Multifaceted Approaches to Tailor Zeolite Properties and Elucidate the Role of Precursors in Nonclassical Crystallization
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As one of the most important crystalline materials of industrial relevance, zeolites are utilized in an expanding list of applications ranging from energy to medicine. Exploiting the well-defined channel networks and tunable active sites of zeolite crystals, however, requires rationally designed syntheses to tailor their physicochemical properties according to specific requirements. We have performed systematic studies of zeolite synthesis on different framework types with pore networks spanning from one to three dimensions. Collectively, our findings reveal general guidelines that can be used to tailor zeolite properties while providing fundamental understanding of zeolite crystallization, which is necessary to select appropriate synthesis parameters a priori. We explored versatile and facile methods for the control of zeolite properties, including adjusting synthesis parameters and altering types of reagents – specifically the silicon or aluminum sources. Our findings reveal that with enhanced control of source properties, the combination of these two approaches can significantly optimize zeolite crystal size while offering more practical (i.e., inexpensive and faster) routes to crystallize a range of different structures. The presence of organic molecules imposes strong effects on zeolite products. Interestingly, many of our findings contradict prevailing hypotheses in literature regarding organic molecule - zeolite crystal interactions. Notably, we observed that these interactions are nuanced in that small changes in the structure of organic molecules often result in marked differences in zeolite properties (e.g., crystal size and shape) and/or the formation of polymorphs. We also demonstrated that inorganic ions impose cooperative interactions with co-existing organic molecules, altering the evolution of precursors and/or crystals, crystallization kinetics and the Al incorporation into zeolite crystals. Lastly, we explored the use of seed crystals in zeolite syntheses and examined the fundamental role of seeding in nonclassical crystallization. In addition to the impact on zeolite growth, the possibility of controlling the formation of impurities or zeolite polymorphs by seeding is demonstrated. By integrating the expertise obtained on zeolite crystallization, we developed a novel surface-modified zeolite crystal synthesis process from initial design to scale up using commercial materials. We show that the seed-assisted rational design provides an effective and robust route for different types of zeolite crystals.