Modulating Copper Dispersion and Active Cu ⁰ /Cu ⁺ Sites in Cu/CeO ₂ Catalysts Through Controlled Calcination Atmosphere for Efficient 5‐Hydroxymethylfurfural Hydrogenation

2,5-Bis(hydroxymethyl)furan (BHMF) is a promising intermediate for the synthesis of pharmaceuticals and crown ethers, whereas achieving a high reaction rate in the hydrogenation of 5-hydroxymethylfurfural (5-HMF) to form BHMF remains challenge. In this work, a series of Cu/CeO₂-x catalysts (x denotes H, Air, Ar) were synthesized by calcination under different atmospheres (10% H₂/Ar, Air, Ar) and evaluated for the 5-HMF hydrogenation to BHMF. Cu/CeO₂-Ar exhibited a superior reaction rate of 26.8 mmol·g_cat ^-1·h^-1 and BHMF yield of 99.1% under the condition (180°C, 5 h, 1 MPa H₂), significantly outperforming Cu/CeO₂-H and Cu/CeO₂-Air. The characterizations reveal that the calcination in the oxygen-deficient argon atmosphere led to high Cu dispersion and minimized Cu particle size in the Cu/CeO₂-Ar. These properties resulted in the abundant Cu⁺-O_V-Ce³⁺ sites and increased Cu⁰ number. In situ Fourier transform infrared spectroscopy analysis elucidates the distinct roles of these active sites. Cu⁺ sites are responsible for perpendicular adsorption of the 5-HMF carbonyl group, and Cu⁰ sites drive efficient H₂ dissociation. In contrast, the O_V-Ce³⁺ sites do not adsorb 5-HMF and H₂. The close synergy between numerous Cu⁰ sites and abundant Cu⁺ sites in the Cu/CeO₂-Ar accelerates the process of 5-HMF hydrogenation to BHMF.