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Festkörper-NMR-Untersuchungen der Struktur und Dynamik in anorganischen Materialien Dieter Freude Abteilung Grenzflächenphysik, Universität Leipzig, www.grenzflaechenphysik.de.

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Präsentation zum Thema: "Festkörper-NMR-Untersuchungen der Struktur und Dynamik in anorganischen Materialien Dieter Freude Abteilung Grenzflächenphysik, Universität Leipzig, www.grenzflaechenphysik.de."—  Präsentation transkript:

1 Festkörper-NMR-Untersuchungen der Struktur und Dynamik in anorganischen Materialien Dieter Freude Abteilung Grenzflächenphysik, Universität Leipzig, Vortrag am 10. Februar 2004 an der Universität Karlsruhe, Forschergruppe 338, Professor Hans Buggisch Faujasite

2 Current Contents ® The Current Contents © (Physical, Chemical and Earth Sciences) referred in the last years to more than publications, among them spectroscopic studies, about NMR studies, among them to studies of solids. From all NMR studies refer ca. 35% to 1 H, ca. 25 to 13 C, ca. 8 to 31 P, ca. 8 to 15 N, ca. 4 to 29 Si and ca. 2 to 19 F as I ½ nuclei. Ca. 3% refer to 27 Al and ca. 1% to 11 B, 1% to 7 Li, 1% to 23 Na, 1% to 51V (half-integer spin nuclei I >½). Ca. 4% refer to 2H, ca. 0.5% to 14N and 0,5% to 6Li (integer spin nuclei with I = 1).

3 Vergleich im Jahre 2000 zwischen Physical, Chemical & Earth Sciences und Life Sciences NMR IR Raman MS EPR X-ray spectroscopy DK X-ray structure Phys Life

4 Harry Pfeifer's NMR-Experiment 1951 in Leipzig H. Pfeifer: Über den Pendelrückkoppelempfänger und die Beobachtungen von magnetischen Kernresonanzen, Diplomarbeit, Universität Leipzig, 1952

5 Laser-Einsatz: Laser supported high-temperature MAS NMR

6 Stop-and-go A laser beam makes it possible to switch from room temperature, at which chemical reactions in zeolites are commonly too slow to be measured, to temperatures up to 800 K, at which the reaction takes place within a few seconds. Irreversible reactions: The stop-and-go technique utilizes the heating rate of the laser-supported probe to expose the sample to short periods at high temperatures and splits the measuring time in consecutive stop and go periods. During the go periods the time development of irreversible reactions can be monitored at high temperatures by equidistant 1H MAS NMR signals. The reaction state after each go period is recorded by a 13C MAS NMR spectrum at room temperature during the stop period. Reversible reactions: FID accumulation and phase cycling can be realized by multiple repetition of the heating-cooling cycle. The recording of one complete heating and cooling cycle by means of several FIDs equidistant in time is denoted herein as one FID set.

7 Hochfeld-Festkörper-NMR: Festkörper-NMR-Spektroskopie im hohen Magnetfeld, einschließlich DOR und MQMAS für Quadrupolkerne wie 17 O The Bruker Avance 750 spectrometer in Leipzig, painting by Dr. Taro Ito 3QMAS pulse program DOR rotor

8 Was ist Ziel neuer Festkörper-NMR-Techniken zur Untersuchung von Quadrupolkernen? Verbesserung der Auflösung zur genaueren Bestimmung der chemischen Verschiebung von Signalen Verbesserung der Auflösung zur genaueren Bestimmung von Quadrupolparametern Verbesserung der Nachweisempfindlichkeit Theoretische Linienform des Zentralübergangs mit Anisotropiefaktor = 0,2 und geringer Gaußverbreiterung für das ohne Probenrotation aufgenommene statische Spektrum, das MAS- Spektrum und das MQMAS NMR-Spektrum. DOR-Spektrum sieht wie MQMAS aus, hat aber meist viele Seitenbänder.

9 Einquanten- und Multiquantenübergänge Der Aluminiumkern hat den Spin I = 5/2. Entsprechend ergeben sich sechs Energieniveaus im starken äußeren Magnetfeld.

10 Satelliten, Zentralübergang, Verbreit. 2. Ordnung

11 MAS, Verbr. 2. Ordnung, symmetrische Übergänge

12 double rotation: 2 = 54,74° 1 = 30,56° I y / I x tuned to J Z Na,K-LSX 17 O MAS 17 O DOR 11,7 T 17,6 T MQMAS pulse sequences: Selection of the desired coherence transfer path by the phase cycling. Na-LSX 3QMAS MQMAS and DOR

13 wide-bore probe ν outer 1.8 kHz, ν inner 7.6 kHz, narrow-bore probe ν outer 1.5 kHz, ν inner 7.5 kHz, Double rotation

14 NMR-Diffusometrie (Kärger): PFG NMR-Messtechnik

15 Festkörper-Technik für Diffusometrie: SFG NMR-Messtechnik für Temperaturen bis 700 K Result: The magnetic field gradient in the fringe field of the BRUKER wide-bore 17.6 T magnet amounts T m -1 for a proton resonance frequency of 303 MHz.

16 1 H MAS NMR of porous materials

17 1 H MAS NMR spectra modul30 I/D calc. temp. 550 °C dehydrated / ppm modul30 II/D calc. temp. 900 °C dehydrated / ppm ppm 2.9 ppm 2.2 ppm 1.7 ppm 2.2 ppm 1.7 ppm 2.9 ppm with dephasing without dephasing difference spectrum 2 with and without dipolar dephasing by 27 Al high power irradiation and difference spectra. Non- framework aluminium (EF), OH group of the framework (F). Spectra shows SiOH groups at framework defects, at the surface, SiOHAl-bridging hydroxyl groups, Al – OH group.

18 29 Si MAS NMR

19 29 Si MAS NMR-Spektrum von Silicalit 1, das aus einem SiO 2 -Gerüst mit 24 unterschiedlichen Si-Positionen pro Einheitszelle besteht (Fyfe 1987)

20 27 Al MAS NMR

21 Hydrothermally treated zeolites ZSM-5 L = 195 MHz Rot = 15 kHz L = 130 MHz Rot = 10 kHz four-fold coordinated five-fold coordinated six-fold coordinated AlPO 4 -14, 27 Al 3Q MAS spectrum L = 195 MHz Rot = 30 kHz

22 17 O NMR, hydrothermal enrichment N 2 H 2 17 O zeolite reactor heater N 2 condenser H 2 17 O ( % enriched), vapor pressure of 2.4 kPa in a nitrogen stream zeolite embedded in quartz glass particles temperature between 150 °C and 250 °C duration of some hours, water is recycled ice

23 Question: Exists a correlation between 17 O chemical shift and T-O-T bond angle ? 17 O DOR NMR for the oxygen sites of hydrated Na-A ( ) and Na,K-LSX ( ). ( 17 O) /ppm = ( 17 O) /ppm = 0.65 /° correlation coefficients: and 0.91 Grandinetti et. al. [2] and Bull et. al. [3], [4] claimed that a monotone correlation between Si-O-Si bond angle and 17 O chemical shift does not exist. In 29 Si NMR a relation exists between the isotropical value of the chemical shift and the mean value of the Si-O-T angles (T=Si, Al), cf. Radeglia and Engelhardt [1]: ( 29 Si) = m. = cos /(cos 1) is the s-character of the oxygen hybrid orbitals, and m the coordination number of Si atoms to Al atoms, commonly Q4(m Al). 17 O DAS NMR studies of the SiO 2 polymorph coesite by Grandinetti et. al. [2] yielded the correlations: [1] Chem. Phys. Lett. 114 (1985) 28 [2] J. Phys. Chem. 99 (1995) [3] J. Am. Chem. Soc. 120 (1998) 3510 [4] J. Am. Chem. Soc. 122 (2000) 4948

24 Mobility in the Brønsted Center Proton mobility of bridging hydroxyl groups in zeolites H-Y and H-ZSM-5 was monitored in the temperature range from 160 to 790 K. The full width at half maximum of the 1 H MAS NMR spectrum narrows by a factor of 24 for zeolite H-ZSM-5 and a factor of 55 for zeolite 85 H-Y. For the latter an activation energy of 78 kJ mol has been determined. zeolite 85 H-Y E a = 78 kJ/mol zeolite H-ZSM-5 E a = 18 kJ/mol The values of the activation energy for the proton mobility around an aluminum atom are useful for the evaluation of quantum chemical models.

25 Proton transfer between Brønsted sites and benzene molecules in zeolites H-Y In situ 1 H MAS NMR spectro- scopy of the proton transfer between bridging hydroxyl groups and benzene molecu- les yields temperature depen- dent exchange rates over more than five orders of magnitude. H-D exchange and NOESY MAS NMR experiments were performed by both conventional and laser heating up to 600 K.

26 Exchange rate as a dynamic measure of Brønsted acidity Arrhenius plot of the H-D and H-H exchange rates for benzene molecules in the zeolites 85 H-Y and 92 H-Y. The values which are marked by blue or red were measured by laser heating or conventional heating, respectively. The variation of the Si/Al ratio in the zeolite H-Y causes a change of the deprotonation energy and can explain the differences of the exchange rate of one order of magnitude in the temperature region of K. However, our experimental results are not sufficient to exclude that a variation of the pre- exponential factor caused by steric effects like the existence of non-framework aluminium species is the origin of the different rates of the proton transfer.

27 Herzlichen Dank für die Beiträge von Horst Ernst Thomas Loeser Johanna Kanellopoulos Jörg Kärger Bernd Knorr Dieter Michel Lutz Moschkowitz Ulf Pingel Dagmar Prager Daniel Prochnow Deutsche Forschungsgemeinschaft Max-Buchner-Stiftung

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