THE INCORPORATION OF SULFATE IN VANADYLPHOSPHATE CATALYST PHASES AND ITS PRECURSORS - ESR INVESTIGATION OF MAGNETIC-INTERACTIONS BETWEEN VO2+ CENTERS

The substitution of phosphate by sulfate anions in the lattices of dif ferent VOHPO4 . 0.5 H2O Precursors and (VO)2P2O7 catalYStS has been st udied by ESR investigation of magnetic interactions between neighbouri ng VO2+ centres. In the monophosphates the exchange integrals for this interaction, J, do not depend on the sulfate content. The observed li ne broadening of ESR signals is interpreted in terms of a statistical incorporation of sulfate in the lattice. In the diphosphates J decreas es with increasing lattice distortion caused by the sulfate substituti on. The strongest effect is observed at the lowest sulfate content ind icating a non statistical incorporation. Exchange coupling in carrier- supported diphosphate is more effective than in the bulk material and is mainly determined by the influence of the carrier.