Hydrogen Bonding Promotes Alcohol C-C Coupling

Photocatalytic C-C bond formation coupled with H2 production provides a sustainable approach to producing carbon-chain-prolonged chemicals and hydrogen energy. However, the involved radical intermediates with open-shell electronic structures are highly reactive, experiencing predominant oxidative or reductive side reactions in semiconductors. Herein, we demonstrate that hydrogen bonding on the catalyst surface and in the bulk solution can inhibit oxidation and reverse reaction of alpha- hydroxyethyl radicals (alpha HRs) in photocatalytic dehydrocoupling of ethanol over Au/CdS. Intentionally added water forms surface hydrogen bonds with adsorbed alpha HRs and strengthens the hydrogen bonding between alpha HRs and ethanol while maintaining the flexibility of radicals in solution, thereby allowing for alpha HRs' desorption from the Au/CdS surface and their stabilization by a solvent. The coupling rate of alpha HR increases by 2.4-fold, and the selectivity of the target product, 2,3-butanediol (BDO), increases from 37 to 57%. This work manifests that nonchemical bonding interactions can steer the reaction paths of radicals for selective photocatalysis.

Automated summary

Hydrogen bonding on the catalyst surface and in the bulk solution can inhibit oxidation and reverse reaction of α-hydroxyethyl radicals, resulting in increased selectivity of the target product.