AVS 59th Annual International Symposium and Exhibition
    Surface Science Tuesday Sessions
       Session SS-TuM

Paper SS-TuM6
Infrared Spectroscopy of CO2 Adsorbed on TiO2(110)

Tuesday, October 30, 2012, 9:40 am, Room 21

Session: Surface Reactivity of Oxides
Presenter: N.G. Petrik, Pacific Northwest National Laboratory
Authors: N.G. Petrik, Pacific Northwest National Laboratory
G.A. Kimmel, Pacific Northwest National Laboratory
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We have studied the adsorption of CO2 on TiO2(110) using reflection-absorption infrared spectroscopy (RAIRS) and temperature programmed desorption (TPD). Infrared spectra were obtained for s- and p-polarized light with the plane of incidence parallel and perpendicular to the [001] azimuth of TiO2(110). As a result, the RAIRS provide detailed information on the adsorption geometry for the CO2 versus coverage. Initially, CO2 adsorbs in vacancies in the bridge-bonded oxygen (BBO) rows with the peak for the asymmetric stretch seen at 2346.5 cm-1 for both s- and p-polarized light. Hydroxylation or oxidation of the vacancies suppresses this feature. After filling the vacancies, CO2 adsorbs on Ti5c sites (CO2(Ti)). The asymmetric stretch for CO2(Ti) starts at ~2342 cm-1 and then red-shifts to 2332 cm-1 at 1 ML. CO2 TPD spectra show that the shift in the RAIRS spectra correlates with a decrease in the CO2 binding energy from ~47 to ~34 kJ/mol as the coverage increases from 0 to 1 ML. For CO2(Ti), the absorbances for the s-polarized spectra are similar for both azimuths indicating that the ensemble-average of the adsorbed CO2 has approximately equal components along both azimuths. The p-polarized RAIRS spectra show that CO2(Ti) also adsorbs with a component normal to the surface. Between 1 and 1.5 ML, CO2 adsorbs on BBO sites. These CO2 absorb only s-polarized light with its plane of incidence parallel to the BBO rows indicating that the molecules are oriented parallel to the surface and perpendicular to the BBO rows. The CO2 RAIRS spectra are compared with STM results and DFT theory to provide detailed insight into its molecular orientation and coverage-dependent mobility.