AVS 52nd International Symposium
    Surface Science Thursday Sessions
       Session SS2-ThA

Paper SS2-ThA1
Why is Formate Synthesis Insensitive to Copper Surface Structures?

Thursday, November 3, 2005, 2:00 pm, Room 203

Session: Gas-Surface Reaction Dynamics
Presenter: J. Nakamura, University of Tsukuba, Japan
Authors: J. Nakamura, University of Tsukuba, Japan
Y. Morikawa, Osaka University, Japan
G. Wang, Nankai University, China
Correspondent: Click to Email
Unique structure sensitivity has been experimentally observed for the formate synthesis from CO@sub2@ and H@sub2@ (CO@sub2@ + 1/2 H@sub2@ ---> HCOOa) on copper surfaces and the reverse reaction of formate decomposition. That is, the reaction rate of formate synthesis and the activation energy are very similar among Cu(110), Cu(100), and Cu(111), meaning a structure insensitive reaction. On the other hand, the reverse reaction of formate decomposition on copper was a structure sensitive reaction with different activation energies. Also, an Eley-Rideal (E-R) type reaction mechanism has been suggested for the formate synthesis, in which CO@sub2@ molecule directly reacts with adsorbed hydrogen without passing through adsorption of CO@sub2@. Here, we report the results of ab initio density functional theory (DFT) calculation for the formate synthesis. The DFT-GGA calculation has reproduced adsorption energies and adsorption structure of bidentate formate experimentally measured on Cu(111), Cu(100), and Cu(110), which further reproduces the structure insensitive and structure sensitive features for formate synthesis and formate decomposition, respectively. The structure insensitivity is due to the presence of monodentate formate with similar adsorption energies on Cu(111), Cu(100), and Cu(110), giving a similar energetic pathway from CO@sub2,g@ + 1/2 H@sub2,g@ to monodentate formate. The structure sensitive feature for the decomposition of bidentate formate is due to a significant difference in the adsorption energy of bidentate formate depending on the Cu surface structure. The structure insensitivity is due to the E-R type reaction mechanism without passing through adsorption of CO@sub2@, which enables a similar reaction pathway with similar local structures as revealed in the snapshot for the structural change of intermediates.