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

Abstract

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 “NaO_x”/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 “NaO_x”/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 “NaO_x”/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 “NaO_x”/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.