Catalytic behavior of BiPO4 in the multicomponent bismuth phosphate system on the propylene ammoxidation

We found that the multicomponent bismuth phosphate (MBP) with multiphase activates catalytically the ammoxidation reaction of propylene and consists of 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 volume measurements. The DTA curve clearly shows that there are phase transitions with sharp breaks of the curve. The specific surface area and total pore volume decrease with increasing of the BiPO4 phase content, showing that the BiPO4 phase remains essentially on the catalyst surface and blocks the active sites and catalyst pores. It would mean that the catalytic behavior in the MBP depends on the catalyst surface covered with the BiPO4 phase adequately. The pathway of the selective oxidation due to the controlled amounts of the BiPO4 phase favors the formation of acrylonitrile. The improvement of catalytic performances of the mixture of phases is explained by the synergy effect.