Synergistic Effect of Oxygen Vacancies and Acid Sites on Selective Furfural Hydrodeoxygenation over Hollow Co@TiO <i> <i>x</i> </i> Catalysts

Abstract The development of supported non-noble metal catalysts with tailored defect structures and optimized active sites is a promising strategy for the selective hydrodeoxygenation of furfural (FAL) to 2-methylfuran (2-MF). In this study, a series of Co@TiOx-X catalysts (X = 400, 500, 600, 700, and 800, denoting the reduction temperature) with hollow flower-like spherical architectures were fabricated via two steps: deposition–precipitation of cobalt sulfate on amorphous hollow @TiO2 to obtain @Co(OH)2–TiO2 precursors, followed by reduction at different temperatures. The catalytic performance in FAL hydrodeoxygenation was systematically evaluated, and the structure–activity relationship was established through comprehensive characterizations, including XRD, SEM, Raman, EPR, XPS, TEM, FTIR, and NH3-TPD. Under optimized reaction conditions (170 °C, 2 MPa H2, and 180 min), the Co@TiOx-600 catalyst achieved complete FAL conversion with 87% selectivity to 2-MF. Structural analysis revealed that its superior performance stems from the synergistic effects of a high concentration of oxygen vacancies (OV) and an appropriate density of surface acid sites. These features collectively enhance the activation of the C═O bond in FAL, promote hydrogen spillover from Co0 sites to OV, and facilitate the cleavage of the C–O bond in intermediate furfuryl alcohol (FOL). Kinetic studies revealed that the hydrodeoxygenation of FAL follows first-order kinetics, with the Co@TiOx-600 catalyst exhibiting the lowest activation energy (57.5 kJ/mol). The catalyst also demonstrated excellent cycling stability.