Manipulation of the crystallization of SSZ-13 transformed from coal fly ash-derived analcime

Abstract

Interzeolite transformation (IZT) has been used to produce zeolite with novel structure and composition. However, the complicated interactions between synthesis parameters and the resultant zeolites remained ambiguous. Herein, we synthesized zeolite SSZ-13 via an IZT strategy by using coal fly ash-derived analcime as parent zeolite. The effects of feeding H2O/SiO2, OH-/SiO2, and SiO2/Al2O3 ratios on the crystallization of zeolite SSZ-13 were examined. The crystallinity, pore structure, building units, and chemical environment of the products were investigated by XRD, SEM, XRF, N2 adsorption-desorption, FT-IR, and NMR, respectively. Zeolite SSZ-13 with high crystallinity and regular pore structure can be obtained under feeding H2O/SiO2 ratios of 17.5–25, OH-/SiO2 ratios of 0.2–0.6, and Al2O3/SiO2 ratios of 30–40. The absence of external water limited the mass transfer between reactants. While excessive water lessened the driving force for synthesizing zeolite SSZ-13 with regular structure. Small amounts of OH- ions triggered the dissociation of zeolite analcime. But high concentrations of OH- ions blocked the condensation of Si reactants and nucleation of zeolite SSZ-13. Increasing SiO2/Al2O3 ratio boosted the nucleation frequency. Insufficient contents of external Si species delayed nucleation and formed amorphous aluminosilicate impurities. The superfluous SiO2/Al2O3 ratio caused the overgrowth of zeolite SSZ-13 with irregular structures. Our findings benefited in understanding the interaction among synthesis parameters and the crystallization mechanism of IZT. It also gained new strategies for synthesizing high-silica zeolite using Al-rich natural and industrial aluminosilicate solid wastes.