Different active sites in a bifunctional Co@N-doped graphene shells based catalyst for the oxidative dehydrogenation and hydrogenation reactions

Abstract

Abstract Low-cost, active and stable catalysts, with a bifunctional capability if possible, are required to achieve the chemical transformations between saturated and unsaturated N-heterocycles. In this work, Co@N-doped graphene shells (Co@NGS) was used as a bifunctional catalyst with high activity and stability for the oxidative dehydrogenation (ODH) and hydrogenation (HYD) of quinolines. The excellent performance can be attributed to the synergetic effect of N-doped graphene, underlying Co nanoparticles, and the encapsulation structure in which carbon shells protect Co from leaching and aggregation. Poisoning tests with KSCN and spectroscopic analysis clearly unveil that the active sites for ODH and HYD are quite different: N-doped graphene shells modified by Co NPs via electron transfer serve as active sites for the O2 activation in ODH, while the underlying Co NPs promoted by N dopants favor the H2 activation in HYD. This finding challenges the previous concept of N-doped carbon sites as active sites for both ODH and HYD. The bifunctional property is due to the access of both N-doped graphene and Co sites to small molecules in our one-pot pyrolyzed Co@NGS catalysts.