The kinetics of the catalytic oxidation of hydrogen sulfide by molecular oxygen have been studied in the temperature range 20–250 °C. The primary reaction product is sulfur which may undergo further oxidation to SO2 at temperatures above 200 °C. From the kinetics of this autocatalytic reaction we derived an oxidation-reduction mechanism. The two rate influencing steps are the chemisorption of oxygen and the reaction between dissociatively chemisorbed H2S and chemisorbed oxygen. The high activation energy for the formation of SO2 (120 kJ mol−1) explains the high selectivity towards sulfur, although SO2 is thermodynamically the most favored product. At temperatures above 300 °C, where the formation of SO2 occurs readily, the SO2 may be an intermediate in the reaction of H2S with O2 leading to S and H2O.
Steijns, M., Derks, F., Verloop, A., & Mars, P. (1976). The mechanism of the catalytic oxidation of hydrogen sulfide: II. Kinetics and mechanism of hydrogen sulfide oxidation catalyzed by sulfur. Journal of catalysis, 42(1), 87-95. https://doi.org/10.1016/0021-9517(76)90094-4