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• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
  • B01J23/00—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00
  • B01J23/38—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of noble metals
  • B01J23/54—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of noble metals combined with metals, oxides or hydroxides provided for in groups B01J23/02 - B01J23/36
  • B01J23/56—Platinum group metals
  • B01J23/58—Platinum group metals with alkali- or alkaline earth metals
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D53/00—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
  • B01D53/34—Chemical or biological purification of waste gases
  • B01D53/92—Chemical or biological purification of waste gases of engine exhaust gases
  • B01D53/94—Chemical or biological purification of waste gases of engine exhaust gases by catalytic processes
  • B01D53/9445—Simultaneously removing carbon monoxide, hydrocarbons or nitrogen oxides making use of three-way catalysts [TWC] or four-way-catalysts [FWC]
  • B01D53/945—Simultaneously removing carbon monoxide, hydrocarbons or nitrogen oxides making use of three-way catalysts [TWC] or four-way-catalysts [FWC] characterised by a specific catalyst
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
  • B01J23/00—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00
  • B01J23/38—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of noble metals
  • B01J23/54—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of noble metals combined with metals, oxides or hydroxides provided for in groups B01J23/02 - B01J23/36
  • B01J23/56—Platinum group metals
  • B01J23/63—Platinum group metals with rare earths or actinides
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
  • B01J23/00—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00
  • B01J23/70—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of the iron group metals or copper
  • B01J23/76—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of the iron group metals or copper combined with metals, oxides or hydroxides provided for in groups B01J23/02 - B01J23/36
  • B01J23/78—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of the iron group metals or copper combined with metals, oxides or hydroxides provided for in groups B01J23/02 - B01J23/36 with alkali- or alkaline earth metals
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
  • B01J23/00—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00
  • B01J23/70—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of the iron group metals or copper
  • B01J23/76—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of the iron group metals or copper combined with metals, oxides or hydroxides provided for in groups B01J23/02 - B01J23/36
  • B01J23/83—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of the iron group metals or copper combined with metals, oxides or hydroxides provided for in groups B01J23/02 - B01J23/36 with rare earths or actinides
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
  • B01J23/00—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00
  • B01J23/70—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of the iron group metals or copper
  • B01J23/89—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of the iron group metals or copper combined with noble metals
  • B01J23/8933—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of the iron group metals or copper combined with noble metals also combined with metals, or metal oxides or hydroxides provided for in groups B01J23/02 - B01J23/36
  • B01J23/894—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of the iron group metals or copper combined with noble metals also combined with metals, or metal oxides or hydroxides provided for in groups B01J23/02 - B01J23/36 with rare earths or actinides
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
  • B01J23/00—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00
  • B01J23/70—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of the iron group metals or copper
  • B01J23/89—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of the iron group metals or copper combined with noble metals
  • B01J23/8933—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of the iron group metals or copper combined with noble metals also combined with metals, or metal oxides or hydroxides provided for in groups B01J23/02 - B01J23/36
  • B01J23/8946—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of the iron group metals or copper combined with noble metals also combined with metals, or metal oxides or hydroxides provided for in groups B01J23/02 - B01J23/36 with alkali or alkaline earth metals
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
  • B01J37/00—Processes, in general, for preparing catalysts; Processes, in general, for activation of catalysts
  • B01J37/16—Reducing
• • C—CHEMISTRY; METALLURGY
  • C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
  • C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
  • C04B38/00—Porous mortars, concrete, artificial stone or ceramic ware; Preparation thereof
  • C04B38/0006—Honeycomb structures
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D2255/00—Catalysts
  • B01D2255/10—Noble metals or compounds thereof
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D2255/00—Catalysts
  • B01D2255/20—Metals or compounds thereof
  • B01D2255/207—Transition metals
  • B01D2255/20715—Zirconium
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D2258/00—Sources of waste gases
  • B01D2258/01—Engine exhaust gases
  • B01D2258/012—Diesel engines and lean burn gasoline engines
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
  • B01J35/00—Catalysts, in general, characterised by their form or physical properties
  • B01J35/30—Catalysts, in general, characterised by their form or physical properties characterised by their physical properties
  • B01J35/33—Electric or magnetic properties
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
  • B01J35/00—Catalysts, in general, characterised by their form or physical properties
  • B01J35/50—Catalysts, in general, characterised by their form or physical properties characterised by their shape or configuration
  • B01J35/56—Foraminous structures having flow-through passages or channels, e.g. grids or three-dimensional monoliths
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
  • B01J35/00—Catalysts, in general, characterised by their form or physical properties
  • B01J35/60—Catalysts, in general, characterised by their form or physical properties characterised by their surface properties or porosity
  • B01J35/61—Surface area
  • B01J35/612—Surface area less than 10 m2/g
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
  • B01J37/00—Processes, in general, for preparing catalysts; Processes, in general, for activation of catalysts
  • B01J37/34—Irradiation by, or application of, electric, magnetic or wave energy, e.g. ultrasonic waves ; Ionic sputtering; Flame or plasma spraying; Particle radiation
  • B01J37/348—Electrochemical processes, e.g. electrochemical deposition or anodisation
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02T—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO TRANSPORTATION
  • Y02T10/00—Road transport of goods or passengers
  • Y02T10/10—Internal combustion engine [ICE] based vehicles
  • Y02T10/12—Improving ICE efficiencies

Definitions

• the present invention relates to the field of structures for purifying a gas charged with gaseous pollutants essentially of NO x type. More particularly, the invention relates to honeycomb structures, in particular used to treat the exhaust gas of a diesel engine, and incorporating a catalytic system for the depollution of said polluting species.
• a conventional three-way catalyst allows the joint treatment of pollutants NO x , CO and HC and their conversion into neutral and chemically harmless gases such as N 2 , CO 2 and H 2 O.
• a very good efficiency of the system is not achieved only by a continuous adjustment of the richness of the air-fuel mixture. It is thus known that the slightest deviation from the stoichiometry of said mixture causes a large increase in pollutant emissions.
• the materials used to adsorb NOx are most often alkali or alkaline earth metal oxides, in particular barium oxide, which is today considered to be the most effective material in this domain.
• barium oxide which is today considered to be the most effective material in this domain.
• SOx sulfur oxides
• the precursors of barium being difficult to disperse on the support material, it is necessary to provide significant amounts. This leads to reducing the accessibility of the noble metals of the catalytic system by a "covering" effect by barium oxide. A possible but too expensive solution would be to increase the contribution of noble metals in the system.
• these barium-based NOx trap systems pose hygiene and environmental problems, barium being listed as heavy metal.
• NOx reduction systems incorporating a zirconia type support material are also known, but these systems are not very efficient.
• a Zirconia can be used as catalyst support in 3-way NOx reduction systems.
• the zirconia employed described in this publication is a zirconia stabilized by Yttrium doping possibly comprising additions of cerium oxide or Lanthanum. In such systems, zirconia serves only to support the catalyst but does not allow storage of NOx.
• the object of the present invention is to provide a solution for solving the problems described above, in particular with regard to the NOx storage function.
• one of the aims of the present invention is to provide a structure for the purification of a polluted gas, in particular a structure for filtering an exhaust gas resulting from a diesel engine loaded with gaseous and particulate pollutants.
• solid capable of functioning in the absence of specific NOx traps based on oxides of alkali or alkaline earth metals, in particular barium.
• the invention consists of a filtration structure of a gas resulting from a diesel engine, charged with gaseous pollutants of the NO x nitrogen oxide type and solid particles, of the particulate filter type, said structure comprising a set longitudinal adjacent channels of axes parallel to each other separated by porous filtering walls constituted by said porous inorganic material, said channels being alternately plugged at one or the other end of the structure to define inlet channels and outlet channels for the gas to be filtered, and to force said gas to pass through the porous walls separating the inlet and outlet channels, said filtration structure being characterized by it comprises a catalytic system comprising at least one noble or transition metal suitable for the reduction of NOx and a support material, wherein said support material comprises or consists of a zirconium oxide partially substituted with a trivalent cation M 3+ or by a divalent cation M ' 2+ , said zirconium oxide being in a reduced state, under stoichiometric oxygen.
• the catalytic system is advantageously chosen to also be suitable for the oxidation of polluting species of the HC, CO or H 2 hydrocarbon type.
• a catalytic system comprises at least one precious metal selected from Pt and / or Pd and / or Rh and / or Ag and / or Au and / or transition metals, in particular Cu, Fe, Ni, Co , and transition metal oxides such as Mn 2 ⁇ 3 , Co 3 O 4 .
• the support material corresponds to the formulation (Zr ⁇ 2- X) i- y (M 2 ⁇ 3- X) y, M being a cation of valency 3 preferably selected from the group consisting of Y 3+, Sc 3+, or rare earths and being strictly greater than 0 and preferably less than 2.
• y is less than or equal to 0.5, more preferably y is less than or equal to 0.25, and most preferably y is less than or equal to 0.1.
• the support material corresponds to the formulation (ZrO 2 -x) iy ' (M'Oi x ) y' , M 'being a cation of valence 2 preferably chosen from the group consisting of Ca 2+ and Sr 2+ and y 'being strictly greater than 0 and strictly less than 2.
• y ' is less than 0.6, more preferably y' is less than 0.3, and most preferably y 'is less than or equal to 0.15.
• the reduced filtration structure according to the invention is such that x is less than 0.5, preferably less than 0.1, and very preferably less than 0.05.
• x is greater than 0.005, preferably greater than 0.01.
• This support material of the catalytic system based on zirconia according to the invention preferably has, even after a calcination of 800 and 1000 0 C, a specific surface area of at least 5 m 2 / g, preferably at least 10 m 2 / g, or even at least 50 m 2 / g.
• the zirconia forming all or part of the support material can be obtained by different doping by substituting the zirconium atoms with lower valence transition metal cations such as Y 3+ , Sc 3+ , Ca 2+ , Sr 2+ or rare earth.
• the ionic conductivity is preferably between 1 and 10 -4 S / cm in the temperature range from 150 to 800 ° C.
• the porous inorganic material has an open porosity, conventionally measured by mercury porosimetry, greater than 10%, preferably greater than 20%, or even greater than 30%. Too little porosity of the material constituting the filtering walls leads to a too high pressure drop.
• the porous inorganic material comprises or consists of an electrically conductive inorganic material of the carbide type, for example SiC, or a silicide, for example MoSi 2 or boride, for example TiB 2 , or of the Lai x Sr x MnO 3 family. or mixed oxides of gadolinium and cerium (CGO).
• an electrically conductive inorganic material of the carbide type for example SiC
• a silicide for example MoSi 2 or boride, for example TiB 2 , or of the Lai x Sr x MnO 3 family. or mixed oxides of gadolinium and cerium (CGO).
• the porous inorganic material is based on silicon carbide SiC, preferably recrystallized at a temperature of between 2100 and 2400 ° C.
• the inorganic material may be based on doped SiC, for example with aluminum or nitrogen, and such that its electronic resistivity is preferably lower than 20 Ohm. cm, more preferably at 15 Ohm. cm, more preferably 10 Ohm. cm at 400 ° C.
• SiC-based is meant in the sense of the present description that the material consists of at least 25% by weight, preferably at least 45% by weight and so very preferred at least 70% by weight of SiC.
• the porous inorganic material is based on Cordierite or Aluminum Titanate.
• the invention relates to a powder that can be used as a support material in a filtration structure as previously described, said powder comprising particles of zirconium oxide partially substituted by a cation M or M ', free of metal precious metals of the Pt, Pd, Rh, Ag, Au and transition metal type, in particular Cu, Fe, Ni, Co, said substituted zirconium oxide being in the reduced state, under stoichiometric oxygen and corresponding to the formulation (ZrO 2 - X) i- y (M 2 ⁇ 3_ x) y, M being a cation of valency 3 preferably selected from the group consisting of Y 3+, Sc 3+, or rare earths and being strictly greater than 0 and strictly less at 2 or responding to the formulation
• the reduced state of the partially substituted zirconium oxide can be obtained by a heat treatment at a temperature above 400 ° C. under a reducing atmosphere or by an electrochemical treatment consisting of the polarization of the material by application of a voltage or bias current thereon.
• a powder as described above is advantageous as support material for an NO x reduction catalyst, in a particulate filter type filter structure as previously described.
• the powder makes it possible, in particular, to obtain a catalytic system such as has been previously described, characterized in particular by comprising at least one noble or transition metal suitable for the reduction of NO x and said support material. as previously described, comprising or consisting of zirconium oxide in a reduced state partially substituted by a trivalent M 3+ or divalent M ' 2+ cation.
• the catalyst used would allow a selective oxidation reaction of NOx to NO2.
• the NO2 would then, surprisingly and never before, be captured at the catalyst support in a ZrO (NO 2 ) form. Such a phenomenon would occur in particular during the operating phases of the lean fuel engine.
• the catalyst used would also allow, during subsequent phases, the NOx reduction reaction (NO and NO2) in N2, in particular during the engine operating phases in fuel-rich mixture, that is to say say in a reducing atmosphere.
• NO and NO2 NOx reduction reaction
• the tests carried out by the applicant have indeed shown that during such phases, the zirconia-based carrier would release the nitrogen oxides previously stored. Without being considered definitive, the proposed mechanism could be as follows:
• the metal catalysts can be deposited in a conventional manner by impregnation with the surface of a zirconia powder as described according to the invention, for example by processes such as those described in particular by US5884473.
• the introduction of the catalytic system whose support material acts as a NOx trap advantageously makes it possible to greatly increase the catalyst surface area accessible to the pollutants, and consequently the probability of contact and exchanges between the reactive species,
• the support material constituted according to the invention also has a high thermal stability with respect to alumina-type support materials, in particular because of a better sintering resistance of the metal catalyst particles deposited in contact with the oxygen vacancies of the material support, - the support material formed according to the invention has a high reactivation in a fuel-rich medium compared to previous solutions.
• the catalytic system according to the invention not comprising barium is therefore much less sensitive to the presence of sulfur oxides (SO x ) in the gases to be treated.
• the present invention is particularly applicable in the filter wall structures used for purification and the most effective for filtering an exhaust gas from a diesel engine.
• Such structures generally referred to as particle filters, comprise at least one and preferably a plurality of monolithic honeycomb blocks joined by a joint cement.
• the block or blocks comprising a set of adjacent ducts or channels of axes parallel to each other separated by porous walls, closed by plugs to one or the other. other of their ends to define inlet ducts opening on a gas inlet face and outlet ducts opening on a gas evacuation face, so that the gas passes through the porous walls.
• Examples of such assembled or unassembled structures are for example described in EP 0816065, EP 1142619, EP1306358 or EP 1591430.
• the porous inorganic structure is impregnated with an aqueous solution comprising zirconia particles having the characteristics according to the invention, that is to say that the support is a reduced zirconium oxide corresponding to the formulations (Zr ⁇ 2- X) iy (M 2 ⁇ 3_ x) y or (ZrO 2 - x) y '(me IM-x) y', wherein M is a cation of valence 3 and M 'is a cation of valency 2 .
• said substituted zirconia type support is in a form reduced, that is to say that it has undergone a reduction treatment having brought it in a deficit state (or stoichiometric) oxygen
• said reduction treatment can be chosen according to the invention among all known treatments for this purpose and in particular by heating in a reducing atmosphere, by electrochemistry, etc.
• the reduced state of the support can be obtained in particular by a reduction treatment by thermal means that is to say by a high temperature treatment, for example between 400 and 1000 0 C, under a reducing atmosphere.
• the reduction treatment can also be carried out under a reducing atmosphere of light hydrocarbon such as for example methane, propane, propene or carbon monoxide CO, in a temperature range between 400 and 1000 ° C.
• the duration heat treatment can be adapted to the starting granulometry and / or the specific surface of the powder intended for the deposition on the structure and / or the temperature. This duration is in general at least equal to 10 minutes and preferably greater than or equal to 60 minutes.
• the reduction treatment is carried out in a step prior to the impregnation of the structure with the substituted zirconia particles.
• the structure comprising the support in the reduced state is then impregnated in one or more steps by the catalytic system (s) necessary for the conversion of NO x to N 2 .
• the porous inorganic structure is this time first impregnated with an aqueous solution comprising doped zirconia particles by substituting the zirconium atoms with lower valence transition metal cations (3 or 4). 2) such as Y 3+ , Sc 3+ , Ca 2+ , Sr 2+ or rare earths to ultimately obtain a material of the previously described formulation.
• the heat reduction treatment is performed this time on the structure impregnated with the support material, ie after the deposition of the zirconia.
• the reduction treatment can be carried out under the same conditions as those already described in the previous mode.
• the structure is impregnated in one or more steps by the catalytic system (s) necessary for the conversion of NO x to N 2 .
• This second embodiment has the advantage of permitting the impregnation of the porous structure under conditions that are not necessarily reducing, for example under air.
• the porous inorganic structure is impregnated with an aqueous solution comprising doped zirconia particles by substituting the zirconium atoms with lower valence (3 or 2) transition metal cations such as Y 3+ , Sc 3+ , Ca 2+ , Sr 2+ or rare earths to ultimately obtain a material of the previously described formulation.
• the structure is impregnated in one or more steps by the catalytic system or systems to the conversion of NO x to N 2 .
• the catalysts and the zirconia are deposited at the same time on the structure.
• the thermal reduction treatment which may be of the same type as that previously described, is carried out on the structure already impregnated by the catalyst and its support material.
• This third embodiment makes it possible to carry out the heat treatment at a lower temperature, typically at a temperature between 400 and 600 ° C., because of the reducing activity of the catalytic metals.
• the reduced state of the partially substituted zirconium oxide can also be obtained according to the invention by an electrochemical treatment consisting of the polarization of the material by applying a voltage or a polarization current thereon. .
• cylindrical honeycomb monoliths of recrystallized silicon carbide (SiC) cylindrical shape have been synthesized according to the conventional techniques already well known in the art and for example described in patent application EP 1 142 619 A1.
• a mixture of silicon carbide particles with a purity greater than 98% was first produced in a kneader in accordance with the method of manufacturing an R-SiC structure described in application WO 1994/22556.
• the mixture is obtained from a coarse fraction of SiC particles (75% by weight) whose median particle diameter is greater than 10 microns and a fraction of fine granulometry (25% weight) with a median particle size of less than 1 micron.
• the median diameter refers to the diameter of the particles below which 50% by mass of the population is found.
• Water is also added up to 20% by weight of the sum of the preceding constituents and kneaded to obtain a homogeneous paste whose plasticity allows the formation of monoliths or the extrusion through a die of a structure honeycomb.
• the recrystallized SiC honeycomb monoliths are dried deliantes, corked and fired under a neutral atmosphere at a temperature of 2200 ° C.
• the optimal experimental conditions are as follows: rise in temperature of 20 ° C. / hour up to 2200 0 C then temperature plateau of 6 hours at 2200 0 C.
• the monoliths are immersed in an embodiment similar to that described in US Pat. No. 5,866,210 in this solution so as to impregnate about 1.5% by weight of zirconia doped with respect to the monolith. Drying is carried out at 40 ° C. and then calcination at 500 ° C. under air is carried out at a heating rate of 100 ° C./h and a plateau at the maximum temperature of one hour.
• the monolith is impregnated with an aqueous solution of platinum dinitrodiamine chloride.
• the monolith is dried at 40 ° C. and then calcined at 500 ° C. in air, according to a heating rate of 100 ° C./hour and a plateau at the maximum temperature of one hour.
• the monolith is impregnated with an aqueous solution of Rhodium nitrate, the monolith is then dried at 40 ° C. and then calcined to 500 ° C. under air, with a heating rate of 100 ° C./h, with a bearing at the maximum temperature of one hour.
• the concentration of precious metal solutions and the deposition process are adapted to constitute catalysed monoliths whose chemical analysis shows the following characteristics:
• Example 1 The experimental protocol already described in Example 1 was entirely taken up in this example, except that this second series of monoliths underwent after impregnation of the supported catalyst additional reduction treatment in pure H 2 at 600 0 C for 1 hour.
• the analyzes have shown that the zirconia substituted and reduced substantially corresponded to the formulation (Zr ⁇ 2- X) i- y (M 2 ⁇ 3_ x) y, wherein y is about 0.08 and x is close to 0.02 .
• the test is carried out as follows: The mixture of lean gas 1 passes first on the catalysed monolith maintained in an electric oven at 250 or 300 ° C.
• the composition of the gases passing through the monolith is alternated according to the following protocol: first mixture 1 for 3 minutes and then rocking to the gas mixture 2 (rich) for 2 minutes, then to mixture 1 (3 minutes) and so on.
• the composition of the gases at the furnace outlet is analyzed after stabilization of the system so as to know the amount of NO x converted into N 2 .
• the test as just described was carried out under the same conditions for each temperature 250 and 300 ° C. on the monolith according to Example 1 (unreduced zirconia) and on the monolith according to Example 2 (zirconia). scaled down) .
• the gas flow rate is 10 1 / h for both mixtures.
• Thermocouple type temperature sensors are placed about 5mm from the exit surface of the monolith.
• the gas analysis is performed at the outlet of the reactor by IR and ⁇ GC

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