Temperature-Dependent evolution of the molecular configuration of oxo-tungsten(VI) species deposited on the surface of titania

Antonios Tribalis, George D. Panagiotou, George Tsilomelekis, Angelos G. Kalampounias, Kyriakos Bourikas, Christos Kordulis, Soghomon Boghosian, Alexis Lycourghiotis

Research output: Contribution to journalArticle

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Abstract

The pH and temperature evolution of the molecular configuration of oxo-tungsten(VI) species deposited on TiO2 by equilibrium deposition filtration and the temperature evolution of the samples texture are studied using in situ Raman spectroscopy, DR spectroscopy, N2 adsorption-desorption measurements, and TGA. Prior to drying, WO 42- monomers retained above a bridging surface hydroxyl of TiO2 through H bonding (with a Ti 2OH···O-WO3 umbrella configuration) prevail at pH = 9. A pH decrease results in a gradual transformation to an inner sphere monosubstituted species located above terminal surface oxygen (Ti-O-WO3). At pH = 7 both species coexist, whereas at pH = 5 the latter prevails with electrostatically retained polyoxotungstes also present. Heating to 100 °C causes the same effect resulted by the pH decrease at room temperature, that is, transformation of Ti2OH·· ·O-WO3 into Ti-O-WO3, attributed to the removal of H2O molecules upon heating, thereby liberating surface Ti atoms. Progressive heating to higher temperatures causes further removal of surface hydroxyls (confirmed also by TGA) liberating more neighbor surface Ti atoms and favoring further anchoring. This leads to formation of bisubstituted dioxo (Ti-O)2-W(=O)2 sites in the range 120-250 °C and to the prevalence of trisubstituted mono-oxo (Ti-O)3-W=O sites at 430 °C. Polyoxotungstates are also detected in the sample with the highest W loading. The DRS spectra indicate a charge transfer effect between the surface O and Ti atoms proceeding via Ti-O-W surface bridges. Calcination of the support causes a decrease of the pore volume and pore area in the range of pores with small width and an increase in the range of pores with large width. This effect is not affected by the presence of the well dispersed "bi-dimensional" W species inferred by the Raman study.

Original languageEnglish (US)
Pages (from-to)11319-11332
Number of pages14
JournalJournal of Physical Chemistry C
Volume118
Issue number21
DOIs
StatePublished - May 29 2014

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Tungsten
tungsten
titanium
Titanium
configurations
porosity
Temperature
temperature
Heating
Hydroxyl Radical
Atoms
heating
causes
atoms
titanium dioxide
Calcination
roasting
drying
Raman spectroscopy
Charge transfer

All Science Journal Classification (ASJC) codes

  • Electronic, Optical and Magnetic Materials
  • Energy(all)
  • Physical and Theoretical Chemistry
  • Surfaces, Coatings and Films

Cite this

Tribalis, Antonios ; Panagiotou, George D. ; Tsilomelekis, George ; Kalampounias, Angelos G. ; Bourikas, Kyriakos ; Kordulis, Christos ; Boghosian, Soghomon ; Lycourghiotis, Alexis. / Temperature-Dependent evolution of the molecular configuration of oxo-tungsten(VI) species deposited on the surface of titania. In: Journal of Physical Chemistry C. 2014 ; Vol. 118, No. 21. pp. 11319-11332.
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abstract = "The pH and temperature evolution of the molecular configuration of oxo-tungsten(VI) species deposited on TiO2 by equilibrium deposition filtration and the temperature evolution of the samples texture are studied using in situ Raman spectroscopy, DR spectroscopy, N2 adsorption-desorption measurements, and TGA. Prior to drying, WO 42- monomers retained above a bridging surface hydroxyl of TiO2 through H bonding (with a Ti 2OH···O-WO3 umbrella configuration) prevail at pH = 9. A pH decrease results in a gradual transformation to an inner sphere monosubstituted species located above terminal surface oxygen (Ti-O-WO3). At pH = 7 both species coexist, whereas at pH = 5 the latter prevails with electrostatically retained polyoxotungstes also present. Heating to 100 °C causes the same effect resulted by the pH decrease at room temperature, that is, transformation of Ti2OH·· ·O-WO3 into Ti-O-WO3, attributed to the removal of H2O molecules upon heating, thereby liberating surface Ti atoms. Progressive heating to higher temperatures causes further removal of surface hydroxyls (confirmed also by TGA) liberating more neighbor surface Ti atoms and favoring further anchoring. This leads to formation of bisubstituted dioxo (Ti-O)2-W(=O)2 sites in the range 120-250 °C and to the prevalence of trisubstituted mono-oxo (Ti-O)3-W=O sites at 430 °C. Polyoxotungstates are also detected in the sample with the highest W loading. The DRS spectra indicate a charge transfer effect between the surface O and Ti atoms proceeding via Ti-O-W surface bridges. Calcination of the support causes a decrease of the pore volume and pore area in the range of pores with small width and an increase in the range of pores with large width. This effect is not affected by the presence of the well dispersed {"}bi-dimensional{"} W species inferred by the Raman study.",
author = "Antonios Tribalis and Panagiotou, {George D.} and George Tsilomelekis and Kalampounias, {Angelos G.} and Kyriakos Bourikas and Christos Kordulis and Soghomon Boghosian and Alexis Lycourghiotis",
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Tribalis, A, Panagiotou, GD, Tsilomelekis, G, Kalampounias, AG, Bourikas, K, Kordulis, C, Boghosian, S & Lycourghiotis, A 2014, 'Temperature-Dependent evolution of the molecular configuration of oxo-tungsten(VI) species deposited on the surface of titania', Journal of Physical Chemistry C, vol. 118, no. 21, pp. 11319-11332. https://doi.org/10.1021/jp500909x

Temperature-Dependent evolution of the molecular configuration of oxo-tungsten(VI) species deposited on the surface of titania. / Tribalis, Antonios; Panagiotou, George D.; Tsilomelekis, George; Kalampounias, Angelos G.; Bourikas, Kyriakos; Kordulis, Christos; Boghosian, Soghomon; Lycourghiotis, Alexis.

In: Journal of Physical Chemistry C, Vol. 118, No. 21, 29.05.2014, p. 11319-11332.

Research output: Contribution to journalArticle

TY - JOUR

T1 - Temperature-Dependent evolution of the molecular configuration of oxo-tungsten(VI) species deposited on the surface of titania

AU - Tribalis, Antonios

AU - Panagiotou, George D.

AU - Tsilomelekis, George

AU - Kalampounias, Angelos G.

AU - Bourikas, Kyriakos

AU - Kordulis, Christos

AU - Boghosian, Soghomon

AU - Lycourghiotis, Alexis

PY - 2014/5/29

Y1 - 2014/5/29

N2 - The pH and temperature evolution of the molecular configuration of oxo-tungsten(VI) species deposited on TiO2 by equilibrium deposition filtration and the temperature evolution of the samples texture are studied using in situ Raman spectroscopy, DR spectroscopy, N2 adsorption-desorption measurements, and TGA. Prior to drying, WO 42- monomers retained above a bridging surface hydroxyl of TiO2 through H bonding (with a Ti 2OH···O-WO3 umbrella configuration) prevail at pH = 9. A pH decrease results in a gradual transformation to an inner sphere monosubstituted species located above terminal surface oxygen (Ti-O-WO3). At pH = 7 both species coexist, whereas at pH = 5 the latter prevails with electrostatically retained polyoxotungstes also present. Heating to 100 °C causes the same effect resulted by the pH decrease at room temperature, that is, transformation of Ti2OH·· ·O-WO3 into Ti-O-WO3, attributed to the removal of H2O molecules upon heating, thereby liberating surface Ti atoms. Progressive heating to higher temperatures causes further removal of surface hydroxyls (confirmed also by TGA) liberating more neighbor surface Ti atoms and favoring further anchoring. This leads to formation of bisubstituted dioxo (Ti-O)2-W(=O)2 sites in the range 120-250 °C and to the prevalence of trisubstituted mono-oxo (Ti-O)3-W=O sites at 430 °C. Polyoxotungstates are also detected in the sample with the highest W loading. The DRS spectra indicate a charge transfer effect between the surface O and Ti atoms proceeding via Ti-O-W surface bridges. Calcination of the support causes a decrease of the pore volume and pore area in the range of pores with small width and an increase in the range of pores with large width. This effect is not affected by the presence of the well dispersed "bi-dimensional" W species inferred by the Raman study.

AB - The pH and temperature evolution of the molecular configuration of oxo-tungsten(VI) species deposited on TiO2 by equilibrium deposition filtration and the temperature evolution of the samples texture are studied using in situ Raman spectroscopy, DR spectroscopy, N2 adsorption-desorption measurements, and TGA. Prior to drying, WO 42- monomers retained above a bridging surface hydroxyl of TiO2 through H bonding (with a Ti 2OH···O-WO3 umbrella configuration) prevail at pH = 9. A pH decrease results in a gradual transformation to an inner sphere monosubstituted species located above terminal surface oxygen (Ti-O-WO3). At pH = 7 both species coexist, whereas at pH = 5 the latter prevails with electrostatically retained polyoxotungstes also present. Heating to 100 °C causes the same effect resulted by the pH decrease at room temperature, that is, transformation of Ti2OH·· ·O-WO3 into Ti-O-WO3, attributed to the removal of H2O molecules upon heating, thereby liberating surface Ti atoms. Progressive heating to higher temperatures causes further removal of surface hydroxyls (confirmed also by TGA) liberating more neighbor surface Ti atoms and favoring further anchoring. This leads to formation of bisubstituted dioxo (Ti-O)2-W(=O)2 sites in the range 120-250 °C and to the prevalence of trisubstituted mono-oxo (Ti-O)3-W=O sites at 430 °C. Polyoxotungstates are also detected in the sample with the highest W loading. The DRS spectra indicate a charge transfer effect between the surface O and Ti atoms proceeding via Ti-O-W surface bridges. Calcination of the support causes a decrease of the pore volume and pore area in the range of pores with small width and an increase in the range of pores with large width. This effect is not affected by the presence of the well dispersed "bi-dimensional" W species inferred by the Raman study.

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