Influence of adsorbed CH 3O on CO desorption from Ni/Al 2O 3

Abstract

The desorption rate of CO from the Ni surface of a 5.1% Ni/Al 2O 3 catalyst was significantly increased by the presence of CH 3O on the support. The CH 3O was formed by CO and H 2 coadsorption at 385 K. Reverse spillover of CH 3O, as CO desorbed, maintained the Ni surface at a high coverage of CO and H 2. This increased the rate of CO desorption because of the repulsive interactions present between CO molecules on Ni at high coverages and because readsorption on Ni was decreased. These studies show that CH 3O must undergo reverse spillover onto the Ni surface in order to decompose. Decomposition directly on the A1 2O 3 surface does not occur at these temperatures. Carbon isotope labeling and temperature-programmed desorption were used to study this process. For hydrogen isotope labeling, a kinetic isotope effect for CH 3O decomposition indicated that C-H bond breaking or surface diffusion limited CH 3O decomposition. Oxygen isotope labeling showed that the carbon-oxygen bond did not break upon the formation or decomposition of CH 3O.