Progress in Plasma-Assisted Catalysis for Carbon Dioxide Reduction

Production of chemicals and fuels based on CO2 conversion is attracting a special attention nowadays, especially regarding the fast depletion of fossil resources and increase of CO2 emissions into the Earth’s atmosphere. Recently, plasma technology has gained increasing interest as a non-equilibrium medium suitable for CO2 conversion, which provides a promising alternative to the conventional pathway for greenhouse gas conversion. The combination of plasma and catalysis is of great interest for turning plasma chemistry in applications related to pollution and energy issues. In this chapter a short review of the current progress in plasma-assisted catalytic processes for CO2 reduction is given. The most widely used discharges for CO2 conversion are presented and briefly discussed, illustrating how to achieve a better energy and conversion efficiency. The chapter includes the recent status and advances of the most promising candidates (plasma catalysis) to obtain efficient CO2 conversion, along with the future outlook of this plasma-assisted catalytic process for further improvement

Role of Plasma Catalysis in the Microwave Plasma‐Assisted Conversion of CO2

Climate change and global warming caused by the increasing emissions of greenhouse gases (such as CO2) recently attract attention of the scientific community. The combination of plasma and catalysis is of great interest for turning plasma chemistry in applications related to pollution and energy issues. In this chapter, our recent research efforts related to optimization of the conversion of CO2 and CO2/H2O mixtures in a pulsed surface‐wave sustained microwave discharge are presented. The effects of different plasma operating conditions and catalyst preparation methods on the CO2 conversion and its energy efficiency are discussed. It is demonstrated that, compared to the plasma‐only case, the CO2 conversion and energy efficiency can be enhanced by a factor of ∼2.1 by selecting the appropriate conditions. The catalyst characterization shows that Ar plasma treatment results in a higher density of oxygen vacancies and a comparatively uniform distribution of NiO on the TiO2 surface, which strongly influence CO2 conversion and energy efficiencies of this process. The dissociative electron attachment of CO2 at the catalyst surface enhanced by the oxygen vacancies and plasma electrons may explain the increase of conversion and energy efficiencies in this case. A mechanism of plasma‐catalytic conversion of CO2 at the catalyst surface in CO2 and CO2/H2O mixtures is proposed

Enhancing the Greenhouse Gas Conversion Efficiency in Microwave Discharges by Power Modulation

Scientific interest to the plasma-assisted greenhouse gas conversion continuously increases nowadays, as a part of the global Green Energy activities. Among the plasma sources suitable for conversion of CO2 and other greenhouse gases, the non-equilibrium (low-temperature) discharges where the electron temperature is considerably higher than the gas temperature, represent special interest. The flowing gas discharges sustained by microwave radiation are proven to be especially suitable for molecular gas conversion due to high degree of non-equilibrium they possess. In this Chapter the optimization of CO2 conversion efficiency in microwave discharges working in pulsed regime is considered. The pulsed energy delivery represents new approach for maximization of CO2 conversion solely based on the discharge “fine-tuning”, i. e. without the additional power expenses. In our work several discharge parameters along the gas flow direction in the discharge have been studied using various diagnostic techniques, such as optical actinometry, laser-induced fluorescence, and gas chromatography. The results show that CO2 conversion efficiency can be essentially increased solely based on the plasma pulse frequency tuning. The obtained results are explained by the relation between the plasma pulse parameters and the characteristic time of the relevant energy transfer processes in the discharge

Ion density evolution in a high-power sputtering discharge with bipolar pulsing

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Synthesis of Allylamine Plasma Polymer Films: Correlation between Plasma Diagnostic and Film Characteristics

peer reviewedPrimary amine-based plasma polymer films (NH2-PPF) were synthesized using plasma polymerization of allylamine in continuous wave (CW) and pulsed radio-frequency (RF) modes. Plasma chemistry, studied by residual gas analysis mass spectrometry, revealed that the precursor fragmentation is a function of the equivalent power (Peq) dissipated in the discharge, independently of the plasma mode used. X-ray photoelectron spectroscopy combined with time-of-flight secondary ion mass spectrometry suggests as the precursor fragmentation in the plasma increases: (i) a decrease of the primary amine concentration in the NH2-PPF (%NH2) and (ii) an increase of the cross-linking degree. For a given Peq, similar to the precursor fragmentation in the plasma, the NH2-PPF characteristics were found to be independent of the plasma mode used. Therefore, the main advantage of using pulsed RF processes over CW ones is the possibility to work at very low Peq which enables low precursor fragmentation, optimization of %NH2, and reduction of the film cross-linking degree. The chemical composition and the cross-linking degree of the NH2-PPF synthesized by allylamine plasma polymerization can thus be tailored by adjusting the equivalent RF power injected in the plasma

Functionalization of carbon nanotubes by atomic nitrogen formed in a microwave plasma Ar+N2

peer reviewedMulti-walled carbon nanotubes (MWNTs) are placed under atomic nitrogen flow formed through an Ar + N2 microwave plasma in order to functionalize covalently their side walls with nitrogen-containing groups. The MWNT surface analyzed by X-ray photoelectron spectroscopy shows the presence of amides, oximes and mainly amine and nitrile functions grafted in this way. In order to highlight the actual location of the amine functions grafted on MWNTs, they were considered as initiation species in ring-opening polymerization of £-caprolactone using triethylaluminium as activator. The so-generated poly(e-caprolactone) chains remain grafted on the MWNTs via amide bonds and form polyester islets along the nanotubes surface. TEM images of these MWNT surfaces grafted with poly(e-caprolactone) show a good amino-sidewall distribution. This work demonstrates the side-wall amino-functionalization of carbon nanotubes readily achieved by microwave plasma with the possibility to reach within a short time period very high contents in nitrogen-based functions (~10 at.%)

The wrinkling concept applied to plasma deposited polymer-like thin films: a promising method for the fabrication of flexible electrodes

peer reviewe

The wrinkling concept applied to plasma deposited polymer-like thin films: a promising method for the fabrication of flexible electrodes

peer reviewe

Functionalization of MWCNTs with atomic nitrogen

peer reviewedIn this study of the changes induced by exposing MWCNTs to a nitrogen plasma, it was found by HRTEM that the atomic nitrogen exposure does not significantly etch the surface of the carbon nanotube (CNT). Nevertheless, the atomic nitrogen generated by a microwave plasma effectively grafts amine, nitrile, amide, and oxime groups onto the CNT surface, as observed by XPS, altering the density of valence electronic states, as seen in UPS