Contributions of Oxide Support Reducibility for Selective Oxidation of 5-Hydroxymethylfurfural over Ag-Based Catalysts

As a type of sustainable and renewable natural source, biomass-derived 5-hydroxymethyl furfural (HMF) can be converted into high-value chemicals. This study investigated the interactions between silver (Ag) and oxide supports with varied reducibility and their contributions to tuning catalytic performance in the selective oxidation of HMF. Three representatives of manganese dioxide (MnO2), zirconium dioxide (ZrO2), and silicon dioxide (SiO2) were selected to support the Ag active sites. The catalysts were characterized by techniques such as STEM (TEM), Raman, XPS, H2-TPR, and FT-IR spectroscopy to explore the morphology, Ag dispersion, surface properties, and electronic states. The catalytic results demonstrated that MnO2 with the highest reducibility exhibited superior catalytic performance, achieving 75.4% of HMF conversion and 41.6% of selectivity for 2,5-furandicarboxylic acid (FDCA) at 120 °C. In contrast, ZrO2 and SiO2 exhibited limited oxidation capabilities, mainly producing intermediate products like FFCA and/or HMFCA. The oxidation ability of these catalysts was governed by support reducibility, because it determined the density of oxygen vacancies (Ov) and surface hydroxyl groups (OOH), and eventually influenced the catalytic activity, as demonstrated by the reaction rate: Ag/MnO2 (3214.5 molHMF·gAg−1·h−1), Ag/ZrO2 (2062.3 molHMF·gAg−1·h−1), and Ag/SiO2 (1394.4 molHMF·gAg−1·h−1). These findings provide valuable insights into the rational design of high-performance catalysts for biomass-derived chemical conversion.