Abstract: The diverse network of confined pores in zeolites have been widely used for shape-selective catalysis in the (petro)chemical industry. A common objective of zeolite catalyst design is to overcome the inherent mass transport limitations of nanopores; however, the complex pathways of zeolite crystallization make it difficult to control their physicochemical properties.
In this talk, I will highlight several methods to tailor zeolite crystal size, morphology, and composition in ways that collectively reduce diffusion limitations, thereby enabling the design of catalysts with superior performance compared to materials obtained by conventional synthesis routes.
We have discovered new methods to generate 2-dimensional (single layer) zeolites with high external surface area, while also developing methods to passivate external sites via epitaxial growth of core-shells. We demonstrate how a combination of these two techniques allows for the deconstruction of zeolites with distinct topological features to elucidate the origins of improved catalyst performance (i.e., selectivity and lifetime), which we have applied in combination with collaborative computational studies to examine the unique performance of zeolite catalysts in toluene alkylation with methanol. Additional findings in our group have revealed that core-shell (or zoned) zeolites with Si-rich exterior surfaces can dramatically reduce diffusion limitations, thereby resulting in catalysts that are far superior to analogues with homogeneous distributions of acid sites. As additional examples of zeolite crystal engineering, we will describe structure-performance relationships of various hierarchical materials, such as self-pillared pentasils that exhibit four-fold increases in both lifetime and total turnovers. Lastly, we will introduce a new class of catalysts, referred to as finned zeolites, which are prepared by seeded growth to introduce fin-like protrusions (size α) with identical crystallographic registry as the interior crystal (size β).
Examples of both 2- and 3-dimensional zeolites will be discussed using methanol to hydrocarbons (MTH) as benchmark reaction and state-of-the-art characterization using techniques such as high-resolution electron tomography, operando spectroscopy, novel acid titration methods, and molecular modeling to correlate structural features of finned zeolites and their diffusion properties with enhanced catalyst performance.