Photothermal Heterogeneous Oxidation of Ethanol over Pt/TiO2

Photothermal catalytic oxidation of ethanol over TiO2and Pt/TiO2has been investigated. Platinum was deposited on the titania using both photoreduction and adsorption of the PtCl2−6anion. The nominal weight loadings of Pt were less than 1 wt%. Thermal contributions to ethanol oxidation over Pt could be distinguished from photo-contributions to ethanol oxidation over TiO2by comparing illuminated and dark reactions under the same conditions. A significant photothermal synergistic effect was seen for Pt/TiO2catalysts. The activity for complete oxidation to CO2is much greater than the contribution from photo-oxidation over TiO2plus thermal oxidation over Pt. Experiments were conducted to investigate the mechanistic nature of the synergistic effect. The synergistic effect was found to be sensitive to preparation conditions, with photoreduced catalysts having higher activities compared to thermally reduced catalysts prepared by adsorption of the PtCl2−6anion: The differences between the photo and thermally reduced Pt/TiO2are attributed to differing extents of etching of the TiO2surface by the acidic solution of chloroplatinic acid. An experiment with layered beds of Pt/TiO2and TiO2showed that adding unetched TiO2to etched Pt/TiO2could improve CO2production. The photothermal synergistic enhancement of CO2production appears to be caused primarily by gas phase transport of intermediates between the two catalyst phases in a mixed series-parallel kinetic pathway. Increased levels of acetaldehyde produced by photo-oxidation over TiO2can lead to CO2production by thermal reaction of the acetaldehyde over Pt.