Competitive role of sodium and potassium cations during hydrothermal zeolite crystallization from Na_2O-K_2O-Al_2O_3-SiO_2-H_2O gels

摘要

Zeolites A, F, Q, X and sodalite were synthesized hydrothermally from Na_2O-K_2OAl_2O_3-rnSiO_2-H_2O gels. The crystallization processes were monitored as a function of thernfraction of sodium cations in the sodium-potassium cation gel system. Pure phases werernobtained in three distinct alkali composition ranges: zeolite A was crystallized atrnNa_2O/(Na_2O+K_2O) ~ 0.9 to 1.0, zeolite X at Na_2O/(Na_2O+K_2O) ~ 0.7 to 0.8, and zeolite Frnat Na_2O/(Na_2O+K_2O) ￡ 0.5. The structure-directing roles of these alkali cations, the phasernevolution of products, as well as size and morphology of the crystals are discussed.