Kinetics and Selectivity of 2-Propanol Conversion on Oxidized Anatase TiO2

The steady-state kinetics of 2-propanol decomposition on oxidized anatase TiO2have 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 O2and 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 O2and 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−1for dehydrogenation and 130 kJ mol−1for 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 TiO2by recognizing the influence of both surface hydroxyls and the use of an oxidizing carrier gas on the dehydrogenation and dehydration pathways at steady state.