Selective Oxidation of Alcohols in Gas Phase Using Light-Activated Titanium Dioxide

Abstract

Selective oxidation of various primary and secondary alcohols was studied in a gas-phase photochemical reactor using immobilized TiO 2 catalyst. An annular photoreactor was used at 463 K with an average contact time of 32 s. The system was found to be specifically suited for the selective oxidation of primary and secondary aliphatic alcohols to their corresponding carbonyl compounds. Benzylic alcohols gave higher conversions, however, with more secondary reaction products. The reaction mechanism for various products formed is explained. The effects of different reaction parameters, such as O 2/alcohol ratio, water vapor, UV light, and contact time, were studied. The presence of oxygen was found to be critical for the photooxidation. Water vapor in the feed was also found to be helpful in the reaction, although it was not as critical as in hydrocarbon oxidation, where it was necessary for hydroxylating the catalyst surface and sustaining its activity. In alcohol oxidation, surface hydroxylation could be partially provided by the hydroxyl groups of the alcohol itself. Catalyst deactivation was also observed and is attributed to the surface accumulation of reaction products. However, the catalyst regained its original activity after regeneration by calcination in air for 3 h at 723 K.