The methanol synthesis by hydrogenation of CO₂ attracts a great deal of attention because this process can realize the direct conversion of CO₂ into a useful chemical feedstock. In a present industrial process using Cu/ZnO- based catalyst, however, the reaction requires high pressure (50-100 bar) and high temperature (200-300°C). If this reaction proceeds at a mild reaction condition, it would be a very attractive process to convert CO₂. But the detailed process of the reaction is not well understood. We focus on the formate synthesis on Cu surfaces, which is the first step of the methanol synthesis reaction. Our previous studies suggest that this process proceeds by the translational and vibrational energy of CO₂ molecules. The kinetic analysis of formate synthesis suggests that the mechanism of the reaction can be an Eley-Rideal type, in which gaseous CO₂ directly reacts with hydrogen atoms on Cu surfaces [1]. DFT calculation also suggests that the activation barrier can be overcome by supplying energy to CO₂ molecules [2]. In this work, we conduct formate synthesis with transnationally and vibrationally hot CO₂ molecules to prove the mechanism of formate synthesis on Cu surfaces.

The translational and vibrational energy of CO₂ molecules is controlled by the supersonic molecular beam technic. Firstly hydrogen atoms are pre-adsorbed on Cu single crystal with hot tungsten filament. Then CO₂ molecular beam is irradiated to H/Cu surface. The relation between the energy of incident CO₂ molecules and the formation of formate are investigated using temperature programmed desorption and infrared reflection absorption spectroscopy.

[1] H. Nakano, I. Nakamura, T. Fujitani, and J. Nakamura, J. Phys. Chem. B 2001, 105, 1355

[2] G. Wang, Y. Morikawa, T. Matsumoto, and J. Nakamura, J. Phys. Chem. B 2006, 110, 9