PROCESS FOR THE PREPARATION OF A SILVER CATALYST

1400758 Electrolytically producing silver powder SNAMPROGETTI SpA 12 Dec 1972 [28 Dec 1971] 57357/72 Heading C7B Ag is electrolytically deposited on a cathode by electrolysis of a solution containing cations of Ag complexed with ammonia and, during the electrolysis, the Ag is removed from the cathode as a powder as it is formed. The removal may be by brushes (3, 3') rotated by a motor (4) as illustrated in the Fig. (not shown). Alternatively, the removal may be by ultrasonic vibrations, jets of liquid under pressure or by vigorous stirring of the electrolyte. Porous Ag powder can be produced having particle sizes of 300 to 1500 Angstroms. the complexed Ag cations may be derived from silver nitrate, sulphate, acetate, halide, oxalate or ammoniacal silver hydroxides. A colloid such as carboxymethylcellulose may be added to the electrolyte to prevent agglomeration of the powder. The electrolyte may be circulated through a heat exchanger (6) by a peristaltic pump (5). Specified electrolyzing conditions are a temperature of 10-50‹C, a current density of 2-50 ma/cm2 , an aqueous electrolyte made up from AgNO 3 , Na 2 B 4 O 7 NaOH, NH 4 OH and carboxymethylcellulose. In the Examples the cathodes employed are ( 1 and 3) silver plates, (2) a silver net, (4) a silver or stainless steel plate tightly coupled to a graphite plate to form a bi-polar electrode. The Ag produced may be deposited on ceramic material and used as catalyst in the conversion of ethylene to ethylene oxide.