EP2307123A1 - Texturierter partikelfilter für katalytische anwendungen - Google Patents

Texturierter partikelfilter für katalytische anwendungen

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Publication number
EP2307123A1
EP2307123A1 EP09737072A EP09737072A EP2307123A1 EP 2307123 A1 EP2307123 A1 EP 2307123A1 EP 09737072 A EP09737072 A EP 09737072A EP 09737072 A EP09737072 A EP 09737072A EP 2307123 A1 EP2307123 A1 EP 2307123A1
Authority
EP
European Patent Office
Prior art keywords
grains
filter
grain boundaries
texturizing material
texturizing
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
EP09737072A
Other languages
English (en)
French (fr)
Inventor
Damien Philippe Mey
Daniel Aubert
Patrice Signoret
William Pierre Michel Mustel
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Saint Gobain Centre de Recherche et dEtudes Europeen SAS
Original Assignee
Saint Gobain Centre de Recherche et dEtudes Europeen SAS
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Saint Gobain Centre de Recherche et dEtudes Europeen SAS filed Critical Saint Gobain Centre de Recherche et dEtudes Europeen SAS
Publication of EP2307123A1 publication Critical patent/EP2307123A1/de
Withdrawn legal-status Critical Current

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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D39/00—Filtering material for liquid or gaseous fluids
    • B01D39/14—Other self-supporting filtering material ; Other filtering material
    • B01D39/20—Other self-supporting filtering material ; Other filtering material of inorganic material, e.g. asbestos paper, metallic filtering material of non-woven wires
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D39/00—Filtering material for liquid or gaseous fluids
    • B01D39/14—Other self-supporting filtering material ; Other filtering material
    • B01D39/20—Other self-supporting filtering material ; Other filtering material of inorganic material, e.g. asbestos paper, metallic filtering material of non-woven wires
    • B01D39/2068—Other inorganic materials, e.g. ceramics
    • B01D39/2072—Other inorganic materials, e.g. ceramics the material being particulate or granular
    • B01D39/2075—Other inorganic materials, e.g. ceramics the material being particulate or granular sintered or bonded by inorganic agents
    • 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
    • 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
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    • 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
    • B01J37/00—Processes, in general, for preparing catalysts; Processes, in general, for activation of catalysts
    • B01J37/02—Impregnation, coating or precipitation
    • 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
    • B01J37/02—Impregnation, coating or precipitation
    • B01J37/0201—Impregnation
    • B01J37/0207—Pretreatment of the support
    • 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
    • B01J37/024—Multiple impregnation or coating
    • B01J37/0242—Coating followed by impregnation
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    • C04B35/00—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products
    • C04B35/01—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products based on oxide ceramics
    • C04B35/46—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products based on oxide ceramics based on titanium oxides or titanates
    • C04B35/462—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products based on oxide ceramics based on titanium oxides or titanates based on titanates
    • C04B35/478—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products based on oxide ceramics based on titanium oxides or titanates based on titanates based on aluminium titanates
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    • C04B35/00—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products
    • C04B35/515—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products based on non-oxide ceramics
    • C04B35/56—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products based on non-oxide ceramics based on carbides or oxycarbides
    • C04B35/565—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products based on non-oxide ceramics based on carbides or oxycarbides based on silicon carbide
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    • C04B38/00—Porous mortars, concrete, artificial stone or ceramic ware; Preparation thereof
    • C04B38/0006—Honeycomb structures
    • 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
    • F01N3/022—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 characterised by specially adapted filtering structure, e.g. honeycomb, mesh or fibrous
    • 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
    • F01N3/022—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 characterised by specially adapted filtering structure, e.g. honeycomb, mesh or fibrous
    • F01N3/0222—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 characterised by specially adapted filtering structure, e.g. honeycomb, mesh or fibrous the structure being monolithic, e.g. honeycombs
    • 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
    • B01D2255/102—Platinum group metals
    • B01D2255/1021—Platinum
    • 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
    • B01D2255/102—Platinum group metals
    • B01D2255/1023—Palladium
    • 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
    • B01D2255/102—Platinum group metals
    • B01D2255/1025—Rhodium
    • 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
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D2255/00—Catalysts
    • B01D2255/90—Physical characteristics of catalysts
    • B01D2255/92—Dimensions
    • B01D2255/9202—Linear dimensions
    • 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
    • B01D—SEPARATION
    • B01D2258/00—Sources of waste gases
    • B01D2258/01—Engine exhaust gases
    • B01D2258/014—Stoichiometric gasoline engines
    • C—CHEMISTRY; METALLURGY
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    • C04B2111/00—Mortars, concrete or artificial stone or mixtures to prepare them, characterised by specific function, property or use
    • C04B2111/00474—Uses not provided for elsewhere in C04B2111/00
    • C04B2111/00793—Uses not provided for elsewhere in C04B2111/00 as filters or diaphragms
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    • 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
    • C04B2111/00—Mortars, concrete or artificial stone or mixtures to prepare them, characterised by specific function, property or use
    • C04B2111/00474—Uses not provided for elsewhere in C04B2111/00
    • C04B2111/0081—Uses not provided for elsewhere in C04B2111/00 as catalysts or catalyst carriers
    • C—CHEMISTRY; METALLURGY
    • C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
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    • C04B2235/00—Aspects relating to ceramic starting mixtures or sintered ceramic products
    • C04B2235/02—Composition of constituents of the starting material or of secondary phases of the final product
    • C04B2235/50—Constituents or additives of the starting mixture chosen for their shape or used because of their shape or their physical appearance
    • C04B2235/54—Particle size related information
    • C04B2235/5418—Particle size related information expressed by the size of the particles or aggregates thereof
    • C04B2235/5436—Particle size related information expressed by the size of the particles or aggregates thereof micrometer sized, i.e. from 1 to 100 micron
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    • C04B2235/5445—Particle size related information expressed by the size of the particles or aggregates thereof submicron sized, i.e. from 0,1 to 1 micron
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    • C04B2235/00—Aspects relating to ceramic starting mixtures or sintered ceramic products
    • C04B2235/02—Composition of constituents of the starting material or of secondary phases of the final product
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    • C04B2235/5463—Particle size distributions
    • C04B2235/5472—Bimodal, multi-modal or multi-fraction
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    • C04B2235/00—Aspects relating to ceramic starting mixtures or sintered ceramic products
    • C04B2235/65—Aspects relating to heat treatments of ceramic bodies such as green ceramics or pre-sintered ceramics, e.g. burning, sintering or melting processes
    • C04B2235/656—Aspects relating to heat treatments of ceramic bodies such as green ceramics or pre-sintered ceramics, e.g. burning, sintering or melting processes characterised by specific heating conditions during heat treatment
    • C04B2235/6562—Heating rate
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    • C04B2235/656—Aspects relating to heat treatments of ceramic bodies such as green ceramics or pre-sintered ceramics, e.g. burning, sintering or melting processes characterised by specific heating conditions during heat treatment
    • C04B2235/6567—Treatment time
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    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
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    • 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
    • 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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    • Y02T10/10—Internal combustion engine [ICE] based vehicles
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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
    • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
    • Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
    • Y10T428/00—Stock material or miscellaneous articles
    • Y10T428/24—Structurally defined web or sheet [e.g., overall dimension, etc.]
    • Y10T428/24149—Honeycomb-like

Definitions

  • the present invention relates to the field of porous filter materials. More particularly, the invention relates to typically honeycomb structures that can be used for the filtration of solid particles contained in the exhaust gases of a diesel engine or gasoline and additionally incorporating a catalytic component that jointly enables the elimination of polluting gases of the type NO x , carbon monoxide CO or unburned hydrocarbons HC.
  • Filters for the treatment of gases and the removal of soot typically from a diesel engine are well known in the prior art. These structures most often have a honeycomb structure, one of the faces of the structure allowing the admission of the exhaust gas to be treated and the other side the evacuation of the treated exhaust gas.
  • the structure comprises, between these intake and discharge faces, a set of adjacent ducts or channels, most often of square section, with axes parallel to each other separated by porous walls.
  • the ducts are closed at one or the other of their ends to delimit inlet chambers opening on the inlet face and outlet chambers opening along the discharge face.
  • the channels are alternately closed in an order such that the exhaust gases, during the crossing of the honeycomb body, are forced to pass through the sidewalls of the inlet channels to join the outlet channels.
  • the filters according to the invention have a matrix of an inorganic material, preferably ceramic, chosen for its ability to form a structure with porous walls and for acceptable thermomechanical resistance for application as a particulate filter in an automobile exhaust system.
  • a material is typically based on silicon carbide (SiC), in particular recrystallized silicon carbide, or based on aluminum titanate.
  • SiC silicon carbide
  • the increase in porosity and in particular the average pore size is generally sought for catalytic filtration gas treatment applications. Such an increase makes it possible to limit the pressure drop caused by the positioning of a particulate filter as previously described in an automobile exhaust line.
  • pressure loss is meant the gas pressure difference existing between the inlet and the outlet of the filter.
  • this increase in porosity finds its limits with the associated decrease in thermomechanical strength properties of the filter, especially when it is subjected to successive phases of accumulation of soot particles and regeneration, that is to say say soot removal by their combustion within the filter.
  • the filter can be raised to average inlet temperatures of the order of 600 to 700 ° C., while local temperatures of more than 1000 ° C. can be reached.
  • These hot spots are all defects that are likely over the life of the filter to alter its performance or to disable its catalytic function.
  • At very high porosity levels, for example greater than 70% it has notably been observed on silicon carbide filters. a sharp decrease in thermomechanical resistance properties.
  • the greater thickness of the catalyst deposit can lead to a lower catalytic efficiency as mentioned in US2007 / 0049492 (paragraph [005]) which can result from a bad distribution of the active sites, that is to say say sites sites of the catalyzed reaction, making them less accessible to the gases to be treated.
  • This has a significant impact on the initiation temperature of the catalytic reaction and consequently on the activation time of the catalyzed filter, that is to say on the time required for the cold filter to reach a temperature permitting effective treatment of pollutants.
  • the integration of a catalytic component in a particle filter also poses the following problems: the adhesion of the impregnating solution on the substrate porous must be as uniform and homogeneous as possible but also allow to fix a large amount of catalytic solution. This problem is more critical on matrices in the form of grains bonded to each other and whose surface is relatively smooth and / or convex, including SiC based matrices.
  • the catalytic coating deposited in the porosity of the walls of the filter must be sufficiently stable over time, that is to say that the activity
  • the catalytic converter must remain acceptable throughout the life of the filter, within the meaning of the current and future anti-pollution standards.
  • the solution adopted is to impregnate a larger amount of catalyst solution and therefore noble metals, in order to compensate for the loss of catalytic activity in the filter. time as described in JP2006 / 341201.
  • This solution leads not only to increase the pressure drop, as mentioned above, but also the cost of the process, due to the necessarily greater use of noble metals. The problem therefore still remains to limit the aging of the catalyst to ensure the stability of its performance.
  • the object of the present invention is to provide an improved solution to all of the previously discussed problems.
  • one of the objects of the present invention is to provide a porous filter suitable for application as a particulate filter in an automobile exhaust line, which is subjected to successive stages of accumulation and combustion of soot, and having a catalytic component whose effectiveness is enhanced.
  • the catalytic filters according to the invention can have a catalytic charge substantially greater than current filters.
  • the catalytic filters according to the invention may have a better homogeneity, that is to say a more uniform distribution of the catalytic charge in the porous matrix.
  • Such an increase and / or the better homogeneity of the catalytic charge notably makes it possible to appreciably improve the treatment efficiency of the polluting gases without a joint increase in the pressure drop generated by the filter.
  • the invention thus makes it possible in particular to obtain porous structures having thermomechanical properties that are acceptable for the application and a catalytic efficiency that is substantially increased throughout the lifetime of the filter.
  • Another object of the present invention is to obtain catalyzed filters having a better resistance to aging, as previously described.
  • the subject of the invention is a catalytic filter for the treatment of solid particles and gaseous pollutants resulting from the combustion gases of an internal combustion engine, comprising a porous matrix forming a set of longitudinal channels separated by walls.
  • porous filtering agents based on or consisting of silicon carbide or aluminum titanate in the form of grains connected to one another.
  • the filter is characterized in that: - said grains and grain boundaries of said porous filtering walls are covered on at least 70% of their surface with a texturizing material, said texturing consisting of irregularities whose dimensions are between 10 nm and 5 micrometers, a catalytic coating at least partially covers said texturizing material and optionally, at least partially, the grains of said porous filtering walls.
  • the texturizing material advantageously covers at least 80% or 90% or even 95% of the total surface area of the grains and grain boundaries of the porous filtering walls. This very large coverage and better distribution between the surface of the grains and that of the grain boundaries further improves the catalytic efficiency, without penalizing the pressure drop of the filter. This greater coverage also makes it possible to avoid to a large extent the detachment of the texturizing material from the surface of the filtering walls during the thermal cycles accompanying the use of the filter, in particular the regeneration cycles.
  • a bonding layer is advantageously formed at the interface between the texturizing material and the grains and grain boundaries of the filtering walls.
  • This bonding layer preferably has one or more of the following advantageous features: the bonding layer preferably has a chemical composition different from the composition of the grains and grain boundaries of the filtering walls and the composition of the texturizing material.
  • the bonding layer may in particular be materialized by a composition gradient between the composition of the grains and grain boundaries of the filtering walls and the composition of the texturizing material.
  • the binding layer is preferably obtained by a chemical oxidation reaction, in particular due to a thermal oxidation treatment under an oxidizing atmosphere at a temperature of between 900 and 1500 ° C., in particular between 1000 and 1400 ° C., even more preferred between 1100 and 1300 0 C.
  • This oxidation thermal treatment is described in more detail in the rest of the text.
  • the tie layer preferably comprises at least
  • silica 25% by weight, especially 50% and even 80% by weight, of silica. It will for example be obtained by an oxidation reaction of SiC grains, optionally coupled to a chemical reaction with the texturizing material.
  • this bonding layer makes it possible to improve the adhesion between the grains and grain boundaries on the one hand and the texturizing material on the other hand. It is thus possible to avoid any detachment of the texturizing material during the life of the filter.
  • the porous walls consist of grains connected to each other so as to form between them cavities such that the open porosity is between 30 and 70% and the median pore diameter of between 5 and 40 microns.
  • the texturizing material is generally inorganic in nature. It can be totally or partially crystallized, or totally or partially vitreous. It is preferably ceramic. Its thermal stability is preferably at least equal to that of alumina which is generally the main constituent of the catalytic coating.
  • the texturizing material is preferably constituted by aluminosilicates. These aluminosilicates can be defined compounds, perfectly crystallized, but are most often mixtures of different crystalline phases (such as mullite) and vitreous phases often siliceous.
  • the texturizing material is composed or consists of mullite crystallites in a predominantly amorphous siliceous phase. Mullite has the advantage of having a coefficient of thermal expansion close to that of silicon carbide.
  • the irregularities may consist of crystallites or clusters of crystallites of a material fired or sintered on the surface of the grains and grain boundaries of the porous walls.
  • the irregularities may for example consist essentially of beads of an oxide such as alumina, silica, magnesia or iron oxide.
  • the irregularities may also be in the form of craters dug in a material such as silica or alumina, said material being baked or sintered on the surface of the grains of the porous matrix.
  • the irregularities forming the texturing preferably have one or more of the following advantageous characteristics: the irregularities may be in the form of rods or acicular or globular structures, recesses or craters, the said irregularities preferably having a mean equivalent diameter of between about 10 nm and about 5 micrometers, especially between 100 nm and 2.5 micrometers and / or an average height h or a mean depth p between about 10 nm and about 5 micrometers, especially between 100 nm and 2.5 micrometers.
  • the average equivalent diameter d and / or the height h or the average depth p of the irregularities are preferably smaller than the average grain size of the inorganic material constituting the matrix by a factor of between 1/2 and 1/1000, especially between 1/5 and 1/100.
  • the irregularities preferably have a size distribution (equivalent diameters, heights or depths) such that at least 80% of the dimensions are greater than or equal to half the median dimension and less than or equal to twice that median dimension. This texturing homogeneity is remarkable, and results in the formation of a more homogeneous catalytic deposit and consequently a higher catalytic activity.
  • mean diameter d it is understood in the sense of the present description the mean diameter of the irregularities, these being individually defined from the plane tangent to the surface of the grain or grain joint on which they are located.
  • average height h it is understood in the sense of the present description the average distance between the top of the relief formed by the texturing and the plane mentioned above.
  • average depth p it is understood in the sense of the present description the average distance between on the one hand the deepest point formed by the impression, for example the trough or the crater of the texturing and on the other hand the plane cited previously.
  • the invention also relates to methods specially designed for obtaining the filter according to the invention.
  • the process comprises the following steps: preparation of a paste comprising grains and ceramic powders, - shaping of the dough, drying and baking,
  • the deposition of the texturizing material may in particular be obtained by the application of a suspension of said texturizing material or of one of its precursors to the surface of the grains and grain boundaries, which may or may not be followed by a heat treatment cooking or sintering.
  • the suspension may be a slip comprising a powder or a mixture of powders in a liquid such as water.
  • the powders are generally inorganic in nature, preferably ceramic. They preferably comprise oxides of silicon and aluminum, and may for example be alumina silicates, especially synthetic or natural aluminosilicates, such as andalusite (for example of the kerphalite or purusite type), cyanite (calcined or not). ), or possibly sillimanite, or a mixture of these different minerals.
  • the deposition of the texturizing material may also be obtained by the application of a sol or a gel (sol-gel solution) comprising in particular a filler in the form of inorganic particles, followed by a heat treatment calcination or by the application of a sol or gel (sol-gel solution) comprising a filler in the form of beads or organic particles, followed by a thermal calcination treatment.
  • a sol or a gel sol-gel solution
  • sol or gel sol-gel solution
  • the sol-gel solution may for example be a sol of silica and / or alumina, preferably an alumina sol.
  • the sol, in particular alumina may comprise fillers in the form of oxide particles, such as iron or magnesium oxide, or alumina silicates.
  • the alumina silicate may be in particular a synthetic or natural aluminosilicate, such as an andalusite (for example of the kerphalite or purusite type), a cyanite (calcined or no), or possibly sillimanite or a mixture of these different minerals.
  • the suspension, the sol or the gel may further contain additives chosen from: at least one dispersant (for example an acrylic resin or an amine derivative), at least one binder of organic nature (for example an acrylic resin or a cellulose derivative) or even of mineral nature (clay), at least one wetting or film-forming agent
  • PVA polyvinyl alcohol at least one porogen (for example polymers such as latex or polymethylmethacrylate).
  • porogen for example polymers such as latex or polymethylmethacrylate.
  • the oxidation thermal treatment is preferably carried out at a temperature of between 1100 and 1400 ° C., in particular between 1100 ° C. and 1300 ° C.
  • This thermal oxidation treatment makes it possible to considerably increase the surface covered by the texturizing material as well as the homogeneity of the latter.
  • it advantageously makes it possible to form a bonding layer at the interface between the grains and grain boundaries of the filtering walls and the texturizing material.
  • the textured surface obtained has large irregularities over a large part of the surface of the grains and grain boundaries. The catalytic activity of the filter is thus improved, as is the adhesion between the filtering walls and the texturizing material.
  • An oxidation heat treatment temperature that is too low does not provide a coverage area by the texturizing material that is sufficient. At too high a temperature, however, a crystallized silica phase, in particular cristobalite, may appear, reducing the thermal shock resistance of the filter.
  • the oxidation thermal treatment generally comprises a rise in temperature followed by a step carried out at the actual processing temperature. The duration of the stage is preferably between 0.5 and 10 hours. The rate of rise in temperature before reaching the treatment temperature is typically between 20 and 500 ° C / hour.
  • the method comprises the following steps: preparation of a paste comprising grains and ceramic powders and at least one precursor of a texturizing material,
  • the paste is generally obtained in a known manner by mixing water with a mixture of ceramic powders, in particular silicon carbide. After mixing, the dough is shaped by extrusion. Cooking, generally at more than 2000 ° C. under a neutral atmosphere (in the case of silicon carbide), makes it possible to obtain the filter.
  • the precursor of the texturizing material preferably comprises aluminum and / or silicon in the form of metal, oxide, nitride or oxynitride, or any of their mixtures, solid solutions or alloys. For example, oxynitrides of silicon and aluminum from SiAlON type or SiAl metal alloys. It may also be optionally hydrated alumina or aluminum nitride.
  • the precursor of the texturizing material may also be a silicate of alumina, synthetic or natural, such as andalusite (especially of the kerphalite or purusite type), cyanite (calcined or not) or possibly sillimanite or a mixture comprising these various minerals.
  • the precursor of the texturizing material preferably has a median diameter of between 0.01 and 5 microns, especially between 0.05 and 3 microns.
  • the firing when carried out under a very high temperature neutral atmosphere, generally more than 2000 ° C., as in the case of silicon carbide, does not reveal the presence of the precursor and generates no texturing. The latter is only revealed after oxidation treatment, by the creation of the texturizing material. It appears that the oxidative treatment has the effect of migrating the precursor to the surface of grains and grain boundaries, where it chemically reacts with them to form a very characteristic texturizing material.
  • the oxidation thermal treatment is preferably carried out at a temperature of between 1000 and 1400 ° C., in particular between 0 ° C. and 1300 ° C.
  • the oxidation heat treatment is generally carried out in a separate step of cooking. This is particularly the case for silicon carbide filters, for which the firing must be carried out under a neutral atmosphere. However, it is possible to carry out the thermal oxidation treatment during the temperature reduction following cooking. Alternatively, the Oxidation heat treatment can be implemented during cooking. This may be the case for aluminum titanate filters, which are generally fired under an oxidizing atmosphere, in the temperature range of the treatment according to the invention.
  • the oxidative heat treatment forms a texturizing material covering a large part of the surface of the grains and grain boundaries.
  • the heat treatment advantageously makes it possible to create a bonding layer as defined above.
  • the textured surface obtained by this treatment has strong irregularities over a large part of the surface of the grains and grain boundaries.
  • the catalytic activity of the filter is thus improved, as is the adhesion between the filtering walls and the texturizing material.
  • the oxidation thermal treatment generally comprises a rise in temperature followed by a step carried out at the actual processing temperature.
  • the duration of the stage is preferably between 0.5 and 10 hours.
  • the rate of rise in temperature before reaching the treatment temperature is typically between 20 and 500 ° C / hour.
  • the common points between the two embodiments of the method according to the invention are therefore on the one hand the introduction of a texturizing material or one of its precursors (after shaping and baking the filter in the first mode embodiment, or before shaping and baking in the second embodiment), and other part final oxidation treatment between 900 and 1500 0 C or between 1100 and 1500 0 C after cooking.
  • This oxidation treatment makes it possible, as indicated above, to increase very significantly the coverage of grains and grain boundaries by the texturizing material, and generally makes it possible to create a particularly advantageous bonding layer in terms of adhesion of the material. texturing.
  • the oxidation treatment after deposition of the texturizing material or addition of a precursor of this material made it possible to considerably increase the mechanical strength of the filter, in particular its resistance to bending.
  • the oxidizing gas partial pressure during the oxidation thermal treatment may be adapted to result in passive or active oxidation.
  • a catalytic coating is defined as a coating comprising an inorganic support material of high specific surface area (typically of the order of 10 to 100 m 2 / g) ensuring the dispersion and the stabilization of an active phase, such as metals, which are generally noble, acting as catalytic centers proper for oxidation or reduction reactions.
  • the active phase may catalyze the conversion of gaseous pollutants, ie mainly carbon monoxide (CO) and unburnt hydrocarbons and nitrogen oxides (NO x), into less harmful gases such as nitrogen gas (N 2 ) or carbon dioxide (CO 2 ) and / or facilitate the combustion of soot stored on the filter.
  • the catalyst therefore comprises at least one support material and at least one active phase.
  • the support material is typically based on oxides, more particularly on alumina or silica, or other oxides, for example based on ceria, zirconia or titanium oxide, or even mixtures of these different mixtures. oxides.
  • the size of the support material particles constituting the catalytic coating on which the catalytic metal particles are arranged is of the order of a few nanometers to a few tens or exceptionally a few hundred nanometers.
  • the catalytic coating is typically obtained by impregnating a solution comprising the catalyst, in the form of the support material or its precursors and an active phase or a precursor of the active phase.
  • the precursors used are in the form of salts or organic or inorganic compounds, dissolved or suspended in an aqueous or organic solution.
  • the impregnation is followed by a heat treatment aimed at obtaining the final deposition of a solid and catalytically active phase in the porosity of the filter.
  • the cost of the deposited catalysts which most often contain platinum group precious metals (Pt, Pd, Rh) as an active phase on an oxide support, represents a significant part of the overall cost of the process. impregnation. For the sake of economy, it is therefore important that the catalyst is deposited in the most uniform manner possible, so as to be easily accessible by the gaseous reactants.
  • platinum group precious metals Pt, Pd, Rh
  • the invention finally relates to an intermediate structure for obtaining a catalytic filter according to the invention.
  • This intermediate structure corresponds to the filter before any deposit of a catalytic coating.
  • the intermediate structure according to the invention comprises a porous matrix based on or consisting of silicon carbide or aluminum titanate, in the form of grains connected to each other, said grains and grain boundaries being covered by at least 70% of their surface of a texturing material as defined above.
  • a tie layer is formed at the interface between the texturizing material and the grains and grain boundaries of the filter walls.
  • the preferred features of the tie layer are detailed above.
  • FIGS. 1 to 6 are photographs taken using a scanning electron microscope (SEM) of the filter walls of the following examples.
  • an SiC-based catalytic filter is typically synthesized.
  • Mixture was initially 70 wt% of an SiC powder whose grains have a median diameter d 5 o of 10 micrometer with a second SiC powder whose grains have a median diameter d 5 o of 0.5 micrometer , in a first mode comparable to the mixture of powders described in the application EP 1 142 619.
  • the median pore diameter d 5 o denotes the diameter of the particles such that respectively 50% of the total population of grain has a size less than or equal to this diameter.
  • a porogen of the polyethylene type in an equal proportion at 5% by weight of the total weight of the SiC grains and a methylcellulose type shaping additive in a proportion equal to 10% by weight of the total weight of the SiC grains.
  • the green microwaved monoliths are then dried for a time sufficient to bring the water content not chemically bound to less than 1% by weight.
  • each face of the monolith are alternately plugged according to well-known techniques, for example described in application WO2004 / 065088.
  • the monolith is then baked under argon with a rise in temperature of 20 ° C./hour until a maximum temperature of 2200 ° C. is reached which is maintained for 6 hours.
  • a crude SiC filtering structure is thus obtained.
  • the filtering walls of the filter consist of a matrix of SiC grains with a smooth surface and interconnected by grain boundaries, the porosity of the material being ensured by the cavities formed between the grains.
  • the raw structure obtained according to Example C1 was then subjected to a first texturing treatment, the material used for the texturing being introduced into the porosity of the filter in the form of an SiC-based slip.
  • the slurry comprises, as a percentage by weight, 96% of water, 0.1% of nonionic type dispersant, 1.0% of a PVA type binder (polyvinyl alcohol) and 2.8% of a
  • SiC with a median diameter of 0.5 ⁇ m whose purity is greater than 98% by weight.
  • the slip is prepared according to the following steps:
  • the PVA used as a binder, is firstly dissolved in water heated to 80 ° C. In a stirred tank containing the PVA dissolved in water, the dispersant and then the SiC powder are introduced. to obtain a homogeneous suspension.
  • the slip is deposited in the filter by simple immersion, the excess of the suspension being removed by suction under vacuum, under a residual pressure of 10 mbar.
  • the monoliths thus obtained are subjected to a drying step at 120 ° C. for 16 hours and then to a treatment thermal sintering at 1700 0 C under argon for 3h.
  • This treatment under a neutral atmosphere does not allow, unlike the treatment according to the invention, to obtain a high coverage of the surface of the grains and grain boundaries and to form a bonding layer.
  • FIG. 2 is a photograph of the filtering walls of the texture filter thus obtained, showing the irregularities at the surface of the SiC grains constituting the porous matrix.
  • the irregularities are in this example in the form of crystallites and clusters of SiC crystallites.
  • the area covered by the texturizing material is relatively small.
  • the parameter d measured corresponds to the mean diameter, in the sense previously described, of the crystallites present on the surface of the grains of SiC.
  • the parameter h corresponds to the average height h of said crystallites.
  • Example 3 the crude structure obtained according to Example C1 was subjected to another texturing treatment.
  • the texturizing material is introduced into the porosity of the filter in the form of an alumina sol marketed by Sasol under the reference Disperal®.
  • This sol of a pH of the order of 2, comprises 5% by weight of boehmite in an aqueous solution of nitric acid.
  • the monolith is impregnated with alumina sol by simple immersion, the excess being removed by suction under vacuum, under a residual pressure of 10 mbar.
  • the monolith is then subjected to a calcination heat treatment of 500 ° C. under air for two hours and then to an oxidation thermal treatment in air at 1200 ° C. for 4 hours. for reacting the deposition of alumina with the SiC substrate.
  • Figures 3a and b show that the texturing is obtained in the form of acicular or globular structures.
  • These irregularities are composed of crystallites of aluminosilicates, in particular mullite, in a mainly amorphous siliceous phase: this attests to the chemical reaction between the deposited alumina and the silica resulting from the oxidation of the substrate. Between these irregularities and grains was formed a thin layer very rich in silica from the oxidation of grains and grain boundaries as shown in Figures 3 a and b.
  • the irregularities have on the surface of the grains an average height h of 0.7 ⁇ m and an average diameter d of 2.0 ⁇ m, which respectively correspond to the diameter and the length of the rods observed in Figure 3b.
  • the irregularities also have an average depth p of 0.7 ⁇ m.
  • Irregularities cover almost the entire surface of grains and grain boundaries.
  • the coverage of the surface by the texturizing material can be estimated to be greater than 95%.
  • Comparative example C3 is distinguished from Example 3 only in that it has not undergone the heat treatment of oxidation under air at 1200 ° C.
  • Example 1 the crude structure obtained according to Example 1 was impregnated with a magnesia-loaded alumina sol (MgO) at a weight of 5% relative to the amount of alumina, and in oxide
  • MgO magnesia-loaded alumina sol
  • Iron Fe2O3 with a weight contribution of 5% relative to the amount of alumina. Magnesia was brought in the form of hydrate. Iron oxide is brought in powder form sold under the name CRM 50 by the company Rana Gruber. The purity of the iron oxide is of the order of 97% and the median diameter is of the order of 0.6 micrometer.
  • the monolith thus obtained underwent the same thermal oxidation treatment as that according to Example 3.
  • Figures 4a and b show that the texturing obtained is in the form of globular and acicular structures. These irregularities are composed of crystallites of aluminosilicates, in a siliceous phase mainly amorphous. Between these irregularities and the grains was formed a thin layer very rich in silica resulting from the oxidation of grains and grain boundaries.
  • Comparative example C4 differs from Example 4 only in that it has not undergone the heat treatment of oxidation under air at 1200 ° C.
  • the crude structure was obtained according to Example C1 except that a precursor of the texturizing material is added to the mixture of SiC powders.
  • the precursor of the texturizing material is reactive alumina in the form of a powder having a median diameter of approximately 0.8 ⁇ m, sold under the reference CT3000SG by the company Almatis.
  • the added content is 2% by weight, based on the amount of silicon carbide powders.
  • the monoliths were then subjected to an oxidation thermal treatment at 1200 ° C. under air for 4 hours.
  • FIG. 5b shows that the texturization obtained by this heat treatment of oxidation has a globular structure.
  • the irregularities are composed of crystallites of aluminosilicates, in particular mullite, in a mainly amorphous siliceous phase. Between these irregularities and the grains was formed a thin layer very rich in silica resulting from the oxidation of grains and grain boundaries.
  • Comparative example C5 differs from Example 5 only in that it has not undergone the heat treatment of oxidation under air at 1200 ° C. Comparative example C5 is therefore illustrated by FIG. 5a. .
  • Examples 6 (according to the invention) and C6 (comparative): Unlike the previous example 5, the precursor of the texturizing material is aluminum nitride. 2% of an aluminum nitride (AlN) powder having a median diameter of 2.5 ⁇ m was added to the extrusion mixture instead of the alumina powder. Monoliths are carried out according to the same method as that described in Example 5.
  • AlN aluminum nitride
  • FIG. 6 b shows that the texturization obtained by virtue of the heat treatment of oxidation has a very characteristic globular structure. These irregularities are composed of about 2% alumina in a siliceous phase. Between these irregularities and the grains was formed a thin layer very rich in silica resulting from the oxidation of grains and grain boundaries.
  • Comparative example C6 is distinguished from Example 6 only in that it has not undergone the heat treatment of oxidation in air at 1200 ° C. It is thus illustrated by FIG. 6a.
  • A- Mass input when adding the texturing element or its precursor The weight gain due to the deposition of the texturizing material or the addition of its precursor was measured for each monolith before oxidation thermal treatment and relative to the weight of the reference monolith. This weighting corresponds to the amount of texturing agent involved.
  • the bound weight gain was measured on each monolith after heat treatment of oxidation and relative to the weight of the monolith before this heat treatment.
  • the open porosity was determined according to conventional high-pressure mercury porosimetry techniques, using a porosimeter of the Micromeritics 9500 type.
  • the flexural strength was measured at ambient temperature according to ISO 5014, by 3-point bending with a 40 mm center distance and a punch down speed of 0.4 mm / min.
  • the samples are strips that are fired and extruded at the same time as the monoliths, the dimensions of which are 60 * 6 * 8 mm 3 .
  • the monoliths were subjected to an impregnation treatment with a catalytic solution, according to the following experimental protocol.
  • the monolith is immersed in a bath of an aqueous solution containing the appropriate proportions of a platinum precursor in the form of H 2 PtCl 3, a precursor of cerium oxide CeO 2 (in the form of cerium nitrate) and a precursor of zirconium oxide ZrO 2 (in the form of zirconyl nitrate) according to the principles described in the publication EP 1 338 322 A1.
  • the monolith is impregnated with the solution according to an embodiment similar to that described in US Pat. No. 5,866,210.
  • the load in impregnation solution reported in Table 3 corresponds to the amount of impregnation solution (in grams) relative to the impregnated filter volume (in liters).
  • the monolith is then dried at about 150 0 C and then calcined at a temperature of about 500 0 C.
  • the test was performed on samples of about 25 cm 3 cut in a monolith.
  • the monoliths are previously impregnated with catalyst as described in paragraph E and then placed in an oven at 800 ° C. under a moist air atmosphere for a period of time. 5 hours.
  • the humidity of the air is such that the molar concentration of water is kept constant at 3%.
  • the CO conversion rate at 420 ° C. and the light-off temperature of the HCs are measured according to the same experimental protocol as that described in the previous G-point.
  • the HC light off temperature increase is calculated as the difference between the light off temperature of the HC on the aged sample and that measured on the unaged sample. According to these tests, the lower the temperature of light off on aged sample or the increase in light-off temperature due to aging, the higher the aging resistance of the catalytic system. The higher the conversion rate after aging, the better the catalytic system.
  • Table 2 summarizes the results in terms of flexural strength.
  • Table 3 summarizes the main characteristics measured according to the tests described above.
  • the filters according to the invention have a surface covered by the texturizing material of greater than 95%, and therefore an almost complete coverage, unlike Examples C2 to C4, which have not undergone oxidation thermal treatment.
  • the filters of Examples 3, 4 and 5 show a substantially higher level of catalytic coating filler to that of the comparative examples, for porosity characteristics equivalent or slightly lower. It is noted that the pressure drop caused by the filters according to the invention is very little affected by the significant increase in the catalytic charge present in the textured filters according to the invention. The measured pressure drop values thus remain quite acceptable for the filtering application.
  • All the filters according to the invention have a higher catalytic activity than that of the comparative examples.
  • Example 6 With a quantity of catalytic coating equal, Example 6 has a catalytic efficiency much higher than that of Comparative Example C2, which could be interpreted as the result of better distribution of the catalyst or easier access to sites assets for the gases to be purified.
  • All the filters according to the invention show, after aging, a higher catalytic performance than that of the comparative examples.
  • Examples 5 and 6 show the best resistance to aging.
  • the filters 3 and 4 according to the invention have a smaller reduction in catalytic performance after aging than the comparative filters C3 and C4.
  • the filters according to the invention retain all their mechanical strength properties, while maintaining their filtration efficiency, unlike the solutions known to date for increasing the catalyst load present in the porosity of the filtering structures, in particular by by increasing the porosity quantities (open porosity, pore diameter).
  • the flexural strength measurements show that a reinforcement can be obtained thanks to to the texturization, considerably more important reinforcement for the samples having furthermore undergone a heat treatment of oxidation (examples 5 and 6). This advantage can make it possible to further reduce the wall thickness of the filters and to increase the catalyst load and / or to reduce the loss of load with equivalent mechanical strength.

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EP09737072A 2008-07-17 2009-07-16 Texturierter partikelfilter für katalytische anwendungen Withdrawn EP2307123A1 (de)

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FR0854877A FR2933880B1 (fr) 2008-07-17 2008-07-17 Filtre a particules texture pour applications catalytiques
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WO2010007324A1 (fr) 2010-01-21
JP2011527938A (ja) 2011-11-10
KR20110041471A (ko) 2011-04-21
FR2933880B1 (fr) 2011-04-22
FR2933880A1 (fr) 2010-01-22
US20110185711A1 (en) 2011-08-04

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