AVS 64th International Symposium & Exhibition
    Fundamental Discoveries in Heterogeneous Catalysis Focus Topic Tuesday Sessions
       Session HC+SS-TuA

Paper HC+SS-TuA3
CO2 Dynamics as a Product of Formate Decomposition on Cu(111)

Tuesday, October 31, 2017, 3:00 pm, Room 25

Session: Advances in Theoretical Models and Simulations of Heterogeneously Catalyzed Reactions
Presenter: Fahdzi Muttaqien, Osaka University, Japan
Authors: F. Muttaqien, Osaka University, Japan
H. Oshima, Osaka University, Japan
Y. Hamamoto, Osaka University, Japan
K. Inagaki, Osaka University, Japan
I. Hamada, Osaka University, Japan
Y. Morikawa, Osaka University, Japan
Correspondent: Click to Email

Formate (HCOO) synthesis has been experimentally clarified to occur by the Eley-Rideal (ER) mechanism,1 which suggests that the reaction rate depends on the initial energy of impinging CO2. Since HCOO synthesis and decomposition are reversible reactions, the energy of impinging CO2 must be related to the energy states of desorbed CO2 from formate decomposition. Therefore, elucidation of HCOO decomposition dynamics is important to deduce optimal conditions for catalytic HCOO synthesis.

We performed ab initio molecular dynamics analysis to elucidate the dynamics of CO2 from HCOO decomposition on Cu(111). We first investigated the translational energy of desorbed CO2 from the velocity of center of mass of CO2. The calculated translational energy (shown in Fig. 1 of Supp. Info) using PBE, PBE-D2, vdW-DF1, rev-vdW-DF2, and optB86b-vdW are 0.30 eV, 0.05 eV, 0.18 eV, 0.16 eV, and 0.11 eV, respectively. Those calculated CO2 translational energy using PBE-D2 and vdW-DFs are in reasonable agreement with the experimental estimation (0.10 eV),2 while PBE fails in predicting this energy.

We then explored the rotational and vibrational energies of CO2 from HCOO decomposition. The rotational energy of CO2 was calculated from its moment of inertia and angular momentum. We obtained that calculated CO2 rotational energy varies between 0.08−0.11 eV. The CO2 vibrational energies are evaluated based on the time evolution of the bond angle, C−O bond length, and difference between two C−O bond lengths of desorbed CO2 (shown in Fig. 2 of Supp. Info). The vibrational energy of bending, symmetric stretching, and antisymmetric stretching modes are 0.25 eV, 0.11 eV, and 0.0015 eV, respectively. The vibrational energy of desorbed CO2 bending mode is close to the third excitation energy of the vibrational energy of bending of isolated CO2.

In summary, the vibrational energy of desorbed CO2 bending mode is twice larger than the translational energy. Since HCOO synthesis from CO2 and H2, reverse reaction of the HCOO decomposition, is experimentally suggested to occur by the ER mechanism, our results indicate that the reaction rate of formate synthesis can be enhanced if the bending vibrational mode of CO2 is excited rather than the translational, rotational, and/or stretching modes. These results are in contrast to the case of CO2 dissociation, in which the CO2 symmetric and antisymmetric stretching modes are more important to increase the dissociation rate.3,4

References:

  1. H. Nakano et. al., J. Phys. Chem. B105, 1355 (2001).
  2. J. Quan et. al., Angew. Chem. Int. Ed. 56, 3496 (2017).
  3. T. Yamanaka, Phys. Chem. Chem. Phys.10, 5429 (2008).
  4. B. Jiang and H. Guo, J. Chem. Phys.144, 091101 (2016).