Cesium-free synthesis of aluminosilicate RHO zeolite in the presence of cationic polymer

The synthesis of aluminosilicate RHO zeolite with small pores (3.6 Å) is normally carried out in the presence of high-cost inorganic template of cesium cations. This work shows cesium-free synthesis of aluminosilicate RHO from an aluminosilicate gel with molar composition of 12Na2O:Al2O3:32SiO2:768H2O by the use of low-cost cationic polymer (polydiallyldimethylammonium chloride, PDADMAC). The sample has been characterized by X-ray diffraction (XRD), scanning electron micrograph (SEM), the isotherms of probing molecules, and thermogravimetric and differential thermal analysis (TG–DTA) techniques. Characterization tests show that pure phase of RHO zeolite can be synthesized in the presence of cationic polymer. DTA and TG curves indicate that as-synthesized sample exhibits obvious peaks associated with the decomposition of cationic polymer, demonstrating that cationic polymer is occluded in RHO crystals. The factors affecting the synthesis and the mechanism of cationic polymer templating RHO zeolite have also been discussed.