Metal/oxide support effects in the H 2H 2O deuterium exchange reaction catalyzed by nickel

Abstract

Catalysts of nickel supported on BeO, MgO, ZnO, Al 2O 3, Cr 2O 3, SiO 2, TiO 2, ZrO 2, ThO 2, and UO 2 have been prepared by coprecipitation with different precipitants and by impregnation of the basic nickel carbonate with a salt of the support. Nickel surface areas, which are required to measure the specific rates, were determined by hydrogen chemisorption. The fraction of nickel exposed increases when the support content is increased up to a saturation value. The most efficient supports for nickel dispersion are silica and alumina, while the least efficient is titania. Specific rates for hydrogen-water deuterium exchange over unsupported and supported nickel catalysts have been measured. Each support increases the specific catalytic activity value of nickel in comparison with that of the unsupported nickel. When the support content is increased, the specific catalytic activity increases up to a limiting value. This limit is attained when the number of metal-support contacts reaches a maximum. The most efficient supports are TiO 2 and ZrO 2, which increase the specific rate by about three orders of magnitude, and the least efficient are ZnO and SiO 2, which increase it only by one order of magnitude. The influence of the support on the specific catalytic activity is attributed to the participation of the support surface in the activation of the water molecule.