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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

Old and New Ideas for VPO? Application to DuPont Catalysts

Elisabeth BORDES-RICHARD

Laboratoire de Catalyse de Lille


Dupont vpo catalysts
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.


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


Dupont vpo catalyst

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


Dupont vpo catalyst1
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


Dupont vpo catalyst2

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)


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.


  • (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


Experiments
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.!


  • Acknowledgements

    • DuPont, G. Patience

    • L. Gengembre, M. Lefrère, L. Burylo, N. Bouremma: XPS, XRD, SEM-EDX

    • G. Franceschini, A. Thomazic (undergraduate students)


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,


Laser raman spectroscopy
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.


In situ redox xrd

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


Xps fresh and used cats
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.


Xps fresh and used cats1
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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