Evidence of the reverse Claus reaction on metal oxides: Influence of their acid–base properties

Different metal oxides have been impregnated by sulfur S8 and treated under H2O at increasing temperature up to 330°C. In case of TiO2 and Al2O3, H2S and SO2 emissions have been detected by gas chromatography, showing that the reverse Claus reaction between sulfur and water occurs. Addition of sulfate ions to TiO2 and Al2O3 prevents the reaction, whereas addition of sodium to SiO2 promotes H2S and SO2 formations. Our results evidence that the reverse Claus reaction is sensitive to the acid–base properties of the metal oxides used, as the direct reaction does. However, H2S is always evolved at lower temperature than SO2, which is discussed in relation with the chemisorption of each product on the metal oxides used, and their possible reactivity. In particular, thiosulfate species are evidenced by infrared spectroscopy on Na/SiO2 after reaction.