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• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
  • F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
  • F01N3/00—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust
  • F01N3/08—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous
  • F01N3/10—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by thermal or catalytic conversion of noxious components of exhaust
  • F01N3/24—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by thermal or catalytic conversion of noxious components of exhaust characterised by constructional aspects of converting apparatus
  • F01N3/28—Construction of catalytic reactors
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  • 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
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  • B01D53/32—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 by electrical effects other than those provided for in group B01D61/00
  • B01D53/326—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 by electrical effects other than those provided for in group B01D61/00 in electrochemical cells
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  • B01D53/34—Chemical or biological purification of waste gases
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  • 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
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  • B01J37/00—Processes, in general, for preparing catalysts; Processes, in general, for activation of catalysts
  • B01J37/0009—Use of binding agents; Moulding; Pressing; Powdering; Granulating; Addition of materials ameliorating the mechanical properties of the product catalyst
  • B01J37/0018—Addition of a binding agent or of material, later completely removed among others as result of heat treatment, leaching or washing,(e.g. forming of pores; protective layer, desintegrating by heat)
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  • B01J37/00—Processes, in general, for preparing catalysts; Processes, in general, for activation of catalysts
  • B01J37/02—Impregnation, coating or precipitation
  • B01J37/03—Precipitation; Co-precipitation
• • B—PERFORMING OPERATIONS; TRANSPORTING
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  • B01J37/00—Processes, in general, for preparing catalysts; Processes, in general, for activation of catalysts
  • B01J37/02—Impregnation, coating or precipitation
  • B01J37/03—Precipitation; Co-precipitation
  • B01J37/031—Precipitation
• • C—CHEMISTRY; METALLURGY
  • C01—INORGANIC CHEMISTRY
  • C01G—COMPOUNDS CONTAINING METALS NOT COVERED BY SUBCLASSES C01D OR C01F
  • C01G1/00—Methods of preparing compounds of metals not covered by subclasses C01B, C01C, C01D, or C01F, in general
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  • C01G—COMPOUNDS CONTAINING METALS NOT COVERED BY SUBCLASSES C01D OR C01F
  • C01G55/00—Compounds of ruthenium, rhodium, palladium, osmium, iridium, or platinum
  • C01G55/002—Compounds containing, besides ruthenium, rhodium, palladium, osmium, iridium, or platinum, two or more other elements, with the exception of oxygen or hydrogen
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
  • F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
  • F01N3/00—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust
  • F01N3/02—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for cooling, or for removing solid constituents of, exhaust
  • F01N3/021—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for cooling, or for removing solid constituents of, exhaust by means of filters
  • F01N3/033—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for cooling, or for removing solid constituents of, exhaust by means of filters in combination with other devices
  • F01N3/035—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for cooling, or for removing solid constituents of, exhaust by means of filters in combination with other devices with catalytic reactors, e.g. catalysed diesel particulate filters
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  • F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
  • F01N3/00—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust
  • F01N3/08—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous
  • F01N3/0892—Electric or magnetic treatment, e.g. dissociation of noxious components
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
  • F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
  • F01N3/00—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust
  • F01N3/08—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous
  • F01N3/10—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by thermal or catalytic conversion of noxious components of exhaust
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D2255/00—Catalysts
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  • B01D2255/1021—Platinum
• • B—PERFORMING OPERATIONS; TRANSPORTING
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  • B01D2255/00—Catalysts
  • B01D2255/10—Noble metals or compounds thereof
  • B01D2255/102—Platinum group metals
  • B01D2255/1025—Rhodium
• • B—PERFORMING OPERATIONS; TRANSPORTING
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  • B01D2255/00—Catalysts
  • B01D2255/20—Metals or compounds thereof
  • B01D2255/206—Rare earth metals
  • B01D2255/2065—Cerium
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
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  • B01D2255/20—Metals or compounds thereof
  • B01D2255/207—Transition metals
  • B01D2255/20707—Titanium
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
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• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D2255/00—Catalysts
  • B01D2255/80—Type of catalytic reaction
  • B01D2255/806—Electrocatalytic
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  • B01D2255/92—Dimensions
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• • B—PERFORMING OPERATIONS; TRANSPORTING
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  • B01D2258/01—Engine exhaust gases
• • B—PERFORMING OPERATIONS; TRANSPORTING
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• • 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
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  • 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 the purification of a gas charged with gaseous pollutants essentially of NO x and CO / HC type. More particularly, the invention relates to catalytic systems for treating the exhaust gases of a diesel engine or gasoline enabling the elimination of said polluting species, by reduction of said NO x species and by oxidation of HC hydrocarbons and / or or CO.
• 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 0.
• a very good efficiency of the system is however 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 the mixture causes a large increase in pollutant emissions.
• the catalysts A and B are deposited on a metal support, mixed with an ionic conductor D.
• the metal support provides the electrons necessary for the proper functioning of the electrochemical system.
• the use of such a support in an exhaust line of an automobile engine, especially diesel, is problematic mainly because of its low resistance to oxidation and its poor chemical resistance.
• this type of metal support has the major disadvantage of having a low chemical and dilatometric compatibility with the catalysts, which must furthermore integrate, according to the teaching provided in US Pat. No. 6,878,354, oxide-type NO x or HC traps. barium, zeolites or other mixed oxides, also of low chemical compatibility with the metal support.
• the four constituents A, B, C and D are introduced in a mixture on a non-conducting ceramic support consisting of cordierite.
• the efficiency of such a system then strongly depends on the deposition conditions of the catalysts A and B and the electronic conductors C and ion D. Indeed, the properties obtained are highly dependent on the dispersion of the different phases corresponding to the different constituents on the medium used, a connection being necessary between these four elements for the proper functioning of the electrochemical system. Finally, since the electrochemical system consists of small grains randomly arranged in relation to each other, its efficiency is necessarily limited, on the one hand, by the connections between the grains and, on the other hand, by the small quantity of electrolytes (electrons and or ions) available for the proper functioning of the electrochemical catalysis system.
• the object of the present invention is to provide an electrocatalytic system suitable for purifying a gas charged with gaseous pollutants of the HC and / or CO type and NOx type pollutants, and their simultaneous and simultaneous conversion into gases.
• neutral and chemically harmless such as N 2 , CO 2 and H 2 0, said system being able to operate whatever the atmosphere: oxidizing, neutral or reducing.
• the present invention relates to an electrocatalytic system for the joint treatment of oxidizing pollutant species of the NOx type and reducing polluting species of the HC or CO hydrocarbons type, contained in a gas to be purified, in particular an exhaust gas. from a combustion engine, said system comprising:
• a catalyst B for the oxidation of polluting species of the HC hydrocarbons and CO type a catalyst B for the oxidation of polluting species of the HC hydrocarbons and CO type
• said catalysts A and B being in contact with compound E, said compound E being constituted by an ionic and electronically conductive oxide corresponding to the molar formulation:
• M is an element chosen from: Gd, Y, Se, Sm, La, Pr, Nd, Er, Tb,
• N is an element having several valence degrees selected from: Ti, V, Cr, Mn, Fe, Co, Ni, Cu,
• x is greater than 0.05.
• Catalyst A used for the reduction reaction is selected from catalysts well known in the art for their activity and preferably their selectivity to NOx reduction reactions. They may especially be chosen from compounds including precious metals impregnated on the surface of a powder with a large specific surface area, for example alumina. These metals are preferably Rh, Cu, Ni.
• the catalyst B used for the oxidation reaction of the hydrocarbons is chosen from catalysts well known in the art for their activity and preferably their selectivity with respect to the oxidation reactions of hydrocarbons.
• the reforming and steam reforming catalysts used in the field of petrochemistry and refining can be used according to the invention. They are in particular catalysts based on Pt, Pd, Ag, Fe, Co, Au.
• the ionic conductive oxide and electronic the formula CEI y - z 0 2 - x M y, and wherein y is between about 0.1 and about 0.3.
• the oxide ion and electronic conductor is of the formula CEI y 0 2 - x Gd y, and y is between about 0.1 and about 0.3.
• the ionic and electronically conductive oxide corresponds to the formula Ce- y - z O 2 - x Y y Ti z , y being between about 0.1 and about 0.3 and z being between 0.01 and 0.1.
• x is between 0.1 and 0.4, preferably between 0.1 and 0.3.
• the compound E comprises oxygen vacancies and part of the Ce 4+ cations of the crystal lattice is converted into Ce 3+ cations.
• the proportion of Ce 3+ ions is preferably between 25 and 75%, in particular between 40 and 70%.
• proportion of the cations Ce 3+ we mean the proportion of trivalent cations as calculated according to the Ce 3+ / Ce 4+ ratio.
• the method of determining such a ratio by magnetic susceptibility dies is well known and for example described in the publication "Catalysis Today, vol. 54, pp. 93-100 (1999).
• the ionic and electronic conductive oxide has a specific surface area of between 0.5 and 100 m 2 / g, preferably between 1 and 30 m 2 / g.
• the electronic resistivity of compound E is less than 20 ohms. cm at 400 ° C and wherein the ionic conductivity of the compound E is between 1 and 10 ⁇ 4 Siemens / cm at 400 ° C.
• the invention also relates to a structure for the depollution and / or filtration of a gas loaded with gaseous pollutants and possibly solid particles, consisting of a porous inorganic material on which is deposited a catalytic system as described in one of the preceding claims.
• the present invention is particularly applicable in the structures used for the purification and / or filtration of an exhaust gas of a diesel engine.
• Inorganic porous foam type structures or honeycombs that may be constituted by the inorganic material E or on which, or in the porosity of which can be deposited the electrocatalytic system according to the invention are appropriate.
• structures, generally referred to as particle filters comprise at least one and preferably a plurality of monolithic honeycomb blocks. Unlike the purification devices previously described, in such filters, the block or blocks comprising a set of adjacent ducts or channels of axes parallel to each other separated by porous walls, for example whose open porosity is greater than 30%.
• the introduction of the catalytic system into the porosity of the filtering structure advantageously makes it possible to greatly increase the probability of contact between the polluting species and the catalytic system
• the catalytic system which operates continuously on the model of a battery, allows the joint conversion of the NOx oxidizing polluting species and the reducing polluting species whatever the nature and the atmosphere of the exhaust gases: oxidizing, neutral or reducing, that is to say whatever the initial richness of the air / fuel mixture,
• the constituents of the system can be deposited in the filter in a single impregnation, which greatly reduces the dependence of the performance of the system compared to at the catalyst deposition conditions.
• the electrochemical system according to the invention can be implemented according to various possible modes, according to any technique known in the art.
• the porous inorganic structure is impregnated with an aqueous solution comprising particles of the mixed conductor and catalysts A and B so as to form the system according to the invention.
• the inorganic material constituting all or part of the inorganic structure is chosen from the following list alone or in combination: metal or sintered metal, cordierite, aluminum titanate, alumina, mullite, silicon nitride, silicon carbide.
• Electronically conductive inorganic material structures such as silicon carbide or metals can regenerate the catalytic system by polarization. Such a system also contributes to improving the regeneration efficiency of the filter by promoting a higher oxidation rate of the soot.
• a precursor of the ionic and electronically conductive oxide is first prepared by a sol-gel method, by mixing the reagents given below, in equivalent proportions to obtain in the initial mixture, in moles: 0.2 parts of Y, 0.75 part Ce, 0.05 part Ti.
• yttrium acetate tetrahydrate Y (CH 3 COO) 3 , 4H 2 O (99-102%, Alfa Aesar),
• Titanium isopropoxide Ti (OC 3 H 5 ) 4 (99.9%, Alfa Aesar).
• precursor salts are dissolved in ultrapure distilled water.
• a salt solution and an organic solution are prepared.
• the precursor salts in proportions desired in order to obtain the compound Ceo, 75YO, 2T10, 05O2, as described above, are dissolved in ultrapure distilled water at ambient temperature and with stirring.
• PEG 2000 creates a three-dimensional periodic polymeric network in which salts can be incorporated.
• the drying and evaporation of the solvent is carried out on a rotary evaporator under a pressure of 1100 mbar.
• the organic compound removal step is carried out by heating at 600 ° C for 30 minutes.
• the climb ramp is 50 ° C / h.
• the previous gel is placed in an alumina crucible to be certain to eliminate all organic residues.
• the oxide thus recovered from composition Ceo, 75Y0, 2T10, 05O2 has a yellow color after manual grinding with the mortar. Its specific surface is measured by a conventional surface analysis according to the BET method. This method of measuring specific surface area by adsorption of inert gas has been developed by S. Brunauer, PHEmmet and J. Teller and is well known to those skilled in the art. The specific surface of the product thus obtained is about 57 m 2 / g.
• the powder thus obtained is impregnated with a platinum precursor in the form of platinum dinitrite diamine, (NH 3 ) 2 Pt (NO 2 ) 2 (Alfa Aesar, 1.7% by weight of Pt), then poured into a flask and mixed with a solution of platinum precursor and ultrapure water.
• the flask is immersed in a water bath and heated to a temperature of 70 ° C, with stirring for 70 minutes. At the end of agitation, the flask is removed from the water bath and cooled to room temperature. The ball is then re-plunged and gently heated under primary vacuum to 60 ° C. After the solvent has completely evaporated after about 2 hours at 60 ° C., the powder is oven-dried at 110 ° C. for 3 hours and then ground.
• the catalyst thus obtained is then calcined in air at 500 ° C. for one hour.
• Rhodium is then impregnated on the oxide Ceo, 75Y0, 2T 10, 05O2 from a solution of nitrate (solution of nitrates of Rhodium , Rh (NC> 3) 3, Alfa Aesar, 10% by weight of Rh metal).
• the oxide of the general formulation Ceo, 75Y0, 2 T 10, 05O2 has weight contents of about 0.3% for Pt and Rh with respect to the mass of the system Pt / Ce May 7 Yo Io, o50 2 / Rh.
• the rate of oxygen deficiency x of the oxide has been evaluated according to the invention according to conventional techniques by reduction in programmed temperature (often called in the technique temperature-programmed reduction or TPR).
• the samples are heated under an atmosphere comprising 3 ⁇ 4 (3 ⁇ 4 / He mixture with 1 mol% 3 ⁇ 4 1.8 L / h, 10 ° C / min) up to 900 ° C.
• the x value of the deficit oxide is obtained directly by dividing the number of moles of hydrogen gas consumed by the number of moles of the oxide deficit tested.
• the step of reduction at high temperature in a hydrogen atmosphere according to the invention makes it possible to eliminate a part of the oxygens not only at the surface but also in the entire volume of the oxide, with the creation of oxygen vacancies throughout the crystal lattice.
• a step of creating oxygen vacancies could be accompanied by a partial conversion of a part of the Ce 4+ cations of the Ce 3+ cation network.
• the two catalysts being in contact with the ionic and electronic conductive oxide.
• Example 1 was reproduced identically, except that the last step of removing part of the oxygens from the crystal lattice of the oxide was not carried out.
• the stoichiometric oxide is first impregnated with the two catalysts based on Pt and Rh, according to the same protocol as previously described in relation to Example 1.
• an oxide of general Ceo formulation is obtained, sGdo, 202, non-oxygen vacancy, having mass contents of about 0.3% for Pt and Rh.
• the oxide is then subjected to a treatment under an atmosphere of hydrogen and at a high temperature, for a time sufficient to obtain an oxide, this time very deficient in oxygen.
• Example 2 was reproduced in the same manner except that the last step of removing part of the oxygens from the crystal lattice of the oxide was not carried out.
• an oxide of general formulation Ceo, sGdo, 202 is obtained, this time not lacunary. in oxygen, having mass contents of about 0.3% for Pt and Rh.
• the samples of the examples of the invention and previous comparative, finely ground in the form of a powder are placed in a U-shaped fixed-bed quartz reactor. More precisely, about 500 mg of the catalytic system are introduced into the reactor. , equipped with a porous quartz frit supporting the powder.
• the volume of the catalyst is of the order of 0.3-0.4 cm 3 .
• the catalyst is heated under a current of He (5 L / h) at 250 ° C and at atmospheric pressure. Once the temperature of 250 ° C. has been stabilized, a reaction mixture composed of a 02 / He mixture is introduced onto the catalyst at a total flow rate of 10 L / h and a hourly space velocity of between 25,000 and 35,000 h -1 .
• the gaseous mixture to be cleaned up initially comprises 500 ppm of O2. It is representative of a highly oxidizing atmosphere, in the sense for example of an exhaust gas from a diesel engine operating in lean mixture or a gas from a burner of a glass furnace.
• On-line gas analysis is performed by an infra-red analyzer for NO and 2O, ultraviolet for NO2, and by a microchromatograph equipped with two analysis modules and two catharometric detectors, for oxygen analysis and nitrogen.
• the evolution of the concentrations of NO, NO 2 and N 2 and N 2 O in the gases to be treated is monitored as a function of time as soon as the NO 2 / He mixture is introduced onto the catalyst for approximately 2 hours (6500 seconds).
• An overall molar percentage of conversion of NO x to N2 by the catalytic system is then calculated over this period, as reported in Tables 1 and 2. It is also verified at the outlet of the device the selectivity of the N 2 catalyst, that is to say its ability to transform exclusively NO x N 2 .
• the degree of conversion of O 2 to 2 is 412 ymol / g with the Pt / Ceo system, sGdo, 2 Oi, 9 / Rh and is increased to 512 ymol / g with the use of a Pt / Ce 0 system. , 75 Yo, 2 TiO, 5 OI, 7 / Rh.
• the conversion activity of NO x in 2 thus appears even more important for an oxide mixed conductor further incorporating an N element having several degrees of valence (oxidation) in the sense previously described.
• the selectivity of the systems according to the invention is very high. Selectively, it is understood that more than 80% or more than 90 mol% of the converted NOx are converted to N 2 . This was determined by measuring the percentage of product (in ymol) relative to the amount of converted NO x (N 2 + 2 O) by the catalyst system during the test period (6500 seconds). In this case, the systems according to the invention do not show the presence of ⁇ converted to N 2 0 because the selectivity is 100%.
• the proportion of the cations is measured by the Ce 3+ / Ce 4+ ratio, obtained by means of magnetic susceptibility measurements (also called “Magnetic Balance Measurement”), in a manner well known in the art. .
• the proportion of Ce 3+ ion is of the order of 40 to 60%.
• the conductivities can be measured by conventional impedance techniques, for example as described in the publication "Acta Materialia, vol. 56, pp. 4658-4672 (2008).
• the ionic and electronic conductivities of the samples according to Examples 1 and 2 according to the invention are much lower than those of the comparative examples, and are the only ones to be in accordance with the subject of the present invention: electronic resistivity less than 20 ohms. cm at 400 ° C and ionic conductivity of between 1 and 10 ⁇ 4 Siemens / cm at 400 ° C.
• the catalytic system according to the invention thus particularly finds its use for the depollution of a gas this time loaded with both HC, CO and NOx species, including the depollution of an automobile exhaust gas.
• the catalytic system proves to be capable of operating whatever the operation of the engine, a rich mixture as a fuel-poor mixture.
• the electrons released on one side by the conversion of the HC and CO species at the catalyst B are conveyed by the conductive oxide to the Catalyst A site and allow the joint reduction of polluting species of the NOx type.
• the oxygen ions released by the reduction reaction are freely transported via the incomplete oxygen network of the oxide to the sites of the catalytic oxidation reaction of HC, CO.
• Such a system makes it possible in particular to treat the NOx species present in an oxidizing atmosphere typically resulting from a lean air / fuel mixture fed to an internal combustion engine or from a glass furnace.
• the electrochemical system according to the invention also does not require any prior trapping of NOx.
• successive cycles incorporating feed phases of the rich mixture filter (reducing medium) could remain useful, particularly in use as a particulate filter, in particular to maintain a value of x greater than 0.05, allowing the continuous and most efficient conversion of NOx.
• the frequency of a cycle for a catalytic system according to the invention is of the order of one hour, or even several hours, while this frequency, for obtaining an equivalent conversion of NOx according to the systems Catalysts of the prior art incorporating NOx trap, is of the order of only a few minutes.

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