The structure sensitivity of CO and H adsorption on vicinal Rh surfaces: A density functional theory and X-ray photoelectron spectroscopy study

How active a catalyst depends strongly on its morphology and surface structure. There is an increasing awareness of the fact that heterogeneous catalytic processes on vicinal surfaces can be radically different from planar surfaces due to the existence of edges, kinks and steps. However, there is little knowledge concerning the influence of different type of steps on reactivity up to now. Such detailed information could be valuable in optimizing activity and slectivity of catalytic reaction. To provide insight into the influence of different type of steps on the reactivity, density functional theory (DFT) calculations and X-ray Photoelectron Spectroscopy (XPS) measurements have been used to study the CO and H adsorption on Rh(553) and Rh(322) surfaces, which have same width of (111) terrace but different type of steps (111) and (100), respectively. We found that CO molecules prefer to adsorb atop sites at the step edge. For Rh(553), the step adsorption site is atop, whereas for Rh(322) both atop and bridge sites are taken. With increase of the coverage, CO will populate the terrace sites. At low coverage of CO, adding H to the system, CO molecules are moved entirely to the terraces on Rh(553), while stays at the step edge but changes to bridge sites on Rh(322). The cooperation and interplay between DFT calculations and XPS meaurements will be highlighted, and the influence of exchange-correlation functionals (PW91 and hybrid functionals) on the site preference between CO adsorption will be discussed