Role of adsorbed hydrogen species on ruthenium and molybdenum sulfides. Characterization by inelastic neutron scattering, thermoanalysis methods and model reactions

Abstract The interaction of hydrogen over unsupported MoS 2 and RuS 2 has been investigated as a function of the sulfur to metal ratio. On these solids the presence of sulfur deficient sites is required to generate an activity and to allow hydrogen chemisorption. The nature of the adsorbed species differs depending on the catalyst under investigation. On RuS 2 , two types of hydrogen were evidenced by thermoflash desorption and inelastic neutron scattering: one was assigned to hydrogen adsorbed on surface sulfur anions while the other one is retained on coordinatively unsaturated ruthenium cations. By contrast, only SH groups were detected on MoS 2 . ESR measurements have shown that a fraction of chemisorbed hydrogen induces a modification of the concentration of paramagnetic Mo(V) and Mo(III) species. Thus both solids behave differently towards an hydrogen atmosphere. RuS 2 has a pseudometallic comportment whereas for MoS 2 redox or acid base properties are involved.