Effect of metal element modification on the hydrothermal stability of Y zeolite

The effect of metal element(Y,Ga,Cr,Zn and Cu) modification on the hydrothermal stability of Y zeolite was studied by X-ray diffraction(XRD),solid-state NMR spectroscopy(MAS NMR) and scan electron microscopy(SEM).The results showed that the introduction of yttrium element can suppress the condensation of unite cell and the formation of extra-framework alumina and hence remarkably enhance the hydrothermal stability of Y zeolite.The introduction of zinc or copper can also strengthen the stability of Y zeolite to some extent,however,the framework structure of Y zeolite modified by zinc or copper may be destroyed heavily by high temperature(800 ℃) steam treatment.Unlike yttrium,zinc and copper,gallium or chromium element can not stabilize the structure of Y zeolite,but the hydrothermal stability of Y zeolite modified by gallium or chromium lies between that of Zn/Cu-modified zeolites and that of Y-modified zeolite.