Selective Oxidation of Aliphatic Alcohols using Molecular Oxygen at Ambient Temperature: Mixed-Valence Vanadium Oxide Photocatalysts

Here we report a class of photocatalysts: mixed-valence vanadium oxide particles grafted onto a variety of oxide supports. In these catalysts V6O13 species with mixed oxidation states (V4+ or V5+) are believed to be catalytically active sites. These catalysts successfully enable alcohol oxidation to selectively produce aldehydes and ketones using O2 as the oxidant. The catalytic process is driven by visible light irradiation at room temperature and, most importantly, progresses with negligible overoxidation. The catalysts can even selectively oxidize aliphatic alcohols, which are much more challenging to control in comparison to aromatic analogues. They can also be applied to the activation and oxidation of the otherwise stable C-H bonds of saturated aromatic hydrocarbons, such as toluene and xylene, under irradiation. Both experimental results and density functional theory (DFT) simulations suggest the formation of V6O13-alkoxide species as the initial step in the catalytic cycle. The V6O13-alkoxide then acts as the light harvester, being excited by light of wavelength shorter than 550 nm. Facile room-temperature C-H bond cleavage in the excited state V6O13-alkoxide in the presence of O-2 leads to the carbonyl-containing products. These findings demonstrate an example of light-driven selective oxidation of diverse alcohols via in situ formation of photoresponsive V6O13-alkoxide species. This catalytic process is especially valuable for the synthesis of temperature-sensitive products and represents an alternative pathway to many conventional thermal oxidation reactions.