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

The photocatalytic oxidation of acetone is investigated in a flow-circulating reactor over Pt/TiO2 prepared by photodeposition (Pt/TiO2-P) as well as by reduction with NaBH4 (Pt/TiO2-C). Compared to untreated TiO2, Pt/TiO2-P is less active and Pt/TiO2-C more active at 40-120 degrees C, water concentration of 4500 ppm, and light intensity of 1.10 x 10(-6) E/(min cm(2)). The increased activity of Pt/TiO2-C is related to the stronger adsorption of acetone and higher rate constant, as revealed by dependence of the reaction rate on concentration. Adsorption constants obtained from adsorption isotherms are significantly lower than those constants obtained from the dependence of the rate on acetone concentration. This suggests the presence of acetone photoadsorption during photocatalytic oxidation, Platinized samples did not demonstrate steady state deactivation, which was observed over TiO2 at temperatures above 100 degrees C. However, there was a decrease in the oxidation rate while reaching steady state after an increase of temperature to 80 degrees C and above. Apparent activation energy of photocatalytic oxidation over platinized samples was 10-13 kJ/mol; the apparent activation energy of thermal acetone oxidation was 84 kJ/mol for Pt/TiO2-P and about 40 kJ/mol for Pt/TiO2-C. At 80-140 degrees C, photoinduced oxidation could occur on Pt particles, as shown by acetone photoinduced oxidation over Pt/gamma-Al2O3. The lack of deactivation of Pt/TiO2 above 100 degrees C may be related to the modification of the TiO2 surface during Pt deposition because TiO2 treated with NaBH4 demonstrated a higher deactivation temperature. The dependence of activity on Pt content in Pt/TiO2-C had a peak at Pt content of about 0.1 wt%. The TiO2 used in this study had higher adsorption and rate constants compared to TiO2 Degussa P25, An estimate showed that there were no concentration gradients inside the photocatalyst film under experimental conditions of this study. (C) 2000 Academic Press.