Controllable synthesis of micro-mesoporous Pd@N-doped carbon derived from ZIF@NiCoLDH for enhanced phenol hydrogenation to cyclohexanone

A hollow nitrogen-doped carbon (CN) material, featuring abundant mesopores and high content of graphitic nitrogen, has been synthesized by annealing of the core-shell precursor composed of zeolitic imidazolate framework-67 as core and layered double hydroxides as shell. The proportion of mesopores and nitrogen species in the CN materials significantly vary with the shell thickness of layered double hydroxides in the core-shell precursor by adjusting the etching amount and etching time of nickel nitrate. The as-prepared Pd@CN-1.4–30 catalyst exhibits superior catalytic performance in the hydrogenation of phenol to cyclohexanone, and its turnover frequency (TOF) value is about ten times higher than Pd@CN obtained without the nickel etching, resulting from the abundant mesopores, high graphitic N content, and easy reduction of palladium species. Moreover, Pd@CN-1.4–30 has good reusability during at least six reaction cycles.