(63h) Elucidating the Mechanism of Nanosheet Pillaring in MFI-Type Zeolites

Nanoporous aluminosilicates (zeolites) are used commercially as catalysts and sorbents for ion exchange and separation applications. Their tunable physicochemical properties make zeolites desirable catalysts for various chemical reactions; however, it is challenging to synthesize zeolite crystals with sizes smaller than 100 nm where the deleterious effects of mass transport limitations in confined pores can be limited, thereby improving the overall performance of zeolite catalysts for diverse applications. One strategy to address mass transport problems is the synthesis of hierarchical zeolites via the introduction of larger pore networks (e.g., mesopores and/or macropores). Here, we will discuss how such materials can be made through the generation of self-pillared pentasil (SPP) zeolites, which are comprised of intergrown nanosheets of five-membered ring zeolites (MFI and MEL types). The synthesis of these materials is accomplished using a seed-assisted technique that does not require costly organic structure-directing agents [1].

We will discuss diverse ways to tailor synthesis parameters to optimize the physicochemical properties of SPP zeolites. Parametric studies reveal the importance of zeolite synthesis composition, reagent selection, and the choice of the seed crystal structure. Our findings indicate that pillared nanosheets form within a relatively limited compositional space near the intersection of three zeolite phases: MFI, MEL, and MOR. Changes in growth conditions can markedly impact the degree of nanosheet pillaring and branching, as well as the kinetics of zeolite crystallization. Structural evolution from amorphous precursors to crystalline SPP products was tracked using state-of-the-art techniques, such as pair distribution function and solid-state NMR analyses. Collectively, these studies have improved our fundamental understanding of hierarchical zeolite crystallization, which is a rapidly growing area of research owing to the potential of these materials to replace conventional zeolites in numerous industrial applications.

References:

[1] Jain, R., Chawla, A., Linares, N., Garcia Martinez, J., Rimer, J.D.: “Spontaneous Pillaring of Pentasil Zeolites” Adv. Mater.33 (2021) 2100897