| Our research focuses on taking advantage of the ability of scanning tunneling microscopy (STM) to operate at high-temperatures and high-pressures while still providing real-time atomic resolution images. We also utilize high-pressure x-ray photoelectron spectroscopy (HPXPS) to monitor systems under identical conditions thus giving us chemical information to compare and contrast with the structural and dynamic data provided by STM.; STM was employed to study the structures formed by cyclic C6 hydrocarbon monolayers adsorbed on a platinum (111) crystal surface. Cyclohexane, cyclohexene, 1,3-cyclohexadiene, 1,4-cyclohexadiene and benzene were exposed to the platinum surface in the 10-6 Torr pressure regime. Upon adsorption on Pt(111) both cyclohexane and cyclohexene produced the same (√7 x √7) R19.1° hexagonal structure, which corresponds to the partially dehydrogenated pi-allyl (C6H9). 1,3-cyclohexadiene and benzene produced a (2√3 x 2√3) R30.0° structure composed of pure benzene. 1,4-cyclohexadiene forms a structure very different from the others, which we attributed to a (√43 x √43) R7.6° structure composed of molecular 1,4-cyclohexadiene.; STM and XPS studies on several catalytic reaction systems and their poisoning with carbon monoxide on Pt(111) were also performed. Systems studied include cyclohexene hydrogenation/dehydrogenation, benzene hydrogenation and hydrogen/deuterium exchange. In all situations studied the adsorbed monolayer of molecules was highly mobile during catalytic reactions. Upon poisoning with CO at room temperature, an ordered immobile overlayer forms and all catalytic turnover ceases. Heating the surface disorders the CO overlayer. Hydrogen deuterium exchange still proceeds, albeit more slowly, but cyclohexene hydrogenation/dehydrogenation and benzene hydrogenation are poisoned. XPS shows that the majority of the CO is still present on the surface. From these data, a mobile CO dominated surface with small congregations of vacancies is proposed. |
