Synthesis and characterization of MFI-type zincosilicate zeolites with high zinc content using mechanochemically treated Si–Zn oxide composite

Abstract

Modification of zeolites by the incorporation of divalent Zn in the silicate framework is attracting extensive attention because it results in higher anionic charge density and creates new active acid sites. However, it is a great challenge to incorporate Zn into the framework of highly siliceous MFI-type zeolites without Al. In this study, ball milling, a mechanochemical method, was employed to prepare Si–Zn oxide composites from mixtures of fumed silica and ZnO as the starting materials for the zeolite synthesis. The dispersion of Zn on an atomic level inside the silica matrix was realized by mechanical forces. Then, the Si–Zn oxide composites were subjected to hydrothermal treatment in the presence of an additional Si source and a structure-directing agent to synthesize MFI-type zincosilicate zeolites with high Zn contents (Si/Zn = 36.9–13.4) but negligible Al impurity (Si/Al>900). The successful incorporation of Zn into the zeolite framework was confirmed by several characterization techniques. Ion exchange experiments showed the superior selectivity and capacity of MFI-type zincosilicate zeolites for divalent cations (Co2+ as a model cation) as compared with those of aluminosilicate analogs. The mechanochemically treated Si–Zn oxide composite plays a crucial role in the synthesis of MFI-type zincosilicate zeolites with high Zn contents and minor extra-framework Zn species.