Photocatalytic destruction of gaseous diethyl sulfide over TiO₂

Photooxidation of gaseous diethyl sulfide (DES) at a concentration in the order of hundreds of ppm was carried out in a flow reactor over four different samples of TiO₂ under ambient conditions. (C₂H₅)₂S₂, CH₃CHO, CH₃CH₂OH, C₂H₄, and CO₂ were detected as the major products in gaseous effluent of the reactor. The trace products in gas phase included CH₃COOH, C₂H₅SC(O)CH₃, and SO₂. All the catalysts studied showed deactivation with a characteristic temporal range of 100-300 min. The surface products extracted by isopropanol included (C₂H₅)₂S₂, (C₂H₅)₂S₃, (C₂H₅)₂SO, (C₂H₅)₂SO₂, and C₂H₅SCH₂CH₂OH. The residual activity was the highest for TiO₂ Hombikat UV 100. At relatively low light intensities (1.1 mW/cm2), the increase in humidity from less than 1% to ∼20 and ∼60% resulted in the increase of the quantities of diethyl sulfide converted. However, at relatively high light intensities (11 mW/cm²) such an increase in humidity had an adverse effect on the conversions of diethyl sulfide. The quantifies of (C₂H₅)₂S converted and the products formed correlate well with the specific surface area of the TiO₂ samples, thus indicating the importance of surface reactions in gas phase photooxidation of diethyl sulfide. Additions of H₂O₂ in the reactor feed stream increased the rate of diethyl sulfide destruction, but also altered the product distribution throughout the reaction time. Steps of the reaction mechanism are proposed to explain the formation of this set of products and observed kinetic dependencies. The main routes of this mechanism are C-S bond cleavage, S-oxidation, and C-oxidation.