Effect of Pd and Au on Hydrogen Abstraction and C–C Cleavage in Photoconversion of Glycerol: Beyond Charge Separation

Abstract

Photocatalytic conversion of polyols to value-added products is of great interest for the utilization of biomass as a chemical feedstock. Current research focuses on boosting the reaction rate and selectivity by employing metal nanoparticles (NPs) as charge separators and cocatalysts. However, the promotional role of metal NPs in such photocatalytic processes still remains unclear because of the lack of mechanistic understanding. Here, we have explored the role of supported Pd and Au NPs on TiO2 in photocatalytic glycerol conversion under water-free, deaerated conditions by in situ spectroscopic methods. While the presence of Au NPs only results in partial conversion of glycerol at a low rate, Pd decoration promotes glycerol oxidation to a much higher conversion. In situ mass and vibrational spectrometry reveals that Pd/TiO2 exhibits faster cleavage of O–H and C–H bonds in both glycerol and the derived intermediates as compared to Au/TiO2, thus leading to a higher glycerol conversion accompanied by the formation of additional molecular hydrogen. X-ray photoelectron spectroscopy suggests that the preferential adsorption of glycerol on the surface of Pd via hydroxyl groups results in an enhanced interfacial charge transfer, thus yielding a better photocatalytic activity.