Phase and morphology control of LTA/FAU zeolites by adding trace amounts of inorganic ions

Zeolites were hydrothermally synthesized by adding different amounts of NaCl, KCl, NaF, or KF into a standard LTA (Lind type A zeolite) synthesis system and the effects of Cl−, F−, and K+ on the phase selection were identified by comparing the obtained zeolites. The addition of trace amounts of the salts could change the resulting zeolites, and the cations and anions of the salts showed synergetic or antergic effects. Cl− strongly promoted the formation of FAU (Faujasite type zeolite), whereas F− favored FAU in a very low concentration but inhibited it in higher concentrations. K+ favored the synthesis of LTA and could cooperate with F− when adding KF in the synthesis system but offset the effect of Cl− when adding KCl. The addition of ions also influenced the morphology of zeolites significantly. This study provides a simple approach to control the phase composition and morphology of zeolites and calls attention to the significant effects of impurities on hydrothermal synthesis, especially when using natural materials or industrial waste as feedstock.