Efficient assembly of hierarchical NaY aggregates by using an organosilane modified SDA

Abstract

We demonstrate an efficient method for the assembly of hierarchical NaY aggregates by using a modified structure-directing agent (SDA) in an extremely dense aqueous system at 373K. By introducing the dimethylhexadecyl[3-(trimethoxysilyl)propyl] ammonium chloride (TPHAC) into the aluminosilicate sol, an organo-modified sol was formed and after ageing it was used as SDA in the feedstock gel to generate the well-aligned hierarchical NaY aggregates. The structure evolution of sol and formation of NaY aggregates were systematically investigated by FT-IR, XRD, SEM, TEM and synchrotron radiation small angel X-ray scattering (SR-SAXS), which confirmed the dominant impact of the organosilane on the aluminosilicate species and further on the outcome of the NaY aggregates. The results show that by adding the minimal amount of TPHAC in the sol, the sol promotes long period structure, forming a large amount of aluminosilicate species with suitable size and distribution, which are responsible for tuning the morphology and properties of NaY aggregates under the dense synthetic system. The typical NaY aggregate has high SiO2/Al2O3 of 5.3, consisting of particles (2–4 μm) orderly assembled from 20 to 80 nm crystalline domains of NaY zeolites with high pore volume of 0.43 cm3/g and external surface area of 100 m2/g. The morphology, crystal sizes, mesopore sizes, volume ratios of mesopore/micropore of NaY aggregate can be adjusted by varying the amount of TPHAC, the reaction time and solid content in the dense system. The new insight into regulating sol species structure by TPHAC and forming NaY crystal aggregates were discussed.