FR2763259A1 - Catalyst-reinforced composite material for use in an automobile catalytic converter - Google Patents

Abstract

A composite catalytic material for exhaust gas convertors of automobiles comprising a metallic matrix reinforced with a homogeneous dispersion of catalytic particles. Also claimed is the catalytic convertor and its construction.

Description

The present invention relates to a novel catalyst made of

  composite, a catalytic converter whose active phase comprises such a composite material and an exhaust line element for motor vehicles

understanding it.

  It also relates to a method for

  manufacture of such a converter, in particular for the preparation of the composite material.

  The presence of toxic compounds in motor vehicle exhaust contributes significantly to air pollution, particularly in

Urban.

  JI Moreover, faced with the development of the automobile industry and the increasing number of vehicles, the public authorities have been led to introduce increasingly strict standards setting the maximum amounts of pollutants that can be emitted by vehicles.

2 cars.

  Currently, the solution to meet these standards and reduce the amount of toxic substances in the exhaust is their transformation into compounds

  not harmful by the use of catalysts.

  2F For this purpose, we know three-way converters that act on both the two main reducing pollutants, namely carbon monoxide and unburned hydrocarbons, and on oxidizing pollutants

such as nitrogen oxides.

  e, These converters generally consist of a ceramic or metal support which ensures the mechanical strength of the assembly and a catalytic phase most often including precious metals or other

active ingredient.

  They are optionally provided with an intermediate layer, generally of alumina 7, on the surface of which is dispersed the catalytic phase, whose function is essentially to increase the surface of

gas-solid contact.

  The known converters have a relatively satisfactory catalytic activity and stability, but nevertheless they have several disadvantages such as high production cost, recycling difficulties, particularly of recovery of the materials within a ceramic mass, thermal inertia. related to the high thermal resistivity of the ceramic, low resistance to thermal shock, integration difficulties in a metal exhaust line due to their thermal expansion differential, etc. There is therefore a need to find new catalysts that make it possible to remedy, in particular,

aforementioned drawbacks.

  Furthermore, it has been found that the precious metals or metal oxides forming the active phase of the converters could give rise, under the conditions of practical use of the latter, to a change of structure and / or sintering. by warming up

  ! of the converter during operation.

  This change of structure and this sintering of active ingredients in the converter leads to a loss

conversion efficiency.

  Accordingly, the object of the invention is to provide a new three-way catalyst that can meet the aforementioned need, which is particularly effective with

a reduced production cost.

  An object of the present invention is still to provide a catalyst developed, at least partially, to

  from compounds other than precious metals.

  Another objective is also to provide converters having improved catalytic and mechanical properties, which can be maintained under the conditions of practical use of said converters, making it possible in particular to avoid the phenomenon of

sintering previously discussed.

  To this end, the subject of the invention is a catalyst made of a composite material, in particular for a converter for motor vehicle exhaust gas, characterized in that it comprises a metal matrix in which are in the dispersed state, in such a way that substantially homogeneous, particles of at least one catalytic backing material. According to other features of the invention: the catalytic reinforcing material consists of precious metal particles and / or transition metal oxide powders; 2 <> - the metal matrix is chosen from copper, nickel, cobalt, chromium, iron, zinc, cadmium, silver, platinum, rhodium, ruthenium, titanium, molybdenum, vanadium, tungsten, and their

  alloys, or aluminum alloys.

  The invention also relates to a catalytic converter comprising a composite material as defined above and a line element.

  exhaust equipped with this converter.

  The invention also relates to a process for the manufacture of such a converter, characterized in that it comprises the steps of: preparing metal powders and optionally metal oxides having the appropriate dimensions and morphology or precursors thereof, for forming the metal matrix and the catalytic reinforcement material (s) of the composite material; - Prepare a metal or ceramic support for receiving the composite material; forming, on at least one face of said support, a coating made of a composite material comprising a metal matrix in which particles of at least one catalytic reinforcing material chosen from precious metals and / or metals are dispersed in a substantially homogeneous manner; transition metal oxides;

  heat-treating the assembly obtained.

  The invention will be described in more detail in the

  description which will follow given for illustrative purposes and

  nonlimiting, with reference to the accompanying drawings in which: - Figure 1 shows curves illustrating the variation of the catalytic conversion rates of hydrocarbons at 500 ° C depending on the characteristics of the

  2 particles of cobalt oxide according to the legend given below.

  after and their contents in a nickel matrix composite material (Ni / Co304) according to the invention: legend: a) spherical particles with a specific surface area 22 m 2 / gb) acicular particles with a specific surface area 19 m 2 / gc) surface spherical particles specific 2 m2 / gd) acicular particles with a specific surface area of 2 m 2 / g - FIGS. 2 and 3 illustrate the conversion rates of ethane and nitrogen oxides, respectively, at 400 ° C., obtained with various catalysts made of composite material (M / Co304) according to the invention, containing 10% of cobalt oxide indicated in a and with the matrix

metallic M alone.

  - Figures 4 and 5 illustrate the conversion rates of hydrocarbons (HC) indicated in J and oxides of nitrogen (NOx) indicated in o at 400 ° C obtained with different catalysts in composite material respectively cobalt matrix (Figure 4 ) and chromium (FIG.) containing different percentages of catalytic reinforcing material consisting of Co304 (C), Co2.84 Zn0.1604 (CZ) and Co2CrO4 (CR); FIGS. 6 and 7 are diagrammatic partial sectional views of the surface of a support provided with catalytic coatings comprising a composite material according to the present invention as observed by Scanning Electron Microscopy; Figures 8 and 9 show the influence of the content of particles of Co304 (spherical particles with a specific surface area of 22 m2 / g) of the electrolyte (Figure 8) and of the current density (Figure 9) respectively. different types of particles of Co304 (a) to (d) (see Figure 1) on the final amount of active phase) incorporated into the metal matrix for a Ni / Co304 composite material produced by electrolytic coding; - Figures 10 and 11 show a converter according to the invention obtained by concentric winding of strips and introduction into a cylindrical tube, respectively during its introduction (Figure 10) and once completed (Figure 11); FIG. 12 illustrates the variations in catalytic activity from the point of view of the conversion of hydrocarbons (HC) at 300 ° C., indicated in a, and the conversion of carbon monoxide (CO) to 300 ° C., indicated in FIG. , for converters according to the invention with FeCrAlY ferritic stainless steel support containing 79% iron, 16% chromium, 4.6% aluminum, 0.2% yttrium, provided with an interface layer nickel, a chromium (R) or cobalt (C) matrix composite coating alone, or provided with additional active coating (s) by electrophoresis and / or impregnation as indicated on the legend below: (e) composite coating only heat treatment at 400 ° C (f) composite coating + impregnation of copper chromite precursor (RQ) in a non-aqueous solution under the conditions given in table 6 heat treatment at 500'C IF (g) composite coating + impregnation of cobalt oxide precursor (C) in a non-aqueous solution under the conditions given in Table 6 heat treatment at 500 ° C. (h) composite coating + cobalt oxide coating 0 (specific surface area 23 m 2 / g) by electrophoresis + coating type C by impregnation heat treatment at 700 ° C. C - Figures 13 and 14 compare the catalytic performance for different compounds according to the legend, a catalyst according to the invention (Fig. 13) with FeCrAlY steel support, provided with a nickel interface layer, with a Co / Co304 composite coating whose surface has been enriched in platinum, with a conventional catalyst

  (fig 14) with cordierite support, equipped with a wash-coat E of alumina and whose active phase is based on platinum.

  legend: (i) CO; (j) C3H6; (k) HC; (1) C3H8; (m) NO; (n) NO2;

(o) NOx.

  The inventors have demonstrated, unexpectedly, that the phenomenon of sintering of the active materials forming the catalytic phase of converters could in particular be avoided, by providing a composite catalytic coating for such converters. The inventors have furthermore shown that catalytic reinforcement materials of different natures can be advantageously employed within the composite material and that this makes it possible to obtain a more effective and more selective conversion of the toxic substances and

  pollutants present in the exhaust gas.

  In5 the expression "catalytic reinforcing material" designates a material inherently having catalytic properties which make it possible, in particular, to exalt the

  performance of the coated converter.

  The catalytic reinforcing material according to the invention 2 (, consists of particles of precious metals and / or

  powders of transition metal oxides.

  The precious metals are advantageously chosen from the group comprising platinum, rhodium and / or palladium. As for the transition metal oxides, they advantageously correspond to the following general formula: AxByO 4 in which A and B are metal cations chosen from the transition metals of the

  Periodic classification of Mendeleiev.

  These oxides are preferably of spinel or perovskite structure.

  Examples of particularly useful oxides according to the invention are cobalt oxide Co304, cobaltite zinc Co2,84Zn0o, 1604 and cobaltite chromium Co2CrO4. The composite material may comprise mixtures of reinforcing materials of different natures (precious metals and transition metal oxides) chosen from the abovementioned materials. The specific surface area of the reinforcing material particles is advantageously between 1 to 100 m 2 / g, preferably between 20 and 40 m 2 / g. A lower surface area is not desirable from the point of view of conversion efficiency

  especially for reducing compounds such as carbon monoxide and unburned hydrocarbons.

  A surface area greater than 100 m 2 / g is not desirable either because it can be the source of

  problems of stability in time or incorporation2 in the metal matrix.

  The size of the particles forming the catalytic reinforcing material is in general between 0.5 μm and 10 μm, preferably between 0.5 μm and 5 μm. Size particles outside this range are undesirable, in particular for good incorporation of the particles into the metal matrix. The morphology of the reinforcing material particles is not critical. However, according to the invention, spherical particles are preferred, which, in general, better incorporate into the metal matrix, further consolidate the final composite material and, under thermal stress, prevent the growth of the grains of the

  matrix with better isotropy.

  Examples of catalytic reinforcing materials that can be used for the purposes of the invention,

  alone or in combination are given in Table 1 below.

below:

TABLE 1

  Composition Origin Surface area Size, Morphology 1i) Goodfellow metal pt 2 mV / g <5mn. spheres Metal Pt CERAC I im spherical Rh metal CERAC 2 mL spherical Co304 Soft chemistry 40 m2 / g 0.5 pI spheres CoO04 Soft chemistry 25 ai / g I pam. acicular Cr: Cu04 Soft chemistry 20 mg / g I yah. sphenques The metal matrix of the composite material according to the invention is based on a metal advantageously chosen from copper, nickel, chromium, cobalt, iron, 2) zinc, cadmium, silver, platinum , ruthenium,

rhodium and their alloys.

  This choice can be extended to other metals such as titanium, molybdenum, vanadium, tungsten or

  aluminum alloys, especially according to the technique used for the preparation of the material.

  Of these metals, cobalt and chromium are

  particularly preferred for the purposes of the invention.

  The aforementioned metals and alloys are suitable for relatively high temperature applications as encountered in motor vehicle exhaust media. Low melting metals are not

  desirable for the purpose of the invention.

  The metal matrix developed based on these metals has a good resistance to corrosion, especially in low temperature aqueous media such as dry or wet high temperature. It also has good thermal conductivity. Some metal matrices also have intrinsic catalytic activity. The choice of the metal matrix is moreover conditioned by the technique of elaboration of the composite material used as well as by the thickness of the final catalytic coating in the converter, as is

described later.

  The metal matrix constitutes between 85 and 95%

weight of the composite material.

  An essential role of the metal matrix within the composite material is to prevent the sintering of the particles of catalytic reinforcement material (s) between them. The metal matrix also brings cohesion

  to the composite material and induces its geometry.

  From the point of view of the catalytic activity of the composite materials according to the invention, the variation of the conversion rates according to the characteristics (morphology, specific surface area) of the particles of

  catalytic reinforcement material and their rate of incorporation into the metal matrix was studied.

  FIG. 1 gives results obtained for a composite material Ni / Co304, with respect to the

  conversion of hydrocarbons (HC) to 500 ° C.

  We see that the particles with higher specific surface area lead to the highest conversion rates, at

  catalytic reinforcement identical in the composite material.

  The influence of the nature of the metal matrix on

  overall catalytic activity has also been studied.

  Figures 2 and 3 illustrate the results obtained for the conversion of ethane and nitrogen oxides at 400 C, with catalysts of composite material whose catalytic reinforcement material is cobalt oxide (Co304). It can be seen that the best conversion rates are obtained with chromium or cobalt matrix composite materials. The comparison of FIGS. 2 and 3 also shows that certain matrices of the composites (in particular chromium, cobalt, zinc, copper) have an intrinsic catalytic activity. The influence of nature and the content of particles of catalytic reinforcing material has also been studied from the point of view of the overall catalytic activity of the

composite material.

  FIGS. 4 and 5 illustrate the results obtained for catalytic reinforcement materials made of cobalt-based transition metal oxides of the Co304 (C), C02, 84 Zn0, 16 O4 (CZ) and Co2CrO4 (CR) type. whose activities

  intrinsic catalytic properties are relatively equivalent.

  It can be seen from these histograms that the catalytic activity of the composite material is closely related to the content of catalytic backing material without incidence.

notable of their nature.

  The invention also relates to catalytic converters for motor vehicles

  comprising a composite material as described above.

  Referring to FIG. 6, there is shown a converter 1 according to the invention comprising a support 2 provided with a coating comprising a composite material 4

  having catalytic properties.

  The support 2, which essentially ensures the mechanical strength of the converter as a whole, is of the type conventionally used for the manufacture of converters. Thus, according to the invention, the support 2 may be metallic or ceramic with a structure of any type known for the manufacture of converters, adapted to the

exhaust gas conversion.

  For metallic supports, it is advantageous to use steels containing chromium,

  preferably of ferritic or austenitic structure.

  Materials as described in patent applications EP 497 992 and EP 246 939 are particularly suitable for the manufacture of converters according to the invention. The support may, for example, be in the form of strips whose thickness is preferably between 30 μm and 100 μm, advantageously Im. 2, (According to other variants of embodiment, it is possible to use threads of diameter preferably comprising

between 10 and 350 gm.

  We can still predict the use of foams

  metal made of strands of diameter equivalent to that of the aforementioned son.

  The techniques of formatting the support from

  these materials are of any known type.

  By way of example, in the case of strips, the stacking of individual layers of steel sheets may be mentioned, the formation of honeycomb or honeycomb structures as described in the documents

  FR 2,577,616, EP 317,075, EP 117,602, WO 90/03220,

  EP 336 106, DE 4 129 893, WO 92/02716, EP 434 539 and EP

693 316.

  In the case of metal son, one can also provide for example the formation of a honeycomb structure through the manufacture of woven fabrics, lattices, knits in particular as described in the application

FR 2,257,340.

  In the case of metal foams, the shaping operation can consist of a simple cut to

selected dimensions.

  In the case of ceramic substrates, cordierite monoliths, preferably of 64 cells per inch and of formula 5SiO 2, are advantageously used.

2A1203, 2MgO.

  According to the invention, preferred metal supports, stainless steel, which have certain advantages over ceramic substrates including their low thermal inertia and their better

thermal shock resistance.

  According to the invention, the support 2 is shaped advantageously in a honeycomb structure promoting exchanges between the catalytic coating and the gases

exhaust to convert.

  We can proceed to shaping the front support

  or after formation of the catalytic coating as described hereinafter, this second mode being preferred.

  In the case of a ceramic support, the definitive shaping of the support is carried out before the elaboration of the

catalytic coating.

  Furthermore, the support 2 may be provided with one or more interface layers 3 which promote adhesion

  composite material coating.

  It may be for example a layer based on nickel, zinc or copper. For some composite materials including chromium matrix, the support is at the

  once equipped with a layer of nickel coated with a layer of zinc or copper. These interface or intermediate layers are thin, generally less than 1.5 Mm.

  In addition, according to the technique of forming their catalytic coating based on the composite material, the support can also be modified. For example, for a ceramic support, it may be necessary to proceed with a metallization, as described below. According to the invention, the support is provided on at least one of its faces with the composite material described above, forming a catalytic coating on the surface of the support. It advantageously has a thickness of less than 100 μm, and more preferably a

  thickness between 1 and 10 gm.

  According to another aspect of the present invention, the composite material as described above is used

  for the conversion of polluting substances, without support.

  In this case, the coating of composite material is formed on a support as described below, then is separated from this support and shaped to form a catalytic converter itself. A coating of composite material of a sufficient thickness is then provided so that it has mechanical properties suitable for shaping, alone, in a structure suitable for the conversion of exhaust gases. This thickness is then preferably between 30 and 100 μm, more preferably still

between 40 and 80 pm.

  The converter can thus be for example in the form of a winding of the composite material produced in the form of "sheet" according to different types of structures, for example to form a structure

  alveolar, similar to a converter with support.

  Whatever the embodiment of the invention, the surface of the composite material may be locally

  enriched with additional active material (s).

  With reference to FIG. 7, the presence of a layer 5 containing such active material (s) is shown.

  additional (s) to the surface of the composite material 4.

  These are chosen from precious metals and metal oxides, preferably transition metal oxides, and may comprise these materials alone or

J5 in combination.

  Their content is advantageously between 0.1 and%. In the case of precious metals for example, the content is advantageously lower than those of

2) current commercial catalysts.

  The method of producing the converter according to

  the invention will now be described.

  This process comprises, first of all the preparation of the powders used as raw materials to form the! metal matrix and reinforcing material (s)

catalytic material of the composite material.

  The preparation of metal powders and transition metal oxides, dimensions and morphology

  appropriate, is done by methods known per se.

  According to one embodiment of the invention, it is also possible to incorporate into the metal matrix precursor particles of the desired catalytic reinforcing materials. These precursors condition the morphology and size of the particles

  catalytic reinforcing material.

  For precious metals, the precursors may consist of precious metal hydroxides but are not particularly limited according to the invention. We

  proceeds as is known in the art.

  For the metal oxides, the precursors may consist for example of hydroxides, oxalates, citrates, carbonates, hydroxycarbonates, oxyhydroxides, etc. containing a metal of a metal selected from the group of metals defined for the catalytic backing material, in which case a single metal oxide, or a plurality of different cations, is ultimately obtained;

  In the end, a mixed oxide is obtained.

  According to one embodiment of the invention, precursors of oxides can be obtained by addition of two distinct solutions, one of which contains a salt of at least one desired metal and the other contains an acid precipitating agent or basic as described in

application FR 95 13 810.

  The salts of the first solution are chosen from

  transition metal salts, alkali metal

  earth and lanthanides such as Mn, Fe, Cr, Co, Ni, Zn, Y, La, Ca, Sr, etc., especially among the nitrates,

  sulphates and chlorides of these elements.

  The precipitating agent of the second solution is chosen from oxalic acid, citric acid, ammonium oxalate, ammonium carbonate, sodium hydroxide, potassium hydroxide,

  ammonia and organic bases.

  The solvent of each solution comprises distilled water. The concentration of reagents in each

  solution is between 0.2 and 2 mol / l.

  Optionally, the solvent also comprises an alcohol or polyol, the volume ratio of alcohol or polyol and distilled water in the solvent being between 0 and 60% for the first solution, and 0 and 100% for the first solution.

second solution.

  Each solution may be slightly acidified, in particular to improve the dissolution of the starting salts. Solutions can be prepared and added at room temperature. In certain cases, the solutions 1 can be heated to a temperature of between 20 and 60 ° C., either to improve the dissolution of the salts or to increase the rate of precipitation during

the addition of the two solutions.

  Preferably, the addition of one solution to the other is controlled by means of a peristaltic pump whose flow rate

is set between 1 and 1000 ml / min.

  In a variant, the addition of the solutions can be almost instantaneous by rapidly pouring a solution into the other. After addition of the solutions, the precursor is separated from the precipitation medium (mother liquors) by filtration, centrifugation or spinning, and this precursor is then washed several times, preferably four to six times, using a volume of water. distilled about one liter per 100 g

of precursor.

  The precursor is then dried, in an oven or on a sand bath, at a temperature of between 50.degree.

and 90 C, for 10 to 30 hours.

  Preferably, prior to drying the precursor, the latter is washed with 95% ethanol to optimize the drying, and after drying of the precursor, the particles of the latter are calibrated to reach a size of between 100 and 500 Mm, in particular by forced sieving. A smaller size is too expensive to obtain. A larger size would lead to temperature heterogeneities of the heat treatment

subsequent precursor. After formation of the precursor, the latter is thermally treated

to form the oxide powder,

  this powder comprising at least one simple or mixed oxide.

  The heat treatment of the precursor is carried out so as to preserve the general shape of the particles of the

precursor.

  The heat treatment of the precursor comprises two successive stages of heating, a so-called low

  temperature and the other said high temperature.

  The low temperature step comprises two phases, namely a first phase of rapid temperature rise

  and a second phase of slow rise in temperature.

  During the first phase, the precursor is heated to a temperature of 150 ° C, at a rate of 100 to 200 ° C / h, to complete the dehydration of the

2> precursor.

  During the second phase, the precursor is heated to a final temperature of between 300 and 500 ° C., at a rate of 10 ° C./h, to decompose the precursor into oxides while retaining the initial general shape of the particles. the final temperature being maintained for 0.5 to 2 hours. The high temperature stage of the heat treatment comprises heating the oxidized precursor to a temperature of between 300 and 1000lC, either instantaneously, for example by introducing it into a hot oven, or gradually, at a speed of 150 ° C./h. ,

  to homogenize the oxides by ion diffusion.

  The heat treatment of the precursor just described is carried out in a conventional atmosphere, particularly in air, the heating of the precursor being

  performed in conventional ovens.

  Preferably, the high temperature stage of the heat treatment is followed by a cooling of the oxidized and heated precursor, either very rapidly, in particular by soaking, or slowly at a speed of between 50 and 200 ° C./h, so as to keep the

  initial general shape of the particles.

  1X} This process allows the preparation, by soft chemistry, of metal oxide powders with characteristics

determined morphological

  The method according to the invention further comprises the possible manufacture of the ceramic support itself which is done in known manner as indicated for example above. As regards metal supports, these generally have a low specific surface area and have no activity in the reduction of

main harmful gaseous effluents.

  Once formed, a surface treatment is advantageously carried out so as to artificially increase the roughness, the specific surface and

  catalytic activity, and promote the adhesion of subsequently formed coatings.

  It is thus possible to carry out a mechanical attack treatment such as by sandblasting, or by chemical means

such as using an acid.

  In this way, roughness is created in the steel of the support, which contributes to the increase of the specific surface and to the improvement of the adhesion of the

  subsequently formed coatings.

  Moreover, it is also possible to carry out a degreasing treatment, in particular electrolytically. In addition to its micro-degreasing power, this makes it possible to eliminate the aluminum oxides that may be formed after acid pickling. Solid or liquid foreign bodies, such as surface oxides or hydroxides, are removed as far as necessary which could hinder the adhesion of the catalytic coating to the surface of the surface.

  especially if the coating is electrolytically formed.

  By these preliminary surface treatments, the surface of the support is thus made more receptive to the coating.

  catalytic based composite material.

  To further improve the adhesion of active JI coatings, it is advantageous to form one or more interface layers on the surface of the support, beforehand

  to the formation of the composite material.

  For this purpose, it is preferable to provide the formation of an intermediate layer (between support and composite material) based on nickel (nickel plating), zinc or copper. We proceed conventionally by

electrolytic, in acidic medium.

  It is possible to provide the formation of several successive intermediate layers, in particular for chromium matrix composite material coatings, as has already been

been stated previously.

  These intermediate metal layers are also advantageous in that, after heat treatment, the highly oxygen-hungry metal compounds they contain, such as for example copper, diffuse on at least one face of the material and can thus participate in

the conversion of gaseous effluents.

  The process according to the invention is essentially characterized by the formation of the composite material on the

least one side of the support.

  This step can advantageously be carried out wet, for example by electrolytic coding, chemical coding or electophoresis. Electrolytic coding is a preferred route

according to the invention.

  According to this first method of forming the composite material, a cathodic codode is produced on the support

(forming cathode).

  The support is then made of conducting material or is made conductive, in particular by metallization. It's the

  case for example ceramic supports.

  The metallization can be carried out electrolessly by oxidation-reduction chemistry or by physical means, for example by condensation of atoms, PVD, CVD, with the aid of a plasma torch or by any other method.

  known, adapted to the desired metallization.

  2> The anode may be of the soluble anode type in which case it is based on metal or alloy selected from those mentioned above, intended to form the matrix of the composite material. The metal dissolves in the electrolytic medium as the process progresses, which

  allows to enrich the environment continuously.

  Alternatively, an insoluble anode can be provided which is inert and does not interfere in the electrolytic process. It can be a titanium anode

platinum or platinum.

  In this case the metals (or alloys) are added to

  electrolyte bath, especially in the form of salts.

  Moreover, particles of catalytic reinforcing materials or precursors thereof are incorporated in the electrolyte bath containing the metals (or alloys).

  dissolved to form the matrix.

  The particles incorporated are advantageously

kept in homogeneous suspension.

  For this, one proceeds either chemically with the aid of appropriate surfactants. This route is however not preferred according to the invention since these surfactants can be pollutants for plating baths and / or

electrolytic deposits.

  According to the invention, it is preferable to maintain the particles in suspension mechanically with the aid of

  vibratory movements of low amplitude.

  The particles are set in motion by pumping the electrolyte and the particles it contains and injecting the assembly into the electrolytic cell, advantageously of conical shape.

in its lower part.

* Too little agitation causes sedimentation

particles in suspension.

  ) Excessive agitation causes a turbulent regime that can cause the agglomeration of fine particles and a bouncing effect of the particles on the surface of the electrode because of the kinetic energy too much

important to them.

  Whatever the technique adopted, the agitation will be adjusted so as to allow homogenization of the assembly formed by the electrolyte and the particles in suspension therein and prevent the sedimentation of these particles. In the electrolytic process, the matrix is

  formed by reducing cations in solution.

  According to this embodiment, it is possible to carry out a galvanic coding where the particles of catalytic reinforcement material (s) or precursor (s) thereof are kept in suspension during the formation of the cathodic deposition on the support, cathodic deposition to which these

particles are incorporated.

  Advantageously, this embodiment is used for the formation of a composite material on vertical electrodes (support) of more or less

less complex.

  According to another variant embodiment, sedimentation is coded o the particles of reinforcing material (s) or precursor (s) thereof are suspended by intermittently stirring the electrolyte giving thus a sedimentation

  particles between two periods of agitation.

  1> This variant is preferred for the formation of a composite material on horizontal electrodes (case of sheet or sheet supports for example) at high rate

of particles.

  The intrinsic characteristics of the particles 2 <> used, in particular their nature, morphology, particle size, as well as their concentration and the homogeneity of the suspension condition the deposits obtained. According to the invention, the electrolyte contains water, metal salts (such as chlorides, sulphates, sulphamates, nitrates, etc.), a buffer agent for

maintain the pH.

  The concentration of the metal salts is generally between 0.1 and 5 M, preferably between 0.3 and 3 M. As regards the particles of catalytic reinforcement material (s) incorporated, they advantageously have a spherical and surface morphology

  specific from 20 to 40 m 2 / g, and sizes from 0.5 to 5 Mm.

  The size of the particles is preferably comprised

between 1 and 10 mm.

  The particle content of the electrolyte is advantageously between 50 and 500 g / l. She is

  closely related to the amount of active phase deposited.

  The electrolysis current density is between 1 and 40 A / dm 2 and depends closely on the metal to be

  deposit which will constitute the matrix.

  The formation speed of the composite material is

  advantageously from 0.1 to 0.5 pm / min.

  The influence of the content of particles of catalytic reinforcing material contained in the electrolyte as well as the influence of the current density have been studied, as regards the quantity of reinforcement material.

  catalyst incorporated in the metal matrix.

  Figures 8 and 9 illustrate the results obtained in the case of incorporation of Co304 cobalt oxide into a nickel matrix leading to the formation of a

Ni / Co304 composite material.

  FIG. 8 shows that the final content of active material in the composite material is closely

  related to the particle content of the electrolyte.

  Figure 9 shows that the current density has

also a considerable effect.

  This figure shows, moreover, that the particles of lower specific surface are incorporated more easily. On the other hand, the influence of morphology (spherical or acicular) is notable only for

  particles of low specific surface area.

  By the electrolytic codéposition process, microstructures are obtained that are very aerated on the surface as well as

  heart, and containing particles on their surface.

  The specific surface area of the material obtained is relatively low (generally less than 2.5 m2 / g) but

  it has satisfactory catalytic activity.

  According to a second mode of forming the material

  Composite is made by chemical deposition.

  In a manner similar to the electrolytic coding described above, particles of catalytic reinforcing material (s) or precursor (s) thereof are suspended in a liquid medium.

  containing dissolved metal cations.

  However, the growth of the metal matrix is done by reducing the metal cations contained in the medium thanks, this time, to the use of a reducer

  which, for its part, oxidizes during the process.

  The incorporation of the particles of catalytic reinforcing material (s) or precursor (s) thereof

  mechanically during growth.

  The growth of the deposit is done in a way

  substantially homogeneous on the surface of the support.

  Unlike the embodiment previously described, it does not require the use of a current generator and the substrate (support) is not

not necessarily driver.

  According to this second embodiment, it is preferred to choose the constituent metals of the metal matrix

  among nickel, cobalt and zinc.

  In the case of a nickel metal matrix, the medium may consist of an aqueous solution containing nickel salts in the form of chloride or sulphate

  bringing about 4 to 7 g / l of nickel metal.

  The reduction of metal cations results from the oxidation of sodium hypophosphite (10 to 30 g / l) which

is a powerful reducer.

  The medium may also include complexing agents which avoid the precipitation of, for example, nickel phosphite, contribute to setting the pH and accelerate the deposition rate. The use of stabilizers allows

  to increase the life of the bath.

  Among the complexing agents that can be used are lactic acid, glycolic acid and citric acid. Examples of stabilizers are thiourea,

lead, indium.

  The speeds of elaboration of the composite material are in this case lower, generally of the order of 10 Mm / h

or less.

  According to a third mode of formation of the composite material, displacement is carried out by solid particles under the effect of an electric field in a liquid medium. A cataphoresis or anaphoresis is thus carried out, according to

cases.

  In this way, the metal particles intended to form the metal matrix and the particles of catalytic reinforcing material (s) or precursor (s) thereof are suspended in an aqueous solution.

and / or organic.

  We. preferably uses a solvent or mixture of

  solvents selected from acetone, ethanol, isopropanol.

  A potential difference is applied between the electrode to be coated and an auxiliary electrode. The applied electric field is from 50 to 500 V. It induces an intensity that depends on the electrochemical reactions that occur at the electrodes. This intensity is of the order

of 10 mA / dm2.

  The particles in suspension move under the influence of the electric field and are deposited

on the support.

  The metal particles and particles of catalytic reinforcing material or precursor thereof are suitably selected based on their displacement velocity characteristics so as to achieve the desired rate of incorporation of catalytic reinforcing material into the composite material. A coherent surface is obtained for the coating of composite material after heat treatment at a temperature of

  temperature close to the melting temperature of the metal (or alloy).

  After the elaboration of the composite material with the growth of the metal matrix and the incorporation of the particles of catalytic reinforcing material (s) or precursor (s) of that (s) -ci, a precursor decomposition thermal treatment is carried out. and / or stabilization. If necessary, the heat treatment allows the decomposition of precursors of reinforcing materials

  catalytic, for the formation of metal and / or active oxides as defined.

  In the case of precious metal precursors, the decomposition treatment is adapted as is known per se, for example by providing, for example, a reduction under a hydrogenated atmosphere. The final heat treatment is carried out at a temperature at least equal to the temperature of

  catalyst operation, with a minimum of 400 C.

  According to another aspect of the invention, the surface of the material coating can be locally enriched.

  composite with one or more additional active ingredients.

  This makes it possible to further improve the catalytic properties.

  These additional active materials may consist of precious metals and / or metal oxides, especially transition metal oxides, these oxides may be simple or mixed. We can proceed with the deposit for example by

  electrophoresis or by impregnation.

  This additional step can be performed after stabilization treatment and / or decomposition for the composite coating or before it, in which case it is a single final treatment. Alternatively, this step can also be performed on the converter, once formed, that is to say after deposition of the composite material coating on its support, for example by strapping and shaping, for example by

  concentric winding of several strips. One can also make several successive deposits, before and / or after formatting of the converter.

  Advantageously, a heat treatment is provided after deposition, before shaping of the converter, as well as another heat treatment after deposition and after shaping of the converter according to another aspect of the invention. of a composite material on a support by any one of the aforementioned methods and then to the separation of said composite material from its support, in this case, a composite material of sufficient thickness is produced to confer in particular the necessary mechanical properties in The separation is carried out chemically, for example by selective etching (dissolution), for example 100 g / l of trichloroacetic acid and 500 ml / l of 32% ammonia are used for this purpose. allow to dissolve

  selectively copper supports.

  We can also obtain the desired separation

  mechanically, especially by delamination or peeling.

  According to this embodiment of the invention, the adhesion between the composite material and the support is not promoted, particularly by particular surface treatments as mentioned above, prior to the formation of the

composite material.

  The catalytic composite material thus isolated can be shaped, in particular by concentric winding from strips previously separated from their

I5 manufacturing supports.

  According to the invention, the configuration of the various constituent elements of the composite material makes the substantially homogeneous distribution of the particles of catalytic reinforcement material (s) in the metallic matrix 2, leads to a physical separation of the

particles between them.

  The metal matrix acts as a diffusion barrier at temperatures encountered in exhaust media. The growth of particles by diffusion and

  decrease in their number is thus limited.

  This barrier thus avoids or delays the sintering of the powders inside the composite material.

  use temperatures, which then retain their original surface area and catalytic activity.

  The particles of catalytic reinforcing material (s) have a similar effect on the metal matrix since they prevent the magnification of the grains and allow the material to retain its properties

  mechanical after several thermal cycles.

  In addition, the invention has the advantage of allowing the development of catalytic phases containing various active substances, which can selectively and efficiently convert the harmful substances contained in the

exhaust gas.

  It also has the advantage of making it possible to locally enrich the surface of the already catalytically active composite material by adding other materials

  active, leading to even better efficiency.

  It is also noticeable that it is thus possible to enrich the surface of the precious metal composite catalyst in amounts substantially lower than the current catalysts, thus making it possible to gain efficiency.

cheaper.

  The present invention is illustrated in greater detail by the following examples given by way of illustration and not limitation: 2i)

EXAMPLES

EXAMPLE 1

  On a ferritic stainless steel support type! FeCrAlY sheet-shaped 50 μm thick (1000 x 60 x 0.05 mm), the following surface treatments are carried out: The support is immersed in degreasing and stripping baths to eliminate from the surface all foreign bodies, solid and liquid, which can cover it and also dissolve or detach the chemical compounds present such as oxide layer or other compounds of the metal. The degreasing bath consists essentially of caustic soda and a surfactant marketed under the

  GH50 name by the company Frappaz.

  The following table 2 indicates the conditions of use: The pickling bath consists of a solution

  hydrochloric acid at a rate of 400 ml / 1 of 37% HCl.

  The stripping is carried out between the degreasing steps and

electrolytic degreasing.

  1 (Table 2: Conditions of use of the bath of

GH50 degreasing.

  Degreasing Quantity Temperance Current density Cluster time 80 g 700C O 10 Electrochemistry 80 I 20 C 5 A / dm2 3 min A nickel electrolytic interface layer is then produced, very thin, less than 1 μm in thickness. hydrochloric acid from a

Wood's bath.

  The electrolysis is carried out at a relatively high current density and with a low faradic efficiency. 2, in the case of the subsequent formation of a cobalt matrix composite material, zinc or copper sublayers are advantageously produced in acid baths,

  following a pre-nickel plating of Wood as mentioned above.

  These layers do not exceed 1.5 mm in thickness. Table 3 below indicates the electrolytic conditions for producing the intermediate metal layers of the

layers of nickel and copper.

  Table 3: Laying Conditions

metal intermediates.

  Wood Nickel Formula j Quality Quantity (M / I) Quantity (g / I) Nickel ChlorideNiCI :. 5 H: O RP 1.00 240 l (> Hydrochloric acid HCI - 37% 1.21 100 mIl / Temperature 20 C pH 0 Density 10 A / dm2 Deposition time (speed) 360 s (0.12 in / min) Copper Formula Quality Quantity (M / I) Amount (g / I) Copper sulphate SO 4 .5 H-O RP 0.84 210 Sulfuric acid H2SO4 RP 0.51 53 Temperature 20 C pH 0 Current density 2 A / dm2 Deposition time (speed ) 90 s (0. 32un / min) The surface treatments carried out for the FeCrAlloy type ferritic steel support are as follows: - chemical degreasing at 70 ° C. for 10 minutes, - chemical etching in a hydrochloric medium for 5 minutes followed by an electrolytic etching of 24 seconds at A / dm 2, electrolytic degreasing at 20 ° C. for 3 minutes at 5 A / dm 2, pre-nickel plating at 20 ° C. for 6 minutes at 10 A / dm 2, copper plating at 20 ° C. for 1 hour. , 5 minutes at 2 A / dm 2, this last treatment not being performed if the composite

later is chromium matrix.

  Two rinses are performed between each treatment.

  A chromium or cobalt matrix composite coating is then made on the surface of the

previously obtained support.

  The procedure is electrolytically coded as I (indicated hereinafter: A Co304 cobalt oxide powder obtained by soft chemistry is used from oxalic precursors having a specific surface area of 40 m 2 / g for

  Spherical morphology and a size of 1 Mm on average.

  This is suspended in each of the electrolytes defined in Table 4, hereinafter

150 g / l.

  A cobalt soluble anode is used for the cobalt matrix composites and an insoluble anode

  platinum titanium for chromium matrix composites.

  The dissolved metal content (chromium, cobalt) is

0.3 M in cobalt and 3 M in chromium.

  The suspension of the particles in the electrolyte is obtained by the use of an upward flow

nitrogen at a rate of 150 ml / min.

  The following table 4 indicates the electrolytic conditions of elaboration of the composite material to

cobalt or chromium matrix.

  Table 4: Conditions of elaboration of coatings in composite material Composite i matrix Formula Quality Quantity (M / A) Quantity (g /) cobalt Cobalt sulphate CoSO4. 7HO0 RP 0.300 85 Calcium Chloride CaCI: RP 0.315 Potassium Chloride KCI RP 4.024 300 Hy barium hydroxide Ba (OH) -, 8HO RP 0.006 2 Temperature 55 C pH 2 Current Density 1.5 A / dn2 Deposition time (speed 20 min (0, 0 gn / min) Matrix composite Formula Quality Quantity (M / l) Amount (g / l) Chromium Chromic acid CrO3 RP 3,000 300 Ethanol C2H60 95% 0.027 1.6 Na Hexafluoride: SiF6 RP 0.005 sodium Acid nitric HNO3 65% 0.015 Hydroxyl of barium Ba (OH) 2, 8H.O0 RP 0.002 0.5 Temperature 15 C pH 0 Current density 25 A / dm2 Deposition time (speed) 16 rmin (0.35 xm / min) Stabilization heat treatment is performed

at 400 ° C for 1 hour.

  The average duration of production of the composite material coating, in a thickness of 6 μm, is

less than 1 hour.

  The thickness of the coating is here limited to a few micrometers because of the presence of the stainless steel metal support and its intrinsic mechanical properties, the mechanical contribution of the matrix of the composite material, especially with regard to the holding

  material, then becoming negligible.

  A catalyst of the type illustrated in FIG. 6 is thus obtained formed on a ferritic stainless steel support 2 of the FeCrAlY type, and provided with an intermediate layer 3 of nickel optionally covered with a copper layer in the case of a chromium matrix composite material and a coating 4 of Co / Co304 or Cr / Co304 composite material formed above the intermediate layer (s). The material has a very aerated microstructure, the specific surface of the matrix being from 0.2 to 0.8 m 2 / g and that of the catalytic reinforcing material 2 (> being 40 m 2 / g) .The specific surface of the composite material is 1 to 3 m2 / g, its surface is black, very rough, and its mechanical resistance is

equivalent to that of the support.

  The catalytic properties of these materials for an apparent area of 2 x 12 cm 2 are shown in Table 5 below. These properties were determined under static conditions at 400 ° C. with simple gases (HC or NOx) according to the reactions:

2NO + 2CO -> N2 + 02 + 2CO2

  HC with for example for C2H6 ethane:

C2H6 + 7/202 ---> 2CO2 + 3H20

  Table 5: Catalytic properties Catahseur Cataheur NO, (400 C) HC (400 C) Conversion rate Conversion rate 0% reinforcement 60% 21 / no support + nmance Cobalt 6.2% Co304 76 '% o 46 "0% reinforcements 13'Y 2% support FeCrAIY + maince Cobalt 6.2% Co30O48 (% 31 0% reinforcements 20% 21% [t no support + matnce Chrome 2.3% Co30468% 72% 0% reinforcements 18% 16% support FeCrAIY + matnce Cr 2.3% Co304 76% 60% 1 5

EXAMPLE 2

  The procedure is as described in Example 1.

  After formation of the Co / Co304 or Cr / Co304 composite material coating, a coating is produced on the surface.

  2t additional catalytic material, by electrophoresis.

  The electrophoresis coating is performed after rinsing and drying the composite material coating

previously filed.

  It is obtained in an organic solution containing

g / 1 cobalt oxide Co304.

  All the particles (50 g / l) are loaded into a solution containing 5 ml of isopropanol per gram of powder, 0.14 ml / g of a 2.5% solution of polyvinylpyrrolidone (PVP), 0.125 ml / g acetic acid and 50 ml / g

of sodium acetate.

  The electrical charge of the particles is obtained by ion exchange between the solution and the surface of the particles. The particles of Co304 are suspended in

  the solution by mechanical stirring for 2 hours.

  After separation of the liquid and solid phases, the

  powder is dried at 140 ° C for 20 hours.

  The powder is then resuspended in a

  pure solution of isopropanol under the same conditions.

  This solution is strongly stirred before deposition so as to suspend all the particles. 1) The deposit is made under a difference of

  potential of 240 volts, the agitation then being zero.

  The duration of application of the voltage is 60 seconds. The displacement and deposition of approximately 11 g of Co304 cobalt oxide particles on a surface is thus obtained.

of 100 x S x 2 cm2.

  After the coatings have been deposited, sintering is carried out

700'C in a passage oven.

  A catalyst of the type illustrated in FIG. 7 is thus obtained, formed on a ferritic steel support 2 FeCrAlY provided with a nickel interface layer 3 optionally covered with a copper layer in the case of a material composite chromium matrix, then a layer 4 of the composite material Co / Co304 or Cr / Co304 and finally coated with an oxide layer 5 obtained by electrophoresis.

EXAMPLE 3

  A tube-shaped converter 51 mm in length and 25 mm in diameter is made from the supports provided with the coatings as obtained from the

Examples 1 or 2.

  The converter 10, illustrated in FIG. 11, is formed from 50 cm of corrugated strip 11 and 50 cm of flat strip 12 by concentric winding (as shown diagrammatically in FIG. 10) of these two stripes around

  a shaft 13 of stainless steel 3 mm in diameter.

  As can be seen in FIG. 10, the assembly is introduced into a 25 mm stainless steel tube 14

  of diameter and 51 mm in length.

  After forming this converter, the

  deposit of Co304 cobalt oxide or chromium-mixed

  Cr2CuO4 copper. I ") For this, one operates by impregnation either with a solution of cobalt nitrate or with a mixed solution

  of chromium nitrate and copper nitrate.

  Chemical impregnation conditions are indicated

in the following table 6.

  Table 6: Table of catalyst impregnation conditions. Impremation Solution composition Impregnation time Cobalt. Co304 100 ml of acetone Impregnation C 120 g of cobalt nitrate 30 min Dissolution I hour of absolute ethanol Chromium-copper: Cr: CuO4 25.3 g of chromium nitrate 30 min Impregnation RQ 8.8 g of copper nitrate Dissolution hour The impregnation is followed by a thermal decomposition treatment at 500 ° C. for one hour which causes the

  formation of oxides on the surface of the converter.

  The heat treatment is carried out in the following manner: - heating up to a temperature of 150 ° C. with a temperature rise rate of 50 ° C. per hour, - one hour dwell at 150 ° C., - heating up to at 500 C with a temperature rise rate of 85 ° C per hour, - one hour stand at 500 ° C, - lowering temperature to 1 () ambient temperature (20 ° C) with a speed decrease

150 ° C per hour.

  The weight gain of the converters after impregnation and thermal decomposition is of the order of 1.14 g for the impregnation Co304 and 0.65 g for

17 Cr2CuO4 impregnation.

  The increase in mass is related on the one hand to the weight saving which comes from the chemical impregnation of active compounds forming oxides chemically and mechanically hooked to the support and on the other hand, to the gain of 2 () mass which results from the oxidation of the metals forming the support. This last mass gain is difficult to estimate because it is likely to evolve according to the

nature of the different layers.

  The thickness of the oxide layer formed is impregnated and decomposed in a wide range of% around 1 mm for Co304 and 50% around 2 mm.

for Cr2CuO4.

EXAMPLES 4 TO 27:

  (, It is made different coatings composite material alone or successively composite material

  then in additional active matter (s).

  The procedure is similar to the previous examples on a FeCrAlY type ferritic steel support. According to these examples, the nature of the intermediate layer which is either nickel or copper is varied, the nature of the matrix of the composite material which is either chromium or cobalt, the presence or the absence of an additional coating oxide (additional active ingredient) produced by cataphoresis or by impregnation. I () The cobalt oxide powder is manufactured from the decomposition at 400 ° C of cobalt oxalate and

  has a specific surface area of 40 m 2 / g.

  The cobalt and chromium matrices are obtained according to the preceding indications from the reduction

Electrolyte of their salts.

  Impregnations C0304 and Cr2CuO4 are derived from the decomposition of organic solutions (Table 6). Their intrinsic characteristics can not be determined because their quantity is too small on the surface of

catalysts.

  The following Table 7 summarizes the compositions of the samples prepared. Table 7: Composition Table of the Samples Manufactured. Coating support Coating Additional coating (s) Number of Example Coat Composite Layers Absence 2 4 Impregnation CoO04 3 5 1 0 l Impregnation CrCuO4 3 6 Chromium Cataphoresis Co0O4 3 7 Cataphoresis then impregnation CotO4 4 8 Nickel Cataphoresis then impregnation Cr7CuO4 4 9 i Absence 2 10 Impregnation Co1O4 3 1 1 Impregnation CrCuO4 3 12 Cobalt Cataphoresis CotO4 3 13 Cataphoresis then impregnation CoQO4 4 14 Steel Cataphoresis then impregnation CrCuOA 4 15 Ferritic Absence 2 16 FeCrAlloy Impregnation CoO4 3 17 Impregnation CrCuO4 3 18 Chromium Cataphoresis Co104 3 19 2 5 Cataphoresis then impregnation CoOA 4 20 Copper Cataphoresis then impregnation CrCuO4 4 21 Absence 2 22 Impregnation CoIO4 3 23 Impregnation CrCuO4 3 24 3 0 Cobalt Cataphoresis CotO4 3 25 Cataphoresis then impregnation CobO1 4 26 - 1. _ Cataphorese then impregnation Cr7CuO4 4 27 EXAMPLES 4, 10, 16 and 22: A tube-shaped converter 51 mm in length and 25 mm in diameter is produced. be equipped with coatings as obtained at the end of Example 1, with more particularly the sucessive coatings indicated in FIG.

table 7.

  EXAMPLES 5, 6, 11, 12, 17, 18, 23 and 24: A tube-shaped converter 51 mm in length and 25 mm in diameter, provided with coatings as obtained at the end of FIG. Example 3, with more particularly the successive coatings indicated in FIG.

table 7.

  EXAMPLES 7, 13, 19 and 25: In5 A tube-shaped converter having a length of 51 mm and a diameter of 25 mm provided with coatings as obtained according to Example 2, with more particularly the successive coatings indicated in

table 7.

  EXAMPLES 8, 9, 14, 15, 20, 21, 26 and 27: A tube-shaped converter having a length of 51 mm and a diameter of 25 mm provided with coatings as obtained from FIG. Example 2 and additional coatings as obtained at the end of Example 3, with more particularly coatings

in Table 7.

  Catalytic Properties Catalytic tests are carried out using a dynamic analysis bench. Measurement systems are closer to the actual conditions of an automobile exhaust medium, depending on the temperature, the conversion rates of carbon monoxide (CO), hydrocarbons

(HC) and nitrogen oxides (NOx).

  The main characteristics of the measuring bench used are the following: - high gas flow rate: 30 l / min, - heating of gaseous flow and not of the catalyst, - operation in dynamic mode by linear increase of the temperature,

  - addition of water and CO2 in the gas stream.

  The test is carried out by passing over a catalyst obtained according to the preceding examples, a gaseous mixture preheated in an oven and whose temperature is increased linearly up to 500 ° C.

at a rate of 40 ° C / min.

  The mixture is analyzed after passage through the catalyst, almost in real time, by spectrometry

IR.

  The composition of the gaseous flow passing through the converter is the following: - CO 250 ppm - C2 10% - C3H6 (propene) 250 ppm -H20 10% - NO 500 ppm -N2 QSP

- 02 2.5%

  Figure 12 shows the catalytic conversion rates of unburned hydrocarbons (HC) and carbon monoxide (CO) at 300 ° C, obtained with converters comprising 1 to 3 layers of active material coating

  on a nickel interface layer.

  The first layer of active material is formed by a cobalt matrix (C) or a chromium matrix (R) composite material, the reinforcing material consisting of oxide

Cobalt Co304.

  According to the cases, it has been realized on this composite material a deposit of additional active ingredient is

  by impregnation either by electrophoresis and impregnation.

  The results obtained show that cobalt-matrix compounds are more intrinsically active than chromium-matrix composite materials and convert carbon monoxide more readily but are less active with respect to hydrocarbons, in particular because of

  their lower surface area.

  In contrast, chromium-matrix composite materials are less generally active but have a larger surface area and contribute more efficiently to the oxidation of hydrocarbons. It is also observed from the results obtained that a chemical impregnation leading to the deposition of cobalt oxide Co304 allows the preservation, even after heat treatment, of the initial catalytic properties of the cobalt-matrix compounds while an impregnation leading to the deposition of mixed chromium / copper oxides can improve the performance of intrinsically

2, weak.

EXAMPLE 28

  The formation of a composite material coating is carried out on a ferritic stainless steel support of the FeCrAlY type of 50 .mu.m thick. A nickel interface sub-layer was electrolytically deposited after treatment of the surface of the support

as shown in Example 1.

* A coating is made of composite material having on both sides of the support and having a

thickness of 3 pm.

  This composite material is cobalt matrix, black cobalt having a high roughness in sand pink, and contains 6% spherical particles of Co304 cobalt oxide with a specific surface area of 40 m 2 / g obtained by soft chemistry. We proceed to the concentric winding of 2

  strips thus coated, one being made on a flat support and the other being corrugated.

  The final dimensions of the converter thus formed are part of a cylinder 25 mm in diameter and

51 mm in length.

  A thermal stabilization treatment is carried out

1 2 hours at 500 ° C.

  An additional active ingredient consisting of platinum is then deposited by chemical impregnation. The catalyst completely absorbs 2 ml of a

  solution containing 50 mg of hexachloroplatinate.

  The resulting catalyst contains 17 mg of platinum after a new heat treatment at 300.degree.

  hours and under humid atmosphere at 5% hydrogen.

  This figure corresponds to a content of 0.7 g of platinum per 1000 cc of catalyst volume and is 2 times smaller than that of current commercial catalysts.

EXAMPLE 28 COMPARATIVE

  The catalytic performances of the converter prepared according to Example 28 are analyzed by comparison

with a reference catalyst.

  This reference consists of a monolithic cordierite support, equipped with a wash-coat of alumina

  and 1.4 g of platinum per liter of catalyst.

  Figures 13 and 14 show the results of

conversion achieved.

  The composition of the gases is as follows: CO: 300 ppm NO: 300 ppm C3H6: 150 ppm C3H8: 150 ppm

C02: 10%

02: 10%

H20: 10%

  Flow rate: 30 l / min According to these results, it can be seen that: the catalyst initiation temperatures comprising a coating of composite material are higher, of the order of 50.degree. C., the conversion rates at 300.degree. C, obtained for carbon monoxide (CO) and propane (C3H6) are substantially the same for both types of catalyst, - at 450 ° C, the conversion rates of nitrogen oxides (NOx) are substantially identical but on the other hand, the catalyst comprising a composite material according to the invention makes it possible to achieve conversion rates of

  propane, hydrocarbon difficult to oxidize, more important.

EXAMPLE 29

  ) On a ferritic stainless steel support of FeCrAlY type in sheet form of 50 μm in thickness of dimensions 40 × 30 mm, the treatments of

  conventional preparation surfaces, indicated in Example 1.

  After completion, if necessary, of the electrolyte nickel interface layer, the support is immersed in a nickel electrolyte electrolyte containing nickel salts and a reducing agent based on sodium hypophosphite. In particular, a distributed electrolyte is used

  by the company Frappaz called Ni216 containing 6 g / l of nickel metal. The temperature is set at 90 ° C.

  Co304 cobalt oxide powder of 22 m 2 / g was obtained by mild chemistry as previously indicated. The amount of suspended particles is 100 g

  per liter of nickel electrolyte chemical.

  The speed of obtaining the deposit is 10 to 15 Mm / h.

  A deposit of 4 Mm was made in 20 minutes.

  The specific surface of the Ni / Co304 composite containing

  about 4.5% Co304 is less than 0.03 m2 / g.

  The catalytic conversion rates of HC and NOx by static analysis at 400 ° C are shown in

Table 8 below.

  i (> TABLE 8: Catalyst Specific Area Conversion Rate Conversion Rate

_____ __ HC 400 C NO1 400 C

  Co304 powder 22 m2 / g 100% 93% Composite 0.03 m2 / g 15% 10% Ni / Co304 21) D

Claims (29)

  1 / Catalyst of composite material, especially for converter for automobile exhaust gas, characterized in that it comprises a metal matrix in which are dispersed, in a substantially homogeneous manner, particles of at least   a catalytic reinforcing material.   2 / Catalyst of composite material according to claim 1, characterized in that the particles of catalytic reinforcing material consist of precious metal particles and / or oxide powders of transition metals.   3 / Catalyst of composite material according to one   any of claims 1 and 2, characterized in that the particles of catalytic reinforcing material are   particles of platinum, rhodium and / or palladium.   4 / Catalyst made of composite material according to one   any of claims 1 and 2, characterized in that   that the particles of catalytic reinforcing material consist of an oxide powder of formula AxByO4 in which A and B are metal cations chosen from transition metals.   Composite material catalyst according to Claim 4, characterized in that the oxide powder   is of spinel or perovskite structure.   6 / Catalyst of composite material according to one   any of claims 4 and 5, characterized in that   the catalytic reinforcing material consists of a powder of coltan oxide (Co304), zinc cobaltite   (Co2,84Zn0,1604) or cobaltite chromium (Co2CrO4).   7 / Catalyst of composite material according to one   any of the preceding claims, characterized in that   what it includes a mixture of reinforcing materials from different natures.   8 / Catalyst of composite material according to one   any of the preceding claims, characterized in that   the particles of catalytic reinforcing material have a specific surface area of between 1 and 100   m2 / g, preferably between 20 and 40 m 2 / g.   9 / Catalyst of composite material according to one   any of the preceding claims, characterized in that   the particle size of catalytic reinforcing material is less than 30 μm and is preferably between 0.5 and 5 μm.   / Composite material catalyst according to one of   any of the preceding claims, characterized in that   what particles of catalytic backing material   are spherical or acicular forms.   11 / Catalyst of composite material according to one   any of the preceding claims, characterized in that   the metal matrix is selected from copper, nickel, cobalt, chromium, iron, zinc, cadmium, silver, platinum, rhodium, ruthenium, titanium, molybdenum, vanadium , tungsten and   their alloys or aluminum alloys.   12 / Catalyst of composite material according to one   any of the preceding claims, characterized in that   what the metal matrix is selected from cobalt and chromium.   13 / Catalyst of composite material according to one   any of the preceding claims, characterized in that   that the metal matrix constitutes between 85 and 95% by weight of the composite coating.   14 / catalytic converter, characterized in that it comprises a composite material according to one   any of the preceding claims.   Catalytic converter according to claim 14, characterized in that it comprises a metal or ceramic support of a shape adapted to the conversion of the exhaust gases and in that said composite material forms a catalytic coating on at least one face of said support. 16 / catalytic converter according to claim 1, characterized in that the composite coating has a thickness of less than 100 μm, preferably between 1 and 10 Mm.   17 / Catalytic converter according to any one   claims 14 to 16, characterized in that   comprises a metallic support of stainless steel containing chromium, of ferritic or austenitic structure. 18 / Catalytic converter according to any one   claims 14 to 17, characterized in that   includes one or more interface layers between the   support and composite coating.   19 / catalytic converter according to claim 18, characterized in that the interface layer is a   layer of nickel, zinc and / or copper.   Converter according to claim 14, characterized in that it consists of a material   composite according to any one of claims 1 to   13, shaped according to a structure adapted to the exhaust gas conversion.   21 / Converter according to claim 20, characterized in that the composite material has a thickness between 30 and 100 Mm, preferably between 40 and 80 Mm.   22 / Catalytic converter according to any one   Claims 14 to 21, characterized in that the   surface of the composite material is enriched in additional active material (s) comprising one or more   transition metal oxides and / or precious metals.   23 / catalytic converter according to claim 22, characterized in that the content of material (s)   catalytic active (s) is between 0.1 and 10%.   24 / exhaust line element especially for a motor vehicle, characterized in that it comprises a catalytic converter according to any one of Claims 14 to 23.   Process for the manufacture of a catalytic converter comprising a composite material, according to one of   any of claims 14 to 23, characterized in that   it comprises the steps of: - preparing metal powders and optionally metal oxides having the appropriate dimensions and morphology or precursors thereof, for forming the metal matrix and the material (s) ) catalytic reinforcement of the composite material; - preparing a metal or ceramic support for receiving the composite material; forming, on at least one face of said support, a coating made of composite material comprising a metal matrix in which particles of at least one catalytic reinforcing material chosen from precious metals and / or oxides are dispersed in a substantially homogeneous manner transition metals;   heat-treating the assembly obtained.   26 / A method according to claim 25, characterized in that the coating of composite material is formed by electrolytic coding in the presence of a support of conductive material or made conductive, the electrolyte containing dissolved metals constituting the metal matrix and the particles in suspension of at least one catalytic reinforcing material or precursor thereof (s) -ci.   27 / Method according to any one of the claims   and 26, characterized in that a soluble anode comprising the metal or alloy for forming the   metal matrix of the composite material.   28 / A method according to any one of the claims   at 27, characterized in that the particle content   solids of the electrolyte is between 50 and 500 g / l.   29 / A method according to any one of the claims   at 28, characterized in that the current density is between 1 and 40 A / dm2.   / Method according to any one of the claims   at 29, characterized in that the concentration of metal salts in the electrolyte is between 0.1 and M, preferably 0.3 and 3 M. 31 / A process according to claim 25, characterized in that the coating of material composite is formed by) chemical coding using a chemical reducer, in a medium containing dissolved metals constituting the metal matrix and particles of at least one   catalytic reinforcement material or precursor of that (s) - in suspension.   32 / A method according to claim 25, characterized in that the coating of composite material is formed by cataphoresis or anaphoresis, by applying an electric field of 50 to 500 V to an aqueous solution and / or organic containing metal particles constituting the matrix and particles of at least one catalytic reinforcing material or precursor of that (s) -ci.   33 / Method according to any one of the claims   and 32, characterized in that the metal matrix and the catalytic reinforcing material are such that   defined by any one of claims 3 to 13.   34 / Method according to any one of the claims   at 33, characterized in that the particles of catalytic reinforcing material are obtained from precursors of these.   / Method according to any one of the claims   31 to 34, characterized in that the metal matrix is   selected from nickel, cobalt and zinc.   36 / Method according to any one of the claims   at 35, characterized in that, prior to the formation of the coating of composite material, a surface etching and / or degreasing treatment is carried out   support for receiving this coating.   37 / Method according to any one of the claims   at 36, characterized in that, prior to the production of the composite material coating, two <> one or more interface layers are formed on the surface of the support intended to receive this coating in particular based on nickel, zinc and / or copper.   38 / A method according to any one of the claims   at 37, characterized in that the surface of the composite material coating is enriched with one or more additional active substances, in particular by electrophoresis or by impregnation, selected from among the   precious metals and / or transition metal oxides.   39 / A method for preparing a composite material according to any one of claims 1 to 13,   characterized in that a coating of composite material is formed on a support as described in one of the   any of claims 25 to 38, and this   coating said support, in particular by peeling or dissolving.