Oxidation-State-Modulated Cobalt Catalysts for Ambient Selective Hydrogenation of Bio-Derived Aldehydes: Toward Bio-Based Polyesters

Abstract

Selective hydrogenation is a crucial process in the synthesis of chemical intermediates. Here, we report the efficient hydrogenation of 5-hydroxymethylfurfural (HMF) to 2,5-bishydroxymethylfuran (BHMF) over N-doped C-supported cobalt catalysts (CoNC) derived from ZIF-67 for the enzymatic synthesis of poly(2,5-furandimethylene adipate) (PFAd). By varying the oxidative pretreatment temperature, a series of CoNCX catalysts (where X denotes the oxidation temperature) were obtained, enabling effective tuning of catalytic activity. The optimized catalyst, CoNC200, achieved 93% HMF conversion and 99% BHMF selectivity, with a BHMF yield approximately 30% higher than that of the nonoxidized sample at 100 °C within 20 min. Notably, near-complete conversion and high selectivity can be achieved at room temperature within 8 h, while similar performance is obtained at 120 °C within 30 min, demonstrating high selectivity and efficiency across a wide temperature range. The low apparent activation energy (39.9 kJ mol^–1) further confirms the high intrinsic activity of CoNC200. The enhanced low-temperature performance is attributed to the synergistic effect of CoOOH and Co₃O₄ species with high-valence cobalt sites on the N-doped carbon support, as revealed by comprehensive characterization. Furthermore, the catalytic system is compatible with enzymatic polymerization, enabling direct conversion of crude BHMF mixtures containing residual HMF into polyesters using dimethyl adipate. The presence of HMF allows modulation of the polymer molecular weight without compromising the thermal properties. These findings underscore a robust and versatile strategy for integrating selective hydrogenation with mild enzymatic polycondensation toward bio-based polyesters.