Mechanistic Study of Glucose Photoreforming over TiO-Based Catalysts for H Production.

Glucose is a key intermediate in cellulose photoreforming for H production. This work presents a mechanistic investigation of glucose photoreforming over TiO and Pt/m-TiO catalysts. Analysis of the intermediates formed in the process confirmed the α-scission mechanism of glucose oxidation forming arabinose (C sugar) and formic acid in the initial oxidation step. The selectivity to sugar products and formic acid differed over Pt/TiO and TiO, with Pt/TiO showing the lower selectivity to formic acid due to enhanced adsorption/conversion of formic acid over Pt/TiO. ATR-IR spectroscopy of glucose photoreforming showed the presence of molecular formic acid and formate on the surface of both catalysts at low glucose conversions, suggesting that formic acid oxidation could dominate surface reactions in glucose photoreforming. Further ATR-IR of formic acid photoreforming showed Pt-TiO interfacial sites to be key for formic acid oxidation as TiO was unable to convert adsorbed formic acid/formate. Isotopic studies of the photoreforming of formic acid in DO (with different concentrations) showed that the source of the protons (to form H at Pt sites) was determined by the relative surface coverage of adsorbed water and formic acid.