Kinetics and selectivity of 2-propanol conversion on oxidized anatase TiO2
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The steady-state kinetics of 2-propanol decomposition on oxidized anatase 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 O2 and water to the carrier gas were also investigated. The steady-state reaction results primarily in the formation of a dehydration product, propylene, and a dehydrogenation product, acetone, with small amounts of carbon oxides also being observed. Depending on the reaction conditions, the selectivity to either propylene or acetone can range between 5 and 95%. The rate of dehydrogenation increases dramatically with the addition of both O2 and water, while the dehydration rate is unaffected by their presence. Accordingly, the kinetics of 2-propanol decomposition were investigated using both air and an inert carrier. Using air as the carrier gas, the dehydration and dehydrogenation reactions were determined to be approximately one-half order with respect to 2-propanol partial pressure. The activation energies determined for the two processes are substantially different, 68 kJ mol-1 for dehydrogenation and 130 kJ mol-1 for dehydration, as evidenced by the strong temperature dependence of the decomposition selectivity. Using an inert carrier, the reaction kinetics depend in a complex fashion on the conversion of 2-propanol. The dependence on conversion was found to arise from the influence of water on the dehydrogenation kinetics. The presence of water, whether produced by 2-propanol dehydration or added independently, was found to increase the rate of 2-propanol dehydrogenation. The results of the present study can be reconciled with previously reported steady-state and temperature-programmed desorption investigations of 2-propanol on TiO2 by recognizing the influence of both surface hydroxyls and the use of an oxidizing carrier gas on the dehydrogenation and dehydration pathways at steady state. 1997 Academic Press, Inc.
