Density functional theoretical and NMR study of Hammett bases in acidic zeolites

Journal Article · Wed Dec 13 04:00:00 EST 1995 · Journal of the American Chemical Society

DOI:https://doi.org/10.1021/ja00154a044· OSTI ID:171380

Nicholas, J B ^[1]; Haw, J F; Beck, L W; Krawietz, T R; Ferguson, D B ^[2]

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1. Pacific Northwest Lab., Richland, WA (United States)
2. Texas A&M Univ., College Station, TX (United States)

We demonstrate here that theoretical calculations using density functional theory (DFT) accurately model proton transfer reactions between Bronsted sites in zeolites (the archetypal solid acids) and Hammett bases. The validity of the theoretical results is verified by NMR measurements of key nuclei of the same Hammett bases in zeolites HZSM-5 (MFI) and HY (FAU), the first such experiments. The accuracy of the predictions of the DFT calculations for the HZSM-5 zeolite model suggests that they may be extended to other zeolite cluster models, including those which have not yet been realized experimentally and hence are not available for NMR study. We optimized the adsorbate zeolite complexes with this angle constrained to larger values; to our surprise, the SVWN/DNP calculations resulted in the proton being transferred from p-fluoronitrobenzene back to the zeolite, even if the Si-O-Al angle was held fixed at 180{degree}. Further tests at higher levels of theory are in progress. This investigation used a choice of indicators that necessarily resulted in wide limits on zeolite acid strength, but the theoretical and experimental methodologies have been established. 21 refs., 3 figs.

• Sponsoring Organization: USDOE
• DOE Contract Number: FG03-93ER14354; AC06-76RL01830
• OSTI ID: 171380
• Journal Information: Journal of the American Chemical Society, Journal Name: Journal of the American Chemical Society Journal Issue: 49 Vol. 117; ISSN JACSAT; ISSN 0002-7863
• Country of Publication: United States
• Language: English

Related Subjects

40 CHEMISTRY
66 PHYSICS
ADSORPTION
BASES
CALCULATION METHODS
INDICATORS
MATHEMATICAL MODELS
NMR SPECTRA
PH VALUE
PROTON DENSITY
ZEOLITES