关键词: 原位, 固体核磁共振, 机理, 催化反应, 低碳烷烃

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