Selective oxidation of H2S over CuO/Al2O3: Identification and role of the sulfurated species formed on the catalyst during the reaction

A CuO/Al2O3 catalyst was used for selective oxidation of hydrogen sulfide i nto sulfur at low temperature (383 K). H2S is totally consumed during the 2 8 first hours of the reaction, without detection of SO2 nor S-n. The decrea se of H2S conversion is concomitant with the detection of sulfur at the bot tom of the reactor. Analysis of the catalyst evidenced the presence of seve ral sulfurated species, such as sulfate, sulfur, and especially sulfide spe cies. The sulfide/copper molar ratio varies versus reaction time and reache s values greater than 1, which suggests the formation of polysulfide specie s. Its maximum value (3.5) is concomitant with the conversion decrease and the formation of S-n. Complementary reactivity experiments show that the ac tive phase cannot be a simple copper sulfide CuS and underline the peculiar role of oxygen in the network. It finally seems that the oxidation step ca n be divided into three parts: adsorption of H2S to create the active coppe r oxysulfide phase, insertion of SO from oxidation of H2S leading to the cr eation of polysulfide species, desorption of S-n sulfur when the polysulfid e chain becomes too long. Deactivation of the catalyst can be due to the st orage of sulfur in its porosity or to the impoverishment of the network oxy gen. Regeneration treatment at 603 K under water leads to the removal of S- n and sulfate species. (C) 2000 Academic Press.