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Old and New Ideas for VPO? Application to DuPont Catalysts

Old and New Ideas for VPO? Application to DuPont Catalysts. Elisabeth BORDES-RICHARD Laboratoire de Catalyse de Lille. DuPont VPO Catalysts. VPO cats for n-butane to maleic anhydride: Especially designed by DuPont to be operated in the CFBR (Circulating Fluid Bed Reactor)

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Old and New Ideas for VPO? Application to DuPont Catalysts

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  1. Old and New Ideas for VPO? Application to DuPont Catalysts Elisabeth BORDES-RICHARD Laboratoire de Catalyse de Lille

  2. DuPont VPO Catalysts • VPO cats for n-butane to maleic anhydride: Especially designed by DuPont to be operated in the CFBR (Circulating Fluid Bed Reactor) • CFBR: Different from usual fixed or fluidized bed reactors: • Riser: transported bed of powder cat (lean phase) • Regenerator: fluidized bed of powder cat • In between: pipes and slide valves, cyclone(s), heat exchangers, etc.

  3. CFBR • Characteristics [1,2] Riser: • nearly plug flow • high heat & mass transfers Transient cyclic state ==> improve performance Controlled and separated delivery: • of O2- from solid to molecule: oxocapacity • of gaseous O2to solid Solid flux > 50 kg.m-2s-1 Superficial gas velocity > 2 ms-1 Residence time: few seconds [1] R.M. Contractor et al. Catal.Today, 1 (1987) 49 etc [2] G. Patience et al. Trans.I.ChemE, 68 (1990) 301 etc

  4. SEM on used cat; EDX: V, P, Si, Fe (LCL) DuPont VPO Catalyst • Composition: V,P,O,Si • Silica matrix embedding catalyst particles: attrition and erosion resistant [3] • [3] R.M. Contractor et al., Fluidization VI, Engineering Foundation New-York, • 1989; pp. 589-596

  5. DuPont VPO Catalyst DuPont recipe(R.M. Contractor et al.) • V2O5/isobutyl/benzyl alcohols + H3PO4 (85%) + TEOS • P/V = 1.0x/1.0 Spray-drying of VPO(Si) precursorwith silicic acid (ca. 1Owt%)  microspheres ø = 60-100 mm Calcination 400°C  Catalyst

  6. Topotactic dehydration, pseudomorphism [5] Control of VOHPO4•0.5H2O ==> Control of (VO)2P2O7 DuPont VPO Catalyst • Precursor: VOHPO4•0.5H2OJohnson et al., Torardi et al., 1984Face-sharing octahedraLayered structure, • Platy primary particles, rosets as secondary particles • Oxidation of prec. (air, 400°C)  d-VOPO4[4] • Catalyst: (VO)2P2O7 (mean oxidation state: V4.0x+)Gorbunova 1978, Sleight et al. 1990Edge-sharing octahedraLayered structure, • Platy primary particles, rosets as secondary particles • Oxidation of cat. (air, 400°C)  d-VOPO4[4] [4] E. Bordes, unpublished results [5] E. Bordes et al., J.Solid State Chem. (1984); Torardi et al., Inorg. Chem. (1984)

  7. O2 O2 MA n-C4 MA C4 MA C4 O2- O2- O2- O2- O2- O2- O2- O2- O2- O2- CFBR • Redox decoupling: optimize the working conditions <==> Same particle alternatively reduced (riser) and oxidized (regenerator) Co-feed CFBR Oxocapacity: O2- delivery vs. MA prod. • E. Bordes and R.M. Contractor, Topics Catal., 3 (1996) 365.

  8. (slightly) different properties of VPO catalyst Fixed B. Fluidized B. CFBR P/V ratio 1.1 1.1 1.0 Texture Attrition-resistant Other phases a,b-VOPO4 d-VOPO4 "bulky" (VO)2P207 layered (VO)2P207 (100) O2 CFBR (foll.) E. Bordes et al., Catal. Lett. 1999

  9. Experiments Keypoints: Oxocapacity, reactivity • Benchmarking • Precursor/Catalyst: Oxocapacity • Precursor dehydration and activation: genesis and control of morphology (topotaxy), V oxidation state, P/V,.... • Influence of pO2 during dehydration on the resulting phase(s), P/V, oxidation states, morphology, acidity… • Catalytic experiments with in situ or ex situ activation • Ageing of fresh cat and comparison with used cat • Catalytic experiments using different reactors • Comparison of properties with home VPO cats • Etc.!

  10. Acknowledgements • DuPont, G. Patience • L. Gengembre, M. Lefrère, L. Burylo, N. Bouremma: XPS, XRD, SEM-EDX • G. Franceschini, A. Thomazic (undergraduate students)

  11. b-VOPO4 024 200 032 XRD • Identification • Precursor: usual pattern of layered VOHPO4.0.5H2O • Catalyst • Fresh cat: (VO)2P2O7 Used cat: (VO)2P2O7 + b-VOPO4,

  12. Laser Raman Spectroscopy • Fresh and used cats • Fresh: • (VO)2P2O7 (9/10 particles): 929 (+ 1129, 1180) cm-1 • d-VOPO4 (1/10): 931, 1013, 1074 cm-1 • Used: heterogeneous mixture • (VO)2P2O7 (6/10 particles): 931 (+ 1128, 1180) cm-1 • b-VOPO4 (3/10): 884, 987, 1060 cm-1 • and aII-VOPO4 (1/10): 938, 990, 1087 cm-1 J.C. Volta et al., G.L. Schrader et al.

  13. b-VOPO4 In situ Redox XRD • In situ reactivity of fresh and used cats • Reduction by H2/He (1 h at 300, 400, 500°C) followed by reoxidation in air(1 h 500°C) • Fresh cat: (VO)2P2O7 Used cat: (VO)2P2O7 + b-VOPO4

  14. XPS (fresh and used cats) • As is and after grinding • Systematic higher V/Si when ground • P/V = 1.8-1.9 • After redox pre-treatment with ethane (20 mn at 200, 300, 400°C and air at 400°C) • Reduction steps • Very little modification of V2p3/2 photopeak • P/V = 1.80 up to 300°C;  1.92 at 400°C • V/Si = 1.19  1.07 for fresh; 0.87  0.81 for used cat. • Reoxidation • V5+ + V4+ for fresh cat.; V5+ for used cat • P/V = 1.8-1.9 • V/Si = 1.14 for fresh; 0.92 for used cat.

  15. XPS (fresh and used cats) • XPS • As received and ground samples:  no difference • P/V  1.80 up to 400°C; 1.91 at 500°C

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