Structure sensitivity in acetylene reactions over bimetallic Pd/W surfaces

Acetylene reactions over a Pd/W(111)surface are found to exhibit size effec ts on the nanometer scale. Upon annealing 1 ML Pd/W(111). pyramidal facets are formed having bcc(111) faces with nanometer dimensions. The facets grow as a function of annealing time and temperature. Temperature-programmed de sorption (TPD) spectra of benzene and ethylene, formed reactively following acetylene adsorption, change as a function of relative facet size. Results are compared to spectra from a similar experiment performed on planar Pd/W (211). TPD of chemisorbed benzene from several different Pd/W surface morph ologies are also presented. The data show that structure sensitivity is exh ibited for reactively-formed ethylene and benzene, as well as for chemisorb ed benzene.