Solid-State Ion-Exchanged Cu/Mordenite Catalysts for the Direct Conversion of Methane to Methanol

http://pubs.acs.org/doi/abs/10.1021/acscatal.6b02372

Ha V. Le†, Samira Parishan‡, Anton Sagaltchik§, Caren Göbel∥, Christopher Schlesiger⊥, Wolfgang Malzer⊥, Annette Trunschke# , Reinhard Schomäcker‡, and Arne Thomas*† 

† Institute of Chemistry−Functional Materials, Technische Universität Berlin, BA2, Hardenbergstraße 40, 10623 Berlin, Germany

‡ Institute of Chemistry−Technical Chemistry, Technische Universität Berlin, TC8, Straße des 17. Juni 124, 10623 Berlin, Germany

§ BasCat−UniCat BASF Joint Lab, Technische Universität Berlin, EW K 01, Hardenbergstraße 36, 10623 Berlin, Germany

∥ Institute of Chemistry, Technische Universität Berlin, TK01, Straße des 17. Juni 135, 10623 Berlin, Germany

⊥ Institute of Optics and Atomic Physics, Technische Universität Berlin, Hardenbergstraße 36, 10623 Berlin, Germany

# Department of Inorganic Chemistry, Fritz Haber Institute of the Max Planck Society, Faradayweg 4-6, 14195 Berlin, Germany

ACS Catal., 2017, 7, pp 1403–1412

DOI: 10.1021/acscatal.6b02372

The selective oxidation of methane to methanol is a highly challenging target, which is of considerable interest to gain value-added chemicals directly from fuel gas. Copper-containing zeolites, such as Cu/mordenite, have been currently reported to be the most efficient catalysts for this reaction. In this work, it is shown that solid-state ion-exchanged Cu/mordenites exhibit a significantly higher activity for the partial oxidation of methane to methanol than comparable reference catalysts, i.e., Cu/mordenites prepared by the conventional liquid-phase ion exchange procedure. The efficiency of these Cu/mordenites remained unchanged over several successive cycles. From temperature-programmed reduction (TPR) measurements, it can be concluded that the solid-state protocol accelerates Cu exchange at the small pores of mordenite: those are positions where the most active Cu species are presumably located. In situ ultraviolet–visible (UV-vis) spectroscopy furthermore indicates that different active clusters including dicopper- and tricopper-oxo complexes are formed in the catalyst upon oxygen treatment. Notably after activation of methane, different methoxy intermediates seem to be generated at the Cu sites from which one is preferably transformed to methanol by reaction with water. It is furthermore described that the applied reaction conditions have considerable influence on the finally observed methanol production from methane.

Keywords: 

methane hydroxylation; methane monooxygenase; microporous; mordenite; selective oxidation; zeolites

Potential of Ru(III/II) Couple Increases with Increased Sterics of Scorpionate Ligands

http://www.sciencedirect.com/science/article/pii/S0020169313000674.

Volume 405, 24 August 2013, Pages 470–476

Synthesis and electrochemical characterization of [Ru(NCCH₃)₆]²⁺, tris(acetonitrile) tris(pyrazolyl)borate, and tris(acetonitrile) tris(pyrazolyl)methane ruthenium(II) complexes

• Christopher C. Underwood,
• Bradley S. Stadelman,
• Mark L. Sleeper,
• Julia L. Brumaghim^,

http://dx.doi.org/10.1016/j.ica.2013.02.027

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Abstract

Tris(acetonitrile) tris(pyrazolyl)borato- and tris(pyrazolyl)methano ruthenium(II) complexes would make good synthons in ruthenium chemistry for synthesis of catalysts and DNA binding drugs. However, these complexes are not widely used as starting materials due to the long reaction times and multiple synthetic steps required or the lack of their successful synthesis. We have developed a new synthesis for the ruthenium(II) acetonitrile complex [Ru(NCCH₃)₆]²⁺ with noncoordinating BF₄⁻ or OTf (OTf = trifluoromethanesulfonate) counterions. Using this [Ru(NCCH₃)₆]²⁺ complex, the previously reported tris(acetonitrile) tris(pyrazolyl)borato ruthenium(II) complexes [Tp^RRu(NCCH₃)₃]⁺ (Tp^R = tris(pyrazolyl)borate; R = H, Me) and the unreported tris(acetonitrile) tris(pyrazolyl)borato ruthenium(II) complex (R = Ph) have been synthesized using an improved synthetic pathway that reduces the number of required steps by up to six and the average synthesis times by up to 45 h. Novel tris(acetonitrile) tris(pyrazolyl)methano ruthenium(II) complexes of the formula [Tpm^RRu(NCCH₃)₃]²⁺ (Tpm^R = tris(pyrazolyl)methane; R = Me, Ph) have also been synthesized in one step in 12 h using this method. Cyclic voltammetry studies of the synthesized complexes show that Ru^2+/3+ redox potentials generally increase with increasing steric bulk of the Tp^R or Tpm^R ligand. The ability to sterically tune Ru^2+/3+ redox potentials may be used to promote catalysis development and in the development of ruthenium-based drugs.

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Graphical abstract

We report improved syntheses for [Ru(NCCH₃)₆]²⁺ and complexes of the formula [Tp^RRu(NCCH₃)₃]⁺ (Tp^R = tris(pyrazolyl)borate; R = H, Me, Ph), as well as syntheses for unreported [Tpm^RRu(NCCH₃)₃]²⁺ (Tpm^R = tris(pyrazolyl)methane; R = Me, Ph) complexes. Electrochemical studies indicate that the Ru^2+/3+ redox potentials of these complexes vary by up to 427 mV, a trait that may be useful for ruthenium-based drug and catalysis development.

Unexpected, Latent Radical Reaction of Methane Propagated by Trifluoromethyl Radicals

Unexpected, Latent Radical Reaction of Methane Propagated by Trifluoromethyl Radicals
Nima Zargari,† Pierre Winter,‡ Yong Liang,§ Joo Ho Lee,† Andrew Cooksy,*,‡ K. N. Houk,*,§ and Kyung Woon Jung*,†
†Loker Hydrocarbon Research Institute, Department of Chemistry, University of Southern California, 837 Bloom Walk, Los Angeles, California 90089, United States
‡Department of Chemistry and Biochemistry, San Diego State University, 5500 Campanile Drive, San Diego California 92182, United States
§Department of Chemistry and Biochemistry, University of California, Los Angeles, California 90095, United States

J. Org. Chem. 2016, 81, 9820-9825.
http://pubs.acs.org/doi/pdf/10.1021/acs.joc.6b01903

Abstract:
 

Thorough mechanistic studies and DFT calculations revealed a background radical pathway latent in metal-catalyzed oxidation reactions of methane at low temperatures. Use of hydrogen peroxide with TFAA generated a trifluoromethyl radical (•CF3), which in turn reacted with methane gas to selectively yield acetic acid. It was found that the methyl carbon of the product was derived from methane, while the carbonyl carbon was derived from TFAA. Computational studies also support these findings, revealing the reaction cycle to be energetically favorable. 

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