SYNTHESIS OF HIGH SILICA CHA ZEOLITES WITH CONTROLLED Si/Al RATIO

Abstract

Zeolites with the CHA topology have been synthesized with Si/Al ratios ranging from 15 to 133. ICP-AES analysis shows that the Si/Al ratio in the material is close to linearly related to the Si/Al ratio in the reaction mixture, while powder XRD shows that the unit cell parameters decrease with increasing Si/Al ratio. The difference between the unit cell parameters for the as-synthesized and the calcined samples show that the structure directing agent sterically hinders the contraction in the c-axis direction for the as-synthesized samples. A relationship between the Si/Al ratio in the material and the a-axis has been established. The particle size of the material also shows a dependency on the Si/Al ratio of the material.