Reactions at Surfaces: Delving Below and Beyond

Sylvia T. Ceyer

Department of Chemistry, Massachusetts Institute of Technology

Abstract

Catalytic surface reactions depend not only on adsorbed species but also on absorbed species. Experiments that document the distinctive reactivity of H embedded in the bulk of a Ni metal catalyst are described. Specifically, a transient H atom emerging from the bulk onto the surface is observed to be the reactive species in hydrogenation of ethylene and acetylene adsorbed on Ni to form ethane and ethylene, respectively. A H atom adsorbed on the Ni surface does not hydrogenate ethylene or acetylene. These results demonstrate that bulk H is not solely a source of surface bound H in catalytic hydrogenation as proposed 50 years ago, but rather, a reactant with a chemistry of its own. XeF2 etches Si at a 103-104 times faster rate than that of F2. The remarkable reactivity of XeF2 was discovered 30 years ago, with no understanding of the physical basis for its high reactivity over that of F2. A molecular beam-ultrahigh vacuum surface scattering approach has shown that the origin of the high reactivity arises from significant vibrational excitation of the Si(100) lattice upon initial collision of the massive XeF2, prior to abstraction of the first F atom by Si. This study is the first example of collisional energy transfer to a surface playing a critical role in the probability of a molecule-surface reaction.

Bio: Sylvia T. Ceyer completed her Ph.D. from the University of California at Berkeley, investigating Molecular Beam Photoionization and Gas-Surface Scattering under the advisement of Professors Y. T. Lee and G. A. Somorjai in 1979 after receiving her B.A. from Hope College in Holland, Michigan. Following her graduate work, she received a two-year post-doctoral fellowship at NIST in Gaithersburg, MD. From there, she accepted an assistant professorship in the Chemistry Department at MIT, and in 1987 earned a full professorship. She is currently the J. C. Sheehan Professor of Chemistry and the Head of the Department of Chemistry at MIT.

March 28, 2014, 10:40, UC G030 Cinema Hall