(655d) Aging Studies of Dual Functional Materials for Direct Air Capture with in Situ Methanation Under Simulated Ambient Conditions: Ru Thrifting for Cost Reduction

Direct Air Capture (DAC) is under investigation for achieving the goal of “net zero-CO2 emission” to curb the global warming effect. Dual function materials (DFM) comprised of 0.25%Ru, 6.1%Na₂O/g -Al₂O₃ //Monolith were evaluated at low levels of Ru for about 250 hours (TOS) at various simulated ambient climate capture conditions followed by methanations at up to 280°C. This paper focuses on the impact of thrifting Ru below 1% in a DFM on the extent of CO₂ ambient capture and conversion to CH₄. This is consistent with the positive effect of Ru loading on enhancing CO₂ adsorption, as previously reported. The CO₂ conversion to CH₄ (~50%) was the same as with 1%Ru regardless decrease in Ru loading from 1% to 0.25% in the DFM, suggesting even lower levels may be possible. Much of the 50% unreacted CO₂ will mostly be converted to CH₄ when 100% renewable H₂ is used in the final process.

The technology readiness of DFM is very competitive compared to other DAC technologies. Applying DFM on monolithic substrates (supports used in catalytic converters) has been verified with a lower pressure drop than using particle structures in a packed bed. The presented low Ru alkaline DFM's stable performance would significantly decrease the overall capital cost and give more potential to a large-scale direct air capture and methanation (DACM) application, based on the current price of Ru of $16.4/g (April 2023).

Ru crystallite size before and after aging is essential in relating its role in performance changes. Often in other catalytic systems, an increased catalyst size would cause impaired catalytic activity. For the first time, the Ru crystallites with a wide size range from < 2nm to ~25nm were observed by using STEM-EDS elemental mapping, and the increased Ru crystallite sizes after aging showed no decreased catalytic activity.