Surface spectroscopic studies of mono- and bimetallic model catalysts

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Title: Surface spectroscopic studies of mono- and bimetallic model catalysts
Author: Yi, Cheol-Woo
Abstract: This dissertation is focused on understanding heterogeneous bimetallic catalysts using model catalyst systems , such as Pd -Au /Mo (110 ) , Pd /Au (111 ) and Pd /Au (100 ) . Monometallic and bimetallic model catalysts , composed of Pd and Au , were prepared by physical vapor deposition (PVD ) onto well -characterized metal substrates . Subsequent characterization was performed using an arsenal of modern surface science tools : low energy ion scattering spectroscopy (LEISS ) , infrared absorption spectroscopy (IRAS ) , temperature programmed desorption (TPD ) , and x -ray photoelectron spectroscopy (XPS ) . Electronic , morphological , and chemical properties of the prepared model catalysts were compared to those observed from monometallic single -crystal model catalysts such as Cu (100 ) , Pd (111 ) , Au (100 ) , and Au (111 ) . Between 700 K and 1000 K , formation of stable alloy surfaces of Pd -Au mixtures on Mo (110 ) was accompanied by substantial enrichment in Au . Annealing a 1 :1 Pd -Au mixture at 800 K yields a Pd0 .2Au0 .8 surface alloy ; the concentration of isolated Pd sites in this surface alloy can be systematically controlled by a judicious selection of initial bulk Pd -Au concentration . Pd -Au catalysts supported on Au (111 ) and Au (100 ) substrates generated a surface ensemble of Pd monomers surrounded by Au after annealing the systems at or above 550 K . To test the activity and selectivity of the prepared bimetallic model catalysts , the formation rate of vinyl acetate monomer (VAM ) was examined . More significant enhancement of VAM formation rate was observed for bimetallic catalysts supported on Au (100 ) compared to those on Au (111 ) . A critical surface ensemble composed two non -contiguous Pd monomers was proposed for the VAM synthesis . Oxygen plays a critical role in the efficiency of the synthetic route . Structure -reactivity correlations were established based on the suggested elementary reactions leading to the oxidative coupling of ethylene and acetic acid to form VAM .
URI: http : / /hdl .handle .net /1969 .1 /4787
Date: 2007-04-25

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Surface spectroscopic studies of mono- and bimetallic model catalysts. Available electronically from http : / /hdl .handle .net /1969 .1 /4787 .

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