Manganese Catalyzed Partial Oxidation of Light Alkanes

Nathan Coutard, Charles B. Musgrave, Jisue Moon, Nichole S. Liebov, Robert M. Nielsen, Jonathan M. Goldberg, Meijun Li, Xiaofan Jia, Sungsik Lee, Diane A. Dickie, William L. Schinski, Zili Wu, John T. Groves, William A. Goddard, T. Brent Gunnoe

Research output: Contribution to journalArticlepeer-review

Abstract

The catalytic partial oxidation of methane is achieved at low temperatures (<200 °C) using manganese oxides and manganese salts in mixtures of trifluoroacetic acid and trifluoroacetic anhydride. Dioxygen is used as the in situ terminal oxidant. For Mn oxides (e.g., MnO2, Mn2O3, and Mn3O4), we studied stoichiometric methane partial oxidation in HTFA (TFA = trifluoroacetate). Using a Mn trifluoroacetate salt, at 180 °C and under 25 psig of methane, product selectivity for the mono-oxidized product methyl trifluoroacetate (MeTFA) is observed to be >90% at ∼35% methane conversion at approximately 6 turnovers. Under our catalytic methane oxidation reaction conditions, MeTFA is stable against overoxidation, which explains the likely high selectivity at conversions >15%. Using combined experimental studies and DFT calculations, a mechanism involving soluble and molecular Mn species in the catalytic cycle is proposed. The proposed reaction pathway involves initial activation of MnIIby dioxygen, cleavage of a methane C-H bond by a MnIIIhydroxo intermediate, rebound of the methyl radical to generate MeTFA, and finally regeneration of the starting MnIIcomplex. Also, this process is shown to be applicable to the oxidation of ethane, favoring the mono-oxidized product ethyl trifluoroacetate (EtTFA) and reaching ∼46% conversion.

Original languageEnglish (US)
Pages (from-to)5356-5370
Number of pages15
JournalACS Catalysis
Volume12
Issue number9
DOIs
StatePublished - May 6 2022

All Science Journal Classification (ASJC) codes

  • Catalysis
  • Chemistry(all)

Keywords

  • manganese
  • methane functionalization
  • methanol
  • natural gas
  • oxy-esterification
  • partial oxidation

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