N,P-dual-doped multilayer graphene as an efficient carbocatalyst for nitroarene reduction: A mechanistic study of metal-free catalysis

Metal-free carbocatalysts are one of the most promising candidates for reducing the dependency on metal-based catalysts in organic reactions. In this work, we develop an N,P-dual-doped multilayer graphene (NPG) carbocatalyst by directly pyrolyzing a homogenous mixture of microwave-exfoliated graphite and hexachlorocyclotriphosphazene under an inert atmosphere. Attributed to the synergistic effect of N,P co-doping in graphene, the as-prepared NPG shows enhanced catalytic activity and excellent hydrophilic properties. Our findings demonstrate that NPG carbocatalysts exhibited superior catalytic activity in the reduction reaction of nitroarenes, as well as excellent selectivity, stability, and recyclability. The turnover frequency for the reduction of 4-nitrophenol is up to 2.37 x 10(-2) min(-1), exceeding that of conventional graphene-based catalysts by a factor of 10, and is higher than that of many previously reported noble-metal-based catalysts and even comparable with that of commercial Pd/C (5%). A catalytic mechanism of NPG carbocatalysts for 4-NP reduction was proposed based on analysis of adsorption/reaction processes and density functional theory calculations. (C) 2018 Elsevier Inc. All rights reserved.