Synthesis of Cs–aluminosilicate zeolites and thermal phase transformation from BIK to CAS frameworks

The hydrothermal synthesis of zeolite from a gel containing Cs to some alkali cations is thoroughly investigated, and a new route for the synthesis of CAS-type zeolite is found by the thermal treatment of BIK-type zeolite, which was prepared by the conventional synthesis method from aluminosilicate gel containing cesium and additional alkali metal ions. The effect of the alkali cations on the phase transformation of BIK into CAS at 900 °C is also investigated. It is found that lithium cations play an important role in the transformation and that the time required for the transformation into CAS decreases with the lithium content in the starting mixture. The required time for the transformation in potassium-containing BIK is more than that in lithium-containing BIK. The mechanism of structural transformation is considered.