Morphological changes of vanadyl pyrophosphate due to thermal excursions

Vanadyl pyrophosphate (VPP) is the active catalytic phase that converts n-butane to maleic anhydride in fixed beds, fluidized and DuPont’s circulating bed (CFB). The original CFB concept was based on Mars van-Krevelen reaction mechanism which solid lattice contributes all of oxygen partially oxidize n-butane. However, maintain high activity selectivity requires surface oxidized; thus, DuPont co-fed pure through 926 nozzles at three levels CFB. Since fed independently butane stream, gas composition nozzle crosses explosion envelope local temperature could rise several 100 ∘C. Furthermore, exhaust pipe downstream cyclone within envelope. these two regions periodically exceeded 700∘C, sufficiently deactivate catalyst turn it black. Here, we reproduced conditions examine changes morphology. A TA-Q500 heated fresh 800 ∘C under nitrogen air flow. VPP turned black above 700 but not nitrogen. area pore volume calcined decreased from 23 m2g−1 0.14 cm3g−1 12 m2g−1, 0.09 equilibrated catalyst. New bonds form reacts with silica VO(P2SiO8).