Influence of Synthesis Parameters with Low Seed Addition on the Crystallinity of ZSM-5

ZSM-5 zeolite microparticles (MPs) were synthesized under hydrothermal condition using a low crystal seed addition approach without template. The synthesis parameters such as the seed addition amount, the SiO2/Al2O3 ratio, the aluminum source, the feeding addition method, aging, and crystallization were investigated. The structure, morphology and composition of the as-synthesized ZSM-5 zeolite MPs were characterized by X-ray powder diffraction (XRD), scanning electron microscopy (SEM), laser particle size distribution (PSD) measurements, and inductively coupled plasma-atomic emission spectrometry (ICP-AES). The SiO2/Al2O3 ratio of ZSM-5 zeolite MPs was in the range of 20—80. The low seed addition was beneficial to improving the crystallinity and shortening the crystallization time, and the suitable amount of seed was 0.25% (SiO2). The ZSM-5 zeolite MPs synthesized with aluminium nitrate nonahydrate used as the aluminum source exhibited a relatively high crystallinity. An appropriate aging time could eliminate the effect of feeding addition method and effectively adjust particle size. The particle size of ZSM-5 zeolite obtained at an aging time of 20 h was around 2.0 μm. Prolonging the aging time appropriately could also shorten the high-temperature crystallization time. The suitable aging time was 24 h, and the relative crystallinity of ZSM-5 zeolite could reach up to 99% after crystallization for 24 h at 180 ℃.