Acid properties of solid acid catalysts characterized by solid-state (31)P NMR of adsorbed phosphorous probe molecules
Resource
PHYSICAL CHEMISTRY CHEMICAL PHYSICS, 13(33), 14889-14901
Journal
Physical Chemistry Chemical Physics
Pages
14889
Date Issued
2011
Date
2011
Author(s)
Zheng, Anmin
Huang, Shing-Jong
Liu, Shang-Bin
Deng, Feng
Abstract
A brief review is presented on acidity characterization of solid acid catalysts by means of solid-state phosphor-31 magic-angle-spinning nuclear magnetic resonance ((31)P MAS NMR) spectroscopy using phosphor-containing molecules as probes. It is emphasized that such a simple approach using (31)P MAS NMR of adsorbed phosphorous probe molecules, namely trimethylphosphine (TMP) and trialkylphosphine oxides (R(3)PO), represents a unique technique in providing detailed qualitative and quantitative features, viz. type, strength, distribution, and concentration of acid sites in solid acid catalysts. In particular, it will be shown that when applied with a proper choice of probe molecules with varied sizes and results obtained from elemental analysis, the amounts and locations (intracrystalline vs. extracrystalline) of different types (Brønsted vs. Lewis) of acid sites may be determined. In addition, by incorporating the NMR results with that obtained from theoretical density functional theory (DFT) calculations, correlations between the (31)P chemical shifts (δ(31)P) and acidic strengths of Brønsted and Lewis acid sites may also be derived, facilitating a suitable acidity scale for solid acid catalysts.
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journal article
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