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  IR Spectroscopic Investigation of Heteropolymolybdate Catalysts: Acidic Properties and Reactivity towards Propene

Jentoft, F. C., Kröhnert, J., & Schlögl, R. (2005). IR Spectroscopic Investigation of Heteropolymolybdate Catalysts: Acidic Properties and Reactivity towards Propene. Zeitschrift für Physikalische Chemie, 219(7), 1019-1045. doi:10.1524/zpch.219.7.1019.67090.

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 Creators:
Jentoft, Friederike C.1, Author           
Kröhnert, Jutta1, Author           
Schlögl, Robert1, Author           
Affiliations:
1Inorganic Chemistry, Fritz Haber Institute, Max Planck Society, ou_24023              

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Free keywords: heteropoly compounds, propene oxidation, in situ, DRIFTS, infrared spectroscopy, adsorption, CO, CO2 Project 5: Acid-base & redox properties of heteropoly compounds
 Abstract: Compounds of the general type CsxH3+y-xPVyMo12-yO40 (x = 0, 2–4 with y =1, or x = 0, 2 with y =0) were investigated by IR spectroscopy. After thermal treatment at 473–773 K in vacuum or N2, the probe molecules CO (at 77 K, in transmission) or CO2 (at 298 K, in diffuse reflectance) were adsorbed. On the surface of Cs2H2PVMo11O40 and Cs2HPMo12O40, Brønsted acid sites were indicated by a CO band at 2162 cm-1. All Cs containing compounds produced CO bands at 2152 cm-1 or CO2 bands at 2341 cm-1. Weak Lewis acid sites in at least two oxidation states were detected after treatment at 673 K. The fraction of the reduced species decreased in the order H4PVMo11O40 > Cs2H2PVMo11O40 > Cs3HPVMo11O40. In situ DRIFT spectra of these three compounds taken during interaction with propene at up to 673 K revealed that the pattern of IR bands typical of the Keggin anion was unaffected at x = 3, altered severely for the acid and to an intermediate extent for x = 2. The changes are consistent with a diminishing of the splitting of the P–O frequency. The Keggin structure represents the initial oxidized state of the heteropoly compound catalysts. Reduction affects but does not destroy the local structure as probed by IR spectroscopy. The more easily reducible H4PVMo11O40 is active for propene oxidation at 513 K, Cs2H2PVMo11O40 only at 617 K.

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Language(s): eng - English
 Dates: 2005
 Publication Status: Issued
 Pages: -
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 Rev. Type: Peer
 Identifiers: eDoc: 219883
DOI: 10.1524/zpch.219.7.1019.67090
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Title: Zeitschrift für Physikalische Chemie
  Alternative Title : Z. Phys. Chem.
Source Genre: Journal
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Pages: - Volume / Issue: 219 (7) Sequence Number: - Start / End Page: 1019 - 1045 Identifier: -