Highly Dispersed Pd Nanoparticles Immobilized on N-Doped Hollow Carbon Spheres for Efficient Catalytic Hydrodeoxygenation of Biomass-Derived Vanillin under Atmospheric Conditions

Catalytic hydrodeoxygenation (HDO) of bio-oil is an effective and challenging route to the efficient utilization of biomass with rich oxygen-containing groups. Herein, highly dispersed Pd nanoparticles (NPs) anchored on a N-doped hollow carbon sphere (NHCS) were constructed to effectively catalyze the chemoselective HDO of bio-oil-derived vanillin. The optimized Pd/NHCS-900 catalyst presented a high 99% conversion and 98% selectivity to 2-methoxy-4-methylphenol (MMP) within 45 min under very mild conditions of 50 °C and 1 atm H2. The incorporated N species in the NHCS support and its hierarchical porous structure facilitate the dispersion and stabilization of Pd NPs, resulting in the formation of highly dispersed Pd NPs with excellent structure stability. Moreover, the presence of a strong electronic metal–support interaction between N and highly dispersed Pd NPs produced the surface electron-rich active Pd NPs, which could enhance the adsorption and activation of reactants, thereby exhibiting high intrinsic catalytic activity with a large turnover frequency (TOF) of 1700.3 h–1. Kinetic study and density functional theory (DFT) calculations demonstrated the HDO reaction pathway and the corresponding reaction mechanism. These findings pave the way for the development of efficient and stable metal catalysts for sustainable biomass conversion.