NMR spectra are needlessly confusing when spinning sidebands and isotropic peaks lie on the same curve. Qualitative analysis is impossible if these spinning sidebands cannot be distinguished from isotropic peaks and quantitative measurement is frustrated whenever any sideband overlaps any other peak. Resolving a spectrum into several curves, one containing only isotropic peaks, another only first higher frequency sidebands, still another only first lower, etc., eliminates these problems. These extra curves, which can be generated by an echo technique, do not require extra acquisition time. An ordinary echo spectrum refocused after two revolutions has the same S/N ratio as each curve in a separated spectrum which is made with the same total number of acquisitions.

Spinning‐sideband‐free and spinning‐sideband‐only NMR spectra in spinning samples

Nearly all atoms contributing to the local structure of Br⊘nsted acid sites in zeolites exhibit isotopes accessible for multinuclear solid-state nuclear magnetic resonance (NMR) investigations. Therefore, in the last 15 years, NMR spectroscopy has found numerous applications for the determination of the types of hydroxyl proton in zeolites, of their concentration, accessibility, and mobility, and for the characterization of their acid strength and local structure. It allows the study of the role of hydroxyl groups in the formation of adsorbate complexes and in heterogeneously catalyzed reactions. Meanwhile, NMR spectroscopy belongs to the most powerful techniques for the characterization of Br⊘nsted acid sites in zeolites and related materials. The basis of this success is the invention of new sample preparation techniques, external magnetic fields with high-flux densities, effective line-narrowing methods, and new two-dimensional experiments, making the detection of highly resolved solid-state N...

Br⊘nsted Acid Sites in Zeolites Characterized by Multinuclear Solid-State NMR Spectroscopy

W.P Aue

Papers

Two-dimensional rotational spin-echo nmr in solids: Resolution of isotropic and anisotropic chemical shifts

Uniform chemical shift scaling in rotating solids