Synergy Effects between Oxygen Groups and Defects in Hydrodeoxygenation of Biomass over a Carbon Nanosphere Supported Pd Catalyst

This work reports an innovative route for biomass upgrading via hydrodeoxygenation (HDO) reactions which avoids external high-pressure hydrogen supply and harsh conditions (such as high-temperature or additives). A novel Pd/CFR catalyst with controllable oxygen groups and defects was synthesized with low-load Pd supported on resorcinol–formaldehyde resin carbon spheres (CFR) for selective hydrodeoxygenation of vanillin under mild conditions. The as-prepared Pd/CFR-800 catalyst shows excellent activity (>99.5% yield of 2-methoxy-4-methylphenol) using polymethylhydrosiloxane (PMHS) as green hydride source within 1 h at 70 °C, in the absence of additives. According to spectral analyses, the concentration of carbon skeleton defects and hydroxyl functional groups on the catalyst can be adjusted by the carbonization temperature. Combined with experimental results and mechanistic studies, the synergistic effect of hydroxyl groups and adjacent defects was deemed as the main reason for the strong adsorption of the substrate, which significantly facilitated the key hydrogenolysis step. Furthermore, the as-prepared Pd/CFR-800 catalyst has shown excellent recyclability after used for five times. The in situ regulation of functional groups and defects on carbon materials provides new ideas for designing high-performance catalysts for the catalytic transformation of various lignin derivatives.