ALCOHOL DECOMPOSITION BY REVERSE SPILLOVER

Temperature-programmed desorption (TPD) was used to study methanol, ethanol, and l-propanol decomposition on Al2O3 and Ni/Al2O5 catalysts. These alcohols adsorb on the Al2O3 support of Ni/Al2O3 and dehydrogenate by reverse spillover to the Ni surface. Thus, the presence of Ni dramatically increases their decomposition rates. Methanol adsorbed on Al2O3 alone decomposes to form (CH3)2O at lower temperature and CO, H2, and CO2 above 600 K. On Ni/Al2O3 most CH3OH dehydrogenates to form CO and H2. Ethanol adsorbed on Al2O3 mostly dehydrates to form C2H4 and (C2H5)2O, but C2H4O and H2 are also observed. On Ni/Al2O3, C2H5OH dehydrogenation to CO, H2, and surface carbon is the main reaction. 1-Propanol decomposes on Al2O5 to form C3H6, H2, (C3H7)2O, and C3H6O. When Ni is present, propanol decomposition to H2, CO, and surface carbon is the dominant process, but some C3H6, C3H6O, and CO2 also form. On Al2O3, the alcohols decomposition rates are in the order l-C3H7OH > C2H5OH > CH3OH, but on Ni/Al2O3 the rates are almost identical. The increase in the decomposition rate of alcohols, when Ni is present, is attributed to alcohol diffusion along the Al2O3 surface and decomposition on the Ni surface or at the Ni-Al2O3 interface. The diffusivity of CH3O on the Al2O3 surface at 534 K is estimated to be larger than 6.6 × 10-11 cm2/s. © 1993 Academic Press, Inc.