The role of Fe and Co dopants during the activation of the VO(HPO4)center dot 0.5H(2)O precursor of the vanadium phosphorus catalyst as studied by in situ laser Raman spectroscopy .1. Study of VO(HPO4)center dot 0.5H(2)O precursors prepared by reduction of V2O5 by isobutanol

The activation of two Fe- and Co-doped VO(HPO4).0.5H(2)O precursors under n-butane/air catalytic atmosphere (1.5%) has been compared to the corresponding undoped precursor prepared under the same conditions by the organic route of reduction of V2O5 by isobutanol, The modification of the structure of the VPO materials has been followed by in situ laser Raman spectroscopy during the activation on line. It is evidenced that doping promotes the first time the oxidation of the catalysts favoring the VOPO4/(VO)(2)P2O7 balance, This is confirmed by an analysis of the bulk and surface composition of the final catalysts by UV-visible, XPS spectroscopy and P-31 NMR by spin-echo mapping. The role of the two dopants is shown to be different on the catalytic performances: both Co and Fe dopants improve strongly selectivity to maleic anhydride but n-butane conversion is decreased for Co and increased for Fe, This has been explained by a different dispersion of VOPO, phases on the (VO)(2)P2O7 matrix during the activation process as compared to the same undoped VPO catalyst. (C) 1995 Academic Press, Inc.