Comparative adsorption of H2S, CH3SH and (CH3)2S on alumina. Structure of species and adsorption sites

Abstract

The adsorption of H₂S, CH₃SH and (CH₃)₂S has been studied by gravimetry and infrared spectroscopy. Some experiments have been carried out with preadsorbed pyridine as a poison. The results show that (CH₃)₂S is bonded to Lewis acid sites and that 60 µmol g^–1 are irreversibly coordinated to stronger sites of this type. Dissociative chemisorption has been observed for H₂S and CH₃SH. Poisoning experiments lead us to conclude that the first adsorption steps involve either a coordinative adsorption (ca. 30 µmol g^–1) or a hydrogen bond between a surface basic oxygen atom and the H atom of the SH bond (ca. 50 µmol g^–1). The reversible adsorption of CH₃SH is thought to occur by these two processes besides another one in which the S atom is H bonded to a hydroxyl surface group. These results clarify the nature of the adsorption sites of alumina.