Methane production via photocatalytic degradation of glucose on PtOx and PdOx-loaded TiO2

Sustainable production of CH₄, an industrially important gas, from renewable resources presents a critical solution to energy security challenges. This study demonstrates photocatalytic conversion of glucose, a model biomass compound, to CH₄ using a metal co-catalyst loaded TiO₂ photocatalyst under ambient conditions. We confirmed that CH₄ was formed through photocatalytic reduction of CO₂, which was generated in situ during glucose oxidation, establishing a closed-loop conversion of biomass-derived carbon within a single reaction system. PtO_x-TiO₂ (x = 0, 1) exhibited significantly higher activity for CH₄ production than PdO_x-TiO₂ (x = 0, 1). The CH₄ yield with PtO_x loading was approximately ten times greater than that obtained with PdO_x loading, with an optimal PtO_x loading of 2.0 wt% yielding the highest CH₄ amount of 10.600 µmol L^{- 1} after 6 h. In contrast, PdO_x-TiO₂ showed a higher selectivity for H₂ generation. Analysis of the reaction products, including sugars (arabinose, erythrose, and glyceraldehyde) and organic acids (formic acid, acetic acid, and gluconic acid), elucidated the glucose degradation pathways. The mechanism of CH₄ formation was identified as the methanation of CO₂ and H⁺, both produced during photocatalytic oxidation of glucose and water. Deuterium-labeling experiments further revealed that the hydrogen atoms in CH₄ originated from both glucose decomposition and water splitting. These findings demonstrate a novel and sustainable tandem photocatalytic process that integrates oxidation and reduction reactions on a single catalyst surface, providing mechanistic and practical insights into the direct conversion of biomass into CH₄ under mild conditions.