Catalyst comprising palladium and nickel on titanium dioxide; method for preparing same; and method for h2-scr therewith

Abstract

Catalyst comprising an active phase comprising palladium and nickel, and a support comprising at least titanium dioxide, characterized in that the palladium content is between 0.1 and 8% by weight of palladium element relative to the total weight of the catalyst, the nickel content is between 1 and 20% by weight of nickel element relative to the total weight of the catalyst, said molar ratio between the palladium and the nickel being between 0.001 and 5 mol / mol.

Description

[0001] PdNi CATALYST FOR THE CATALYTIC REDUCTION OF NITROGEN OXIDES (NOx) IN THE PRESENCE OF HYDROGEN

[0002] TECHNICAL FIELD

[0003] The present invention relates to the field of nitrogen oxide (NOx) emission treatment systems by catalytic reduction in the presence of hydrogen.

[0004] PREVIOUS TECHNIQUE

[0005] Nitrogen oxide (NOx) emissions from combustion are a major concern for society. Increasingly stringent standards are being implemented by government agencies to limit the impact of combustion emissions on the environment and human health. Selective catalytic reduction, known by its acronym "SCR," is emerging as an effective technology for eliminating nitrogen oxides from oxygen-rich exhaust gases in both industrial and mobile applications, such as diesel engines, hydrogen engines, and, more generally, lean-burn engines. Selective catalytic reduction is achieved using a reducing agent, typically ammonia, and can therefore be referred to as NH3-SCR.This technology achieves good performance in denitrification (DeNOx) through the use of highly active and selective catalysts. However, the use of ammonia is often questioned due to its hazardous and toxic nature. Instead, aqueous urea is used as a reducing agent (known as AdBlue® in Europe). Aqueous urea decomposes into ammonia and carbon dioxide upstream and / or at the catalyst, thus reducing NOx. However, when gas temperatures are below 180-200°C, this system cannot effectively treat NOx emissions. Indeed, the decomposition of the aqueous urea solution, which requires temperatures above 180°C, limits the efficiency of NH3-SCR. Furthermore, DeNOx efficiency is generally not maximized before 220-250°C, which represents a limitation for a number of processes.This is why much research has focused on new technologies based on alternative reducing agents, particularly those using hydrogen (H2-SCR). Indeed, the catalysts used in such applications are more efficient at low temperatures, for example between 100°C and 250°C, where gaseous hydrogen can react selectively with NOx on the catalyst surfaces. However, there are known problems with H2-SCR catalysts, such as their rather limited efficiency range for effective NOx conversion and / or the high formation of undesirable byproducts such as nitrous oxide (N2O).

[0006] Indeed, the conversion window in existing H2-SCR processes is rather narrow and generally centered at low temperatures (<250°C). However, the operation of current combustion engines (diesel, gasoline, H2) results in significant exhaust temperature variations, and H2-SCR technology alone cannot currently address NOx treatment. It must be combined with an NH3-SCR system. To become an effective solution on its own, the operating range would need to be extended to higher temperatures (for example, up to 450-500°C).

[0007] Furthermore, existing H2-SCR processes can generate high levels of N2O, with N2O yields reaching between 20 and 40% under certain conditions. Since N2O is a potent greenhouse gas, heavily regulated in most global automotive markets, its formation by an H2-SCR catalyst must be minimized before the H2-SCR catalyst composition is selected for NOx control.

[0008] Finally, at higher temperatures, gaseous hydrogen reacts preferentially with oxygen, which exists in large quantities in the exhaust gases of most compression-ignition engines.

[0009] The Applicant has made a surprising discovery: a palladium-nickel-based catalyst on a support containing titanium dioxide, obtained using a specific preparation process, can convert NOx over a wide temperature range, particularly between 160°C and 300°C, with low N2O emissions. The catalyst according to the invention exhibits high selectivity for the formation of NH3. Therefore, such a catalyst can be used in a specific chain of catalysts to convert the NH3 formed.

[0010] OBJECTS OF THE INVENTION

[0011] The present invention relates to a catalyst comprising an active phase of palladium and nickel, and a support comprising at least titanium dioxide, characterized in that the palladium content is between 0.1 and 8% by weight of the elemental palladium relative to the total weight of the catalyst, and the nickel content is between 1 and 20% by weight of the elemental nickel relative to the total weight of the catalyst, said molar ratio of palladium to nickel being between 0.001 and 5 mol / mol. According to one or more embodiments of the invention, the titanium dioxide is in its anatase and rutile forms, the rutile:anatase mass ratio being between 95:5 and 50:50.

[0012] According to one or more embodiments of the invention, the specific surface area of ​​the support is between 10 m 2 / g and 300 m 2 / g.

[0013] According to one or more embodiments of the invention, the palladium content is between 0.1 and 5% by weight of palladium element relative to the total weight of the catalyst, the nickel content is between 3 and 10% by weight of nickel element relative to the total weight of the catalyst, the molar ratio between palladium and nickel being between 0.05 and 0.9 mol / mol.

[0014] According to one or more embodiments of the invention, the specific surface area of ​​the support is between 40 m 2 / g and 80 m 2 / g.

[0015] According to one or more embodiments of the invention, the catalyst is shaped by deposition as a coating on a honeycomb structure or a plate structure, or is shaped as an extrudate containing up to 100% of said catalyst.

[0016] According to one or more embodiments of the invention, the honeycomb structure is formed of parallel channels open at both ends or comprises porous filtering walls for which the adjacent parallel channels are alternately blocked on either side of the channels.

[0017] According to one or more embodiments of the invention, the quantity of catalyst deposited on said structure is between 50 and 240 g / L for filtering structures and between 80 and 320 g / L for structures with open channels.

[0018] Another object of the invention relates to a process for preparing a catalyst according to the invention comprising at least the following steps: a) preparing a colloidal suspension of palladium oxide or palladium hydroxide in aqueous phase; b) impregnating said suspension onto a support comprising titanium dioxide; c) drying the catalyst precursor obtained in step b) at a temperature below 250°C; d) calcining the catalyst precursor obtained in step c) at a temperature between 250°C and 900°C; e) impregnating the catalyst precursor obtained at the end of step d) with at least one solution containing at least one nickel precursor; f) drying the catalyst precursor obtained in step e) at a temperature below 250°C; g) calcining the catalyst precursor obtained in step f) at a temperature between 250°C and 900°C.

[0019] According to one or more embodiments of the invention, nickel is added in step e) of the dry impregnation preparation process.

[0020] According to one or more embodiments of the invention, said nickel precursor is selected from nickel nitrate, nickel hydroxide, nickel carbonate, nickel chloride, or nickel hydroxycarbonate.

[0021] Another object of the invention relates to a process for the catalytic reduction of nitrogen oxides (NOx) comprising at least a first reduction substep in the presence of hydrogen (H2) by contacting a gaseous feed comprising nitrogen oxides and a catalyst according to the invention or prepared according to the invention, at a temperature between 15°C and 600°C, at a VVH of between 10,000 h -1 and 150,000 h' 1 , the H2 / NOX molar ratio being between 2:1 and 100:1.

[0022] According to one or more embodiments of the invention, the gaseous charge comprises between 10 ppm and 3000 ppm molar of NOx relative to the total weight of the gaseous charge.

[0023] According to one or more embodiments of the invention, the reduction process further comprises at least a second reduction substep in the presence of ammonia (NH3) by contacting the effluent obtained at the end of the first substep in the presence of a zeolite catalyst comprising a zeolite, or a mixture of zeolites, and a transition metal, advantageously copper, the zeolite being chosen from a CHA, AEI, AFX, SFW, RHO, KFI, LTA zeolite.

[0024] According to one or more embodiments of the invention, the transition metal content of the zeolite catalyst is between 0.5 and 5% by weight relative to the total weight of the catalyst. LIST OF FIGURES

[0025] Figure 1 represents the conversion of NOx [C] as a function of the reduction temperature [T]. The curves marked by circles, crosses, squares and triangles correspond respectively to the tests carried out with catalysts A, B, C and C+D synthesized according to example 1, example 2, example 3 and the combination of example 3 and example 4.

[0026] Figure 2 represents the concentration of NH3[Conc] as a function of the reduction temperature [T]. The curves marked by circles, crosses, squares and triangles correspond respectively to the tests carried out with catalysts A, B, C and C+D synthesized according to example 1, example 2, example 3 and the combination of example 3 and example 4.

[0027] DESCRIPTION OF IMPLEMENTATION METHODS

[0028] Other features and advantages of the process according to the invention will become apparent from the following description of non-limiting examples of implementations, with reference to the figures attached and described below.

[0029] 1. Definitions

[0030] In the sense of the present invention, the different embodiments presented can be used alone or in combination with each other, without limitation of combination.

[0031] In the context of the present invention, different parameter ranges for a given step, such as pressure ranges and temperature ranges, can be used alone or in combination. For example, in the context of the present invention, a preferred range of pressure values ​​can be combined with a preferred range of temperature values.

[0032] In the following text, the expressions "between ... and ..." and "between ... and ..." are equivalent and mean that the limit values ​​of the interval are included within the described range of values. If this were not the case and the limit values ​​were not included within the described range, this clarification will be provided by the present invention.

[0033] In this description, the term "include" is synonymous with (means the same as) "include" and "contain," and is inclusive or open-ended, not excluding other elements not mentioned. It is understood that the term "include" includes the exclusive and closed term "consist." According to the present invention, pressures are absolute pressures, also denoted as abs., and are given in absolute MPa (or abs. MPa), unless otherwise specified.

[0034] In the following text, chemical element groups are given according to the CAS classification (CRC Handbook of Chemistry and Physics, publisher CRC Press, editor-in-chief DR Lide, 81st edition, 2000-2001). For example, group VIII (or VI I IB) according to the CAS classification corresponds to the metals in columns 8, 9, and 10 according to the new IIIPAC classification, and group VIB to the metals in column 6.

[0035] The metal content is measured by X-ray fluorescence.

[0036] The BET specific surface area is measured by nitrogen physisorption. The BET specific surface area is measured by nitrogen physisorption according to ASTM D3663-03 as described in Rouquerol F.; Rouquerol J.; Singh K. "Adsorption by Powders & Porous Soils: Principle, methodology and applications", Academic Press, 1999.

[0037] The total pore volume is measured by mercury porosimetry according to ASTM D4284-92 with a wetting angle of 140°, for example using an Autopore® III model device from Microméritics®.

[0038] In this application, ppm values ​​are molar ppm values ​​(unless otherwise defined).

[0039] Gas Hourly Space Velocity (GHSV) refers to the volumetric flow rate of the gas feed at the reactor inlet in m³ / h divided by the catalyst volume in m³ 3 content in the reactor.

[0040] We hear "nitrogen oxides" or "NOx" referring to nitrogen oxides such as NO and NO2.

[0041] 2. Catalyst

[0042] The catalyst according to the invention comprises an active phase of palladium and nickel and a support comprising at least titanium dioxide (TiU2). Preferably, the catalyst comprises an active phase made of palladium and nickel, and a support made of titanium dioxide.

[0043] The palladium content is advantageously between 0.01 and 8% by weight of palladium element relative to the total weight of the catalyst, preferably between 0.05 and 8% by weight, and even more preferably between 0.1 and 5% by weight.

[0044] The nickel content is advantageously between 1 and 20% by weight of nickel element relative to the total weight of the catalyst, preferably between 1 and 18% by weight, and even more preferably between 2 and 15% by weight, and even more preferably between 3 and 10% by weight.

[0045] Advantageously, the molar ratio between palladium and nickel is between 0.001 and 5 mol / mol, preferably between 0.01 and 3 mol / mol, and even more preferably between 0.01 and 2 mol / mol, and even more preferably between 0.05 and 1 mol / mol, and even more preferably between 0.05 and 0.9 mol / mol.

[0046] The specific surface area of ​​the catalyst is generally between 10 m 2 / g and 300 m 2 / g, preferably between 10 m 2 / g and 150 m 2 / g, preferably between 30 m 2 / g and 120 m 2 / g, and even more preferentially between 40 and 80 m 2 / g.

[0047] The pore volume of the catalyst is generally between 0.2 ml / g and 1.1 ml / g, preferably between 0.3 ml / g and 1 ml / g.

[0048] The catalyst support comprises at least titanium dioxide (TiCh). Preferably, the catalyst support is made of titanium dioxide.

[0049] Preferably, TiC>2 is present in its anatase and rutile forms, with the rutile:anatase mass ratio preferably being between 95:5 and 50:50.

[0050] The specific surface area of ​​the support is generally between 10 m 2 / g and 300 m 2 / g, preferably between 10 m 2 / g and 150 m 2 / g, preferably between 30 m 2 / g and 120 m 2 / g, and even more preferentially between 40 and 80 m 2 / g.

[0051] The porosity volume of the support is generally between 0.2 ml / g and 1.1 ml / g, preferably between 0.3 ml / g and 1 ml / g.

[0052] 3. Process for preparing the catalyst by colloidal route

[0053] The deposition of palladium and nickel onto the titanium dioxide-containing support can be carried out using all techniques known to those skilled in the art. Preferably, palladium is deposited by colloidal method and nickel by dry impregnation method.

[0054] More specifically, the catalyst preparation process includes at least the following steps: a) a colloidal suspension of palladium oxide or palladium hydroxide is prepared in aqueous phase; b) said suspension is impregnated onto the support comprising titanium dioxide; c) the catalyst precursor obtained in step b) is dried at a temperature below 250°C; d) the catalyst precursor obtained in step c) is calcined at a temperature between 250°C and 900°C; e) the catalyst precursor obtained at the end of step d) is impregnated with at least one solution containing at least one nickel precursor; f) the catalyst precursor obtained in step e) is dried at a temperature below 250°C; g) the catalyst precursor obtained in step f) is calcined at a temperature between 250°C and 900°C.

[0055] The different stages of the process according to the invention are explained in detail below.

[0056] Colloidal suspension is generally obtained by hydrolysis of the palladium cation in aqueous medium, leading to the formation of suspended palladium oxide or hydroxide particles. Preferably, the colloidal suspension is obtained from an aqueous solution comprising at least one palladium precursor salt and an aqueous solution of alkali or alkaline earth hydroxide.

[0057] The aqueous solution of alkali or alkaline earth hydroxide is generally selected from the group consisting of aqueous solutions of sodium hydroxide and aqueous solutions of magnesium hydroxide. Preferably, the aqueous solution is an aqueous solution of sodium hydroxide.

[0058] Typically, an aqueous solution containing at least one palladium precursor salt [also referred to here as solution (II)] is supplied to a suitable apparatus, followed by an aqueous solution containing at least one alkali or alkaline earth hydroxide [also referred to here as solution (I)]. Alternatively, solutions (I) and (II) can be added to the apparatus simultaneously. Preferably, aqueous solution (II) is added first, followed by aqueous solution (I).

[0059] The palladium precursor salt is generally selected from the group consisting of palladium chloride, palladium nitrate, and palladium sulfate. Palladium nitrate is the preferred precursor salt. The colloidal suspension typically remains in the apparatus for a residence time of between 0.5 and 20 hours.

[0060] The concentrations of solutions (I) and (II) are generally chosen to obtain a pH of the colloidal suspension between 1.0 and 3.5. Thus, the pH of the colloidal suspension can be modified during this residence time by adding quantities of acid or base compatible with the stability of the colloidal suspension.

[0061] In general, the preparation temperature is between 5°C and 40°C and preferably between 15°C and 35°C.

[0062] The palladium concentration is preferably between 5 and 150 millimoles per liter (mmol / L), more preferably between 8 and 80 millimoles per liter. b) Deposition of the colloidal suspension prepared in step a) by impregnation onto a support comprising titanium dioxide

[0063] The colloidal suspension prepared in step a) is then impregnated onto the support.

[0064] The support may optionally undergo a series of treatments prior to the impregnation step, such as calcination or hydration. The support may also already contain one or more metallic elements before the impregnation of the colloidal suspension. Metallic elements may also be introduced into the colloidal suspension. These metallic elements may be introduced either by conventional techniques or by using the process according to the present invention.

[0065] The colloidal suspension is preferably poured onto the support. Preferably, the volume of the colloidal suspension impregnated onto the support is between 0.9 and 1.1 times the porous volume of the support. This process can be carried out either discontinuously, i.e., the preparation step of the colloidal suspension precedes the impregnation step on the support and the bulk of the colloidal suspension is sent in one go to the impregnation step, or continuously, i.e., the product obtained in step a) is sent continuously after adjusting the residence time of the colloidal suspension in step b).

[0066] An example of a continuous process is one in which solutions (I) and (II) are poured simultaneously into a container that continuously pours into an area containing the substrate to be impregnated. After impregnation, the impregnated substrate is generally cured in a wet state for 0.5 to 40 hours, preferably for 1 to 30 hours, and even more preferably for 1 to 24 hours. Longer curing times are not excluded, but do not necessarily provide any improvement. c) Drying of the catalyst precursor obtained in step b)

[0067] The catalyst precursor is dried to remove all or part of the water introduced during impregnation at a temperature below 250°C, preferably between 70°C and 200°C. The drying time is generally between 0.5 and 20 hours. Longer drying times are possible, but do not necessarily result in any improvement.

[0068] Drying is generally carried out under hydrocarbon combustion air, preferably methane, or under heated air containing between 0 and 80 grams of water per kilogram of combustion air, an oxygen content between 5% and 25% by volume, and a carbon dioxide content between 0% and 10% by volume. d) Calcination of the dried catalyst precursor obtained in step c)

[0069] After drying, the catalyst precursor is calcined under air, preferably combustion air, and more preferably methane combustion air, containing between 40 and 80 grams of water per kg of air, an oxygen content of between 5% and 15% by volume, and a CO2 content of between 4% and 10% by volume. The calcination temperature is generally between 250°C and 900°C, preferably between approximately 300°C and approximately 500°C. The calcination time is generally between 0.5 h and 5 h. The volumetric flow rate per hour (VVH) is generally between 150 and 3000, preferably between 300 and 1500 liters of combustion air per hour per liter of catalyst. e) Nickel impregnation

[0070] In step e) of the process, the catalyst precursor obtained at the end of step d) is impregnated with a solution comprising at least one nickel precursor. The impregnation step can be carried out by dry or excess impregnation according to methods well known to those skilled in the art. Preferably, step e) of impregnation is carried out by dry impregnation of an aqueous solution comprising at least one nickel precursor onto the catalyst precursor obtained in step d), the volume of said aqueous solution generally being between 0.9 and 1.1 times the porosity volume of the catalyst precursor to be impregnated.

[0071] When the nickel precursor is introduced in aqueous solution, advantageously a nickel precursor is used in the form of nitrate, carbonate, acetate, chloride, hydroxide, hydroxycarbonate, oxalate, sulfate, formate, complexes formed by a polyacid or an acid-alcohol and its salts, complexes formed with acetylacetonates, tetrammine or hexammine complexes, or any other inorganic derivative soluble in aqueous solution, which is brought into contact with said support. Preferably, nickel nitrate, nickel hydroxide, nickel carbonate, nickel chloride, or nickel hydroxycarbonate are advantageously used as nickel precursors. Most preferably, the nickel precursor is nickel nitrate, nickel carbonate, or nickel hydroxide.

[0072] After impregnation, the resulting catalyst precursor is generally matured in a wet state for 0.5 to 40 hours, preferably for 1 to 30 hours, and even more preferably for 1 to 24 hours. Longer durations are not excluded, but do not necessarily provide any improvement. f) Drying of the catalyst precursor obtained in step e)

[0073] The catalyst precursor obtained at the end of step e) is dried to remove all or part of the water introduced during impregnation at a temperature below 250°C, preferably between 70°C and 200°C. The drying time is generally between 0.5 hours and 20 hours. Longer drying times are possible, but do not necessarily provide any improvement.

[0074] Drying is generally carried out under hydrocarbon combustion air, preferably methane, or under heated air containing between 0 and 80 grams of water per kilogram of combustion air, an oxygen content between 5% and 25% by volume, and a carbon dioxide content between 0% and 10% by volume. (g) Calcination of the dried catalyst precursor obtained in step (f)

[0075] After drying, the catalyst precursor obtained at the end of step f) is calcined under air, preferably combustion air, and more preferably methane combustion air, containing between 40 and 80 grams of water per kg of air, an oxygen content of between 5% and 15% by volume, and a CO2 content of between 4% and 10% by volume. The calcination temperature is generally between 250°C and 900°C, preferably between approximately 300°C and approximately 500°C. The calcination time is generally between 0.5 h and 5 h. The volumetric flow rate per hour (VVH) is generally between 150 and 3000, preferably between 300 and 1500 liters of combustion air per hour per liter of catalyst.

[0076] 4. Catalyst Shaping The catalyst used in the denitrification (DeNOx) process according to the invention is advantageously shaped by deposition as a coating (a "washcoat" in Anglo-Saxon terminology) on a honeycomb structure, primarily for mobile applications, or on a plate structure, particularly common in stationary industrial applications. The invention can also be shaped into extruded or granular forms.

[0077] The honeycomb structure is formed of parallel channels open at both ends (flow-through) or has porous filter walls, in which case adjacent parallel channels are alternately blocked on either side to force the gas flow through the wall (wall-flow monolith). This coated honeycomb structure constitutes a catalytic block. The structure can be composed of cordierite, silicon carbide (SiC), aluminum titanate (AlTi), alpha alumina, mullite, or any other material with a porosity between 30 and 70%. The structure can be made of sheet metal, stainless steel containing chromium and aluminum, or FeCrAl steel.

[0078] The amount of catalyst deposited on said structure is between 50 and 240 g / L for filter structures and between 50 and 320 g / L for structures with open channels.

[0079] The coating itself (the "washcoat") comprises the catalyst, advantageously combined with a binder such as cerium, zirconium oxide, alumina, non-zeolitic silica-alumina, titanium oxide, a cerium-zirconia mixed oxide, tungsten oxide, or spinel. This coating is advantageously applied to the structure by a washcoating method, which consists of immersing the monolith in a slurry of catalyst powder according to the invention in a solvent, preferably water, and potentially binders, metal oxides, stabilizers, or other promoters. This immersion step can be repeated until the desired amount of coating is achieved. In some cases, the slurry can also be sprayed into the monolith. Once the coating has been deposited, the monolith is calcined at a temperature of 300 to 600°C for 1 to 10 hours.

[0080] The structure can be coated with one or more coatings. The coating containing the catalyst is advantageously combined with, or is covered by, another coating exhibiting adsorption or pollutant reduction capabilities, particularly for NOx, and / or promoting the oxidation of pollutants, especially carbon monoxide (CO) and hydrocarbons (HC). Alternatively, the catalyst can be in the form of an extrudate, a bead, or any other form known to those skilled in the art. In this case, the resulting structure can contain up to 100% catalyst.

[0081] The catalyst support used in the process according to the invention can advantageously be shaped by any technique known to those skilled in the art. Shaping can advantageously be carried out, for example, by extrusion, pelletizing, the oil-drop coagulation method, rotary plate granulation, or any other method well known to those skilled in the art. The supports thus obtained can be in various shapes and sizes. Advantageously, the various constituents of the support or catalyst can be shaped by mixing to form a paste and then extruding the resulting paste, or by mixing powders and then pelletizing, or by any other known process for agglomerating a powder containing alumina. The supports thus obtained can be in various shapes and sizes. Preferably, shaping is carried out by mixing and extrusion.

[0082] The catalyst supports according to the invention are generally in the form of cylindrical or multilobed extrudates, such as bilobed, trilobed, or multilobed, with a straight or twisted shape, but may also be manufactured and used in the form of crushed powders, tablets, rings, beads, and / or wheels. Preferably, the catalyst supports according to the invention are in the form of spheres or extrudates. Advantageously, the support is in the form of extrudates with a diameter between 0.5 and 8 mm, and more particularly between 0.7 and 3 mm. The shapes may be cylindrical (which may or may not be hollow) and / or twisted cylindrical and / or multilobed (2, 3, 4, or 5 lobes, for example) and / or rings. The multilobed shape is advantageously preferred.

[0083] The structure, coated with the catalyst or catalyst support, is advantageously integrated into the exhaust line of an industrial process or an internal combustion engine. An oxidation catalyst, whose function is to oxidize volatile organic compounds (VOCs), and a filter for removing particulate matter from the exhaust gases can be placed either upstream or downstream of the structure.

[0084] 5. H2-SCR Process

[0085] The catalytic reduction process for nitrogen oxides (NOx), using the catalyst according to the invention, comprises a step of contacting the catalyst with nitrogen oxides (NOx), preferably at a temperature between 15°C and 600°C, preferably between 30°C and 500°C, and more preferably between 40°C and 400°C. The WH (GHSV) involved is preferably between 10,000 h -1 and 150,000 h -1 preferably between 20,000 and 80,000 hours -1, the H2 / NOx molar ratio being between 2:1 and 100:1, preferably between 5:1 and 40:1.

[0086] According to one or more embodiments, the gaseous load to be treated comprises between 10 ppm and 3000 ppm molar of NOx relative to the total number of moles of the gaseous load, preferably between 50 and 800 ppm, and even more preferably between 70 and 300 ppm.

[0087] The said gaseous charge may further comprise between 2% and 12% molar oxygen (O2), between 0 ppm and 500 ppm molar CO, between 0 and 30% molar H2O, and a sulfur content in the form of SO2 less than 200 ppm, preferably less than 150 ppm molar, relative to the total number of moles of said gaseous charge.

[0088] The amount of catalyst is adjusted by a person skilled in the art according to the amount of NOx present in the gas to be treated.

[0089] The process is advantageously implemented in the presence of the catalyst shaped as described above.

[0090] 6. H2-SCR process followed by NH3-SCR

[0091] The catalyst according to the invention is highly selective for the formation of NH3. Therefore, to treat residual NOx and the NH3 produced by the catalyst, the catalyst can be combined with an NH3-SCR type NOx treatment catalyst. Another object of the invention relates to a catalytic reduction process for nitrogen oxides (NOx) comprising at least:

[0092] - a first reduction substep in the presence of hydrogen (H2) by contacting a gaseous feed comprising nitrogen oxides and a catalyst according to the invention or prepared according to the invention; at a temperature between 15°C and 600°C, at a VVH of between 10,000 h -1 and 150,000 h -1 , the H2 / NOx molar ratio being between 2:1 and 100:1 , then

[0093] - a second reduction substep in the presence of ammonia (NH3) by contacting the effluent obtained at the end of the first substep in the presence of a catalyst of a zeolite catalyst comprising a zeolite, or a mixture of zeolites, and a transition metal, advantageously copper, the zeolite being chosen from a CHA, AEI, AFX, SFW, RHO, KFI, LTA zeolite, and preferably a CHA, AEI and AFX zeolite.

[0094] The transition metal content is advantageously between 0.5 and 5 wt% of the metal element relative to the total weight of the catalyst, preferably between 1.4 and 4 wt%, most preferably between 2.2 and 3.6 wt%, and most advantageously between 2.8 and 3.2 wt%. Preferably, the transition metal is copper. When the zeolite catalyst is of the CHA structural type, the SiCh / AhOs molar ratio of the CHA zeolite-based catalyst is between 7 and 30, preferably between 12 and 26 inclusive.

[0095] The zeolite catalyst can be prepared according to all the techniques of the person skilled in the art, and more particularly as described in documents FR3123006 and FR3123007.

[0096] The zeolite catalyst can be shaped under the same operating conditions as the catalyst according to the invention, as described in paragraph 4 above. The zeolite catalyst can be shaped in a honeycomb structure placed downstream of the honeycomb structure coated with the reduction catalyst in the presence of hydrogen.

[0097] In one embodiment of the invention, the zeolite catalyst is shaped into the same honeycomb structure as the hydrogen reduction catalyst. A first configuration involves a structure coated with several layers. The layer comprising the hydrogen reduction catalyst is advantageously associated with the NH3-SCR type zeolite coating; that is, it either covers or is covered by the NH3-SCR type zeolite coating. A second configuration involves a structure coated in its upstream portion with the hydrogen reduction catalyst and coated in its downstream portion with the NH3-SCR type zeolite catalyst.

[0098] Examples

[0099] The invention is illustrated by the following examples, which are in no way limiting. The specific surface area of ​​the titanium dioxide support (Aldrich™ P25) is 55 m². 2 / g and the total pore volume is 0.75 ml / g.

[0100] Example 1: Impregnation with colloidal solution (1 wt% Pd) [non-compliant]

[0101] A colloidal suspension of palladium oxide is prepared under stirring at 25°C by diluting 2.84 g of a palladium nitrate (Pd(NOs)₂) solution containing 8.5 wt% palladium with approximately 45 mL of demineralized water, followed by the addition of approximately 10 mL of sodium hydroxide solution to achieve a pH of 2.4. This solution is then impregnated onto a support of titanium dioxide (Aldrich P₂5) in powder form. The resulting catalyst precursor is dried in air at 100°C for 12 hours and then calcined for 2 hours at 500°C with a ramp rate of 5°C / min under 1 Lh / g of air. Catalyst A is obtained. The Pd content, analyzed by X-ray fluorescence, is 1 wt% relative to the total weight of the support.

[0102] 2: Ni alone (5% Ni) The Ni / TiC>2 catalyst was prepared by dry impregnation of a titanium dioxide support (Aldrich™ P25) in powder form with a solution containing the nickel precursor (Ni(NC>3)2.6H2O). The resulting catalyst was dried in air at 100°C for 12 hours, then calcined for 2 hours at 500°C with a ramp of 5°C / min under 1 Lh / g of air. Catalyst B was obtained. The Ni content, analyzed by X-ray fluorescence, was 5 wt% relative to the total weight of the support.

[0103] Example 3: Impregnation with 1% by weight Pd colloidal solution followed by 5% by weight Ni (Pd / Ni = 0.11 mol / mol) [compliant!

[0104] A colloidal suspension of palladium oxide is prepared under stirring at 25°C by diluting 2.84 g of a palladium nitrate (Pd(NOa)2) solution containing 8.5 wt% palladium with approximately 45 mL of demineralized water, followed by the addition of approximately 10 mL of sodium hydroxide solution to achieve a pH of 2.4. This solution is then impregnated onto a support of titanium dioxide (Aldrich™ P25) in powder form. The resulting catalyst precursor is dried in air at 100°C for 12 hours and then calcined for 2 hours at 500°C with a ramp rate of 5°C / min under 1 Lh / g of air. A C1 catalyst precursor is obtained. The Pd content, analyzed by X-ray fluorescence, is 1 wt% relative to the total weight of the support. The catalyst precursor C1 obtained above is then dry-impregnated with the solution containing the Ni precursor (Ni(NC>3)2.6H2O).The resulting catalyst precursor is dried in air at 100°C for 12 hours, then calcined for 2 hours at 500°C with a ramp rate of 5°C / min under 1 Lh / g of air. Catalyst C is obtained. The Ni content, analyzed by X-ray fluorescence, is 5 wt% relative to the total weight of the support.

[0105] Example 4: Synthesis of Cu-SSZ-13 zeolitic sample (CHA structural type)

[0106] 27.21 g of an aqueous solution of N,N,N-trimethyl-1-adamantammonium hydroxide (TMAdA, 20.11 wt%, SACHEM™) were mixed with 24.43 g of deionized water. 1.35 g of sodium hydroxide (solid, 98 wt% purity, Aldrich™) were added to the mixture, and the resulting preparation was stirred for 10 minutes. Subsequently, 1.09 g of pseudo-boehmite (Pural SB3, 74.20% Al₂O₃, Condea™) were incorporated, and the synthesis gel was stirred for 15 minutes. In the end, 25.93 g of colloidal silica (Ludox AS40, 40% SiO2 by weight, Aldrich™) were incorporated into the synthesis mixture, which was maintained for half an hour at room temperature under stirring (350 rpm). The molar composition of the precursor gel was as follows: 60 SiO2: 2.75 A Os: 9.0 TMAda: 6.0 Na2O: 1201.0 H2O, resulting in a SiO2 / Al2C ratio >3 of 21.8.The precursor gel, after homogenization, is then transferred to a 160 mL stainless steel reactor equipped with a four-bladed stirring system. The reactor is closed and heated for 120 hours at a rate of 3°C / min up to 160°C, with stirring at 200 rpm, to allow crystallization of the CHA structural zeolite. The resulting crystallized product is filtered, washed with deionized water, and then dried overnight at 100°C. The solid is then introduced into a muffle furnace where a calcination step is carried out. The calcination cycle consists of a temperature increase of 1.5°C / min up to 200°C, a holding period at 200°C for 2 hours, a temperature increase of 1°C / min up to 550°C, followed by a holding period at 550°C for 8 hours, and then a return to room temperature. The resulting material is named SSZ-13.

[0107] 5.0 g of the SSZ-13 material were exchanged 3 times with a 3M aqueous NH4NO3 solution at 80°C for 1 hour under stirring (300 rpm) and a solution volume to zeolite mass ratio of 10 (V / W). The solid was then dried overnight at 100°C.

[0108] SSZ-13 zeolite in ammoniacal form is treated under a dry air stream at 25 to 550°C for 8 hours with a temperature ramp rate of 1°C / min. The resulting product is SSZ-13 zeolite in protonated form (H-SSZ-13).

[0109] Next, the H-SSZ-13 zeolite is contacted with a [Cu(NH3)4](NC>3)2 solution for 1 day under stirring at room temperature. The final solid is separated, washed, and dried.

[0110] The solid obtained after contact with the [Cu(NH3)4](NC>3)2 solution is calcined under a flow of dry air at 550°C for 8 hours.

[0111] XRD analysis shows that the product obtained is an SSZ-13 zeolite of the CHA structural type. X-ray fluorescence (XRF) chemical analysis gives a Cu content of 2.8 wt%. Catalyst D is obtained.

[0112] For catalytic tests, 200 mg of catalysts A, B and C in powder form are placed in a quartz reactor.

[0113] To evaluate the combination of catalyst C followed by catalyst D, a test is carried out with catalysts C and D arranged in successive layers, with 200 mg of catalyst C in powder form being placed on top of 200 mg of catalyst D. This combination is called catalyst C+D. The reactor is fed with 150 L / h of a gas mixture having the following molar compositions: 400 ppm NO, 4000 ppm H2, 10% O2, 15% H2O qpc N2. (qpc = quantity to compensate).

[0114] A Fourier transform infrared spectroscopy (FTIR) analyzer allows the measurement of the concentration of NO, NO2, NH3, and N2O species at the reactor outlet. NOx conversions are calculated as follows:

[0115] NOx conversion = (NOx ent D e - NOx sortie ) / NOx ent D e In these formulas, the input and output indices indicate the content before and after catalytic reduction, respectively.

[0116] The results of NOx conversion are shown in Figure 1. The curves marked by circles, crosses, squares and triangles correspond respectively to the tests carried out with catalysts A, B, C and C+D synthesized according to example 1, example 2, example 3 and the combination of example 3 and example 4.

[0117] It is observed that compliant catalyst C offers NOx conversion efficiency equivalent to catalyst A, with higher efficiency above 300°C. Catalyst B exhibits virtually no NOx conversion. Conversely, the combination of compliant catalysts C and D has an initiation temperature equivalent to catalysts A and C alone, but significantly higher NOx conversion at temperatures above 150°C thanks to the use of ammonia produced by catalyst C.

[0118] NH3 emissions are shown in Figure 2. The curves marked by circles, crosses, squares, and triangles correspond respectively to tests carried out with catalysts A, B, C, and C+D synthesized according to Example 1, Example 2, Example 3, and the combination of Example 3 and Example 4. The compliant catalyst C produces higher quantities of NH3 compared to the non-compliant catalyst A. The compliant combination of catalysts C+D exhibits low quantities of NH3, as the emissions from catalyst C are used to increase the NOx conversion efficiency with catalyst D.

[0119] A summary of the catalyst performance is given in Table 1 below:

[0120] Table 1 It appears that the conformal C catalyst and especially the conformal combination of C and D catalysts allows NOx to be converted over a wide temperature range, particularly for temperatures between 160°C and 300°C, with low N2O emissions.

Claims

DEMANDS 1. Catalyst comprising an active phase comprising palladium and nickel, and a support comprising at least titanium dioxide, characterized in that the palladium content is between 0.1 and 8% by weight as elemental palladium relative to the total weight of the catalyst, the nickel content is between 1 and 20% by weight as elemental nickel relative to the total weight of the catalyst, said molar ratio between palladium and nickel being between 0.001 and 5 mol / mol.

2. Catalyst according to claim 1, characterized in that titanium dioxide is present in its anatase and rutile forms, the rutile:anatase mass ratio being between 95:5 and 50:

50.

3. Catalyst according to claim 1 or 2, characterized in that the specific surface area of ​​the support is between 10 m² 2 / g and 300 m 2 / g.

4. Catalyst according to any one of the preceding claims, characterized in that the palladium content is 0.1 and 5% by weight of element palladium relative to the total weight of the catalyst, the nickel content is between 3 and 10% by weight of element nickel relative to the total weight of the catalyst, the molar ratio between palladium and nickel being between 0.05 and 0.9 mol / mol.

5. Catalyst according to any one of the preceding claims, characterized in that the specific surface area of ​​the support is between 40 m² 2 / g and 80 m 2 / g.

6. Catalyst according to any one of the preceding claims, characterized in that the catalyst is formed by deposition as a coating on a honeycomb structure or a plate structure, or is formed as an extrudate containing up to 100% of said catalyst.

7. Catalyst according to claim 6, wherein the honeycomb structure is formed of parallel channels open at both ends or comprises filtering porous walls for which the adjacent parallel channels are alternately blocked on either side of the channels.

8. Catalyst according to claim 7, wherein the quantity of catalyst deposited on said structure is between 50 and 240 g / L for filter structures and between 80 and 320 g / L for structures with open channels.

9. A process for preparing a catalyst according to any one of the preceding claims, comprising at least the following steps: a) preparing a colloidal suspension of palladium oxide or palladium hydroxide in aqueous phase; b) impregnating said suspension onto a support comprising titanium dioxide; c) drying the catalyst precursor obtained in step b) at a temperature below 250°C; d) calcining the catalyst precursor obtained in step c) at a temperature between 250°C and 900°C; e) impregnating the catalyst precursor obtained after step d) with at least one solution containing at least one nickel precursor; f) drying the catalyst precursor obtained in step e) at a temperature below 250°C; g) calcining the catalyst precursor obtained in step f) at a temperature between 250°C and 900°C.

10. A process according to the preceding claim, wherein nickel is added in step e) of the dry impregnation preparation process.

11. A process according to claims 9 or 10, wherein said nickel precursor is selected from nickel nitrate, nickel hydroxide, nickel carbonate, nickel chloride, or nickel hydroxycarbonate.

12. A process for the catalytic reduction of nitrogen oxides comprising at least a first reduction substep in the presence of hydrogen (H2) by contacting a gaseous feed comprising nitrogen oxides and a catalyst according to any one of claims 1 to 9 or prepared according to any one of claims 10 to 12, at a temperature between 15°C and 600°C, at a VVH of between 10,000 h -1 and 150,000 h' 1 , the H2 / NOx molar ratio being between 2:1 and 100:

1.

13. A method according to the preceding claim, wherein the gaseous feed comprises between 10 ppm and 3000 ppm molar of NOx relative to the total weight of the gaseous feed.

14. A process according to any one of claims 12 or 13 further comprising at least a second reduction substep in the presence of ammonia (NH3) by contacting the effluent obtained at the end of the first substep in the presence of a zeolite catalyst comprising a zeolite, or a mixture of zeolites, and a transition metal, advantageously copper, the zeolite being selected from a CHA, AEI, AFX, SFW, RHO, KFI, LTA zeolite.

15. A process according to the preceding claim, characterized in that the transition metal content of the zeolite catalyst is between 0.5 and 5% by weight relative to the total weight of the catalyst.

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