Patent GB-1068186-A (GB)
Title: Improved supported catalysts
IPC: B01J35/02
Filed: 1964-06-25
Abstract: A crystalline refractory material, for use as a catalyst support, comprises a -alumina and optionally other metal oxides compounded and/or in solid solution with the alumina and is prepared by oxidation of aluminium or an alloy thereof in the presence of a fluxing agent, the refractory material containing at least 30% alumina and at least 1% aluminium in a valence state of less than 3. The fluxing agent, preferably 0.02-20% of the aluminium, may be an alkali metal oxide or hydroxide, the oxide of an alkaline earth metal or of V, Cr, Mo, W, Cu, Ag, Zn, Sb, Bi or a precursor thereof, e.g. the acetate, benzoate, bisulphate, bisulphite, bromate, nitrate, silicate, sulphate, sulfite or thiosulphate or trialkyl tin oxide or lead silicate.  The catalyst support in the form of an alumina-containing skeletal structure may be formed by oxidizing aluminium particles in situ in a porous body.  The unfired body, of porosity at least 20%, may contain up to 8 parts per part aluminium of a particulate filler refractory which may comprise up to 48% of the unfired body.  The filler refractory may be the carbide of Al, B, Hf, Nb, Si, Ta, Th, Ti, U, V or Zr; the boride of Cr, Hf, Mo, Nb, Ta, Ti, W, V or Zr; or the oxide of Al, B, Ce, Hf, La, Mg, U, Y, Zr or Si, or a precursor of any of these, and it may reside in the eventual catalyst support as such or as a compound.  Alternatively, the aluminium particles are so separated that discrete particles are produced instead of a skeletal structure, e.g. by mixing with a powdered refractory that does not react with aluminium or alumina under the firing conditions. The discrete particles may be separated by screening.  The aluminium particles should be clean, free from grease and oil and should have one dimension of at least 7 mils, another of at least 0.5 mils and a third of 0.5 to 200 mils. They may be spheres, short staples, continuous filaments or organized into woven screens or honeycombs.  The flux may be applied to the metal dry, in solution, as a gas or as a melt. A thickener, e.g. sodium carboxymethyl cellulose may be incorporated.  The fluxing agent may be mixed with the filler refractory and the metal shapes added to the mixture.  A suitable filler refractory may also act as the fluxing agent.  The green strength of the shaped body may be increased by addition of H2O, ethyl alcohol, ethylene glycol, acetone, solutions of carboxymethyl cellulose, rubber, gum arabic, polyvinyl alcohol, natural gums or Sorel cement.  The moulded green body is dried to remove volatiles and produce the desired porosity, heated in air at a low temperature, e.g. less than 400 DEG  C. until a stress-bearing oxide film develops when the temperature may be increased up to 1350 DEG  C.  The oxidation of the aluminium should be 10-90% complete and the product preferably contains no more than 10% metallic aluminium. A catalyst support in particulate form may also be prepared by firing the aluminium and fluxing agent in the form of thin porous sheets which are subsequently comminuted to the desired particle size. These may be refired if required for further oxidation.  The support may be formed as a lining on, e.g. steel.  For use in automotive exhaust abatement, a steel pipe is dipped into molten aluminium, cooled, coated with sodium silicate and fired in air.  Alternatively, a mixture of aluminium fibres and sodium silicate is pressed on to the inner surface and fired.  The skeletal structure comprises pores or cells of size 0.5-200 mils, each cell corresponding to an aluminium particle if these were sufficiently remote.  The skeletal structure is observable by dissolving away all other materials.  The product is greyish, probably due to incompletely oxidized aluminium. The catalyst component may be incorporated in the unfired mixture or the fired body may be impregnated. The catalyst, e.g. platinum, palladium, chromium oxide, molybdenum oxide, nickel cobalt or iron, zinc chromite or manganese chromite is applied by known methods, together with promoters such as SiO2, TiO2, ThO2.  In additio to automotive exhaust gas treatment, the supported catalyst is used in organic oxidations and reductions, e.g. methane to formaldehyde, and interconversion of sulphur dioxide and trioxide.ALSO:A crystalline refractory material, for use as a catalyst support, comprises a -alumina and optionally other metal oxides compounded and/or in solid solution with the alumina and is prepared by oxidation of aluminium or an alloy thereof in the presence of a fluxing agent, the refractory material containing at least 30% alumina and at least 1% aluminium in a valance state of less than 3.  The fluxing agent, preferably 0.02 - 20% of the aluminium, may be an alkali metal oxide or hydroxide, the oxide of an alkaline earth metal or of V, Cr, Mo, W, Cu, Ag, Zn, Sb, Bi or a precursor thereof e.g. the acetate, benzoate, bisulphate, bisulphite, bromate, nitrate, silicate, sulphate, sulfite, or thiosulphate or trialkyl tin oxide or lead silicate.  The catalyst support in the form of an alumina-containing skeletal structure may be formed by oxidising aluminium particles in situ in a porous body.  The unfired body, of porosity at least 20%, may contain up to 8 parts per part aluminium of a particulate filler refractory which may comprise up to 48% of the unfired body.  The filler refractory may be the carbide of Al, B, Hf, Nb, Si, Ta, Th, Ti, U, V or Zr; the boride of Cr, Hf, Mo, Nb, Ta, Ti, W, V or Zr; or the oxide of Al, B, Ce, Hf, La, Mg, U, Y, Zr, or Si, or a precursor of any of these, and it may reside in the ventual catalyst support as such or as a compound.  A thickener, e.g. sodium carboxymethyl cellulose may be incorporated.  The green strength of the shaped body may be increased by addition of H2O, ethyl alcohol, ethylene glycol, acetone, solutions of carboxymethyl cellulose, rubber, gum arabic, polyvinyl alcohol, natural gums or Sorel cement.  The catalyst component may be incorporated in the unfired mixture or the fired body may be impregnated.  The catalyst, e.g. platinum, palladium, chromium oxide, molybdenum oxide, nickel cobalt or iron, zinc chromite or manganese chromite is applied by known methods, together with promotors such as SiO2, TiO2, ThO2.  The supported catalyst is used in organic oxidations and reductions, e.g. methane to formaldehyde and interconversion of sulphur dioxide and trioxide.