Disparate product distributions observed in Mo(3-x)W xOy - (x=0-3; Y=3-9) reactions with D 2O and CO2

David W. Rothgeb, Ekram Hossain, Jennifer E. Mann, Caroline Chick Jarrold

Research output: Contribution to journalArticle

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Abstract

Results of gas phase reactivity studies on group six transition metal suboxide clusters, Mo3Oy -, Mo 2WOy -, MoW2Oy -, and W3Oy - (Mo (3-x)WxOy -, x=0-3; y=ca. 3-9) with both D2O and CO2 are reported. Sequential oxidation for the more reduced species, Mo(3-x)WxOy - + D2O/ CO2 → Mo(3-x)W xOy+1 - + D2/CO, and dissociative addition for certain species, Mo(3-x)WxOy - + D2O/ CO2 → Mo(3-x)W xOy+1D2 -/Mo(3-x)W xOy+1CO-, is evident in the product distributions observed in mass spectrometric measurements. Reactions with D2O proceed at a rate that is on the order of 102 higher than for CO2. The pattern of reaction products reveals composition-dependent chemical properties of these group six unary and binary clusters. At the core of this variation is the difference in Mo-O and W-O bond energies, the latter of which is significantly higher. This results in a larger thermodynamic drive to higher oxidation states in clusters with more tungsten atoms. However, addition products for more oxidized W-rich clusters are not observed, while they are observed for the more Mo-rich clusters. This is attributed to the following: In the higher oxides (e.g., y=8), addition reactions require distortion of local metal-oxygen bonding, and will necessarily have higher activation barriers for W-O bonds, since the vibrational potentials will be narrower. The binary (x=1,2) clusters generally show sequential oxidation to higher values of y. This again is attributed to higher W-O bond energy, the result being that stable binary structures have W atoms in higher oxidation states, and Mo centers both in more reduced states and sterically unhindered. The reduced Mo center provides a locus of higher reactivity. An unusual result that is not readily explained is the chemically inert behavior of Mo3O6 -.

Original languageEnglish (US)
Article number064302
JournalJournal of Chemical Physics
Volume132
Issue number6
DOIs
StatePublished - 2010
Externally publishedYes

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Oxidation
products
oxidation
Atoms
Addition reactions
Tungsten
Carbon Monoxide
reactivity
Reaction products
Oxides
Chemical properties
Transition metals
Gases
Metals
Chemical activation
Thermodynamics
loci
Oxygen
chemical properties
reaction products

ASJC Scopus subject areas

  • Physics and Astronomy(all)
  • Physical and Theoretical Chemistry

Cite this

Disparate product distributions observed in Mo(3-x)W xOy - (x=0-3; Y=3-9) reactions with D 2O and CO2 . / Rothgeb, David W.; Hossain, Ekram; Mann, Jennifer E.; Jarrold, Caroline Chick.

In: Journal of Chemical Physics, Vol. 132, No. 6, 064302, 2010.

Research output: Contribution to journalArticle

Rothgeb, David W. ; Hossain, Ekram ; Mann, Jennifer E. ; Jarrold, Caroline Chick. / Disparate product distributions observed in Mo(3-x)W xOy - (x=0-3; Y=3-9) reactions with D 2O and CO2 . In: Journal of Chemical Physics. 2010 ; Vol. 132, No. 6.
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abstract = "Results of gas phase reactivity studies on group six transition metal suboxide clusters, Mo3Oy -, Mo 2WOy -, MoW2Oy -, and W3Oy - (Mo (3-x)WxOy -, x=0-3; y=ca. 3-9) with both D2O and CO2 are reported. Sequential oxidation for the more reduced species, Mo(3-x)WxOy - + D2O/ CO2 → Mo(3-x)W xOy+1 - + D2/CO, and dissociative addition for certain species, Mo(3-x)WxOy - + D2O/ CO2 → Mo(3-x)W xOy+1D2 -/Mo(3-x)W xOy+1CO-, is evident in the product distributions observed in mass spectrometric measurements. Reactions with D2O proceed at a rate that is on the order of 102 higher than for CO2. The pattern of reaction products reveals composition-dependent chemical properties of these group six unary and binary clusters. At the core of this variation is the difference in Mo-O and W-O bond energies, the latter of which is significantly higher. This results in a larger thermodynamic drive to higher oxidation states in clusters with more tungsten atoms. However, addition products for more oxidized W-rich clusters are not observed, while they are observed for the more Mo-rich clusters. This is attributed to the following: In the higher oxides (e.g., y=8), addition reactions require distortion of local metal-oxygen bonding, and will necessarily have higher activation barriers for W-O bonds, since the vibrational potentials will be narrower. The binary (x=1,2) clusters generally show sequential oxidation to higher values of y. This again is attributed to higher W-O bond energy, the result being that stable binary structures have W atoms in higher oxidation states, and Mo centers both in more reduced states and sterically unhindered. The reduced Mo center provides a locus of higher reactivity. An unusual result that is not readily explained is the chemically inert behavior of Mo3O6 -.",
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