Acta Phys. -Chim. Sin. ›› 2004, Vol. 20 ›› Issue (08S): 1024-1031.doi: 10.3866/PKU.WHXB200408zk20

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In situ MAS NMR Spectroscopy Study on Catalytic Reaction Mechanism of Light Alkanes

He He-Yong;Zou Yan;Ma Zhuo-Na;Yue Bin   

  1. Department of Chemistry and Shanghai Key Laboratory of Molecular Catalysis and Innovative Materials, Fudan University, Shanghai 200433
  • Received:2004-02-16 Revised:2004-04-01 Published:2004-08-15
  • Contact: He He-Yong

Abstract: In situ MAS NMR spectroscopy has been successfully applied to study catalytic reaction mechanisms. Examples taken from our own study illustrate that the batch-like condition in situ MAS NMR technique with strategically 13C labeled reactants can contribute to the understanding of reaction pathway. The results indicate that the ion-exchanged and/or its related Ga species are the highly active catalytic components for the activation of propane under mild condition over Ga-modified H-MFI catalysts. Reaction mechanism of skeletal isomerization of n-butane over a series of solid acid catalysts in the acidic strength order of SO42-/ZrO2, CsxH3-xPW12O40 and H-MOR was also studied. The mechanism of n-butane isomerization is dependent on the type of solid acid catalyst. Under low temperature, n-butane isomerization on SO42-/ZrO2 and CsxH3-xPW12O40 catalysts proceeds through a monomolecular pathway in the initial stage of the reaction. At the later stage, C3 and C5 are detected, giving the evidence of the contribution of the bimolecular process. On H-MOR catalyst, n-butane isomerization occurs primarily via a bimolecular pathway. Further study shows that the kinetics of n-butane isomerization on SO42-/ZrO2 catalyst at ambient temperature can be well represented by Langmuir-Hinshelwood equation for a reversible first order surface reaction. The calculated isomerization reaction rate constant can be used as a measure of the solid superacidity of the catalysts.

Key words: In situ, Solid state NMR, Mechanism, Catalytic reaction, Light alkanes