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Open AccessArticle

Theoretical Determination of Size Effects in Zeolite-Catalyzed Alcohol Dehydration

1
National Renewable Energy Laboratory, 15013 Denver West Pkwy, Golden, CO 80401, USA
2
Chemical Sciences and Engineering Division, Argonne National Laboratory, 9700 South Cass Avenue, Lemont, IL 60439, USA
3
Materials Science Division, Argonne National Laboratory, 9700 South Cass Avenue, Lemont, IL 60439, USA
*
Author to whom correspondence should be addressed.
These authors contributed equally to this work.
Catalysts 2019, 9(9), 700; https://doi.org/10.3390/catal9090700
Received: 31 July 2019 / Revised: 15 August 2019 / Accepted: 16 August 2019 / Published: 21 August 2019
(This article belongs to the Special Issue Catalytic Fast Pyrolysis)
In the upgrading of biomass pyrolysis vapors to hydrocarbons, dehydration accomplishes a primary objective of removing oxygen, and acidic zeolites represent promising catalysts for the dehydration reaction. Here, we utilized density functional theory calculations to estimate adsorption energetics and intrinsic kinetics of alcohol dehydration over H-ZSM-5, H-BEA, and H-AEL zeolites. The ONIOM (our Own N-layered Integrated molecular Orbital and molecular Mechanics) calculations of adsorption energies were observed to be inconsistent when benchmarked against QM (Quantum Mechanical)/Hartree–Fock and periodic boundary condition calculations. However, reaction coordinate calculations of adsorbed species and transition states were consistent across all levels considered. Comparison of ethanol, isopropanol (IPA), and tert-amyl alcohol (TAA) over these three zeolites allowed for a detailed examination of how confinement impacts on reaction mechanisms and kinetics. The TAA, seen to proceed via a carbocationic mechanism, was found to have the lowest activation barrier, followed by IPA and then ethanol, both of which dehydrate via a concerted mechanism. Barriers in H-BEA were consistently found to be lower than in H-ZSM-5 and H-AEL, attributed to late transition states and either elevated strain or inaccurately estimating long-range electrostatic interactions in H-AEL, respectively. Molecular dynamics simulations revealed that the diffusivity of these three alcohols in H-ZSM-5 were significantly overestimated by Knudsen diffusion, which will complicate experimental efforts to develop a kinetic model for catalytic fast pyrolysis. View Full-Text
Keywords: biomass pyrolysis; alcohol dehydration; zeolite; DFT; ONIOM biomass pyrolysis; alcohol dehydration; zeolite; DFT; ONIOM
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MDPI and ACS Style

Kunz, L.Y.; Bu, L.; Knott, B.C.; Liu, C.; Nimlos, M.R.; Assary, R.S.; Curtiss, L.A.; Robichaud, D.J.; Kim, S. Theoretical Determination of Size Effects in Zeolite-Catalyzed Alcohol Dehydration. Catalysts 2019, 9, 700.

AMA Style

Kunz LY, Bu L, Knott BC, Liu C, Nimlos MR, Assary RS, Curtiss LA, Robichaud DJ, Kim S. Theoretical Determination of Size Effects in Zeolite-Catalyzed Alcohol Dehydration. Catalysts. 2019; 9(9):700.

Chicago/Turabian Style

Kunz, Larissa Y.; Bu, Lintao; Knott, Brandon C.; Liu, Cong; Nimlos, Mark R.; Assary, Rajeev S.; Curtiss, Larry A.; Robichaud, David J.; Kim, Seonah. 2019. "Theoretical Determination of Size Effects in Zeolite-Catalyzed Alcohol Dehydration" Catalysts 9, no. 9: 700.

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