1. IC T IC-1/35 Lecture-5 07-10-2004 Characterzation of Catalysts Investigate: Structure/morphology Surface area Number of active sites Pore distributions Nature of active site Overall reactivity Turn over frequency (TOF) Selectivity Stability Heat and mass transport ?

2. IC T IC-2/35 Lecture-5 07-10-2004 The Surface Science Approach Simpler system - Detailed studies Fundamental insight Input to catalyst design The structure gap The pressure gap The materials gap Single crystal surfaces as model catalysts.

3. IC T IC-3/35 Lecture-5 07-10-2004 Catalysts are complex Nano-materials

4. IC T IC-4/35 Lecture-5 07-10-2004 Most often used methods

5. IC T IC-5/35 Lecture-5 07-10-2004 X-Ray Diffraction (XRD) Bragg ´s Law catalyst X-rays in X-rays out Can be used in situ Gives information on phases and sizes of particles if big enough.

6. IC T IC-6/35 Lecture-5 07-10-2004 X-Ray Diffraction (XRD) Position reveals crystalline structure Width of peaks reveals particle size 4.5 Å 2.5 Å

7. IC T IC-7/35 Lecture-5 07-10-2004 X-ray Photoelectron Spectroscopy (XPS) E kin =h  B -  catalyst X-rays Photo-electrons Can be not used in situ as it require vacuum Gives information on elementary coposition and chemical state

8. IC T IC-8/35 Lecture-5 07-10-2004 Decays following creation of core hole Photoelectron: E kin =h – E b -  X-ray emission (Electron dispersive x-ray emission - EDX): (h ’)=E b(K) -E b(L) K L Auger electron emission: E kin =E b(K) -E b(L1) -E b(L2) K L After ~10 -14 s

9. IC T IC-9/35 Lecture-5 07-10-2004 Surface Sensitive Electrons traveling though a solid has a short mean free path I(z)=I 0 exp(-z/ )

10. IC T IC-10/35 Lecture-5 07-10-2004 X-ray Photoelectron Spectroscopy (XPS) Notice how the E B is influenced by chemical environnement

11. IC T IC-11/35 Lecture-5 07-10-2004 X-ray Photoelectron Spectroscopy (XPS) On combustion catalyst the loading of Pt may be so small that it cannot be detected by XPS (0.1% and 2-5 nm particles).

12. IC T IC-12/35 Lecture-5 07-10-2004 Extended X-Ray Absorption Fine Structure (EXAFS) catalyst Measure adsorbtion An in situ method Gives information on local atomic distances and coordination number

13. IC T IC-13/35 Lecture-5 07-10-2004 Extended X-Ray Absorption Fine Structure (EXAFS)

14. IC T IC-14/35 Lecture-5 07-10-2004 Extended X-Ray Absorption Fine Structure (EXAFS)

15. IC T IC-15/35 Lecture-5 07-10-2004 Electron Microscopy Does not work in situ Gives information on partiles size, shape, composition.

16. IC T IC-16/35 Lecture-5 07-10-2004 TEM images of Cu on ZnO (a model methanol catalyst).

17. IC T IC-17/35 Lecture-5 07-10-2004 Ni Graphite ~1000 Å Environnemental EM from Haldor Topsøe A/S

18. IC T IC-18/35 Lecture-5 07-10-2004 Mössbauer spectroscopy An in situ method Rather specialized method since it works only on Fe, Sm,.. h =14.4 keV  E=10 -9 eV

19. IC T IC-19/35 Lecture-5 07-10-2004 Mössbauer spectroscopy example Reveals oxidation state and chemical sourroundings of particular Fe and Mo catalysts

20. IC T IC-20/35 Lecture-5 07-10-2004 Ion spectroscopy: SIMS catalyst Ions in Ions out SIMS is not an in situ method Is very sensitive for some elements on the ppm level

21. IC T IC-21/35 Lecture-5 07-10-2004 Ion spectroscopy: LEIS catalyst Ions in Ions out Very surface sensitive Why a shoulder?

22. IC T IC-22/35 Lecture-5 07-10-2004 Temperature programmed reduction, oxidation and sulfidation

23. IC T IC-23/35 Lecture-5 07-10-2004 Temperature programmed reduction, oxidation and sulfidation Sulfidation in a H 2 S/H 2 mixture

24. IC T IC-24/35 Lecture-5 07-10-2004 Infrared spectroscopy catalyst IR in IR out IR through An in situ method

25. IC T IC-25/35 Lecture-5 07-10-2004 Infrared spectroscopy IR is used for identifying intermediates Active sites by adsorption of probe molecules like NO, CO,.. Line position may reveal bonding geometry and bonding strength Surface Science metod is HREELS High Reflection Electron Energy Loss Spectroscopy - photons replaced by electrons

26. IC T IC-26/35 Lecture-5 07-10-2004 A Surface Science Approach to Heterogeneous Catalysis N 2 +Fe, Ru CH 3 OH Cu Natural Gas H2H2 CH 4 +H 2 O CO + 3H 2 +(CO 2 ) NH 3 Ni

27. IC T IC-27/35 Lecture-5 07-10-2004 Low Electron Energy Diffraction (LEED) Requires well-defined surfaces under UHV

28. IC T IC-28/35 Lecture-5 07-10-2004 LEED picture Reconstruction of a Fe(111) surface into a 5x5 N-Fe(111) surface

29. IC T IC-29/35 Lecture-5 07-10-2004 LEED a1a1 a2a2 (-1,1) (1,-1) (0,0) (-1,0) (-1,-1) (0,-1) (0,1) (1,1) (1,0) a2*a2* a1*a1* Diffracted beamsScreen Primary beam Crystal

30. IC T IC-30/35 Lecture-5 07-10-2004 The Scanning Probe Methods Requires well-defined surfaces. For STM they must also be conducting

31. IC T IC-31/35 Lecture-5 07-10-2004 Scanning tunneling microscopy (STM) L. P. Nielsen University of Århus (80Åx80Å) Length scales ”Seeing” atoms Electron tunneling Hardware realisation Applications Basic research

32. IC T IC-32/35 Lecture-5 07-10-2004 Crystallites and STM-tip SEM image 35 micrometer A. Emundts und H.P. Bonzel A sharp tip

33. IC T IC-33/35 Lecture-5 07-10-2004 STM Au/Ni(111) 0.02ML Au 0.8 Ml Au Let you sometime, but not always, see the atoms

34. IC T IC-34/35 Lecture-5 07-10-2004 Pt diffusion on Pt(110)

35. IC T IC-35/35 Lecture-5 07-10-2004 STM Model Catalyst MoS 2 on Au(111) Sulfur removed by atomic hydrogen

36. IC T IC-36/35 Lecture-5 07-10-2004 CO/Pt(111) ”CO-man” Fe/Cu(111) Kanji ”atom” Manipulating atoms 5 nm Scanned at very low temperatures http://www.almaden.ibm.com/vis/stm/gallery.html

37. IC T IC-37/35 Lecture-5 07-10-2004 Quantum Corrals Fe/Cu(111) http://www.almaden.ibm.com/vis/stm/gallery.html