Edwin Devid

Molecular transition-metal complexes were evaluated as catalysts for CO ₂ conversion in a low-pressure radio-frequency inductively coupled plasma systems. The complexes [Re(N∩N)(CO) ₃ Cl], [Fe(NPhP ^iso )Cl](BPh ₄ ), and [Ru(bpy) ₃ ](PF ₆ ) ₂ were exposed to CO ₂ and CO ₂ /H ₂ plasmas to assess their stability and their influence on CO ₂ conversion. In pure CO ₂ plasma, all complexes degraded rapidly, consistent with the strongly oxidative chemistry characteristic of CO ₂ discharges. To suppress oxidative pathways, CO ₂ /H ₂ mixtures were employed to modify the plasma environment. Adding H ₂ shifted the conversion chemistry towards the reverse water-gas shift reaction, consistent with control experiments with Al ₂ O ₃ , which produced CO and H ₂ O under CO ₂ /H ₂ plasma conditions. A CO ₂ /H ₂ gas ratio of 1:2.3 provided a comparatively low-oxidative plasma environment while maintaining measurable CO ₂ conversion. Under these conditions, both [Re(N∩N)(CO) ₃ Cl] and [Ru(bpy) ₃ ](PF ₆ ) ₂ exhibited CO ₂ conversion levels comparable to Al ₂ O ₃ , indicating no measurable catalytic enhancement. In contrast, [Fe(NPhP ^iso )Cl](BPh ₄ ) increased CO and H ₂ O yields relative to the Al ₂ O ₃ 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 CO ₂ conversion.

Electrodeless Low-Frequency (LF)/Radio-Frequency (RF) plasma sources often suffer from low power coupling efficiencies due to the lack of overlapping field with the dynamic plasma load. However, the power supplies for these plasma sources typically have very high power efficiencies (>90%) and are more cost-effective compared to microwave sources. If the coupling efficiency to the plasma can be increased, these plasma sources offer a competitive technology for the sustainable electrification of the chemical industry. This work experimentally investigates five power coupling methods, applied to toroidal CO₂ plasmas in a quartz vessel. The research was based on similar ferrite coupling as used in energy-efficient plasma lamps. The higher resistance of the CO₂ plasma decreased the power coupling from 90% (for mercury-vapor plasma) to 66% at 1 mbar. High coupling efficiencies in LF/RF powered discharges can be achieved in two manners: either the inductance of the transformer cores can be increased, or the electromagnetic wave frequency can be increased. Furthermore, additional ferrite cores in parallel with the primary coils can be used to increase the impedance transformation. An experiment with six ferrite cores with a single primary winding in parallel, at a frequency of about 10 MHz and a power of 1 kW, showed that this frequency has a detrimental effect on the magnetic permeability and the losses in the ferrite result in a decrease of coupling to 33% at 1.5 mbar. At a frequency of 66 kHz with a nanocrystalline soft magnetic material core, a coupling of 89% was achieved in 1.5 mbar plasma for a power of 3.1 kW. This configuration exhibits decreasing coupling efficiencies at higher pressures since the plasma impedance increases, which again limits the coupling of the transformer due to a lack of inductance. The investigation of alternative coreless coil plasma configurations resulted in coupling efficiencies up to 89% decreasing to 50% at 102 mbar for a toroidal plasma enclosed by toroidally spiraling coils.

The photocatalytic efficacy of a novel mononuclear rhenium(I) complex in CO2 reduction is remarkable, with a turnover number (TONCO) of 1517 in three hours, significantly outperforming previous Re(I) catalysts. This complex, synthesized via a substitution reaction on an aromatic ring to form a bromo-bipyridine derivative, L1 = 2-Bromo-6-(1H-pyrazol-1-yl)pyridine, and further reacting with [Re(CO)5Cl], results in the facial-tricarbonyl complex [ReL1(CO)3Cl] (1). The light green solid was obtained with an 80% yield and thoroughly characterized using cyclic voltammetry, NMR, FTIR and UV-vis spectroscopy. Cyclic voltammetry under CO2 atmosphere revealed three distinct redox processes, suggesting the formation of new electroactive compounds. The studies on photoreduction highlighted the ability of the catalyst to reduce CO2, while NMR, FTIR, and ESI mass spectrometry provided insights into the mechanism, revealing the formation of solvent-coordinated complexes and new species under varying conditions. Additionally, computational studies (DFT) were undertaken to better understand the electronic structure and reactivity patterns of 1, focusing on the role of the ligand, spectroscopic features, and redox behavior. This comprehensive approach provides insights on the intricate dynamics of CO2 photoreduction, showcasing the potential of Re(I) complexes in catalysis.

The synergy between catalysis and plasma chemistry often enhances the yield of chemical reactions in plasma-driven reactors. In the case of CO₂ splitting into CO and O₂, no positive synergistic effect was observed in earlier studies with plasma reactors, except for dielectric barrier discharges, that do not have a high yield and a high efficiency. Here, we demonstrate that introducing metal meshes into radio frequency-driven plasma reactors increases the relative reaction yield by 20%–50%, while supported metal oxide catalysts in the same setups have no effect. We attribute this to the double role of the metal mesh, which acts both as a catalyst for direct CO₂ dissociation as well as for oxygen recombination.

Plasma technology, combined with activation on surfaces, is a novel way to convert CO₂using green electricity.

CO₂ decomposition is a very strongly endothermic reaction where very high temperatures are required to thermally dissociate CO₂. Radio frequency inductively-coupled plasma enables to selectively activate and dissociate CO₂ at room temperature. Tuning the flow rate and the frequency of the radio frequency inductively-coupled plasma gives high yields of CO under mild conditions. Finally the discovery of a plasma catalytic effect has been demonstrated for CO₂ dissociation that shows a significant increase of the CO yield by metallic meshes. The metallic meshes become catalysts under exposure to plasma to activate the recombination reaction of atomic O to yield O2, thereby reducing the reaction to convert CO back to CO₂. Inductively-coupled hybrid plasma catalysis allows access to study and to utilize high CO₂ conversion in a non-thermal plasma regime. This advance offers opportunities to investigate the possibility to use radio frequency inductively-coupled plasma to store superfluous renewable electricity into high-valuable CO in time where the price of renewable electricity is plunging.

Dry reforming of methane (DRM) is a challenging process wherein methane reacts with CO₂ to give syngas. This reaction is strongly endothermic, typically requiring temperatures higher than 500 °C. Catalysts can be used, but the high temperatures (which are a thermodynamic requirement) often lead to catalyst deactivation. Herein, the reaction from another conceptual direction is approached, using low‐power radio frequency inductively coupled plasma (RF‐ICP). It is demonstrated that this system can give high conversions of methane and CO₂ at near‐ambient temperatures. Importantly, the energy costs in this system are considerably lower compared with other plasma‐driven DRM processes. Furthermore, it is shown that the yield of hydrogen can be increased by minimizing the C2 compound formation. The factors that govern the DRM process and discuss H_α emission and its influence on H atom recycling in the process are examined.