Studies on bulk metal phosphate catalysts for the ammoxidation of 2-methylpyrazine

Various bulk metal (Nb, Zr, Al, Fe, Sb) phosphates were prepared, characterized and evaluated for the vapour phase selective synthesis of 2-cyanopyrazine by the ammoxidation of 2-methylpyrazine. Furthermore, well-known vanadium phosphates like α- and β-VOPO4 were also prepared, tested and compared their performance with that of bulk metal phosphates as described above. Catalysts containing the MO bond seemed to be highly active compared to those not containing it. The ease of transformation of the catalysts into their ammonium compounds facilitates high selectivity. FePO4 exhibited extremely high selectivity (ca. 100%) at ca. 20% conversion of 2-methylpyrazine compared to all other metal phosphates. Acidity characteristics of the different metal phosphates are found to show strong influence on the catalytic performance of the catalysts. Among all the metal phosphates investigated in the present study, α-VOPO4 displayed the highest acidity.