Mechanistic Study of Glucose Photoreforming over TiO2-Based Catalysts for H2 Production.

ABSTRACT

Glucose is a key intermediate in cellulose photoreforming for H2 production. This work presents a mechanistic investigation of glucose photoreforming over TiO2 and Pt/m-TiO2 catalysts. Analysis of the intermediates formed in the process confirmed the α-scission mechanism of glucose oxidation forming arabinose (Cn-1 sugar) and formic acid in the initial oxidation step. The selectivity to sugar products and formic acid differed over Pt/TiO2 and TiO2, with Pt/TiO2 showing the lower selectivity to formic acid due to enhanced adsorption/conversion of formic acid over Pt/TiO2. In situ 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 in situ ATR-IR of formic acid photoreforming showed Pt-TiO2 interfacial sites to be key for formic acid oxidation as TiO2 was unable to convert adsorbed formic acid/formate. Isotopic studies of the photoreforming of formic acid in D2O (with different concentrations) showed that the source of the protons (to form H2 at Pt sites) was determined by the relative surface coverage of adsorbed water and formic acid.