Synthesis of EMT/FAU-type zeolite with high crystallinity and high EMT yield

Abstract

EMT/FAU-type zeolite was synthesized by hydrothermal synthesis (initial gel composition: 10SiO2: 1Al2O3: xNa2O: 0.5 18-crown-6: 140H2O; x = 2.3, 2.7, 3.1 and 3.5) using 18 crown-6 as the template. The samples were characterized via XRD, BET and SEM techniques. The results illustrated that sodium hydroxide concentration in the initial gel (or in other words equivalent of Na2O) markedly affected the type and yield of the phases formed, morphology and textural property of the synthesized zeolites. With 3.1 equivalent of Na2O in the initial gel, the SEM result showed regular hexagonal platelets (2–5 μm in diameter), implying formation of well crystalline EMT phase being confirmed by XRD results as well. However, with lower or higher addition of Na2O amorphous or fujasite phases formed, respectively. In addition, the increase of the amount of sodium hydroxide reagent enhanced the BET surface area and microporous volume of the obtained zeolites. The high yield Na-EMT zeolite (∼70 %) produced in a short crystallization time (8 d) could be easily recovered from the synthesis slurry by filtration and washing without needing high-speed centrifugation.