Oxygen Vacancy-Rich Mn–Zr Composite Oxide-Supported Ruthenium Catalyst for Base-Free Oxidation of 5-Hydroxymethylfurfural to 2,5-Furandicarboxylic Acid with High Productivity

2,5-Furandicarboxylic acid (FDCA) is one of the most promising biodegradable alternatives to the petroleum-derived terephthalic acid (PTA) and adipic acid. In pursuit of Ru-based catalysts with high FDCA productivity, we herein designed an oxygen vacancy (OV)-rich Mn–Zr composite oxide as a support for low ruthenium loading. The synthesized Ru/Mn9Zr1OZ-VC catalyst showed record high productivity for the aerobic oxidation of 5-hydroxymethylfurfural (HMF) to FDCA under base-free conditions in water. Complete HMF conversion (100%) and a high FDCA yield of 97.5% were achieved within 3 h, corresponding to a productivity of 26.65 molFDCA·molRu–1·h–1. Besides, the catalyst maintains both high yield and productivity even at elevated HMF concentrations (10 wt %), representing the first reported example of such good activity. Catalyst characterization revealed that Zr doping effectively increased the OV concentration by 13.6% in this catalyst. A mechanistic study proposed that the Ru–OL–Mn structure in the catalyst is critical and that during the HMF oxidation process, lattice oxygen (OL) is the active species that is being consumed, which can be replenished by ·O2– radicals generated by OV captured O2. This work provides a method for OV-rich material generation, which can effectively enhance the catalytic oxidation capability of the supported catalysts.