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Catalytic activity of highly ordered mesoporous VMCM-48

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Title Catalytic activity of highly ordered mesoporous VMCM-48
 
Creator SELVAM, P
DAPURKAR, SE
 
Subject promising heterogeneous catalysts
microporous vanadium silicates
(cr)mcm-48 molecular-sieves
solid acid catalyst
x-ray-diffraction
selective oxidation
aromatic-hydrocarbons
room-temperature
mcm-41
phase
mesoporous molecular sieves
vmcm-48
vanadium
selective cyclohexane oxidation
cyclohexanol
cyclohexanone
 
Description Mesoporous VMCM-48 molecular sieves with Si/V (molar) ratios of 25-200 were synthesized hydrothermally and systematically characterized by various analytical and spectroscopic techniques, viz., XRD, N-2 sorption, TG-DTA, TEM, EPR, V-51 MAS-NMR, FT-IR, and DRUV-VIS. XRD studies suggest that the substitution of vanadium occurs in the silicate framework structure of MCM-48. TEM and ED investigations confirm the highly ordered cubic structure of VMCM-48. EPR and V-51 NMR studies indicate the presence of pentavalent vanadium ions in tetrahedral framework positions, while DRUV-VIS spectra show their existence in two different environments. The catalytic activity of these well-characterized (both in the calcined and the washed forms) materials was evaluated for cyclohexane oxidation under mild reaction conditions. All these catalysts gave high substrate conversion and excellent product (cyclohexanol) selectivity. Furthermore, unlike many other vanadium-based heterogeneous catalysts reported, the mesoporous VMCM-48 catalysts show minimal leaching of the active vanadium species. This was confirmed by washing, recycling and quenching experiments where only a small amount of vanadium ions leaches out in the case of calcined samples, while vanadium was not detected for the washed ones. Finally, the catalytic activity of VMCM-48 was also compared with mesoporous VMCM-41 as well as microporous VS-1 catalyst. The results indicate that the former showed superior activity to those of the latter two, such superiority could, however, be directly related to the amount of vanadium incorporated in MCM-48 being larger than the amounts in MCM-41 and MF1structures. (C) 2004 rights reserved.
 
Publisher ELSEVIER SCIENCE BV
 
Date 2011-07-24T12:06:20Z
2011-12-26T12:54:05Z
2011-12-27T05:41:27Z
2011-07-24T12:06:20Z
2011-12-26T12:54:05Z
2011-12-27T05:41:27Z
2004
 
Type Article
 
Identifier APPLIED CATALYSIS A-GENERAL, 276(1-2), 257-265
0926-860X
http://dx.doi.org/10.1016/j.apcata.2004.08.012
http://dspace.library.iitb.ac.in/xmlui/handle/10054/6418
http://hdl.handle.net/10054/6418
 
Language en