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Title: Adsorption and Photodesorption of CO from Charged Point Defects on TiO 2 (110)

Abstract

Adsorption and photodesorption of weakly-bound carbon monoxide, CO, from reduced and hydroxylated rutile TiO2(110) (r- and h- TiO2(110)) at sub-monolayer coverages is studied with atomically-resolved scanning tunneling microscopy (STM) along with ensemble-averaged temperature-programmed desorption (TPD) and angle-resolved photon-stimulated desorption (PSD) at low temperatures ( 50 K). STM data weighted by the concentration of each kind of adsorption sites on r-TiO2(110) give an adsorption probability which is the highest for the bridging oxygen vacancies (VO) and very low for the Ti5c sites closest to VO. Occupancy of the remaining Ti5c sites with CO is significant, but smaller than for VO. The probability distribution for the different adsorption sites corresponds to a very small difference in CO adsorption energies: < 0.02 eV. We also find that UV irradiation stimulates both diffusion and desorption of CO at low temperature. CO photodesorbs primarily from the vacancies with a bi-modal angular distribution. In addition to a major, normal to the surface component, there is a broader cosine component indicating scattering from the surface which likely also leads to photo-stimulated diffusion. Hydroxylation of VO’s does not significantly change the CO PSD yield and angular distribution, indicating that not atomic but rather electronic surface defects are involvedmore » in the site-specific PSD process. We suggest that photodesorption can be initiated by recombination of photo-generated holes with excess unpaired electrons localized near the surface point-defect (either VO or bridging hydroxyl), leading to the surface atoms rearrangement and ejection of the weakly-bound CO molecules.« less

Authors:
 [1];  [2];  [2]; ORCiD logo [3];  [4]; ORCiD logo [4];  [4]
  1. Physical and Computational Sciences Directorate and Institute for Integrated Catalysis, Pacific Northwest National Laboratory, Richland, Washington 99352, United States; Key Laboratory for Green Chemical Technology of Ministry of Education, School of Chemical Engineering and Technology, Tianjin University, Collaborative Innovation Center of Chemical Science and Engineering, Tianjin 300072, China
  2. Environmental Molecular Sciences Laboratory and Institute for Integrated Catalysis, Pacific Northwest National Laboratory, Richland, Washington 99352, United States
  3. Physical and Computational Sciences Directorate and Institute for Integrated Catalysis, Pacific Northwest National Laboratory, Richland, Washington 99352, United States; Voiland School of Chemical Engineering and Bioengineering, Washington State University, Pullman, Washington 99163, United States
  4. Physical and Computational Sciences Directorate and Institute for Integrated Catalysis, Pacific Northwest National Laboratory, Richland, Washington 99352, United States
Publication Date:
Research Org.:
Pacific Northwest National Laboratory (PNNL), Richland, WA (US), Environmental Molecular Sciences Laboratory (EMSL)
Sponsoring Org.:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22)
OSTI Identifier:
1406732
Report Number(s):
PNNL-SA-128233
Journal ID: ISSN 1948-7185; 49144; KC0301050
DOE Contract Number:
AC05-76RL01830
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Physical Chemistry Letters; Journal Volume: 8; Journal Issue: 18
Country of Publication:
United States
Language:
English
Subject:
Environmental Molecular Sciences Laboratory

Citation Formats

Mu, Rentao, Dahal, Arjun, Wang, Zhi-Tao, Dohnálek, Zdenek, Kimmel, Greg A., Petrik, Nikolay G., and Lyubinetsky, Igor. Adsorption and Photodesorption of CO from Charged Point Defects on TiO 2 (110). United States: N. p., 2017. Web. doi:10.1021/acs.jpclett.7b02052.
Mu, Rentao, Dahal, Arjun, Wang, Zhi-Tao, Dohnálek, Zdenek, Kimmel, Greg A., Petrik, Nikolay G., & Lyubinetsky, Igor. Adsorption and Photodesorption of CO from Charged Point Defects on TiO 2 (110). United States. doi:10.1021/acs.jpclett.7b02052.
Mu, Rentao, Dahal, Arjun, Wang, Zhi-Tao, Dohnálek, Zdenek, Kimmel, Greg A., Petrik, Nikolay G., and Lyubinetsky, Igor. 2017. "Adsorption and Photodesorption of CO from Charged Point Defects on TiO 2 (110)". United States. doi:10.1021/acs.jpclett.7b02052.
@article{osti_1406732,
title = {Adsorption and Photodesorption of CO from Charged Point Defects on TiO 2 (110)},
author = {Mu, Rentao and Dahal, Arjun and Wang, Zhi-Tao and Dohnálek, Zdenek and Kimmel, Greg A. and Petrik, Nikolay G. and Lyubinetsky, Igor},
abstractNote = {Adsorption and photodesorption of weakly-bound carbon monoxide, CO, from reduced and hydroxylated rutile TiO2(110) (r- and h- TiO2(110)) at sub-monolayer coverages is studied with atomically-resolved scanning tunneling microscopy (STM) along with ensemble-averaged temperature-programmed desorption (TPD) and angle-resolved photon-stimulated desorption (PSD) at low temperatures ( 50 K). STM data weighted by the concentration of each kind of adsorption sites on r-TiO2(110) give an adsorption probability which is the highest for the bridging oxygen vacancies (VO) and very low for the Ti5c sites closest to VO. Occupancy of the remaining Ti5c sites with CO is significant, but smaller than for VO. The probability distribution for the different adsorption sites corresponds to a very small difference in CO adsorption energies: < 0.02 eV. We also find that UV irradiation stimulates both diffusion and desorption of CO at low temperature. CO photodesorbs primarily from the vacancies with a bi-modal angular distribution. In addition to a major, normal to the surface component, there is a broader cosine component indicating scattering from the surface which likely also leads to photo-stimulated diffusion. Hydroxylation of VO’s does not significantly change the CO PSD yield and angular distribution, indicating that not atomic but rather electronic surface defects are involved in the site-specific PSD process. We suggest that photodesorption can be initiated by recombination of photo-generated holes with excess unpaired electrons localized near the surface point-defect (either VO or bridging hydroxyl), leading to the surface atoms rearrangement and ejection of the weakly-bound CO molecules.},
doi = {10.1021/acs.jpclett.7b02052},
journal = {Journal of Physical Chemistry Letters},
number = 18,
volume = 8,
place = {United States},
year = 2017,
month = 9
}
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