New photocatalyst achieves superior oxidative methane coupling

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New photocatalyst achieves superior oxidative methane coupling

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The mechanism of lattice oxygen looping in OCM. Credit: Prof. Xiong’s group

Researchers have developed a novel catalyst Au/BiO_x-TiO₂ for efficient, selective and stable photocatalytic light-driven oxidative coupling of methane (OCM).

Producing value-added chemicals through OCM is a promising approach to alleviate energy issues. However, OCM requires strict reaction conditions due to its high reaction energy barrier. Compared with the anaerobic coupling of methane, the aerobic coupling of methane has a lower reaction barrier, yet it still faces challenges such as poor product selectivity and slow reaction rate. Therefore, it is necessary to design efficient catalysts and optimize reaction pathways to address issues of stability, selectivity and reactivity in OCM.

The group designed and synthesized a dual-site photocatalyst, Au/BiO_x-TiO₂, which is a composite system of BiO_x clusters and Au nanoparticles. The BiO_x clusters are uniformly distributed around the Au nanoparticles, tightly bound together. The synergistic effect of Au nanoparticles and BiO_x clusters enables the activation of C-H bonds in CH₄ and the coupling of CH₃ at separate sites, preventing overoxidation of CH₄ at a single site. This significantly improves the selectivity for C₂₊ products.

Using a self-designed flow reactor, the photocatalytic OCM achieved a CH₄ conversion rate of 20.8 mmol g⁻¹ h⁻¹ and a C₂H₆ production rate of 9.6 mmol g⁻¹ h⁻¹. The selectivity for C₂₊ products exceeded 97%, with stability lasting up to 50 hours, outperforming many previously reported catalysts.

The group also verified the mechanism of lattice oxygen participation in OCM based on in-situ spectroscopy and theoretical calculations. The lattice oxygen can effectively enhance the C-H activation, and introducing an appropriate amount of oxygen can replenish lattice oxygen via the Mars-Van Krevelen mechanism, achieving high selectivity and stability simultaneously.

This work highlights the importance of employing catalytic site engineering in chemical reactions and sheds light on sustainable and energy-efficient CH₄ conversion.

The study is published in

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. The groups were led by Prof. Xiong Yujie, Prof. Liu ***** and Prof. Zhang Ning from the University of Science and Technology of China (USTC).

More information:
Guangyao Zhai et al, Highly efficient, selective, and stable photocatalytic methane coupling to ethane enabled by lattice oxygen looping, Science Advances (2024).

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University of Science and Technology of China

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New photocatalyst achieves superior oxidative methane coupling (2024, September 13)
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