Abstract
Time-resolved in situ X-ray diffraction was used to study the formation of the vanadium phosphorous oxide (VPO) catalytic precursor phase VOHPO4 · 0.5H2O in organic media. In situ energy-dispersive X-ray diffraction has identified a new phase at early reaction times (less than 300 s) at d-spacings of 7.5 and 3.1 Å. At short reaction times, thin symmetrical platelets of 10 by 10 μm dimensions were observed. Scanning Electron Microscopy combined with energy-dispersive X-ray analysis (EDXA) indicated that these platelets contained vanadium and phosphorus. The features at 7.5 Å, which shift to 6.7 Å during the first 20 min of synthesis, are associated with VOPO4 · 2H2O and VOPO4 · H2O and disappear as VOHPO4 · 0.5H2O forms. The platelets appeared to delaminate, possibly associated with the strain generated when a d-spacing shifts from 7.5 Å to 6.7 Å, from which epitaxial growth of the VOHPO4 · 0.5H2O into the familiar rosette morphology occurs.
Original language | English |
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Pages (from-to) | 171-175 |
Number of pages | 5 |
Journal | Catalysis Letters |
Volume | 90 |
Issue number | 3-4 |
DOIs | |
Publication status | Published - Sep 2003 |
Keywords
- Crystallization
- In situ energy-dispersive X-ray diffraction
- Nucleation
- Vanadyl hydrogen phosphate hemihydrate