structural types, the purity obtained being advantageously greater than 90% by weight, preferably greater than 95% and very preferably greater than 99.8% by weight.

[0060] In other words, the palladium-containing zeolite composite catalyst according to the invention based on AFX / BEA zeolite composite contains less than 5% by weight, preferably less than 1% by weight, more preferably less than 0.2% by weight of impurities and / or crystalline or amorphous phases other than AFX and BEA (limits not included).Highly advantageously, the process of the present invention results in the formation of a catalyst based on AFX-BEA zeolite composite that is free of other crystalline or amorphous phases.

[0061] This technique also makes it possible to determine the relative proportions of each of the zeolites, AFX and BEA, contained in the catalyst according to the invention or obtained by the process of the invention by any one of its variants.

[0062] Advantageously, the solid obtained by the process according to the invention has an X-ray diffraction pattern comprising at least the lines recorded in Table 1.

[0063] This diffraction pattern is the K α1 The diffraction peaks are obtained by synchrotron radiation crystallography using a conventional powder diffractometer with 1.5406 Å radiation. Based on the positions of the diffraction peaks, expressed as the angle 2θ, the interplanar spacing d of the sample can be calculated using Bragg's law. hkl Calculate the characteristics. d hkl Measurement error Δ(d hkl ) is calculated by the Bragg relation as a function of the absolute error Δ(2θ) assigned to the measurement of 2θ. The absolute error Δ(2θ) is typically ±0.02°. hkl The relative intensity I assigned to each value of rel are measured according to the height of the corresponding diffraction peak. The X-ray diffraction pattern of the crystalline solid obtained at the end of step ii) of the process according to the invention has at least the d given in Table 1 hkl The value of d measured on the X-ray diffraction pattern of the zeolite composite catalyst according to the present invention hkl d hkl The value column shows the average lattice spacing in angstroms (Å). Each value has a measurement error Δ(d hkl ) must be assigned.

[0064] [Table 1]

[0065] According to the invention, the mass composition of the prepared composite material, in particular the relative mass fractions of zeolites of AFX and BEA structure types present in said catalyst based on the composite material, is advantageously determined by comparison of the areas of the peaks at angles (2θ) 20.38±0.1 (hkl:211); 23.67±0.1 (hkl:105); 26.1±0.1 (hkl:303) and 28.02±0.1 (hkl:303) of reference zeolites of AFX structure type, preferably of high purity, using a method similar to that of the standard ASTM D3906 03. The mass ratio of the two zeolites AFX and BEA in the composite material according to the invention is thus evaluated by comparing the sum of the areas of the peaks at the above angles (2θ) obtained for the composite material prepared according to the invention with a zeolite reference sample, using the following calculation formula: AFX / BEA=S AFXc / (S AFXr -S AFXc ) Here, S AFXc is the sum of the areas of the peaks present at angles (2θ) of 20.38±0.1 (HKL: 211), 23.67±0.1 (HKL: 105), 26.1±0.1 (HKL: 303) and 28.02±0.1 (HKL: 106) in the diffraction pattern of the AFX-BEA composite material prepared according to the present invention, and S AFXr is the sum of the areas of the peaks present at angles (2θ): 20.38 (hkl: 211); 23.67 (HKL: 105); 26.1 (hkl: 303) and 28.02 (hkl: 106) in the diffraction pattern of the pure zeolite of AFX structure used as standard. The pure zeolite of AFX structure used as standard can be prepared, for example, according to the method illustrated in Example 5 of the present invention.

[0066] X-ray fluorescence spectrometry (XRF) is a chemical analysis technique that utilizes the fluorescence of X-rays, a physical property of matter. It can provide accurate and reproducible analysis of most chemical elements, starting with beryllium (Be), in concentrations ranging from a few ppm to 100%. X-rays are used to excite atoms in a sample, causing them to emit X-rays with energies characteristic of each element. The intensity and energy of these X-rays are then measured to determine the concentration of elements in the material.

[0067] The loss on ignition (LOI) of the catalyst obtained after the drying step (and before calcination) or after the calcination step of step iii) of the method according to the invention is generally between 2% and 20% by weight. The loss on ignition of a catalyst sample, referred to by the abbreviation LOI, corresponds to the difference in mass of the sample before and after heat treatment at 1000°C for 2 hours. It is expressed as a percentage of the mass loss. The loss on ignition generally corresponds to the loss of solvents (such as water) contained in the solid, but also to the removal of organic compounds contained in the inorganic solid components.

[0068] Particle dispersion (D) is a unitless number, often expressed as a percentage. The smaller the particle, the greater the dispersion. It is defined in the paper by R. Van Hardeveld and F. Hartog, “The statistics of surface atoms and surface sites on metal crystals”, Surface Science 15, 1969, 189-230. Dispersion can be measured by CO chemisorption.

[0069] Catalyst according to the present invention The Applicant has discovered that the catalysts obtained by the method according to the invention have different properties than the palladium-containing microporous aluminosilicate materials known from the prior art: in particular, the palladium-containing AFX-BEA zeolite composite catalysts obtained by any of the method variants according to the invention have increased adsorption capacity, increased desorption temperature and higher hydrothermal resistance.

[0070] Without being bound by any theory, it appears that the method for preparing the catalyst according to the invention allows in particular a better dispersion of palladium, which contributes to improved catalytic NOx reduction performance quality. Furthermore, the improved dispersion of palladium allows the amount of readily available and active palladium to be optimized, allowing the use of lower palladium contents while still obtaining very good catalytic performance quality.

[0071] Advantageously, the SiO 2 of the obtained catalyst based on the AFX-BEA composite zeolite 2 / Al 2 O 3 The molar ratio is from 6 to 80 (limits included), preferably from 10 to 40 (limits included).

[0072] The content of palladium in the zeolite composite catalyst according to the invention is advantageously between 0.5% and 5% by weight, preferably between 0.8% and 3% by weight, very preferably between 0.9% and 2% by weight and very advantageously about 1% by weight, relative to the total mass of the anhydrous catalyst.

[0073] In the zeolite composite catalyst prepared according to the present invention, the dispersion of palladium is advantageously between 40% and 100%, preferably between 50% and 100%.

[0074] Use of the catalyst according to the invention The present invention also relates to the use of a catalyst according to the invention, either prepared directly or preparable by the method described above according to any one of its variants, for the adsorption of NOx at temperatures below 200° C., advantageously formed by deposition in the form of a coating (or “washcoat”) on a honeycomb structure, mainly for mobile applications.

[0075] The honeycomb structure consists of open parallel channels open at both ends ("flow-through channels") or porous filtering walls, where adjacent parallel channels are alternately blocked at both ends of the channel to force the gas flow through the walls ("wall-flow monolith"). The honeycomb structure thus coated constitutes the catalyst block. The structure can be made of cordierite, silicon carbide (SiC), aluminum titanate (AlTi), α-alumina, mullite, or other materials with a porosity of 30% to 70%. The structure can be made of metal plate, stainless steel with chromium and aluminum, FeCrAl steel.

[0076] The amount of catalyst according to the invention deposited on the structure is between 50 and 240 g / L for filtering structures and between 50 and 320 g / L for structures with open channels.

[0077] The actual coating ("wash coat") consists of the catalyst according to the invention in combination with a binder, advantageously ceria, zirconium oxide, alumina, non-zeolitic silica-alumina, titanium oxide, mixed oxides of the ceria-zirconia type, tungsten oxide, spinel, etc. Said coating is advantageously applied to the structure by a deposition technique known as wash coating, which consists in immersing the monolith in a suspension (or slurry) of the powdered catalyst according to the invention in a solvent, preferably water, and optionally binders, metal oxides, stabilizers or other promoters. This immersion step can be repeated until the desired amount of coating is obtained. Optionally, the slurry is sprayed inside the monolith. Once the coating has been deposited, the monolith is calcined at a temperature between 300 and 600 °C for 1 to 10 hours.

[0078] The structure can be coated with one or more coatings. The coating containing the catalyst according to the invention is advantageously combined with, i.e. coated or coated with, another coating having the ability to reduce pollutants, especially NOx, and / or to promote the oxidation of pollutants, especially carbon monoxide (CO) and hydrocarbons (HC).

[0079] Another possibility is that the catalyst is in the form of extrudates, in which case the resulting structure can contain up to 100% of the catalyst according to the invention.

[0080] The structure coated with the catalyst according to the invention is advantageously integrated into the exhaust line of an internal combustion engine. Under such engine operating conditions, the exhaust gases contain, among other pollutants: soot, unburned hydrocarbons (HC), carbon monoxide (CO) and nitrogen oxides (NOx). The structure coated with the catalyst according to the invention is advantageously integrated into the exhaust line of an internal combustion engine. Under such engine operating conditions, the exhaust gases contain, among other pollutants: soot, unburned hydrocarbons (HC), carbon monoxide (CO) and nitrogen oxides (NOx). 3 - Located upstream of a NOx treatment catalyst, which may be an SCR catalyst, a NOx trap or a three-way catalyst. An oxidation catalyst, whose function is to oxidize HC and CO, and a filter for removing soot from the exhaust gas, may be located either upstream or downstream of said structure.

[0081] The function of the coated structure is to adsorb NOx and its operating range is as follows: in the adsorption phase, between -20 and 300°C, preferably between -20 and 200°C; In the desorption stage, the temperature is between 150°C and 500°C, preferably between 250°C and 400°C.

[0082] Advantages of the Invention The catalyst according to the invention, based on a zeolite composite material consisting of an intimate mixture of zeolites of AFX and BEA structure types and containing palladium, 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 adsorb NOx at temperatures between -20°C and 200°C.

[0083] In addition, it has excellent resistance to hydrothermal degradation, and maintains high adsorption performance even after degradation. EXAMPLES

[0084] example The present invention is illustrated by the following examples which are in no way limiting.

[0085] Example 1: Preparation of 1,6-bis(methylpiperidinium)hexane dihydroxide (organic structuring agent MPC6) 50 g of 1,6-dibromohexane (0.20 mol, 99%, Alfa Aesar) are added to a 1 L round-bottom flask containing 50 g of N-methylpiperidine (0.51 mol, 99%, Alfa Aesar) and 200 mL of ethanol. The reaction medium is stirred and refluxed for 5 hours. The mixture is then cooled to ambient temperature and filtered. The mixture is poured into 300 mL of cold diethyl ether and the precipitate formed is filtered and washed with 100 mL of diethyl ether. The solid obtained is recrystallized in an ethanol / ether mixed solvent. The solid obtained is dried under vacuum for 12 hours. 71 g of a white solid is obtained (i.e. a yield of 80%).

[0086] The product is 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(8Hm);2.85(6H,s);3.16(12H,m).

[0087] 18.9g Ag 2O (0.08 mol, 99%, Aldrich) is added to a 250 mL Teflon beaker containing 30 g of the prepared structurant 1,6-bis(methylpiperidinium)hexane dibromide (0.07 mol) and 100 mL of deionized water. The reaction is stirred for 12 hours in the absence of light. The mixture is then filtered. The filtrate obtained consists of an aqueous solution of 1,6-bis(methylpiperidinium)hexane dihydroxide (MPC6). This type of measurement is performed by proton NMR using formic acid as the standard.

[0088] Example 2: Preparation of the Palladium-Containing AFX-BEA Zeolite Catalyst of the Present Invention 275.3 g of an aqueous solution of 1,6-bis(methylpiperidinium)hexane dihydroxide (18.36 wt%) prepared according to Example 1 is mixed with 390.61 g of deionized water at ambient temperature with stirring. 7.18 g of sodium hydroxide (98 wt%, Aldrich) is dissolved in the mixture at ambient temperature with stirring. Then, 6.32 g of amorphous aluminum hydroxide gel (Al(OH) 3 Amorphous gel, Al 2 O 3 58.55% by weight based on the total weight of the suspension (Merck) is added to the synthesis mixture, which is kept under stirring for 30 minutes at ambient temperature. As soon as the resulting suspension is homogeneous, 70.9 g of zeolite of the FAU structure type (CBV780, SiO 2 / Al 2 O 3 = 90.54, Zeolyst, LOI = 8.52%) and the resulting suspension is stirred for 30 minutes at ambient temperature. Then, 5.73 g of calcined zeolite seeds of AFX structural type (SiO 2 in anhydrous form present in the mixture) are added. 2 and Al 2 O 3 Add 1000 mL of SiO (8.36% relative to the total mass of the sources) to the synthesis mixture and keep stirring for 30 min. The molar composition of the precursor gel is as follows: 1 SiO 2 :0.05 Al 2 O 3 :0.167 MPC6:0.093 Na 2 O:36.73 H 2O, i.e. SiO 2 / Al 2 O 3 The ratio is 20. Then, after homogenization, the precursor gel is transferred to a 1000 mL stainless steel reactor equipped with a stirring system with four inclined blades. The reactor is sealed and heated to 180 °C at 3 °C / min with stirring at 200 rpm for 18 hours to crystallize the mixture of AFX and BEA structure types of zeolite. The crystallized product obtained is filtered, washed with deionized water and then dried at 100 °C for 12 hours. The loss on ignition of the dry solid is 16.38%. The solid is then introduced into a muffle furnace where a calcination step is carried out: the calcination cycle includes a temperature increase of 1.5 °C / min to 200 °C, a stationary phase maintained at 200 °C for 2 hours, a temperature increase of 1 °C / min to 550 °C, followed by a stationary phase at 550 °C maintained for 12 hours, followed by a return to ambient temperature.

[0089] After calcination, 40.0 g of this zeolite mixture was dissolved in 3 M NH 4 NO 3 The mixture was then exchanged three times with an aqueous solution of 100 ml of NH 4 -It will be named AFX-BEA1.

[0090] 0.25 g hydrated Pd(NH 3 ) 4 Cl 2 Dilute with 12 mL of demineralized water and add 10 g or more of the solid NH 4 - Impregnate with AFX-BEA1 at 25°C (dry impregnation method).

[0091] The obtained catalyst Pd-NH 4 -AFX-BEA1 is dried in air at 120°C for 2 hours and then calcined by HSV at 550°C for 2 hours in a combustion air stream at 3000 litres of combustion air per litre of catalyst per hour. The combustion air contains approximately 60g of water per kg of dry air.

[0092] The catalyst Pd / AFX-BEA1 thus prepared contains 1% by weight of palladium relative to the total weight of the catalyst. The metal dispersion of Pd obtained by CO chemisorption is 60%.

[0093] The catalyst Pd / AFX-BEA1 was analyzed by X-ray diffraction and identified as a zeolite composite consisting of a mixture of about 78% by mass of AFX-type zeolite and about 22% by mass of BEA-type zeolite, with an AFX / BEA mass ratio of 3.55. The X-ray diffraction pattern of the product produced by the catalyst Pd / AFX-BEA1 is shown in Figure 1. The product had an SiO2 content of 16.64 as measured by XRF. 2 / Al 2 O 3 The molar ratio is:

[0094] Example 3: Preparation of a catalyst containing a zeolite of AFX-BEA structural type with palladium according to the invention 23.9 g of FAU structure type zeolite (CBV712 Zeolyst, SiO 2 / Al 2 O 3 = 11.42, LOI = 12.81%) was mixed with 495.2 g of deionized water. 57.3 g of FAU structure type zeolite (CBV780 Zeolyst, SiO 2 / Al 2 O 3 = 98.22, LOI = 8.52%) is added to the above mixture and the resulting preparation is stirred for 10 minutes. 290.5 g of an aqueous solution of 1,6-bis(methylpiperidinium)hexane dihydroxide (20.91 wt%) prepared according to Example 1 is added to the above mixture. The mixture is then kept stirring for 10 minutes. 33.0 g of an aqueous solution of 20 wt% sodium hydroxide (solution prepared from 98 wt% sodium hydroxide, Aldrich) is added to the mixture and kept stirring for 10 minutes. The molar composition of the precursor gel is as follows: 1 SiO 2 :0.03 Al 2 O 3 :0.167 MPC6:0.072 Na 2 O:36.73 H 2O, i.e. SiO 2 / Al 2 O 3 The ratio is 33.3. The precursor gel is transferred to an autoclave after homogenization. The autoclave is sealed and heated at 180 °C for 6 days with stirring at 35 rpm with a rotating spit system. The resulting crystalline product is filtered and washed with deionized water, then dried at 100 °C overnight.

[0095] The solid is then introduced into a muffle furnace where a calcination step is carried out under air flow: the calcination cycle involves a temperature increase of 1.5°C / min to 200°C, a stationary phase held at 200°C for 2 h, followed by a temperature increase at a rate of 1°C / min to 550°C, followed by a stationary phase at 550°C held for 8 h, followed by a return to ambient temperature.

[0096] After calcination, 40.0 g of this zeolite mixture was dissolved in 3 M NH 4 NO 3 The mixture was exchanged three times with an aqueous solution of 100 ml of NH 4 -It will be named AFX-BEA2.

[0097] 0.25 g hydrated Pd(NH 3 ) 4 Cl 2 Dilute with 13 mL of demineralized water and impregnate with at least 10 g of the zeolite NH4-AFX-BEA2 prepared above at 25 °C (dry impregnation method).

[0098] The obtained catalyst Pd-NH 4 - AFX-BEA2 is dried under air at 120°C for 2 hours and then calcined by HSV at 550°C for 2 hours in a combustion air stream of 3000 litres / hour per litre of catalyst. Combustion air contains approximately 60g of water per kg of dry air.

[0099] The catalyst Pd / AFX-BEA2 thus prepared contains 1% by weight of palladium relative to the total weight of the catalyst. The metal dispersion of Pd obtained by CO chemisorption is 58%.

[0100] The catalyst Pd / AFX-BEA2 was analyzed by X-ray diffraction and identified as a zeolite composite consisting of a mixture of approximately 50% by mass of AFX structure type zeolite and approximately 50% by mass of BEA structure type zeolite, with an AFX / BEA mass ratio of 1. The X-ray diffraction pattern generated by the catalyst Pd / AFX-BEA2 is shown in Figure 2.

[0101] Example 4 (Comparative Example): Preparation of a Catalyst Containing a BEA-Structural-Type Zeolite with Pd Commercially available zeolite NH 4 -BEA(CP814E, SiO 2 / Al 2 O 3 = 25.16, Zeolyst) was used as a support for impregnation of the palladium precursor.

[0102] 0.25 g hydrated Pd(NH 3 ) 4 Cl 2 Dilute with 17 mL of demineralized water and add at least 10 g of zeolite NH 4 -BEA(CP814E SiO 2 / Al 2 O 3 = 25.16, Zeolyst) at 25°C (dry impregnation method).

[0103] The solid obtained is dried under air at 120 °C for 2 h. The catalyst obtained, Pd-NH 4 -BEA is dried in air at 120°C for 2 hours and then calcined by HSV at 550°C for 2 hours in a combustion air stream at 3000 litres of combustion air per litre of catalyst per hour. The combustion air contains approximately 60g of water per kg of dry air.

[0104] The catalyst Pd / BEA thus prepared contains 1 wt.% palladium with respect to the total weight of the catalyst. The metal dispersion of Pd obtained by CO chemisorption is 28%. The X-ray diffraction pattern generated for the catalyst Pd / BEA is shown in Figure 4.

[0105] Example 5 (Comparative Example): Preparation of a Catalyst Containing a Mechanical Mixture of AFX and BEA Structure-Type (78 / 22) Zeolites with Palladium 1) Preparation of catalysts containing palladium-containing AFX-type zeolites 275.8 g of an aqueous solution of 1,6-bis(methylpiperidinium)hexane dihydroxide (18.36 wt%) prepared according to Example 1 is mixed with 391.23 g of deionized water at ambient temperature under stirring. 7.18 g of sodium hydroxide (98 wt%, Aldrich) is dissolved in the above mixture at ambient temperature under stirring. Then, 6.33 g of amorphous aluminum hydroxide gel (Al(OH) 3 Amorphous gel, 58.55% by weight Al 2 O 3 , Merck) is added to the synthesis mixture, which is kept under stirring at room temperature for 30 minutes. As soon as the resulting suspension becomes homogeneous, 70.88 g of zeolite of the FAU structure type (CBV780, SiO 2 / Al 2 O 3 = 90.54, Zeolyst, LOI = 8.52%) is started and the resulting suspension is stirred for 30 minutes at ambient temperature. To promote the formation of zeolite of AFX structure type, 6.14 g of calcined zeolite seeds of AFX structure type (8.7% with respect to the mass of CBV780 zeolite) are added to the synthesis mixture and stirring is continued for 5 minutes. The reaction mixture is then left to age for 24 hours at ambient temperature under stirring (200 rpm). 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 O:36.73 H 2 O, i.e. SiO 2 / Al 2 O 3The ratio is 20. Then, after homogenization, the precursor gel is transferred to a 1000 mL stainless steel reactor equipped with a stirring system with four inclined blades. The reactor is sealed and heated to 180 ° C at 5 ° C / min and stirred at 200 rpm for 14 hours to crystallize the zeolite of AFX structure type. The crystalline product obtained is filtered, washed with deionized water and then dried at 100 ° C overnight. The solid is then introduced into a muffle furnace where a calcination step is carried out: the calcination cycle includes a temperature increase of 1.5 ° C / min to 200 ° C, a stationary phase maintained at 200 ° C for 2 hours, a temperature increase at 1 ° C / min to 550 ° C, followed by a stationary phase at 550 ° C for 12 hours, followed by a return to ambient temperature.

[0106] After calcination, 40.0 g of this zeolite mixture was dissolved in 3 M NH 4 NO 3 The mixture was exchanged three times with an aqueous solution of 100 ml of NH 3 at 80 °C for 1 h under stirring (300 rpm) and with a ratio of the volume of the solution to the mass of the zeolite equal to 10 (V / W). 4 The -AFX was filtered and dried at 100°C overnight.

[0107] 0.25 g hydrated Pd(NH 3 ) 4 Cl 2 Dilute with 8.2 mL of demineralized water and add more than 10 g of the above-prepared zeolite NH 4 -AFX is impregnated at 25°C (dry impregnation method).

[0108] The obtained catalyst Pd-NH 4 -AFX-BEA1 is dried in air at 120°C for 2 hours and then calcined by HSV at 550°C for 2 hours in a combustion air stream at 3000 litres of combustion air per litre of catalyst per hour. The combustion air contains approximately 60g of water per kg of dry air.

[0109] The catalyst Pd / AFX thus prepared contains 1% by weight of palladium relative to the total weight of the catalyst. The metal dispersion of Pd obtained by CO chemisorption is 55%.

[0110] The catalyst Pd / AFX was analyzed by X-ray diffraction and identified as consisting of a zeolite of AFX structure type with a purity of over 99% by weight. The X-ray diffraction pattern generated for the calcined solid is shown in Figure 3. The product had an SiO of 14.46 as measured by XRF. 2 / Al 2 O 3 The molar ratio is:

[0111] 2) Preparation of Pd AFX-BEA catalyst obtained by mechanical mixing (Comparative Example) 156 mg of the prepared palladium-containing AFX-structured zeolite was mixed with 44 mg of palladium-containing BEA-structured zeolite prepared according to Example 4 (i.e., AFX / BEA mass ratio 3.55). The material obtained was named Pd / AFX-BEA-mecal.

[0112] The catalyst Pd / AFX-BEA-meca1 thus prepared contains 1% by weight of palladium relative to the total weight of the catalyst. The metal dispersion of Pd obtained by CO chemisorption is 50%.

[0113] The catalyst Pd / AFX-BEA-meca1 was analyzed by X-ray diffraction and identified as a zeolite composite consisting of a mixture of approximately 78% by mass of AFX structure type zeolite and approximately 22% by mass of BEA structure type zeolite, with an AFX / BEA mass ratio of 1. The X-ray diffraction pattern of the catalyst Pd / AFX-BEA-meca1 is shown in Figure 5.

[0114] Example 6 (Comparative Example): Preparation of a Catalyst Containing a Mechanical Mixture of AFX and BEA Structure-Type Zeolites (50 / 50) with Palladium 100 mg of AFX-structure type zeolite containing palladium prepared according to Example 5 was mixed with 100 mg of BEA-structure type zeolite containing palladium prepared according to Example 4 (i.e., AFX / BEA mass ratio of 1). The material obtained was named Pd / AFX-BEA-meca2.

[0115] The catalyst Pd / AFX-BEA-meca2 thus prepared contains 1% by weight of palladium relative to the total weight of the catalyst. The metal dispersion of Pd obtained by CO chemisorption is 48%.

[0116] Example 7: Hydrothermal aging process 550 mg of each sample synthesized according to Example 2 (Pd / AFX-BEA1), Example 3 (Pd / AFX-BEA2), Example 4 (Pd / BEA), Example 5 (Pd / AFX-BEA-meca1), and Example 6 (Pd / AFX-BEA-meca2) are placed in a quartz reactor in powder form. A mixture of the following molar composition is passed through the sample at a flow rate of 150 L / h: 10% H 2 O, 20% O 2 , the rest is N 2 .

[0117] The samples are exposed to these conditions for 4 hours at a temperature of 750 °C, after which they are cooled to room temperature under a nitrogen stream.

[0118] The sample synthesized according to Example 2 and aged under the conditions of Example 7 was named Pd / AFX-BEA1-aged.

[0119] The sample synthesized according to Example 3 and aged under the conditions of Example 7 was named Pd / AFX-BEA2-aged.

[0120] The sample synthesized according to Example 4 and aged under the conditions of Example 7 was named Pd / BEA-aged.

[0121] The sample synthesized according to Example 5 and aged under the conditions of Example 7 was named Pd / AFX-BEA-meca1-aged.

[0122] The sample synthesized according to Example 6 and aged under the conditions of Example 7 was named Pd / AFX-BEA-meca2-aged.

[0123] Example 8: NOx adsorption / desorption test To demonstrate the adsorption capacity, catalysts synthesized according to Example 2 (Pd / AFX-BEA1 according to the invention), Example 3 (Pd / AFX-BEA2 according to the invention), Example 4 (Pd / BEA), Example 5 (Pd / AFX-BEA-meca1) and Example 6 (Pd / AFX-BEA-meca2) were used to carry out NOx adsorption tests at 120°C followed by a temperature ramp from 120°C to 600°C at 10°C / min. For each sample to be tested, 523 mg of powdered catalyst was placed in a quartz reactor. -10% O 2 , 5% CO 2 , 10% H 2 O, the rest is N 2 A pretreatment is carried out in a mixture consisting of a temperature increase from ambient temperature (20°C) to 550°C at a gradient of 10°C / min. A temperature decrease is carried out in the same mixture down to 120°C. - The adsorption is carried out at 120 °C under the following mixing conditions: 200 ppm NO + 300 ppm CO + 5% CO 2 +10% H 2 O, the rest N 2 The duration of this adsorption step is 10 min. - To desorb the adsorbed NOx, the samples were rinsed with 10% CO 2 +10% H 2 O, the rest N 2 The temperature is increased to 550° C. following a gradient of 10° C. / min under the mixture.

[0124] Using an FTIR analyzer, NO, NO were detected at the reactor outlet. 2 , N.H. 3 , N 2 O, CO, CO 2 , H 2 O, O 2 The concentration is measured.

[0125] 6 shows the concentration of NOx desorbed during the temperature ramp. The curves marked with squares, diamonds, triangles, crosses, and circles correspond to tests carried out with catalysts synthesized according to Example 2 (Pd / AFX-BEA1 according to the invention), Example 3 (Pd / AFX-BEA2 according to the invention), Example 4 (Pd / BEA), Example 5 (Pd / AFX-BEA-meca1), and Example 6 (Pd / AFX-BEA-meca2), respectively. The amount of NOx desorbed per unit mass of catalyst during the temperature ramp and the maximum desorption temperature are shown below.

[0126] [Table 2]

[0127] The catalysts Pd / AFX-BEA1 and Pd / AFX-BEA2 synthesized according to the invention provide better adsorption performance quality in terms of adsorption amount than the catalysts Pd / BEA, Pd / AFX-BEA-meca1 and Pd / AFX-BEA-meca2. Unlike the catalysts Pd / BEA, Pd / AFX-BEA-meca1 and Pd / AFX-BEA-meca2, which show NOx desorption from 150°C, NOx desorption appears only at about 250°C for the catalysts Pd / AFX-BEA1 and Pd / AFX-BEA2 according to the invention. NOx desorption above 250°C is a great advantage in suppressing NOx emissions.

[0128] Example 10: NOx adsorption and desorption tests after hydrothermal aging Using the aged catalysts from Example 7: Pd / AFX-BEA1-aged, Pd / AFX-BEA2-aged, Pd / BEA-aged, Pd / AFX-BEA-meca1-aged and Pd / AFX-BEA-meca2-aged, NOx adsorption tests were carried out at 120°C, followed by a temperature gradient from 120°C to 600°C at 10°C / min.

[0129] For each sample to be tested, 523 mg of powdered catalyst is placed in a quartz reactor. -10% O 2 , 5% CO 2 , 10% H2 The pretreatment consists of increasing the temperature from ambient (20 °C) to 550 °C at a rate of 10 °C / min in a mixture of 1000 sulphuric acid (O) and the remainder N2. The temperature drop is performed in the same mixture down to 120 °C. - The adsorption is carried out at 120 °C under the following mixing conditions: 200 ppm NO + 300 ppm CO + 5% CO 2 +10% H 2 O, the rest N 2 The duration of this adsorption step is 10 min. - To desorb the adsorbed NOx, the samples were rinsed with 10% CO 2 +10% H 2 O, the rest N 2 The temperature is increased to 550° C. following a gradient of 10° C. / min under the mixture.

[0130] Using an FTIR analyzer, NO, NO were detected at the reactor outlet. 2 , N.H. 3 , N 2 O, CO, CO 2 , H 2 O, O 2 Measure the concentration of.

[0131] Figure 7 shows the concentration of NOx desorbed during the temperature ramp. The curves marked with squares, diamonds, triangles, crosses, and circles correspond to tests performed on Pd / AFX-BEA1-aged, Pd / AFX-BEA2-aged, Pd / BEA-aged, Pd / AFX-BEA-meca1-aged, and Pd / AFX-BEA-meca2-aged catalysts, respectively. The amount of NOx desorbed per unit mass of catalyst during the temperature ramp and the maximum desorption temperature are shown below.

[0132] [Table 3]

[0133] The Pd / AFX-BEA1-aged and Pd / AFX-BEA2-aged catalysts synthesized according to the present invention provide better adsorption performance characteristics in terms of adsorption amount than the Pd / BEAaged catalyst and than the Pd / AFX-BEA-meca1-aged and Pd / AFX-BEA-meca2-aged catalysts prepared by mechanical mixing synthesized according to the prior art. The Pd / BEAaged, Pd / AFX-BEA-meca1-aged and Pd / AFX-BEA-meca2-aged catalysts show NOx desorption from 150°C, while the Pd / AFX-BEA1-aged and Pd / AFX-aged catalysts according to the present invention show NOx desorption only at about 250°C.

Claims

1. A method for preparing a zeolite composite catalyst comprising a mixture of AFX-type and BEA-type zeolites and palladium, comprising at least the following steps: Step i) In an aqueous medium, a total SiO ２（ＦＡＵ） / Al ２ O ３（ＦＡＵ） Mixing a zeolite or mixture of zeolites of FAU structure type having a molar ratio, an organic nitrogen compound MPC6 (MPC6 is 1,6-bis(methylpiperidinium)hexane dihydroxide), and at least one source of sodium cations until a homogeneous precursor gel is obtained, the reaction mixture having the following molar composition: (SiO ２（ＦＡＵ） ) / (Al ２ O ３（ＦＡＵ） ) is 20 to 60, H ２ O / (SiO ２（ＦＡＵ） ) is 5 to 60; MPC6 / (SiO ２（ＦＡＵ） ) is 0.10 to 0.50, Na ２ O / (SiO ２（ＦＡＵ） ) is between 0.05 and 0.11 (limits included); SiO ２（ＦＡＵ） is SiO supplied by FAU Zeolite ２ indicates the amount of Al ２ O ３（ＦＡＵ） is Al supplied by FAU Zeolite ２ O ３ indicates the amount of; step ii) hydrothermally treating the precursor gel obtained at the end of step i) at a temperature between 160° C. and 220° C. for 12 to 150 hours in order to obtain the AFX-BEA zeolite composite material; step iii) filtering, washing and drying of the AFX-BEA zeolite composite material obtained at the end of step ii), said drying being carried out at a temperature of 60-120° C. for a period of 5-24 hours to obtain a dried AFX-BEA zeolite composite material, followed by calcination of said dried AFX-BEA zeolite composite material at a temperature of 500-700° C. for a period of 2-20 hours to obtain a calcined AFX-BEA zeolite composite material, said calcination optionally being carried out at a gradually increasing temperature; step iv) at least one step of ion exchange of the calcined AFX-BEA zeolite composite material obtained in step iii) by contacting said calcined AFX-BEA zeolite composite material obtained in step iii) with a solution containing ammonium cations at a temperature between 20 and 95° C. for 1 hour to 2 days under stirring in order to obtain the calcined material in ammonium form, followed by re-drying at a temperature between 60° C. and 120° C.; Step v) depositing a palladium solution onto the calcined and dried AFX-BEA zeolite composite material in ammonium form.

2. 2. The method according to claim 1, wherein in step v) the palladium solution is deposited by dry impregnation or via a colloidal route.

3. The reaction mixture of step i) is ２ O ３（Ｃ） 3. The method according to claim 1 or 2, further comprising at least one additional source of aluminum in oxide form, wherein the reaction mixture of step i) has the following molar composition: SiO ２（ＦＡＵ） / (Al ２ O ３（ＦＡＵ） +Al ２ O ３（Ｃ） ) is between 20 and 60 (inclusive); H ２ O / SiO ２（ＦＡＵ） is 5 to 60, MPC6 / SiO ２（ＦＡＵ） is 0.10 to 0.50, Na ２ O / SiO ２（ＦＡＵ） is 0.05 to 0.11 (including the limit value), and SiO ２（ＦＡＵ） is SiO provided by FAU Zeolite ２ is the amount of Al ２ O ３（ＦＡＵ） is Al provided by FAU Zeolite ２ O ３ is the amount of Al ２ O ３（Ｃ） is the Al provided by the additional aluminum source, considered to be in oxide form. ２ O ３ and MPC6 is the dihydroxide form of 1,6-bis(methylpiperidinium)hexane, an organic nitrogen compound.

4. 4. The method of claim 3, wherein the additional aluminum source is selected from aluminum hydroxide or aluminum salts, sodium aluminate, aluminum alkoxides, or alumina, either alone or in mixture.

5. 3. The method of claim 1 or 2, wherein the source of sodium cations is sodium hydroxide.

6. Seed crystals of zeolite of AFX structure type or of zeolite of BEA structure type or of a mixture of the two are added to the SiO2 in anhydrous form present in the mixture. ２ and Al ２ O ３ The seed crystals are added to the reaction mixture of step i) in an amount of 0.01% to 10% by weight based on the total mass of the source, and the seed crystals are SiO ２ and Al ２ O ３ 3. The method according to claim 1 or 2, wherein the total mass of the source is not taken into account.

7. 3. The process according to claim 1 or 2, wherein step i) comprises aging the reaction mixture at a temperature between 20 and 100° C., with or without stirring, for a period between 30 minutes and 48 hours.

8. The process according to claim 1 or 2, wherein the content of palladium introduced by deposition step v) is between 0.5% and 5% by weight, relative to the total weight of the anhydrous composite catalyst.

9. A palladium-containing AFX-BEA zeolite composite catalyst obtained by the process according to claim 1 or 2.

10. The SiO ２ / Al ２ O ３ The AFX-BEA zeolite composite catalyst according to claim 9, wherein the ratio is between 6 and 80, limits included.

11. The AFX-BEA zeolite composite catalyst according to claim 9, wherein the mass ratio of the amount of the AFX-structure-type zeolite to the amount of the BEA-structure-type zeolite is 0.9 to 5.

7.

12. 10. The AFX-BEA zeolite composite catalyst according to claim 9, wherein the palladium content is 0.5% to 5% by weight, based on the total weight of the anhydrous final catalyst, and the metal dispersion of palladium, as measured by CO chemisorption, is 40% to 100%.

13. N.H. ３ Or H ２ 10. Use of the catalyst according to claim 9 or the catalyst obtainable by the process according to claim 1 or 2 for the selective reduction of NOx with a reducing agent such as

14. 14. The use according to claim 13, wherein the catalyst is formed by deposition in the form of a coating on a honeycomb or plate structure.

15. 15. Use according to claim 14, wherein the honeycomb structure comprises a porous filtering wall formed by parallel channels which are open at both ends or adjacent parallel channels are alternately blocked at both ends of the channels.

16. The use according to claim 15, wherein the amount of catalyst deposited on the structure is between 50 and 240 g / L for filtering structures and between 50 and 320 g / L for structures with open channels.

17. 15. The method according to claim 14, wherein the catalyst is combined with a binder, such as ceria, zirconium oxide, alumina, non-zeolitic silica-alumina, titanium oxide, mixed oxides of the ceria-zirconia type, tungsten oxide and / or spinel, to form by deposition in the form of a coating.

18. 15. The use according to claim 14, wherein the coating is combined with another coating having the ability to adsorb pollutants, reduce pollutants or promote the oxidation of pollutants.

19. 14. The use according to claim 13, wherein the catalyst is in the form of an extrudate comprising up to 100% of the catalyst.

20. 14. The use according to claim 13, wherein a structure coated with said catalyst or obtained by extrusion of said catalyst is integrated into the exhaust line of an internal combustion engine.

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