English

Stable Photocatalytic Coupling of Methane to Ethane with Water Vapor Using TiO₂ Supported Ultralow Loading AuPd Nanoparticles

• Jun Xie ^{1, 2, †,} ,
• Yuheng Jiang ^{1, 2, 3, †,} ,
• Siyang Li ^{1, 2,} ,
• Peng Xu ^4, ,
• Qiang Zheng ^4, ,
• Xiaoyu Fan ^{1, ,} ,
• Hailin Peng ^{3, 5,} ,
• Zhiyong Tang ^{1, 2, ,}

• 1.

  Chinese Academy of Science (CAS) Key Laboratory of Nanosystem and Hierarchy Fabrication, CAS Center for Excellence in Nanoscience, National Center for Nanoscience and Technology, Beijing 100190, China

• 2.

  University of Chinese Academy of Sciences, Beijing 100049, China

• 3.

  Academy for Advanced Interdisciplinary Studies, Peking University, Beijing 100871, China

• 4.

  CAS Key Laboratory of Standardization and Measurement for Nanotechnology, National Center for Nanoscience and Technology, Beijing 100190, China

• 5.

  Center for Nanochemistry, Beijing Science and Engineering Center for Nanocarbons, Beijing National Laboratory for Molecular Sciences, College of Chemistry and Molecular Engineering, Peking University, Beijing 100871, China

• ^†These authors contributed equally to this work.

Corresponding author: Xiaoyu Fan, fanxy2022@nanoctr.cn Zhiyong Tang, zytang@nanoctr.cn

• Received Date: 26 June 2023
  Accepted Date: 21 July 2023
  Revised Date: 19 July 2023
  Available Online: 15 October 2023
• Fund Project:

Abstract: The selective conversion of methane to C₂ hydrocarbons offers a sustainable approach to utilize natural gas efficiently and reduce reliance on conventional fossil fuels. Unlike the conventional thermal catalytic conversion that requires high temperatures and pressures, the photocatalytic pathway enables methane activation and selective conversion under mild conditions, holding great promise as a sustainable method. However, achieving the efficient generation of C₂ compounds under flowing conditions using cost-effective photocatalysts remains great challenge. In this work, we synthesized an ultralow loading AuPd alloy nanoparticle-supported on TiO₂ (Au_0.05-Pd_0.05/TiO₂) photocatalyst via simple chemical reduction. Characterization using X-ray diffraction (XRD), aberration corrected high-angle annular dark field scanning transmission electron microscopy (AC-HAADF-STEM) and in situ CO-diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) confirmed its composition and structure. The performance of the Au_0.05-Pd_0.05/TiO₂ photocatalyst in methane conversion was evaluated under flow-reaction conditions. Remarkably, the photocatalyst efficiently converted methane containing water vapor into C₂ compounds, including ethane and ethylene, with a remarkable C₂ production rate of up to 10092 μmol∙g⁻¹∙h⁻¹ and a selectivity of 77%. While water vapor was not essential for methane conversion, its presence enhanced the production of ethane and ethylene while suppressing overoxidation to CO₂. The photocatalyst demonstrated excellent stability, maintaining its catalytic activity even after continuous reaction for 32 h, surpassing previously reported results. With the assistant of transient photocurrent response test, in situ X-ray photoelectron spectroscopy spectra and in situ DRIFTS, we uncovered that the exceptional catalytic activity of Au_0.05-Pd_0.05/TiO₂ originates from the synergistic effect of Au and Pd, which promotes the separation of photogenerated carriers and facilitates the C-C bond coupling of ·CH₃ to produce C₂ compounds. Furthermore, XPS characterization revealed that the introduction of water vapor replenished consumed lattice oxygen during the methane activation process, thus contributing to the catalyst's stability. This study not only offers a cost-effective and efficient photocatalyst for methane conversion but also provides insights into the fundamental mechanism of photocatalytic methane conversion. We believe that our work will inspire the exploration of inexpensive catalysts with simple preparation methods, driving advancements in efficient methane to C₂ compound conversion and contributing to sustainable photocatalytic pathways for the future.

Key words:
• Photocatalysis
•  /  Methane
•  /  Flow-reaction
•  /  Water vapor
•  /  AuPd alloy nanoparticle
•  /  C₂ compounds

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