The effect of hierarchical pore structure SAPO-34 catalyst on the diffusion and reaction behavior in MTO reaction

Abstract

Establishing the hierarchical pore structure is considered as a feasible approach for enhancing diffusion and improve catalytic efficiency of SAPO-34 zeolite in the methanol-to-olefin process. Nevertheless, under reaction conditions, the correlation among the diffusion behavior in the crystal, coke deposition behavior and catalytic performance of SAPO-34 catalysts with varying pore structures remains to be clarified. Herein, we revealed the structure–activity relationship between the hierarchical pore structure, the catalytic performance and the anti-coke deposition performance of the catalyst in the MTO reaction via the synergy of reaction–diffusion experiments and molecular simulation, then the mechanism of the hierarchical pore SAPO-34 catalyst to eliminate the diffusion limit and improve the accessibility of acid sites was clarified. The results demonstrated that the establishment of a hierarchical pore structure strengthened the diffusion of reactant methanol in the pores, leading to the diffusion resistance being reduced by 5 times and the diffusion coefficient being improved by two orders of magnitude. The key reaction rate-determining step shifted from micropores diffusion to the adsorption of acid sites in hierarchical pores, and the catalytic efficiency of the catalyst was increased by 3 times. Furthermore, with the establishing hierarchical pore technique, the expansion of the accommodation space for coke deposition led to a reduction in the blocking of pores due to coke deposition, particularly around the orifices. Moreover, the accessibility of the reactant molecules to the acid sites within the pores was enhanced, resulting in a balanced ratio between pore blockage and acid site coverage, thereby improving the anti-coke deposition performance of the SAPO-34 catalyst. This work can provide important foundational data and theoretical guidance for the study of reaction–diffusion synergistic interaction in zeolite catalysis reactions.