This project is in the general area of analytical and surface chemistry and in the subfield of heterogeneous catalysis. This research program will investigate the ensemble (site-size) requirements for surface-catalyzed reactions using adsorbed bismuth atoms as inert, site-blocking agents. The studies will focus on determining quantitatively the ensemble effects for a number of hydrocarbon conversion reactions on platinum single-crystal surfaces at system pressures near one atmosphere and in characterizing the carbonaceous residue. Correlation of the results of these studies with those from similar studies in ultrahigh vacuum will assist in developing a fundamental undestanding of the reaction mechanisms of hydrocarbon conversion reactions that are of importance in the chemical and petroleum industries and in the development of improved catalysts.