Molecular Tuning of Reactivity of Zeolite Protons in HZSM-5

Yaxin Chen; Xinyou Ma; John H. Hack; Shuhao Zhang; Anyang Peng; James P. Dombrowski; Gregory A. Voth; Andrei Tokmakoff; Mayfair Kung; Harold H. Kung

doi:10.1021/jacs.3c12680

Molecular Tuning of Reactivity of Zeolite Protons in HZSM-5

Yaxin Chen, Xinyou Ma, John H. Hack, Shuhao Zhang, Anyang Peng, James P. Dombrowski, Gregory A. Voth, Andrei Tokmakoff, Mayfair Kung, Harold H. Kung^*

^*Corresponding author for this work

Chemical and Biological Engineering

Research output: Contribution to journal › Article › peer-review

2 Scopus citations

Abstract

In acidic HZSM-5 zeolite, the reactivity of a methanol molecule interacting with the zeolite proton is amenable to modification via coadsorbing a stochiometric amount of an electron density donor E to form the [(E)(CH₃OH)(HZ)] complex. The rate of the methanol in this complex undergoing dehydration to dimethyl ether was determined for a series of E with proton affinity (PA) ranging from 659 kJ mol^-1 for C₆F₆ to 825 kJ mol^-1 for C₄H₈O and was found to follow the expression: Ln(Rate) - Ln(Rate_N₂) = β(PA - PA_N₂)^γ, where E = N₂ is the reference and β and γ are constants. This trend is probably due to the increased stability of the solvated proton in the [(E)(CH₃OH)(HZ)] complex with increasing PA. Importantly, this is also observed in steady-state flow reactions when stoichiometric quantities of E are preadsorbed on the zeolite. As demonstrated with E being D₂O, the effect on methanol reactivity diminishes when E is present in excess of the [(E)(CH₃OH)(HZ)] complex. It is proposed that the methanol dehydration reaction involves [(E)(CH₃OH)(CH₃OH)(HZ)] as the transition state, which is supported by the isotopologue distribution of the initial dimethyl ether formed when a flow of CH₃OH was passed over ZSM-5 containing one CD₃OH per zeolite proton. The implication of this on the mechanism of catalytic methanol dehydration on HZSM-5 is discussed.

Original language	English (US)
Pages (from-to)	10342-10356
Number of pages	15
Journal	Journal of the American Chemical Society
Volume	146
Issue number	15
DOIs	https://doi.org/10.1021/jacs.3c12680
State	Published - Apr 17 2024

Funding

Y.C., X.M., J.H.H., J.D., G.V., A.T., and H.K. were supported as a part of the Advanced Materials for Energy Water Systems (AMEWS) Center, an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Basic Energy Sciences. S.Z., A.P., and M.K. were supported by ICEP, funded by the U.S. DOE Office of Science, Basic Energy Sciences (DOE DE-FG02-03-ER15457). The authors acknowledge the computational resources provided by the University of Chicago Research Computing Center (RCC) and the U.S. Department of Defense High-Performance Computing Modernization Program.

ASJC Scopus subject areas

Catalysis
General Chemistry
Biochemistry
Colloid and Surface Chemistry

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10.1021/jacs.3c12680

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title = "Molecular Tuning of Reactivity of Zeolite Protons in HZSM-5",

abstract = "In acidic HZSM-5 zeolite, the reactivity of a methanol molecule interacting with the zeolite proton is amenable to modification via coadsorbing a stochiometric amount of an electron density donor E to form the [(E)(CH3OH)(HZ)] complex. The rate of the methanol in this complex undergoing dehydration to dimethyl ether was determined for a series of E with proton affinity (PA) ranging from 659 kJ mol-1 for C6F6 to 825 kJ mol-1 for C4H8O and was found to follow the expression: Ln(Rate) - Ln(RateN2) = β(PA - PAN2)γ, where E = N2 is the reference and β and γ are constants. This trend is probably due to the increased stability of the solvated proton in the [(E)(CH3OH)(HZ)] complex with increasing PA. Importantly, this is also observed in steady-state flow reactions when stoichiometric quantities of E are preadsorbed on the zeolite. As demonstrated with E being D2O, the effect on methanol reactivity diminishes when E is present in excess of the [(E)(CH3OH)(HZ)] complex. It is proposed that the methanol dehydration reaction involves [(E)(CH3OH)(CH3OH)(HZ)] as the transition state, which is supported by the isotopologue distribution of the initial dimethyl ether formed when a flow of CH3OH was passed over ZSM-5 containing one CD3OH per zeolite proton. The implication of this on the mechanism of catalytic methanol dehydration on HZSM-5 is discussed.",

author = "Yaxin Chen and Xinyou Ma and Hack, {John H.} and Shuhao Zhang and Anyang Peng and Dombrowski, {James P.} and Voth, {Gregory A.} and Andrei Tokmakoff and Mayfair Kung and Kung, {Harold H.}",

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doi = "10.1021/jacs.3c12680",

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T1 - Molecular Tuning of Reactivity of Zeolite Protons in HZSM-5

AU - Chen, Yaxin

AU - Ma, Xinyou

AU - Hack, John H.

AU - Zhang, Shuhao

AU - Peng, Anyang

AU - Dombrowski, James P.

AU - Voth, Gregory A.

AU - Tokmakoff, Andrei

AU - Kung, Mayfair

AU - Kung, Harold H.

PY - 2024/4/17

Y1 - 2024/4/17

N2 - In acidic HZSM-5 zeolite, the reactivity of a methanol molecule interacting with the zeolite proton is amenable to modification via coadsorbing a stochiometric amount of an electron density donor E to form the [(E)(CH3OH)(HZ)] complex. The rate of the methanol in this complex undergoing dehydration to dimethyl ether was determined for a series of E with proton affinity (PA) ranging from 659 kJ mol-1 for C6F6 to 825 kJ mol-1 for C4H8O and was found to follow the expression: Ln(Rate) - Ln(RateN2) = β(PA - PAN2)γ, where E = N2 is the reference and β and γ are constants. This trend is probably due to the increased stability of the solvated proton in the [(E)(CH3OH)(HZ)] complex with increasing PA. Importantly, this is also observed in steady-state flow reactions when stoichiometric quantities of E are preadsorbed on the zeolite. As demonstrated with E being D2O, the effect on methanol reactivity diminishes when E is present in excess of the [(E)(CH3OH)(HZ)] complex. It is proposed that the methanol dehydration reaction involves [(E)(CH3OH)(CH3OH)(HZ)] as the transition state, which is supported by the isotopologue distribution of the initial dimethyl ether formed when a flow of CH3OH was passed over ZSM-5 containing one CD3OH per zeolite proton. The implication of this on the mechanism of catalytic methanol dehydration on HZSM-5 is discussed.

AB - In acidic HZSM-5 zeolite, the reactivity of a methanol molecule interacting with the zeolite proton is amenable to modification via coadsorbing a stochiometric amount of an electron density donor E to form the [(E)(CH3OH)(HZ)] complex. The rate of the methanol in this complex undergoing dehydration to dimethyl ether was determined for a series of E with proton affinity (PA) ranging from 659 kJ mol-1 for C6F6 to 825 kJ mol-1 for C4H8O and was found to follow the expression: Ln(Rate) - Ln(RateN2) = β(PA - PAN2)γ, where E = N2 is the reference and β and γ are constants. This trend is probably due to the increased stability of the solvated proton in the [(E)(CH3OH)(HZ)] complex with increasing PA. Importantly, this is also observed in steady-state flow reactions when stoichiometric quantities of E are preadsorbed on the zeolite. As demonstrated with E being D2O, the effect on methanol reactivity diminishes when E is present in excess of the [(E)(CH3OH)(HZ)] complex. It is proposed that the methanol dehydration reaction involves [(E)(CH3OH)(CH3OH)(HZ)] as the transition state, which is supported by the isotopologue distribution of the initial dimethyl ether formed when a flow of CH3OH was passed over ZSM-5 containing one CD3OH per zeolite proton. The implication of this on the mechanism of catalytic methanol dehydration on HZSM-5 is discussed.

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JO - Journal of the American Chemical Society

JF - Journal of the American Chemical Society

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ER -

Molecular Tuning of Reactivity of Zeolite Protons in HZSM-5

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