AVS 50th International Symposium
    Surface Science Tuesday Sessions
       Session SS1-TuM

Paper SS1-TuM1
Adsorption Energies of Small Alkane Molecules on MgO(100) and on Pd Nanoparticles on MgO by Temperature Programmed Desorption

Tuesday, November 4, 2003, 8:20 am, Room 327

Session: Catalysis II: Hydrocarbons at Metal Surfaces
Presenter: S.L. Tait, Jr., University of Washington
Authors: S.L. Tait, Jr., University of Washington
Z. Dohnalek, Pacific Northwest National Laboratory
B.D. Kay, Pacific Northwest National Laboratory
C.T. Campbell, University of Washington
Correspondent: Click to Email
Catalysts consisting of Pd nanoparticles supported on oxides are active in a variety of important reactions involving small alkanes. Molecular beams and temperature programmed desorption (TPD) were used to study the adsorption of small alkane molecules, C@sub n@H@sub 2n+2@ (n=1-10), on the MgO(100) surface and on Pd nanoparticles on MgO(100) at low temperatures (24 K), a regime little explored for such well-defined model catalysts. High quality MgO films are grown on the Mo(100) surface, producing an MgO(100) surface with defect densities comparable to those obtained by UHV-cleavage of MgO crystals. Hydrocarbon molecules are deposited on the surface by a highly collimated molecular beam with a well-defined kinetic energy. King and Wells style sticking measurements are made by quadrupole mass spectrometer (QMS) during deposition. The initial sticking probability increases with alkane chain length until it reaches unity for octane (n=8). The sample is heated at a controlled rate and desorption products are observed by line-of-sight QMS. The adsorption energies and kinetic prefactors for desorption are extracted from these TPD data. Adsorption energy increases non-linearly with alkane chain length. The alkanes bind more strongly to Pd particles than to MgO(100). We plan to present preliminary results also concerning Pd particle size effects in alkane adsorption and dissociation. Pacific Northwest National Laboratory is a multiprogram National Laboratory operated for the U.S. Department of Energy by Battelle Memorial Institute under contract DE-AC06-76RLO 1830. SLT supported by a UW/PNNL Joint Institute for Nanotechnology fellowship.