Studies on vanadium-doped iron phosphate catalysts for the ammoxidation of methylpyrazine

Abstract

Bulk and vanadium-doped iron phosphate catalysts were prepared and studied for the vapor phase ammoxidation of 2-methyl pyrazine. The vanadium-doped catalyst showed better activity than bulk catalysts as the vanadium doping leads to formation of quartz-type iron phosphate with additional phases of V 2 O 5 and (VO) 2 P 2 O 7 . Vanadium-doped iron phosphates (with 1, 3 and 5 wt.% V) were prepared and characterized by XRD, FTIR, UV-DRS, TPR, TEM, Laser Raman, XPS, and potentiometric titration techniques. Both undoped and V-doped catalysts displayed predominant formation of quartz type iron phosphate. In addition, the V-doped catalysts indicated formation of two more phases: V 2 O 5 and (VO) 2 P 2 O 7 . The nitrile yield of V-doped catalysts in the ammoxidation of methyl pyrazine to cyanopyrazine were found to be higher than the yield of bulk FePO 4 , V 2 O 5 and (VO) 2 P 2 O 7 . The increase in the redox property of the catalyst, as obtained by benzyl alcohol oxidation to benzaldehyde, was found to be the reason for enhanced activity. The variation of V-content in FePO 4 revealed that the catalyst reached its optimum activity at 3 wt.% V. However, the acid strength of the V-doped catalysts decreased with V-content and this reflected in their cyanopyrazine selectivity.