Steady-state surface species during toluene photocatalysis

Adsorbed species and pathways on TiO2 and Pt/TiO2 during photocatalytic oxidation (PCO) of toluene were studied by combining transient and continuous-flow PCO with temperature-programmed hydrogenation (TPH) and oxidation (TPO). Toluene reacts quickly to form benzaldehyde, and benzaldehyde oxidizes quickly to form less-reactive intermediates. At short reaction times, benzaldehyde and its oxidation products are on the catalyst surface, but at longer reaction times, only the less-reactive intermediates are on the surface. The rate of PCO was greater initially than at longer reaction times for all experimental conditions, and this initial deactivation may be due to the accumulation of these less-reactive intermediates. The catalysts completely deactivated within 7 h during PCO without water in the feed. With the addition of water vapor, catalyst deactivation was slowed, and the catalyst was active even after 19 h of PCO. The addition of Pt to TiO2 significantly increased the PCO rate and slowed catalyst deactivation. (C) 2002 Elsevier Science B.V. All rights reserved.