(318f) Computational Studies of Novel Structure-Directing Agents and Crystal Growth Modifiers for Zeolite Catalysts

1. John Clark and Jeremy C. Palmer

Department of Chemical and Biomolecular Engineering, University of Houston, Houston, Texas, 77204, USA

ABSTRACT

Designing nanoporous zeolite materials with tailored properties is critical to industrial applications ranging from fluid separations and ion exchange to hydrocarbon cracking and methanol reformation. Organic structure-directing agents (OSDAs) are commonly used to facilitate the formation of specific zeolite framework types. Effective OSDAs exhibit a size and shape that is commensurate with the geometry of porous channels and cages of zeolites, thereby directing their formation in situ¹. Zeolite growth modifiers (ZGMs) can also be used in conjunction with OSDAs to further tune material properties. Whereas OSDAs play a critical role in zeolite polymorph selection, ZGMs are molecular additives that influence bulk crystal shape and size by adsorbing to specific crystal faces and altering anisotropic rate(s) of growth during synthesis¹. Although the combination of OSDAs and ZGMs allows for unprecedented control over zeolite properties to be achieved, identifying new and inexpensive compounds suitable for industrial scale synthesis remains a major challenge.

We present results from three recent combined computational and experimental studies of novel OSDAs and ZGMs for designing improved zeolite catalysts. In the first study², we show that a common surfactant (cetrimonium bromide) can be used as an alternative to the standard OSDA (tetrapropylammonium) for stabilizing ZSM-5, which is a widely used industrial catalysts. In the second study, we demonstrate that an unusual synergistic effect between a pair of OSDAs leads to the formation of mordenite nanocrystals, which cannot be produced using either OSDA alone. Finally, we examine the effect of several alcohol-based ZGMs on the shape and size of TON and LTL structured zeolite crystals. In each case, advanced molecular simulation techniques are used to elucidate the mechanisms by which the specific OSDAs and ZGMs influence zeolite stability and growth. Predictions from the simulations are shown to be in agreement with zeolite synthesis, NMR, and immersion calorimetry experiments.

References

[1] A. I. Lupulescu, M. Kumar and J. D. Rimer, “A Facile Strategy to Design Zeolite L Crystals with Tunable Morphology and Surface Architecture”, J. Am. Chem. Soc., 2013, 135, 6608-6617.

[2] A. Chawla, R. Li, R. Jain, R. J. Clark, J. G. Sutjianto, J. C. Palmer and J. D. Rimer, “Cooperative Effects of Inorganic and Organic Structure-Directing Agents in ZSM-5 Crystallization”, Mol. Syst. Des. Eng., 2018, 3, 159-170.