| abstract |
A shell impregnated catalyst of Pd-Au produced on a silica support by impregnating the support with aqueous solutions of palladium and gold salts or acids and thereafter precipitating water insoluble compounds of Pd and Au on the support with alkali metal silicate or hydroxide fixing agents, then drying the support which has precipitated compounds of Pd and Au on its surface and reducing the surface precipitated compounds of Pd and Au until substantially all of the Pd and Au contents are reduced to a free metal state, after which the catalyst precursor is impregnated with potassium acetate and then dried. Improvements in the catalyst are realized by (1) impregnating the support particles with aqueous solutions of water-soluble palladium and gold compounds so that (a) that the weight ratio of palladium to gold is in the range from 2:8 to 8:2, (b) the volume of the impregnation solution corresponds to from 70 to 100% of the total pore volume of the support particles, (2) precipitating water-insoluble palladium and gold compounds onto the support particles from alkali metal silicates or hydroxides as a precipitating agent (a) containing a 1.1 to 2.2 molar excess, (b) wherein the impregnated support is contacted with the precipitating agent for three hours up to seventy-two hours, (c) in an environment protected from light or, (d) powder, (3) washing the precipitated support with water at a temperature of from 50 to 80 DEG C until a decant of said wash water is negative to a silver nitrate test, (4) reducing the catalyst precursor in nitrogen, (5) impregnating the support particles with potassium alkanoate in a solution of 5-12 wt.% to a point of incipient wetness of the support particles, or (5) final drying the catalyst in nitrogen at 90 DEG C to 150 DEG C for one hour to twenty-four hours. |