KINETICS AND SELECTIVITY OF 2-PROPANOL CONVERSION ON OXIDIZED ANATASETIO2

The steady-state kinetics of 2-propanol decomposition on oxidized anat ase TiO2 have been determined at temperatures ranging from 448 to 598 K and 2-propanol partial pressures from 8.9 to 102.7 Torr. The effects of the addition of O-2 and water to the carrier gas were also investi gated. The steady-state reaction results primarily in the formation of a dehydration product, propylene, and a dehydrogenation product, acet one, with small amounts of carbon oxides also being observed. Dependin g on the reaction conditions, the selectivity to either propylene or a cetone can range between 5 and 95%. The rate of dehydrogenation increa ses dramatically with the addition of both O-2 and water, while the de hydration rate is unaffected by their presence. Accordingly, the kinet ics of 2-propanol decomposition were investigated using both air and a n inert carrier. Using air as the carrier gas, the dehydration and deh ydrogenation reactions were determined to be approximately one-half or der with respect to 2-propanol partial pressure. The activation energi es determined for the two processes are substantially different, 68 kJ mol(-1) for dehydrogenation and 130 kJ mol(-1) for dehydration, as ev idenced by the strong temperature dependence of the decomposition sele ctivity. Using an inert carrier, the reaction kinetics depend in a com plex fashion on the conversion of 2-propanol. The dependence on conver sion was found to arise from the influence of water on the dehydrogena tion kinetics. The presence of water, whether produced by 2-propanol d ehydration or added independently, was found to increase the rate of 2 -propanol dehydrogenation. The results of the present study can be rec onciled with previously reported steady-state and temperature-programm ed desorption investigations of 2-propanol on TiO2 by recognizing the influence of both surface hydroxyls and the use of an oxidizing carrie r gas on the dehydrogenation and dehydration pathways at steady state. (C) 1997 Academic Press, Inc.