Polyoxometalate–zirconia (POM/ZrO2) nanocomposite prepared by sol–gel process: A green and recyclable photocatalyst for efficient and selective aerobic oxidation of alcohols into aldehydes and ketones

A polyoxometalate–zirconia (POM/ZrO2) nanocomposite was prepared through entrapment of H3PW12O40 polyoxometalate into zirconia matrix by sol–gel technique involving the hydrolysis of zirconium (IV) n-butoxide, Zr(n-OBu)4, as the ZrO2 source. The catalyst was characterized by using XRD, FT-IR, SEM, TEM and surface area measurement and used as an efficient heterogeneous photocatalyst for aerobic oxidation of alcohols. Various primary and secondary benzylic alcohols were oxidized into the corresponding aldehydes and ketones in high yields under O2 atmosphere in the presence of photoexcited POM/ZrO2 nanocomposite. Also, nonactivated aliphatic alcohols were oxidized in good yields albeit after longer reaction times in comparison with benzylic alcohols, so that the selective oxidation of a benzylic OH group in the presence of a non-benzylic OH group could be achieved by the appropriate choice of the reaction time. The photocatalyst has been reused several times, without observable loss of activity and selectivity. Indeed, the photocatalytic activity of the POM/ZrO2 was higher than that of pure POM.