SIMILARITIES AND DIFFERENCES IN THE C-C BOND SCISSION OF ETHYLENE AND ACETYLENE ON SUPPORTED IR AND PT CLUSTERS

We have used NMR to study the C-C bond scission of adsorbed acetylene and ethylene on supported Pt and Ir clusters. We have monitored the extent of C-C bond scission by measuring the 13C-13C dipolar interaction. We have found that C-C bond scission of adsorbed ethylene has the same reaction path and activation energy (36 kcal/mol) on Pt and Ir. On the other hand, the predominant intermediate undergoing C-C scission in the case of adsorbed acetylene is different for the metals, and the activation energies are also different (37 kcal/mol on Ir and 53 kcal/mol on Pt). By measuring the 13C-1H dipolar interaction, we have found an extensive dehydrogenation of adsorbed acetylene prior to C-C bond scission on Pt clusters. The results are discussed in relation to Sinfelt's studies of the reaction kinetics of ethane hydrogenolysis and are shown to support the conclusions drawn by Sinfelt. © 1990 American Chemical Society.