Dry reforming of methane (DRM) is a widely studied method for converting carbon dioxide (CO₂) and methane (CH₄) into syngas. Traditionally, this reaction operates with a CO₂/CH₄ feed ratio of 1. However, future feedstocks—such as CO₂-rich natural gas—are expected to contain much higher concentrations of CO₂, requiring costly separation processes to achieve the desired CH₄.

In a study published in Nature Chemistry, a team led by Profs. WANG Guoxiong, XIAO Jianping, and BAO Xinhe from the Dalian Institute of Chemical Physics of the Chinese Academy of Sciences developed a novel process for the direct production of syngas via super-dry reforming of methane (CO₂/CH₄ ≥ 2), and offered a promising way for efficient and direct utilization of CO₂-rich natural gas using high-temperature tandem electro-thermocatalysis based on solid oxide electrolysis cells (SOECs).

Operating at 600 to 850 °C, SOECs are capable of converting CO₂ and H₂O into CO and H₂. With high reaction rates, high energy efficiency, and low operating costs, they have great potential for CO₂ utilization, hydrogen production, and renewable energy storage. Considering the similar temperature range of SOECs and DRM, researchers developed a novel process that coupled DRM, reverse water-gas shift (RWGS), and H₂O electrolysis at the SOEC cathode. 

In this setup, the in situ electrochemical reduction of H₂O byproduct generates H₂ and O^2- ions. These O^2- ions then migrate through the electrolyte and are electrochemically oxidized to O₂ at the anode under an applied potential. This process drives the RWGS equilibrium forward, enhancing CO₂ conversion and H₂ selectivity beyond conventional thermodynamic limitations.

Moreover, researcher in suit exsolved Rh nanoparticles onto a CeO_2-x support, creating high-density Ce³⁺-V_O-Rh^δ+ interfacial active sites. When operating at a CO₂/CH₄ ratio of 4, the system achieved CH₄ conversion of 94.5% and CO₂ conversion of 95.0%, with nearly 100% selectivity toward CO and H₂. The apparent methane reducibility reached the theoretical maximum of 4.0.

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Further investigation revealed that Rh^δ+ sites are primarily responsible for CH₄ dissociation, while the Ce³⁺-V_O-Rh^δ+ interface—rich in oxygen vacancies—promotes CO₂ adsorption, activation, and the RWGS reaction. This same interface also catalyzed electrochemical H₂O reduction, boosting both CO₂ conversion and H₂ selectivity.

“Our study may open a new avenue for the direct utilization of CO₂-rich natural gas and industrial tail gases using renewable energy,” said Prof. WANG.

IMAGE CREDIT: DICP