AVS 52nd International Symposium
    Surface Science Wednesday Sessions
       Session SS2-WeM

Paper SS2-WeM11
Structure-Activity Relationship: The Case of CO and CO@sub 2@ Adsorption on ZnO(0001), H/ZnO(0001), Cu/ZnO(0001)

Wednesday, November 2, 2005, 11:40 am, Room 203

Session: Reactions on Metals & Oxides
Presenter: U. Burghaus, North Dakota State University
Authors: J. Wang, North Dakota State University
S. Funk, North Dakota State University
B. Hokkanen, North Dakota State University
E. Johnson, North Dakota State University
U. Burghaus, North Dakota State University
Correspondent: Click to Email
Molecular beam scattering techniques were combined with thermal desorption spectroscopy (TDS) and applied to a number of different Zn-terminated ZnO systems; namely, clean ZnO(0001), defected ZnO(0001), H precovered ZnO(0001), and Cu precovered ZnO(0001). Furthermore, CO and CO@sub 2@ have been used as probe molecules with the goal to address the Structure-Activity Relationship (SAR). The CO@sub 2@-TDS curves consist of two distinct structures. By modifying the surface with Ar+ ion sputtering (more defects) and H-preadsorption (fewer defects), the two TDS structures could be assigned to adsorption of CO@sub 2@ on pristine and intrinsic defect sites with binding energies of 34.4 kJ/mol and 43.6 kJ/mol, respectively. Furthermore, He atom reflectivity curves indicated adsorption of CO@sub 2@ on defects. Thus, a kinetic SAR is evident. (See, Chemical Physics Letters 403 (2005) 42). Furthermore, a dynamic SAR was present in CO adsorption on the Cu/ZnO(0001) model catalyst. Whereas on small Cu sized-deposits, direct Langmuirian adsorption dynamics were observed; larger cluster sizes lead to the detection of precursor mediated adsorption dynamics of CO. Thus, the energy transfer processes governing the adsorption of a gas phase species on the surface depended distinctly on the morphology of the metal-on-metal oxide system. In the case of CO@sub 2@-Cu/ZnO(0001) a strong metal support interaction was observed; TDS and beam scattering data provide consistent hints that CO@sub 2@ populates predominantly along the rim of the Cu clusters. Monte Carlo Simulations have been applied for modeling of the molecular beam scattering data.