Researchers in AIST developed a process for producing high-concentration methane from low-concentration CO₂ in collaboration with the Delft University of Technology. The concentration of CO₂ as a feed covers the concentration range from dilute atmospheric CO₂ to CO₂ originating from power plants. This process does not require a CO₂ capture and separation process prior to the conversion process.

In order to achieve carbon neutrality, it is essential to develop technology to capture CO₂ emitted from power plants and other industrial sectors, CO₂ already released into the atmosphere, and convert it to hydrocarbon fuels and valuable chemicals. However, CO₂ is generally diluted to concentrations of several percent to tens of percent by gases such as nitrogen and oxygen (approximately 400 ppm in the atmosphere). Thus, an energy-intensive and expensive CO₂ purification process is generally required prior to the CO₂ conversion process.

Dual-functional catalysts were developed that has the two functions of absorbing CO₂ and reacting the absorbed CO₂ with hydrogen to convert it into methane. In addition, direct CO₂ capture and conversion technology for dilute CO₂ was developed that consumes less energy and does not require a CO₂ capture and separation pretreatment process. This technology enabled to directly prepare methane with up to 1,000 times or higher concentration from 100 ppm CO₂, which is a lower concentration than atmospheric CO₂.

Since the atmosphere contains approximately 20 % oxygen, oxidation of the catalyst was suspected to be the cause of the lower methane yield. Some experiments were conducted to investigate the degradation behavior of catalyst performance with and without oxygen during the CO₂ capture. As a result, although some performance degradation was observed, it was found that CO₂ could be captured even in an oxygen-containing atmosphere and converted to methane with high efficiency.

In the future, we will develop dual-functional catalysts with high CO₂ capture capacity and high methane production per unit catalyst weight and develop highly efficient processes suitable for practical applications.