Characterization. of solid catalysts. 7. X-ray Absorption. XANES and EXAFS. Prof dr J W (Hans) Niemantsverdriet.

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1 Characterization of solid catalysts 7. X-ray Absorption XANES and EXAFS Prof dr J W (Hans) Niemantsverdriet Schuit Institute of Catalysis J.W. Niemantsverdriet, TU/e, Eindhoven, The Netherlands

2 How often are techniques used XRD Adsorption XPS TP Techniques Infrared TEM SEM UV-vis NMR Raman ESR EXAFS XANES EDX Mossbauer Calorimetry ISS / LEIS Neutron Scattering SIMS <0.1 <0.1 <0.1 Journals: Applied Catalysis A & B Catalysis Letters Journal of Catalysis Jan 00 and Oct 006 Total Number of Articles: 811 J.W. Niemantsverdriet, TU/e, Eindhoven, The Netherlands percentage

3 X-ray absorption in a free atom absorption edge binding energy lie in XPS

4 X-ray absorption by atoms in solids XANES: X-ray absorption near-edge structure EXAFS: Extended X-ray absorption fine structure

5 Synchrotron beamline for XAFS and XRD synchrotron XRD position sensitive X-ray detector slit slit double crystal monochromator in situ cell ionization chamber I 0 Courtesy Dr B S Clausen ionization chamber I XAFS

6 XANES of Cobalt Phases XANES: /Al O 3 phase identification oxidation state 53% Co 0 in situ measurement 80% Co 0 85% 88% at synchrotron LURE, ORSAY 89% LURE, ORSAY quantitation straightforward Abdool Saib, Armando Borgna

7 XANES of Cobalt Fischer-Tropsch Catalyst wax coated/protected catalysts from FT demonstration reactor A.M. Saib, A. Borgna, J. van de Loosdrecht, P.J. van Berge, J.W. Niemantsverdriet Appl. Catal. A: General 31 (006) 1 /Al O 3 53% Co 0 80% Co 0 85% 88% 89%

8 From: Dr Matt Newville, Consortium for Advanced Radiation Sources, University of Chicago

9 From: Dr Matt Newville, Consortium for Advanced Radiation Sources, University of Chicago

10 Dr Simon Bare -UOP

11 Dr Simon Bare -UOP

12 XANES: Oxidation state analysis Some structure information In situ!!! Analysis convenient (by fingerprinting) Very powerful in situ method but needs a synchrotron

13 EXAFS Extended X-ray Absorption Fine Structure

14 X-ray absorption by atoms in solids XANES: X-ray absorption near-edge structure EXAFS: Extended X-ray absorption fine structure

15 Information from EXAFS EXAFS: ( ) = A () sin ( r + ()) = h m e E = h interatomic distances m e (h - E b )

16 Information from EXAFS EXAFS: ( ) = A () sin ( r + ()) = h m e E interatomic distances = me (h - Eb ) h Amplitude: A ( ) = N e coordination numbers - r / ( r ) S o () F () e bacscattering factor chemical sensitivity -

17 A ( ) = N e - r / ( r ) S o () F () e - The bacscattering factor F() extends to higher energy -values) for heavier elements contains chemical information of the neighbours

18 Information from EXAFS EXAFS: ( ) = A () sin ( r + ()) = h m e E interatomic distances = me (h - Eb ) h Amplitude: A ( ) = N e coordination numbers - r / ( r ) S o () F () e bacscattering factor chemical sensitivity - Fourier Transform: n(r) = 1 max min n () e ir d radial distribution function

19 () Simulated EXAFS of Cu Dimer and Cu O Trimer () 0.3 nm 0. nm 0.3 nm F() F()/ ( ) = A () sin ( r + ()) A ( ) = N e - r / ( r ) S o () F () e -

20 EXAFS of Rhodium Compounds: Chemical Information J.B.A.D. van Zon, D.C. Koningsberger, H.F.J. van 't Bli and D.E. Sayers, J. Chem. Phys. 8 (1985) 574. EXAFS Fourier Transform 1 st shell EXAFS Rh metal Rh O RhCl (Å -1 ) r (Å) 1 4 (Å -1 )

21 B.S. Clausen, Catal. Today, 39 (1998) 93 Quic EXAFS / XRD Cu /ZnO/Al O 3 reduction Energy (ev) Cu o QEXAFS 9040 ev x XRD Cu(111) ( ) Reduction temperature (K)

22 EXAFS: Highly precise structure information Also on amorphous phases In situ studies Synchrotron needed Complicated analysis

23 Courtesy: Matt Newville, Consortium for Advanced Radiation Sources, University of Chicago

24 Comparison of X-ray diffraction and XAFS XRD: information on crystalline structures Phase identification Particle size estimate from line broadening In situ studies Careful: only crystalline phases detected EXAFS: local structure information Highly precise structure information Also on amorphous phases In situ studies Synchrotron needed Complicated analysis XANES: chemical state information Oxidation state analysis Some structure information In situ!!! Analysis convenient (by fingerprinting)

25 Download the handout for this lecture from Read more about XRD, XANES and EXAFS in Chapter 6 of Spectroscopy in Catalysis: An Introduction, Third Edition J. W. Niemantsverdriet Copyright 007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim ISBN: gives many examples and references to the literature J.W. Niemantsverdriet, TU/e, Eindhoven, The Netherlands Version 000