Plasmon‐Induced Radical‐Radical Heterocoupling Boosts Photodriven Oxidative Esterification of Benzyl Alcohol over Nitrogen‐Doped Carbon‐Encapsulated Cobalt Nanoparticles
Quanguo Hao, Zhenhua Li, Yiqiu Shi, Ruizhe Li, Yuan Li, Liang Wang, Hong Yuan, Shuxin Ouyang, Tierui Zhang
Abstract
Abstract Selective oxidation of alcohols under mild conditions remains a long‐standing challenge in the bulk and fine chemical industry, which usually requires environmentally unfriendly oxidants and bases that are difficult to separate. Here, a plasmonic catalyst of nitrogen‐doped carbon‐encapsulated metallic Co nanoparticles (Co@NC) with an excellent catalytic activity towards selective oxidation of alcohols is demonstrated. With light as only energy input, the plasmonic Co@NC catalyst effectively operates via combining action of the localized surface‐plasmon resonance (LSPR) and the photothermal effects to achieve a factor of 7.8 times improvement compared with the activity of thermocatalysis. A high turnover frequency (TOF) of 15.6 h −1 is obtained under base‐free conditions, which surpasses all the reported catalytic performances of thermocatalytic analogues in the literature. Detailed characterization reveals that the d states of metallic Co gain the absorbed light energy, so the excitation of interband d‐to‐s transitions generates energetic electrons. LSPR‐mediated charge injection to the Co@NC surface activates molecular oxygen and alcohol molecules adsorbed on its surface to generate the corresponding radical species (e.g., ⋅O 2 − , CH 3 O⋅ and R‐⋅CH‐OH). The formation of multi‐type radical species creates a direct and forward pathway of oxidative esterification of benzyl alcohol to speed up the production of esters.