On the synergy between Ru and K2CO3 supported on carbon nanofibers for the direct air capture and conversion of CO2

Dual functional materials for CO₂ capture (DFMs) combine a CO₂ sorbent and hydrogenation catalyst on the same support material. Here, we present a DFM specifically designed for direct air capture of CO₂ and subsequent conversion of the captured CO₂. The DFM consists of K₂CO₃ (sorbent) and ruthenium (catalyst) on a carbon nanofiber support. We will show that synergy between the sorbent and catalyst exists and we will explore the nature of this synergy. DFMs were tested in cycles of direct air capture and subsequent conversion of CO₂ in H₂. By comparing a physical mixture of sorbent and catalyst to the DFM it was found that conversion over the DFM was higher by more than threefold. This indicates that a synergy due to the physical interaction between sorbent and catalyst is present. Examination of the evolved gasses during the conversion phase showed that CO₂ that desorbed from the sorbent under H₂ re-adsorbed on the DFM. The amount of these re-adsorption sites, and therefore the conversion, increased with Ru loading. By varying the sorption time, K₂CO₃ loading (2.5–15 wt%), and Ru loading (0.8–3.1 wt%) it will be shown that 100 % of captured CO₂ can be converted at temperatures below 225 °C, as long as the amount of CO₂ does not exceed the number of re-adsorption sites.