Ammoxidation activity of in situ synthesized ammonium salt of molybdophosphoric acid on VOPO4 catalysts

Two isomorphous VOPO4 samples were synthesized by means of well-known aqueous and organic preparation methods. These materials are further used for the in situ generation of ammonium salt of 12-molybdophosphoric acid (AMPA) from their solid phase phosphate components. Formation of AMPA was confirmed by XRD, FTIR, Raman and XPS analyses. The activity of the catalysts was tested in a fixed bed tubular glass reactor at atmospheric pressure for the selective ammoxidation of 2-methylpyrazine (MP) to 2-cyanopyrazine (CP). The reaction was carried out in the temperature range of 360–420 °C. Between the two mono-phosphates tested, the α-VOPO4 is observed to show somewhat better activity compared to β-VOPO4. Interestingly, in situ synthesized AMPA catalysts displayed significantly better performance compared to their corresponding parent VOPO4 solids. Among all catalysts tested, AMPA-α-VOPO4 exhibited the best performance (conversion (MP) = ca. 90%, selectivity (CP) = 65% at T = 420 °C). The differences in catalytic performance of the tested catalysts are ascribed to the structural differences of the used VOPO4 solids.