Facile and efficient synthesis of Pd²⁺@CN catalysts for enhanced phenol hydrogenation to cyclohexanone

One-step phenol hydrogenation over Pd@N-doped carbon (CN) is a sustainable approach to produce cyclohexanone, a key intermediate in the production of nylon. In this work, cobalt sources and 2-methylimidazole (2-MeIm) were mixed and directly carbonized to synthesize CN materials. After acid etching and Pd loading, the Pd²⁺@CN catalysts were achieved, and the porous structures and surface properties can be modulated by tuning the kind of cobalt sources and the molar ratio of 2-MeIm and cobalt. The Pd²⁺@CN(D) (prepared by the direct carbonization strategy) demonstrates comparable performance in the phenol hydrogenation to the ZIF-67-derived Pd²⁺@CN(67), and more importantly, the obtained weight of Pd²⁺@CN(D) is 2.1 times higher than that of Pd²⁺@CN(67). The optimum Pd²⁺@CN-4 (synthesized with a molar ratio of 4 between 2-MeIm and cobalt acetate tetrahydrate) achieves superior and durable catalytic performance (a turnover frequency (TOF) of 125.9 h⁻¹) for the well-developed hierarchically porous structures, rich defects and abundant alkaline.