Kinetics of the photocatalytic oxidation of gaseous acetone over platinized titanium dioxide

The photocatalytic oxidation of acetone was studied in a flow-circulating reactor over Pt/TiO₂ prepared by deposition (Pt/TiO₂-P) and by reduction with NaBH₄ (Pt/TiO₂-C). Compared with untreated TiO₂, Pt/TiO₂-P was less active and Pt/TiO₂-C more active at 40°-120°C, water level of 4500 ppm, and light intensity of 1.10 x 10^-6 E/min-sq cm. The increased activity of Pt/TiO₂-C was due to the stronger adsorption of acetone and higher rate constant, as seen in the reaction rate's dependence on concentration. Adsorption constants obtained from adsorption isotherms were significantly lower than those taken from the dependence of the rate on acetone concentration, suggesting that acetone photoadsorption occurred during photocatalytic oxidation. Platinized samples did not exhibit the steady state deactivation seen over TiO₂ at temperatures > 100°C. However, the oxidation rate was reduced while reaching steady state following a temperature rise to ≥ 80°C. Apparent activation energy of photocatalytic oxidation over platinized samples was 10-13 kJ/mole; the apparent activation energy of thermal acetone oxidation was 84 and 40 kJ/mole for Pt/TiO₂-P and Pt/TiO₂-C, respectively. Photoinduced oxidation could occur on Pt particles at 80°-140°, manifested by acetone photoinduced oxidation over Pt/α-Al₂O₃. The lack of deactivation of Pt/TiO₂ above 100°C may be linked to the modification of the TiO₂ surface during Pt deposition because TiO₂ treated with NaBH₄ showed a higher deactivation temperature. The dependence of activity on Pt content in Pt/TiO₂-C peaked at Pt content of ~ 0.1 wt %.