First-principles evaluation of material stability

The relative proximity of Al atoms substituted in zeolite lattices is an important parameter that influences both hydrothermal stability and catalytic function, but the underlying chemistry that governs Al site proximity is not well understood. Here, we examine relationships between exchanged counter-cations and different Al−Al arrange- ments in a chabazite (CHA, SSZ-13) zeolite lattice. We report periodic supercell density functional theory (DFT) calculations for structures and energies of SSZ-13 lattices with systematically enumerated and varied Al-Al proximity, both charge-uncompensated and charge-compensated by either proton pairs (H⁺/H⁺) or divalent copper cations (Cu²⁺). Al−Al interactions are electrostatically repulsive without charge compensa- tion, but the relative energies of certain Al-Al site arrangements change upon compen- sation by counter-cations. Al-Al interactions are uniformly attractive when compen- sated by H⁺/H⁺ pairs, but are attractive at long and repulsive at short Al−Al distances when compensated by Cu²⁺, highlighting the role of the counter-cation in stabilizing different Al−Al arrangements. Through descriptor analysis, we find Cu²⁺ energy land- scape can be described by models consisting of electrostatics and a binary term that specifies whether or not Cu²⁺ resides in the 6-MR. The H⁺/H⁺ and Cu²⁺ energy land- scapes together imply that Cu²⁺ prefers to site at 6-MR Al−Al pairs. These results shed light on how counter-cations influence Al distribution and rearrangement during synthesis and post-synthetic treatments of SSZ-13 zeolite, which potentially influences its susceptibility to dealumination during hydrothermal aging.

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First-Principles Comparison of Proton and Divalent Copper Cation Exchange Energy Landscapes in SSZ-13 Zeolite

S. Li, H. Li, R. Gounder, A. Debellis, I. B. Mueller, S. Prasad, A. Moini and W. F. Schneider*. J. Phys. Chem. C, 2018, 122, 41, 23564-23573

Supporting Information

Effect of Water on Exchanged Copper Siting and Speciation in SSZ-13 Zeolites

S. Li , R. Gounder, A. Debellis, I. B. Mueller, S. Prasad, A. Moini and W. F. Schneider*. Submission-ready

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2018 International Conference on Theoretical Aspects of Catalysis, Los Angeles, CA (click the poster for high-resolution file)

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Development of characterization methods

The systematic DFT computation workflow is further used to perform high-throughput screening of 10 ion types, including a range of alkaline earth (Mg, Ca, Sr, and Ba) and 3d transition metals (Mn, Fe, Co, Ni, Cu, and Zn), and use density functional theory (DFT) methods to determine the energy landscapes of lattices substituted with various Al-Al arrangements, and charge-compensated by the divalent cation forms of these metals. Analyzing the energy landscapes through descriptor model, we rationalize the observed differences by the ionic radii differences. Results were leveraged to develop a experimental characterization method of using different ions as chemical titrants for Al pairs with distinct proximities and further inferring Al distribution in zeolite materials. The feasibility of the method is well validated by our collaborators at Purdue University and it has now become a standard characterization technique used in their daily research.

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Developing Al Proximity Titration Strategy for SSZ-13 Zeolite from First-Principles

S. Li, C. B. Jones, Y. Wang, J. R. Di Iorio, A. Debellis, I. B. Mueller, S. Prasad, A. Moini, R. Gounder, W. F. Schneider*. In preparation

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2018 International Conference on Theoretical Aspects of Catalysis, Los Angeles, CA (click the poster for high-resolution file)

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2018 AIChE Annual Meeting, Pittsburgh, PA

Machine learning models for quick energy estimation

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