Synthesis and characterization of high silica HY zeolite by basicity reduction

Abstract

A High silica NaY zeolite was prepared by sol-gel method using sulfuric acid to adjust the alkalinity of solution for leaching the framework aluminum and increase extraframework aluminum species inside the zeolite structure, in order to enhance acidity, thermal and hydrothermal stability, and catalytic activity. The prepared zeolite was transformed into H-form by the ion exchange process. The Y zeolites characterized by using X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) X-ray fluorescence (XRF), Atomic force microscopy (AFM), Brunauer –Emmet-Teller (BET) nitrogen adsorption method, and thermogravimetric analysis (TGA). The X-ray pattern of dealuminated zeolite was NaY type. In general peaks intensities decreased and the crystallinity increased at pH=12.8. The FTIR of dealuminated zeolite were matched the standard FTIR peaks of nanocrystalline zeolite Y, except it has high intensity in the band of hydroxyl groups (3400-3600) cm−1 which indicates to stronger Bronsted acid sites. The Si content of Y zeolites was sharply increased after dealumination, Si/Al ratio increased to 5.6 for dealuminated HY zeolite. The AFM of dealuminated HY indicates small nano particles with an average size of 64 nm, compared with HY before dealumination of 77.5 nm. The surface area and pore size decreased with alkalinity decrease to 101.988 m²/g and 2.73 nm respectively. The TGA shows low hydration in HY after dealumination which lost in two steps and mainly at 248.5°C, while four steps were required for dehydration for zeolite before dealumination. This result gives a confirmed for the change the morphology of the dealuminated HY zeolite resulted from alkalinity change, which reduced the hydrophilicity and increased hydrophobicity.