AVS 45th International Symposium
    Surface Science Division Monday Sessions
       Session SS-MoP

Paper SS-MoP13
The Kinetics of Methanol Synthesis by Hydrogenation of CO@sub 2@ Over a Zn-deposited Cu(111) Surface

Monday, November 2, 1998, 5:30 pm, Room Hall A

Session: Surface Science Division Poster Session
Presenter: I. Nakamura, University of Tsukuba, Japan
Authors: I. Nakamura, University of Tsukuba, Japan
H Nakano, University of Tsukuba, Japan
T. Fujitani, National Institute for Resources and Environment, Japan
T. Uchijima, University of Tsukuba, Japan
J. Nakamura, University of Tsukuba, Japan
Correspondent: Click to Email
We have found that Zn deposited on a Cu(111) surface promotes methanol synthesis by the hydrogenation of CO@sub 2@. In this study, we examined the kinetics of methanol synthesis over the Zn-deposited Cu(111) surface by measuring the rates of elementary steps such as formation, decomposition and hydrogenation of formate species to clarify the promotional effect of Zn. The experiments were carried out in an infrared reflection absorption spectroscopy (IRAS) apparatus with a closed-reactor. The formate synthesis was performed using a gas mixture of CO@sub 2@/H@sub 2@=1 at a total pressure of 760 Torr and reaction temperatures of 323-353 K. The formate decomposition was carried out at a constant temperature of 373-403 K under vacuum. The initial formation rate of formate species on a clean Cu(111) surface was obtained by the initial slope of the formate coverage estimated from the peak intensity of the symmetric OCO stretching bands of formate species versus exposure to the CO@sub 2@/H@sub 2@ gas mixture. For example, at 353 K the initial formation rate was estimated to be 8.2 x 10@super -4@ formate molecules/site/sec, which agreed with that measured by the previous XPS experiment under the same reaction conditions. From the arrhenius plot of the initial formation rates, the activation energy for the formate synthesis on the clean Cu(111) surface was found to be 56.7 kJ/mol. The rates of formate decomposition was found to be first-order for the formate coverage and the activation energy was 100.7 kJ/mol. Furthermore, the equilibrium coverage of formate species was calculated by the kinetic data of formation and decomposition, which was in good agreement with experimentally measured coverage.