Oxidative Restructuring of Rhodium Metal Surfaces: Correlations between Single Crystals and Small Metal Particles

Article abstract of DOI:10.1021/j100167a038

The influence of oxidation on the activity and selectivity of rhodium for n-pentane hydrogenolysis has been studied.The catalytic behavior of Rh(100) and Rh(111) single crystals was contrasted with that of a 2 wt percent Rh/SiO2 supported catalyst to elucidate the role of the support.It was found that the activation energy for hydrogenolysis and the product distribution were significantly different on Rh(111) and Rh(100).The product distribution and activity of the annealed (773 K in H2) Rh/SiO2 catalyst matched very well the behavior of the Rh(111) single crystal.Oxidation of the Rh(111) single-crystal surface as well as the Rh/SiO2 catalyst at 773 K and P_O2 = 70 Torr led to an enhancement in activity, a change in activation energy, and hydrogenolysis selectivity.No surface oxygen could be detected by Auger electron spectroscopy (AES) on the oxidized single-crystal metal surface after reaction, suggesting that the reactivity changes were associated with differences in morphology.Oxidation of rhodium leads to an apparent "roughening" of the metal surfaces that persists under reaction conditions.The roughening is manifested by multiple cleavage of C-C bonds within the n-pentane molecule at temperatures where the annealed surfaces cleave a single C-C bond during hydrogenolysis.