Synthesis and Growth Mechanism of the Core-Shell SAPO-34/AlPO-18 Molecular Sieves

The core-shell molecular sieves comprised of SAPO-34 as core and AlPO-18 as shell were hydrothermally synthesized and characterized by X-ray diffraction, scanning electron microscopy (SEM), and ultra-high resolution field-emission scanning electron microscopy (FE-SEM) techniques. The SEM results show that the growth of the shell AlPO-18 nanocrystals with different orientations and compactness can be controlled by adjustment of the synthesis conditions such as core pretreatment, liquid to solid ratio, and growth number. The ultra-high resolution FE-SEM images confirm that the growth performance of the shell AlPO-18 is closely related to the surface microstructure of SAPO-34, indicating the mechanism that the microstructure on the external surface of the core directs the growth of the shell.