Kinetics of ethane hydrogenolysis over silica-supported ruthenium-group IB metal catalysts

Abstract

We have studied the ethane hydrogenolysis reaction to determine the effect of adding copper and silver to a silica-supported ruthenium catalyst. Specific activities were measured at a number of temperatures as a function of the fraction of Group IB metal. In addition, the effect of changing the ratio of hydrogen to ethane in the feed gas was used to measure apparent orders of reaction as a function of temperature and Group IB metal added. At the lower temperatures studied we found that the effect of adding copper or silver to the catalyst was virtually the same, the differences being attributed to the greater affinity of copper for defect-like sites on the ruthenium crystallites. At higher temperatures, copper and silver acted differently; copper seemed to be active for the removal of site-blocking hydrogen from the active ruthenium surface, while silver merely blocked the ruthenium sites most active for the removal of hydrogen from the surface. We postulate that the defect-like sites of supported ruthenium crystallites are most active for the desorption of weakly adsorbed hydrogen while the actual carbon-carbon bond cleavage takes place on the basal planes. The increase in specific activity observed as the dispersion of the catalyst decreased was attributed to the increase in relative number of carbon-carbon bond-breaking sites. The order of reaction with respect to hydrogen partial pressure suggests that the adsorbed hydrocarbon intermediate has a stoichiometry of C 2H 3.