Microwave-Assisted Oxidation of Glucose Using H2O2 and Au/CePO4 Catalysts: A Comparative Study of Gold Deposition Methods and Analysis of Reaction Pathways

Abstract

This study aligns with microwave-assisted selective oxidation processes using H₂O₂ as an environmentally relevant oxidant over heterogeneous gold-based catalysts. The research is focused on assessing the influence of the gold deposition method on the surface properties and catalytic behavior of Au/CePO₄ catalysts in the selective oxidation of glucose. A significant part of the study involved also unraveling the nature of active sites and species involved in the oxidation process. For this purpose, three gold deposition methods were applied for the synthesis of Au/CePO₄ catalysts, namely deposition–reduction (DR), deposition–precipitation with urea (DPU), and anchoring of gold species on functionalized support (grafting; GR). Au/CePO₄-GR was found to significantly outperform the other two materials in terms of H₂O₂ decomposition efficiency and glucose oxidation. This catalyst enabled highly efficient glucose conversion to gluconic acid in a short reaction time (90% glucose conversion in 20 min, at 120 °C) and could be successfully reused without any significant deactivation. The observed enhancement in the reactivity of Au/CePO₄-GR was attributed to its strong surface acidity and the smallest size of gold particles. Furthermore, Au/CePO₄-GR exhibited approximately 1.5 times higher activity in glucose oxidation than commercial Au/TiO₂ (Mintek), despite its lower efficiency in H₂O₂ decomposition.