Study of TiO2 deactivation during gaseous acetone photocatalytic oxidation

The kinetics of the deep photocatalytic oxidation of acetone was studied, S pecial attention was paid to the thermal deactivation process, The rate of the reaction reaches a peak at about 100 degrees C. With increasing concent ration of water vapor the peak shifts towards higher temperature, whereas w ith increasing acetone concentration the peak shifts towards lower temperat ure. An increase in water vapor concentration slightly decreases the rate o f oxidation at 40 degrees C and increases it at temperatures above the rate maximum, The presence of two types of acetone adsorption sites was deduced from two nu(C=O) bands of adsorbed acetone at 1683 and 1710 cm(-1) and can explain the dependence of the rate on acetone concentration. The rate of o xidation increases at temperatures below the peak, mainly because of the in crease in the rate coefficient at the sites of the first type. This behavio r has been ascribed to the thermal oxidation of an intermediate of the phot ocatalytic process. Abrupt drop in rate at temperatures above the peak is d ue to the partial oxidation products of acetone thermal oxidation that modi fy the TiO2 surface. (C) 1999 Academic Press.