EFFECTS OF TITANIA SURFACE SPECIES ON NICKEL: COADSORPTION OF CO AND H//2.

The authors investigate the possibility that the changes in relative CO and hydrogen adsorption strengths induced by titania result in a significant shift of the respective CO and H-adatom surface concentrations under steady-state methanation conditions between a clean Ni and a titania-containing surface. Using kinetic parameters for adsorption and desorption obtained from UHV experiments, mathematical models were developed which allowed calculation of the steady-state H and CO surface concentrations at reaction temperatures and moderate pressures (. 01-1 atm) under non-reactive and reactive conditions. It is found that changes in CO and hydrogen adsorption strengths caused by titania adspecies of nickel lead to significantly greater H-adatom coverages on Ni sites (uncovered by carbidic or graphitic carbon) under steady-state methanation conditions. This could be responsible for the higher methanation reaction rates typically observed for nickel supported on titania relative to nickel on silica or alumina.