(4nz) Mechanistic Studies of Zeolite Catalysis

Conversion of large hydrocarbons into lighter molecules through catalytic cracking is an important process in the refining industry. These reactions are carried out using strong microporous acid catalysts known as zeolites. Zeolites contain a high density of active sites and the confining space within them allows for modification of reaction rates and selectivity through the addition of extra framework atoms. Specifically, extra framework aluminum (EFAl) species and rare earth cations, such as La and Ce, have been shown to influence the rates of dehydrogenation and catalytic cracking in zeolite pores and improve the hydrothermal stability of the zeolite, protecting it from the loss of active sites. However, the mechanism driving these effects remains unclear. Understanding the location and nature of extra framework species is useful in fine tuning a zeolite’s behavior. It is also valuable to understand the fundamental behavior involved in the interaction between transition states and the extra framework species.

Research Interests:

I am currently a graduate student at the University of Oklahoma (OU), completing my PhD study. My undergraduate, Masters, and PhD programs are all in chemical engineering with the graduate portions focusing on heterogeneous catalysis. My research thus far has been using density functional theory (DFT) calculations to enhance fundamental understanding of the behavior within zeolite pores. In my first project I carried out computational NMR calculations to compare with solid state NMR experimental results. Following this study, lanthanum was introduced into the zeolite in seven unique locations with varied hydroxide coordination and clustering configurations. This study showed that, from a thermodynamic perspective, lanthanum prefers to be sited within the sodalite cages. While studying reactions critical to the refining industry, it is apparent that a large ensemble of differing computational methods have been employed. Specifically, the different approaches to correct dispersion energy in DFT calculations often changes adsorption energies drastically. It was then pertinent to benchmark several different dispersion correction methods and compare their calculated adsorption energy, apparent barrier, and intrinsic barrier before moving on to study industrially relevant reactions. This study showed that while the adsorption and apparent activation energies change substantially, the dispersion correction nearly cancels out when calculating the intrinsic activation energy, implying reliability of these barriers. I am currently working to study the effects of extra framework cations in MFI zeolite and their effect on transition state stabilization for catalytic cracking reactions using propane as a probe molecule. This study focuses on deconvoluting the energetic contributions from dipole-dipole interactions, dispersion forces, and structural deformation energies present at the transition state. I am interested in applying my studies to further understand the fundamental aspects of heterogenous porous structures for catalytic processes and energy transformation.

Publications:

[1] Crouch, J.; Mou, T.; Li, G.; Resasco, D.; Wang, B., How van der Waals Approximation Methods Affect Activation Barriers of Cyclohexene Hydrogenation over a Pd Surface. ACS Engineering Au 2022, 2 (6), 547-552.

[2] 1. Kuizhi Chen, A. Z., Reda Bababrik, Jacob Crouch, Walter Alvarez, Matt Wulfers, Daniel Resasco, Bin Wang, Steven Crossley, and Jeffery L. White, First-Formed Framework Species and Phosphate Structure Distributions in Phosphorus-Modified MFI Zeolites. The Journal of Physical Chemistry 2022.