Impacts of Binder-Zeolite Interactions on the Structure and Surface Properties of NaY-SiO2 Extrudates

NaY-SiO2 extrudate was prepared by blending NaY powder with silica gel, followed with kneading, extruding, and calcination. The impact of silica binder on the structure and surface properties of NaY-SiO2 extrudate was investigated. The nitrogen adsorption/desorption isotherm suggests the formation of cylindrical mesopores for NaY-SiO2. X-ray powder diffraction, transmission electron microscopy, and Fourier transform infrared suggest that in kneading, dealumination and cleavage of the intracrystalline Si-O-Al bond via acid hydrolysis occur. This acid hydrolysis causes shrinkage of the zeolite lattice along the zeolite channel due to dislodgement of Al3+ cations. The dealumination increases the silica/alumina ratio of NaY concomitantly with the removal of Na+, leading to an increase in the hydrophobicity of NaY, while reaction of the silica binder with NaY debris and/or aluminum residue forms new Bronsted acid sites. Moreover, backfilling the vacancies created in the dealumination by mobile Si(OH)(4) makes the zeolite more thermally stable, which lends the extrudate itself to industrial applications.