In-situ DRIFTS study of two-step CO2 capture and catalytic methanation over Ru,“Na2O”/Al2O3 Dual Functional Material

Abstract

Dual Function Materials (DFM) are composed of an alkali or alkaline earth CO2 adsorbent phase and a supported catalyst. It selectively captures CO2 which is then methanated using renewable H2. Both the capture and methanation steps are conducted at about 320 °C so no temperature swings are required allowing for continuous operation using two parallel reactors operating in tandem. This process approaches carbon neutral power generation by recycling the CH4 produced for re-combustion. This two-step process was studied by in-situ DRIFTS at 320 °C over 5%Ru-6.1%“Na2O”/Al2O3 DFM and compared with the 5%Ru/Al2O3 traditional methanation catalyst. In the DFM the Na2CO3/Al2O3 pre-curser is reduced to “Na2O” catalyzed by Ru metal. For both Ru/Al2O3 and DFM CO2 adsorbs on Ru active sites and Al2O3 OH groups during the capture step. For DFM large amounts of CO2 absorb on the Al-O−-Na+ species forming bidentate carbonates. During the H2 reduction step (i.e., methanation step), adsorbed bicarbonates and bidentate carbonates spill over onto the Ru-support interface, where methanation takes place through sequential hydrogenation with formates as reaction intermediaries. Although CO2 was mainly adsorbed on the alkaline support methanation occurs over Ru, supporting the hypothesis that the reaction occurs at the Ru-support interface. Therefore, the multiple adsorption sites over the DFM explain the high CO2 adsorption capacity by the formation of bidentate carbonates that spill over onto the Ru-support interface, during the two-step methanation process.