Photoreactive Capture and Conversion of Dilute Carbon Dioxide into Synthetic Natural Gas

This study introduces a photoreactive system that integrates the capture of dilute CO₂ streams with their catalytic conversion to synthetic natural gas (CH₄), utilizing a Ru nanoparticle (NP)-doped TiO₂ composite loaded with linear polyethylenimine (L-PEI) and enhanced with plasmonic titanium nitride (TiN). This light-driven approach mitigates challenges that have plagued traditional thermal reactive carbon capture (RCC) methods, such as CO₂ slip and amine degradation. We demonstrate that L-PEI enables stable CO₂ capture and conversion, achieving ∼70% conversion of captured CO₂ to CH₄ across multiple reaction cycles using nonflammable forming gas (∼5% H₂) as the reductant. In contrast, branched PEI (B-PEI)-loaded composites exhibited significant catalyst deactivation after several RCC cycles. Scanning transmission electron microscopy (STEM) imaging confirms that significant sintering of the Ru NPs occur in the B-PEI sample under RCC conditions, whereas their size remains stable in more rigid L-PEI composites. Technoeconomic analysis (TEA) estimates that CH₄ production using this system could cost less than $5/kg based on current electrocatalytic H₂ prices. These results represent one of the most promising demonstrations of amine-based RCC employing dilute CO₂ sources to date.