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Synergy of Oxygen and Water in Ceria-Catalyzed Direct Conversion of Methane to Methanol under Continuous Flow

Li, Wen ; Shi, Junjie ; Tangpakonsab, Parinya Lewis ; Zhang, Bin ; Haunold, Thomas ; Genest, Alexander ; Yigit, Nevzat ; Atzl, Leonard ; Kokkonen, Esko LU orcid and Qin, Yong , et al. (2025) In ACS Catalysis 15. p.20496-20511
Abstract

The direct conversion of methane to methanol (DCMM) under continuous flow and atmospheric pressure offers notable environmental benefits and industrial promise, but remains a long-standing challenge due to the difficulty of activating CH4while avoiding overoxidation of methanol. Here, we demonstrate that pure ceria (CeO2), without any metal promoters, enables gas-phase DCMM with up to 80% selectivity at 300–350 °C, upon optimization of the H2O/O2ratio. At 550 °C, methanol and formaldehyde are formed at rates of 24 and 38 μmol g–1h–1, respectively, both dropping below 1 μmol g–1h–1in the absence of O2. Ex situ transmission electron... (More)

The direct conversion of methane to methanol (DCMM) under continuous flow and atmospheric pressure offers notable environmental benefits and industrial promise, but remains a long-standing challenge due to the difficulty of activating CH4while avoiding overoxidation of methanol. Here, we demonstrate that pure ceria (CeO2), without any metal promoters, enables gas-phase DCMM with up to 80% selectivity at 300–350 °C, upon optimization of the H2O/O2ratio. At 550 °C, methanol and formaldehyde are formed at rates of 24 and 38 μmol g–1h–1, respectively, both dropping below 1 μmol g–1h–1in the absence of O2. Ex situ transmission electron microscopy, X-ray photoelectron spectroscopy, and Raman spectroscopy confirm that CeO2maintains structural integrity and resists carbon deposition during reaction. Combining kinetic studies, steady-state in situ diffuse reflectance infrared Fourier transform spectroscopy (in situ DRIFTS), and density functional theory (DFT) reveals that hydroxyl groups (OH), generated from water dissociation, play a multifaceted role: they facilitate C–H bond activation, promote methoxy formation, and enhance methanol desorption. In situ ambient-pressure X-ray photoelectron spectroscopy (AP-XPS) directly reveals the evolution of surface intermediates and shows that cofeeding O2and H2O suppresses CH3O and CHxaccumulation while boosting methanol yield, indicating a rapid intermediate turnover as key to sustained activity. AP-XPS O 1s spectra further highlight that O2promotes H2O dissociation, regenerating reactive OH groups and maintaining performance at elevated temperature. These findings offer molecular-level insights into how water and oxygen cooperatively tune reactivity, enabling efficient methane-to-methanol conversion on a metal-free oxide catalyst.

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organization
publishing date
type
Contribution to journal
publication status
published
subject
keywords
CeO, DFT, in situAP-XPS, in situDRIFTS, methane to methanol, reaction mechanism
in
ACS Catalysis
volume
15
pages
16 pages
publisher
The American Chemical Society (ACS)
external identifiers
  • scopus:105023174856
ISSN
2155-5435
DOI
10.1021/acscatal.5c05829
language
English
LU publication?
yes
id
b9260740-5e9e-480b-93aa-33ef6e7a5445
date added to LUP
2026-02-04 12:11:41
date last changed
2026-02-04 12:12:43
@article{b9260740-5e9e-480b-93aa-33ef6e7a5445,
  abstract     = {{<p>The direct conversion of methane to methanol (DCMM) under continuous flow and atmospheric pressure offers notable environmental benefits and industrial promise, but remains a long-standing challenge due to the difficulty of activating CH<sub>4</sub>while avoiding overoxidation of methanol. Here, we demonstrate that pure ceria (CeO<sub>2</sub>), without any metal promoters, enables gas-phase DCMM with up to 80% selectivity at 300–350 °C, upon optimization of the H<sub>2</sub>O/O<sub>2</sub>ratio. At 550 °C, methanol and formaldehyde are formed at rates of 24 and 38 μmol g<sup>–1</sup>h<sup>–1</sup>, respectively, both dropping below 1 μmol g<sup>–1</sup>h<sup>–1</sup>in the absence of O<sub>2</sub>. Ex situ transmission electron microscopy, X-ray photoelectron spectroscopy, and Raman spectroscopy confirm that CeO<sub>2</sub>maintains structural integrity and resists carbon deposition during reaction. Combining kinetic studies, steady-state in situ diffuse reflectance infrared Fourier transform spectroscopy (in situ DRIFTS), and density functional theory (DFT) reveals that hydroxyl groups (OH), generated from water dissociation, play a multifaceted role: they facilitate C–H bond activation, promote methoxy formation, and enhance methanol desorption. In situ ambient-pressure X-ray photoelectron spectroscopy (AP-XPS) directly reveals the evolution of surface intermediates and shows that cofeeding O<sub>2</sub>and H<sub>2</sub>O suppresses CH<sub>3</sub>O and CH<sub>x</sub>accumulation while boosting methanol yield, indicating a rapid intermediate turnover as key to sustained activity. AP-XPS O 1s spectra further highlight that O<sub>2</sub>promotes H<sub>2</sub>O dissociation, regenerating reactive OH groups and maintaining performance at elevated temperature. These findings offer molecular-level insights into how water and oxygen cooperatively tune reactivity, enabling efficient methane-to-methanol conversion on a metal-free oxide catalyst.</p>}},
  author       = {{Li, Wen and Shi, Junjie and Tangpakonsab, Parinya Lewis and Zhang, Bin and Haunold, Thomas and Genest, Alexander and Yigit, Nevzat and Atzl, Leonard and Kokkonen, Esko and Qin, Yong and Rupprechter, Günther}},
  issn         = {{2155-5435}},
  keywords     = {{CeO; DFT; in situAP-XPS; in situDRIFTS; methane to methanol; reaction mechanism}},
  language     = {{eng}},
  pages        = {{20496--20511}},
  publisher    = {{The American Chemical Society (ACS)}},
  series       = {{ACS Catalysis}},
  title        = {{Synergy of Oxygen and Water in Ceria-Catalyzed Direct Conversion of Methane to Methanol under Continuous Flow}},
  url          = {{http://dx.doi.org/10.1021/acscatal.5c05829}},
  doi          = {{10.1021/acscatal.5c05829}},
  volume       = {{15}},
  year         = {{2025}},
}