AVS 62nd International Symposium & Exhibition
    Surface Science Wednesday Sessions
       Session SS+AS-WeA

Paper SS+AS-WeA11
Eley-Rideal Typed Mechanism of Formate Synthesis by Hydrogenation of Carbon Dioxide on Cu Surfaces

Wednesday, October 21, 2015, 5:40 pm, Room 112

Session: Surface Dynamics, Non-Adiabaticity, and Single Molecule Phenomena
Presenter: Junji Nakamura, Univerisity of Tsukuba and ACT-C, Japan
Authors: J. Quan, University of Tsukuba, Japan
T. Ogawa, Universityy of Tsukuba, Japan
T. Kondo, University of Tsukuba, Japan
G. Wang, Nankai University, China
J. Nakamura, Univerisity of Tsukuba and ACT-C, Japan
Correspondent: Click to Email
Methanol synthesis by hydrogenation of CO2 using Cu catalysts is one of the promising reactions to convert CO2 into useful chemicals. Formate species is the pivotal intermediates formed as the initial step of CO2 hydrogenation (CO2 ＋ Ha → HCOOa). The reaction rate of formate synthesis is very low and the reaction probabilities are about 10-12 at 340K. Our previous kinetic measurements have suggested that formate is synthesized via Eley-Rideal typed mechanism, in which CO2 molecules directly attack adsorbed hydrogen atoms on Cu surfaces. The structure insensitivity observed for formate synthesis experiments on Cu(111), Cu(100), and Cu(110) were well explained by the Eley -Rideal mechanism based on DFT calculations. In addition, sharp angular desorptions of CO2 have been observed for formate decomposition as the reverse reaction of formate synthesis, indicating thermal non- equilibrium reaction. In the present study, we performed molecular beam experiments to prove the Eley-Rideal typed mechanism, in which CO2 molecules with controlling vibrational and translational energies were reacted with adsorbed hydrogen on cold Cu(111) and Cu(110) surfaces (TS =150-215 K). We confirmed the formation of formate species on Cu(111) and Cu(110) with reaction probabilities of 10-5 by heating nozzle above 1000 K, while no formate is formed at nozzle temperatures below 1000 K. The results indicate the Eley-Rideal typed mechanism with thermal non-equilibrium character. DFT calculations also reproduce the Eley-Rideal typed mechanism, in which vibrational excitations of CO2 are required to overcome the barrier of formate synthesis.