Propane hydrogenolysis on sulfur- and copper-modified nickel catalysts

The rates and selectivity of propane hydrogenolysis on Ni/ MgAl2O4 catalyst s modified by preadsorbed sulfur and on Ni/SiO2 catalysts modified by coppe r alloying have been measured. On both types of catalysts, the rate of etha ne production goes through a maximum at high temperatures. For the NiCu/SiO 2 catalysts, this behavior correlates with the onset of secondary hydrogeno lysis of ethane, but not for the sulfur-modified Ni/MgAl2O4 catalysts. The selectivity for ethane formation on Ni/MgAl2O4 catalysts was higher with su lfur than without, but a decreasing function of sulfur at high coverage. Th e selectivity on NiCu/SiO2 catalysts was found to increase monotonically wi th the copper content, Comparisons with a previous propane hydrogenolysis s tudy on nickel-copper catalysts with very different surface properties reve al surprising agreements. Our NiCu/SiO2 catalysts have been shown to be str ongly enriched in copper in the surface of the alloy particles after reduct ion. This is similar to previous results for unsupported NiCu catalysts but in contrast to the NiCu/SiO2 catalysts used by Dalmon and Martin (J. Catal . 66, 31 (1980)), reported to have bulk composition also in the surface aft er reduction. The hydrogenolysis results of the two NiCu/SiO2 catalyst stud ies are, nevertheless, in close agreement, but deviate strongly from the hy drogenolysis results for the unsupported NiCu particles. It is difficult to reconcile the various hydrogenolysis results with simple ensemble models. It is suggested that special sites may dominate hydrogenolysis activity on nickel catalysts. (C) 2000 Academic Press.