Sol-gel derived Pd supported TiO2-ZrO2 and TiO2 photocatalysts; their examination in photocatalytic reduction of carbon dioxide

Abstract

Pure and palladium-enriched TiO2 and TiO2-ZrO2 photocatalysts were prepared by the sol–gel process controlled within reverse micelles and impregnated under vacuum. The catalysts were characterized by ICP MS, nitrogen physisorption, X-ray diffraction, UV–vis diffuse reflectance spectroscopy, X-ray photoelectron spectroscopy and TEM/SEAD and investigated in the CO2 photocatalytic reduction in a batch annular photoreactor. Methane and hydrogen were the main reduction products in the gas phase. Low amounts of carbon monoxide were also detected. The observed order of product yields (μmol/g of a catalyst) was: H2 > CH4 > CO. The catalyst performance (expressed as μmol of products per grams of a photocatalyst) ranking was TiO2-ZrO2 > Pd/TiO2-ZrO2 > TiO2 > Pd/TiO2 > TiO2 Evonic P25. The detrimental effect of surface modification by Pd on the photocatalytic properties of both TiO2 and TiO2-ZrO2 photocatalysts can be explained by the presence of PdO clusters masking the supports surface and/or playing the role of the recombination centres.