| AVS 59th Annual International Symposium and Exhibition | |
| Surface Science | Thursday Sessions |
| Session SS+EN+OX-ThM |
| Session: | Catalysis and Photocatalysis on Oxides |
| Presenter: | X. Lin, Pacific Northwest National Laboratory |
| Authors: | X. Lin, Pacific Northwest National Laboratory Y. Yoon, Pacific Northwest National Laboratory N.G. Petrik, Pacific Northwest National Laboratory G.A. Kimmel, Pacific Northwest National Laboratory Z. Li, Pacific Northwest National Laboratory Z.-T. Wang, Pacific Northwest National Laboratory B.D. Kay, Pacific Northwest National Laboratory I. Lyubinetsky, Pacific Northwest National Laboratory R. Rousseau, Pacific Northwest National Laboratory Z. Dohnalek, Pacific Northwest National Laboratory |
| Correspondent: | Click to Email |
Rutile TiO2(110) was employed as a model oxide surface to investigate the adsorption behavior of CO2 by means of scanning tunneling microscopy (STM) and density functional theory (DFT). STM images of partially reduced TiO2(110) surfaces obtained before and after in-situ dosing of CO2 molecules at 50 K show that CO2 adsorbs preferentially on oxygen vacancy (VO) sites. Since the reaction of CO2 with oxygen adatoms (surface hydroxyl groups) may lead to the formation of carbonate (bicarbonate), O2 (H2O) was predosed to form oxygen adatom (hydroxyl) covered TiO2 surfaces. On the oxygen precovered surfaces, CO2 molecules were found to preferentially bind on the Ti sites next to oxygen adatoms (Oa’s) and form CO2/Oa complexes, while on hydroxylated surfaces no interactions were observed between CO2 and hydroxyl groups. CO2 binding to Oa’s is weak as revealed by the dissociation of the CO2/Oa complexes at 50 K where CO2 diffuses away along the Ti row. The weak binding indicates that CO2 is bound to Oa only via dispersion forces. Temperature dependent studies (100 - 150 K) show that the CO2 binding energy next to Oa’s is smaller by ~20 mV than that on VO’s. At 50 K, however, the adsorption of CO2 on VO is partially hindered by the higher adsorption barrier. CO2 molecules diffusing between two CO2/Oa complexes are found to move fast compared to the STM sampling rate and are imaged as a time average of all CO2 binding configurations on Ti sites. DFT studies reveal the rotation-tumbling mechanism for CO2 diffusion with a very low diffusion barrier (~ 50 meV) in agreement with the experiment.
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X.L. is grateful for the support of the Linus Pauling Distinguished Postdoctoral Fellowship Program at PNNL. This work was supported by the US Department of Energy, Office of Basic Energy Sciences, Division of Chemical Sciences, Geosciences & Biosciences. A portion of the research was performed using EMSL, a national scientific user facility sponsored by the Department of Energy's Office of Biological and Environmental Research and located at Pacific Northwest National Laboratory (PN NL). PNNL is a multiprogram national laboratory operated for DOE by Battelle.