(174as) Theoretical Investigations of Lewis Acid-Catalyzed Alkane C-H Activation in Metal-Modified Zeolites

The increasing availability of large shale gas reserves worldwide, has stimulated interest in finding routes for the valorization of C₂-C₄ alkanes. C-H Activation over metal-modified zeolites such as Ga/H-MFI yields higher selectivities to alkenes and aromatics than those observed over unmodified H-MFI which contains only protons [1]; In earlier characterization [2] and computational studies [3], [GaH]²⁺ cations were found to be stable under reducing conditions and active for alkane dehydrogenation. In the present study, insights into alkane cracking and dehydrogenation on [GaH]²⁺, Zn²⁺ and other Group 13 hydrides exchanged into MFI are developed for the activation of C₂-C₄ alkanes. A long-range corrected QM/MM scheme was used where the QM region is represented using the dispersion-corrected density functional ωB97X-D, while the MM region uses CHARMM Force fields. Reported activation energies are computed using a triple-ζ, split valence basis set: 6-311++G(3df,3pd). Our theoretical results suggest that alkyl-activated pathways are relevant for both butane and propane conversions on [GaH]²⁺ sites in Ga/H-MFI and Zn²⁺ sites in Zn/H-MFI and that the mechanistic insights obtained here are of broader relevance to the rational design of other metal-exchanged zeolites for light alkane activation.

References

1. Ono, Y. Catal. Rev. Eng. 34, 179–226 (1992).
2. Phadke, N., Van der Mynsbrugge, J., Mansoor, E., Getsoian, A., Head-Gordon, M., and Bell, A.T. ACS Catal. 8, 6106 (2018).
3. Mansoor, E., Head-Gordon, M., and Bell, A. T. ACS Catal. 8, 6146 (2018).