Physisorption of N2, O2, and CO on Fully Oxidized TiO2(110)
Physisorption of N2, O2 and CO was studied on fully oxidized TiO2(110) using beam reflection and temperature programmed desorption (TPD) techniques. Sticking coefficients for all three molecules are nearly equal (0.75 ± 0.05) and approximately independent of coverage suggesting that adsorption occurs via a precursor mediated mechanism. Excluding multilayer coverages, the TPD spectra for all three adsorbates exhibit three distinct coverage regimes that can be interpreted in accord with previous theoretical studies of N2 adsorption. At low coverages (0 to 0.5 N2/Ti4+), N2 molecules bind head-on to five-coordinated Ti4+ ions. The adsorption occurs preferentially on the Ti4+ sites that do not have neighboring adsorbates. This arrangement minimizes the repulsive interactions between the adsorbed molecules along the Ti4+ rows resulting in a relatively small shift of the TPD peak (105 → 90 K) with increasing coverage. At higher N2 coverages (0 to 1.0 N2/Ti4+) the nearest-neighbor Ti4+ sites become occupied. The close proximity of the adsorbates results in strong repulsion thus giving rise to a significant shift of the TPD leading edges (90 → 45 K) with increasing coverage. For N2/Ti4+ > 1, an additional low temperature peak (~ 43 K) is present and is ascribed to N2 adsorption on bridge-bonded oxygen rows. The results for O2 and CO are qualitatively similar. The repulsive adsorbate-adsorbate interactions largest for CO, most likely due to aligned CO dipole moments. The coverage dependent binding energies of O2, N2, and CO are determined by inverting TPD profiles.
- Research Organization:
- Pacific Northwest National Lab. (PNNL), Richland, WA (United States). Environmental Molecular Sciences Lab. (EMSL)
- Sponsoring Organization:
- USDOE
- DOE Contract Number:
- AC05-76RL01830
- OSTI ID:
- 882962
- Report Number(s):
- PNNL-SA-47092; 7192; 8195; KC0301020; TRN: US200702%%778
- Journal Information:
- Journal of Physical Chemistry B, 110(12):6229-6235, Journal Name: Journal of Physical Chemistry B, 110(12):6229-6235
- Country of Publication:
- United States
- Language:
- English
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