Location, acid strength, and mobility of the acidic protons in Keggin 12-H3PW12O40

A combined solid-state NMR spectroscopy and DFT quantum chemical calculation study

Jun Yang, Michael John Janik, Ding Ma, Anmin Zheng, Mingjin Zhang, Matthew Neurock, Robert J. Davis, Chaohui Ye, Feng Deng

Research output: Contribution to journalArticle

106 Citations (Scopus)

Abstract

Solid-state 13C NMR experiments and quantum chemical Density Functional Theory (DFT) calculations of acetone adsorption were used to study the location of protons in anhydrous 12-tungstophosphoric acid (HPW), the mobility of the isolated and hydrated acidic protons, and the acid strength heterogeneity of the anhydrous hydroxyl groups. This study presents the first direct NMR experimental evidence that there are two types of isolated protons with different acid strengths in the anhydrous Keggin HPW. Rotational Echo DOuble Resonance (REDOR) NMR experiments combined with quantum chemical DFT calculations demonstrated that acidic protons in anhydrous HPW are localized on both bridging (Oc) and terminal (Od) atoms of the Keggin unit. The CP/MAS NMR experiments revealed that the isolated acidic protons are immobile, but hydrated acidic protons are highly mobile at room temperature. The isotropic chemical shift of the adsorbed acetone suggested that the acid strength of the H(H2O)n+ species in partially hydrated HPW is comparable to that of a zeolite, while the acidity of an isolated proton is much stronger than that of a zeolite. Isolated protons on the bridging oxygen atoms of anhydrous HPW are nearly superacidic.

Original languageEnglish (US)
Pages (from-to)18274-18280
Number of pages7
JournalJournal of the American Chemical Society
Volume127
Issue number51
DOIs
StatePublished - Dec 28 2005

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Quantum Theory
Nuclear magnetic resonance spectroscopy
Density functional theory
Protons
Magnetic Resonance Spectroscopy
Acids
Nuclear magnetic resonance
Zeolites
Acetone
Atoms
Experiments
Chemical shift
Acidity
Hydroxyl Radical
Adsorption
Oxygen

All Science Journal Classification (ASJC) codes

  • Catalysis
  • Chemistry(all)
  • Biochemistry
  • Colloid and Surface Chemistry

Cite this

Yang, Jun ; Janik, Michael John ; Ma, Ding ; Zheng, Anmin ; Zhang, Mingjin ; Neurock, Matthew ; Davis, Robert J. ; Ye, Chaohui ; Deng, Feng. / Location, acid strength, and mobility of the acidic protons in Keggin 12-H3PW12O40 : A combined solid-state NMR spectroscopy and DFT quantum chemical calculation study. In: Journal of the American Chemical Society. 2005 ; Vol. 127, No. 51. pp. 18274-18280.
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Location, acid strength, and mobility of the acidic protons in Keggin 12-H3PW12O40 : A combined solid-state NMR spectroscopy and DFT quantum chemical calculation study. / Yang, Jun; Janik, Michael John; Ma, Ding; Zheng, Anmin; Zhang, Mingjin; Neurock, Matthew; Davis, Robert J.; Ye, Chaohui; Deng, Feng.

In: Journal of the American Chemical Society, Vol. 127, No. 51, 28.12.2005, p. 18274-18280.

Research output: Contribution to journalArticle

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