In Situ Crystallization of Macroporous Monoliths with Hollow NaP Zeolite Structure

Macroporous NaP zeolite monoliths (M-ZPMs) with designed shapes such as cylinder, rectangular-prism, and donut shapes were synthesized via gelcasting of the aged zeolite gel with colloidal silica as a binder and subsequent vapor-phase-transport (VPT) synthesis. X-ray diffraction (XRD), scanning electron microscopy (SEM), mercury porosimetry, and nitrogen gas adsorption were used to characterize the samples at different synthesis stages. SEM images revealed that the resulting macroporous NaP zeolite monoliths were composed of interconnected hollow particles. Mercury porosimetry showed that the macroporous NaP zeolite monoliths possessed bimodal macropore size distributions involving the textural macropores (ca. 100 μm) and skeletal macropores (ca. 3.5 μm). Furthermore, colloidal silica played a crucial role in the formation of robust macroporous NaP zeolite monoliths. Specifically, as the mass loading of colloidal silica in the zeolite-gel monoliths increases, the mechanical strength and Si/Al ratio of the resulting zeolitic monoliths increased; dispersible and individual hollow NaP zeolite particles with lower Si/Al ratios were produced in the absence of colloidal silica. The formation mechanisms of the hollow NaP zeolites in the VPT synthesis process were discussed. The incorporation of functional magnetic Fe 3 O 4 in M-ZPMs was finally presented.