Morphological control of DDR zeolite crystals in Sigma-1 assisted hydrothermal synthesis using reduced organic agents

Morphological control of zeolite crystals is useful for fabrication of high performance zeolite adsorbents and membranes. Here we report a simple way of controlling decadodecasil 3R (DDR) zeolite crystal morphology by varying the pH of the Sigma-1-seeded precursor solution and hydrothermal crystallization under static conditions. The precursors contained Ludox sol as silica source and reduced amounts of structure-directing agent, 1-adamantane amine (ADA), and organic solubility enhancer, ethylenediamine (EDA), as compared to those used in the literature. DDR zeolite crystals with shapes of hexagonal thin plate, rhombus block, and hexagonal prism were obtained from precursors with identical SiO₂:ADA:EDA:H₂O molar ratios when the pH was adjusted by HCl or NaOH solutions to ~8.6, 10–12, and ~12.4, respectively. The morphologically different DDR zeolite crystals exhibited similar BET surface areas and gas adsorption capacities for N₂, O₂, CH₄, and CO₂.