2, University of California, Los Angeles, Los Angeles, California, United States
Deposition of size-selected clusters in ultrahigh vacuum is used to create catalysts and electrocatalysts with well defined initial catalytic site size. Spectroscopy in UHV is used to characterize the catalysts, and then reactions are studied using either gas-surface interaction methods in UHV, or by electrochemical methods. For gas-surface catalysis, the focus will be on methods for post-deposition modification of clusters, allowing preparation of size-selected bimetallic clusters. Alloying of Pt clusters by boron and tin, and the effects on alkene dehydrogenation will be discussed. Electrochemistry can be studied either in situ in the vacuum system, thus avoiding issues of contamination and electrochemical cleaning, or ex situ, allowing studies using more elaborate electrochemical techniques. For example, Scanning ElectroChemical Cell Microscopy (SECCM) is used to study reactions on electrode areas down to a few hundred nanometers in diameter, and at cluster coverages where processes such as Ostwald ripening or cluster diffusion/agglomeration are negligible. We are, thus, able to study fundamental processes such as proton reduction on well defined catalytic sites down to single atoms.