Highly efficient selective hydrogenation of nitrocyclohexane to cyclohexanone oxime in ethylenediamine over MOF-derived catalysts: Effects of Ni-Co alloy and solvent

Abstract

High-efficiency Ni-Co alloy encapsulated in N-doped carbon layer (Ni1Co2@NC-APTES) catalysts were prepared via simple Ni-Co-MOF pyrolyzation and applied in the selective hydrogenation of nitrocyclohexane (NCH) to cyclohexanone oxime (CHO). The results show that the alloy effects between Ni and Co can highly promote catalytic activity. The appropriate Ni addition can facilitate the reduction of CoOx and increase zero-valent Co (Co0) amounts. Moreover, pyridinic-N doping increases the Lewis basicity, which favors the intermediate cyclohexylhydroxylamine (N-CHH) conversion to CHO. Additionally, the in-situ DRIFT and density functional theory (DFT) calculations propose the mechanism for NCH hydrogenation in ethylenediamine (EDA) and the results show that the EDA changes the reaction path of NCH hydrogenation to CHO, prefers to form N-CHH, and significantly reduces the whole reaction energy barrier of NCH to CHO. Moreover, the Ni1Co2 (111) crystal surface with the lowest d-band center and the strongest Ni-Co alloy effects presents the highest adsorption energies of H2 and NCH, the lowest adsorption energies of H* and CHO, and the lowest energy barrier of the α-H transfer which is conducive to form the N-CHH. Under the optimum conditions, the Ni1Co2@NC-APTES gives 93.6% selectivity to CHO at 94.5% NCH conversion in EDA.