Old and New Ideas for VPO? Application to DuPont Catalysts Elisabeth BORDES-RICHARD Laboratoire de Catalyse de Lille E. Bordes-Richard - 2006 CONCORDE-Thessaloniki 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. E. Bordes-Richard - 2006 CONCORDE-Thessaloniki 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 O2 to 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 E. Bordes-Richard - 2006 CONCORDE-Thessaloniki 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 SEM on used cat; EDX: V, P, Si, Fe (LCL) E. Bordes-Richard - 2006 CONCORDE-Thessaloniki 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) precursor with silicic acid (ca. 1Owt%) microspheres ø = 60-100 mm Calcination 400°C Catalyst E. Bordes-Richard - 2006 CONCORDE-Thessaloniki DuPont VPO Catalyst Precursor: VOHPO4•0.5H2O Johnson et al., Torardi et al., 1984 Face-sharing octahedra Layered structure, Catalyst: (VO)2P2O7 (mean oxidation state: V4.0x+) Gorbunova 1978, Sleight et al. 1990 Edge-sharing octahedra Layered structure, Topotactic dehydration, [5] primary particles, Platy primary particles, pseudomorphism Platy rosets as secondary particles rosets as secondary particles Control of VOHPO4•0.5H2O ==> Control of (VO)2P2O7 Oxidation of prec. (air, 400°C) d-VOPO4 [4] 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 (air, 400°C) d-VOPO4 [4] [4] E. Bordes, unpublished results [5] E. Bordes et al., J.Solid State Chem.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) E. Bordes-Richard - 2006 CONCORDE-Thessaloniki CFBR Redox decoupling: optimize the working conditions <==> Same particle alternatively reduced (riser) and oxidized (regenerator) Co-feed O2 C4 MA O2- C4 O2- MA CFBR n-C4 MA 2O2- O2- O O2- O2 2O2- O2- O O2- Oxocapacity: O2- delivery vs. MA prod. E. Bordes and R.M. Contractor, Topics Catal., 3 (1996) 365. E. Bordes-Richard - 2006 CONCORDE-Thessaloniki CFBR (foll.) (slightly) different properties of VPO catalyst P/V ratio Fixed B. Fluidized B. CFBR 1.1 1.1 1.0 Texture Other phases Attrition-resistant a,b-VOPO4 d-VOPO4 "bulky" (VO)2P207 layered (VO)2P207 (100) O2 E. Bordes et al., Catal. Lett. 1999 E. Bordes-Richard - 2006 CONCORDE-Thessaloniki 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.! E. Bordes-Richard - 2006 CONCORDE-Thessaloniki Acknowledgements DuPont, G. Patience L. Gengembre, M. Lefrère, L. Burylo, N. Bouremma: XPS, XRD, SEM-EDX G. Franceschini, A. Thomazic (undergraduate students) E. Bordes-Richard - 2006 CONCORDE-Thessaloniki XRD Identification Precursor: usual pattern of layered VOHPO4.0.5H2O Catalyst 024 200 b-VOPO4 032 Fresh cat: (VO)2P2O7 Used cat: (VO)2P2O7 + b-VOPO4, E. Bordes-Richard - 2006 CONCORDE-Thessaloniki 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. E. Bordes-Richard - 2006 CONCORDE-Thessaloniki 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) b-VOPO4 Fresh cat: (VO)2P2O7 E. Bordes-Richard - 2006 CONCORDE-Thessaloniki Used cat: (VO)2P2O7 + b-VOPO4 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. E. Bordes-Richard - 2006 CONCORDE-Thessaloniki 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 Fresh Used Fresh Used Fresh Used Fresh Used Fresh Used R.T. C2-300 C2-400 C2-500 O2-500 P/V 1,81 1,80 1,79 1,81 1,80 1,80 1,91 1,92 1,80 1,80 O/V corr 6,51 6,44 6,26 6,13 6,33 5,92 6,53 5,98 6,19 6,16 E. Bordes-Richard - 2006 CONCORDE-Thessaloniki V/Si 1.19 0.87 1.16 0.81 1.12 0.81 1.07 0.82 1.14 0.92