Cobalt Encapsulated in Nitrogen-Doped Graphite-like Shells as Efficient Catalyst for Selective Oxidation of Arylalkanes.

Abstract

Selective oxidation of ethylbenzene to acetophenne is an important process in both organic synthesis and fine chemicals diligence. The cobalt-based catalysts combined with nitrogen-doped carbon have received great attention in ethylbenzene (EB) oxidation. Here, a series of cobalt catalysts with metallic cobalt nanoparticles (NPs) encapsulated in nitrogen-doped graphite-like carbon shells (Co@NC) have been constructed through the one-pot pyrolysis method in the presence of different nitrogen-containing compounds (urea, dicyandiamide and melamine), and their catalytic performance in solvent-free oxidation of EB with tert-butyl hydrogen peroxide (TBHP) as an oxidant was investigated. Under optimized conditions, the UCo@NC (urea as nitrogen source) could afford 95.2% conversion of EB and 96.0% selectivity to acetophenone, and the substrate scalability was remarkable. Kinetics show that UCo@NC contributes to EB oxidation with an apparent activation energy of 32.3 kJ/mol. The synergistic effect between metallic cobalt NPs and nitrogen-doped graphite-like carbon layers was obviously observed and, especially, the graphitic N species plays a key role during the oxidation reaction. The structure-performance relationship illustrated that EB oxidation was a free radical reaction through 1-phenylethanol as an intermediate, and the possible reaction mechanistic has been proposed.