Regulating Zeolite Nucleation using Alkali Cations and Higher Valence Elements

As the number of possible applications for zeolite catalysts and adsorbents continues to expand, development and commercialization of these materials is hindered by a limited ability to tune their physicochemical properties. Conventional strategies involving costly organic chemicals or multi-step post-synthesis protocols are prohibitively expensive. In this dissertation, I describe how the addition of earth abundant elemental species to zeolite growth mixtures can be used to elucidate formation mechanisms and control crystallization pathways. Insights from these studies are used to develop advanced strategies for zeolite products and design nuclear waste glass formulations with higher stability against degradation via zeolite nucleation.

One traditional strategy for manipulating zeolite crystallization involves tuning the type and concentration of inorganic structure-directing agents, which include sodium and potassium. These cationic species counterbalance the negatively-charged zeolite framework and can lead to distinct framework types, acidity levels, and/or morphologies. In addition to alkali metal cations, higher valence species, such as tin and zinc, are known to alter crystallization mechanisms according to alternative chemical pathways. Through the addition of various alkali, alkaline earth, and higher valence elements to zeolite synthesis mixtures treated according to conventional hydrothermal methods, we have elucidated multiple facile strategies for controlling zeolite syntheses.

We have discovered that the organic-free synthesis of zeolites in potassium-media is dissimilar to those in sodium-media, which leads to unique challenges to understanding the universality of zeolite crystallization mechanisms and opportunities to control synthesis outcomes. We also investigate the benefits of using combinations of inorganic elements to control crystallization, including the addition of small quantities of lithium, strontium, zinc, and germanium, which can direct zeolite syntheses towards desired outcomes.

The insights gleaned from these studies assisted in the development of a model system for predicting the stability of nuclear waste glass forms against the formation of zeolites, which are known accelerants of waste glass degradation. The results of the research described in this dissertation have led to a greater understanding of unique and facile approaches for tuning zeolite crystallization using inexpensive inorganic additives. These advancements can benefit applications ranging from zeolite design, crystal engineering, petrochemical processing, sustainable chemical manufacturing, and nuclear waste disposal.