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 into sulfur at low temperature (383 K). H2S is totally consumed during the 28 first hours of the reaction, without detection of SO2 nor S-n. The decrease of H2S conversion is concomitant with the detection of sulfur at the bottom of the reactor. Analysis of the catalyst evidenced the presence of several sulfurated species, such as sulfate, sulfur, and especially sulfide species. The sulfide/copper molar ratio varies versus reaction time and reaches values greater than 1, which suggests the formation of polysulfide species. Its maximum value (3.5) is concomitant with the conversion decrease and the formation of S-n. Complementary reactivity experiments show that the active 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 can be divided into three parts: adsorption of H2S to create the active copper oxysulfide phase, insertion of SO from oxidation of H2S leading to the creation of polysulfide species, desorption of S-n sulfur when the polysulfide chain becomes too long. Deactivation of the catalyst can be due to the storage of sulfur in its porosity or to the impoverishment of the network oxygen. Regeneration treatment at 603 K under water leads to the removal of S-n and sulfate species. (C) 2000 Academic Press.