Oxidation of Aromatic Alcohols in Irradiated Aqueous Suspensions of Commercial and Home‐Prepared Rutile TiO2: A Selectivity Study

Abstract

The photocatalytic oxidation of benzyl alcohol (BA) and 4-methoxy-benzyl alcohol (MBA) has been performed in pure water by using commercial TiO2 samples (Sigma-Aldrich, Merck, Degussa P25) and rutile TiO2 prepared from TiCl4 at low temperature. Particular attention has been devoted to the identification of the produced aromatic compounds along with the formed CO2. Oxidation products such as the corresponding aromatic aldehyde and acid, as well as mono- and dihydroxylated aldehydes have been detected. The home-prepared rutile sample showed a marked selectivity towards the formation of the aromatic aldehyde (38 and 60 % for BA and MBA, respectively), resulting in a three- to sevenfold improvement relative to commercial samples, with the only byproduct being CO2. This catalyst was found to be the most selective in the formation of aldehyde in water. By using the commercial or the calcined home-prepared samples, many hydroxylated aromatic compounds were detected besides the aldehyde and the acid. This finding points to a higher selectivity performance of the home-prepared rutile relative to the commercial TiO2 samples. Some of the home-prepared samples were also dialysed to check the influence of the presence of Cl- species on catalyst reactivity and selectivity. We have attempted to explain the different reaction rate and selectivity observed for MBA and BA.