Selective oxidation of alcohols to carbonyl compounds over small size colloidal Ru nanoparticles

The selective oxidation of alcohols to corresponding aldehydes is one of the most challenging problems in modern chemistry due to over-oxidation of these products further into corresponding acids and esters. Herein, we report an efficient and eco-friendly method for selective oxidation of aliphatic, unsaturated and aromatic alcohols to aldehydes (>90 %) using small size (2 nm) non-supported colloidal Ru nanoparticles. The selectivity rapidly decreases with increase of the size of nanoparticles (from 2 to 10 nm) or after their deposition over support. X-ray photoelectron spectroscopy suggests that this catalytic performance can be attributed to high content Ru-O species on the surface of small size Ru nanoparticles, which undergo reduction with formation of water and aldehyde and easy oxidation cycles during the reaction according to the Mars-van Krevelen mechanism. The presence of surface oxide layer over small size Ru nanoparticles suppresses over-oxidation of aldehydes to acids.