Gold nano-size effect in Au/SiO2 for selective ethanol oxidation in aqueous solution

Narrowly sized colloidal Au particles of varying average sizes (3-30 nm) were immobilized on an inert support (SiO2) to study the Au size effect on the aerobic oxidation of ethanol in aqueous solution. Au particles with an average diameter of 5 nm showed an areal activity that was about three times that of the smaller (3 nm), and 15 times that of larger (10-30 nm) Au particles. Investigation on the dependence of product yields on ethanol conversion over these differently sized Au particles clearly uncovered that the yield of acetic acid increased always with the ethanol conversion, while that of acetaldehyde passed a maximum at an ethanol conversion of 20-30%, therefore well demonstrating that acetaldehyde is the intermediate product in the oxidation of ethanol to acetic acid.