Robert A. SCHOONHEYDT Center for Surface Chemistry and Catalysis K.U. Leuven

1. ULTRAVIOLET-VISIBLE-NEAR INFRARED • (UV-VIS-NIR) SPECTROSCOPY • ELECTRON PARAMAGNETIC RESONANCE (EPR) or ELECTRON SPIN RESONANCE (ESR) • OF ZEOLITES Robert A. SCHOONHEYDT Center for Surface Chemistry and Catalysis K.U. Leuven Kasteelpark Arenberg 23, 3001 Leuven Belgium Robert.schoonheydt@biw.kuleuven.ac.be

2. OUTLINE • 1. Principles of UV-VIS-NIR • - physical basis • - methodology • 2. In-situ UV-VIS • 3. Optical and fluorescence microscopies • 4. Principles of EPR • - physical basis • - methodology • 5. In-situ EPR • 6. Pulse EPR • 7. Coordination of transition metal ions (TMI) • 8. Conclusions

3. UV-VIS-NIR

4. * Antibonding Antibonding π* π π* n π* n  *   * Nonbonding π π Bonding  Bonding What do we measure ? Molecules: unsaturated   * and n  * transitions Energy level diagramme

5. Transitions Metal Ions d – d transitions Ligand- to Metal Charge Transfer (LMCT)

6. Transitions Metal Ions d – d transitions Metal - to Ligand Charge Transfer (MLCT) example: [Cr(benzene)2]+

7. x I0 J0 I J + J x I + I J UV - VIS - NIR: Methodology Powdered samples  Diffuse Reflectance Spectroscopy (DRS) Principle

8. Ideal Case: Kubelka – Munck formula scattering intensity from infinitely thick sample scattering intensity from infinitely thick white standard R∞ = K : Kubelka-Munck absorption coefficient S : Kubelka-Munck scattering coefficient

9. Conditions for use of K M-formula • diffuse monochromatic irradiation • isotropic scattering • infinite sample thickness • low concentration of absorbing centers • uniform distribution of absorbing centers • absence of fluorescence

10. UV – VIS – NIR: instrumentation • Every compagny has a UV-VIS-NIR spectrophotometer with • two sources ( Nerst glower, D2 lamp) and two detectors (PbS, PM). • Integration sphere for DRS • White standards: MgO, BaSO4, HALON.

11. hn Gas inlet • Gas outlet IN – SITU UV-VIS-NIR Praying Mantis Optical fibre technology Most sensitive region: VISIBLE  low background  sensitive detection: PM

12. IN – SITU UV-VIS-NIR Examples: d  d (pseudo)tetrahedral Co2+ O  Cr6+ charge transfer (chromate, dichromate) O  Cu2+ bis(µ-oxo)dicopper

13. O O O O - 1 +1 - 1 Al P Al O O O O O O O O O O Microporous crystalline metal-containing Aluminiumphosphates:isomorphous substitution Isomorphous + Co 2 substitution O O O O - 2 +1 - 1 Co P Al O O AlPO - 5 4 AFI

14. CoAPO-5: in situ synthesis Absorbance Wavelength (nm) Synthesis time

15. CoAPO-5 synthesis: spectra at RT

16. Chromate reduction with CO in zeolite Y

17. bis( µ-oxo )dicopper in ZSM-5

18. OPTICAL and FLUORESCENCE MICROSCOPIES

19. Intergrowth structure of ZSM-5 Accessibility?

20. Applications Oligomerization of furfurylalcohol in ZSM-5 and mordenite

21. Applications Oligomerization of styrene in ZSM-5

22. oligomerization of styrene: absorption spectra

23. Decomposition of template molecules in CrAPO-5

24. Decomposition of template molecules and intergrowth structures CrAPO-5 SAPO-34 SAPO-5 ZSM-5

25. ELECTRON PARAMAGNETIC RESONANCE magnetic moment of the unpaired elelctron = dimensionless spin angular momentum vector of the electron S2 = s(s+1) s = ½ SZ =ms ms = 1/2, -1/2 = Borhmagneton g, spectroscopic splitting factor = 2.0023 ħ = h/2π γ = gyromagnetic ratio

26. E ms = 1/2 E = gβB0 ms = - 1/2 B0 ZEEMAN INTERACTION EZ = -µZB0 = gβB0ms ms = ½: 1/2g βB0 ms = -½: -1/2g βB0 Resonance condition: hν = E = gβB0

27. EPR: powder spectra • All possible orientations of the spins • Each orientation has its own resonance condition • Spectra are superpositions of all those individual spectra isotropic axially symmetric orthorhombic

28. EPR: Measurement of g values • measurement at constant frequency and varying magnetic field Band name band range, GHz L 1.5 S 2.6-4 C 4-6 X 8.2-12.4 K 18-26.5 Q 33-50 V 50-75 W 75-100 • g = = 7,145x10-9 ν/B0 to be measured with gaussmeter to be read from microwave bridge • reference: DPPH gr = 2,0036 (diphenylpicrylhydrazine)

29. EPR: METHODOLOGIES Resonance cavities

30. EPR: Spin Hamiltonian • Hyperfine interaction: unpaired electron-nuclear spin: I mI = I, I - 1,…..,- I • each energy level of the electron is split according to mI • selection rule for EPR: ms = 1: mI = 0 • S > ½  more than one unpaired electron: ZERO FIELD SPLITTING • QUADRUPOLAR INTERACTION: nuclear spins with I > 1/2 • SPIN HAMILTONIAN

31. EPR: Quantitative

32. In situ EPR Set-up

33. FeAPO-5 Example: calcination of FeAPO-5

34. PULSE EPR D. Goldfarb, Weizmann Institute, Israel ESEEM: electron spin echo envelope modulation ENDOR: electron nuclear double resonance Examples: 1. Interaction of Cu2+ with Al nuclei in the zeolite lattice 2. Copper –histidine complexes in supercages of zeolite Y.

35. Copper – histidine complexes in supercages of zeolite Y

36. TRANSITION METAL IONS IN ZEOLITES

37. Coordination to lattice oxygens • Characteristics • Low coordination number • Free coordination sites • Low symmetry • Examples: Cu2+, Co2+

38. Cu2+: DRS + EPR ZSM-5 Zeolite A

39. Cu2+: Summary of EPR parameters and d – d transitions

40. Coordination of Co2+ and Cu2+ to sixrings: LF or AOM Fixed oxygens: Cu2+/Co2+ in the center of the six- ring on trigonal axis Cu2+: doubly degenerate ground-state  Jahn-Teller distorsion Co2+: off-axial displacement by 0.078 – 0.104nm

41. Coordination to six-rings in LTA and FAU Cu2+

42. Cu2+:orbital interactions between d(Cu2+) and p(0)

43. Cu2+in ZSM-5: α sites with zero, one and two Al’s

44. Cu2+in ZSM-5: β sites with zero, one and two Al’s

45. Cu2+in ZSM-5: γ sites with zero, one and two Al’s 0 1 2 3 binding energy g-factors -698 2.25 2.06 2.06 -680 2.26 2.07 2.05 -662 2.27 2.07 2.06 4 5 6 -656 2.29 2.07 2.06 -523 2.27 2.06 2.06 -505 2.28 2.08 2.05

46. Cu2+in ZSM-5: δ sites with zero, one and two Al’s

47. ν (cm-1) = 30,000[χopt(0)-χopt(Cu2+)] cm-1/1000 Cu2+in Zeolite: O  Cu2+ charge transfer

48. DRS spectrum of Co2+in Zeolite A

49. DRS spectrum of Co2+in Zeolite Y and its decomposition

50. DRS spectrum of Co2+in LTA and FAU:visible region