Controlling Radical Intermediates in Photocatalytic Conversion of Low-Carbon-Number Alcohols

Abstract

Low-carbon number alcohols (LCNAs) are important platform molecules that can be derived from many resources, such as coal, oil, natural gas, biomass, and CO2, creating a route to value-added chemicals and fuels. Semiconductor photocatalysis provides a novel method for converting LCNAs into a variety of downstream products. Photocatalysis is initiated by light-excited charge carriers that are highly oxidative and reductive. The polarity and bond dissociation energy (BDE) of Cα–H bonds are small for alcohols, so it can be homolytically dissociated by the participation of photogenerated holes. Consequently, photocatalytic LCNA conversion overcomes the challenge of Cα–H bond activation in thermocatalysis. Apart from carbon radicals generated from Cα–H bond cleavage, many other radicals are formed during photocatalysis, which are active and have multiple conversion pathways, resulting in complex product distributions. In this Perspective, we summarize the methods of controlling the generation of radical intermediates and subsequent reactions in photocatalytic conversion of LCNAs. The intrinsic properties of photocatalysts and external solution environments are the two main factors that affect the selectivity of the final products. On this basis, we summarize the challenges in current photocatalytic conversion of LCNAs and propose directions for future research, with the aim to inspire studies on the selective conversion of small molecular radicals.