PHOTOTHERMAL HETEROGENEOUS OXIDATION OF ETHANOL OVER PT TIO2/

Photothermal catalytic oxidation of ethanol over TiO2 and Pt/TiO2 has been investigated. Platinum was deposited on the titania using both ph otoreduction and adsorption of the PtCl62- anion. The nominal weight l oadings of Pt were less than 1 wt%. Thermal contributions to ethanol o xidation over Pt could be distinguished from photo-contributions to et hanol oxidation over TiO2 by comparing illuminated and dark reactions under the same conditions. A significant photothermal synergistic effe ct was seen for Pt/TiO2 catalysts. The activity for complete oxidation to CO2 is much greater than the contribution from photo-oxidation ove r TiO2 plus thermal oxidation over Pt. Experiments were conducted to i nvestigate the mechanistic nature of the synergistic effect. The syner gistic effect was found to be sensitive to preparation conditions, wit h photoreduced catalysts having higher activities compared to thermall y reduced catalysts prepared by adsorption of the PtCl62- anion: The d ifferences between the photo and thermally reduced Pt/TiO2 are attribu ted to differing extents of etching of the TiO2 surface by the acidic solution of chloroplatinic acid. An experiment with layered beds of Pt /TiO2 and TiO2 showed that adding unetched TiO2 to etched Pt/TiO2 coul d improve CO2 production. The photothermal synergistic enhancement of CO2 production appears to be caused primarily by gas phase transport o f intermediates between the two catalyst phases in a mixed series-para llel kinetic pathway. Increased levels of acetaldehyde produced by pho to-oxidation over TiO2 can lead to CO2 production by thermal reaction of the acetaldehyde over Pt. (C) 1998 Academic Press.