Maximizing the Accessibility of Acid Sites Within Zeolite Catalysts for Syngas Conversion

Abstract

Mass transport within zeolites is pivotal in determining the accessibility of active sites to reactants and hence the catalytic performance. However, there lacks of quantitative guidance for synthesis of desired zeolites with reduced diffusion limitation. Herein, we take mordenite (MOR) zeolite as a model, which is characterized by 12-membered rings (MR) channels as transport path towards the active sites within the 8MR side pockets for syngas conversion to light olefins. By correlating the effective diffusion lengths ($$ ) with the Thiele modulus and the effectiveness factors of reaction rates over a composite catalyst ZnAlO_x-MOR, we determine that the shortest 12MR channel length ($$ ) of 60 nm in this study is close to the threshold length necessary for full access to the 8MR acid sites. As a result, it exhibits excellent catalytic performance with CO conversion reaching 33 % and ethylene selectivity 69 %. Furthermore, the methodology is general and essential for further development of efficient zeolite catalysts with fully accessible active sites.