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 TiO(2) under ambient conditions. (C(2)H(5))(2)S(2), CH(3)CHO, CH(3)CH(2)OH. C(2)H(4), and CO(2) were detected as the major products in gaseous effluent of the reactor. The trace products in gas phase included CH(3)COOH, C(2)H(5)SC(O)CH(3), and SO(2). All the catalysts studied showed deactivation with a characteristic temporal range of 100-300 min. The surface products extracted by isopropanol included (C(2)H(5))(2)S(2), (C(2)H(5))(2)S(3), (C(2)H(5))(2)SO, (C(2)H(5))(2)SO(2). and C(2)H(5)SCH(2)CH(2)OH. The residual activity was the highest for TiO(2) Hombikat UV 100. At relatively low light intensities (1.1 mW/cm(2)), the increase in humidity from less than 1 % to similar to 20 and similar to 60% resulted in the increase of the quantities of diethyl sulfide converted. However, at relatively high light intensities (11 mW/cm(2)) such an increase in humidity had an adverse effect on the conversions of diethyl sulfide. The quantities of (C(2)H(5))(2)S converted and the products formed correlate well with the specific surface area of the TiO(2) samples, thus indicating the importance of surface reactions in gas phase photooxidation of diethyl sulfide. Additions of H(2)O(2) 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. (C) 2001 Elsevier Science B.V. All rights reserved.