Low-temperature denox catalyst for industrial flue gases

Abstract

The present invention comprises an active phase comprising manganese (Mn), at least one first group VIII element chosen from iron (Fe), cobalt (Co), and nickel (Ni), said catalyst comprising a porous support comprising at least one refractory oxide chosen from titanium dioxide, silica, alumina, silica-alumina, zirconia and ceria, used pure or as a mixture with one another, particularly intended for the reduction of nitrogen oxides (NOx). Said catalyst comprises between 0.1% and 15% by weight of manganese element and between 0.1% and 20% by weight of group VIII element relative to the total weight of the catalyst such that the molar ratio between the manganese and the group VIII element is between 0.1 and 30 mol / mol. The active phase is characterized in the form of nanoparticles having a size of between 1 nm and 30 nm, measured by transmission electron microscopy.

Description

[0001] LOW TEMPERATURE DeNOx CATALYST FOR INDUSTRIAL FUMES

[0002] Technical field

[0003] The present invention relates to a supported manganese-based multi-metallic catalyst particularly intended for the reduction of nitrogen oxides (NOx), preferably in the presence of a reducing agent.

[0004] State of the art

[0005] Emissions from fossil fuel combustion and biomass burning have environmental and health consequences at local, regional, and global levels. Nitrogen oxides (NOx=NO+NO2), mainly emitted by power plants, factories, and automobiles, are considered the main source of atmospheric pollution, significantly influencing the global environment. Tropospheric chemistry has become the main cause of greenhouse effects and acid rain. To address the serious damage caused by NOx, governments around the world have adopted increasingly stringent legislation and policies to control NOx emissions.

[0006] The ever-increasing demand for improved air quality has created a strong momentum to control NOx emissions from stationary sources and automobiles.

[0007] Several denitrification (DeNOx) technologies, including selective catalytic reduction (SCR), selective non-catalytic reduction (SNCR), and non-selective catalytic reduction (NSCR), are available for NOx reduction. Currently, the SCR process using ammonia NH3 as the reducing agent has been commercially applied in stationary source combustion units, which exhibit higher NOx removal efficiencies than SNCR or combustion controls. In the United States alone, more than 1,000 SCR systems have been implemented to reduce NOx from industrial boilers, process heaters, steel mills, and chemical plants.

[0008] For mobile sources, SCR systems are increasingly used in diesel vehicles because three-way catalysts (which convert three pollutants: hydrocarbons (HC), carbon monoxide (CO), and nitrogen oxides (NOx)) are not suitable for NOx reduction in lean-burn engines. Catalysts are therefore at the heart of SCR technologies to efficiently and selectively convert NOx to N2. V2Os-WO3(MoO3) / TiO2 catalysts have been used commercially in thermal power plants due to their high NOx removal efficiency at a temperature between 300 and 400°C. However, traditional vanadium (V)-based catalysts are gradually deactivated by the poisoning of alkali / alkaline earth metals, phosphorus, and heavy metals in the flue gas.Furthermore, traditional vanadium (V) catalysts are not applicable in steel, cement and glass plants due to low temperature flue gases (<250°C) and are also not suitable for diesel engine due to the requirement of a wider temperature window (150-500°C). Indeed, for steady-state diesel operation, the exhaust gas temperature is in the range of 180 - 280°C, but it can reach 440°C when the engine is running at high speed.

[0009] The increasing requirements for wide operating temperature window, high resistance to SO2 / alkali / heavy metals and high hydrothermal stability have stimulated the development of new types of NH3-SCR catalyst. Another challenge is to carry out the Nox reduction reaction (DeNOx) at a temperature below 150°C in order to drastically reduce operating costs by avoiding the need to heat the off-gas.

[0010] Among the vanadium (V)-free metal oxide catalysts, many articles and patent documents use certain transition metals such as the noble metals Pt, or Pd but also Mn, Ce, Cu, Fe, Ag, Rh and Co (cf. B. Tu et al. (ACS Sustainable Chem. Eng. 2017, 5, 5200)). G. Xu et al. (Applied Catalysis B: Environmental 2019, 244, 909) have carried out work on the development of Pt / AhCh catalysts but these solids operate at high temperatures (300-400°C).

[0011] Recently, a number of studies have shown interest in manganese oxide-based solids (see Y. Qi et al., Water, Air, & Soil Pollution 2020, 231, 289) which have shown good performance for low-temperature NH3-SCR application. Furthermore, the NH3-SCR performance of manganese-containing catalysts is improved by the addition of other metals, or additives such as cerium (see Q. Yan et al., Applied Catalysis B: Environmental 2019, 255, 117749). The article by Zhang, et al. (Chemical Engineering Journal 2018, 348, 618) also shows that the performance of all these catalysts can also be improved by changing the support. The catalyst support not only contains interesting intrinsic properties (and adjusts acidity and alkalinity), but it induces appropriate particle shape and size. In 2016, W.Li et al.(Fuel Processing Technology 154) have shown that the deposition of manganese (Mn) on a TiC>2 support allows the complete elimination of NOx at 150°C. Two other types of catalysts such as MnCo-LDO solids (LDO for layered double oxides) and MnFe-LDO are interesting candidates as low-temperature NH3-SCR catalysts. Indeed, layered double oxide catalysts (clay family) not only have a unique two-dimensional structure but also have large specific surfaces with large amounts of active sites. The most used procedure for the synthesis of LDOs is the simultaneous coprecipitation of two or more metals from the corresponding inorganic salts in an alkaline medium with a pH of about 10.

[0012] This preparation is based on a laboratory-type operating mode that cannot be extrapolated to an industrial scale, particularly due to the numerous preparation steps, double precipitation in the sol-gel process, a process that is very difficult to manage on an industrial scale. Furthermore, in order to obtain an LDO-type structure, 30% by weight of manganese, 30% by weight of cobalt and 30% by weight of nickel are used, which leads to a solid that has a completely prohibitive cost outside of a laboratory scale.

[0013] Subject of the invention

[0014] In order to solve the problems associated with prior art products and methods in the field of ammonia selective catalytic reduction (NH3-SCR) catalysts for the reduction of nitrogen oxides (NOx), the methods and products of the present invention have been developed.

[0015] Surprisingly, the Applicant has discovered that a bi- or tri-metallic catalyst comprising an active phase comprising manganese, and at least one element (e.g. one or two elements) from group VIII chosen from iron (Fe), cobalt (Co), nickel (Ni) and a porous support comprising a refractory oxide, in particular titanium dioxide, prepared by impregnation of said porous support with one or more solutions of metallic precursors according to defined molar ratios and / or a very specific protocol makes it possible to obtain performances at least as good, or even better, in terms of activity and selectivity in the context of DeNox reactions in a wide temperature range and at low temperature while using a quantity of metallic phase lower than that used in the catalysts of the prior art allowing a lower manufacturing cost (low metal content).The selectivity appears to be provided by the modification of the electronic state of manganese provided by the addition of at least one second metal from group VIII which is in proximity at the atomic level to the manganese (Mn) atoms. A first subject according to the invention relates to a catalyst comprising an active phase comprising manganese (Mn), at least one first element from group VIII chosen from iron (Fe), cobalt (Co), and nickel (Ni), said catalyst comprising a porous support comprising at least one refractory oxide chosen from titanium dioxide, silica, alumina, silica-alumina, zirconia, ceria, used pure or as a mixture between them, said catalyst being characterized in that:.

[0016] - the manganese content is between 0.1% and 15% by weight of manganese element relative to the total weight of the catalyst;

[0017] - the content of said first element of group VIII is between 0.1% and 20% by weight of element of group VIII relative to the total weight of the catalyst;

[0018] - the molar ratio between manganese and said first element of group VIII is between 0.1 mol / mol and 30 mol / mol;

[0019] - the active phase is in the form of nanoparticles comprising manganese and at least said first element of group VIII chosen from iron (Fe), cobalt (Co), and nickel (Ni), said size of the nanoparticles being between 1 nm and 30 nm, measured by transmission electron microscopy.

[0020] Preferably, the active phase is bimetallic, the metals being chosen from Mn-Fe, Mn-Co, Mn-Ni.

[0021] Preferably, the active phase comprises a second element of group VIII chosen from iron (Fe), cobalt (Co), and nickel (Ni), different from said first element of group VIII.

[0022] Preferably, the active phase is in the form of nanoparticles comprising manganese, and at least said first element of group VIII and said second element of group VIII, said size of the nanoparticles being between 1 nm and 30 nm, measured by transmission electron microscopy.

[0023] Preferably, the content of said second element of group VIII is between 0.1% and 20% by weight of element of group VIII relative to the total weight of the catalyst.

[0024] Preferably, the molar ratio between manganese and said second element of group VIII is between 0.1 mol / mol and 30 mol / mol.

[0025] Preferably, the active phase is trimetallic, the metals being chosen from Mn-Co-Fe, Mn-Ni-Fe, Mn-Ni-Co.

[0026] Preferably, said porous support comprises at least titanium dioxide. Preferably, said porous support comprises a specific surface area of ​​between 10 m 2 / g and 300 m 2 / g.

[0027] Preferably, said porous support is in the form of powder or in the form of grains in the form of extrudates or balls.

[0028] A second subject matter according to the invention relates to a method for preparing a catalyst according to the invention comprising the following steps: a) a porous support is provided comprising at least one refractory oxide chosen from titanium dioxide, silica, alumina, silica-alumina, zirconia, ceria, used pure or as a mixture with each other; b) the following sub-steps are carried out to obtain a catalyst precursor: b1) the porous support is brought into contact with at least one solution containing at least one manganese precursor; b2) the porous support is brought into contact with at least one solution containing at least one precursor of the first element of group VIII chosen from iron (Fe), cobalt (Co), and nickel (Ni); sub-steps b1) and b2) being carried out separately in any order, or simultaneously;c) drying said catalyst precursor obtained at the end of step b) at a temperature below 250°C to obtain a dried catalyst precursor; d) calcining the dried catalyst precursor obtained in step c) at a temperature between 250°C and 900°C to obtain said catalyst.;

[0029] Preferably, step b) comprises a sub-step b3) in which said porous support is brought into contact with at least one solution containing at least one precursor of the second element of group VIII chosen from iron (Fe), cobalt (Co), and nickel (Ni) different from said first element of group VIII, said sub-step b3) being carried out either separately from sub-steps b1) and / or b2), in any order, or simultaneously.

[0030] Preferably, when said first element of group VIII is cobalt, sub-steps b1) and b2) are carried out separately in any order.

[0031] Preferably, when said second element of group VIII is cobalt, sub-step b3) is carried out separately from sub-steps b1) and / or b2). A third subject according to the invention relates to the use of the catalyst for the catalytic reduction of nitrogen oxides (NO X ).

[0032] A fourth subject matter according to the invention relates to a process for the catalytic reduction of nitrogen oxides (NOx), using the catalyst according to the invention or prepared according to the invention, the process comprising bringing the catalyst into contact with a nitrogen oxide.

[0033] Detailed description of the invention

[0034] 1. Definitions

[0035] The term "NOx" refers to nitrogen oxides (NOx=NO+NO2), x refers to the number of oxygens present in the molecule, x can take the value 1 for NO and 2 for NO2.

[0036] In the following, 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 of columns 8, 9 and 10 according to the new IUPAC classification.

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

[0038] The BET specific surface area is measured by nitrogen physisorption according to ASTM D3663-03, a method described in the book Rouquerol F.; Rouquerol J.; Singh K. “Adsorption by Powders & Porous Solids: Principle, methodology and applications”, Academic Press, 1999.

[0039] "Nanoparticle size" means the average size of one or more metallic nanoparticles (present as clusters or agglomerates of nanoparticles) that can be distinguished and measured by transmission electron microscopy (TEM).

[0040] Analysis of the composition of nanoparticles is possible via EDS (Energy Dispersion Spectroscopy) analysis, when observing samples in TEM.

[0041] The content of manganese, iron, nickel and cobalt metals is measured by X-ray fluorescence and is given as a percentage by weight relative to the total mass of the catalyst. Gas Hourly Space Velocity (GHSV) is the volume flow rate of the gaseous feedstock entering the reactor in m 3 / h divided by the catalyst volume in m 3 contained in the reactor.

[0042] In this application, values ​​in ppm are values ​​in ppm by weight (unless otherwise defined).

[0043] 2. Catalyst

[0044] The catalyst comprises an active phase comprising manganese (Mn), at least one first element of group VIII chosen from iron (Fe), cobalt (Co), and nickel (Ni) and a porous support comprising a refractory oxide chosen from titanium dioxide, silica, alumina, silica-alumina, zirconia, ceria, used pure or as a mixture between them, said catalyst being characterized in that:

[0045] - the manganese content is between 0.1% and 15% by weight of manganese element relative to the total weight of the catalyst;

[0046] - the content of said first element of group VIII is between 0.1% and 20% by weight of element of group VIII relative to the total weight of the catalyst;

[0047] - the molar ratio between manganese and said first element of group VIII is between 0.1 mol / mol and 30 mol / mol;

[0048] - the active phase is in the form of nanoparticles comprising manganese and at least one first element from group VIII chosen from iron (Fe), cobalt (Co), and nickel (Ni), said size of the nanoparticles being between 1 nm and 30 nm, measured by transmission electron microscopy.

[0049] The manganese content in said catalyst according to the invention is advantageously between 0.1% and 15% by weight relative to the total weight of the catalyst, preferably between 0.5% and 15% by weight, more preferably between 2% and 12% by weight.

[0050] The content of said first element of group VIII is advantageously between 0.1% and 20% by weight of element of group VIII relative to the total weight of the catalyst, preferably between 0.5% and 15% by weight, more preferably between 1% and 12% by weight.

[0051] The molar ratio between manganese and said first element of group VIII is between 0.1 mol / mol and 30 mol / mol, preferably between 0.2 mol / mol and 20 mol / mol, more preferably between 0.3 mol / mol and 15 mol / mol. According to a preferred embodiment of the present invention, the active phase is bimetallic, the metals being chosen from Mn-Fe, Mn-Co, and Mn-Ni, preferably Mn-Fe and Mn-Ni, and more preferably Mn-Fe.

[0052] According to a preferred embodiment of the present invention, the active phase comprises a second element of group VIII chosen from iron (Fe), cobalt (Co), and nickel (Ni), different from said first element of group VIII. The active phase is said to be trimetallic, the metals being chosen from Mn-Co-Fe, Mn-Ni-Fe, and Mn-Ni-Co, preferably Mn-Ni-Co and Mn-Fer-Co, and more preferably Mn-Ni-Co.

[0053] The content of said second element of group VIII is advantageously between 0.1% and 20% by weight of element of group VIII relative to the total weight of the catalyst, preferably between 1% and 15% by weight, and more preferably between 2% and 14% by weight.

[0054] According to one or more embodiments, when the catalyst is trimetallic, the molar ratio between manganese and said first element of group VIII is between 0.1 mol / mol and 30 mol / mol, preferably between 0.2 mol / mol and 20 mol / mol, more preferably between 0.3 mol / mol and 15 mol / mol and the molar ratio between manganese and said second element of group VIII is between 0.1 mol / mol and 30 mol / mol, preferably between 0.2 mol / mol and 20 mol / mol, more preferably between 0.3 mol / mol and 15 mol / mol.

[0055] The active phase is in the form of isolated nanoparticles or clusters of nanoparticles comprising all the metals present as the active phase. When the catalyst is bimetallic, said nanoparticles comprise at least manganese, and said first element of group VIII chosen from iron (Fe), cobalt (Co), and nickel (Ni). When the catalyst is trimetallic, said nanoparticles comprise at least manganese, said first element of group VIII chosen from iron (Fe), cobalt (Co), and nickel (Ni) and said second element of group VIII chosen from iron (Fe), cobalt (Co), and nickel (Ni) different from the first element of group VIII. The contents obtained on the final catalyst are analyzed on the final catalyst by X-ray fluorescence. The multi-metallic character (egbi or trimetallic) within all the nanoparticles observed by transmission electron microscopy (TEM) is confirmed by EDS (Energy Dispersion Spectroscopy according to the Anglo-Saxon terminology).

[0056] Said nanoparticles have a size between 1 nm and 30 nm, measured by transmission electron microscopy, preferably between 2 and 30 nm, and even more preferably between 3 and 30 nm. Preferably, the support comprises at least titanium dioxide (TiCh), a support known to be more resistant to sulfur poisoning due to the stability of the sulfates on the surface. Thus the support protects the active phase.

[0057] Optionally, the porous support comprising at least titanium dioxide (TiCh) can be sulfated according to techniques known to those skilled in the art in order to improve its resistance to sulfur.

[0058] Preferably, the TiC>2 is in its anatase and rutile forms, the rutile:anatase mass ratio preferably being between 95:5 and 50:50.

[0059] The specific surface area of ​​the porous support is generally between 10 m 2 / g and 300 m 2 / g, preferably between 10 m 2 / g and 150 m 2 / g, more preferably between 30 m 2 / g and 120 m 2 / g.

[0060] The pore 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.

[0061] According to one or more embodiments, the porous support is in the form of powder with a particle size between 20 μm and 500 μm. According to one or more embodiments, the porous support is in the form of grain shaped into extrudates or balls with a diameter between 0.5 mm and 10 mm. The term “diameter” of the extrudates is understood to mean the diameter of the circle circumscribed to the cross-section of these extrudates.

[0062] 4. Method of

[0063] A second subject matter according to the invention relates to a method for preparing the catalyst according to the invention comprising the following steps: a) a porous support is provided comprising a refractory oxide chosen from titanium dioxide, silica, alumina, silica-alumina, zirconia, ceria used pure or as a mixture with each other; b) the following sub-steps are carried out to obtain a catalyst precursor: b1) the porous support is brought into contact with at least one solution containing at least one manganese precursor; b2) the porous support is brought into contact with at least one solution containing at least one precursor of the first element of group VIII chosen from iron (Fe), cobalt (Co), and nickel (Ni); sub-steps b1) and b2) being carried out separately in any order, or simultaneously, c) said catalyst precursor obtained at the end of step b) is dried at a temperature below 250°C to obtain a dried catalyst precursor;d) calcining the dried catalyst precursor obtained at the end of step c) at a temperature between 250°C and 900°C;

[0064] Intermediate steps may be interspersed (including additional drying and maturation steps) and some steps may be carried out several times in a row.

[0065] Said sub-step b1) can be carried out by impregnation, dry or in excess, according to methods well known to those skilled in the art. The pH of said solution can be modified by the possible addition of an acid or a base.

[0066] Preferably, said sub-step b1) is carried out by dry impregnation, which consists of bringing the porous support into contact with at least one solution preferably containing at least one manganese precursor, the volume of the solution of which is between 0.25 times and 1.5 times the pore volume of the support to be impregnated.

[0067] According to one or more embodiments, the manganese precursor salt is selected from organic manganese precursors such as manganese acetate, manganese oxalate, manganese citrate, and inorganic manganese precursors, such as manganese nitrate, manganese carbonates, manganese sulfates. Preferably, the manganese precursor salt is manganese nitrate.

[0068] The pore volume of the support and the manganese concentration are adjusted according to the type of impregnation (dry or excess impregnation) so as to obtain for the supported catalyst, a manganese content of between 0.1% and 15% by weight of manganese element relative to the total weight of the catalyst, preferably between 0.5% and 15% by weight, more preferably between 2% and 12% by weight.

[0069] Said sub-step b2) can be carried out by impregnation, dry or in excess, according to methods well known to those skilled in the art. The pH of said solution can be modified by the optional addition of an acid or a base. Preferably, said sub-step b2) is carried out by dry impregnation, which consists of bringing the porous support into contact with at least one solution, containing, preferably consisting of, at least one precursor of a first element of group VIII chosen from iron (Fe), cobalt (Co), and nickel (Ni), the volume of the solution of which is between 0.25 times and 1.5 times the pore volume of the support to be impregnated.

[0070] According to one or more embodiments, the pore volume of the support and the concentration in solution of the first element of group VIII chosen from iron (Fe), cobalt (Co), and nickel (Ni), are adjusted according to the impregnation type (dry or excess impregnation) so as to obtain for the supported catalyst a content of the first element of group VIII, chosen from iron (Fe), cobalt (Co), and nickel (Ni) of between 0.1% and 20% relative to the total weight of the catalyst, preferably between 0.5% and 15% by weight, more preferably between 1% and 12% by weight.

[0071] Likewise, the concentration of the first element of group VIII, chosen from iron (Fe), cobalt (Co), and nickel (Ni) in solution is supplied so that the atomic ratio between manganese and the first element of group VIII, chosen from iron (Fe), cobalt (Co), and nickel (Ni) is between 0.1 mol / mol and 30 mol / mol, preferably between 0.2 mol / mol and 20 mol / mol, more preferably between 0.3 mol / mol and 15 mol / mol.

[0072] According to one or more embodiments, when sub-steps b1) and b2) are carried out separately, in any order, an intermediate maturation and then drying step is carried out between sub-steps b1) and b2), or between sub-steps b2) and b1), in which the catalyst precursor obtained at the end of sub-step b1), or of sub-step b2), is dried at a temperature below 250°C, preferably between 70°C and 200°C.

[0073] Drying time is generally between 0.5 hours and 20 hours. Longer times are not excluded, but do not necessarily bring an improvement.

[0074] When the first element of group VIII is cobalt, step b2) is preferably carried out separately in any order.

[0075] According to one or more embodiments, step b) further comprises a sub-step b3) in which said porous support is brought into contact with at least one solution containing at least one precursor of the second element of group VIII chosen from iron (Fe), cobalt (Co), and nickel (Ni) different from said first element of group VIII. Said step b3) can be carried out by impregnation, dry or in excess, according to methods well known to those skilled in the art. The pH of said solution can be modified by the optional addition of an acid or a base. Preferably, said sub-step b3) is carried out by dry impregnation, which consists of bringing the porous support into contact with at least one solution, containing, preferably consisting of, at least one precursor of a first element of group VIII chosen from iron (Fe), cobalt (Co), and nickel (Ni), the volume of the solution of which is between 0.25 times and 1.5 times the pore volume of the support to be impregnated.

[0076] The pore volume of the support and the concentration in solution of the second element of group VIII chosen from iron (Fe), cobalt (Co), and nickel (Ni), are adjusted according to the type of impregnation (dry or excess impregnation) so as to obtain for the supported catalyst, a content of second element of group VIII, chosen from iron (Fe), cobalt (Co), and nickel (Ni), different from the first element, of between 0.1% and 20% by weight relative to the total weight of the catalyst, preferably between 0.5% and 15% by weight, more preferably between 1% and 12% by weight.

[0077] Similarly, the concentration of element of group VIII, chosen from iron (Fe), cobalt (Co), and nickel (Ni) in solution is supplied so that the atomic ratio between manganese and the second element of group VIII, chosen from iron (Fe), cobalt (Co), and nickel (Ni) (different from the first element) is between 0.1 mol / mol and 30 mol / mol, preferably between 0.2 mol / mol and 20 mol / mol, more preferably between 0.3 mol / mol and 15 mol / mol.

[0078] Said sub-step b3) being carried out either separately from sub-steps b1) and / or b2), in any order, or simultaneously. For example, sub-step b3) can be carried out alone, or simultaneously with sub-step b1) and / or sub-step b2), or simultaneously with steps b1) and b2).

[0079] According to one or more embodiments, when sub-step b3) is carried out separately in any order from steps b1) and b2), an intermediate maturation then drying step is carried out between the sub-steps carried out separately, in which the catalyst precursor (obtained at the end of the previous sub-step) is dried at a temperature below 250°C, preferably between 70°C and 200°C. The maturation time is generally between 0.5 and 5 hours. Longer times are not excluded, but do not necessarily provide an improvement.

[0080] Drying time is generally between 0.5 hours and 20 hours. Longer times are not excluded, but do not necessarily bring an improvement.

[0081] When the first element of group VIII is cobalt, sub-step b3) is preferably carried out separately in any order. According to one or more embodiments, the iron precursor is chosen in the form of nitrate, carbonate, chloride, sulfate, hydroxide, hydroxycarbonate, formate, acetate, oxalate, complexes formed with acetylacetonates, or tetrammine or hexammine complexes, or any other inorganic derivative soluble in aqueous solution, which is brought into contact with said support. Preferably, iron nitrate, iron chloride, iron hydroxide are used as iron precursor. Very preferably, the iron precursor is iron nitrate, iron sulfate or iron hydroxide.

[0082] According to one or more embodiments, the cobalt precursor is chosen in the form of nitrate, carbonate, chloride, sulfate, hydroxide, hydroxycarbonate, formate, acetate, oxalate, complexes formed with acetylacetonates, or tetrammine or hexammine complexes, or any other inorganic derivative soluble in aqueous solution, which is brought into contact with said support. Preferably, cobalt nitrate, cobalt carbonate, cobalt chloride, cobalt hydroxide, cobalt hydroxycarbonate are used as cobalt precursor. Very preferably, the cobalt precursor is cobalt nitrate, cobalt carbonate or cobalt hydroxide.

[0083] According to one or more embodiments, the nickel precursor is chosen in the form of nitrate, carbonate, chloride, sulfate, hydroxide, hydroxycarbonate, formate, acetate, oxalate, complexes formed with acetylacetonates, or tetrammine or hexammine complexes, or any other inorganic derivative soluble in aqueous solution, which is brought into contact with said support. Preferably, nickel nitrate, nickel carbonate, nickel chloride, nickel hydroxide, nickel hydroxycarbonate are used as nickel precursor. Very preferably, the nickel precursor is nickel nitrate, nickel carbonate or nickel hydroxide. get a dried

[0084] The catalyst precursor obtained from step b) is dried 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 times are not excluded, but do not necessarily provide an improvement.

[0085] The drying is generally carried out under combustion air of a hydrocarbon, preferably methane, or under heated air comprising between 0 grams and 80 grams of water per kilogram of combustion air, an oxygen level of between 5% and 25% volume and a carbon dioxide level of between 0% and 10% volume. Optionally, the catalyst precursor obtained at the end of the intermediate drying step is subjected to a heat treatment under air, preferably combustion air, and more preferably methane combustion air, comprising between 40 grams and 80 grams of water per kg of air, an oxygen level of between 5% and 15% volume and a CO2 level of between 4% and 10% volume. dried to obtain the said

[0086] The dried catalyst precursor obtained at the end of step c) is then calcined. The calcination temperature is generally between 250°C and 900°C, preferably between 300°C and approximately 500°C. The calcination time is generally between 0.5 hours and 5 hours. The hourly volumetric velocity (WH) is generally between 150 h' 1 and 3000 h' 1 , preferably between 300 h' 1 and 1500 h' 1 .

[0087] At the end of steps a) to d), the catalyst according to the invention is obtained. The formulation and the preparation process according to the present invention lead to an active phase in the form of nanoparticles comprising at least manganese, a first element of group VIII chosen from iron (Fe), cobalt (Co), and nickel (Ni) and optionally a second element of group VIII chosen from iron (Fe), cobalt (Co), and nickel (Ni) when the catalyst is trimetallic. Said nanoparticles or clusters of nanoparticles have a size of between 1 nm and 30 nm, measured by transmission electron microscopy.

[0088] 5. Use of the

[0089] A third object according to the invention relates to the use of the catalyst as a selective catalytic reduction (SCR) system in a process for reducing NOx in exhaust gases.

[0090] The process for the catalytic reduction of nitrogen oxides (NOx), using the catalyst according to the invention or prepared according to the invention, comprises a step of bringing the catalyst into contact with a nitrogen oxide, preferably at a temperature between 30°C and 600°C, preferably between 40°C and 500°C, and more preferably between 50°C and 400°C. The WH (GHSV) involved are preferably between 6000 h' 1 and 240,000 h' 1 .

[0091] The quantity of catalyst is adjusted by the person skilled in the art according to the quantity of NOx present in the gas to be treated.

[0092] According to one or more embodiments, the gases to be treated by said catalyst comprise NOx between 200 ppm and 3000 ppm by weight of oxygen O2 between 2% and 8% by weight, CO between 0 ppm and 500 ppm, H2O between 0 and 10% by weight, a sulfur content in SO2 form of less than 200 ppm, preferably less than 150 ppm by weight.

[0093] An SCR system can be integrated into various systems requiring NOx reduction. Applications include passenger vehicle and truck engine systems, stationary applications (utility boiler, industrial boiler, solid waste boiler), or marine applications.

[0094] Preferably, the catalyst is used in stationary applications.

[0095] The reducing agents that can be used in the NOx reduction method according to the invention are preferably chosen from hydrogen (H2-SCR), a hydrocarbon (HC-SCR) or ammonia (NH3-SCR). Preferably, the catalyst is used with ammonia and / or its derivatives as the reducing agent. In this case, the catalytic system is preferably suitably connected to an ammonia source so that the latter comes into contact with the exhaust gases. The ammonia can be supplied in the form of anhydrous ammonia, aqueous ammonia, urea, ammonium carbonate, ammonium formate or ammonium carbamate.

[0096] In one or more embodiments, the catalyst may be applied, deposited on an inert substrate in the form of a metal plate or foam, or a honeycomb. In one or more embodiments, the catalyst may be combined with other solids such as fillers and binders to provide an extrudable paste that may be formed into a porous structure such as a honeycomb.

[0097] Examples of an aqueous solution S1 of precursor of Mn and Ni

[0098] The aqueous solution S1 used for the preparation of catalysts A and C is prepared by dissolving 2.28 g of manganese nitrate (Mn(NC>3)3-6H2O, supplier Strem Chemicals®) and 1.1 g of nickel nitrate (Ni(NC>3),6H2O, supplier Strem Chemicals®) in a volume of 6 mL of distilled water. of an aqueous solution S2 of precursor of Mn and Fe

[0099] The aqueous solution S2 used for the preparation of catalyst B is prepared by dissolving 3.7 g of manganese nitrate (Mn(NC>3)3-6H2O, supplier Strem Chemicals®) and 5.90 g of iron nitrate (Fe(NC>3)3,9H2O, supplier Strem Chemicals®) in a volume of 6 mL of distilled water. of Co

[0100] The aqueous solution S3 used for the preparation of catalyst C (second impregnation sub-step b3) is prepared by dissolving 1.9 g of cobalt nitrate (CoNO3,6H2O, supplier Strem Chemicals®) in a volume of 5 mL of distilled water.

[0101] In Examples 2 to 4, the support used for the preparation of catalysts A to C is the powder support TiO2(TiO2-NP, P25) (CAS No. 13463-67-7) supplied by Aldrich. This support is composed of 80% by weight of rutile and 20% by weight of anatase relative to the total weight of the support and comprises a SBET specific surface area of ​​55 m 2 / g and a pore volume of 0.5 ml / g.

[0102] Example 2: Preparation of catalyst A

[0103] In this example, steps b1) of manganese impregnation and b2) of impregnation of the first element of group VIII are carried out simultaneously. In fact, a single solution S1 containing a mixture of manganese nitrate and nickel nitrate is impregnated onto the support.

[0104] 5 ml of solution S1 prepared according to example 1a is added dropwise to 10 g of support.

[0105] The impregnated support obtained is statically matured in a saturator for 1 hour and then dried at 120°C for 16 hours.

[0106] The dried catalyst precursor is then calcined in a tube furnace at 400°C for 2 h with a ramp of 5°C / min under 1 L / h / g of air.

[0107] A catalyst A is obtained comprising a Mn content of 5% by weight and a Ni content of 2.14% by weight relative to the total weight of catalyst A, measured by X-ray fluorescence. The molar ratio of Mn to Ni is 0.4 mol / mol.

[0108] The size of the nanoparticles measured by transmission electron microscopy is centered on 15 nm. EDS (Energy Dispersion Spectroscopy) analysis shows that all the particles are bimetallic and include both Mn and Ni. Example 3: preparation of catalyst B

[0109] In this example, steps b1) of manganese impregnation and b2) of impregnation of the first element of group VIII are carried out simultaneously. In fact, a single solution S2 containing a mixture of manganese nitrate and iron nitrate is impregnated onto the support.

[0110] 5 ml of solution S2 prepared according to example 1b is added dropwise to 10 g of support.

[0111] The impregnated support is statically matured in a saturator for 1 hour then dried in an oven at 120°C for 16 hours.

[0112] The solid is calcined in a tubular furnace at 400°C for 2 hours with a ramp of 5°C / min under 1 L / h / g of air.

[0113] A catalyst B is obtained comprising an Mn content of 8% by weight, the Fe content is 8% by weight relative to the total weight of catalyst B, measured by X-ray fluorescence. The molar ratio of Mn to Iron is 1 mol / mol.

[0114] The size of the nanoparticles measured by transmission electron microscopy is centered on 20 nm. EDS (Energy Dispersion Spectroscopy) analysis shows that all the particles are bimetallic and include both Mn and Iron.

[0115] Example 4: Preparation of catalyst C

[0116] In this example, sub-steps b1) of impregnation of manganese and b2) of impregnation of the first element of group VIII are carried out simultaneously. Indeed, a single solution S1 containing a mixture of manganese nitrate and nickel nitrate is impregnated onto the support. On the other hand, sub-step b3) of impregnation of the second element of group VIII is carried out separately since the solution S3 is introduced separately from steps b1) and b2) after an intermediate maturation and drying step.

[0117] 5 ml of solution S1 prepared according to example 1a is added dropwise to 10 g of support.

[0118] The impregnated support is statically aged in a saturator for 1 hour and then dried in an oven at 120°C for 16 hours. Then, 5 ml of the S3 solution based on cobalt nitrate and prepared according to example 1c is added dropwise onto the impregnated support.

[0119] The mixture obtained is statically matured in a saturator for 1 hour then dried in an oven at 120°C for 16 hours.

[0120] The solid is calcined in a tubular furnace at 400°C for 2 hours with a ramp of 5°C / min under 1 L / h / g of air.

[0121] A catalyst C is obtained comprising a Mn content of 5% by weight, a Ni content of 2.14% by weight and a Co content of 5% by weight relative to the total weight of catalyst C, measured by X-ray fluorescence. The molar ratio of Mn to Ni is 0.4 mol / mol. The molar ratio of Mn to Co is 0.9 mol / mol.

[0122] The average size of the nanoparticles measured by transmission electron microscopy is 20 nm. EDS (Energy Dispersion Spectroscopy) analysis shows that all the nanoparticles are trimetallic and include both Mn, Ni and Co.

[0123] Example 5: Characterization of catalysts

[0124] The characterization of the catalysts is presented in Table 1 below.

[0125] The composition of Mn, Fe, Ni, Co is measured by X-ray fluorescence and given in % by weight relative to the total weight of the catalyst. The molar ratios between elements, expressed in mol / mol, are calculated from these mass compositions.

[0126] Nanoparticle size is measured by transmission electron microscopy (TEM). "Nanoparticle size" refers to the average size of one or more metal nanoparticles (present as clusters or agglomerates of nanoparticles).

[0127] The analysis of the composition of the nanoparticles is carried out via EDS analysis (Energy Dispersion Spectroscopy), during the observation of the samples in TEM. Table

[0128] Example 6: Catalytic Tests

[0129] The catalysts are tested in a catalytic reactor. The gas to be purified is a mixture of reconstituted gases with 500 ppm by weight NO, 500 ppm by weight NH3 and 5% O2 by weight relative to the mass of gas to be purified, the rest of the mixture being supplemented by a neutral carrier gas, here nitrogen.

[0130] The hourly volumetric velocity (HVV or Gas Hourly Space Velocity GHSV) is 30,600 h -1 In addition to these operating conditions, we chose a temperature increase with a speed of 10°C / min over a temperature range from 30°C to 450°C.

[0131] The analysis of the gaseous effluents at the inlet and outlet of the reactor is carried out by chromatography and UV spectroscopy. The conversion to NO, expressed in %, is calculated as the difference between the mass content of NO in the gaseous stream at the inlet minus the mass content of NO in the gaseous stream at the outlet; divided by the mass content of NO in the gaseous stream at the inlet.

[0132] The results presented in Table 2 below are the conversion of NO expressed in % at 150°C.

[0133] These results are compared to a commercial reference composed of Titanium, Tungsten and Vanadium on TiO2 from the DNX-series range for SCR DeNOx sold by Umicore. Table 2

[0134] Compared to the reference catalyst, the three catalysts (A to C) according to the invention are more active (higher NO conversion at 150°C). The most active catalyst is the trimetallic catalyst with the Mn-Ni-Co formulation.

Claims

CLAIMS 1. Catalyst comprising an active phase comprising manganese (Mn), at least one first element of group VIII chosen from iron (Fe), cobalt (Co), and nickel (Ni), said catalyst comprising a porous support comprising at least one refractory oxide chosen from titanium dioxide, silica, alumina, silica-alumina, zirconia, ceria, used pure or as a mixture between them, said catalyst being characterized in that: - the manganese content is between 0.1% and 15% by weight of manganese element relative to the total weight of the catalyst; - the content of said first element of group VIII is between 0.1% and 20% by weight of element of group VIII relative to the total weight of the catalyst; - the molar ratio between manganese and said first element of group VIII is between 0.1 mol / mol and 30 mol / mol; - the active phase is in the form of nanoparticles comprising manganese and at least said first element of group VIII chosen from iron (Fe), cobalt (Co), and nickel (Ni), said size of the nanoparticles being between 1 nm and 30 nm, measured by transmission electron microscopy.

2. Catalyst according to claim 1, characterized in that the active phase is bimetallic, the metals being chosen from Mn-Fe, Mn-Co, Mn-Ni.

3. Catalyst according to claim 1, characterized in that the active phase comprises a second element of group VIII chosen from iron (Fe), cobalt (Co), and nickel (Ni), different from said first element of group VIII.

4. Catalyst according to claim 3, characterized in that the active phase is in the form of nanoparticles comprising manganese, and at least said first element of group VIII and said second element of group VIII, said size of the nanoparticles being between 1 nm and 30 nm, measured by transmission electron microscopy.

5. Catalyst according to one of claims 3 or 4, characterized in that the content of said second element of group VIII is between 0.1% and 20% by weight of element of group VIII relative to the total weight of the catalyst.

6. Catalyst according to any one of claims 3 to 5, characterized in that the molar ratio between manganese and said second element of group VIII is between 0.1 mol / mol and 30 mol / mol.

7. Catalyst according to any one of claims 3 to 6, characterized in that the active phase is trimetallic, the metals being chosen from Mn-Co-Fe, Mn-Ni-Fe, Mn-Ni-Co.

8. Catalyst according to any one of the preceding claims, characterized in that said porous support comprises at least titanium dioxide.

9. Catalyst according to any one of the preceding claims, characterized in that said porous support comprises a specific surface area of ​​between 10 m 2 / g and 300 m 2 / g.

10. Catalyst according to any one of the preceding claims, characterized in that said porous support is in the form of powder or in the form of grains in the form of extrudates or balls.

11. A process for preparing a catalyst according to any one of claims 1 to 10 comprising the following steps: a) a porous support is provided comprising at least one refractory oxide chosen from titanium dioxide, silica, alumina, silica-alumina, zirconia, ceria, used pure or as a mixture with each other; b) the following sub-steps are carried out to obtain a catalyst precursor: b1) the porous support is brought into contact with at least one solution containing at least one manganese precursor; b2) the porous support is brought into contact with at least one solution containing at least one precursor of the first element of group VIII chosen from iron (Fe), cobalt (Co), and nickel (Ni); sub-steps b1) and b2) being carried out separately in any order, or simultaneously; c) drying said catalyst precursor obtained at the end of step b) at a temperature below 250°C to obtain a dried catalyst precursor;d) calcining the dried catalyst precursor obtained in step c) at a temperature between 250°C and 900°C to obtain said catalyst.; 12. Method according to claim 11, in which step b) comprises a sub-step b3) in which said porous support is brought into contact with at least one solution containing at least one precursor of the second element of group VIII chosen from iron (Fe), cobalt (Co), and nickel (Ni) different from said first element of group VIII, said sub-step b3) being carried out either separately from sub-steps b1) and / or b2), in any order, or simultaneously.

13. Method according to one of claims 11 or 12, in which, when said first element of group VIII is cobalt, sub-steps b1) and b2) are carried out separately in any order.

14. A method according to any one of claims 12 to 13, wherein, when said second group VIII element is cobalt, sub-step b3) is carried out separately from sub-steps b1) and / or b2).

15. Use of the catalyst according to any one of claims 1 to 10 or prepared according to any one of claims 11 to 14 for the catalytic reduction of nitrogen oxides (NO X ).

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