The chemical and electronic properties of a series of Zn/S/Mo(110) and Co/S/Mo(110) systems have been investigated using photoemission, thermal desorption mass spectroscopy, and hydrogen (H 2 , D 2 , or D) chemisorption. Sulfur multilayers supported on Mo(110) are very reactive toward admetals like Zn and Co. The behavior of the Zn/S/Mo(110) and Co/S/Mo(110) systems indicates that Zn and Co promote Mo T S interactions, inducing the formation of molybdenum sulfide films. The ZnMoS and CoMoS films were unreactive toward H 2 or D 2 under ultrahigh vacuum conditions. As gas-phase hydrogen atoms (D) impinged on the surfaces, gaseous hydrogen sulfide was formed. Thus, the slow step in the D 2,gas + S solid f D 2 S gas reaction is the dissociation of molecular hydrogen. A good correlation exists between trends seen in the hydrodesulfurization (HDS) activity of ZnMoS and CoMoS catalysts and trends found for the sulfidation of Mo and hydrogenation of S in ZnMoS and CoMoS films. The systems that contain Co show the larger HDS activity, the stronger metal T metal interactions with a subsequent increase in the reactivity of Mo toward S-containing molecules, and the bigger tendency to create unsaturated Mo sites through the hydrogenation of Mo-bonded S atoms.

The interaction of gas phase atomic hydrogen with chemisorbed oxygen on Ru(001) and RuOx films has been investigated by means of Auger electron spectroscopy and thermal desorption spectroscopy at surface temperatures between 120 and 320 K. Although molecular hydrogen does not adsorb on oxygen saturated Ru(001) or RuOx films even at 120 K, atomic hydrogen reacts with oxygen on Ru(001) surfaces, and both D2 and D2O desorb at temperatures below 500 K. The 2Dgas+Oad→D2Ogas reaction is approximately six times faster at 310 K than at 120 K. For RuOx films, a unity reaction probability was found at oxygen coverages above 3 monolayers (ML), while it decreased to 0.4 at Θ0<3 ML. Such variation can be attributed to a change in the structure of the oxide film. The reaction probably follows an Eley–Rideal mechanism where gas phase atomic hydrogen reacts with oxygen prior to thermal accommodation within the surface. The desorption of water is the rate limiting step at surface temperatures below 200 K, whereas the formation of water is the rate limiting step at higher temperatures.