549437 Low-Temperature One-Step Conversion of Methane to Methanol and Acetic Acid with Supported Rhodium Single Cations Using Molecular Oxygen

Wednesday, June 5, 2019
Texas Ballroom Prefunction Area (Grand Hyatt San Antonio)
Mengwei Li1, Junjun Shan2 and Maria Flytzani-Stephanopoulos1, (1)Department of Chemical and Biological Engineering, Tufts University, Medford, MA, (2)NICE AMERICA RESEARCH, Inc, Mountain View, CA

Low-temperature one-step conversion of methane to methanol and acetic acid with supported rhodium single cations using molecular oxygen

Mengwei Li, Junjun Shan, Maria Flytzani-Stephanopoulos*

Department of Chemical and Biological Engineering, Tufts University, MA 02155, USA

Current address: NICE America Research, Inc., Mountain View, California 94043, USA

*Corresponding author: maria.flytzani-stephanopoulos@tufts.edu

Methane, the main component of natural gas, is the most stable hydrocarbon. The first C-H bond in methane possesses bond energy of ~104 kcal/mol. Due to the recent breakthrough in hydraulic fracturing, there has been renewed interest in methane conversion to valuable liquid oxygenates. The industrial process to synthesize oxygenates from methane involves first converting methane to syngas and then perform methanol synthesis and methanol carbonylation as separate steps. This process is energy intensive and not economical for small scale production. On the other hand, one-step conversion which utilizes oxidation reaction at mild conditions, offers an alternative small-scale process. The potential application of this process to stranded natural gas is highly desirable.

The direct catalytic conversion of methane to methanol and other liquid oxygenates with high yield has long been considered the holy grail of catalysis. The first C-H bond requires either harsh conditions or highly energized species to activate, while the desired product is prone to over oxidation under the same conditions. Recently, extensive studies have been directed to methane-to-oxygenates using heterogeneous catalyst at temperatures below 250⁰C, including low temperature gas phase reaction [1], electrophilic C-H bond activation in acidic media [2] and aqueous phase conversion using peroxide [3]. However, these systems either require expensive oxidant, e.g. peroxide or sulfuric acid that poses economic and environmental concerns, or the rate is too low to be considered applicable. Here we report that supported rhodium single cations catalyze the selective one-step oxidation of methane to methanol and acetic acid using molecular oxygen as oxidant, carbon monoxide as additive gas, in aqueous solutions under mild conditions (110-150 ⁰C, 20-30 bar) [4]. Liquid oxygenates are formed with rate of 3000 µmol/g/h and conversion up to 4% when anchoring rhodium single cations on zeolite. The Brønsted acidity of zeolite is required for the carbonylation of methane to form acetic acid while the direct oxygen insertion route to form methanol can proceed on non-acidic oxide support.

[1] Narsimhan, K., Iyoki, K., Dinh, K., and Román-Leshkov, Y. ACS Cent. Sic. 2, 424 (2016).

[2] Soorholtz, M., White, R. J., Zimmermann, T., Titirici, M., Antonietti, M., Palkovits, R. and Schüth, F. Chem. Commun. 49, 240 (2013).

[3] Hammond, C., Forde, M. M., and Ab Rahim, M. H., et al. Angew. Chem. Int. Ed. 51, 5129 (2012).

[4] Shan, J., Li, M., Allard, L. F., Lee, S. and Flytzani-Stephanopoulos, M. Nature 551, 605 (2017).

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