Abstract
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: V2O5 and (VO)(2)P2O7. 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 FePO4, V2O5 and (VO)(2)P2O7. 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 FePO4 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. (c) 2008 Published by Elsevier B.V.