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Hydrogenation of CO on Alumina Supported Metals: A Tunneling Spectroscopy Study.

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The hydrogenation of CO on alumina supported metals has been the subject of many research efforts. This report is about the application of a relatively new technique, tunneling spectroscopy, to the problem of identifying the reaction intermediates that are formed on the catalyst surface. Tunneling spectroscopy is a vibrational spectroscopy that presents information about the system being studied in much the same way as do infrared and raman spectroscopy. The selection rules of tunneling are very weak the spectrum observed consists of both the infrared and raman allowed vibrations. This similarity between techniques invites comparison of the results obtained in this work with those of previous infrared studies, such as those done by G. Blyholder, et al. 1, and R. A. Dalla Betta, et al. 2. From such comparisons it is possible to say that all three techniques find the observation of submonolayers of hydrocarbons to be technically demanding. No experimental method is yet available that allows the complete determination of all reaction pathways on a catalyst surface. As a first step toward this ultimate goal we report the observation of the hydrogenation of CO chemisorbed on alumina-supported metal particles with tunneling spectroscopy. Inelastic Electron Tunneling Spectroscopy IETS measures the energies, and thus the frequencies, of the normal modes of vibration of molecules that are incorporated in order near the insulator of a metal-insulator-metal tunnel junction. In this work all junctions are made with an aluminum-aluminum oxide-dopant-lead structure, where the dopant consists of small metal particles with 10-40 Angstrom diameters that are exposed to CO and hydrogen. Author

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  • Atomic and Molecular Physics and Spectroscopy

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