| Transient, isothermal photocatalytic oxidation (PCO) was combined with temperature-programmed desorption (TPD), hydrogenation (TPH) and oxidation (TPO) to identify reaction pathways and intermediates for the PCO of toluene on TiO2 and Pt/TiO2. Toluene oxidizes quickly to benzaldehyde, which then reacts to less-reactive, strongly-bound surface species. Benzoic acid does not appear to be the less-reactive intermediate formed during benzaldehyde PCO. Benzaldehyde adsorbs both parallel and perpendicular to the catalyst surface, and the parallel form is more reactive. Toluene reacts predominantly to form benzaldehyde adsorbed parallel to the catalyst surface.; Both TiO2 and Pt/TiO2 deactivated during PCO of a continuous flow of toluene. The addition of Pt increased the PCO rate and slowed deactivation. The addition of water vapor also significantly slowed catalyst deactivation. The same surface species that form during transient toluene PCO appear to form during PCO of a continuous flow of toluene. At short reaction times, benzaldehyde and its oxidation products are on the catalyst surface, but at long reaction times only the less-active intermediates formed from benzaldehyde oxidation are on the surface.; The photocatalytic decomposition of aliphatic alcohols, acids, aldehydes, and esters in an inert atmosphere on TiO2 and Pt/TiO2 was studied using transient reaction techniques. The addition of Pt to TiO 2 increased the rate of reaction and changed the selectivity significantly. Hydrogen formed during PCD on Pt/TiO2 for all of the organics with H bonded to the carbon in a -C-O- group. When only alkyl groups were bonded to the carbon in a -C-O- group, alkanes formed, but H2 did not. Alcohols decomposed to H2 or alkanes and their corresponding aldehyde during PCD. The PCD rates for aldehydes were low. Acids and esters decomposed through two parallel pathways. The PCD pathways are consistent with a reaction consumed during PCD, and diffusion of bulk oxygen during dark time replenished the lattice oxygen. |
