Organic-free synthesis of zincoaluminosilicate zeolites from homogeneous gels prepared by a co-precipitation method

Abstract

Zeolites containing Zn in their frameworks are promising materials for ion-exchange and catalysis because of their unique ion-exchange capabilities and characteristic Lewis acidity. However, expensive organic compounds often required in their synthesis can prevent their practical uses. Here, a facile organic-free synthesis route for new zincoaluminosilicate zeolites having MOR topology, in which both Zn and Al are substituted in the framework, is demonstrated for the first time. The use of homogeneous zincoaluminosilicate gels prepared by a co-precipitation technique as raw materials is vital for the successful incorporation of both Zn and Al into the zeolite frameworks as revealed by several characterization techniques including solid-state NMR and UV-vis spectroscopy, and ion-exchange experiments. The obtained zincoaluminosilicate zeolites had high Zn contents comparable to those in the initial zincoaluminosilicate gels. In contrast, the uses of conventional sources of Si, Al, and Zn resulted in zeolites with very low contents of framework Zn or zeolites with extra-framework zinc oxide-species. FT-IR measurements using probe molecules and ion-exchange experiments suggested that there are two different environments of Zn in the zeolite frameworks. The obtained zincoaluminosilicate zeolites showed a higher ion-exchange efficiency for divalent cations such as nickel compared to the aluminosilicate analog. It is expected that the present co-precipitation technique is efficient for the incorporation of Zn (and other metals) into a variety of zeolite frameworks. To show its extended applicable scope, the synthesis of zincoaluminosilicate *BEA zeolite is also demonstrated.