Two vanadium phosphorus oxide precursors doped by Co and Fe have been prepared by a new route consisting of a reduction of VOPO₄, 2H₂O by isobutanol which is known to give a particular morphology of VOHPO₄, 0.5H₂O, developing crystallites in the [110] direction. Their activation under n-butane/air catalytic atmosphere (1.5%) has been compared to the corresponding undoped precursor prepared under the same conditions and used as a reference. The modification of the structure of the VPO materials has been followed on-line by in situ laser Raman spectroscopy. In a first period of the activation, the nucleation of α₁-VOPO₄ is favoured for the undoped VPO precursor, while (VO)₂P₂O₇ appears in a second period. For the Co-doped VPO precursor, α_I- and α_II-VOPO₄ first appear, and then (VO)₂P₂O₇ appears. At variance, the Fe-doped VPO precursor promotes the only nucleation of α_I-VOPO₄. When comparing with the classical organic route, catalytic performances are markedly improved when the VOHPO₄, 0.5H₂O precursor is prepared via this new route both for the undoped and the Co-doped VPO catalysts. At variance, the Fe-doped catalyst gives poorer performances which have been explained by a high oxidation state for this catalyst (almost (V⁵⁺) as α_I-VOPO₄). This is confirmed by an analysis of the bulk and surface composition of the final catalysts by XRD and XPS spectroscopy. The role of the two dopants on this new morphology of VOHPO₄, 0.5H₂O is then quite different at variance with what was observed on the same precursor prepared by the classical route of reduction of V₂O₅ by isobutanol (see B. Abdelouahab et al., 1995, J. Catal., 157, 687. The present study demonstrates that the preparative route for the formation of doped VPO precursors is most important in controlling the VOPO₄/(VO)₂P₂O₇ dispersion and catalytic performance of the final catalyst.

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{{Explor lien
   |wiki=    Wicri/Terre
   |area=    CobaltMaghrebV1
   |flux=    Main
   |étape=   Merge
   |type=    RBID
   |clé=     Pascal:96-0492337
   |texte=   On the role of Fe and Co dopants during the activation of the VO(HPO4), O.5H2O precursor of the vanadium phosphorus catalyst as studied by in situ laser Raman spectroscopy. II. Study of VO(HPO4), 0.5H2O precursors prepared by reduction of VOPO4, 2 H2O by isobutanol
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