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

Interzeolite transformation (IZT) has been used to produce zeolite with novel structure and composition. How-ever, 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.

Automated summary

Interzeolite transformation (IZT) was used to synthesize zeolite SSZ-13 with novel structure and composition. The effects of synthesis parameters on the crystallization of zeolite SSZ-13 were investigated. It was found that a feeding H2O/SiO2 ratio of 17.5-25, OH-/SiO2 ratio of 0.2-0.6, and Al2O3/SiO2 ratio of 30-40 resulted in zeolite SSZ-13 with high crystallinity and regular pore structure. Excessive water and high concentrations of OH- ions had negative effects on the synthesis of zeolite SSZ-13.