Hollow Co@HCN Derived from ZIF-67 as a Highly Efficient Catalyst for Hydrogenation of o-Cresol to o-Methyl Cyclohexanol

The selective hydrogenation of o-cresol to produce o-methyl cyclohexanol, an important chemical intermediate, is an attractive approach. The design and development of efficient non-precious metal catalysts for the selective o-cresol hydrogenation remain a great challenge. Herein, cobalt nanoparticles embedded in nitrogen-doped carbon with hollow structure (Co@HCN) were fabricated by direct pyrolysis of hollow zeolitic imidazolate framework-67 (HZIF-67), and were applied in the selective hydrogenation of o-cresol to o-methyl cyclohexanol for the first time. The pyrolysis temperature and Co(NO₃)₂·6H₂O concentration jointly regulate the morphology and physicochemical properties of the Co@HCN-T-x catalysts (T represents the pyrolysis temperature and x represents the Co(NO₃)₂·6H₂O concentration in octanol), and significantly affect their catalytic properties. Co@HCN-500-0.1 exhibits superior catalytic activity, which is 3.3 times higher than Co@HCN-700-0.1 and 1.3 times higher than Co@HCN-500-0.4. Large ratio of meso-/macro-porous specific surface area and pore volume, small Co size with uniform dispersion, and abundant surface Co and CoN_x contents together contribute to the superior catalytic activity of Co@HCN-500-0.1. More importantly, Co@HCN-500-0.1 displays convenient magnetic recoverability, superior catalytic recyclability and universal applicability. This work provides significant insights for the design of efficient non-precious metal catalysts to be applied in the selective hydrogenation of o-cresol. Graphical Abstract: Hollow Co@HCN nanospheres were synthesized by one-step pyrolysis of HZIF-67, and the morphology, pore structure, Co size and distribution, surface composition, and yield can be adjusted by the pyrolysis temperature and Co(NO₃)2·6H₂O concentration. The presence of the hollow shell layer not only enhances the diffusion of the reactants, but also facilitates the dispersion and exposure of Co species, which in turn improves the catalytic performance for the selective hydrogenation of o-cresol to o-methyl cyclohexanol.[Figure not available: see fulltext.]