|Tuning the Electronic and Chemical Properties of Bimetallic Surfaces
Laboratory for Surface Modification
|Jingguang Chen, Center for Catalytic Science and Technology (CCST) Department of Chem. Eng., University of Delaware
12pm in Room 260, Wright-Rieman Chemistry Laboratory
It is well known that bimetallic surfaces often show novel properties that are not present on either of the parent metal surfaces. However, it is difficult to know a priori how the chemical properties of a particular bimetallic surface will be modified relative to the parent metals. There are two critical factors that contribute to the modification of the chemical properties of a metal in a bimetallic surface. First, the geometry of the bimetallic structure is typically different from that of the parent metals, e.g. the average metal-metal bond lengths change. This gives rise to strain effects that are known to modify the electronic structure of the metal through changes in orbital overlap. Second, the presence of other metals around a metal atom also changes its electronic environment, giving rise to further modifications of its electronic structure through the ligand effect. We have investigated the electronic and chemical properties of model bimetallic surface structures, epitaxial monolayers and subsurface epitaxial monolayers, using a combination of experimental and theoretical modeling to gain further insights into these factors [1-6]. In the current presentation we will first utilize the adsorption and desorption of hydrogen to demonstrate the correlation between the hydrogen binding energy and the center of the d-band in various bimetallic surfaces. We will also provide a general equation that allows one to predict how the electronic properties, especially the d-band center, will be affected in bimetallic systems. We will then use the hydrogenation of cyclohexene to demonstrate the effect of weakly-bonded hydrogen on the novel low-temperature hydrogenation activities on the bimetallic surfaces. Finally, we will use the results from the hydrogenation of cyclohexene to demonstrate a strong correlation between UHV studies on model bimetallic surfaces and reactor studies on corresponding supported bimetallic catalysts.
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