Control of Particle Size and Surface Properties of Crystals of NaX Zeolite

Abstract

We have successfully synthesized NaX zeolite crystals with controlled sizes from 20 nm to 0.8 μm, using a novel organic-additive-free approach. We show that the NaX crystal size depends on the silicate source and hydrothermal crystallization conditions, especially crystallization temperature and agitation. The physical properties of NaX-nano (20−100 nm) were characterized by X-ray diffraction, high-resolution scanning electron microscopy, FT-IR spectroscopy, 29Si solid-state NMR spectroscopy, and N2 adsorption. The results were compared with those for micrometer-sized NaX crystals, NaX-μ. As expected, the external surface area of NaX-nano was found to be significantly enhanced compared with that of NaX-μ. Porosity analysis indicates that NaX-nano has a broad distribution of mesopores from 2 to 20 nm, associated with interparticle voids. Both FT-IR and 29Si solid-state NMR spectra revealed the presence of Q3 silicon atoms in NaX-nano. All four Q3 species were assigned in the 29Si NMR spectra.