Cobalt Nanoparticles Apically Encapsulated by Nitrogen-doped Carbon Nanotubes for Oxidative Dehydrogenation and Transfer Hydrogenation of N-Heterocycles

摘要

It is important to develop a highly active and stable transition-metal catalyst with dual-functional properties in the reversible transformations between various saturated and unsaturated N-heterocycles. Herein, we prepared the cobalt nanoparticles (Co NPs) apically encapsulated by the N-doped carbon nanotubes catalyst (Co@NCNTs) via a multiple pyrolysis of low-cost dicyandiamide and cobalt (II) acetylacetonate. The catalyst shows excellent activity and recyclability towards the oxidative dehydrogenation (ODH) and the catalytic transfer hydrogenation (CTH) for various N-heterocycles. The structure of outer N-doped carbon nanotubes (NCNTs) can protect Co NPs from aggregation and leaching. Moreover, the encapsulated Co NPs and the NCNTs may generate a synergistic effect. Both of them facilitate the high performance. The poisoning tests with KSCN were to clarify the different active sites for ODH and CTH reactions: the Co NPs could modify the NCNTs through electrons redistribution, therefore the NCNTs could directly activate O-2 in ODH. The encapsulated Co NPs is enhanced by the doped N atoms which is good for the H-2 activation in CTH. What's more, the mechanisms of ODH and CTH reactions were also proposed. This work provides a facile and low-cost method to design catalysts, which are dual-functional, highly active and stable, for industrial applications.