Studies on Natural CXN Zeolite: Modification, Framework De-alumination and Ion-exchange

摘要

A natural CXN zeolite (stilbite, type code-STI) discovered in China was modified with NH_4~+ exchange by using ammonium salt and calcinations (procedure I), or with NH_4~+ exchange followed by treatment with acid (procedure Ⅱ). The coordination state of Si and Al atoms in the framework, the property of ion exchange, and the adsorption of the H-STI zeolite samples prepared by different modification procedure were investigated with XRD, EDX, ~(29)Si and ~(27)Al MAS NMR, Ag~+ ion exchange and N_2 adsorption. The results of the investigations indicate that different procedure of the modification made variety on the distribution of the framework Si atoms and Al atoms, the content of non-framework aluminum, and the blocking channels and the shielding effect to the positions of the exchangeable cations. The H-STI zeolite prepared by the procedure Ⅱ possesses high ion exchange capacity, open and perfect pore system, and high thermal stability.