(387g) A Mutlidirectional Approach to Understanding and Controlling Zeolite Crystallization

Enhancing fundamental understanding of zeolite crystallization processes facilitates the design of microporous materials with tailored properties. Here, we will discuss collaborative efforts to finely control zeolite crystallization through unique approaches that are motivated by opposing applications that seek to either inhibit or optimize zeolite formation. Efforts to inhibit zeolite formation focus on the crystallization of structures (notably the GIS-type framework) that are known to accelerate the degradation of nuclear waste glasses [1]. We have identified several ways by which zeolite formation rates can be suppressed, thereby slowing the rate of degradation. These approaches include the addition of species, such as metals, that dramatically suppresses zeolite crystallization kinetics. Through the mechanistic insights gleaned from these studies, we have additionally developed a range of facile techniques for controlling both phase purity and the physicochemical properties of zeolites. We have demonstrated the applicability of these techniques for industrially relevant zeolite frameworks. For example, we have shown that the introduction of metals affords the ability to inhibit the transformation of FAU (a highly metastable zeolite) to GIS, while altering the chemical composition of the former. These findings have further implications for the development of fundamental understandings of zeolite synthesis, most notably in the preparation of transition metal-substituted zeolites, which are materials of growing importance for commercial applications. Finally, we will discuss new insights into the growth of zeolite GIS, which has a twofold benefit. First, we strengthened the link between intentional synthesis of GIS and waste glass stability tests (which unintentionally yield zeolite crystals), thus facilitating future stability testing. Second, we have been able to bypass intermediate phases, such as metastable FAU, and examine the direct crystallization of GIS where our studies reveal the ability to significantly alter the properties of GIS materials, most notably its silicon-to-aluminum ratio.