Studies of the Structure of Vanadium Species in VAPO-5 Molecular Sieves via Density Functional Theory Computation and Raman Spectroscopy

Cheng, H. S.; Yang, E.; Chao, Kuei‐Hsiang; Wei, A.C.; Liu, P.H.

doi:10.1021/jp001721n

Cited by 5 publications

(1 citation statement)

References 23 publications

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“…Such an approach has been successfully used by Pierloot and co-workers − for the calculation of d−d transitions and g -values of Co(II) and Cu(II) ions occupying cationic positions in aluminosilicate zeolites, and recently also by Carl et al in DFT calculations of g -values and hyperfine coupling constants of VO 2+ exchanged zeolites. Cheng et al , have applied DFT in combination with X-ray absorption spectroscopy (XANES and EXAFS) to study the structure of vanadyl(IV) and vanadium(V) in cluster models of AlPO 4 -5. The calculated clusters indicated that while the substitution of either P or Al in the framework is not feasible, the parameters of optimized models representing an extraframework substitution site are comparable with those obtained from the in-situ X-ray absorption experiments …”

Section: Introductionmentioning

confidence: 99%

Isomorphous Substitution of Mn(II) into Aluminophosphate Zeotypes: A Combined High-Field ENDOR and DFT Study

et al. 2002

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The incorporation of low levels of Mn(II) (Mn/Al∼0.001) into five aluminophosphate zeotypes was studied by high-field echo-detected EPR, and by 31P and 1H electron−nuclear double resonance (ENDOR) spectroscopies. The zeotype structures investigatedSOD, AEL, AFI, SBS, and SBTcover a variety of channel morphologies, and span a range of framework densities. The highly resolved EPR spectra could distinguish between two types of Mn with different 55Mn hyperfine couplings in structures containing more than one T site. Mims and Davies 31P ENDOR spectra, recorded at a field set to one of the |−/2, m I 〉 → |+1/2, m I 〉 55Mn hyperfine components consist of a symmetric doublet, with a splitting in the range of 5−8 MHz. The large open structures showed smaller couplings than the denser morphologies. A similar 31P hyperfine was also detected for Fe(III) incorporated into aluminophosphate zeotype with the SOD structure. Variations in the 1H ENDOR spectra of the various Mn(II) substituted zeotypes, particularly in the relative intensity of the 1H matrix line, were detected as well. These ENDOR results indicate a common mechanism of framework substitution in which Mn(II) and Fe(III) are replacing Al (or Mg). Moreover, the spectra serve as a probe for the differences in the local environment and bonding topology of these substituted framework sites. A qualitative interpretation of the 31P ENDOR data is provided, based on relevant crystallographic information, and the 1H ENDOR signals are partially attributed to the interactions with the templates occluded in the zeotype cages. To further relate the isotropic 31P hyperfine couplings to structural properties, DFT methods were employed for cluster model optimizations and hyperfine coupling constants calculations. Geometry optimizations of substituted rings, derived from the SOD and AEL framework structures, indicate considerable distortions of the coordination environment of framework Mn as compared to Al. A systematic study of the hyperfine interactions of a series of model structures containing tetrahedral and octahedral Mn(II) show that both Mn−O bond lengths and Mn−O−P bond angles contribute significantly to the variation in the isotropic and anisotropic 31P hyperfine coupling.

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Section: Introductionmentioning

confidence: 99%

Isomorphous Substitution of Mn(II) into Aluminophosphate Zeotypes: A Combined High-Field ENDOR and DFT Study

et al. 2002

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Study on Chromium‐Containing Aluminophosphate CrAPO‐5 via Density Functional Theory

Cheng

Chang

2008

J Chinese Chemical Soc

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Various structures of CrAPO-5 clusters are studied via density functional B3LYP exchange-correlation method. The optimized structures are compared with data from X-ray absorption. Their total energies and atomic net charges are also analyzed. Results indicate that the substitution of the aluminum site of an AFI framework by chromium is in general not feasible. The chromium ion is more likely docked in between two neighboring 12-membered rings of the framework of AFI. To further verify our claim, the excitation energies of the representative chromium structures of CrAPO-5 clusters are calculated via the TDDFT method. The results for excitation energies further support that Cr 3+ is not incorporated into the framework.

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Spectroscopic investigation into the nature of the active sites for epoxidation reactions using vanadium-based aluminophosphate catalysts

Vishnuvarthan

Paterson

Raja

et al. 2011

Microporous and Mesoporous Materials

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Studies of the Structure of Vanadium Species in VAPO-5 Molecular Sieves via Density Functional Theory Computation and Raman Spectroscopy

Cited by 5 publications

References 23 publications

Isomorphous Substitution of Mn(II) into Aluminophosphate Zeotypes: A Combined High-Field ENDOR and DFT Study

Isomorphous Substitution of Mn(II) into Aluminophosphate Zeotypes: A Combined High-Field ENDOR and DFT Study

Study on Chromium‐Containing Aluminophosphate CrAPO‐5 via Density Functional Theory

Spectroscopic investigation into the nature of the active sites for epoxidation reactions using vanadium-based aluminophosphate catalysts

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