Long-Range Metal–Sorbent Interactions Determine CO2 Capture and Conversion in Dual-Function Materials

Carbon capture and utilization involve multiple energy- and cost-intensive steps. Dual-function materials (DFMs) can reduce these demands by coupling CO2 adsorption and conversion into a single material with two functionalities: a sorbent phase and a metal for catalytic CO2 conversion. The role of metal catalysts in the conversion process seems salient from previous work, but the underlying mechanisms remain elusive and deserve deeper investigation to achieve maximum utilization of the two phases. Here, preformed colloidal Ru nanoparticles were deposited onto a "NaOx"/Al2O3 sorbent to prepare prototypical DFMs with controlled phases for CO2 capture and hydrogenation to CH4. Ru addition was found to double the high-temperature CO2 adsorption capacity by activating the "NaOx"/Al2O3 sorbent phase during a reductive pretreatment step. Most importantly, low Ru loadings were sufficient to ensure maximum CO2 adsorption and conversion. This was attributed to the key role of the metal–sorbent interactions, wherein Ru was required to hydrogenate strongly bound CO2 on the "NaOx"/Al2O3 sorbent to CH4 via the H2 activated on Ru. This interaction facilitated rate-determining carbonate migration and subsequent hydrogenation at the metal–sorbent interface. Overall, Ru controlled the CO2 hydrogenation reaction rate, while the "NaOx"/Al2O3 sorbent dictated the CO2 uptake capacity. By controlling metal–sorbent interactions at the molecular level, we demonstrate the critical role of the two phases and their synergy, facilitating the design of DFMs with maximum CO2 capture and conversion efficiency.