Classifications

• • 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
  • B01D53/944—Simultaneously removing carbon monoxide, hydrocarbons or carbon making use of oxidation catalysts
• • 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
  • B01J23/02—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of the alkali- or alkaline earth metals or beryllium
• • 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
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D2255/00—Catalysts
  • B01D2255/20—Metals or compounds thereof
  • B01D2255/204—Alkaline earth metals
  • B01D2255/2045—Calcium
• • 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
  • B01D2255/00—Catalysts
  • B01D2255/40—Mixed oxides
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D2255/00—Catalysts
  • B01D2255/90—Physical characteristics of catalysts
  • B01D2255/915—Catalyst supported on particulate filters
  • B01D2255/9155—Wall flow filters
• • 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
  • F01N2330/00—Structure of catalyst support or particle filter
  • F01N2330/06—Ceramic, e.g. monoliths
• • 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
  • F01N2510/00—Surface coverings
  • F01N2510/06—Surface coverings for exhaust purification, e.g. catalytic reaction
  • F01N2510/068—Surface coverings for exhaust purification, e.g. catalytic reaction characterised by the distribution of the catalytic coatings
  • F01N2510/0682—Surface coverings for exhaust purification, e.g. catalytic reaction characterised by the distribution of the catalytic coatings having a discontinuous, uneven or partially overlapping coating of catalytic material, e.g. higher amount of material upstream than downstream or vice versa
• • 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

Definitions

• the invention relates to particulate filters, including those fitted to the exhaust lines of combustion engines, and more particularly the exhaust lines of thermal engines of vehicles of the motor vehicle type.
• Gasoline or diesel-type thermal engines produce particles, the emission of particles being generally greater in the case of diesel engines than in that of gasoline engines.
• the exhaust lines of combustion engines most often include, at least when it comes to diesel engines, a particle filter for trapping solid particles. To prevent clogging of the particulate filter, it must be regenerated by burning the trapped particles.
• the particulate filters are, for example, constituted by a mineral matrix, of ceramic type, of cellular structure, defining channels arranged substantially parallel to the general direction of flow of the exhaust gases in the filter, and alternatively closed on the side of the inlet face of the filter gases and the side of the outlet face of the filter gases, as described in patent EP-2 426 326.
• the particulate filters are, for example, constituted by a mineral matrix, of ceramic type, of cellular structure, defining channels arranged substantially parallel to the general direction of flow of the exhaust gases in the filter, and alternatively closed on the side of the inlet face of the filter gases and the side of the outlet face of the filter gases, as described in patent EP-2 426 326.
• one can also confer additional functions to the particulate filter including depositing on all or part of the walls of the channels, one or more catalytic coatings.
• oxidation catalyst type capable of reducing carbon monoxide (CO) and hydrocarbon oxidation (HC) emissions
• oxidation reduction catalyst type capable of reducing carbon monoxide (CO) and hydrocarbon oxidation (HC) emissions
• NOx-type nitrogen in particular those catalyzing the reduction of NOx with injection into the exhaust line upstream of the filter of a gaseous ammonia or liquid urea-type reducing agent.
• NOx trap type coatings which become active vis-à-vis NOx when the diesel type engine goes temporarily in rich regime.
• the burning of the particles of the filter is carried out periodically by increasing the temperature of the exhaust gas, for example by directly injecting fuel into the exhaust gas.
• an oxidation catalyst for oxidizing carbon monoxide and unburned hydrocarbons
• the combustion of this fuel in the oxidation catalyst makes it possible to significantly increase the exhaust gas temperature at the particulate filter, which can then, at least temporarily, reach temperatures of more than 550 ° C up to 600 ° C, and thus reach the temperature of the car soot inflammation.
• inlet / "outlet” or “upstream” / “downstream” are understood to refer to the general direction of flow of the exhaust gas intended to pass through the particulate filter, once it is mounted on an exhaust line of a heat engine, from the motor output to the exit of gases in the open air at the end of line.
• To trigger a regeneration of the particulate filter it is usually measured the pressure drop inside the particulate filter by measuring the pressure upstream and downstream. When the pressure drop exceeds a threshold, it is considered that the particulate filter has accumulated a sufficient amount of soot and the periodic regeneration of the particulate filter is initiated.
• catalytic composition makes generally used for rare metals or their compounds, for example based on platinum or based on mixed oxides of cerium, zirconium and praseodymium, or based on a mixed oxide of zirconium and yttrium, such as that the oxide marketed by TOSOH Corporation under the trade name Tosoh TZ-8Y.
• the noble metals or rare earths necessary for the formulation of these catalytic compositions induce a significant additional cost of the manufacture of particulate filters, with a potential risk of difficulty of supply, particularly with regard to the rare earths.
• their effectiveness is still likely to improve, especially with oxides containing praseodymium, low efficiency at low temperatures, requiring long regenerations and significant fuel consumption.
• the invention therefore aims to improve the design of particulate filters. It aims in particular catalyzed filters with catalytic compositions which are more effective, in particular by becoming active at temperatures close to the temperatures of the exhaust gases under normal driving conditions.
• the invention firstly relates to a particulate filter comprising a porous ceramic filter substrate and a catalytic phase, such that the catalytic phase comprises a mixed oxide of zirconium and calcium.
• This type of oxide has indeed a double advantage. On the one hand, it does not contain any rare earth, no noble metal that can pose problems in terms of the cost of raw materials, in terms of supply and recycling.
• the mixed oxide according to the invention is preferably of formulation (Zr0 2 ) x (CaO) y, with x of between 80 and 95 mol%, especially between 85 and 90 mol%, and including between 5 and 20 mol%, especially between 10 and 15 mol%.
• its formulation is (Zr0 2 ) o, 875 (CaO) 0 , -i 25-
• This oxide is likely to contain other elements, especially in the form of trace or impurities.
• it contains only zirconium oxide and calcium (and possible impurities).
• the mixed oxide has a fluorite structure.
• the mixed oxide is of formulation (ZrO 2) x (CaO) y as explained above and its crystallographic structure fluorite has ionic conduction by O 2 ions greater than or equal to 10 3 mS / cm at 300 ° C., preferably greater than 10 -2 mS / cm at 300 ° C.
• This conductivity range makes it possible in fact to obtain in the oxide a mobility of oxygen sufficient to oxidize the soot accumulated in In this range, the oxide does indeed exhibit the desired fluorite structure.
• the particulate filter comprises a catalytic phase amount of between 20 g / liter and 250 g. / liter of particulate filter and preferably between 50 g / liter and 150 g / liter of particulate filter The volume is expressed in liters of the geometric volume of the filter.
• the ceramic substrate is selected from silicon carbide, alumina, aluminum titanate, cordierite, mullite, cordierite.
• the porous support of the filter comprises an inlet face and an outlet face, said support being provided with input channels connecting the two faces and closed in the output face, and output channels connecting the two faces and closed in front of the input.
• the filter according to the invention is able to begin to regenerate by combustion of the particles contained in said filter as soon as it reaches substantially at the inlet a temperature of at most 450 ° C, in particular at most 400 ° C, in particular at folds 350 to 370 ° C. It is understood by “begins to regenerate” by the fact that at the temperature considered gives at least 5% soot combustion in the filter.
• the invention also relates to an exhaust line of an internal combustion engine which comprises a particulate filter as described above.
• said exhaust line is such that the filter regenerates continuously at least partially, and in particular completely.
• FIG. 1 is a schematic representation of the internal structure of a particulate filter fitted to an exhaust line of an internal combustion engine of a motor vehicle;
• FIG. 2 is a graph representative of the activity of the catalytic phase of the invention on soot on powder
• FIG. 3 is a representative graph of the activity of the catalytic phase of the invention on particulate filter soot.
• Figure 1 shows schematically the internal structure known per se of a particle filter 1, filter to be mounted on an exhaust line of a thermal combustion engine.
• a particulate filter generally comprises a porous ceramic substrate or support having parallel channels 2. The latter are clogged alternately by ceramic plugs 3, so as to force the exhaust gas whose direction of flow is illustrated by the arrows 4 to enter through inlet channels 2a, then through the porous partition walls 5 to exit through the exhaust gas outlet channels 2b.
• the particulate filter 1 of the invention comprises a silicon carbide ceramic support and a catalytic phase based on mixed zirconium oxide and Calcium Calcium Formulation (Zr0 2 ) o, 875 (CaO) 0 , i25 ⁇
• This oxide may contain trace amounts of compounds such as Ti, Fe, Na, Cl, Si, Al.
• the catalytic phase is deposited on the surface of the porous dividing walls of the inlet channels at least by the forcing method still referred to as "slurry forcing method".
• slurry forcing method it is also possible to deposit the catalytic phase on the surface of the inlet channels of the filter, for example by adopting a so-called “deep-coating" method in a slip. This last variant is the preferred one. It is intended, after drying and calcination, a filter containing a mass of catalytic active phase per unit volume of particulate filter between 20 g / liter and 250 g / liter of particulate filter.
• the performance of the mixed oxide was evaluated on oxide powders placed in contact with a powdery mixture of soot using a comparative example.
• the catalytic performances of the mixed oxide powders are measured using the programmed temperature oxidation method. This consists of oxidizing the mixed oxide / soot mixture with gaseous oxygen.
• the soot used is a soot produced by a burner with the trade name CAST from a flame produced by a propane / air mixture.
• the burner CAST is a burner whose flame is cut in order to generate carbon particles.
• the intimate mixture of soot / mixed oxide (20 mg) is introduced into a U-quartz reactor placed in the oven and then under a flow containing 5% O 2 in helium (total flow rate: 8 L / h).
• the reactor is heated from room temperature to 750 ° C at a rate of 10 ° C / min.
• concentration of the resulting products (CO and CO 2 ) of the soot combustion is measured using a gas chromatograph (commercial name SRA 3000) and an infra-red analyzer (commercial name). HORIBA 3000).
• the conversion of soot is calculated from the concentrations of CO and CO 2 and is expressed as a function of temperature.
• Comparative Example 1 it is a yttria zirconia powder, with a molar percentage of yttrine in zirconia of 8%, sold by the company TOSOH corp. under the reference: Tosoh TZ-8Y.
• Example 2 of the invention it is an oxide powder (Zr0 2 ) o, 875 (CaO) 0 , i25 according to the invention.
• the powder was synthesized according to the principle of the Pechini method (described in US Pat. No. 3,330,697). This method consists of producing a gel by polyesterification of metal chelates heated in the presence of polyol.
• the metal precursors used in this synthesis are hydrated zirconyl (IV) nitrate for zirconium and calcium nitrate tetrahydrate for calcium.
• Anhydrous citric acid was used as a chelating agent and as an acid, and ethylene glycol dimethyl ether as a polyol.
• the metal nitrates are dissolved in distilled water with magnetic stirring.
• the citric acid is then added and the mixture is heated to 100 ° C. After homogenization for 15 minutes, the ethylene glycol dimethyl ether is added. After evaporation of the solvents, the resin thus formed is decomposed in an oven at 300 ° C. (heating rate 5 ° C./min, 2h stage).
• the black powder obtained is ground with the mortar and then calcined in an oven at 600 ° C. (heating rate 5 ° C./min, for 2 hours).
• Graph 2 compares the catalytic activities of the two powders on soot, representative of the catalytic activity of particle filters coated with compositions based on these oxides.
• the regenerations are monitored by measuring the decrease in the pressure drop between the outlet and the inlet of the filter.
• the abscissa of the graph represents the temperature in degrees Celsius, the ordinate represents, expressed in percentage, converting soot into C0 2 .
• Curve C1 corresponds to Comparative Example 1
• Curve C2 corresponds to Example 2 according to the invention.
• Example 2 according to the invention has an early catalytic activity (5% conversion of soot) to 370 ° C, while Example 1 comparatf reached this conversion threshold at a higher temperature of about 435 ° C.
• a threshold of conversion of 20% there is still a temperature difference favorable to the invention, with a temperature of about 465 ° C for the example according to the invention and a temperature of about 480 ° C for the comparative example .
• a conversion threshold of 50% which corresponds approximately to the point of inflection of the two curves
• the performance of a particle filter B according to the invention with respect to a particulate filter A of the prior art is then evaluated by tests described below.
• Filter A The particle filter A of the prior art is a filter whose ceramic support is silicon carbide, SiC, 400 cpsi (designating the number of channels per square inch) as described in document WO 2009 1 18814.
• the particle filter A does not comprise a catalytic phase deposited in the porosity of the ceramic support.
• Filter B In a preferred embodiment and in accordance with the invention, the particulate filter B of the invention comprises a silicon carbide ceramic support and a catalytic phase based on calcined zirconia, that is to say zirconia ZrO 2 containing calcium oxide of chemical formula CaO.
• the powder composition Zr 0 , 875Ca 0 , i25O 2 was synthesized Pechini using citric acid and ethylene glycol.
• the powder thus obtained is calcined in air at 700 ° C.
• the powder after calcination is composed of particles of nanometric size arranged in agglomerates of about 10 ⁇ .
• the catalytic phase is deposited in the porosity of the porous separating walls by a slip technique described by Cordier et al. [AT. Cordier, F. Rossignol, C. Lawrence, T. Chartier, A. Peigney, Appl. Catal. At Gen. 2007, 319, 7].
• a slurry is prepared by adding, with magnetic stirring, the calcined zirconia powder to an aqueous solution of PVA (polyvinyl acetate).
• the load (PVA) of this slurry is 15% by mass.
• the slip is homogenized with the three-dimensional mixer for 5 hours.
• the particulate filter is introduced into a glass bell in which a primary vacuum is produced.
• the slip is introduced with a funnel located in the upper part of the bell. The valve separating the funnel from the filter allows the viscous slip to flow into the filter using the pressure difference.
• the excess slurry is then removed under compressed air.
• the deposit is dried in the open air and then calcined in air at 700 ° C.
• the particulate filter B of the invention may contain an active phase mass per unit volume of particulate filter between 50g / liter and 500g / liter of particulate filter
• the amount of catalytic phase deposited in the particulate filter of the invention is between 80g / liter and 250 g / liter per liter of particulate filter. More preferably, as in this embodiment, the performance of which is evaluated below, the amount of catalytic phase deposited in the particulate filter B of the invention is fixed at 80 g of calcined zirconia per liter of filter. with particles.
• the performance of the particulate filters A and B are evaluated by following an evaluation protocol consisting of two phases:
• regeneration means that the carbonaceous particles contained in the filter burn up as soon as the inlet temperature of the gases in the filter reaches a critical threshold. A release of CO 2 resulting from the combustion of the carbon of the soot makes it possible follow the regeneration process according to the inlet gas temperature in the filter.
• a 1 inch per inch particle filter core comprising a gas inlet face and a gas outlet face is installed downstream of a CAST trademark burner.
• the CAST is a burner whose flame is cut in order to generate carbon particles.
• the flame is generated from the combustion of propane.
• the size of the particles can be adjusted by varying the oxidant / fuel mixture, which has the effect of changing the height of the flame. This is cut by an inert gas such as nitrogen at a variable height.
• a stream of oxygen (5 vol% diluted in nitrogen) of 8 liters / hr passes through the cores of the filters A and B.
• the gas temperature measured on the inlet face of the filters.
• the temperature is then linearly increased up to 725 ° C with a ramp of 10 ° C / min.
• the production of CO 2 from the combustion of soot is analyzed using an infra-red analyzer.
• FIG. 3 shows, in the form of a diagram, the evolution of the production rate of CO 2 as a function of the temperature of the gases entering the A particle filter core of the prior art and of the B core. coated with the composition according to the invention.
• abscissa is represented the temperature in ° C.
• FIG. 3 shows that CO 2 emission downstream is observed by core B at about 350 ° C., which is mainly due to the carbonate composition.
• Figure 3 shows that the rate of CO 2 production related to the soot burning rate stored in the incoming channels of the filters is always higher on the core B of the present invention.
• the production rate of CO 2 is more than two times greater, passing from 0.04 ⁇ / ⁇ for core A to 0.1 ⁇ / ⁇ for core B.
• the maximum C02 production temperature is 20 ° C lower on core B.
• the catalytic phase based on calcined zirconia is deposited on the surface of the gas inlet channels of the particle filter, according to a method known per se impregnation with a liquid composition by immersion in a phase appropriate liquid and then drying.
• the invention has the advantage of providing an effective catalytic particle filter and not containing noble metals such as platinum, palladium or rhodium.

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• Chemical Kinetics & Catalysis (AREA)
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• Organic Chemistry (AREA)
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• Combustion & Propulsion (AREA)
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• 2013
  • 2013-03-22 FR FR1352588A patent/FR3003478B1/fr active Active
• 2014
  • 2014-03-20 EP EP14716900.7A patent/EP2976148A1/de not_active Withdrawn
  • 2014-03-20 WO PCT/FR2014/050651 patent/WO2014147350A1/fr active Application Filing

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