Seed-assisted, template-free synthesis of ZSM-5 zeolite from natural aluminosilicate minerals

The hydrothermal synthesis of zeolite from chemical Al/Si source in the presence of structure directing agent is considered to be a resource extensive, energy consuming, and environmental unfriendly process. Herein, we report a novel, cost-effective, and eco-friendly synthesis for the preparation of ZSM-5 zeolite from silicon-rich diatomite and aluminum-rich rectorite minerals in the absence of organic structure-directing agent and chemical Al/Si source. Synthesis factors (SiO2/Al2O3, Na2O/SiO2, and H2O/SiO2 molar ratios along with seed content) and crystallization behavior were systematically investigated, providing fundamental knowledges on the formation of ZSM-5 from natural minerals. Synthesis under the optimized conditions (SiO2/Al2O3 ratio of around 38, Na2O/SiO2 ratios of 0.12-0.15, H2O/SiO2 ratios of 15-25, and seed content above 0.5%) led to production of highly crystalline ZSM-5 zeolite with hexagonal prism morphology and large surface area. Various characterization techniques tracking the products at different crystallization times revealed that the crystallization process consisted of three stages: short induction stage (0-6 h), rapid growth stage (6-18 h), and stable growth stage (18-36 h). Moreover, the synthesized ZSM-5 crystals can be used as effective seed for producing the next generation of ZSM-5 zeolite.