Methane to Acetic Acid over Cu-Exchanged Zeolites : Mechanistic Insights from a Site-Specific Carbonylation Reaction

Narsimhan, Karthik; Michaelis, Vladimir K.; Mathies, Guinevere; Gunther, William R.; Griffin, Robert G.; Román-Leshkov, Yuriy

Methane to Acetic Acid over Cu-Exchanged Zeolites : Mechanistic Insights from a Site-Specific Carbonylation Reaction

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Datum

2015

Autor:innen

Narsimhan, Karthik

Michaelis, Vladimir K.

Mathies, Guinevere

Gunther, William R.

Griffin, Robert G.

Román-Leshkov, Yuriy

DOI (zitierfähiger Link)

https://doi.org/10.1021/ja5106927

Sammlungen

Chemie

Publikationstyp

Zeitschriftenartikel

Publikationsstatus

Published

Erschienen in

Journal of the American Chemical Society : JACS. 2015, 137(5), pp. 1825-1832. ISSN 0002-7863. eISSN 1520-5126. Available under: doi: 10.1021/ja5106927

Zusammenfassung

The selective low temperature oxidation of methane is an attractive yet challenging pathway to convert abundant natural gas into value added chemicals. Copper-exchanged ZSM-5 and mordenite (MOR) zeolites have received attention due to their ability to oxidize methane into methanol using molecular oxygen. In this work, the conversion of methane into acetic acid is demonstrated using Cu-MOR by coupling oxidation with carbonylation reactions. The carbonylation reaction, known to occur predominantly in the 8-membered ring (8MR) pockets of MOR, is used as a site-specific probe to gain insight into important mechanistic differences existing between Cu-MOR and Cu-ZSM-5 during methane oxidation. For the tandem reaction sequence, Cu-MOR generated drastically higher amounts of acetic acid when compared to Cu-ZSM-5 (22 vs 4 μmol/g). Preferential titration with sodium showed a direct correlation between the number of acid sites in the 8MR pockets in MOR and acetic acid yield, indicating that methoxy species present in the MOR side pockets undergo carbonylation. Coupled spectroscopic and reactivity measurements were used to identify the genesis of the oxidation sites and to validate the migration of methoxy species from the oxidation site to the carbonylation site. Our results indicate that the Cu^II-O-Cu^II sites previously associated with methane oxidation in both Cu-MOR and Cu-ZSM-5 are oxidation active but carbonylation inactive. In turn, combined UV-vis and EPR spectroscopic studies showed that a novel Cu²⁺ site is formed at Cu/Al <0.2 in MOR. These sites oxidize methane and promote the migration of the product to a Brønsted acid site in the 8MR to undergo carbonylation.

Fachgebiet (DDC)

540 Chemie

Zitieren

ISO 690

NARSIMHAN, Karthik, Vladimir K. MICHAELIS, Guinevere MATHIES, William R. GUNTHER, Robert G. GRIFFIN, Yuriy ROMÁN-LESHKOV, 2015. Methane to Acetic Acid over Cu-Exchanged Zeolites : Mechanistic Insights from a Site-Specific Carbonylation Reaction. In: Journal of the American Chemical Society : JACS. 2015, 137(5), pp. 1825-1832. ISSN 0002-7863. eISSN 1520-5126. Available under: doi: 10.1021/ja5106927

BibTex

@article{Narsimhan2015-02-11Metha-43453,
  year={2015},
  doi={10.1021/ja5106927},
  title={Methane to Acetic Acid over Cu-Exchanged Zeolites : Mechanistic Insights from a Site-Specific Carbonylation Reaction},
  number={5},
  volume={137},
  issn={0002-7863},
  journal={Journal of the American Chemical Society : JACS},
  pages={1825--1832},
  author={Narsimhan, Karthik and Michaelis, Vladimir K. and Mathies, Guinevere and Gunther, William R. and Griffin, Robert G. and Román-Leshkov, Yuriy}
}

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