High silica zeolite Y nanocrystals by dealumination and direct synthesis

In this study, dealumination and direct high silica synthesis techniques were applied to zeolite Y nanocrystals in an attempt to produce dispersible zeolite Y nanocrystals in the 30-40 nm size range with high acid resistance. Dealumination of zeolite Y nanocrystals with SiO2/Al2O3 = 4.38 with ammonium hexafluorosilicate was not successful in increasing the acid stability of the nanocrystals. By increasing the TMABr/TMAOH (S) ratio in the synthesis mixture, synthesis of zeolite Y nanocrystals with a SiO2/Al2O3 of ratio of 5.84 was demonstrated. Two distinct regions of supercage TMA weight loss were identified during the TG analyses of our as synthesized and Na+ exchanged zeolite Y nanocrystals. The two distinct weight losses are attributed to the existence of TMA template free within the supercage and template bound to extraframework cation sites on the walls of the supercage. A detailed characterization of our zeolite Y nanocrystals is given, including powder X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), N-2 adsorption, dynamic light scattering (DLS), thermogravimetric (TGA) analyses, and inductively coupled plasma optical emission spectrophotometry (ICP OES) elemental analyses. (C) 2004 Elsevier Inc. All rights reserved.