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Ezenwa S, Montalvo-Castro H, Hoffman AJ, Locht H, Attebery J, Jan DY, Schmithorst M, Chmelka B, Hibbitts D, Gounder R. Synthetic Placement of Active Sites in MFI Zeolites for Selective Toluene Methylation to para-Xylene. J Am Chem Soc 2024; 146:10666-10678. [PMID: 38573868 DOI: 10.1021/jacs.4c00373] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 04/06/2024]
Abstract
Brønsted acidic zeolites are ubiquitous catalysts in fuel and chemical production. Broadening the catalytic diversity of a given zeolite requires strategies to manipulate the acid site placement at framework positions within distinct microporous locations. Here, we combine experiment and theory to elucidate how intermolecular interactions between organic structure-directing agents (OSDAs) and framework Al centers influence the placement of H+ sites in distinct void environments of MFI zeolites and demonstrate the catalytic consequences of active site location on kinetically controlled (403 K) toluene methylation to xylene regioisomers. Kinetic measurements, interpreted using mechanism-derived rate expressions and transition state theory, alongside density functional theory (DFT) calculations show that larger intersection environments similarly stabilize all three xylene isomer transition states without altering well-established aromatic substitution patterns (ortho/para/meta ∼ 60%:30%:10%), while smaller channel environments preferentially destabilize transition states that form bulkier ortho- and meta-isomers, thereby resulting in high intrinsic para-xylene selectivity (∼80%). DFT calculations reveal that the flexibility of nonconventional OSDAs (e.g., 1,4-diazabicyclo[2.2.2]octane) to reorient within MFI intersections and their ability to hydrogen-bond to form protonated complexes favor the placement of Al in smaller channel environments compared to conventional quaternary OSDAs (e.g., tetra-n-propylammonium). These molecular-level insights establish a mechanistic link between OSDA structure, active site placement, and transition state stability in MFI zeolites and provide active site design strategies that are orthogonal to crystallite design approaches harnessing complex reaction-diffusion phenomena to enhance regioisomer selectivity in the industrial production of valuable polymer precursors.
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Affiliation(s)
- Sopuruchukwu Ezenwa
- Davidson School of Chemical Engineering, Purdue University, West Lafayette, Indiana 47907, United States
| | - Hansel Montalvo-Castro
- Department of Chemical Engineering, University of Florida, Gainesville, Florida 32608, United States
| | - Alexander J Hoffman
- Department of Chemical Engineering, University of Florida, Gainesville, Florida 32608, United States
| | - Huston Locht
- Department of Chemical Engineering, University of Florida, Gainesville, Florida 32608, United States
| | - Jordan Attebery
- Department of Chemical Engineering, University of Florida, Gainesville, Florida 32608, United States
| | - Deng-Yang Jan
- Honeywell UOP, Des Plaines, Illinois 60017, United States
| | - Michael Schmithorst
- Department of Chemical Engineering, University of California, Santa Barbara, Santa Barbara, California 93106, United States
| | - Bradley Chmelka
- Department of Chemical Engineering, University of California, Santa Barbara, Santa Barbara, California 93106, United States
| | - David Hibbitts
- Department of Chemical Engineering, University of Florida, Gainesville, Florida 32608, United States
| | - Rajamani Gounder
- Davidson School of Chemical Engineering, Purdue University, West Lafayette, Indiana 47907, United States
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Ryoo R, Liu SB, De Menorval LC, Takegoshi K, Chmelka B, Trecoske M, Pines A. Distribution of hexamethylbenzene in a zeolite studied by xenon-129 and multiple-quantum NMR. ACTA ACUST UNITED AC 2002. [DOI: 10.1021/j100311a003] [Citation(s) in RCA: 45] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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