CO2 conversion in radio-frequency inductively coupled plasmas using molecular transition-metal complexes

Molecular transition-metal complexes were evaluated as catalysts for CO2 conversion in a lowpressure radio-frequency inductively coupled plasma systems. The complexes [Re(NnN)(CO)3Cl], [Fe(NPhPiso)Cl](BPh4), and [Ru(bpy)3](PF6)2 were exposed to CO2 and CO2/H2 plasmas to assess their stability and their influence on CO2 conversion. In pure CO2 plasma, all complexes degraded rapidly, consistent with the strongly oxidative chemistry characteristic of CO2 discharges. To suppress oxidative pathways, CO2/H2 mixtures were employed to modify the plasma environment. Adding H2 shifted the conversion chemistry towards the reverse water-gas shift reaction, consistent with control experiments with Al2O3, which selectively produced CO and H2O under CO2/H2 plasma conditions. A CO2/H2 gas ratio of 1:2.3 provided a comparatively low-oxidative plasma environment while maintaining measurable CO2 conversion. Under these conditions, both [Re(NnN)(CO)3Cl] and [Ru(bpy)3](PF6)2 exhibited CO2 conversion levels comparable to Al2O3 , indicating no measurable catalytic enhancement. In contrast, [Fe(NPhPiso)Cl](BPh4) increased CO and H2O yields relative to the Al2O3 reference. Overall, the results show that feed-gas composition and plasma chemistry are key determinants of both molecular-complex stability and functional contribution in plasma-assisted CO2 conversion.