Theoretical Determination of Size Effects in Zeolite-Catalyzed Alcohol Dehydration
| Autor: | L.A. Curtiss, Larrissa Y. Kunz, Rajeev S. Assary, David J. Robichaud, Mark R. Nimlos, Lintao Bu, Seonah Kim, Brandon C. Knott, Cong Liu |
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| Jazyk: | angličtina |
| Rok vydání: | 2019 |
| Předmět: |
ONIOM
Reaction mechanism physical_chemistry 02 engineering and technology 010402 general chemistry lcsh:Chemical technology 01 natural sciences DFT biomass pyrolysis alcohol dehydration zeolite Catalysis Reaction coordinate lcsh:Chemistry Adsorption Computational chemistry lcsh:TP1-1185 Physical and Theoretical Chemistry Concerted reaction Chemistry 021001 nanoscience & nanotechnology Transition state 0104 chemical sciences Dehydration reaction lcsh:QD1-999 0210 nano-technology |
| Zdroj: | Catalysts, Vol 9, Iss 9, p 700 (2019) Catalysts; Volume 9; Issue 9; Pages: 700 |
| ISSN: | 2073-4344 |
| Popis: | 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. |
| Databáze: | OpenAIRE |
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