(44b) Enhancing Zeolite-Based Catalysts Via Elemental Modification of Precursor States

Engineering zeolite crystals is notoriously challenging owing to complex synthesis media containing diverse (alumino-)silicate species¹. Designing better catalysts is therefore often limited to strategies that are effective for select instances, but do not apply generally. Conversely, other approaches such as hard-templating, organosilane-modification, and demetallation are more broadly effective, but remain prohibitively costly owing to multi-step processing and/or expensive reagents. We propose the use of a class of abundant elemental species that can in principle tailor zeolite nucleation and/or growth. These elements, such as zinc, gallium, germanium, and tin, can form tetrahedral hydroxide species in alkaline solution, similar to silicate and aluminate². Commonly referred to as heteroatoms, elements such as these can isomorphically substitute into zeolite frameworks³; however, we will demonstrate that these elements need not fully incorporate into the zeolite to benefit synthesis outcomes. We will discuss how Zn and Ge can alter crystal properties in interesting, beneficial, and often unpredictable, ways. For example, the introduction of zinc into syntheses of FAU-type zeolites can suppress the formation of impurity phases by interrupting interzeolite transformations. Furthermore, we investigate the benefits of using zinc to engineer crystal defects for enhanced catalytic properties. Separately, we observe that introducing germanium into synthesis mixtures of MFI- and MEL-type zeolites leads to a significant reduction in crystal dimensions. As a result, these zeolite products possess substantially longer catalyst lifetimes, putatively owing to enhanced diffusion properties. Although heteroatoms have been observed to cause diverse effects in zeolite syntheses, we posit that a greater understanding of chemical and colloidal phenomena underlying zeolite crystallization will allow researchers to harness these effects towards the objective of rationally designed zeolites.

References:

[1] Mallette, Adam, et al. Nature Synthesis. Accepted. 2022

[2] Fricke, Rolf, et al. Chemical Reviews 100 2000 2303-2406.

[3] Eliášová, Pavla, et al. Chemical Society Reviews 44 2015 7177-7206.