Pt-w-na-based catalyst for the reduction of nitrogen oxides (NOX) in the presence of hydrogen

Abstract

The present invention relates to a catalyst for the catalytic reduction of nitrogen oxides in the presence of hydrogen (H2-SCR) comprising an active phase comprising platinum, tungsten and sodium, and a support comprising at least titanium dioxide, characterised in that: - the platinum content is between 0.01 and 10% by weight of platinum relative to the total weight of the catalyst; - the tungsten content is between 1 and 30% by weight of tungsten relative to the total weight of the catalyst; - the sodium content is between 0.5 and 5% by weight of sodium relative to the total weight of the catalyst.

Description

[0001] Pt-W-Na based catalyst for the 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 the acronym "SCR" (for "Selective Catalytic Reduction"), is emerging as an effective technology for eliminating nitrogen oxides in oxygen-rich exhaust gases for 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 nature and toxicity. 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). In fact, the conversion window in existing H2-SCR processes is quite narrow and generally centered at low temperatures (i.e., above 150°C and below 250°C).However, the operation of current combustion engines (diesel, gasoline, H2) results in significant exhaust temperature variations, and H2-SCR technology alone is not currently sufficient to treat NOx. 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).

[0006] 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.

[0007] Finally, at higher temperatures, gaseous hydrogen reacts preferentially with oxygen, which exists in large quantities in the exhaust gases of most compression-ignition engines.

[0008] Thus, in recent years, there has been a renewed interest in the search for suitable catalytic compositions for the industrial-scale control of H2-SCR processes. Most scientific publications dedicated to this application have demonstrated that the performance of the H2-SCR catalyst depends strongly on the combination of the nature and metal content of the catalyst's active phase and the nature of the support, in a way that is not obvious, particularly for catalysts with a platinum-based active phase. The promoting effect of tungsten on the activity of platinum-based H2-SCR catalysts was studied by X. Zhang et al. (Chemical Engineering Journal 260, 2015) and by Z. Liu et al. (Applied Catalysis B: Environmental 188, 2016), respectively, on platinum-containing solids deposited on a zeolite and on platinum-containing solids deposited on titanium dioxide.The results show that a catalyst containing between 0.5 and 3 wt% tungsten, with an optimum of 2 wt%, significantly improves the catalyst's activity at low temperatures, shifting the activity window to a temperature range between 100 and 175°C. This improvement is attributed to the favorable interaction between platinum and tungsten, promoting the metallic state of platinum in the catalyst and inhibiting the formation of undesirable nitrates, thereby accelerating the dissociation of NOx at the platinum surface. An objective of the present invention is to provide a hydrogen denitrification (DeNOx) process in the presence of a specific catalyst that simultaneously achieves:

[0009] - an improvement in conversion efficiency at low temperatures, i.e., less than or equal to 200°C, preferably less than 180°C, and even more preferably less than 160°C; and

[0010] - a greater range of conversion in terms of temperature, including up to temperatures reaching 300°C.

[0011] The Applicant has surprisingly discovered that a platinum-tungsten-based catalyst, doped with sodium at specific concentrations on a support containing titanium dioxide, fulfills all the aforementioned objectives. Furthermore, the catalyst used in such a process exhibits very high stability in the presence of water in the gas stream being treated, enabling its use under the harsh conditions of an automotive exhaust system, unlike catalysts as described in the literature.

[0012] OBJECTS OF THE INVENTION

[0013] The present invention relates to a catalyst comprising an active phase comprising platinum, tungsten and sodium, and a support comprising at least titanium dioxide, characterized in that:

[0014] - the platinum content is between 0.01 and 10% by weight of platinum element relative to the total weight of the catalyst;

[0015] - the tungsten content is between 1 and 30% by weight of tungsten element relative to the total weight of the catalyst;

[0016] - the sodium content is between 0.5 and 5% by weight of sodium element relative to the total weight of the catalyst.

[0017] According to one or more embodiments, titanium dioxide is present in its anatase and rutile forms, the rutile:anatase mass ratio being between 95:5 and 50:50.

[0018] Depending on one or more embodiments, the specific surface area of ​​the support is between 10 m 2 / g and 300 m 2 / g.

[0019] According to one or more embodiments, the sodium content is between 1 and 3.5% by weight relative to the total weight of the catalyst.

[0020] Depending on one or more embodiments, the specific surface area of ​​the support is between 40 m 2 / g and 80 m 2 / g. According to one or more embodiments, the tungsten content is between 5 and 25% by weight relative to the total weight of the catalyst.

[0021] According to one or more embodiments, the molar ratio between platinum and sodium is between 0.001 and 0.5 mol / mol.

[0022] According to one or more embodiments, the molar ratio between tungsten and sodium is between 0.001 and 6 mol / mol.

[0023] According to one or more embodiments, 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.

[0024] According to one or more embodiments, 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.

[0025] According to one or more embodiments, 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.

[0026] Another object of the invention relates to a process for preparing a catalyst according to the invention comprising at least the following steps: a) the following substeps are carried out in sequence: a1) the support is contacted with at least one solution comprising at least one sodium precursor; a2) the catalyst precursor obtained in substep a1 is dried at a temperature below 250°C; a3) optionally, the dried catalyst precursor obtained in substep a2 is calcined at a temperature between 250°C and 900°C; b) the following substeps are carried out in sequence: b1) the support is contacted with at least one solution comprising at least one tungsten precursor; b2) the catalyst precursor obtained in substep b1 is dried at a temperature below 250°C; b3) optionally, the dried catalyst precursor obtained in sub-step b2) is calcined at a temperature between 250°C and 900°C;c) the following sub-steps are carried out in sequence: c1) the support is brought into contact with at least one solution comprising at least one platinum precursor; c2) the catalyst precursor obtained in sub-step c1) is dried at a temperature below 250°C; c3) the dried catalyst precursor obtained in sub-step c2) is calcined at a temperature between 250°C and 900°C.

[0027] Preferably, the steps are carried out in the following order: step a), then step b), then step c).

[0028] Another object according to the invention relates to a process for the catalytic reduction of nitrogen oxides in the presence of hydrogen by contacting a gaseous charge comprising nitrogen oxides and a catalyst according to the invention or obtained according to the catalyst preparation process 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.

[0029] According to one or more embodiments, the gaseous charge comprises between 10 ppm and 3000 ppm weight of NOx relative to the total weight of the gaseous charge.

[0030] LIST OF FIGURES

[0031] Figure 1 shows the NOx conversion [C] as a function of the reduction temperature [T] for catalysts with a W content of 10 wt% relative to the total catalyst weight. The curves marked by crosses, squares, triangles, and circles correspond respectively to tests carried out with catalysts A, B, C, and D synthesized according to Example 1, Example 2, Example 3, and Example 4.

[0032] Figure 2 shows the NOx conversion [C] as a function of the reduction temperature [T] for catalysts with a W content of 2 wt% relative to the total catalyst weight. The curves marked by empty squares and crosses correspond respectively to tests carried out with catalysts E and F synthesized according to Example 5 and Example 6. DESCRIPTION OF THE PROCEDURES

[0033] 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.

[0034] 1. Definitions

[0035] 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.

[0036] 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.

[0037] 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.

[0038] 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."

[0039] According to the present invention, pressures are absolute pressures, also noted as abs., and are given in absolute MPa (or abs. MPa), unless otherwise indicated.

[0040] 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.

[0041] Metal content and sodium content are measured by X-ray fluorescence.

[0042] 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. The total pore volume is measured by mercury porosimetry according to ASTM D4284-92 with a wetting angle of 140°, for example, using a Micromeritics® Autopore® III instrument.

[0043] In this application, ppm values ​​are ppm weight values ​​(unless otherwise defined).

[0044] Hourly volumetric velocity (WH or "Gas Hourly Space Velocity GHSV" according to Anglo-Saxon terminology) refers to the volumetric flow rate of the gaseous feed at the reactor inlet in m³ 3 / h divided by the catalyst volume in m 3 content in the reactor.

[0045] We hear "nitrogen oxides" or "NOx" referring to nitrogen oxides such as NO and NO2.

[0046] 2. Catalyst

[0047] The catalyst used in the hydrogen denitrification (DeNoX) process (H2- SCR) comprises an active phase including platinum, tungsten and sodium, and a support including titanium dioxide (TiU2).

[0048] The platinum content is advantageously between 0.01 and 10% by weight of platinum 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.

[0049] The tungsten content is advantageously between 1 and 30% by weight of tungsten element relative to the total weight of the catalyst, preferably between 5 and 25% by weight, more preferably between 7 and 20% by weight, and even more preferably between 8 and 15% by weight.

[0050] The sodium content is advantageously between 0.5 and 5% by weight of sodium element relative to the total weight of the catalyst, preferably between 0.5 and 4% by weight, and even more preferably between 0.5 and 3.5% by weight.

[0051] Advantageously, the molar ratio between platinum and tungsten is between 0.0001 and 5 mol / mol, preferably between 0.0005 and 4 mol / mol, and even more preferably between 0.001 and 3 mol / mol.

[0052] Advantageously, the molar ratio of platinum to sodium is between 0.001 and 0.5 mol / mol, preferably between 0.002 and 0.4 mol / mol, and even more preferably between 0.003 and 0.3 mol / mol. Advantageously, the molar ratio of tungsten to sodium is between 0.001 and 6 mol / mol, preferably between 0.005 and 5 mol / mol, and even more preferably between 0.005 and 4 mol / mol.

[0053] 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 m 2 / g and 80 m 2 / g.

[0054] 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.

[0055] The catalyst support comprises at least titanium dioxide (TiCh). Preferably, the catalyst support is made of titanium dioxide.

[0056] Preferably, TiCh is in its anatase and rutile forms, with the rutile:anatase mass ratio preferably between 95:5 and 50:50.

[0057] 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 m 2 / g and 80 m 2 / g.

[0058] 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.

[0059] 3. Catalyst preparation process

[0060] The catalyst preparation process according to the invention comprises at least the following steps: a) the following substeps are carried out in sequence: a1) the support is contacted with at least one solution comprising at least one sodium precursor; a2) the catalyst precursor obtained in substep a1 is dried at a temperature below 250°C; a3) optionally, the dried catalyst precursor obtained in substep a2 is calcined at a temperature between 250°C and 900°C; b) the following substeps are carried out in sequence: b1) the support is contacted with at least one solution comprising at least one tungsten precursor; b2) the catalyst precursor obtained in substep b1 is dried at a temperature below 250°C; b3) optionally, the dried catalyst precursor obtained in substep b2 is calcined at a temperature between 250°C and 900°C;c) the following sub-steps are carried out in sequence: c1) the support is brought into contact with at least one solution comprising at least one platinum precursor; c2) the catalyst precursor obtained in sub-step c1) is dried at a temperature below 250°C; c3) the dried catalyst precursor obtained in sub-step c2) is calcined at a temperature between 250°C and 900°C.

[0061] In one embodiment according to the invention, the catalyst preparation process according to the invention is carried out in the following sequence of steps: a), then b), then c).

[0062] The different stages of the process according to the invention are explained in detail below.

[0063] The deposition of sodium on the support, in accordance with the implementation of substep a1), can be carried out by impregnation, dry or in excess, or by deposition - precipitation, according to methods well known to those skilled in the art.

[0064] Substep a1) is preferably carried out by impregnating the support, for example by contacting said support with at least one aqueous or organic solution (e.g., methanol, ethanol, phenol, acetone, toluene, or dimethyl sulfoxide (DMSO)), or alternatively, a solution consisting of a mixture of water and at least one organic solvent, containing at least one sodium precursor at least partially dissolved. Preferably, the solution is aqueous. The pH of this solution may be modified by the optional addition of an acid or a base.

[0065] Preferably, said substep a1) is carried out by dry impregnation, which consists of bringing the catalyst support into contact with a solution, containing at least one sodium precursor, the volume of which is between 0.25 and 1.5 times the porous volume of the support to be impregnated.

[0066] Any sodium precursor known to those skilled in the art may be used. Preferably, the sodium precursor is sodium nitrate, sodium chloride, sodium hydroxide, or sodium sulfate. The catalyst precursor obtained at the end of substep a1) 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 not excluded, but do not necessarily provide any improvement.

[0067] Drying is generally carried out under combustion air of a hydrocarbon, preferably methane, or under heated air comprising between 0 and 80 grams of water per kilogram of combustion air, an oxygen level between 5% and 25% by volume and a carbon dioxide level between 0% and 10% by volume.

[0068] Advantageously, after drying, the catalyst precursor obtained at the end of substep a2) is calcined under air, preferably combustion air, and more preferably methane combustion air, comprising 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 hours and 5 hours. The volumetric flow rate per hour (VVH) is generally between 150 and 3000 liters of combustion air per hour per liter of catalyst, preferably between 300 and 1500 liters of combustion air per hour per liter of catalyst.

[0069] The deposition of tungsten on the support, in accordance with the implementation of substep b1), can be carried out by impregnation, dry or in excess, or by deposition - precipitation, according to methods well known to those skilled in the art.

[0070] Substep b1) is preferably carried out by impregnating the support, for example by contacting said support with at least one aqueous or organic solution (e.g., methanol, ethanol, phenol, acetone, toluene, or dimethyl sulfoxide (DMSO)), or alternatively, a mixture of water and at least one organic solvent, containing at least one tungsten precursor at least partially dissolved. Preferably, the solution is aqueous. The pH of this solution may be modified by the optional addition of an acid or a base.

[0071] Preferably, said substep b1) is carried out by dry impregnation, which consists of bringing the catalyst support into contact with a solution, containing at least one tungsten precursor, the volume of which is between 0.25 and 1.5 times the porous volume of the support to be impregnated.

[0072] The tungsten precursor that can be used is well known to those skilled in the art. For example, tungsten sources include oxides and hydroxides, tungstic acids and their salts, particularly ammonium salts such as ammonium tungstate and ammonium metatungstate, phosphotungstic acid and its salts, and possibly silicotungstic acid (H4SiWi2O4O) and its salts. Tungsten sources can also be heteropolycompounds of the Keggin, lacunar Keggin, substituted Keggin, and Dawson types, for example. Ammonium oxides and salts such as ammonium metatungstate or heteropolyanions of the Keggin, lacunar Keggin, or substituted Keggin type are preferred. To allow better dissolution of the tungsten precursor in the impregnation solution, it is possible to use an organic compound comprising at least one carboxylic acid function, such as oxalic acid.The molar ratio between the tungsten element and the organic compound is advantageously between 0.01 and 5 mol / mol, preferably between 0.05 and 3 mol / mol, preferably between 0.05 and 1.5 mol / mol, and even more preferably between 0.1 and 1 mol / mol.

[0073] The catalyst precursor obtained at the end of substep b1) 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 provide any improvement.

[0074] Drying is generally carried out under combustion air of a hydrocarbon, preferably methane, or under heated air comprising between 0 and 80 grams of water per kilogram of combustion air, an oxygen level between 5% and 25% by volume and a carbon dioxide level between 0% and 10% by volume.

[0075] Advantageously, after drying, the catalyst precursor obtained at the end of substep b2) is calcined under air, preferably combustion air, and more preferably methane combustion air, comprising 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 hours and 5 hours. The volumetric flow rate per hour (VVH) is generally between 150 and 3000 liters of combustion air per hour per liter of catalyst, preferably between 300 and 1500 liters of combustion air per hour per liter of catalyst.

[0076] The deposition of platinum on the support, in accordance with the implementation of substep c1) can be carried out by impregnation, dry or in excess, or by deposition - precipitation, according to methods well known to the person skilled in the art.

[0077] Substep c1) is preferably carried out by impregnating the support, for example by contacting said support with at least one aqueous or organic solution (e.g., methanol, ethanol, phenol, acetone, toluene, or dimethyl sulfoxide (DMSO)), or a solution consisting of a mixture of water and at least one organic solvent, containing at least one platinum precursor at least partially dissolved, or by contacting said support with at least one colloidal solution of at least one platinum precursor, in oxidized form (platinum oxide, oxy(hydroxide), or hydroxide nanoparticles) or in reduced form (reduced platinum metal nanoparticles). Preferably, the solution is aqueous. The pH of this solution may be modified by the optional addition of an acid or a base.

[0078] Preferably, said substep c1) is carried out by dry impregnation, which consists of bringing the catalyst support into contact with a solution, containing at least one platinum precursor, the volume of which is between 0.25 and 1.5 times the porous volume of the support to be impregnated.

[0079] When a platinum precursor is introduced into aqueous solution, a mineral or organic platinum precursor is advantageously used. In mineral form, the platinum precursor can be selected from hexachloroplatinic acid, hexahydroxyplatinic acid, platinum dihydroxytetramine, or platinum diaminonitrite. Hexachloroplatinic acid is the preferred precursor salt of platinum. In organic form, the platinum precursor can be selected from organometallic complexes such as platinum bisacetylacetonate.

[0080] The catalyst precursor obtained at the end of substep c1) 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 provide any improvement. Drying is generally carried out under combustion air of a hydrocarbon, 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.

[0081] After drying, the catalyst precursor obtained at the end of substep c2) 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 hours and 5 hours. The volumetric flow rate per hour (VVH) is generally between 150 and 3000 liters of combustion air per hour per liter of catalyst, preferably between 300 and 1500 liters of combustion air per hour per liter of catalyst.

[0082] 4. Catalyst shaping

[0083] The catalyst used in the denitrification (DeNOx) process according to the invention is advantageously formed by deposition as a coating (or "washcoat") on a honeycomb structure, primarily for mobile applications, or on a plate structure, particularly for stationary industrial applications. The invention can also be formed into extruded or granular products.

[0084] The honeycomb structure is formed of parallel channels open at both ends (flow-through) or comprises 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. In one embodiment, the structure is composed of cordierite, silicon carbide (SiC), aluminum titanate (AlTi), alpha alumina, mullite, or any other material with a porosity between 30 and 70%. In another embodiment, the structure is made of sheet metal, stainless steel containing chromium and aluminum, or FeCrAl steel.

[0085] 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.

[0086] The coating itself (the "washcoat") comprises the catalyst, advantageously combined with a binder such as cerine, zirconium oxide, alumina, non-zeolitic silica-alumina, titanium oxide, a cerine-zirconia mixed oxide, tungsten oxide, or spinel. This coating is advantageously applied to the structure by a washcoating method, which consists of dipping the monolith into a slurry of catalyst powder according to the invention in a solvent, preferably water, and potentially binders, metal oxides, stabilizers, or other promoters. This dipping step can be repeated until the desired amount of coating is achieved. In some cases, the slurry can also be sprayed into the monolith. Once the coating has been applied, the monolith is calcined at a temperature of 300 to 600°C, usually for 1 to 10 hours.

[0087] In one embodiment, said structure is coated with one or more coatings. The coating comprising the catalyst is advantageously associated with, i.e. covers or is covered by, another coating having adsorption or reduction capacities for pollutants in particular NOx and / or promoting the oxidation of pollutants, in particular carbon monoxide (CO) and hydrocarbons (HC).

[0088] Another possibility is to provide the catalyst in the form of an extrudate, a bead, or any other shape known to those skilled in the art. In this case, the resulting structure can contain up to 100% catalyst.

[0089] 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.

[0090] 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.

[0091] The structure coated with the catalyst or catalyst support is advantageously integrated into the exhaust line of an industrial process or internal combustion engine. An oxidation catalyst, whose function is to oxidize volatile organic compounds (VOCs), and a filter to remove particulate matter from the exhaust gases can be placed either upstream or downstream of the structure. In some cases, to treat the NH3 produced by the catalyst, the catalyst can be combined with a NOx treatment catalyst of the NH3-SCR type or with an NH3 removal catalyst (Ammonia Slip Catalyst, according to Anglo-Saxon terminology), or even both.

[0092] 5. H2-SCR Process

[0093] The catalytic reduction process of nitrogen oxides (NOx), using the catalyst as mentioned above, includes a step of contacting the catalyst with nitrogen oxides (NOx) in the presence of hydrogen, 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.

[0094] According to one or more embodiments, the gaseous load to be treated comprises between 10 ppm and 3000 ppm weight of NOx relative to the total weight of the gaseous load, preferably between 50 and 800 ppm weight, and even more preferably between 70 and 300 ppm weight.

[0095] The said gaseous charge may further comprise between 2% and 12% by weight of oxygen (O2), between 0 ppm and 500 ppm of CO, between 0 and 30% by weight of H2O, and a sulfur content in the form of SO2 of less than 200 ppm, preferably less than 150 ppm by weight, relative to the total weight of said gaseous charge.

[0096] 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.

[0097] The process is advantageously implemented in the presence of the catalyst shaped as described above. EXAMPLES

[0098] 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. dry, then 0.5%

[0099] First, the TiC>2 support (Aldrich P25) in powder form is dry-impregnated with an aqueous NaOH solution to achieve a 2% Na content by weight in the final catalyst. This solid is then oven-dried at 100°C for 16 hours and subsequently calcined in a tubular kiln at 500°C for 2 hours with a ramp rate of 5°C / min under 1 Lh / g of air.

[0100] Next, this solid is dry-impregnated with a container containing a mixture of the W precursor ((NH4)eH2Wi2O4O) and oxalic acid (molar ratio of W precursor to oxalic acid = 0.2). The addition of oxalic acid improves the solubilization of the W precursor. The resulting mixture is then placed under static maturation in a saturator (water desiccator) for 1 hour and subsequently dried in air at 100°C for 16 hours. This yields a catalyst precursor A1.

[0101] The solid prepared above is then dry-impregnated with a solution containing the Pt precursor (H2PtCl.6H2O). The resulting catalyst precursor is oven-dried at 100°C for 16 hours and then calcined in a tube furnace at 450°C for 2 hours with a ramp of 5°C / min under 1 Lh / g of air.

[0102] Catalyst A is obtained, comprising the following contents:

[0103] The Na content analyzed by X-ray fluorescence is 2% by weight relative to the total weight of the catalyst.

[0104] The W content analyzed by X-ray fluorescence is 10% by weight relative to the total weight of the catalyst.

[0105] The Pt content analyzed by X-ray fluorescence is 0.5% by weight relative to the total weight of the catalyst.

[0106] Example 2: 0.5% wt. Na, 10% wt. W by dry impregnation, then 0.5% wt. Pt by dry impregnation (pre-impregnation 2% wt. Na) [compliant!

[0107] First, the TiC>2 support (Aldrich P25) in powder form is dry-impregnated with an aqueous NaOH solution to achieve a 0.5 wt% Na content in the final catalyst. This solid is then oven-dried at 100°C for 16 hours and subsequently calcined in a tube kiln at 500°C for 2 hours with a ramp rate of 5°C / min under 1 Lh / g of air. Next, this solid is dry-impregnated with a container containing a mixture of the W precursor ((NH4)eH2Wi2O4O) and oxalic acid (W precursor / oxalic acid molar ratio = 0.2). The addition of oxalic acid improves the solubilization of the W precursor. The resulting mixture is then statically matured in a saturator (water desiccator) for 1 hour and subsequently air-dried at 100°C for 16 hours. A precursor of catalyst B1 is obtained.

[0108] The solid prepared above is then dry-impregnated with a solution containing the Pt precursor (H2PtCl6.6H2o). The resulting catalyst precursor is oven-dried at 100°C for 16 hours and then calcined in a tube furnace at 450°C for 2 hours with a ramp of 5°C / min under 1 Lh / g of air.

[0109] Catalyst B is obtained, comprising the following contents:

[0110] The Na content analyzed by X-ray fluorescence is 0.5% by weight relative to the total weight of the catalyst.

[0111] The W content analyzed by X-ray fluorescence is 10% by weight relative to the total weight of the catalyst.

[0112] The Pt content analyzed by X-ray fluorescence is 0.5% by weight relative to the total weight of the catalyst.

[0113] First, the TiU2 (Aldrich P25) support in powder form is dry-impregnated with an aqueous NaOH solution to achieve a final Na content of 8 wt% on the final catalyst. This solid is then oven-dried at 100°C for 16 hours and subsequently calcined in a tubular kiln at 500°C for 2 hours with a ramp rate of 5°C / min under 1 Lh / g of air.

[0114] Next, this solid is dry-impregnated with a container containing a mixture of the W precursor ((NH4)6H2Wi2O4O) and oxalic acid (molar ratio of W precursor to oxalic acid = 0.2). The addition of oxalic acid improves the solubilization of the W precursor. The resulting mixture is then placed under static maturation in a saturator (water desiccator) for 1 hour and subsequently dried in air at 100°C for 16 hours. This yields a C1 catalyst precursor.

[0115] The solid prepared above is then dry-impregnated with a solution containing the Pt precursor (LLPtCle.ShLo). The resulting catalyst precursor is oven-dried at 100°C for 16 hours and then calcined in a tube kiln at 450°C for 2 hours with a ramp of 5°C / min under 1 Lh / g of air.

[0116] The catalyst C is obtained comprising the following contents: The Na content analyzed by X-ray fluorescence is 8% by weight relative to the total weight of the catalyst.

[0117] The W content analyzed by X-ray fluorescence is 10% by weight relative to the total weight of the catalyst.

[0118] The Pt content analyzed by X-ray fluorescence is 0.5% by weight relative to the total weight of the catalyst. (dry, then 0.5% by weight Pt)

[0119] First, the TiCh (Aldrich P25) support in powder form is dry-impregnated with a container containing a mixture of the W precursor ((NhDehLW^CUo)) and oxalic acid (molar ratio of W precursor to oxalic acid = 0.2). The addition of oxalic acid improves the solubilization of the W precursor. The resulting mixture is then placed under static maturation in a saturator (water desiccator) for 1 hour and subsequently air-dried at 100°C for 16 hours. This yields a D1 catalyst precursor.

[0120] The solid prepared above is then dry-impregnated with a solution containing the Pt precursor (LLPtCle.ShLo). The resulting catalyst precursor is oven-dried at 100°C for 16 hours and then calcined in a tube kiln at 450°C for 2 hours with a ramp of 5°C / min under 1 Lh / g of air.

[0121] The catalyst D is obtained, comprising the following contents:

[0122] The W content analyzed by X-ray fluorescence is 10% by weight relative to the total weight of the catalyst.

[0123] The Pt content analyzed by X-ray fluorescence is 0.5% by weight relative to the total weight of the catalyst. (dry, then 0.5% by weight Pt) has

[0124] First, the TiU2 support (Aldrich P25) in powder form is dry-impregnated with a solution containing a mixture of the W precursor ((NhUjehLW^CUo)) and oxalic acid (molar ratio of W precursor to oxalic acid = 0.2). The addition of oxalic acid improves the solubilization of the W precursor. The resulting mixture is then placed under static maturation in a saturator (water desiccator) for 1 hour and subsequently air-dried at 100°C for 16 hours. This yields a catalyst precursor E1.

[0125] The solid prepared above is then dry-impregnated with a solution containing the Pt precursor (LLPtCle.ShLo). The resulting catalyst precursor is oven-dried at 100°C for 16 hours and then calcined in a tube kiln at 450°C for 2 hours with a ramp of 5°C / min under 1 Lh / g of air.

[0126] The catalyst E is obtained, comprising the following contents:

[0127] The W content analyzed by X-ray fluorescence is 2% by weight relative to the total weight of the catalyst.

[0128] The Pt content analyzed by X-ray fluorescence is 0.5% by weight relative to the total weight of the catalyst.

[0129] First, the TiU2 (Aldrich P25) support in powder form is dry-impregnated with an aqueous NaOH solution to achieve a 2% Na content by weight in the final catalyst. This solid is then oven-dried at 100°C for 16 hours and subsequently calcined in a tubular kiln at 500°C for 2 hours with a ramp rate of 5°C / min under 1 Lh / g of air.

[0130] Next, this solid is dry-impregnated with a container containing a mixture of the W precursor ((NH4)eH2Wi2O4O) and oxalic acid (W precursor / oxalic acid molar ratio = 0.2). The addition of oxalic acid improves the solubilization of the W precursor. The resulting mixture is then placed under static maturation in a saturator (water desiccator) for 1 hour and subsequently air-dried at 100°C for 16 hours. This yields a catalyst precursor F1.

[0131] The solid prepared above is then dry-impregnated with a solution containing the Pt precursor (H2PtCl.6H2O). The resulting catalyst precursor is oven-dried at 100°C for 16 hours and then calcined in a tube furnace at 450°C for 2 hours with a ramp of 5°C / min under 1 Lh / g of air.

[0132] The catalyst F is obtained, comprising the following contents:

[0133] The Na content analyzed by X-ray fluorescence is 2% by weight relative to the total weight of the catalyst.

[0134] The W content analyzed by X-ray fluorescence is 2% by weight relative to the total weight of the catalyst.

[0135] The Pt content analyzed by X-ray fluorescence is 0.5% by weight relative to the total weight of the catalyst.

[0136] For catalytic testing, 200 mg of catalysts A to F in powder form is placed in a quartz reactor. The reactor is fed with 150 L / h of a gas mixture with the following molar compositions: 400 ppm NO, 4000 ppm H2, 10% O2, 15% H2O qpc N2. (qpc = quantity to compensate).

[0137] 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:

[0138] NOx conversion — (NOx input — NOx output) / NOx input

[0139] In these formulas, the input and output indices indicate the content before and after catalytic reduction, respectively.

[0140] The NOx conversion results for catalysts containing 10 wt% of W and a variable Na content are shown in Figure 1. The curves marked by crosses, squares, triangles and circles correspond respectively to the tests carried out with catalysts A, B, C and D synthesized according to example 1, example 2, example 3 and example 4.

[0141] The results of NOx conversion for catalysts containing 2 wt% of W are shown in Figure 2. The curves marked by empty squares and crosses correspond respectively to the tests carried out with catalysts E and F synthesized according to example 5 (non-compliant) and example 6 (compliant).

[0142] A summary of the catalyst performance is given in Table 1 below:

[0143] Table 1 Catalysts A and B according to the invention (A: 10 wt% W, 2 wt% Na, 0.5 wt% Pt; B: 10 wt% W, 0.5 wt% Na, 0.5 wt% Pt) exhibit better maximum efficiency over a wider temperature range than catalyst C, which contains 8 wt% Na, and catalyst D, which does not contain Na. Catalyst F according to the invention (2 wt% W, 2 wt% Na, 0.5 wt% Pt) exhibits better maximum efficiency over a wider temperature range than the non-conforming catalyst E (2 wt% W, 0.5 wt% Pt).

Claims

1. DEMANDS 1. Catalyst comprising an active phase comprising platinum, tungsten and sodium, and a support comprising at least titanium dioxide, characterized in that: - the platinum content is between 0.01 and 10% by weight of platinum element relative to the total weight of the catalyst; - the tungsten content is between 1 and 30% by weight of tungsten element relative to the total weight of the catalyst; - the sodium content is between 0.5 and 5% by weight of sodium element relative to the total weight of the catalyst.

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 sodium content is between 1 and 3.5% by weight relative to the total weight of the catalyst.

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 tungsten content is between 5 and 25% by weight relative to the total weight of the catalyst.

7. Catalyst according to any one of the preceding claims, characterized in that the molar ratio between platinum and sodium is between 0.001 and 0.5 mol / mol.

8. Catalyst according to any one of the preceding claims, characterized in that the molar ratio between tungsten and sodium is between 0.001 and 6 mol / mol.

9. 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.

10. Catalyst according to claim 9, wherein the honeycomb structure is formed of parallel channels open at both ends or comprises filtering porous walls for which the adjacent parallel channels are alternately blocked on either side of the channels.

11. Catalyst according to claim 10, 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.

12. A process for preparing a catalyst according to any one of the preceding claims, comprising at least the following steps: a) the following substeps are carried out in sequence: a1) the support is contacted with at least one solution comprising at least one sodium precursor; a2) the catalyst precursor obtained in substep a1 is dried at a temperature below 250°C; a3) optionally, the dried catalyst precursor obtained in substep a2 is calcined at a temperature between 250°C and 900°C; b) the following substeps are carried out in sequence: b1) the support is contacted with at least one solution comprising at least one tungsten precursor; b2) the catalyst precursor obtained in substep b1 is dried at a temperature below 250°C; b3) optionally, the dried catalyst precursor obtained in sub-step b2) is calcined at a temperature between 250°C and 900°C;c) the following sub-steps are carried out in sequence: c1) the support is brought into contact with at least one solution comprising at least one platinum precursor; c2) the catalyst precursor obtained in sub-step c1) is dried at a temperature below 250°C; c3) the dried catalyst precursor obtained in sub-step c2) is calcined at a temperature between 250°C and 900°C.

13. A process for preparing a catalyst according to the preceding claim, wherein the steps are carried out in the following order: step a), then step b), then step c).

14. A process for the catalytic reduction of nitrogen oxides in the presence of hydrogen by contacting a gaseous feed comprising nitrogen oxides with a catalyst according to any one of claims 1 to 11 or prepared according to any one of claims 12 to 13, at a temperature between 15°C and 600°C, at a VVH between 10,000 h -1 and 150,000 h' 1, the H2 / NOx molar ratio being between 2:1 and 100:

1.

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

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