Tuning surface properties of N-doped carbon with TiO₂ nano-islands for enhanced phenol hydrogenation to cyclohexanone

ZIF-derived N-doped carbon (CN) materials were modified in this work by TiO₂ nano-islands with oxygen vacancies (O_V) through a sol-gel method and subsequent thermal treatment. By loading Pd nanoparticles (NPs) on CN@TiO₂, Pd@CN@TiO₂ catalysts were fabricated. Superior catalytic performance of Pd@CN@TiO₂ was found in the selective phenol hydrogenation to cyclohexanone, with a TOF of 30.1 h⁻¹, 2.2-fold as high as that of Pd@CN. The synergistic effect of CN and TiO₂ nano-islands was responsible for the superior catalytic performance. More O_V was generated due to the high specific surface area of CN. At the same time, CN could also enhance the hydrophilicity, and adsorb more phenol in non-planar fashion. The TiO₂ nano-islands with O_V could improve the Pd dispersion, make more Pd element on the support surface, strengthen the antioxidizability of Pd and induce electron-rich Pd NPs. Furthermore, the as-fabricated Pd@CN@TiO₂ showed good recyclability in the phenol hydrogenation, and also exhibited excellent catalytic performance in the catalytic hydrogenation of phenol with diverse functional groups. These findings provide the feasibility of using the high-performance catalysts for the hydrogenation of phenol derivatives.