Methane photoactivation on copper molybdate. An experimental and theoretical study

Michael Ward, James F. Brazdil, S. P. Mehandru, Alfred B. Anderson

Research output: Contribution to journalArticle

Abstract

It is shown experimentally that the activity of UV-irradiated MoO3 for the partial oxidation of methane in the presence of O2 at 100°C, leading to methanol formation, is markedly enhanced when CuII is added to the catalyst. The rate of methanol formation is maximum when the concentrations of copper and molybdenum are equal. Visible light activates CuMoO4 but not MoO3. We have made a molecular orbital study of the photoactivity of CuMoO4 toward hydrogen abstraction from methane at O- centers. The activity of CuMoO4 in the visible region is assigned to O 2p → Cu 3d excitations; the Cu 3d band levels lie below the Mo 4d band and the orbitals have a large O 2p component. Mechanisms are proposed for increasing the lifetimes of the electron-hole pairs and thereby account for the synergistic effect in CuMoO4 which shows enhanced photoactivity compared with either CuO, which is photoinactive, or MoO3. Empty band-gap orbitals serve to stabilize homolytic H and CH3 adsorption on O2- sites relative to MoO3, and filled band-gap orbitals stabilize homolytic adsorption on MoVI sites. Heterolytic adsorption on MoVI and O2- sites is stable but not on CuII and O2- sites. Homolytic adsorption is unstable on CuII sites.

Original languageEnglish (US)
Pages (from-to)6515-6521
Number of pages7
JournalJournal of Physical Chemistry
Volume91
Issue number26
StatePublished - 1987

Fingerprint

molybdates
Methane
Copper
methane
Adsorption
copper
adsorption
orbitals
Methanol
Energy gap
methyl alcohol
Molybdenum
Molecular orbitals
molybdenum
Hydrogen
molecular orbitals
catalysts
life (durability)
Oxidation
oxidation

ASJC Scopus subject areas

  • Physical and Theoretical Chemistry

Cite this

Ward, M., Brazdil, J. F., Mehandru, S. P., & Anderson, A. B. (1987). Methane photoactivation on copper molybdate. An experimental and theoretical study. Journal of Physical Chemistry, 91(26), 6515-6521.

Methane photoactivation on copper molybdate. An experimental and theoretical study. / Ward, Michael; Brazdil, James F.; Mehandru, S. P.; Anderson, Alfred B.

In: Journal of Physical Chemistry, Vol. 91, No. 26, 1987, p. 6515-6521.

Research output: Contribution to journalArticle

Ward, M, Brazdil, JF, Mehandru, SP & Anderson, AB 1987, 'Methane photoactivation on copper molybdate. An experimental and theoretical study', Journal of Physical Chemistry, vol. 91, no. 26, pp. 6515-6521.
Ward, Michael ; Brazdil, James F. ; Mehandru, S. P. ; Anderson, Alfred B. / Methane photoactivation on copper molybdate. An experimental and theoretical study. In: Journal of Physical Chemistry. 1987 ; Vol. 91, No. 26. pp. 6515-6521.
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N2 - It is shown experimentally that the activity of UV-irradiated MoO3 for the partial oxidation of methane in the presence of O2 at 100°C, leading to methanol formation, is markedly enhanced when CuII is added to the catalyst. The rate of methanol formation is maximum when the concentrations of copper and molybdenum are equal. Visible light activates CuMoO4 but not MoO3. We have made a molecular orbital study of the photoactivity of CuMoO4 toward hydrogen abstraction from methane at O- centers. The activity of CuMoO4 in the visible region is assigned to O 2p → Cu 3d excitations; the Cu 3d band levels lie below the Mo 4d band and the orbitals have a large O 2p component. Mechanisms are proposed for increasing the lifetimes of the electron-hole pairs and thereby account for the synergistic effect in CuMoO4 which shows enhanced photoactivity compared with either CuO, which is photoinactive, or MoO3. Empty band-gap orbitals serve to stabilize homolytic H• and •CH3 adsorption on O2- sites relative to MoO3, and filled band-gap orbitals stabilize homolytic adsorption on MoVI sites. Heterolytic adsorption on MoVI and O2- sites is stable but not on CuII and O2- sites. Homolytic adsorption is unstable on CuII sites.

AB - It is shown experimentally that the activity of UV-irradiated MoO3 for the partial oxidation of methane in the presence of O2 at 100°C, leading to methanol formation, is markedly enhanced when CuII is added to the catalyst. The rate of methanol formation is maximum when the concentrations of copper and molybdenum are equal. Visible light activates CuMoO4 but not MoO3. We have made a molecular orbital study of the photoactivity of CuMoO4 toward hydrogen abstraction from methane at O- centers. The activity of CuMoO4 in the visible region is assigned to O 2p → Cu 3d excitations; the Cu 3d band levels lie below the Mo 4d band and the orbitals have a large O 2p component. Mechanisms are proposed for increasing the lifetimes of the electron-hole pairs and thereby account for the synergistic effect in CuMoO4 which shows enhanced photoactivity compared with either CuO, which is photoinactive, or MoO3. Empty band-gap orbitals serve to stabilize homolytic H• and •CH3 adsorption on O2- sites relative to MoO3, and filled band-gap orbitals stabilize homolytic adsorption on MoVI sites. Heterolytic adsorption on MoVI and O2- sites is stable but not on CuII and O2- sites. Homolytic adsorption is unstable on CuII sites.

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