Catalytic oxidation of 5-hydroxymethylfurfural to 2,5-furandicarboxylic acid over Ru/hydrotalcite with tunable basicity

The aerobic oxidation of biomass-derived 5-hydroxymethylfurfural (HMF) represents an efficient and sustainable approach to produce 2,5-furandicarboxylic acid (FDCA), which serves as a potential renewable building block in the manufacturing of bio-polymers. However, this process typically requires the use of homogeneous basic additives (e.g., NaHCO 3 , Na 2 CO 3 , NaOH, etc.), which compromises its efficiency and environmental sustainability. Alternatively, the use of solid-base catalysts integrates the advantages of heterogeneous catalysis and basic functionality, thus improving catalytic activity and enabling the efficient separation of products and catalysts. Herein, a series of hydrotalcite-supported Ru-based catalysts with different divalent metal cations (M = Mg, Ca, Zn) and M/Al molar ratios were prepared and then devoted to the “base-free” aerobic oxidation of HMF. The catalytic performance of the Ru/hydrotalcite catalysts was found to be significantly affected by the structural parameters of hydrotalcite. Notably, the optimized Ru/Mg 2 Al with Mg/Al molar ratio of 2 can afford ∼99.9% HMF conversion and ∼ 93.5% yield of FDCA at 100 °C and 5 MPa air, along with excellent stability. A systematic investigation revealed that appropriate amounts of basic sites in the Ru/hydrotalcite could effectively accelerate the oxidation of HMF and simultaneously minimize the over-oxidation of FDCA, leading to the high yield of FDCA.