关键词: 5-羟甲基糠醛, 选择性加氢, 2,5-二甲基呋喃, 协同催化机制

The selective hydrogenation of 5-hydroxymethylfurfural (HMF) to 2,5-dimethylfuran (DMF) represents a crucial catalytic approach for obtaining high-performance, next-generation biofuels from renewable biomass resources. This conversion is of particular significance as DMF possesses excellent fuel properties, such as high energy density and low solubility in water, rendering it a promising alternative to gasoline. In this study, an innovative Pd²⁺-Pd⁰/activated carbon (AC) bifunctional catalyst, containing synergistic coexistence of Pd²⁺ and Pd⁰ species, was successfully fabricated via a customized adsorption-precipitation-in situ partial reduction strategy. This synthetic methodology allows for precise control over the oxidation states and spatial distribution of Pd species on the AC support. The effects of key reaction parameters, specifically reaction temperature, hydrogen pressure, reaction time as well as catalyst pre-reduction time, on the hydrogenation reaction pathways, product selectivity and overall catalytic performance for HMF conversion were comprehensively investigated in an n-butanol solvent system. Under the meticulously optimized conditions, exceptional catalytic results were attained: the HMF conversion achieved 99.6%, and the yield of the target molecule DMF reached as high as 90.4%, demonstrating outstanding selectivity. To unravel the intrinsic structure-activity relationships and the source of the high DMF yield, the catalysts were subjected to a suite of advanced characterization techniques. X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and H₂ temperature-programmed reduction (H₂-TPR) were employed in tandem. These analyses provided compelling evidence for a synergistic catalytic mechanism between the two types of Pd species: the metallic Pd⁰ sites primarily account for the efficient activation and dissociation of H₂, generating active hydrogen species; concurrently, an appropriate amount of Lewis-acidic Pd²⁺ sites facilitates the critical activation of the C=O group in HMF and its intermediate, and promote the subsequent hydrogenolysis of the hydroxymethyl group. This collaborative action between the two functionalities creates an optimized reaction pathway that minimizes side reactions, thereby directing the selectivity decisively toward DMF formation. This work not only presents a highly efficient catalytic system for DMF production but also offers fundamental insights into the rational design of bifunctional metal catalysts for the selective hydrogenation of biomass-derived platform molecules.

Key words: 5-hydroxymethylfurfural, selective hydrogenation, 2,5-dimethylfuran, synergistic catalytic mechanism