FORMATION AND DECOMPOSITION OF METHOXY SPECIES ON A NI/AL2O3 CATALYST

Temperature-programmed reaction and desorption (TPR, TPD) were combined with isotope exchange to study the forward and reverse spillover of CO on a 5.1% Ni/Al2O3 catalyst. Carbon monoxide adsorbs nondissociatively on Ni at 300 K, but a fraction of adsorbed CO dissociates at 425 K. Carbon monoxide on Ni, in the presence of H2 at elevated temperature, spills over to form CH3O on Al2O3. This CH3O can undergo reverse spillover to form both CO and carbon on Ni. For low CH3O coverages, mostly carbon forms, but at higher CH3O coverages, mostly CO forms on Ni. The reverse spillover is faster at higher temperatures, for longer times, and for higher CH3O coverages. The rate of reverse spillover is comparable to the rate of CH3O hydrogenation, and reverse spillover may be the limiting step in Ch3O hydrogenation. The rate of carbon hydrogenation on Ni is significantly inhibited by the presence of CO adsorbed on Ni, perhaps because H2 adsorption sites are blocked. © 1991.