We have investigated the adsorption of water on a Co(0001) surface by means of temperature-programmed desorption (TPD), X-ray photoelectron spectroscopy (XPS), and low-energy electron diffraction (LEED). At 130 K, the interaction between adsorbed water (H 2 O(a)) and Co(0001) is quite weak, and water adsorption forms an intact, nonwetting, and three-dimensional layer on Co(0001). The monolayer and multilayer of H 2 O(a) could be distinguished by XPS, and they desorb molecularly upon heating but only giving a single water desorption peak. An ordered p(2 × 2) LEED pattern was observed at low exposures of water. At room temperature, water adsorbs dissociatively on Co(0001), forming chemisorbed atomic oxygen (O(a)) and atomic hydrogen (H(a)). Upon heating, H(a) recombines into H 2 desorbing from the surface, whereas O(a) remains on the surface. The interaction of water with Co( 0001) is greatly influenced by the presence and nature of the oxygen species on Co(0001). Water adsorption on Co(0001) precovered with 0.45 ML O(a) at 130 K forms a mixture layer of OH(a) and H(a) via the reaction of 2H 2 O(a) + O(a) f 3OH(a) + H(a). However, on oxide-like Co(0001) surface, the water decomposition is completely passivated even at room temperature. These results broaden our fundamental understanding of water interaction with metal surfaces and provide insights into the water-involved catalytic reactions catalyzed by cobalt. † Part of the "D. Wayne Goodman Festschrift".

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Chemisorption and surface reactions of C2H4, CO, and H2 on clean and graphite carbon-modified Co(0001) surfaces have been investigated by thermal desorption spectroscopy, X-ray photoelectron spectroscopy, and low-energy electron diffraction. The chemisorption and decomposition behaviors of C2H4 depend largely on the vacant sites available on clean Co(0001) at 130 K. C2H4 chemisorbs dissociatively to produce C2H2(a) and H(a) at low exposures but both dissociatively and molecularly to produce C2H4(a), C2H2(a), and H(a) at large exposures. Upon heating, some C2H4(a) desorbs and vacates surface sites, which results in the simultaneous decomposition of C2H4(a) into C2H3(a) and H(a). At 350 K, C2H3(a) either undergoes further dehydrogenation into C2H2(a) and H(a) or hydrogenates to produce C2H4. C2H2(a) then completely dehydrogenates to graphite carbon and H2 at 424 K. Graphite carbon modified Co(0001) surfaces were prepared by the thermal decomposition of C2H4 on clean Co(0001). The graphite carbon exerts both site-blocking effect and electronic effect on the reactivity of Co(0001) surface, suppressing the decomposition of C2H4(a) and weakening the interaction between the Co surface and CO(a) and H2(a). These results provide fundamental understandings of elementary steps of relevant heterogeneous catalytic reactions catalyzed by Co-based catalysts.