Vanadium-containing ordered mesoporous silicates: Does the silica source really affect the catalytic activity, structural stability, and nature of vanadium sites in V-MCM-41?

Shylesh, S.; Singh, Anand

doi:10.1016/j.jcat.2005.05.001

Cited by 82 publications

(53 citation statements)

References 30 publications

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“…2b). Apparently, the incorporation of a large amount of vanadium disrupts the structure of V-MCM-41 over some distance, which is similar to the effect of other transition metal ions on the MCM-41 structure reported elsewhere [29]. The physicochemical properties of Table 1.…”

Section: Nitrogen Physisorptionsupporting

confidence: 76%

A Non-sodium Synthesis of Highly Ordered V-MCM-41 and Its Catalytic Application in Isomerization

Liu

et al. 2009

Catal Lett

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A rapid non-sodium process was developed to synthesize highly ordered V-MCM-41 mesoporous materials with atomic level dispersed vanadium species. NH 3 ÁH 2 O instead of NaOH was used to maintain the moderately basic synthesis condition. The characterization results of N 2 physisorption and XRD showed that the synthesized samples had highly ordered hexagonal structure. UV-Vis, UV-Raman, and EPR spectra provided evidence that most vanadium ions were tetrahedrally incorporated into the framework of siliceous MCM-41. The NH 3 -TPD proved the mild acidity of V-MCM-41 due to the incorporation of vanadium cations. The most important variables were structural order and vanadium loading which can be controlled easily by changing synthesis variables in such a way that collapse of the V-MCM41structure did not occur. The synthesized V-MCM-41 catalysts successfully catalyzed the isomerization of heptene. High conversion and isomer selectivity were achieved with good catalytic stability. The structure of V-MCM-41 can be well preserved after reaction.

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Section: Nitrogen Physisorptionsupporting

confidence: 76%

A Non-sodium Synthesis of Highly Ordered V-MCM-41 and Its Catalytic Application in Isomerization

Liu

et al. 2009

Catal Lett

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“…Further the band at 930 cm -1 shift to lower wave numbers for the Cr-PMO1 sample. This shift can be related to a perturbation of the vibration of the silica structure after the substitution of chromium into the organosilica framework and are indirect proof for the presence of chromium in the wall positions [19].…”

Section: Spectroscopic Characterizationmentioning

confidence: 93%

Catalytic Aerobic Oxidation of Cyclohexane and Ethyl Benzene Over Chromium-Containing Mesoporous Organosilicas

et al. 2009

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Chromium-containing ethane-bridged hybrid periodic mesoporous organosilicas (Cr-PMO) were synthesized using 1,2-bis(triethoxysilyl)ethane (BTEE) and tetraethyl orthosilicate (TEOS) as silica sources and alkyltrimethyl ammonium salts as surfactants by two different synthesis routes. PXRD and N 2 adsorption-desorption analysis shows that the original structure of the materials is maintained after chromium substitution while spectroscopic study proves the incorporation of chromium in the frame wall positions and show the existence of Cr 2 O 3 species in the mixed silica source (BTEE-TEOS) synthesized chromium samples. The catalytic activity of the newly developed chromium samples was evaluated in the liquid phase oxidation of cyclohexane and ethylbenzene using air as an oxidant. Further, the Cr-PMO samples exhibited better cyclohexane conversion and cyclohexanone selectivity than the conventional Cr-MCM-41 and other metal-containing MCM-41 samples. The exceptional activity of the new chromium-containing molecular sieves is attributed to the hydrophobicity of the materials and to the complementary structural features that facilitates the accessibility of substrate to the active framework chromium sites.

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“…Therefore, isomorphous substitution of silicon with a transition metal is an excellent strategy in creating catalytically active sites and anchoring sites for reactive molecules in the design of new heterogeneous nano-structured catalysts. The incorporation of vanadium, an early member of the 3d transition metal series, in the framework of molecular sieves has resulted in active catalysts for the organic transformations of various substrates using aqueous H 2 O 2 as oxidant [10][11][12].…”

Section: Introductionmentioning

confidence: 99%

Mesoporous Silicates with Spherical Morphology Modified with Vanadium Highly Active in Oxidation of Cyclohexene with H2O2

et al. 2011

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Vanadium-containing mesoporous molecular sieves have been prepared by hydrothermal treatment at 373 K. These materials showed spherical morphology with a narrow particle size distribution between 2 and 4 lm. The techniques used for their physicochemical characterization were: XRD, AAS, N 2 physisorption, SEM, TEM and DR-UV-Vis spectroscopy. All the materials presented high specific surface area ([900 m 2 /g), characteristic of MCM-41 materials. A well-defined mesoporous structure was observed by TEM measures although there was no onedimensional ordering of pores characteristic of such materials. Additionally, secondary mesoporosity domains were determined in the BJH size distribution. The sample synthesized with the highest content of V presented marked differences in their structural characteristics, which were attributed to the blockage of channels by the presence of nano-clusters and/or V x O y nano-oxides. From the DR-UV-Vis analysis, a successful incorporation of V ions to silica structure in tetrahedral coordination with oxygen of the network could be inferred. The catalytic activity of these materials was evaluated in the test reaction of cyclohexene oxidation using H 2 O 2 as oxidizing agent, showing a high conversion of about 93% respect to the maximum, resulting dominant the radicalary mechanism over the direct oxidation mechanism. Apparently, the isolated V ions incorporated into the silica structure would be responsible for the high catalytic activity of these materials.

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Vanadium-containing ordered mesoporous silicates: Does the silica source really affect the catalytic activity, structural stability, and nature of vanadium sites in V-MCM-41?

Cited by 82 publications

References 30 publications

A Non-sodium Synthesis of Highly Ordered V-MCM-41 and Its Catalytic Application in Isomerization

A Non-sodium Synthesis of Highly Ordered V-MCM-41 and Its Catalytic Application in Isomerization

Catalytic Aerobic Oxidation of Cyclohexane and Ethyl Benzene Over Chromium-Containing Mesoporous Organosilicas

Mesoporous Silicates with Spherical Morphology Modified with Vanadium Highly Active in Oxidation of Cyclohexene with H2O2

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