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The study is devoted to the comparison between the activity of γ-alumina and titania (anatase) toward CS2 hydrolysis. It is shown that, without any other sulfur compound, like H2S and SO2, and without O2 traces in the feed, alumina is more active than titania at 320°C. The IR study of CS2 adsorption on alumina evidences the participation of the most basic OH groups and the formation of hydrogen thiocarbonate and hydrogen carbonate species, providing some information on the nature of the active sites and the reaction mechanism. Chemisorbed COS appears as a reaction intermediate. Realistic industrial Claus conditions imply, in addition to CS2 and H2O, the presence of H2S, SO2 and O2 traces in the feed. It appears that the presence of O2 traces in the CS2–H2O mixture brings about a decrease in activity of the alumina and titania. This is due to sulfate formation as shown by the IR analysis of the catalysts after the reaction. Moreover, IR studies evidence that sulfate species are reduced by H2S at 320°C on TiO2, contrary to results obtained on Al2O3, explaining why TiO2 is much more effective than Al2O3 when the CS2+H2O feed also contains H2S and O2 traces. |
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