The effect of the framework structure on the chemical properties of the vanadium oxide species incorporated within zeolites

Nature of vanadium species on vanadium silicalite-1 zeolite and their stability in hydroxylation reaction of benzene to phenol

“…The VS-1 catalysts were prepared by direct hydrothermal synthesis method as described in literatures with subtle modification. 25,26 In a typical preparation procedure, 0.05 mol tetrapropylammonium hydroxide (TPAOH) (25%), 10 mL water and 0.07 mol isopropanol were added slowly to a beaker containing 0.5 mol tetraethyl orthosilicate (TEOS). The presence of isopropanol could prevent the hydrolysis of silicate.…”

“…1a). 23,25,26,28 The absence of typical diffraction peaks of vanadium species may be due to the lack of obvious formation of vanadium oxide aggregates, even in the sample with the highest vanadium content (1.9 wt%). However, the XRD patterns could not indicate whether the vanadium species were present actually within the framework, because they could also be present on the external surface as amorphous vanadium oxides.…”

Phthalocyanine- and Calixarene-Templating Effect on the Catalytic Performance of Solid Supported Vanadates

“…Deconvolution of the UV-vis DRS Kubelka-Munk function with Gaussian functions was introduced as an additional valuable tool for studying the nature of vanadium oxide and vanadate species on the surface of silica and mesoporous silica supports [22,23]. Distribution of vanadium oxide deposited on zeolites was studied by Temperature Programmed Reduction (TPR) with H 2 [24], Electron Spin Resonance (ESR), X-ray Absorption Near Edge Structure (XANES), and photoluminescence spectroscopy [25]. There have been several reported attempts to control deposition of vanadium oxide by varying the nature of the precursor employed.…”

Determining the Structure of Silica-Supported Monomeric Vanadium Oxide Catalysts Based on Synthesis Method and Spectral Data from Theoretical Calculations

“…There is a consensus that the monomeric structure present at low loadings is a distorted tetrahedral around the central vanadium atom and that there are one or more VdO bonds present. 29,[44][45][46][47] For the incipient wetness technique, it has been concluded from EXAFS experiments 23,48 that the V-atom is surrounded by three O-atoms at 1.78 Å and one O-atom at 1.58 Å. This is as far as the consensus goes.…”