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. PtOx-TiO2 (x = 0, 1) exhibited significantly higher activity for CH4 production than PdOx-TiO2 (x = 0, 1). The CH4 yield with PtOx loading was approximately ten times greater than that obtained with PdOx loading, with an optimal PtOx loading of 2.0 wt% yielding the highest CH4 amount of 10.600 µmol L- 1 after 6 h. In contrast, PdOx-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.