| 摘要 |
In a process for the production of an alumina monohydrate-containing composition wherein there is formed an aqueous slurry of an alumina hydrogel which is wholly or predominantly in the monohydrate form, the alumina monohydrate is stabilized against conversion to other forms of alumina by contacting the alumina hydrogel slurry at a pH greater than 7 with a chelating agent containing polycarboxylate ions. The alumina hydrogel may be formed by hydrolysing an aluminium alcoholate, or by admixture of an inorganic base and an aluminium salt of an inorganic acid. The chelating agent comprising e.g. 0.5-3% by weight of the alumina in the slurry, may be added together with, or after, the precipitant employed to precipitate the alumina hydrogel from aqueous solution. Specified chelating agents are polycarboxylic acids containing 2 to 10 carbon atoms and salts thereof, e.g. ammonium citrate oxalate and tartrate. Alumina gel containing a stabilized amount of trihydrate may be obtained by adding to the monohydrate gel an amount of chelating agent insufficient for complete prevention of ageing. The stabilized alumina hydrogels may form the precursor of calcined alumina-based catalysts (Division B1).ALSO:A platinum-alumina catalyst is made by adding chloroplatinic acid and hydrogen sulphide or platinum sulphide sol to an aqueous slurry of alumina hydrogel in which the alumina, wholly or predominantly in monohydrate form, has been stabilized by contact with a polycarboxylic compound at pH greater than 7. The composition may be dried, calcined at 800-1200 DEG F. and reduced by hydrogen at 800-1100 DEG F. The catalyst may contain 0,1-1,5% by weight of platinum, or a platinum-group metal, and may also include chromium and molybdenum oxides. Catalysts having surface areas of 418 sq.m./gm. are referred to.
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