日本ゼオライト学会　刊行物 Publication of Japan Zeolite Association

The physicochemical properties of zeolite such as thermal stability and catalytic, sorptive and ion-exchange abilities are known to strongly depend on the number of framework (tetrahedrally coordinated) aluminum in the zeolite structure. Dealumination from the zeolite framework and isomorphous substitution of various metals for the framework aluminum or silicon atoms have therefore been a matter of scientific and industrial interests. In this paper, the dealumination processes of MOR, MFI, FER and BEA zeolites were investigated by means of XRD, ²⁷Al MAS NMR, FT-IR and N₂ adsorption. It was found that the framework structure type is one of major factors that influence the dealumination behavior and that the extent of dealumination decreases in the same order as the number of T-sites in four-member ring: BEA > MOR > MFI > FER. From a study on the reinsertion of aluminums into the zeolite framework of dealuminated zeolite using a post-synthesis liquid modification, it was also found that aluminum species in the solution, which are eliminated from the frameworks of BEA and MOR zeolites by HCl treatment, are easily reinserted into the frameworks by controlling the pH value of the suspension below 7. The post-synthetic galliation of BEA zeolite was also conducted using this method with acidic gallium solutions