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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
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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
  • B01J35/19—Catalysts containing parts with different compositions
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D46/00—Filters or filtering processes specially modified for separating dispersed particles from gases or vapours
  • B01D46/24—Particle separators, e.g. dust precipitators, using rigid hollow filter bodies
• • 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
  • B01J37/0215—Coating
  • B01J37/0219—Coating the coating containing organic compounds
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B05—SPRAYING OR ATOMISING IN GENERAL; APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
  • B05D—PROCESSES FOR APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
  • B05D5/00—Processes for applying liquids or other fluent materials to surfaces to obtain special surface effects, finishes or structures
  • B05D5/08—Processes for applying liquids or other fluent materials to surfaces to obtain special surface effects, finishes or structures to obtain an anti-friction or anti-adhesive surface
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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
  • C04B35/16—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 silicates other than clay
  • C04B35/18—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 silicates other than clay rich in aluminium oxide
  • C04B35/185—Mullite 3Al2O3-2SiO2
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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
  • C04B35/16—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 silicates other than clay
  • C04B35/18—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 silicates other than clay rich in aluminium oxide
  • C04B35/195—Alkaline earth aluminosilicates, e.g. cordierite or anorthite
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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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  • C04B38/00—Porous mortars, concrete, artificial stone or ceramic ware; Preparation thereof
  • C04B38/0006—Honeycomb structures
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  • C04B41/00—After-treatment of mortars, concrete, artificial stone or ceramics; Treatment of natural stone
  • C04B41/009—After-treatment of mortars, concrete, artificial stone or ceramics; Treatment of natural stone characterised by the material treated
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  • C04B41/00—After-treatment of mortars, concrete, artificial stone or ceramics; Treatment of natural stone
  • C04B41/45—Coating or impregnating, e.g. injection in masonry, partial coating of green or fired ceramics, organic coating compositions for adhering together two concrete elements
  • C04B41/46—Coating or impregnating, e.g. injection in masonry, partial coating of green or fired ceramics, organic coating compositions for adhering together two concrete elements with organic materials
  • C04B41/48—Macromolecular compounds
  • C04B41/4857—Other macromolecular compounds obtained by reactions only involving carbon-to-carbon unsaturated bonds
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  • C04B41/00—After-treatment of mortars, concrete, artificial stone or ceramics; Treatment of natural stone
  • C04B41/80—After-treatment of mortars, concrete, artificial stone or ceramics; Treatment of natural stone of only ceramics
  • C04B41/81—Coating or impregnation
  • C04B41/82—Coating or impregnation with organic materials
  • C04B41/83—Macromolecular compounds
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
  • B01J35/00—Catalysts, in general, characterised by their form or physical properties
  • B01J35/60—Catalysts, in general, characterised by their form or physical properties characterised by their surface properties or porosity
  • B01J35/61—Surface area
  • B01J35/613—10-100 m2/g
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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
• • C—CHEMISTRY; METALLURGY
  • C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
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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
  • C04B2111/0081—Uses not provided for elsewhere in C04B2111/00 as catalysts or catalyst carriers

Definitions

• the invention relates to the field of catalyst substrates made of porous inorganic material for the treatment of exhaust gases, in particular from internal combustion engines, particularly motor vehicles, for example diesel engines.
• These substrates 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 gases, and comprise, between these faces, intake and discharge a set of ducts or adjacent channels axes parallel to each other, separated by porous walls.
• the channels may be alternately closed at one or the other end of the structure so as to allow the filtration of soot or particles contained in the exhaust gas.
• a filtering structure commonly known as a particle filter is thus obtained.
• Some inorganic materials such as for example aluminum titanate (Al 2 TiO 5 ) or cordierite, have up to temperatures of about 800 ° C. a very low thermal expansion. This advantageous characteristic is due to the presence of microcracks in the ceramic grains. During heating, the intrinsic expansion of the material leads first to close the microcracks, but without macroscopic expansion of the substrate. Thanks to this low thermal expansion, it is possible to use substrates or monolithic filters, that is to say made of a single ceramic block.
• Al 2 TiO 5 aluminum titanate
• cordierite cordierite
• US application 2006/183632 thus proposes to passivate the surface of the substrate with the aid of gelatin or copolymers of vinyl alcohol with vinylamines or vinylformamides.
• Crosslinking agents are usually added.
• the passivation layer is then calcined at the same time as the catalytic coating.
• This solution leads to a low affinity of the catalytic coating for the substrate, and therefore reduces the amount of catalyst that can be fixed on the substrate.
• the calcination of crosslinking agents generates gaseous effluents often toxic that must be reprocessed.
• the application DE 10 2007 023120 proposes to deposit silanes which will be converted into silicones by crosslinking. However, the decomposition of silicones during calcination generates a lot of gaseous effluents and creates silica which closes the microcracks, resulting in an increase in the coefficient of thermal expansion.
• the object of the invention is to obviate these various disadvantages by proposing a passivation method that is more respectful of the environment. Another goal of the invention is to obtain a better affinity (before and after calcination) between the substrate or the passivation layer and the catalytic coating that is deposited after the passivation step. An object of the invention is also to limit the increase in the coefficient of macroscopic expansion of the substrate provided with its catalytic coating.
• the subject of the invention is a catalyst substrate made of porous inorganic material for the treatment of exhaust gases, the structure of which is in honeycomb, one of the faces of the structure allowing the admission of the gases of exhaust to be treated and the other face the evacuation of the treated exhaust gases, and comprises, between these intake and discharge faces, a set of adjacent ducts or channels of axes parallel to each other, separated by porous walls, said substrate being coated on at least a portion of its inner surface with at least one vinylpyrrolidone polymer or copolymer.
• the subject of the invention is also a process for obtaining a porous inorganic material catalyst substrate according to the invention, comprising a step in which a polymer or copolymer of vinylpyrrolidone is deposited on said substrate, followed by a drying step.
• PVP polyvinylpyrrolidone
• the polymers based on polyvinylpyrrolidone are particularly suitable for passivating a substrate on which a catalytic coating would then be deposited which, after calcination, crystallites of very small size, in particular of size less than 20 nm, in order to increase the catalytic performance of this coating.
• This type of coating for example deposited as boehmite, indeed has the disadvantage of infiltrating easily into the microcracks of the substrate.
• Polyvinylpyrrolidone-based polymers have also been found to be better passivating materials than those known from the prior art. Deposited on the substrate before depositing a catalytic coating, they make it possible to limit the increase in the coefficient of thermal expansion due to the infiltration of the catalyst into the microcracks of the ceramic grains of the support.
• the channels are preferably alternately closed at one or the other end so as to allow the filtration of soot or particles contained in the exhaust gas.
• the resulting substrate is then a particulate filter with a catalytic component, allowing for example the removal of pollutants of the type NO x , carbon monoxide (CO) or unburned hydrocarbons (HC).
• the porous inorganic material is preferably selected from aluminum titanate, cordierite and mullite. Other materials may also be used, such as silicon carbide or sintered metals.
• aluminum titanate is meant not only the aluminum titanate itself, of the formula Al 2 TiO 5 , but also any material based on aluminum titanate, in particular any material comprising at least one less than 70%, even 80% and even 90% of an aluminum titanate phase, the titanium and aluminum atoms possibly being partially substituted, in particular by silicon, magnesium or zirconium atoms.
• the aluminum titanate may contain a minority phase of the mullite type, as taught in the application WO 2004/011124, or of the feldspar type, as taught in the application EP 1 559 696. Examples of materials are also given in WO 2009/156652, WO 2010/001062, WO 2010/001064, WO 2010/001065 or WO 2010/001066.
• the vinylpyrrolidone polymer or copolymer is preferably chosen from polyvinylpyrrolidone, copolymers of vinylpyrrolidone and of vinyl acetate, copolymers of vinylpyrrolidone and vinylimidazole or copolymers of vinylpyrrolidone and vinylcaprolactam, or any of their mixtures. Preferably, no crosslinking agent is added.
• the substrate according to the invention may also be coated on at least part of its internal surface with at least one silane compound, in particular of the silane type comprising at least one carbon chain which has at least one nucleophilic group.
• This compound is generally deposited at the same time as the polymer or copolymer of vinylpyrrolidone. It allows a better grafting of the polymer or copolymer of vinylpyrrolidone on the porous ceramic substrate.
• silane When adding silane, the alkoxide groups of the latter are hydrolyzed by the hydroxyl groups present on the surface of the substrate and bind to this surface.
• Silanes which comprise at least one carbon chain having at least one nucleophilic group can bind the other end of the grafted silane to the polymer or copolymer of vinylpyrrolidone by reaction with the carbonyl groups thereof.
• the silane comprising at least one carbon chain which has at least one nucleophilic group is in particular of the Nu-Ri-Si- (OR 2) 3 type in which R 1 and R 2 are alkyl radicals and the nucleophilic group Nu can be chosen from the NH 2 groups. , SH, OH.
• the silane may be added in the aqueous solution of polymer or copolymer or in a mixture of water and alcohol to promote its dispersion and limit its hydrolysis.
• the polymer or copolymer of vinylpyrrolidone is preferably deposited by impregnation with a liquid solution or dispersion, in particular aqueous dispersion.
• the weight content of polymer or copolymer of vinylpyrrolidone in the solution or dispersion is advantageously between 1 and 30%, preferably between 5 and 15%.
• the average molar mass of the polymer or copolymer of vinylpyrrolidone, especially at the time of deposition, is preferably between 10,000 and 1,000,000 g / mol, especially between 15,000 and 500,000 g / mol, or between 15,000 and 400,000 g / mol, or between 15,000 and 300,000 g / mol or even between 20,000 and 100,000 g / mol.
• weight content in the solution or the dispersion make it possible to adjust the viscosity of the solution or dispersion, and thus the penetration of the polymer in the microcracks of the substrate. It has been observed that for high molar masses, typically of 1,000,000 or more, the The amount of catalytic coating that can subsequently be attached to the substrate decreases substantially.
• the average molar mass of the polymer or copolymer of vinylpyrrolidone is therefore preferably less than 1,000,000 g / mol.
• the impregnation may be carried out in particular by soaking the substrate and / or vacuum impregnation.
• the substrate can be placed in a desiccator under a pressure of 25 mbar or less and the polymer solution or dispersion deposited on the substrate.
• the excess of solvent in particular water
• the drying step is preferably carried out at a temperature of at least 100 ° C., in particular between 130 and 170 ° C., or even between 130 and 160 ° C.
• a temperature of at least 100 ° C. in particular between 130 and 170 ° C., or even between 130 and 160 ° C.
• the adhesion of the polymer to the substrate is reduced.
• the polymer is more soluble in water and may dissolve upon deposition of the catalytic coating. Too high temperatures, especially greater than 180 0 C or 190 0 C, may stiffen the polymer and create mechanical stresses within the substrate, particularly during the deposition of the catalytic coating. It has furthermore been observed that these high drying temperatures have the effect of reducing the amount of catalytic coating that can be subsequently fixed on the substrate.
• the substrate according to the invention is preferably coated on at least a part of its surface with a catalytic coating.
• This coating is deposited on the surface of the walls of the substrate or filter after the passivation step.
• It preferably comprises a base material and a catalyst.
• the base material is usually an inorganic material with a high specific surface area
• the base material is advantageously chosen from alumina, zirconia, titanium oxide, rare earth oxides such as cerium oxide and alkali or alkaline earth metal oxides.
• the catalyst is preferably based on a noble metal, such as platinum, palladium or rhodium, or based on transition metals.
• the size of the base material particles on which the catalyst particles are arranged is generally of the order of a few nanometers to a few tens or exceptionally a few hundred nanometers.
• the process according to the invention is therefore preferably followed by a step of depositing a catalytic coating and then a calcination step, typically in air and between 300 and 900 ° C., preferably between 400 and 600 ° C.
• the invention also relates to a catalyst substrate that can be obtained by this preferred method.
• the substrate according to the invention Before calcination, has at its surface a polymer layer (the polymer or copolymer of vinylpyrrolidone). This polymer layer is removed during calcination. Its presence, however, makes it possible to obtain a calcined substrate different from the substrates known from the prior art.
• the polymer layer may in particular be identified, before calcination, according to the following two methods: by thermogravimetric analysis coupled to a mass spectrometer to identify the decomposition products of the deposited polymer, by extraction, for example by leaching, followed by chromatographic analysis possibly coupled to a mass spectrometer.
• the catalytic coating is typically deposited by impregnating a solution comprising the base material or its precursors and a catalyst or precursor thereof.
• 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 thermal calcination treatment aimed at obtaining the final deposition of a solid and catalytically active phase in the porosity of the substrate or of the filter.
• Catalyst substrates or catalytic filters according to the invention can be used in the exhaust line of an internal combustion engine, typically a diesel engine.
• the catalyst substrates or catalytic filters can be wrapped in a fibrous mat and then inserted into a metal casing, frequently called “canning".
• the fibrous mat is preferably formed of inorganic fibers to impart the thermal insulation properties required by the application.
• the inorganic fibers are preferably ceramic fibers, such as alumina fibers, mullite, zirconia, titanium oxide, silica, silicon carbide or nitride, or glass fibers, such as glass R. These fibers can be obtained by fiberizing from a bath of oxides, fusion, or from a solution of organometallic precursors
• the fibrous mat is preferably non-intumescent. It is advantageously in the form of a needle felt.
• Porous aluminum titanate substrates are obtained by the method described hereinafter.
• aluminum titanate is prepared from the following raw materials:
• alumina with a purity level Al2O3 higher than 99.5% and a median diameter d 5 o of 90 microns commercialized under the reference AR75 ® by Pechiney, - about 50% by weight rutile titanium oxide having more than 95% TiO 2 and about 1% zirconia, and having a median diameter dso of about 120 microns, marketed by the company Europe Minerais,
• silica with a purity level in SiO 2 more than 99.5% and a median diameter d 5 o of the order of 210 .mu.m, marketed by Sifraco,
• magnesia powder with an MgO purity level of greater than 98% and of which more than 80% of particles having a diameter of between 0.25 and 1 mm, sold by the company Nedmag.
• the mixture of the initial reactive oxides is melted in an electric arc furnace, under air, with a step oxidizing electric.
• the molten mixture is then cast into CS mold so as to obtain rapid cooling.
• the product obtained is crushed and sieved to obtain powders of different size fractions. More specifically, the grinding and the sieving are carried out under conditions allowing the final obtaining of two particle size fractions:
• a particle size fraction is characterized by a median diameter d 5 o substantially equal to 50 microns, denoted by the term fat fraction,
• a particle size fraction being characterized by a median diameter d 5 o substantially equal to 1.5 microns, referred to as the fine fraction.
• the median diameter d 5 o denotes the diameter of the particles, measured by sedigraphy, below which 50% of the volume of the population is located.
• microprobe analysis shows that all the grains of the melt phase thus obtained have the composition, in percentage by weight of the oxides, reproduced in Table 1:
• the grains thus obtained are then used to make monoliths (substrates) raw.
• powders are mixed according to the following composition:
• the green microwave monoliths are then dried for a time sufficient to bring the water content not chemically bound to less than 1% by weight.
• the channels of both ends of the monoliths are closed according to well-known techniques, for example described in US Pat. No. 4,557,773 and with a mixture corresponding to the following formulation:
• the porosity characteristics were measured by high-pressure mercury porosimetry analyzes carried out using a Micromeritics 9500 porosimeter.
• the monoliths are then impregnated by immersion in a solution containing the polymer, and then dried.
• the polymer used is a polyvinyl alcohol marketed by Celanese Corporation under the reference Celvol 205. Its hydrolysis rate is greater than 88%.
• the polymer is crosslinked using citric acid.
• Comparative example C6 corresponds to a non-passive monolith (thus without depositing any polymer).
• the polymer is a polyvinylpyrrolidone with an average molar mass of 58000 g / mol.
• the polymer is a polyvinylpyrrolidone having an average molar mass of
• the solution is brought to a pH of 10 by adding NaOH.
• the times and drying temperature denoted respectively t and T
• concentration of the impregnation solution denoted C and expressed as a percentage by weight of polymer relative to the quantity of solution
• the alumina uptake denoted A
• CTE the average coefficient of thermal expansion of the substrate provided with its catalytic coating
• the water intake after passivation makes it possible to estimate the amount of catalyst that can be fixed to the substrate, and therefore the affinity between the substrate and the future catalytic coating.
• the measurement method involves immersing the passive substrate in water and then submitting one of its ends to a sudden suction so as to leave a film of water on the surface of the walls.
• a high residual water content is characteristic of a high chemical affinity between the future catalytic coating and the substrate, and hence the possibility of fixing more catalytic coating.
• the average thermal expansion coefficient (CTE) is measured between 65 ° C. and 1000 ° C. by differential dilatometry under a rise in temperature of 5 ° C./minute according to standard NF B40-308.
• the specimen of material tested is obtained by cutting in the honeycomb in a plane parallel to the direction of extrusion of the monolith. Its dimensions are about 5mm * 5mm * 15mm.
• the measurements are made after deposition of boehmite and calcination to simulate the effect of a catalytic coating having crystallites of very small size after calcination, that is to say of the order of 10 nm.
• the catches or weight losses (Q, P, A, L) are expressed in percentages by weight relative to the mass of the dry substrate before impregnation.
• the passivating effect of the polyvinylpyrrolidone, illustrated by Example 7, is particularly advantageous, since the coefficient of thermal expansion of the passive substrate and then provided with its catalytic coating is reduced by more than 40% relative to a non-passive substrate before deposition. catalytic coating (example C6).
• the passivating effect of the polyvinylpyrrolidone is also better than that of the polyvinyl alcohol (example C3).
• Table 4 below illustrates the influence of the drying temperature on the adhesion of the polymer to the substrate. Unlike Example 7, Examples 9 and 11 were dried at 170 and 190 ° C., respectively.
• Table 4 reports the parameter denoted L, which corresponds to the loss of mass after immersion of the dried substrate in water for one minute at ambient temperature and drying at 105 ° C. in air.
• Comparing Examples 8 and 10 with Examples 7 and 9 respectively shows that the addition of a small amount of silane further improves the adhesion of the polymer layer to the substrate.

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