Transient methods for in situ NMR of reactions on solid catalysts using temperature jumps
- Texas A&M Univ., College Station, TX (United States)
Two methods for carrying out magic angle spinning (MAS) NMR experiments with temperature jumps were evaluated for their suitability for studies of rapid chemical reactions in situ. Temperature profiles, both spatial and temporal, were determined through the use of {sup 207}Pb chemical shift thermometry and melting transitions. Our inductive heating experiments were performed using an unmodified double resonance, single coil MAS probe by injecting a continuous signal 130 kHz off-resonance from the {sup 1}H frequency into the decoupler channel. While the spectrometer used was generally capable of performing continuous wave (CW) heating experiments with 100 W, the standard probe design limited CW heating power to nearly 20 W; thus, the results reported here understate the potential of the method. Using a combination of thermometry techniques, it was possible to establish 30-60-s heating regiments for in situ {sup 1}H and {sup 13}C NMR studies of the reactions of methanol on the acidic zeolite catalyst HZSM-5. Application of 18 W at 199.7 MHz to a 5-mm-o.d. Pt-coated zirconia rotor heated the samples from an initial value of 298 K to a final state fully equilibrated at 623 K in 30 s or less. Single-shot {sup 1}H spectra acquired every 3 s during the dynamic part of the experiment and {sup 13}C Spectra acquired after quenches to 298 K were consistent with established features of the catalytic reaction mechanism. 29 refs., 10 figs.
- Sponsoring Organization:
- USDOE
- DOE Contract Number:
- FG03-93ER14354
- OSTI ID:
- 106764
- Journal Information:
- Analytical Chemistry (Washington), Vol. 67, Issue 18; Other Information: PBD: 15 Sep 1995
- Country of Publication:
- United States
- Language:
- English
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