Nature of the activity increase of surface Raney nickel treated with cadmium nitrate and sulfate solutions

The laws of cadmium adsorption at nickel surface Raney catalysts (Ni /SUB src/ ) were studied and compared following the exposure of these catalysts to solutions of cadmium nitrate and cadmium sulfate. In both cases cadmium adsorption was shown to occur in the underpotential region, and to be irreversible. During the treatment of Ni /SUB SRC/ in Cd (NO3)2 solutions, cadmium hydroxide precipitates at the electrode surfaces in addition to the specific adsorption of cadmium; this is due to a reduction of the NO3- ions and alkalization of the solution layer next to the electrode. It was found that the additional reduction of hydrogen overpotential found in alkaline solutions at Ni /SUB src/ following treatment with nitrate solutions, relative to Ni /SUB src/ treated with sulfate solutions, is due to an optimum surface oxidation of the electrodes by the nitrate ions rather than to the presence of phase cadmium or cadmium hydroxide at the surface