NiAg catalysts prepared by reduction of Ni2+ ions in aqueous hydrazine: II. Support effect

A series of bimetallic NiAg (Ni + Ag = 1% wt) catalysts supported on amorphous silica was synthesized via chemical reduction using hydrazine as the reducing agent at 353 K. Catalysts were prepared via impregnation or precipitation technique. It was found that the reduction of the Ni2+ ions occurred only in the presence of silver, otherwise a stable blue [Ni(N2H4)3]2+ complex was formed. Comparisons with similar NiAg catalysts supported on crystallized silica as prepared in our previous work indicated that the Ni2+ ions weakly interacted with acidic crystallized silica on which they were readily reduced. For both supports, the combination of silver and nickel gave rise to a synergistic effect due to the existence of NiAg groupings. The surface and catalytic properties of the metal particles formed depended on the Ni:Ag ratio, method of preparation, and acidity of the support.

We studied amorphous silica-supported NiAg catalysts prepared by the hydrazine method. We found that silver permitted hydrazine reduction of the strongly bonded supported Ni2+ ions and, more strikingly, sharply enhanced metal dispersion and catalytic activity of nickel. The results suggest the existence of NiAg species in connection with metal reduction mechanisms and support acid–base properties.Figure optionsDownload as PowerPoint slide