AVS 58th Annual International Symposium and Exhibition
    Surface Science Division Tuesday Sessions
       Session SS-TuP

Paper SS-TuP14
Links Between the Surface Atomic Arrangement and Catalytic Properties of Bimetallic Alloys: A First Principles-based Investigation

Tuesday, November 1, 2011, 6:00 pm, Room East Exhibit Hall

Session: Surface Science Poster Session
Presenter: Gyeong S. Hwang, University of Texas at Austin
Authors: J.A. Stephens, University of Texas at Austin
H.C. Ham, University of Texas at Austin
G.S. Hwang, University of Texas at Austin
Correspondent: Click to Email
Catalysts composed of more than one metallic element often exhibit remarkable activity and selectivity compared to their monometallic constituents. These synergistic properties often can be explained in terms of two kinds of effects: modification of catalyst electronic structure due to interactions between dissimilar metal atoms (ligand effects) and the presence of mixed-metal surface sites that, because of their size and shape, promote some chemical reactions more than others (ensemble effects). Understanding in detail how ligand and ensemble effects operate in particular cases is an important step toward realizing the longer term goal of rational catalyst design. Experimental study has provided valuable insight into this problem, but progress has been hampered by the difficulty of studying reacting systems with atomic resolution. We employ the tools of molecular simulation in a two-pronged approach to complement these efforts. First, we use density functional theory to explore how particular atomic arrangements in the surfaces of bimetallic alloys influence their catalytic function. We have found, for example, that the experimentally-observed ability of Au-Pd catalysts to promote the direct synthesis of hydrogen peroxide may depend on the presence of surface Pd monomers surrounded by Au. Our calculations indicate that on larger Pd ensembles, O-O bond scission can more readily occur, leading to the formation of water. We have similarly studied the oxygen reduction reaction and carbon monoxide oxidation on Au-Pd alloys. In the second prong of our work, we attempt to predict how the metal atoms in catalyst surfaces are actually arranged using a combination of density functional theory, the cluster expansion method, and Monte Carlo simulation. From these simulations, we have obtained the temperature- and composition-dependent ensemble size and shape distributions for the (111) and (100) surface facets of Au-Pd and Au-Pt alloys. Our results are in good agreement with available experimental observations.