AVS 46th International Symposium
    Surface Science Division Tuesday Sessions
       Session SS2-TuM

Paper SS2-TuM1
The Microscopic Mechanism of Methanol Synthesis over the Zn-promoted Cu(111)

Tuesday, October 26, 1999, 8:20 am, Room 607

Session: Model Catalysts
Presenter: J. Nakamura, University of Tsukuba, Japan
Authors: J. Nakamura, University of Tsukuba, Japan
I. Nakamura, National Institute for Resources and Environment, Japan
H. Nishimura, University of Tsukuba, Japan
H. Nakano, University of Tsukuba, Japan
M. Sano, University of Tsukuba, Japan
T. Fujitani, National Institute for Resources and Environment, Japan
Correspondent: Click to Email
We had reported that the Zn-deposited Cu(111) could be regarded as a model of Cu/ZnO catalysts in terms of the turnover frequency of methanol formation and the activation energy. After establishing the catalyst model, we had further tried to look into the detailed mechanism on the promotional role of the Zn as well as the microkinetics using in-situ IRAS, XPS and STM apparatuses connected to a high pressure reactor. Very reactive formate species adsorbed in an inclined bidentate state was detected by IRAS, which was found to be responsible for the promotional effect of the Zn. Also the microkinetic picture was established for formate synthesis and formate decomposition. Interesting relationships between the ordered structure of formate observed by STM and the kinetics of decomposition were shown. That is, various ordered structures of formate intermediates synthesized from CO@sub 2@ and H@sub 2@ at 1 atm were very different from the structure of formate prepared by adsorption of formic acid, which cause a difference in the pre-exponential factor of the rate constant for the formate decomposition. This was explained by that a nearest neighbor formate species interfered with the OCO plane vibration of formate, which is probably necessary to overcome the transition state of the decomposition. The STM images of the Zn-deposited Cu(111) showed that Zn atoms were substituted for Cu atoms, leading to a Cu-Zn surface alloy. Upon the deposition of Zn, the alloying started at the step edges of the Cu(111) surface, and then the Zn atoms migrated toward the terrace. The migration rate was measured by time-resolved STM.