Zeolites and zeotypes are widely used in the energy and chemical industries due to their unique pore structures and excellent shape-selective catalytic properties. However, these inherent advantages also lead to diffusion limitations, preventing guest molecules from effectively accessing internal active sites and thereby hindering catalytic efficiency.

In a study published in Angewandte Chemie International Edition, a research group led by Prof. Jiao Feng and Prof. Pan Xiulian from the Dalian Institute of Chemical Physics (DICP) of the Chinese Academy of Sciences has revealed how the accessibility of zeolite acid sites plays a crucial role in determining syngas conversion performance.

Using mordenite (MOR) zeolite as a model catalyst, researchers investigated its unique pore structure, where acid sites within the eight-membered ring (8MR) side pockets serve as active sites for syngas-to-ethylene via OXZEO, while the 12-membered ring (12MR) channels act as molecular transport pathways.

By systematically analyzing the mass transfer effects of MOR catalysts with varying 12MR channel lengths (2L), researchers established a quantitative relationship between active site accessibility and catalytic performance.

Moreover, researchers identified 60 nm as the critical threshold for the 12MR channel length, where the reaction approached kinetic limitation. Using this property, they optimized the ZnAlO_x-MOR bifunctional catalyst, achieving a CO conversion of 33% and an ethylene selectivity of 69%.

“Our study provides new insights into mass transfer mechanisms inside zeolites and offers a framework for designing high-performance zeolite-based catalysts,” said Prof. Jiao.