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.