Ultrafast and continuous-flow synthesis of AFX zeolite via interzeolite conversion of FAU zeolite

Abstract

AFX zeolite is a small-pore zeolite that has attracted significant attention because of its potential as a high-performance catalyst for the selective catalytic reduction of NO_x by ammonia (NH₃-SCR). Long time and high cost for the synthesis of AFX zeolite, however, limit the practical applications of this small-pore zeolite. Herein, we report an ultrafast synthesis route that can yield highly crystalline AFX zeolite in as short as 12 min. The ultrafast synthesis was realized on the basis of interzeolite conversion, where FAU zeolite was employed as a source of silicon and aluminum. Moreover, the addition of acid-leached seeds was found to be crucial for promoting the crystallization of AFX zeolite while effectively eliminating the formation of byproducts. Detailed studies of the original and acid-leached seeds revealed that acid leaching could cause structural alterations to the original seeds, thereby significantly enhancing the seeding effect. Secondary nucleation occurred when the acid-leached seeds were added, which is assumed to be one of the primary reasons for the accelerated crystallization rate. Based on the ultrafast synthesis, continuous-flow synthesis of AFX zeolite in 10 min was also demonstrated. The ultrafast and continuous-flow synthesis of AFX zeolite is expected to facilitate the large-scale production and broad applications of AFX zeolite.