Hydrothermal synthesis of Siliceous Beta Zeolite by an inorganic cation-driven strategy and its crystallization mechanism

Abstract

Siliceous Beta zeolite and its metal-containing counterparts are effective adsorption and catalysis materials. To develop facile and efficient synthesis strategy would facilitate their large-scale production and application. Herein, we report the fluoride-free hydrothermal synthesis of siliceous Beta achieved by an inorganic cation-driven strategy. It is found that the types of inorganic cations are more critical than anions in determining the product phase. Inorganic cations with smaller sizes (such as Li+, Na+ and Mg2+) facilitate the synthesis of siliceous Beta, while the larger ones (such as K+, Ca2+ and NH4+) tend to give rise to impurity or amorphous materials. Crystallization mechanism investigation based on the Na+-added system revealed that inorganic cations can effectively promote the fast polymerization of SiO2 colloids at the initial stage. The crystallization occurs on the polymerized composites, yielding siliceous Beta with high solid yield. The resultant material is well characterized, which possesses few framework defects, high hydrophobicity and large adsorption uptake for toluene (one of the common volatile organic compounds). Breakthrough experiments further evidence the dynamic toluene adsorption capacity of the material is 24% higher than that of siliceous Beta synthesized by fluoride route.