Dry reforming of methane (DRM) is a well-studied reaction for syngas production from CO₂ and CH₄. While the reaction is normally performed at a feed ratio of 1, the envisioned future feedstocks contain far more CO₂ and thus require extensive separation to utilize the desired CH₄.

Recently, a research team led by Profs. WANG Guoxiong, XIAO Jianping, and BAO Xinhe from the Dalian Institute of Chemical Physics(DICP) of the Chinese Academy of Sciences (CAS) developed a novel process for the direct production of syngas via super-dry reforming of methane (CO₂/CH₄ ≥ 2) using high-temperature tandem electro-thermocatalysis. Their findings, published in Nature Chemistry, provides a new approach for the direct and efficient utilization of carbon-rich natural gas and industrial tail gases.

Solid oxide electrolysis cells (SOECs) catalyze the conversion of CO₂ and H₂O into CO and H₂ at temperatures ranging from 600 to 850 °C. With advantages such as fast reaction rates, high energy efficiency, and low costs, SOECs are efficient high-temperature electrochemical devices that can be modularly designed for industrial-scale applications. They exhibit broad application potential in CO₂ conversion, hydrogen production via water electrolysis, and renewable energy storage.

Considering similar operating temperatures of SOECs and DRM reaction, the team developed a novel process for super-dry reforming of methane using electro-thermocatalysis. DRM, reverse water-gas shift (RWGS), and H₂O electrolysis reactions are coupled at the SOEC cathode. In situ electrochemical reduction of H₂O byproduct generates H₂ and O^2-, and O^2- transports through the electrolyte membrane and is then electrochemically oxidized to O₂ at the anode driven by potential difference. This process promotes the forward RWGS reaction, breaking through thermodynamic equilibrium limitations and significantly enhancing CO₂ conversion and H₂ selectivity.

The team in situ exsolved stable Rh nanoparticles on the surface of CeO_2-x support, providing high-density Ce³⁺-V_O-Rh^δ+ interfacial active sites. When the volume ratio of CO₂/CH₄ was 4, the electro-thermocatalytic system achieved CH₄ conversion of 94.5% and CO₂ conversion of 95.0%, with the selectivity of CO and H₂ products approaching 100%. The apparent reduction capacity of CH₄ approached 4.0, reaching the theoretical value. High-temperature atmospheric electron microscopy and high-temperature electrochemical in situ spectroscopy characterizations, in combination with theoretical calculations, revealed that Rh^δ+ was the active site for CH₄ dissociation, while the Ce³⁺-V_O-Rh^δ+ interface with abundant oxygen vacancies was the active site for CO₂ adsorption and activation, as well as the RWGS reaction. Simultaneously, the Ce³⁺-V_O-Rh^δ+ interface catalyzed electrochemical reduction of H₂O to produce H₂, which promoted CO₂ conversion and improved H₂ selectivity.

In the future, more efficient and low-cost catalysts need to be explored, and deep understanding on reaction mechanism of the tandem processes should be well clarified. Furthermore, mature SOEC technology are encouraged to demonstrate the tandem process at large scale for direct utilization of CO₂-rich natural gas and and industrial tail gases using renewable energy.