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In-situ Characterisation of vanadium-phosphorus-oxide (VPO) catalysts for n-butane oxidation by applying X-ray absorption spectroscopy M. Hävecker, R.

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Presentation on theme: "In-situ Characterisation of vanadium-phosphorus-oxide (VPO) catalysts for n-butane oxidation by applying X-ray absorption spectroscopy M. Hävecker, R."— Presentation transcript:

1 In-situ Characterisation of vanadium-phosphorus-oxide (VPO) catalysts for n-butane oxidation by applying X-ray absorption spectroscopy M. Hävecker, R. W. Mayer, A. Knop-Gericke, H. Bluhm, R. Schlögl Electronic Structure, Dept. AC, Fritz-Haber-Institut (MPG), Berlin, Germany DFG Schwerpunktprogramm Workshop, Blankensee, 25.-26. April 2002

2 M. Hävecker, Electronic Structure, Dept. AC, Fritz-Haber-Institut (MPG), Berlin, Germany n-Butane Oxidation to MA by Vanadium Phosphorus Catalysts +3,5 O 2 +4 H 2 O 1,5 Vol%air C 4 H 10 +6,5 O 2 4 CO 2 +5 H 2 O C 4 H 10 +4,5 O 2 4 CO+5 H 2 O VPO 400 °C, 1 bar O O O Maleic Anhydride (MA)

3 M. Hävecker, Electronic Structure, Dept. AC, Fritz-Haber-Institut (MPG), Berlin, Germany Experimental Technique N ear E dge X -ray A bsorption F ine S tructure X-ray absorption spectroscopy local process related to site- and symmetry selected DOS A. Knop-Gericke et al., Nucl. Instr. Meth. A 406 (1998) 311 M. Hävecker et al., Angew. Chem. 110 (1998) 2049; Int. Ed. 37 (1998) 206

4 The Light Source: Synchrotron Radiation M. Hävecker, Electronic Structure, Dept. AC, Fritz-Haber-Institut (MPG), Berlin, Germany Support for dynamic surface concept Comparing VPO catalysts of different catalytic performance Changes of NEXAFS under n- butane oxidation conditions BerlinerElektronenspeicherringgesell- schaft für Synchrotronstrahlung (Photographs: Luftbild u. Pressefoto R.Grahn)

5 M. Hävecker, Electronic Structure, Dept. AC, Fritz-Haber-Institut (MPG), Berlin, Germany V L- and O K-absorption edge VPO V2O5V2O5 V L-edges O K-edge V L 3 V L 2 O-V O-P V L 3

6 M. Hävecker, Electronic Structure, Dept. AC, Fritz-Haber-Institut (MPG), Berlin, Germany The VPO V L 3 -NEXAFS V1 V2 V3 V5 V4 V6 V7 Analysis of spectral shape by unconstrained least squares fit M. Abbate et al., J. Electron Spectrosc. Rel. Phenom., 62 (1993) 185 M. Hävecker et al., J. Electron Spectrosc. Rel. Phenom., in press V valence Details of the local chemical bonding Local geometric structure

7 M. Hävecker, Electronic Structure, Dept. AC, Fritz-Haber-Institut (MPG), Berlin, Germany Catalytic Activity Product Analysis by Online Proton Transfer Reaction Mass Spectrometry (PTR-MS) I(m/e=99) : Maleic Anhydride (MA) Desorption Peak const. MA Yield flow of 1.2 vol % C 4 H 10 / 20 vol % O 2 / 78.8 % He P tot = 2 mbar RT to 400 °C

8 M. Hävecker, Electronic Structure, Dept. AC, Fritz-Haber-Institut (MPG), Berlin, Germany Spectrum Number Changes in NEXAFS while heating PTR-MS Response MA Decrease while active Relative spectral Intensity of V 5 at V L 3 -edge V5V5

9 M. Hävecker, Electronic Structure, Dept. AC, Fritz-Haber-Institut (MPG), Berlin, Germany PTR-MS Response MA Shift to lower Energy Spectrum Number Energy Position of V 5 at V L 3 -edge Changes in NEXAFS while heating

10 M. Hävecker, Electronic Structure, Dept. AC, Fritz-Haber-Institut (MPG), Berlin, Germany Changes in NEXAFS: Relative spectral Intensity rel. Intensity of V 5 heating: RT  400°C cooling: 400°C  RT before first heating cycle =! 1 norm. Intensity V5V5

11 M. Hävecker, Electronic Structure, Dept. AC, Fritz-Haber-Institut (MPG), Berlin, Germany Changes in NEXAFS: Resonance Position rel. Position of V 5 before first heating cycle =! 0 heating: RT  400°C cooling: 400°C  RT rel. Position (meV)

12 M. Hävecker, Electronic Structure, Dept. AC, Fritz-Haber-Institut (MPG), Berlin, Germany Changes in NEXAFS: Relative spectral Intensity rel. Intensity of V 6 before first heating cycle =! 1 heating: RT  400°C cooling: 400°C  RT norm. Intensity V6V6

13 M. Hävecker, Electronic Structure, Dept. AC, Fritz-Haber-Institut (MPG), Berlin, Germany Changes in NEXAFS: Resonance Position rel. Position of V 6 before first heating cycle =! 0 heating: RT  400°C cooling: 400°C  RT rel. Position (meV)

14 M. Hävecker, Electronic Structure, Dept. AC, Fritz-Haber-Institut (MPG), Berlin, Germany Comparison: Catalysts of different performance Investigation of 2 catalysts of different intrinsic catalytic activity higher catalytic activity Y MA (CAT62) = 1.5 x Y MA (CAT63) J. A. Lopez Sanchez et al., to be published

15 M. Hävecker, Electronic Structure, Dept. AC, Fritz-Haber-Institut (MPG), Berlin, Germany rel. Intensity of V 5 before first heating cycle =! 1 Comparison: Catalysts of different performance heat.: RT  400°C cool.: 400°C  RT higher activity norm. Intensity CAT62: high activity CAT63: low activity

16 M. Hävecker, Electronic Structure, Dept. AC, Fritz-Haber-Institut (MPG), Berlin, Germany rel. Intensity of V 6 before first heating cycle =! 1 Comparison: Catalysts of different performance higher activity norm. Intensity heat.: RT  400°C cool.: 400°C  RT CAT62: high activity CAT63: low activity

17 M. Hävecker, Electronic Structure, Dept. AC, Fritz-Haber-Institut (MPG), Berlin, Germany rel. Position of V 5 before first heating cycle =! 0 Comparison: Catalysts of different performance higher activity rel. Position (meV) heat.: RT  400°C cool.: 400°C  RT CAT62: high activity CAT63: low activity

18 M. Hävecker, Electronic Structure, Dept. AC, Fritz-Haber-Institut (MPG), Berlin, Germany Comparison: Catalysts of different performance rel. P osition of V 6 before first heating cycle =! 0 higher activity rel. Position (meV) heat.: RT  400°C cool.: 400°C  RT CAT62: high activity CAT63: low activity

19 M. Hävecker, Electronic Structure, Dept. AC, Fritz-Haber-Institut (MPG), Berlin, Germany Summary NEXAFS changes, at least partially reversible under n-butane oxidation conditions (resonance intensity, resonance position) Observation of dynamic rearrangements (electronic and/or geometric structure) of VPO catalyst under n-butane oxidation conditions in line with: N.-Y. Topsøe et al., Cat. Lett. 76 (2001) 11 (vanadia DeNOx catalysts) Support for dynamic surface concept J.- C. Volta., Catal. Today, 32 (1996) 29 Do structural rearrangements determine the catalytic activity? ? ?

20 M. Hävecker, Electronic Structure, Dept. AC, Fritz-Haber-Institut (MPG), Berlin, Germany Thanks ! The University of Wales: G. J. Hutchings J. A. Lopez-Sanchez The University of Wales: G. J. Hutchings J. A. Lopez-Sanchez BESSY staff FHI Evgueni Kleimenov Detre Teschner FHI Evgueni Kleimenov Detre Teschner


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