Synthesis of high-silica and low-silica zeolite monoliths with trimodal pores

Using macroporous alumina as an aluminum source as well as structural support, high- and low-silica zeolites with trimodal pores have been fabricated in a monolithic form. Trimodally porous zeolites are obtained by the hydrothermal treatment of a monolithic alumina support impregnated with a mixture of AEROSIL 200, H2O, and sodium hydroxide or tetrapropylammonium hydroxide. The results of XRD measurement and 27Al NMR analysis reveal the formation of zeolites and the incorporation of Al into zeolite frameworks in tetrahedrally-coordinated environment. Low-silica zeolites, such as PHI- and ANA-type zeolites are formed when sodium hydroxide is utilized as a base and a structure directing agent (SDA). On the other hand, MFI-type zeolites are crystallized from highly supersaturated solutions with the use of tetrapropylammonium hydroxide. High alkaline resistance of alumina support enables the choice of wide range of OH−/SiO2 ratio, and moreover, the choice of desirable degree of supersaturation. As a result, the homogeneous crystallization of zeolites onto the alumina support has been successfully achieved.