Kinetics guided synthesis and performance of monodisperse zeolite LTA microspheres

Abstract

Monodisperse zeolite microspheres hold great potential for wide industrial applications, but the existing preparation methods could hardly afford a uniform particle size distribution. Herein, the authors, for the first time, achieved the synthesis of monodisperse zeolite microspheres possessing high sphericity and tight particle size distribution with coefficient of variation (CV) less than 5%. Unlike previous methods that produce macroporous zeolites, the current strategy featured as shape-preserving steam assisted crystallization (SAC) successfully transforms aluminum and sodium source impregnated mesoporous silica microspheres into monodisperse zeolite LTA microspheres with tunable particle size between 10 and 30 μm. Spatiotemporal control of crystallization kinetics with balanced silica dissolution and zeolite nucleation is found to be essential for authentically maintaining the monodisperse spherical morphology, with larger-sized silica leading to higher zeolite sphericity. The pore size of the initial silica affects the resulting zeolite crystallinity, viz., larger silica pore size leads to higher zeolite crystallinity. Evolution of the zeolite microspheres involves synchronized silica dissolution and LTA crystallization in trapped domains facilitated by the intermediate, homogenously dispersed gel matrix, allowing to inherit the parent silica morphology. The LTA zeolite microspheres exhibit extremely high crystallinity, mechanical strength, thermal stability, and excellent air separation performance.