Catalyst Characterization

Transcription

1 2 December 2009 page 1 Catalyst Characterization J.W. (Hans) Niemantsverdriet Schuit Institute of Catalysis Eindhoven University of Technology 1 NIOK Course, Schiermonnikoog, December 2009 Catalyst Characterization 1 Introduction 2 Temperature programmed techniques 3 X-ray diffraction 4 EXAFS 5 X-ray photoelectron spectroscopy 6 XANES 7 Ion spectroscopy 8 Electron microscopy 9 Concluding remarks Hans Niemantsverdriet, Schuit Institute of Catalysis

2 2 December 2009 page 2 length and time scales in catalytic processes 10 mm 1 nm shaped catalyst particles catalytic surface 1 m catalyst bed in a reactor catalytically active particles on a support 1 µm microscopic mesoscopic macroscopic Ib Chorkendorff & Hans Niemantsverdriet, Concepts in Modern Catalysis and Kinetics, Wiley-VCH, Weinheim, 2003 Things that Matter in a Supported Catalyst: J. Libuda and H.-J. Freund, Surf. Sci. Rep. 57 (2005) 157

3 2 December 2009 page 3 Aims of Catalyst Characterization Fundamental research: composition & structure of the catalytic surface under reaction conditions in atomic detail Applied research: identification of properties that discriminate between poor and successful catalysts All Characterization Techniques can be derived from: heat ions photons catalyst electrons e.m. field neutrals Additional parameters: Energy Intensity Spatial configuration Time structure Temperature

4 2 December 2009 page 4 Temperature Programmed Techniques TPR TPO TPS TPD TPRS Reduction Oxidation Sulfidation Desorption Reaction Spectroscopy TP-SIMS, TP-IR, etc Paul Weymans TU/e

5 2 December 2009 page 5 Thermodynamic Data Metal Oxide Reduction at 400 C MO n + nh 2 M + n H 2 O o G= G + n RT G = n RT p ln p p ln p H O 2 H 2 H 2 H O 2 p / p H H O 2 2 eq Metal Oxide (p(h 2 O)/p(H 2 )) eq Ti TiO 2 TiO V V 2O 5 VO Fe Fe 2 O 3 FeO Co CoO 50 Ni NiO 500 Cu CuO Cu 2O Mo MoO 3 MoO Rh RhO Pd PdO Ag Ag 2O J.R. Anderson, Structure of Metallic Catalysts, Academic Press, London, TPR: Effect of Particle Size and Support Interaction supported nanoparticles of copper oxide unsupported, large, copper oxide particles unsupported NiO supported NiO nanoparticles S.D. Robertson, B.D. McNicol, J.H. de Baas, S.C. Kloet, and J.W. Jenkins, J. Catal. 37 (1975) 424

6 2 December 2009 page 6 TPR: Effect of Heating Rate - CrO x / Al 2 O 3 heating rate β: β = 17 K/min β = 11 K/min β = 6 K/min J.M. Kanervo and A.O.I. Krause, J. Phys. Chem. B 105 (2001) 9778 TPR of bimetallic catalysts TPR fresh catalyst TPO reduced catalyst TPR oxidized catalyst Rh/SiO 2 H 2 /M= Rh/SiO 2 O 2 /M =0.73 Rh/SiO 2 H 2 /M=1.52 H 2 uptake Fe/SiO 2 H 2 /M =0.62 O 2 uptake 0.05 Fe/SiO 2 O 2 /M =0.24 H 2 uptake Fe/SiO 2 H 2 /M= 0.47 FeRh/SiO 2 H 2 /M = FeRh/SiO 2 O 2 /M =0.75 FeRh/SiO 2 H 2 /M= Temperature ( C) H.F.J. van 't Blik and J.W. Niemantsverdriet, Appl. Catal. 10 (1984) 155.

7 2 December 2009 page 7 Temperature Programmed Sulfidation TPS of MoO 3 /Al 2 O 3 MoO3+ H 2 S MoO2 S + H 2 O Partial pressure (a.u) H 2 H 2 S H 2 O MoO2 S MoO2+ S S H H MoO2+2 H 2 S MoS 2+2 H 2 O S Temperature (K) P. Arnoldy, J.A.M. van den Heijkant, G.D. de Bok and J.A. Moulijn, J. Catal. 92 (1985) 35. XRD: X-ray Diffraction X-rays Bragg s Law d θ d sinθ nλ = 2 d sinθ 2 θ

8 2 December 2009 page 8 XRD: X-ray Diffraction Features of Diffraction (Electron, X-ray, or Neutron) For a known structure, pattern can be calculated exactly. Symmetry of the diffraction pattern given by symmetry of the lattice. Intensities of spots determined by basis of atoms at each lattice point. Sharpness and shape of spots determined by perfection of crystal. Liquids, glasses, and other disordered materials produce broad fuzzy rings instead of sharp spots. Defects and disorder in crystals also result in diffuse scattering. Paul A. Heiney Physics Department University of Pennsylvania XRD: X-ray Diffraction X-ray sources: Mo Kα 0.71 Å Cu Kα 1.54 Å Co Kα 1.79 Å Fe Kα 1.94 Å Cr Kα 2.29 Å Problems with Traditional X-ray Generators X-rays emitted isotropically, so you only utilize a small fraction of the radiation. Radiation only intense at well-defined wavelength. If you turn up the current, the anode melts - water cooling. rotate the anode so that the electron beam travels over the surface. Paul A. Heiney Physics Department University of Pennsylvania

9 2 December 2009 page 9 XRD: linewidth and coherence length G. Fagherazzi, A. Benedetti, A. Martorana, S. Giuliano, D. Duca and G. Deganello, Catal. Lett. 6 (1990) 263. XRD: Identification of Phases XRD Rh-Mn/SiO 2 calcined XRD Rh-Mn/SiO 2 reduced MnRh 2 O 4 Mn 2 O 3 Rh 2 O 3 β-mno 2 unidentified MnRh 2 O 4 Rh 2 O 3 Rh 100 C 900 C 200 C 700 C 300 C 500 C 400 C θ θ by comparing to standard diffraction data (ASTM) K. Kunimori, T. Wakasugi, Z. Hu, H. Oyanagi, M. Imal, H. Asano and T. Uchijima, Catal. Lett. 7 (1990) 337.

10 2 December 2009 page 10 In situ XRD: Reduction of CuO by CO X. Wang, J.C. Hanson, A.I. Frenkel, J.-Y. Kim, and J.A. Rodriguez, J. Phys. Chem. B, 108 (2004), XRD: Phase identification Particle size estimate from line broadening In situ studies Careful:only crystalline phases detected

11 2 December 2009 page 11 XAFS: EXAFS & XANES E k = hν - E b hν hν free atom atoms in a lattice absorption absorption pre edge E b XANES E b edge hν EXAFS hν Simulated EXAFS of Cu 2 Dimer and Cu 2 O Trimer χ(k) 0.3 nm 0.2 nm 0.3 nm F(k) F(k)/k χ(k) k k χ (k ) = A j (k) sin (2 k r j + φ (k)) j j A j (k ) = N j e -2 r / λ (k ) j k r 2 j S 2 o (k) F j (k) e 2-2 k σ 2 j

12 2 December 2009 page 12 EXAFS: χ (k ) = A j (k) sin (2 k r j + φ j (k)) j Amplitude: A j (k ) = N j e -2 r k j / λ (k r 2 j ) S 2 o (k) F j (k) e - 2 k 2 σ 2 j k = 2π h 2 m e E k = 2π h 2 me (hν - Eb ) θ n(r) = 1 2π k k max min k n χ(k)e 2 ikr dk EXAFS of Rhodium Compounds: Chemical Information J.B.A.D. van Zon, D.C. Koningsberger, H.F.J. van 't Blik and D.E. Sayers, J. Chem. Phys. 82 (1985) EXAFS FourierTransform 1 st shell EXAFS Rh metal Rh 2 O RhCl k (Å -1 ) r (Å) k (Å -1 )

13 2 December 2009 page 13 B.S. Clausen, Catal. Today, 39 (1998) 293 Quick EXAFS / XRD Energy (ev) Cu Reduction temperature (K) 1.0 Cu /ZnO/Al 2 O 3 o QEXAFS 9040 ev x XRD Cu(111) reduction θ ( ) Reduction temperature (K) EXAFS: Highly precise structure information Also on amorphous phases In situ studies Synchrotron needed Complicated analysis

14 2 December 2009 page 14 Electron Mean Free Path in Metals 10 Au Mean Free Path (nm) Al Au Au Ag Ag Ag Au Au Ag Be Be Ag Ni Be P Ag Fe Ag W Mo Be Ag C Be Mo Au Ag Ag Au C C Be Mo W Electron Kinetic Energy (ev) Electrons (and ions): surface sensitive G.A. Somorjai, Chemistry in Two Dimensions, Surfaces, Cornell University Press, Ithaca, X-ray Photoelectron Spectroscopy (XPS) photoelectron E k ϕ vacuum level Fermi level E b = hv - E k element specific sensitive to X-ray hν E b oxidation state electronegativity surface sensitive Photo emission

15 2 December 2009 page 15 XPS: Element Specific Photoemission Intensity (a.u.) Rh /Al 2 O 3, impregnated XPS Binding Energy (ev) If Auger peaks interfere with XPS peaks: switch to different X-ray source Cobalt XPS: ev ev

16 2 December 2009 page 16 XPS peak nomenclature l = s p d f n = 0, 1, 2, 3, 4, 5 j = l ± 1/2 2j+1 electrons XPS wide scan of platinum X-ray source hv = ev Core levels Auger peaks valence band E b = hv - E k

17 2 December 2009 page 17 XPS: Oxidation State E i b = k q i + j q r j ij + E ref b Charge potential model (Siegbahn) Carbon XPS C XPS Spectrum 1s ca 285 ev 2s valence band 2p valence band Auger KVV peaks in XPS: Mg Kα 990 ev Al Kα 1223 ev

18 2 December 2009 page 18 X-ray Photoelectron Spectroscopy (XPS) binding energy reflects electronegativity of neighbours 1,1-dihydro perfluoro heptyl methacrylate (FHMA): CH 2 CF 3 (CF 2 ) 5 CH 2 O C C CH 3 O C 1s XPS Spectrum: Binding energy [ev] R.D. van de Grampel, W. Ming, A. Gildenpfennig, W. van Gennip, J. Laven, J.W. Niemantsverdriet, H.H. Brongersma, G. de With, R. van der Linde, Langmuir 20 (2004) XPS: Oxidation State XPS Pt 4f Platinum 4f 4f 7/2 5/2 Pt 0 foil 4f 5/2 4f 7/2 Pt 2+ 4f 5/2 4f 7/2 Pt Binding Energy (ev) J.C. Muijsers, J.W. Niemantsverdriet, I.C.M. Wehman, D.M. Grove and G. van Koten, Inorg. Chem. 31 (1992)

19 2 December 2009 page 19 NIOK Course Schiermonnikoog - Catalyst Characterization - J.W. (Hans) Niemantsverdriet Shake Up particularly in XPS of ionic materials photoelectron E k E k X-ray hν E b shake up E b Photo emission Photo emission with shake up E b = hv E k appears higher Shake up structures: diagnostic value Shake up is prominent in XPS of oxides of Fe, Co, Ni, Cu

20 2 December 2009 page 20 XPS of Catalysts: Charging homogeneous or differential XPS Mo/SiO 2 real catalyst Correct peaks via standard C 1s at 284 ev catalyst support Si 2p at ev evaporated Au deposit or conducting model catalyst Mo SiO 2 Si charge shift Prevent charging by using a flood gun of low energy electrons Binding Energy (ev) XPS: Particle Size Information Low dispersion High dispersion particles support I particle /I support small I particle /I support large

21 2 December 2009 page 21 XPS: Dispersion Si 2s XPS ZrO 2 / SiO 2 Zr 3d 8 wt% (ex nitrate) 16 wt% (ex nitrate) 24 wt% (ex nitrate) 16 wt% (ex ethoxide) Binding Energy (ev) A.C.Q.M. Meijers, A.M. de Jong, L.M.P. van Gruijthuijsen and J.W. Niemantsverdriet, Appl. Catal. 70 (1991) 53. XPS photo electron X-ray hν E k ϕ E b vacuum level Fermi level element specific sensitive to oxidation state Photo emission E b = hv - E k known measured electronegativity surface sensitive dispersion charge correction easy vacuum required

22 2 December 2009 page 22 XAFS: EXAFS & XANES E k = hν - E b hν hν free atom atoms in a lattice absorption absorption pre edge E b XANES E b edge hν EXAFS hν Simon Bare -UOP

23 2 December 2009 page 23 Simon Bare -UOP Simon Bare -UOP

24 2 December 2009 page 24 XANES of Cobalt Phases XANES: /Al 2 O 3 phase identification oxidation state 53% Co 0 80% Co 0 in situ measurement 85% 88% at synchrotron LURE, ORSAY 89% LURE, ORSAY Abdool Saib, Armando Borgna quantitation straightforward XANES of Cobalt Fischer-Tropsch Catalyst wax coated/protected catalysts from FT demonstration reactor /Al 2 O 3 53% Co 0 80% Co 0 85% 88% 89% A.M. Saib, A. Borgna, J. van de Loosdrecht, P.J. van Berge, J.W. Niemantsverdriet Appl. Catal. A: General 312 (2006) 12

25 2 December 2009 page 25 XANES: Oxidation state analysis Some structure information In situ!!! Analysis convenient (by fingerprinting) Very powerful in situ method but needs a synchrotron Ion Spectroscopy SIMS secondary ion mass spectrometry SNMS secondary neutral mass spectrometry ISS RBS LEIS ion scattering spectroscopy Rutherford backscattering spectroscopy low energy ion spectroscopy

26 2 December 2009 page 26 Secondary Ion Mass Spectrometry Primary ion Secondary neutrals and ions kev 1-20 ev - Collision cascade SIMS Fe-Sb-Oxide Ammoxidation Catalyst Si SiO Fe In (sample holder) Sb Herman Borg & K Cu FeO Mo SbO Pieter Gunter, TU/e 1990 H Na 25x 250x Atomic Mass Units (amu) SIMS reveals all elements (also trace amounts)

27 2 December 2009 page 27 NIOK Course Schiermonnikoog - Catalyst Characterization - J.W. (Hans) Niemantsverdriet SIMS intensity: ± ± s p I = I Y R c surf T with I ± s I p Y R ± c surf T intensity of secondary ions (=rate in counts per sec) flux of primary ions sputter yield (number of atoms ejected per incident ion) probability that particle leaves as positive or negative ion fractional concentration of the element in the surface transmission of the mass spectrometer, (typically 10-3 for quadrupole; 10-1 for time-of-flight) SIMS: Information in Relative Intensities atomic mass units Zr(OEt) 4 ZrO 2 Relative Intensities Zr ZrO ZrO2 reflect coordination around Zr: A.C.Q.M. Meijers, A.M. de Jong, L.M.P. van Gruijthuijsen, J.W. Niemantsverdriet, Appl. Catal. 70 (1991) 53

28 2 December 2009 page 28 SIMS: Information in Relative Intensities atomic mass units Zr(OEt) 4 ZrO 2 A.C.Q.M. Meijers, A.M. de Jong, L.M.P. van Gruijthuijsen, J.W. Niemantsverdriet, Appl. Catal. 70 (1991) 53 Ion Scattering Spectroscopy θ K M = E E f i ( = M 2 - M 2 ion 2 1/2 sin θ ) + M ion cosθ M + M ion E f = Mass Spectrum!! 2

29 2 December 2009 page 29 Low Energy Ion Scattering Intensity (10 3 counts)10 sputtered ions O F Al LEIS Cu/Al 2 O 3 4 He, 3 kev Cu J P Jacobs and H H Brongersma, TU/e E f (ev) Ion Spectroscopy SIMS: detection of trace amounts molecular information via clusters quantitation difficult LEIS extreme surface sensitivity reasonably quantitative

30 2 December 2009 page 30 TEM / SEM Morphological information Image analysis particle size, shape, etc Structural information Diffraction crystalline phases Chemical information Energy Dispersive X-ray analysis (EDX): elements (heavier elements work better) (also called Electron Probe Micro Analysis -EPMA) Electron energy loss spectroscopy: elements (particularly light ones) Diffraction: phases reveal composition as well TEM Rh/SiO 2 3 nm 10 nm A.K. Datye and N.J. Long, Ultramicroscopy 25 (1988) 203.

31 2 December 2009 page 31 NIOK Course Schiermonnikoog - Catalyst Characterization - J.W. (Hans) Niemantsverdriet TEM & Diffraction TEM image Fourier Transform (diffraction pattern) model and simulation S. Bernal et al. Catal. Today 77 (2003) 385. STEM images Au/TiO 2 catalyst After 1 h of 1% CO, 21% O 2, 78% Ar at 400 C (left) and 500 C (right) N. Lopez, J.K. Nørskov, T.V.W. Janssens, A. Carlsson, A. Puig- Molina, B.S. Clausen and J.-D. Grunwaldt, J. Catal. 225 (2004) 86

32 2 December 2009 page 32 Scanning Electron Microscopy electron beam X-rays bulk specimen Beam is rastered electron beam Secondary electron detector thin film specimen X-rays SEM: Scanning Electron Microscopy Contrast: -Morphology -Work function Polyethylene around a Cr/SiO 2 catalyst

33 2 December 2009 page 33 Contrast: Contrast in SEM -Morphology: emission peaked towards the normal -Work function: high emission for low work function Generation of X-rays in an electron microscope X-rays are element specific Core hole generated by the electron beam

34 2 December 2009 page 34 Energy Dispersive X-ray Analysis electron beam X-rays bulk specimen electron beam X-ray detector X-rays thin film specimen Energy Dispersive X-ray Analysis electron beam bulk specimen X-rays Bulk may contribute and distort information! electron beam X-rays Better: thin film samples thin film specimen

35 2 December 2009 page 35 Catalyst on a copper sample holder What sort of catalyst is this? Recent Trends in Characterisation problem-oriented approach with a combination of techniques in situ characterisation bridging the gap strategies molecular detail local probes model systems single crystals models of supported catalysts organometallic analogs experiment + theory

36 2 December 2009 page 36 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 2002 and Oct 2006 Total Number of Articles: percentage In situ or under vacuum? real catalyst single crystal reaction conditions XRD, TP techniques Infrared and Raman EXAFS, XANES, AFM Mossbauer, ESR, NMR Infrared TP techniques STM,AFM vacuum XPS, SIMS, SNMS LEIS, RBS, TEM, SEM all surface science techniques

37 2 December 2009 page 37 Catalyst Characterization What do we want to know about a supported catalyst? Composition XPS, XANES, XRD ICP, AAS Surface Composition LEIS, XPS, SIMS Particle size Electron Microscopy H2 chemisorption XRD line broadening Surface Area Total: BET Metal: H2 or CO chemisorption Pore size distribution: Hg porosimetry Morphology Particles: TEM Overall: SEM Adsorbed Gases FTIR, DRIFTS, TPD Structure XRD XPS, EXAFS,TEM Degree of Reduction TPR, XPS, XANES Concept, to be completed