Efficient Photocatalytic Ethylene Oxidation to Acetaldehyde by Asymmetrical Dehydrogenation

Acetaldehyde is an essential commodity chemical with high demand, while its conventional production by homogeneous Wacker oxidation suffers from high corrosivity, high chlorine by-products, and separation difficulties. In this work, a Pd nanoparticle-loaded ZnO (Pd-ZnO) photocatalyst is developed for the selective oxidation of ethylene to acetaldehyde. The ZnO substrate provides hydroxyl radicals (•OH) from water oxidation, and the Pd active sites allow to promote the dehydrogenation of adsorbed symmetrical ethylene to form asymmetrical vinyl specie (^*CH₂═CH) with negatively charged carbon, which can be further attacked by •OH to vinyl alcohol (^*C₂H₃OH) and finally undergo isomerization to produce acetaldehyde products. The Pd-ZnO photocatalyst exhibits a high C₂H₄-to-acetaldehyde yield of >3500 µmol g^-1 h^-1 with 60% selectivity at ambient temperature and pressure under illumination without the use of sacrificial agents, featuring one of the highest performances in both photocatalytic and electrocatalytic conversion. This work suggests an attractive opportunity for the photocatalytic production of acetaldehyde from ethylene.