Synthesis and Structural Properties of Zeolitic Nanocrystals II: FAU-Type Zeolites

Abstract

FAU(Y)-type zeolite nanocrystals with a SiO2/Al2O3 ratio of about 3.4 were synthesized at 95 °C under autoclave pressure from clear solutions of tetramethylammonium hydroxide (TMAOH), aluminum isopropoxide, tetramethyl ammonium bromide (TMABr) as a second source of organic template, and tetraethyl orthosilicate (TEOS) as silica source. Formation of low-dimensional zeolitic crystallites (20−30 nm diameter) was examined by X-ray diffraction (XRD) as a function of reaction time; Fourier transform infrared spectroscopy (FTIR) (with KBr and pyridine), 27Al and 29Si nuclear magnetic resonance (NMR), and high-resolution transmission electron microscopy (HRTEM) were used to characterize structural and textural features of the zeolite nanocrystals. The cell parameters and crystallite size were obtained by Rietveld's method. Also, the inner crystallite structure was studied by high-resolution electron microscopy images using the kinematical approach (Cerius2), and the physicochemical properties of the zeolitic nanocrystallites were compared with macroscopic FAU-type crystals. The external shape of the nanocrystals was cubic, and the unit cell parameter a was equal to 24.74 Å with mean crystallite sizes of about 22.3 nm.