Ph.D. Candidate (2006)

Department of Chemical Engineering
Doherty Hall Room B207
Carnegie Mellon University
Pittsburgh, PA 15213
412-268-3892 (lab)
412-268-4531 (office)
412-268-7139 (fax)

Catalysis is fundamentally a kinetic phenomenon. A surface-catalyzed reaction must consist of at least three elementary steps: reactant adsorption, reaction to stable surface species and product desorption, as illustrated in Fig.1. Reaction mechanisms are formulated from a series of elementary steps, each of which has an associated rate constant. For a given elementary step, the dominant term in the rate constant is the activation barrier (ΔE‡), which is the difference in zero-point energy between the reactant or stable reacting species and the transition state. Past efforts have been focused on the elucidation of reaction mechanisms; however, characterization of transition states is equally important.

In this research area, we are trying to explore the nature of the transition state for an elementary reaction occurring on a metal surface. Over the past decade, experimental approaches to this problem have measured the effects of fluorine substituents on the activation barriers ( ΔE‡ ). Our current project involves studying the dechlorination of chlorofluorocarbon (CFC) on the Pd(111) surface using both thermally programmed desorption (TPD) and x-ray photoemission spectroscopy (XPS) in order to measure the ΔEdes and ΔEapp for dechlorination independently. ΔE C-Cl can be obtained by ΔE C-Cl = ΔEdes + ΔEapp, as indicated in fig.2. Four CFCs are used in this work: CF3CCl3, CF3CFCl2, CF3CFHCl, CF3CF2Cl. The purpose of this work is to try to make a connection between the results of our experiments on a Pd(111) surface and the results from high pressure hydrodechlorination of CFCs over supported Pd catalysts. The long term goal of this research is to understand surface reactivity.