Isolated redox centers within microporous environments.  2.  Vanadium-containing aluminophosphate molecular sieve five

Montes, Consuelo; Davis, Mark E.; Murray, Brendan D.; Narayana, M.

doi:10.1021/j100379a050

Cited by 105 publications

(62 citation statements)

References 2 publications

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“…The spectral similarity of (Co, V)APO-5-0.05-0.03 to VAPO-5 indicates that V sites in the (Co, V)APO-5 and VAPO-5 molecular sieves had a similar local geometry [27], viz. part of them was present in the state of isolated square-pyramidal and/or distorted octahedral vanadyl-like (VO 2+ ) species [3,12,15,22,33,37]. After calcination, no ESR signal was detected, showing that all V 4+ ions were oxidized to the EPR-inactive V 5+ .…”

Section: Catalyst Synthesis and Characterizationmentioning

confidence: 99%

“…However, the exact location of V 4+ in the framework is still in a debate. Some authors suggested that V 4+ substitutes for Al 3+ [38], while other research groups believe it replaces P 5+ [22,33,34]. Nagarajan et al very recently deduced from ESR and hyperfine sublevel correlation (HYSCORE) spectroscopy that VO 2+ species is present in the as-synthesized VAPO-5 by equatorially coordinating to two framework oxygen atoms and presumably three water molecules in a distorted octahedral geometry with phosphorus and aluminum framework atoms in the second coordination shell [37].…”

Section: Catalyst Synthesis and Characterizationmentioning

confidence: 99%

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Synthesis, characterization and catalysis of (Co, V)-, (Co, Cr)- and (Cr, V)APO-5 molecular sieves

Fan

Song

et al. 2006

Microporous and Mesoporous Materials

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Synthesis, characterization and catalysis of (Co, V)-, (Co, Cr)-and (Cr, V)APO-5 molecular sieves ) molecular sieves have been hydrothermally synthesized and characterized. The as-synthesized and calcined samples were investigated with XRD, ICP, DRS UV-vis spectroscopy, ESR, 27 Al MAS NMR techniques to explore the valence, coordination and location of the incorporated transition metal ions. It was shown that isomorphous substitution of Co 2+ for Al 3+ convincingly occurred, and V 4+ also anchored to the sample by coordinating to two framework oxygen atoms and most probably occupying P 5+ sites, while no unambiguous spectroscopic evidence was provided for the incorporation of Cr 3+ in the lattice, although chemical analysis suggests this possibility in the case that Co 2+ or V 4+ are added to the synthesis gel. The preferential sequence for the incorporation of these transition metal ions in the AFI framework is: Co 2+ > V 4+ > Cr 3+ . After calcination, almost all V 4+ ions were oxidized to V 5+ , whereas Cr 3+ ions were oxidized to Cr 5+ and Cr 6+ . As catalysts, the (M, N)APO-5 molecular sieves are highly active for the selective oxidation of cyclohexane with a high cyclohexanone/cyclohexanol ratio in the presence of H 2 O 2 . The reaction temperature and solvent significantly influenced the catalytic behavior. Although some leaching of the transition metal ions was observed, the catalytic performance remained stable at least within five repeated runs.

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Section: Catalyst Synthesis and Characterizationmentioning

confidence: 99%

Section: Catalyst Synthesis and Characterizationmentioning

confidence: 99%

Synthesis, characterization and catalysis of (Co, V)-, (Co, Cr)- and (Cr, V)APO-5 molecular sieves

Fan

Song

et al. 2006

Microporous and Mesoporous Materials

View full text Add to dashboard Cite

show abstract

“…Thus, Rigutto and van Bekkum [53] proposed that in vanadium containing silicalite, vanadium (as vanadyl VO 2 ) is bonded to two framework oxygens, the other ligands around vanadium being OH groups bonded to silicon neighbors. In the models of Montes et al [44] and Prakash and Kevan [54], vanadyl is anchored to the aluminophosphate framework by two bonds Fig. 8.…”

Section: Optimal Conditions For Vapo-11 Synthesismentioning

confidence: 99%

On the synthesis of vanadium containing molecular sieves by experimental design from a VOSO4·5H2O·Al(iPrO)3·Pr2NH·H2O gel: occurrence of VAPO-41 as a secondary structure in the synthesis of VAPO-11

Frunză¹,

Voort²,

Vansant³

et al. 2000

Microporous and Mesoporous Materials

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“…For supported metal particles, the effect of the support on the catalytic properties has been determined by several techniques, for example, XPS, FT-IR analysis of adsorbed CO, and newly developed delta XANES and atomic XAFS (AXAFS) techniques. [8][9][10][11][12][13][14][15] In particular, the application of AXAFS has, in our opinion, led to a better understanding of metal-support interaction effects. [8,[15][16][17] AXAFS is sensitive to changes in the potential around the X-ray absorbing atom.…”

mentioning

confidence: 98%

Application of AXAFS Spectroscopy to Transition‐Metal Oxides: Influence of the Nearest and Next Nearest Neighbour Shells in Vanadium Oxides

Keller

Weckhuysen

Koningsberger

2007

Chemistry A European J

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IntroductionMany parameters affect the catalytic properties of transition-metal oxide catalysts, for example, metal oxide loading, pre-treatment conditions, molecular structure, electronic structure, and the nature of the supporting oxide. [1][2][3][4][5][6][7] Various researchers have investigated the activities and selectivities of metal oxide catalysts. However, little is known about the parameters that are truly responsible for the catalytic action of transition-metal oxides.To study the effect of the support on the catalytic performance, one has to find a tool that is capable of probing the influence of the local environment (e.g., the support or promoters) on the properties of the catalytically active species, that is, a metal particle or metal oxide cluster. Metal-A C H T U N G T R E N N U N G (oxide)-support interactions can be ascribed to a structural (particle/cluster size and shape) effect, but can also have an electronic origin. For supported metal particles, the effect of the support on the catalytic properties has been determined by several techniques, for example, XPS, FT-IR analysis of adsorbed CO, and newly developed delta XANES and atomic XAFS (AXAFS) techniques. [8][9][10][11][12][13][14][15] In particular, the application of AXAFS has, in our opinion, led to a better understanding of metal-support interaction effects. [8,[15][16][17] AXAFS is sensitive to changes in the potential around the X-ray absorbing atom. The potential field around an atom is mainly determined by the first and second coordination spheres. O Grady et al. have shown for Pt/Ru alloys that the AXAFS intensity changes systematically with the composition of the alloy. [18] Thus, when the number of Ru atoms around a Pt atom increases, the intensity of the FT AXAFS peak increases and the peak centroid shifts to lower values of R. Comparison of these effects with the effects observed for a Pt electrode as a function of the applied voltage suggests that the first coordination shell of the Pt in the Pt/Ru alloy influences the electronic properties (inter-A C H T U N G T R E N N U N G atomic potential) of the Pt atom. [18,19] The effect of changes in the coordination around the absorber atom has been further illustrated for Pt by van Dorssen et al., who compared the AXAFS of a Pt foil with that of bulk Na 2 Pt(OH) 6 . The AXAFS intensity was found to be significantly higher in the Abstract: The influence of changes in coordination number, interatomic distances, and oxidation state on the intensity and centroid position of the Fourier transform (FT) of the atomic X-ray absorption fine structure (AXAFS) peak of vanadium oxide bulk model compounds and aluminasupported vanadium oxide clusters has been investigated. Using Na 3 VO 4 and V 2 O 5 as model compounds, it has been shown that the nearest neighbour shells have a pronounced influence on the AXAFS intensity; specifically, a 40 % decrease in intensity was observed between these two compounds. Secondly, the influence of partial reduction of the vanadium oxide species has been dete...

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Isolated redox centers within microporous environments. 2. Vanadium-containing aluminophosphate molecular sieve five

Cited by 105 publications

References 2 publications

Synthesis, characterization and catalysis of (Co, V)-, (Co, Cr)- and (Cr, V)APO-5 molecular sieves

Synthesis, characterization and catalysis of (Co, V)-, (Co, Cr)- and (Cr, V)APO-5 molecular sieves

On the synthesis of vanadium containing molecular sieves by experimental design from a VOSO4·5H2O·Al(iPrO)3·Pr2NH·H2O gel: occurrence of VAPO-41 as a secondary structure in the synthesis of VAPO-11

Application of AXAFS Spectroscopy to Transition‐Metal Oxides: Influence of the Nearest and Next Nearest Neighbour Shells in Vanadium Oxides

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