SPILLOVER OF CO AND H2 ONTO AL2O3 SURFACES

Temperature-programmed reaction and desorption (TPR, TPD) for Al2O3 physically mixed with supported Ni catalysts show directly that one of the two CH4 peaks observed previously for TPR (CO hydrogenation) on Ni/Al2O3 catalysts results from spillover of adsorbed species onto Al2O3 and is not due to adsorption on unreduced Ni sites. Temperature-programmed desorption from physical mixtures of Al2O3 and 19% Ni/Al2O3 indicates that the support-bound species is a HCO complex, and the stoichiometry is consistent with that of a CH3O species. The concentration of CH30 on Al2O3 is estimated to be approximately 1 μmol/m2 A1203 (350 μmol/g A1203). Though CH3O does not form on the SiO2 support of Ni/SiO2, it does form on physical mixtures of Ni/SiO2 and Al2O3 that were prepared to provide good contact between particles. The rate of spillover appears to increase with the closer proximity between the support and the catalyst, higher Ni surface area, and better contact between the particles, but it also depends on the Al2O3 area available for transfer. The rate of CH3O hydrogenation increases with Ni surface area. An unexplained loss in Ni surface area was observed with physical mixtures of Al2O3 and catalysts that were prepared by crushing the particles while wet. © 1990.