Catalytic behavior of BiPO4 in the multicomponent bismuth phosphate systemon the propylene ammoxidation

We found that the multicomponent bismuth phosphate (MBP) with multiphase ac tivates catalytically the ammoxidation reaction of propylene and consists o f mainly BiPO4 and metal molybdates, etc. The MBP has been characterized by several techniques such as DTA, XRD, and BET surface area and total pore v olume measurements. The DTA curve clearly shows that there are phase transi tions with sharp breaks of the curve. The specific surface area and total p ore volume decrease with increasing of the BiPO4 phase content, showing tha t the BiPO4 phase remains essentially on the catalyst surface and blocks th e active sites and catalyst pores. It would mean that the catalytic behavio r in the MBP depends on the catalyst surface covered with the BiPO4 phase a dequately. The pathway of the selective oxidation due to the controlled amo unts of the BiPO4 phase favors the formation of acrylonitrile. The improvem ent of catalytic performances of the mixture of phases is explained by the synergy effect.