Work is focused on examining the reaction pathway for the synthesis of vinyl acetate where we have shown that acetate species react with gas-phase ethylene at pressures of ~10-4 Torr to yield vinyl acetate. By the judicious use of isotopically labeled compounds, we have shown that reaction proceeds by the initial insertion of ethylene to form an ethyl acetate intermediate, which forms vinyl acetate by a subsequent β-hydride elimination step. Industrially, this reaction is carried out using gold-palladium alloys that significantly increase the reaction selectivity from about 85% for pure palladium to over 90% for the alloy. A central goal, therefore is to understand the role of alloy formation in improving selectivity. This work is procceding by growing and characterizing gold- palladium alloys formed on a Pd(111) single crystal substrate. This the surface and catalytic chemistry to be correlated with alloy composition over a wide range. Key to success in this area will rely on a full characterization of the nature of the alloy surface. This is being carried out by a combination of analytical techniques (LEED, low-energy ion scattering, STM) and theoretical methods (diffraction analyses, statistical mechanics and density functional theory calculations).
We are examining the surface chemistry of chiral catalysis in collaboration with Professors Francisco Zaera of UC-Riverside and Andy Gellman and Dave Sholl of Carnegie-Mellon University. We have developed a method to examine enantioselectivity in ultrahigh vacuum by adsorbing a chiral probe molecule onto a chirally templated surface, which allows us to relate the structures of the template and probe to the resulting enantioselectivity. The structure of the adsorbates is determined using a variety of techniques such as infrared spectroscopy and low-energy electron diffraction. Work is focusing on molecules that are expected to operate in a cooperative fashion to yield chiral sites, such as aminoacids as well as those that act in a one-to-one fashion.