The steam reforming of ethane over nickel/alumina catalysts

Abstract

Results are presented for the steam reforming of ethane over several coprecipitated Ni–Al₂O₃ catalysts from which it is concluded that the reaction proceeds via surface carbon species which then react with water to form carbon oxides or with hydrogen to form methane. In the first of a series of reactions over a clean surface, the selectivity was towards methane, and a steady-state coverage of carbon was established on the surface. In subsequent experiments, the selectivity was initially towards carbon oxides but the selectivity towards methane increased as hydrogen was produced. The coverage by carbon was ca. 10 % of the surface nickel atoms. The dependence of the carbon coverage on reaction conditions was similar to that of the rate of reaction. Temperature-programmed reaction of the carbon and of carbon deposited by the Boudouard reaction or by the decomposition of C₂H₆ or C₂H₄ showed that all these types of carbon were similar. Predeposited carbon had no effect on the rate of subsequent C₂H₆+ H₂O reactions. When carbon was deposited by the decomposition of benzene, it was much less reactive and poisoned subsequent C₂H₆+ H₂O reactions. It was found that when potassium was added to one catalyst, it decreased its activity and metallic area but did not appear to affect the behaviour of the adsorbed carbon.