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V 4+ → V 4+ / V 5 + → V 5+ / V 4+

Continuous uptake of oxygen happens after oxygen calcination. Introduction. n-Butane partial oxidation to maleic anhydride over VPO: (VO) 2 P 2 O 7 + ½ O 2 2 VOPO 4 14 VOPO 4 + C 4 H 10 C 4 H 2 O 3 + 4 H 2 O + 7(VO) 2 P 2 O 7

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V 4+ → V 4+ / V 5 + → V 5+ / V 4+

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  1. Continuous uptake of oxygen happens after oxygen calcination Introduction n-Butane partial oxidation to maleic anhydride over VPO: (VO)2P2O7 + ½ O2 2 VOPO4 14 VOPO4 + C4H10 C4H2O3 + 4 H2O + 7(VO)2P2O7 Catalyst synthesis from precursor (VPO hemihydrate): 2 VOHPO4.½H2O (VO)2P2O7 + 2 H2O Weight loss – 12-18% Carbon evolution – at ~260-300oC (most with air co-feed) Water evolution – at 100°C and 260°C Number Duration, hr Two water peaks during argon calcination V4+→ V4+/V5+→ V5+/V4+ Partial pressure What are the optimal conditions? 200 °C ~ 80 °C Number Time, minutes Argon to oxygen switch at 450 °C Atmosphere 450 °C Argon Oxygen Partial pressures Number Time, minutes Temperature, °C Thermogravimetric analysis of VPO calcination A. Shekari, K. M. S. Hansen, C. Fankem, T. Tzakova and G.S. Patience Dép.Génie Chimique, École Polytechnique, C.P. 6079, Succ. “CV”, Montréal, Qc, Canada H3C 3A7 Results Mass loss of water during argon calcination 480 °C Lattice water evolution 390 °C Surface water % Mass loss ~100 °C 260 °C Literature Time, minutes Catalyst Combustion peaks during oxygen calcination Color change during calcination Precursor Partial pressures 390°C, 10 h in Air Temperature, °C 480°C, 10 h in Air Conclusions What are the optimal calcination conditions?! VPO precursor calcination steps: 1- Desorption of surface adsorbed water (~100°C) – Loosely bound and surface water 2- Solid transformation I (280-460°C) 2 VOHPO4.½H2O (VO)2P2O7 + 2 H2O Vanadyl hydrogen phosphate Vanadyl pyrophosphate, V4+ hemihydrate, V4+ 3- Solid transformation II ( ≥460 °C) (VO)2P2O7 + ½ O2 2 VOPO4 Acknowledgements: E.I du Pont de Nemours, NSERC – CRSNG, MDEIE

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