Photoelectron study of the interaction of carbon monoxide with zinc oxide
| Autor: | Robert R. Gay, Mark H. Nodine, Victor E. Henrich, H. J. Zeiger, Edward I. Solomon |
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| Rok vydání: | 1980 |
| Předmět: |
Chemistry
chemistry.chemical_element General Chemistry Zinc Biochemistry Electron spectroscopy Catalysis chemistry.chemical_compound Colloid and Surface Chemistry Adsorption X-ray photoelectron spectroscopy Chemisorption Physical chemistry Molecular orbital Ultraviolet photoelectron spectroscopy Carbon monoxide |
| Zdroj: | Journal of the American Chemical Society. 102:6752-6761 |
| ISSN: | 1520-5126 0002-7863 |
| DOI: | 10.1021/ja00542a014 |
| Popis: | Ultraviolet photoelectron spectroscopy (UPS) has been used to study the chemisorption of CO on four low-index surfaces of ZnO, an active methanol catalyst. These surfaces have significant differences with respect to their coordination unsaturation; thus, a correlation between the adsorption behavior and the surface structure enables the geometric requirements for chemisorption to be determined. The He II photoelectron peak associated with the 4 sigma molecular orbital of the CO molecule serves as a probe of the amount of adsorbed CO. The adsorption is found to be reversible, and measurements of the equilibrium coverage as a function of temperature and pressure demonstrate that the bonding interactions are very similar on all four surfaces, with an initial heat of adsorption of 12.0 +- 0.4 kcal/mol, which decreases approximately linearly with coverage. Chemisorbed CO is readily displaced by NH/sub 3/, indicating the involvement of zinc ions in the bonding of CO to the surface. This is strongly supported by the relative CO coverage of the four surfaces under equivalent conditions, which generally correlates with the availability of unsaturated zinc sites. Angle-resolved measurements of the 4 sigma intensity are used to confirm this binding mode. The bonding of CO to ZnO is cominated bymore » the sigma donor interaction of the carbon end of the molecule with the zinc ion as determined from the observed decrease in the splitting of the energies of the 4 sigma and 5 sigma molecular orbitals. The lack of significant ..pi.. back-bonding is supported by the increase of the dipole moment of the coordinated CO molecule to approximately 0.6 D as determined from He I photoelectron work function measurements. This mode of binding of CO is consistent with the observed increase in the CO stretching frequency relative to the gas-phase value and suggests possible relevance to catalysis.« less |
| Databáze: | OpenAIRE |
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