Hydrogen uptake by MoS 2 and sulfided alumina-supported Mo catalysts

Abstract

Volumetric H 2-uptake measurements on polycrystalline MoS 2 (39 m 2g −1) have been carried out and uptake isotherms in the temperature range 423–573 K have been determined. The equilibrium stoichiometry at 500 mbar and 573 K was H 0.035MoS 2, and at 473 K the H Mo ratio increased to 0.051. Alumina-supported sulfided Mo catalysts provided H Mo ratios that were higher by approximately a factor of 4, indicating either a higher MoS 2 surface area, spillover of H atoms to the support, or both. Two possible mechanisms for H 2 dissociation are discussed, namely, heterolytic dissociation on MoS pairs and homolytic dissociation on disulfide (SS) 2− edge groups. The presence of the latter on MoS 2 is documented by Raman spectroscopy which shows the characteristic v(SS) mode at 529 cm −1. Although molecular analogs for H 2 activation on disulflde groups are known, it is not yet possible to make a clear distinction between the alternative H 2 dissociation routes.