Tailoring collaborative N–O functionalities of graphene oxide for enhanced selective oxidation of benzyl alcohol

Abstract

Benzaldehyde (BzH) is an important chemical for industrial feedstock. However, the conventional production processes heavily rely on precious metal catalysts and bring about unavoidable pollution issues. Here we report a new catalytic process to use N-doped graphene oxide (NGO) as the catalyst for oxidation of benzyl alcohol (BzOH) into BzH by an environmentally benign oxidant, peroxymonosulfate (PMS). Different approaches are developed to synthesize carbonylated NGO, which shows higher catalytic efficiency than CO-deficient NGO. The optimized catalyst could achieve 96% BzOH conversion and unprecedented 82% BzH yield under mild temperature (50 °C), superior to some precious metal catalysts reported. Experimental studies unveil the indispensable roles of pyridinic N and ketonic CO groups in forming an electron bridge between BzOH and PMS for non-radical oxidation, or separately inducing radical oxidation. The non-radical oxidation process is more selective in yielding BzH. Furthermore, the yielded BzH is free from over-oxidation into benzoic acid under various reaction conditions, because the radicals preferentially react with BzOH other than BzH and the BzH can hardly adsorb on graphene sheets, thus inhibiting its further oxidation. This work provides a cheap material and mechanic understanding of carbocatalysis for green organic synthesis with environmental and economic perspectives.