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.