The effect of the phase composition of model VP0 catalysts for partial oxidation of n-butane

X-ray diffraction, Raman spectroscopy, 3’P MAS-NMR and spin-echo NMR indicated that model vanadium phosphorus oxide (VPO) precursors and catalysts contained various minor phases depending oxboth the synthetic approach and P/V ratios used. Raman spectroscopy revealed the presence of a number of micro-crystalline and amorphous V(W) and V(V) phases not evident by XRD. The presence of VOPO, phases was detrimental to the performance of the VP0 catalysts for KN-butane oxidation. The best model organic VP0 catalyst contained only vanadyl pyrophosphate with the highest degree of stacking order and virtually no VOPO, phase impurity. Raman spectroscopy detected vanadyl metaphosphate. VO(PO,),, in the catalysts derived from aqueous precursors possessing P/V ratios greater than I. Pure vanadyl metaphosphate catalyst was inactive in n-butane oxidation. s’P NMR demonstrated the absence of vanadyl metaphosphate and other impurity phases in the best catalyst derived from organic precursors at P/V = 1.18. The experimental data strongly indicate that the best VP0 catalysts for n-butane oxidation contain only vanadyl pyrophosphate with well-ordered stacking of the (200) planes.