THE ROLE OF SPILLOVER IN CARBON-MONOXIDE HYDROGENATION OVER ALUMINA-SUPPORTED PLATINUM

Temperature-programmed reaction and desorption (TPR, TPD) were used to study the formation and hydrogenation of CH3O on a 7.7% Pt/Al2O3 catalyst. Methoxyforms in an activated spillover process following CO and H2 adsorption on Pt, and adsorbed CH3O has the samedesorption and reaction properties as adsorbed CH3OH. The CH3O species hydrogenates faster to CH4than does CO adsorbed on Pt. Spillover is faster than hydrogenation at low temperatures, but the activation energy for spillover is smaller. Water significantly inhibits spillover by poisoning the adsorption sites on Al2O3. A physical mixture of Al2O3 and Pt/Al2O3 was used to show that CH3O was adsorbed on Al2O3. At elevated temperature and in the absence of gas-phase H2, CH3O decomposition limits the formation of gas-phase CO and H2. The processes of spillover and hydrogenation to CH4 were studied by TPR in combination with isotope labeling, interrupted reaction, and H2O preadsorption. The surface coverage, healing rate, and H2 pressure during TPR were also varied. © 1993 Academic Press, Inc.