Simultaneous dehydrogenation and hydrogenolysis of aromatic alcohols in one reaction system via visible-light-driven heterogeneous photocatalysis

Abstract

Photocatalytic selective organic transformation using photoexcited holes and electrons has attracted worldwide interest. Although extensive studies have made significant progress in dehydrogenation of alcohols, hydrogenolysis of alcohols using photoexcited electrons directly constitutes a challenge. Here, photocatalytic selective dehydrogenation and hydrogenolysis of aromatic alcohols into corresponding alkanes/ethers and aldehydes has been achieved by direct use of photoexcited electrons and holes over CdS under visible light irradiation. Compared with other popular visible-light-driven photocatalysts, Sb2S3, Bi2O3, N-doped TiO2, Zn3In2S6, g-C3N4, and Ce2S3, the sum of the yields of alkanes and aldehydes over the as-prepared CdS could reach up to 94% after reaction for 4 h. The high photoactivity and stability of CdS toward dehydrogenation and hydrogenolysis of aromatic alcohols can be ascribed to its appropriate band potentials and effective charge separation–transportation. The optimum positions are that the valence band position should be located between oxidation potentials of alcohol/aldehyde and aldehyde/oxidized aldehyde, and the conduction band position should be more slightly negative than reduction potential of alkane/alcohol. During this reaction, the dehydrogenation reaction consumes two holes and produces two protons; the hydrogenolysis process depletes two electrons and two protons. Therefore, a cooperative, cyclical, and efficient reaction system was established.