PdNi catalyst for the catalytic 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 palladium and nickel, and a support comprising titanium dioxide, the palladium content being between 0.001 and 8% by weight of elemental palladium, the nickel content being between 1 and 20% by weight of elemental nickel relative to the total weight of the catalyst, characterized in that: - the number-average diameter of the palladium particles is between 0.5 and 5 nm; and - the nickel particles are distributed in two distinct populations: a first population of particles whose number-average diameter is between 2.5 and 6 nm, and a second population of particles whose number-average diameter is between 7 and 12 nm.

Description

Title of the invention: PdNi catalyst for the catalytic reduction of nitrogen oxides (NOx) in the presence of hydrogen. Technical field

[0001] The present invention relates to the field of nitrogen oxide (NOx) emission treatment systems by catalytic reduction in the presence of hydrogen. Prior art

[0002] Nitrogen oxide (NOx) emissions resulting from combustion are a major concern for society. Increasingly stringent standards are being implemented by government bodies to limit the impact of combustion emissions on the environment and on health. Selective catalytic reduction, known by the acronym "SCR" (for "Selective Catalytic Reduction"), appears to be an effective technology for eliminating nitrogen oxides in oxygen-rich exhaust gases for both industrial and mobile applications such as diesel engines, hydrogen engines, or, more generally, lean-burn engines. Selective catalytic reduction is achieved using a reducing agent, usually ammonia, and can therefore be designated 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 conversion. efficient NOx and / or high formation of undesirable secondary compounds such as nitrous oxide (N2O).

[0003] Indeed, the conversion window in existing H2-SCR processes is rather narrow and generally centered at low temperatures (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 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).

[0004] 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 reduced before the H2-SCR catalyst composition is selected for NOx control.

[0005] Finally, at higher temperatures, gaseous hydrogen reacts preferentially with oxygen, which exists in large quantities in the exhaust gases of most compression-ignition engines.

[0006] The Applicant has surprisingly discovered that a palladium-nickel based catalyst, in which the sizes of the palladium and nickel nanoparticles are well controlled on a support comprising titanium dioxide obtained by a specific preparation process, notably by the addition of citric acid during the step of contacting the support with the precursor of the active nickel phase, and by carrying out a colloidal impregnation step with palladium, makes it possible to convert NOx at low temperatures, i.e., less than or equal to 180°C, with low N2O emissions. The catalyst according to the invention exhibits high selectivity for the formation of NH3. Thus, such a catalyst can be used in a specific chain of catalysts to convert the NH3 formed. OBJECTS OF THE INVENTION

[0007] The present invention relates to a catalyst comprising an active phase comprising palladium and nickel, and a support comprising at least titanium dioxide, the palladium content being between 0.001 and 8% by weight of palladium element relative to the total weight of the catalyst, the nickel content being between 1 and 20% by weight of nickel element relative to the total weight of the catalyst, characterized in that:

[0008] - the average number diameter of the palladium particles is between 0.5 and 5 nm; and

[0009] - the nickel particles are distributed in two distinct populations: a first population of particles whose average number diameter is between 2.5 and 6 nm, and a second population of particles whose average number diameter is between 7 and 12 nm.

[0010] According to one or more embodiments of the invention, the molar ratio between palladium and nickel is between 0.001 and 5 mol / mol.

[0011] According to one or more embodiments of the invention, titanium dioxide is present 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 palladium content is 0.005 and 5% by weight of the element palladium relative to the total weight of the catalyst, the nickel content is between 3 and 10% by weight of the 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.

[0013] 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.

[0014] Another object according to the invention relates to a process for preparing a catalyst according to the invention comprising at least the following steps:

[0015] a) the support is brought into contact with at least one solution containing at least one nickel precursor and at least one organic compound comprising at least one carboxylic acid function;

[0016] b) the support is brought into contact with at least one solution containing at least one palladium precursor by colloidal means;

[0017] steps a) and b) being carried out in any order;

[0018] c) the catalyst precursor obtained at the end of the sequence of steps a) and b), or b) and a), is dried at a temperature below 250°C;

[0019] d) the catalyst precursor obtained in step c) is calcined at a temperature between 250°C and 900°C.

[0020] According to one or more embodiments of the invention, the nickel precursor and said organic compound are added in step a) of the dry impregnation preparation process.

[0021] According to one or more embodiments of the invention, the palladium precursor is added in step b) of the colloidal impregnation preparation process from an aqueous solution comprising at least one precursor salt of palladium and an aqueous solution of alkali hydroxide or alkaline earth hydroxide.

[0022] According to one or more embodiments of the invention, step a) is carried out before step b).

[0023] According to one or more embodiments of the invention, said nickel precursor is selected from nickel nitrate, nickel chloride, nickel acetate or nickel hydroxycarbonate.

[0024] According to one or more embodiments of the invention, the organic compound of step a) is selected from oxalic acid, malonic acid, glutaric acid, glycolic acid, lactic acid, tartronic acid, citric acid, tartaric acid, pyruvic acid, levulinic acid.

[0025] According to one or more embodiments of the invention, the molar ratio between said organic compound introduced in step a) and the nickel element also introduced in step a) is between 0.01 and 5.0 mol / mol.

[0026] According to one or more embodiments of the invention, the palladium precursor salt is selected from the group consisting of palladium chloride, palladium nitrate and palladium sulfate.

[0027] Another object according to the invention relates to a process for the catalytic reduction of nitrogen oxides comprising at least a first sub-step of reduction in the presence of hydrogen (H2) by bringing into contact a gaseous charge 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 between 10,000 h1 and 150,000 h1, the molar ratio H2 / NOx being between 2:1 and 100:1.

[0028] According to one or more embodiments of the invention, the gaseous charge comprises between 10 ppm and 3000 ppm weight of NOx relative to the total weight of the gaseous charge.

[0029] According to one or more embodiments of the invention, said 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. LIST OF FIGURES

[0030] [Fig.1] Fig.1 represents the conversion of NOx [C] as a function of the reduction temperature [T].

[0031] [Fig.2] Fig.2 represents the concentration of NH3 [Conc] as a function of the reduction temperature [T]. Description of the implementation methods

[0032] Other features and advantages of the method according to the invention will become apparent from the following description of non-limiting examples of embodiments, with reference to the figures attached and described below. 1. Definitions

[0033] 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.

[0034] In the sense of the present invention, the 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 sense of the present invention, a preferred range of pressure values ​​can be combined with a preferred range of temperature values.

[0035] In the following text, the expressions "between ... and ..." and "between ... and ..." are equivalent and mean that the limit values ​​of the interval are included in the range of values ​​described. If this were not the case and the limit values ​​were not included in the range described, such clarification will be provided by the present invention.

[0036] In this description, the term "include" is synonymous with (means the same as) "include" and "contain," and is inclusive or open and does not exclude other elements not mentioned. It is understood that the term "include" includes the exclusive and closed term "consist."

[0037] According to the present invention, the pressures are absolute pressures, also noted as abs., and are given in absolute MPa (or abs. MPa), unless otherwise indicated.

[0038] In the following text, the groups of chemical elements 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 VIIIB) according to the CAS classification corresponds to the metals in columns 8, 9 and 10 according to the new IUP AC classification, and group VIB to the metals in column 6.

[0039] The metal content is measured by X-ray fluorescence.

[0040] 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”, Academy Press, 1999.

[0041] 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 apparatus from the Microméritics® brand.

[0042] The particle sizes of palladium and nickel are measured by transmission electron microscopy. Those skilled in the art are familiar with the appropriate techniques for determining the average particle diameter. The average particle diameter, and therefore the particle size distribution, can be determined by statistical studies of microscopy images, and in particular by transmission electron microscopy (TEM). The number-average diameter is calculated on at least 250 nanoparticles.

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

[0044] By hourly volumetric velocity (WH or "Gas Hourly Space Velocity GHSV according to Anglo-Saxon terminology"), we mean the volumetric flow rate of the gaseous feed at the reactor inlet in m3 / h divided by the volume of catalyst in m3 contained in the reactor.

[0045] "Nitrogen oxides" or "NOx" means nitrogen oxides such as NO and NO2. 2. Catalyst

[0046] The catalyst according to the invention comprises an active phase comprising palladium and nickel, and a support comprising at least titanium dioxide, the palladium content being between 0.001 and 8% by weight of palladium element relative to the total weight of the catalyst, the nickel content being between 1 and 20% by weight of nickel element relative to the total weight of the catalyst, characterized in that:

[0047] - the average number diameter of the palladium particles is between 0.5 and 5 nm, preferably between 0.7 and 4.5 nm, and even more preferably between 0.7 and 4 nm; and

[0048] - the nickel particles are distributed in two distinct populations: a a first population of particles whose average number diameter is between 2.5 and 6 nm, preferably between 3.5 and 5 nm, and even more preferably between 3 and 4.5 nm, and a second population of particles whose average number diameter is between 7 and 12 nm, preferably between 7.5 nm and 11 nm, and even more preferably between 7.5 and 10 nm.

[0049] The particular distribution of palladium and nickel particle sizes is made possible by the implementation of a specific preparation process comprising a step of impregnation with a colloidal palladium solution allowing control of the size distribution of the palladium nanoparticles and a separate step of impregnation of a nickel precursor with a particular organic additive allowing control of the size distribution of the nickel nanoparticles.

[0050] The palladium content is advantageously between 0.001 and 8% by weight of palladium element relative to the total weight of the catalyst, preferably between 0.005 and 8% by weight, and even more preferably between 0.005 and 5% by weight.

[0051] The nickel content is advantageously between 1 and 20% by weight in 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.

[0052] 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.

[0053] The specific surface area of ​​the catalyst is generally between 10 m2 / g and 300 m2 / g, preferably between 10 m2 / g and 150 m2 / g, more preferably between 30 m2 / g and 120 m2 / g, and even more preferably between 40 and 80 m2 / g.

[0054] The porous 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 (TiO2). Preferably, the catalyst support is made of titanium dioxide.

[0056] Preferably, TiO2 is in its anatase and rutile forms, the rutile:anatase mass ratio preferably being between 95:5 and 50:50.

[0057] The specific surface area of ​​the support is generally between 10 m2 / g and 300 m2 / g, preferably between 10 m2 / g and 150 m2 / g, more preferably between 30 m2 / g and 120 m2 / g, and even more preferably between 40 and 80 m2 / g.

[0058] The porous 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. 3. Catalyst preparation process

[0059] The catalyst preparation process according to the invention comprises at least the following steps:

[0060] a) the support is brought into contact with at least one solution containing at least one nickel precursor and at least one organic compound comprising at least one carboxylic acid function;

[0061] b) the support is brought into contact with at least one solution containing at least one palladium precursor by colloidal means;

[0062] steps a) and b) being carried out in any order;

[0063] c) the catalyst precursor obtained at the end of the sequence of steps a) and b), or b) and a), is dried at a temperature below 250°C;

[0064] d) the catalyst precursor obtained in step c) is calcined at a temperature between 250°C and 900°C.

[0065] In step a) of the process, the support is contacted with at least one solution containing at least one nickel precursor and at least one organic compound comprising at least one carboxylic acid functional group. Indeed, it has also been observed that catalysts prepared in the presence of an organic compound (listed below) allow for the formation of two distinct populations of nickel particle sizes, which are not observed in the absence of this organic compound. The addition of palladium and nickel in two separate steps, with very different target concentrations of nickel and palladium, to the final catalyst leads to catalysts that do not exhibit alloy-like characteristics. The nanoparticles analyzed by transmission electron microscopy are either composed exclusively of nickel or exclusively of palladium.

[0066] Steps a) to d) are described in detail below. Other optional steps may also be included in the catalyst preparation process and are described below.

[0067] Step a) bringing the support into contact with the nickel and the organic compound

[0068] The deposition on said support of the nickel precursor and the organic compound comprising at least one carboxylic acid function, in accordance with the implementation of step a), 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.

[0069] Preferably, step a) is carried out by impregnating the support, for example by contacting said support with at least one aqueous or organic solution (for example, 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 nickel precursor at least partially dissolved and at least one organic compound comprising at least one carboxylic acid functional group 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.

[0070] Preferably, said step a) is carried out by dry impregnation, which consists of bringing the catalyst support into contact with a solution, containing at least one nickel precursor and at least one organic compound comprising at least one carboxylic acid function, the volume of the solution of which is advantageously between 0.9 and 1.1 times the porous volume of the support to be impregnated.

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

[0072] The concentration of nickel in solution is adjusted according to the porous volume of the available support so as to obtain for the supported catalyst, a nickel content of between 1 and 20% by weight in nickel element relative to the total weight of the catalyst, more 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.

[0073] Advantageously, the molar ratio between said organic compound and the element nickel is between 0.01 and 5.0 mol / mol, preferably between 0.05 and 2.0 mol / mol, more preferably between 0.1 and 1.5 mol / mol and even more preferably between 0.3 and 1.2 mol / mol.

[0074] Said organic compound comprising at least one carboxylic acid functional group may be an aliphatic organic compound, saturated or unsaturated, or an aromatic organic compound. Preferably, the aliphatic organic compound, saturated or unsaturated, comprises between 1 and 9 carbon atoms, preferably between 2 and 7 carbon atoms. Preferably, the aromatic organic compound comprises between 7 and 10 carbon atoms, preferably between 7 and 9 carbon atoms.

[0075] Said aliphatic organic compound, saturated or unsaturated, or said aromatic organic compound, comprising at least one carboxylic acid function, may be selected from monocarboxylic acids, dicarboxylic acids, tricarboxylic acids, tetracarboxylic acids.

[0076] Advantageously, the organic compound comprising at least one carboxylic acid function is selected from ethanedioic acid (oxalic acid), propanedioic acid (malonic acid), pentanedioic acid (glutaric acid), hydroxyacetic acid (glycolic acid), 2-hydroxypropanoic acid (lactic acid), 2-hydroxypropanedioic acid (tartronic acid), 2-hydroxypropane-1,2,3-tricarboxylic acid (citric acid), 2,3-dihydroxybutanedioic acid (tartaric acid), 2-oxopropanoic acid (pyruvic acid), and 4-oxopentanoic acid (levulinic acid). Most preferably, the organic compound comprising at least one carboxylic acid function is tartaric acid or citric acid.

[0077] 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 durations are not excluded, but do not necessarily provide any improvement.

[0078] Step a) is carried out at least once and may advantageously be carried out several times, for example twice, possibly in the presence of a nickel precursor and / or an identical or different organic compound.

[0079] Each impregnation step is preferably followed by an intermediate drying step. The intermediate drying step is carried out at a temperature below 250°C, preferably between 15°C and 180°C, more preferably between 30°C and 160°C, even more preferably between 50°C and 150°C, and even more preferably between 70°C and 140°C, for a duration typically between 0.5 hours and 12 hours, and even more preferably between 0.5 hours and 5 hours. Longer durations are not excluded, but do not necessarily provide any improvement.

[0080] The drying step can be carried out by any technique known to those skilled in the art. It is advantageously carried out under an inert atmosphere or under an atmosphere containing oxygen or under a mixture of inert gas and oxygen. It is advantageously carried out at atmospheric pressure or at reduced pressure. Preferably, this step is carried out at atmospheric pressure and in the presence of air or nitrogen.

[0081] Similarly, after each intermediate drying step, an intermediate calcination step can be carried out at a temperature between 250°C and 600°C, preferably between 350°C and 550°C, for a period typically between 0.5 and 24 hours, preferably between 0.5 and 12 hours, and even more preferably between 0.5 and 10 hours, preferably under an inert atmosphere or an atmosphere containing oxygen. Longer durations are not excluded, but do not necessarily provide any improvement.

[0082] Step b) bringing the support into contact with the palladium by colloidal means

[0083] The deposition of palladium onto said support, in accordance with step b), is carried out by colloidal impregnation, advantageously by contacting said support with at least one colloidal solution of at least one palladium precursor, in oxidized form (palladium oxide, oxy(hydroxide), or hydroxide nanoparticles) or in reduced form (reduced palladium metallic nanoparticles). Preferably, the solution is aqueous. The pH of this solution may be modified by the optional addition of an acid or a base. Preferably, the volume of the colloidal suspension impregnated onto the support is between 0.9 and 1.1 times the porosity volume of the support.

[0084] The colloidal suspension is generally obtained by hydrolysis of the palladium cation in aqueous medium, which leads to the formation of suspended palladium oxide or hydroxide particles. Preferably, the colloidal suspension is obtained by starting from an aqueous solution comprising at least one precursor salt of palladium and an aqueous solution of alkali hydroxide or alkaline earth hydroxide.

[0085] 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.

[0086] Typically, an aqueous solution comprising at least one palladium precursor salt [also referred to herein as solution (II)] is supplied to a suitable apparatus, followed by an aqueous solution comprising at least one alkali or alkaline earth hydroxide [also referred to herein as solution (I)]. Alternatively, solutions (I) and (II) may be poured into the apparatus simultaneously. Preferably, aqueous solution (II) is poured into the apparatus first, followed by aqueous solution (I).

[0087] The palladium precursor salt is generally selected from the group consisting of palladium chloride, palladium nitrate, and palladium sulfate. Preferably, the palladium precursor salt is palladium nitrate.

[0088] The colloidal suspension generally remains in the apparatus for a residence time of between 0.5 and 20 hours.

[0089] 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.

[0090] In general, the preparation temperature is between 5°C and 40°C and preferably between 15°C and 35°C.

[0091] The concentration of palladium is preferably between 5 and 150 millimoles per liter (mmol / L), more preferably between 8 and 80 millimoles per liter.

[0092] 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 durations are not excluded, but do not necessarily provide any improvement. Implementation of steps a) and b)

[0093] The catalyst preparation process includes several implementation methods. They are distinguished in particular by the order of introduction of the organic compound and the nickel precursor according to step a), and of the palladium precursor according to step b).

[0094] A first method of implementation consists of carrying out said step a) prior to said step b).

[0095] A second implementation method consists of carrying out said step b) prior to said step a).

[0096] Preferably, the preparation process is carried out according to the first embodiment, i.e. the nickel precursor and the organic compound are introduced before the palladium precursor is introduced. c) drying of the catalyst precursor

[0097] The catalyst precursor obtained after the sequence of steps a) and b), or b) and a), 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.

[0098] Drying is generally carried out under hydrocarbon combustion air, preferably methane, or under heated air comprising 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

[0099] After drying, the catalyst precursor 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 h and 5 h. The volumetric hourly velocity (VHV) is generally between 150 and 3000, preferably between 300 and 1500 liters of combustion air per hour per liter of catalyst. 4. Catalyst shaping

[0100] The catalyst used in the denitrification (DeNOx) process according to the invention is advantageously formed by deposition as a coating (or "washcoat" in Anglo-Saxon terminology) 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 sphere-shaped products.

[0101] The honeycomb structure is formed of parallel channels open at both ends (flow-through) or comprises porous filtering walls, in which case the adjacent parallel channels are alternately blocked on either side of the channels in order to force the gas flow through the wall (wall-flow monolith). The honeycomb structure thus coated constitutes a catalytic block. The structure is advantageously composed of cordierite, silicon carbide. (SiC), aluminum titanate (AITi), alpha alumina, mullite or any other material with a porosity between 30 and 70%. Said structure is advantageously made of sheet metal, stainless steel containing chromium and aluminum, or FeCrAl type steel.

[0102] The quantity 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.

[0103] The coating itself (“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 for 1 to 10 hours.

[0104] Said structure is advantageously 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 of pollutants in particular NOx and / or promoting the oxidation of pollutants, in particular carbon monoxide (CO) and hydrocarbons (HC).

[0105] Another possibility is to put the catalyst in the form of an extrudate or 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.

[0106] 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. The 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 different constituents of the support or catalyst can be shaped by a mixing step to form a paste followed by extrusion of the resulting paste, or by mixing powders followed by pelletizing, or by any other known process for agglomerating a powder containing alumina. The resulting supports can be in various shapes and sizes. Preferably, shaping is carried out by mixing and extrusion.

[0107] 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 optionally 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 be hollow or solid) and / or twisted cylindrical and / or multilobed (2, 3, 4, or 5 lobes, for example) and / or rings. The multilobed shape is advantageously preferred.

[0108] Said structure coated by the catalyst or catalyst support is advantageously integrated into an 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 particles from the exhaust gases can be placed either upstream or downstream of said structure. 5. H2-SCR Process

[0109] The catalytic reduction process of nitrogen oxides (NOx), using the catalyst according to the invention, comprises 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, more preferably between 40°C and 400°C. The WH (GHSV) involved are preferably between 10,000 h₁ and 150,000 h₂*, preferably between 20,000 and 80,000 h₁, the H₂ / NOx molar ratio being between 2:1 and 100:1, preferably between 5:1 and 40:1.

[0110] According to one or more embodiments, the gaseous charge to be treated comprises between 10 ppm and 3000 ppm weight of NOx relative to the total weight of the gaseous charge, preferably between 50 and 800 ppm weight, and even more preferably between 70 and 300 ppm weight.

[0111] 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.

[0112] The quantity of catalyst is adjusted by a person skilled in the art according to the quantity of NOx present in the gas to be treated.

[0113] The process is advantageously implemented in the presence of the catalyst shaped as described above. 6. H2-SCR process followed by NH3-SCR

[0114] 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. Thus, another object of the invention relates to a catalytic reduction process for nitrogen oxides (NOx) comprising at least:

[0115] - a first reduction substep in the presence of hydrogen (H2) by putting into contact of a gaseous charge 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 between 10,000 h₁ and 150,000 h₁, the H₂ / NOx molar ratio being between 2:1 and 100:1, then

[0116] - a second reduction substep in the presence of ammonia (NH3) by setting in contact with the effluent obtained at the end of the first sub-step 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.

[0117] The transition metal content is advantageously between 0.5 and 5% by weight of the metal element relative to the total weight of the catalyst, preferably between 1.4 and 4% by weight, most preferably between 2.2 and 3.6% by weight, most advantageously between 2.8 and 3.2% by weight. Preferably the transition metal is copper.

[0118] When the zeolite catalyst is of structural type CHA, the molar ratio SiO2 / Al2O3 of the CHA zeolite-based catalyst is between 7 and 30, preferably between 12 and 26 inclusive.

[0119] The zeolite catalyst can be prepared according to all techniques of the person skilled in the art, and more particularly as described in documents FR3123006 and FR3123007.

[0120] The zeolite catalyst can be shaped under the same operating conditions as for 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.

[0121] In one embodiment according to the invention, the zeolite catalyst is shaped into the same honeycomb structure as the hydrogen-reducing catalyst. A first configuration is to have a structure coated with several Coatings. The coating, including 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 is to have a structure coated in its upstream part by the hydrogen reduction catalyst and coated in its downstream part with the NH3-SCR type zeolite catalyst. Examples

[0122] 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 / g and the total pore volume is 0.75 ml / g.

[0123] Example 1: Impregnation with colloidal solution (1 wt% Pd) [non-compliant]

[0124] A colloidal suspension of palladium oxide is prepared under stirring at 25 °C by diluting 2.84 g of a palladium nitrate solution Pd(NO3)2 containing 8.5 wt% palladium with about 45 m of demineralized water, then adding about 10 ml of a sodium hydroxide solution to reach a pH of 2.4. This solution is then impregnated onto the support of titanium dioxide (Aldrich P25) in powder form.

[0125] The catalyst precursor obtained is dried under air at 100°C for 12 hours, then is calcined for 2 hours at 500°C with a ramp of 5°C / min under ILh / g of air.

[0126] Catalyst A is obtained.

[0127] The Pd content analyzed by X-ray fluorescence is 1% by weight relative to the total weight of the support.

[0128] The average diameter of the palladium nanoparticles determined by Transmission Microscopy (TEM) on 250 measured nanoparticles is 2.5 nm.

[0129] Example 2: Impregnation with colloidal solution (1 wt% Pd+ 5% Ni without tartaric acid) [non-compliant]

[0130] A colloidal suspension of palladium oxide is prepared under stirring at 25 °C by diluting 2.84 g of a palladium nitrate solution Pd(NO3)2 containing 8.5 wt% of palladium with about 45 m of demineralized water, then adding about 10 ml of a sodium hydroxide solution to reach a pH of 2.4. This solution is then impregnated onto the support of titanium dioxide (Aldrich P25) in powder form.

[0131] The resulting solid is dried under air at 100°C for 12 hours, then calcined for 2 hours at 500°C with a ramp of 5°C / min under ILh / g of air. The catalyst precursor B' is obtained.

[0132] The Pd content analyzed by X-ray fluorescence is 1% by weight relative to the total weight of the support.

[0133] The catalyst precursor B' is then dry-impregnated with a solution containing nickel nitrate (Ni(NO3)2.6H2O, supplier Strem Chemicals®).

[0134] The catalyst precursor obtained is dried under air at 100°C for 12 hours, then is calcined for 2 hours at 500°C with a ramp of 5°C / min under ILh / g of air.

[0135] Catalyst B is obtained.

[0136] The Ni content analyzed by X-ray fluorescence is 5% by weight relative to the total weight of the support.

[0137] The average diameter of the palladium nanoparticles determined by Transmission Microscopy (TEM) on 250 measured nanoparticles is 3 nm.

[0138] The size of the Ni particles has a wide distribution ranging from 2 to 15 nm with an average number diameter of 12 nm.

[0139] Example 3: Impregnation Ni alone (5 wt% Ni + tartaric acid) [non-compliant]

[0140] The Ni / TiO2 catalyst was prepared by dry impregnation on a dioxide support of Titanium dioxide (Aldrich P25) in powder form with a solution containing the Ni precursor (Ni(NO3)2.6H2O). The aqueous Ni solution is prepared by dissolving 58 g of nickel nitrate (NiNO3, supplier Strem Chemicals®) and 14.35 g of tartaric acid (CAS 87-69-4; supplier Fluka®) in 42 mL of distilled water. The additive / Ni molar ratio is set at 0.4. The solution is heated to 60°C to facilitate the dissolution of the nickel nitrate and then dry-impregnated onto the titanium dioxide support. 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 of 5°C / min under 11h / g of air. Catalyst C is obtained.

[0141] The Ni content analyzed by X-ray fluorescence is 5% by weight relative to the total weight of the support.

[0142] The average diameter of nickel nanoparticles determined by Transmission Microscopy (TEM) on 250 measured nanoparticles is 6 nm.

[0143] Example 4: Impregnation of 1% Pd colloids and Ni alone (5% wt Ni plus tartaric acid) [compliant]

[0144] A colloidal suspension of palladium oxide is prepared under stirring at 25 °C by diluting 2.84 g of a palladium nitrate solution Pd(NO3)2 containing 8.5 wt% palladium with approximately 45 mL of demineralized water, followed by the addition of approximately 10 mL of a sodium hydroxide solution to achieve a pH of 2.4. This solution is then impregnated onto a titanium dioxide (Aldrich P25) support in powder form. The resulting catalyst precursor is dried under air at 100 °C for 12 hours, then calcined for 2 hours at 500 °C with a ramp of 5 °C / min under 11 h / g of air. A catalyst precursor D' is obtained.

[0145] The catalyst precursor D' is dry-impregnated with a solution containing the Ni precursor (Ni(NO3)2.6H2O) and tartaric acid. The aqueous Ni solution is prepared by dissolving 58 g of nickel nitrate (NiNO3, supplier Strem Chemicals®) and 14.35 g of tartaric acid (CAS 87-69-4; supplier Fluka®) in 42 mL of distilled water. The molar ratio of additive to Ni is set at 0.4. The solution is heated to 60°C to facilitate the dissolution of the nickel nitrate and is impregnated onto the catalyst precursor D'. The resulting catalyst precursor is dried under air at 100°C for 12 hours, then calcined for 2 hours at 500°C with a ramp of 5°C / min under 11h / g of air. Catalyst D is obtained.

[0146] The Pd content analyzed by X-ray fluorescence is 1% by weight relative to the total weight of the support.

[0147] The Ni content analyzed by X-ray fluorescence is 5% by weight relative to the total weight of the support.

[0148] The average diameter of the palladium nanoparticles determined by Transmission Microscopy (TEM) on 250 measured nanoparticles is 2.5 nm.

[0149] The sizes of the nickel particles exhibit a double distribution, a first population with an average diameter of 4 nm and a second population with an average number diameter of 8 nm.

[0150] Example 5: Synthesis of Cu-SSZ-13 zeolitic sample (CHA structural type)

[0151] 27.21 g of an aqueous solution of N,N,N-trimethyl-l- Adamantammonium (TMAdA, 20.11 wt%, SACHEM) was mixed with 24.43 g of deionized water. 1.35 g of sodium hydroxide (solid, 98 wt% purity, Aldrich) was added to the mixture, and the resulting preparation was stirred for 10 minutes. Subsequently, 1.09 g of boehmite (Pural SB3, 74.20% Al2O3, Condea) was incorporated, and the synthesis gel was stirred for 15 minutes. Finally, 25.93 g of colloidal silica (Ludox AS40, 40 wt% SiO2, Aldrich) was incorporated into the synthesis mixture, which was stirred at room temperature (350 rpm) for half an hour. The molar composition of the precursor gel is as follows: 60 SiO2: 2.75 Al2O3: 9.0 TMAda: 6.0 Na2O: 1201.0 H2O, i.e. a SiO2 / Al2O3 ratio of 21.8. The precursor gel is then transferred, after homogenization, into a 160 mL stainless steel reactor equipped with a four-bladed agitation system.The reactor is closed and then heated for 120 hours at a rate of 3°C / min up to 160°C, with stirring at 200 rpm, to allow the 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 includes a temperature increase of 1.5°C / min. The temperature is raised to 200°C, held at 200°C for 2 hours, then increased by 1°C / min to 550°C, held at 550°C for 8 hours, and finally returned to room temperature. The resulting material is named SSZ-13.

[0152] 5.0 g of the SSZ-13 material were exchanged 3 times with a 3M aqueous solution of NH4NO3 was heated at 80°C for 1 hour under stirring (300 rpm) with a volume-to-mass ratio of 10 (V / W). The solid was then dried overnight at 100°C.

[0153] 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 of 1°C / min. The product obtained is SSZ-13 zeolite in protonated form (H-SSZ-13).

[0154] Next, the H-SSZ-13 zeolite is contacted with a [Cu(NH3)4](NO3)2 solution for 1 day under stirring at room temperature. The final solid is separated, washed and dried.

[0155] The solid obtained after contact with the [Cu(NH3)4](NO3)2 solution is calcined under a flow of dry air at 550°C for 8 hours.

[0156] XRD analysis shows that the product obtained is an SSZ-13 zeolite of structural type CHA. Chemical analysis by X-ray fluorescence (XRF) gives a Cu content of 2.8 wt%. Catalyst E is obtained. Example 6: Catalytic Tests

[0157] For catalytic tests, 200 mg of catalysts A, B, C and D in powder form are placed in a quartz reactor.

[0158] To evaluate the association of catalyst D followed by catalyst E, a test is carried out with catalysts D and E arranged in successive layers, 200mg of catalyst D in powder form being placed on 200mg of catalyst E. This association is called catalyst D+E.

[0159] The reactor is supplied with 150 L / h of a gas mixture having the following molar compositions: 200 ppm NO, 6600 ppm H2, 10% O2, qpc N2 (qpc = quantity to compensate).

[0160] A Fourier transform infrared spectroscopy (FTIR) analyzer allows the concentration of NO, NO2, NH3, and N2O species to be measured at the reactor outlet. NOx conversions are calculated as follows:

[0161] [Math.l] NOx conversion = (NOx - NOx / NOx input

[0162] In these formulas, the input and output indices respectively indicate the content before and after catalytic reduction.

[0163] The NOx conversion results are shown in [Fig. 1]. The curves marked by circles, squares, diamonds, crosses and triangles correspond respectively to the tests carried out with catalysts A, B, C, D and D+E synthesized according to example 1, example 2, example 3, example 4 and the combination of example 4 and example 5.

[0164] It is observed that catalyst D according to the invention has a lower activation temperature than catalysts A, B, and C. Catalyst D according to the invention also offers higher NOx conversion efficiency than catalysts A, B, and C across the entire temperature range. Catalyst C exhibits virtually no NOx conversion. The compliant combination of catalysts D and E has an activation temperature equivalent to catalyst D alone, but significantly higher NOx conversion at temperatures above 170°C thanks to the use of ammonia produced by catalyst D.

[0165] A summary of the performance of the catalysts is given in the following Table 1:

[0166] [Table 1] Ignition Temperature Conversion Selectivity Catalyst T (°C) at 30% NOx Conversion Conversion (%) at 160°C Conversion (%) at 300°C Maximum NH3 Concentration (ppm) Catalyst A 126 74 21 111 Catalyst B 131 76 32 163 Catalyst C - 0 3 0 Catalyst D 101 92 48 140 Catalyst D+E 111 92 73 7

[0167] NH3 emissions are shown in [Fig. 2]. The curves marked by circles, crosses, squares, diamonds, and triangles correspond respectively to the tests carried out with catalysts A, B, C, D, and D+E synthesized according to Example 1, Example 2, Example 3, Example 4, and the combination of Example 4 and Example 5. Catalyst D according to the invention produces higher quantities of NH3 compared to catalyst A and close to catalyst B. Catalyst D+E exhibits low quantities of NH3, the emissions from catalyst D being used to increase the NOx conversion efficiency with catalyst E.

Claims

Demands

1. Catalyst comprising an active phase comprising palladium and nickel, and a support comprising at least titanium dioxide, the palladium content being between 0.001 and 8% by weight of element palladium relative to the total weight of the catalyst, the nickel content being between 1 and 20% by weight of element nickel relative to the total weight of the catalyst, characterized in that: - the number average diameter of the palladium particles is between 0.5 and 5 nm; and - the nickel particles are distributed in two distinct populations: a first population of particles whose number average diameter is between 2.5 and 6 nm, and a second population of particles whose number average diameter is between 7 and 12 nm.

2. Catalyst according to claim 1, characterized in that the molar ratio between palladium and nickel is between 0.001 and 5 mol / mol.

3. Catalyst according to any one of claims 1 or 2, 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.

4. Catalyst according to any one of the preceding claims, characterized in that the palladium content is 0.005 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 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.

6. A method for preparing a catalyst according to any one of the preceding claims, comprising at least the following steps: a) the support is contacted with at least one solution containing at least one nickel precursor and at least one organic compound comprising at least one carboxylic acid function; b) the support is contacted with at least one solution containing at least one palladium precursor by colloidal means; steps a) and b) being carried out in any order; c) the catalyst precursor obtained at the end of the sequence of steps a) and b), or b) and a), 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.

7. A process according to the preceding claim, wherein the nickel precursor and said organic compound are added in step a) of the dry impregnation preparation process.

8. A process according to any one of claims 6 or 7, wherein the palladium precursor is added in step b) of the colloidal impregnation process from an aqueous solution comprising at least one palladium precursor salt and an aqueous solution of alkali hydroxide or alkaline earth hydroxide.

9. A method according to any one of claims 6 to 8, wherein step a) is carried out before step b).

10. A method according to any one of claims 6 to 9, wherein said nickel precursor is selected from nickel nitrate, nickel chloride, nickel acetate or nickel hydroxycarbonate.

11. A method according to any one of claims 6 to 10, wherein the organic compound of step a) is selected from oxalic acid, malonic acid, glutaric acid, glycolic acid, lactic acid, tartronic acid, citric acid, tartaric acid, pyruvic acid, levulinic acid.

12. A method according to any one of claims 6 to 11, wherein the molar ratio between said organic compound introduced in step a) and the nickel element also introduced in step a) is between 0.01 and 5.0 mol / mol.

13. A process according to any one of claims 8 to 12, wherein the palladium precursor salt is selected from the group consisting of palladium chloride, palladium nitrate and palladium sulfate.

14. A catalytic reduction process for nitrogen oxides comprising at least one first reduction substep in the presence of hydrogen (H2) by bringing into contact a gaseous charge comprising nitrogen oxides and a catalyst according to any one of claims 1 to 5 or prepared according to any one of claims 6 to 13, at a temperature between 15°C and 600°C, at a VVH between 10,000 h1 and 150,000 h 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.

16. A process according to any one of claims 14 or 15 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.

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