Photocatalytic oxidation of oxygenated air toxics

Photocatalytic oxidation of dilute oxygenated organic compounds in air streams can readily be achieved at ambient conditions over near-ultraviolet (UV) illuminated titanium dioxide. Oxidation rates of acetone and methyl-t-butyl ether (MTBE) as a function of organic concentration exhibit limiting apparent reaction orders of 1.3 and 0.5, respectively. The dependence of oxidation rate on O₂ concentration is approximately first order at low oxygen concentrations, with a saturation in the rate above 15 mol% O₂. At low concentrations in the feed, water vapor has little effect on the reaction rate, but significantly degrades the rate at higher concentrations. In the absence of water vapor in the feed, high initial oxidation rates cannot be sustained and the catalyst eventually becomes completely de-activated. Photocatalytic activity can be maintained for extended time on stream by including water vapor in the reactor feed. Oxidation rates are strong functions of UV intensity. We have measured quantum yields greater than unity, suggesting that oxidation occurs through a complex surface-mediated, free radical chain reaction mechanism.