The carbon-containing molecule can be used as an NMR probe to explore the acidic and structural features of various catalytic materials. Thereinto, although mesityl oxide (MO) has been extensively employed to determine the acidity of solution and ionic liquid systems, could it be utilized to characterize the acidic properties of solid acid catalysts? In this work, on the basis of a series of isolated Brønsted and Lewis acid models with varied acid strengths, the adsorption configurations and corresponding 13C chemical shifts of adsorbed MO molecules have been comprehensively studied by means of a theoretical investigation approach. Among them, both the 13C chemical shift difference between β and α carbon atoms (Δδ), and the 13C chemical shift of β carbon atoms (δ13Cβ) in adsorbed MO molecules were explicitly demonstrated to be closely related to the intrinsic acid strength of Brønsted acid sites. These correlations could be utilized to quantitatively scale the Brønsted acid strength of solid acid catalysts. Besides, a moderate relationship was theoretically derived for the relevant 13C NMR parameters and intrinsic Lewis acid strength.

Relationship between the 13C chemical shifts of adsorbed mesityl oxide and acid strength of solid acid catalysts
    Abstract
    1 Introduction
    2 Experimental and theoretical methods
        2.1 NMR experiments
        2.2 Theoretical calculations
    3 Results and discussion
        3.1 Adsorption of MO over Brønsted acid sites
        3.2 Adsorption of MO over Lewis acid sites
    4 Conclusion
    Anchor 11
    Acknowledgements 
    References

• Fei Liu(Wuhan Institute of Technology)
• Fengqing Liu(Wuhan Institute of Physics and Mathematics)
• Qin Qin(Wuhan Institute of Technology)
• Jing Zou(Wuhan Institute of Technology)
• Jizhou Jiang(Wuhan Institute of Technology)