Abstract IR investigations of H 2S adsorption on faujasite-type zeolites with systematically varied Si/Al ratios (1.05 to 3.24) have been carried out in order to elucidate the mechanism of adsorption and the role of the Si/Al ratio. The results suggest that on aluminium-rich faujasite-type zeolites up to Si/Al ratios of about 2.5 the first H 2S molecules are adsorbed dissociatively. This chemisorption produces OH groups similar to those of hydrogen faujasite giving rise to bands at 3650 and 3580 cm −1. OH groups related to the 3650 cm −1 band are favored. At least a part of the newly formed OH groups exhibit Brønsted acidity. SH groups are indicated by bands around 2560 cm −1. A good correlation has been found between the concentration of dissociatively formed OH and SH species and the population of certain cation sites. From this the conclusion is drawn that the Na + cations at such not well-defined sites at the walls of the supercage are the centers of dissociative H 2S adsorption. The zeolites of Na Y type with Si/A1 > 2.5 adsorb the H 2S molecules practically without dissociation. This physical adsorption occurs in the whole range of Si/Al ratios if higher H 2S pressures are applied; up to Si/Al ≈ 2.5 both mechanisms then overlap. Preliminary studies of H 2S oxidation show that this process is also influenced by the Si/Al ratio.