Influence of the surface structure on the kinetics of ethane hydrogenolysis over Ni/SiO 2 catalysts

Abstract

The rate of ethane hydrogenolysis, which was shown previously to be a structure-sensitive reaction, is studied in a large range of pressure and temperature over Ni/SiO 2 catalysts of different morphology. It is observed that the partial reaction order with respect to ethane is unity at low hydrocarbon pressures, and that the partial reaction order with respect to hydrogen and the apparent activation energies vary with hydrogen pressure and temperature. Moreover, orders and apparent activation energies are independent of the nature and of the activity of the catalyst, indicating that the previously reported variations of reaction rate with nickel particle size do not depend on the standard conditions which were chosen. Furthermore, on less active samples, there is no simple relation between the reaction rate, r, and the resulting hydrogen coverage, θ H (as was the case for a very active sample), from which it is concluded that only a small fraction of the nickel surface is active, (111) planes probably being inactive. On the most active sample, it is supposed that most of the nickel atoms are nearly equivalent from the viewpoint of catalytic activity.