Study on synthesis and characterization of ZSM-20 zeolites from metakaolin-based geopolymers

• ZSM-20 zeolite was obtained from geopolymer by in-situ hydrothermal process.
• The ZSM-20 zeolite without any by-product could get a surface area of 78.52 m2/g.
• The key factors were alkalinity, curing and hydrothermal conditions.
• The optimum synthesis conditions were obtained in this paper.

This paper presents a novel method for the synthesis of ZSM-20 zeolites. This method based on in situ transformation from a metakaolin-based geopolymer gel is more effective than the traditional hydrothermal method. The crystalline phase, micromorphology and microstructure of the geopolymers and the ZSM-20 zeolite samples were investigated using SEM, XRD and an N2 adsorption apparatus. The experimental results showed that pure ZSM-20 zeolite crystals were obtained without any by-product and with a large BET surface area of 78.52 m2/g under optimal conditions. Key factors of the in situ transformation process were studied, such as the alkalinity of the geopolymer gel, the curing conditions and the hydrothermal conditions. The optimum observed conditions were as follows: the modulus of sodium silicate solution (SiO2/Na2O molar ratio) was 1.1, H2O/Na2O molar ratio = 7.5, the geopolymers should be cured at 40 °C for 3 days, and the hydrothermal conditions should be kept at 140 °C for 10 h.