Structure and reactivity of zirconium oxide-supported ammonium salt of 12-molybdophosphoric acid catalysts

A series of catalysts with varying quantities of ammonium salt of 12-molybdophosphoric acid supported on zirconium dioxide was synthesized. The catalysts were characterized by nitrogen adsorption for BET surface area, X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy and 31P MAS NMR techniques to study the nature of the interactions of the active component with the support as a function of salt loading. The nature of the Keggin ion species (intact, fragmented or decomposed) formed on the support varies with the extent of loading of the heteropolyacid salt. A good correlation was obtained between the extent of formation of lacunary Keggin ion species and the activity of the catalysts during the ammoxidation of 2-methylpyrazine at different reaction temperatures.