Paper SS-TuP3
Scanning Tunneling Microscopy Study of Subsurface Atomic Activity in Heterogeneous Catalysis

Tuesday, October 29, 2013, 6:00 pm, Room Hall B

Subsurface species are an enigmatic source of energetic reagents in heterogeneous reactions catalyzed by metal surfaces. As absorbed atoms in the selvedge of a metal, they may be metastable with respect to atoms adsorbed to the surface or in the gas-phase, and so can leave the subsurface with excess energy. Furthermore, when subsurface atoms emerge from beneath adsorbed molecules new reaction geometries are enabled that are otherwise inaccessible between reactants co-adsorbed to a surface. Although believed to be important reactive intermediaries, a systematic study of their fundamental chemistry has yet to be undertaken. To address this, we will develop the basis for a more complete understanding by studying the dynamics of subsurface species. We have selected two model systems for study; hydrogen on Ni(111) and oxygen Ag(111) which will provide basic details of subsurface absorption and reactivity, and further provide guidance for utilization of these species to selectively control chemistry. For catalytic transformations in either system, subsurface atoms are key components of catalytic processes, but it remains unclear how they enhance reactions. To reveal the surface dynamics, scanning tunneling microscopy (STM) will image the surface, tracking the movement of individual atoms as they diffuse across and into the metal surfaces. The unique capabilities of STM to selectively energize and manipulate atoms on surfaces will also be used to further investigate the energetics of subsurface incorporation and emergence. To complement STM images, temperature programmed desorption and Auger electron spectroscopy will identify adsorbates and provide thermodynamic information. Our results will show mechanisms for subsurface migration and we will also probe the energetics of subsurface incorporation. Taken together, this new information seeks to narrow the gap our understanding between model and actual catalytic systems and enable chemists to accurately gauge the role of subsurface species in the transformation of plentiful feedstock into energy-rich chemicals over metal catalysts.