2023 AIChE Annual Meeting

(607b) Steering the Molecular Diffusion Pathway of H-ZSM-5 Zeolites to Regulate Their Catalytic Performances

Authors

Xiaoliang, L. - Presenter, Xiamen University
Jiawei, T., SINOPEC
Jian, Z., SINOPEC
Xie, Z., China Petrochemical Corporation
Wang, Y., Shanghai Research Institute of Petrochemical Technology, SINOPEC Corp.
Increasing social sustainability triggers the persistent progress of industrial catalysis in energy transformation and chemical production. Zeolite catalysts are famous workhorses for most chemical industries. However, the performances of zeolite catalysts are commonly restricted by the molecular transport behaviors (diffusion) between their active sites and pore networks, which have always been overlooked.[1] Herein, we focus on revealing the structure–transport–reactivity relationship in H-ZSM-5 zeolite catalysts and controlling the molecular diffusion pathway to regulate their catalytic efficiencies. A homemade time-resolved in situ FTIR spectrum, directly monitoring the change in molecular concentration by detecting the intensity variation of characteristic IR bands with time, was developed to measure the diffusivities in zeolite catalysts. Employing this method, several molecular transport behaviors, i.e. surface diffusion and intracrystalline diffusion, were studied in detail. It is indicated that the surface diffusion barriers of H-ZSM-5 zeolites may have arisen from the surface silanol defect sites, such as external silanol groups or those near the pore mouths.[2] Decreasing the surface barriers can distinctly increase the catalyst lifetime without loss of the product selectivity in catalytic cracking reaction (OCC) (Figure A). Besides, the diffusion anisotropy in different channels of H-ZSM-5 zeolite was proposed as the descriptor for the morphology effect in OCC performances.[3] Controlling the intracrystalline diffusion pathway via changing the pore channel proportion could modulate the catalytic activity and stability (Figure B). Finally, the effect of binders in practical zeolite particles that are applied in industrial reactors on their molecular diffusion behaviors was preliminarily uncovered. We feel that our findings would offer mechanistic insight into the design of highly efficient zeolite catalysts.

References

  1. [1] Xiaoliang Liu, Zaiku Xie* et al. Chem. Soc. Rev., 2022, 51, 8174.
  2. [2] Xiaoliang Liu, Zaiku Xie* et al. Chem. Commun., 2023, 59, 470.
  3. [3] Xiaoliang Liu, Zaiku Xie* et al. Commun. Chem., 2021, 4, 107.