Reaction of hydrogen with S/Mo(110) and MoSx films: Formation of hydrogen sulfide

The reaction of hydrogen (H-2, D-2, or D) with sulfur multilayers, S-<1/Mo(110), surfaces and MoSx films has been investigated at temperatures between 100 and 400 K. All the surfaces were unreactive toward molecular hydrogen under UHV conditions. However, these systems showed a large reactivity toward atomic hydrogen. As gas-phase hydrogen atoms impinged on the surfaces, gaseous hydrogen sulfide was formed. This reaction was very effective for the removal of sulfur atoms from sulfur multilayers and MoSx films. On MoSx films the 2D(gas) + S(solid) --> D2S(gas) reaction was 3-4 times slower than on sulfur multilayers, and at least 6 times faster than on S-<1/Mo(110) surfaces. A good correlation was found between the rate of formation of gaseous hydrogen sulfide and the stability of the S-S or S-Mo bonds in a surface. The bonding interactions between hydrogen sulfide and S-0.9-0.6/Mo(110) or MoSx were negligible at temperatures above 200 K. Rough MoSx films that exposed unsaturated molybdenum sites were more reactive toward hydrogen sulfide than the sulfur-basal plane of MoSx or S-0.9-0.6/Mo(110) surfaces. The behavior of molybdenum sulfide catalysts in hydrogenation and hydrodesulfurization processes is discussed in light of these results.