HYDROGENATION OF ORGANIC OXYGENATES ON NI/AL2O3 AND NI/SIO2 CATALYSTS

Temperature-programmed reaction (TPR) was used to compare the hydrogenation rates of adsorbed methanol, ethanol, I-propanol, dimethyl ether, formic acid, acetaldehyde, acetone, and methoxy (formed from coadsorbed CO and H-2) on a Ni/Al2O3 catalyst. The oxygenates adsorb on the Al2O3 support, and hydrogenation involves a spillover process since H-2 dissociates on the Ni surface. The rates of hydrogenation to CH4 are essentially the same for all the oxygenates studied. Apparently the same rate-determining step, reverse spillover of an oxygenated species from Al2O3 to Ni, limits the formation of CH4. Similar processes occur on Ni/SiO2 for methanol and ethanol, but their coverages on SiO2 are a factor of 15 lower and hydrogenation to CH4 takes place over a broad temperature range. None of the oxygenates remained on the Ni surface of Ni/Al2O3 in H-2 flow; apparently they spilled over to the Al2O3 or were hydrogenated at room temperature. On Ni/SiO2, only HCOOH adsorbs and dissociates on Ni to form adsorbed CO. Coadsorption shows that (CO)-C-13 and various oxygenates have independent adsorption and hydrogenation behavior. (C) 1994 Academic Press, Inc.