Plasma-assisted Decomposition Research Articles

Non-thermal plasma approach for conversion of greenhouse’s gases to hydrogen and valuable chemical fuels: A short review

An effective alternative energy source as a substitute for fossil-based fuels has become a major area of research for sustainable energy development. It is undeniable that there has been a decline in fossil fuel reserves as the primary energy which forces the development of new energy sources to meet requirements of both renewable and ecological aspects. In both of these aspects, hydrogen (H2) is one of the most promising renewable and environmentally friendly energy sources. Besides being able to be used to produce heat through combustion because it has a high calorific value (142 kJ/g), hydrogen can also be used to activate fuel cells to produce electrical energy without toxic gas emissions. Various applications of hydrogen gas led to the discovery of new sources and methods of producing hydrogen, including from the feedstock of greenhouse gases which has main component of CH4 and CO2. This review describes plasma dry reforming of greenhouse gas along with plasma decomposition of greenhouse components, namely CO2 and CH4 as an alternative process for hydrogen gas formation. Plasma-assisted decomposition of each compound, CO2 and CH4 from the view of plasma parameters and the effect of additional of catalyst are also discussed.

Enhanced moisture resistance of Cu/Ce catalysts for CO oxidation via Plasma−Catalyst interactions

Copper/cerium bimetallic catalyst is an efficient material for the removal of carbon monoxide, while the rapid deactivation under moisture-rich conditions in the conventional thermal-catalysis limited its wide application. Here, we investigated the plasma-assisted catalytic oxidation of CO over Cu/Ce oxides supported on γ-Alumina in comparison with the conventional thermal catalytic oxidation. The TOF values of the Cu/Ce catalysts showed that the plasma catalysis was the better catalytic system for CO oxidation (2.96 s−1 for thermal catalysis, 5.13 s−1 for plasma catalysis). Importantly, the energy barriers for plasma catalysis were much lower than that for thermal catalysis, especially under moisture-rich conditions (e.g. 130.3 kJ/mol versus 246.1 kJ/mol under 9.8 vol% water vapor). The loss of activity caused by water was reversible for the plasma process, but not for the thermal process. The Cu/Ce catalyst remained good stability within 60 h in the presence of 6.1% water for plasma oxidation, while the thermal catalytic activity declines gradually. Also, water could inhibit the formation of gas byproducts (O3 and NOx). The promoting role of plasma could be mainly ascribed to the enhanced strength of oxygen mobility and plasma-assisted decomposition of surface carbonate in the presence of water, as revealed by the in-situ NTP-TPR, XPS, and the ex-situ DRIFTS analyses.

Removal of biomass tar model compound using reverse vortex flow gliding arc discharge

ABSTRACT Removal of tar derived from biomass gasification using plasma discharge was of great interest. In this work, treatment of biomass tar using a high flow rate, reverse vortex flow gliding arc discharge (RVF-GA) was investigated. Naphthalene was used as a light tar model compound. Investigation was carried out at different inlet tar concentrations, total gas feed rates, and applied energy inputs. The naphthalene concentrations considered were low (≈ 610 mg/m3), moderate (≈ 4,330 mg/m3) and high concentration (≈ 10,330 mg/m3). It was demonstrated that the RVF-GA reactor performed well in removal of tar at high flow rates. The removal efficiency in the range of 75–95%, the specific energy input in the range of 0.11–0.33 kWh/m3 and the energy utilization in the range of 1.4–112 g/kWh could be achieved. The plasma assisted decomposition of naphthalene was found to increase with the applied electrical energyinput.

Plasma-assisted decomposition of a biomass gasification tar analogue into lower hydrocarbons in a synthetic product gas using a dielectric barrier discharge reactor

Cleaning product gas from biomass gasification is one of the major challenges for the application of biomass as a renewable energy source for power generation and value-added chemical synthesis. Non-thermal plasmas are a novel alternative technology for decomposing such tar compounds. In this research, the use of a dielectric barrier discharge (DBD) reactor was investigated for the decomposition of toluene (a tar surrogate) in a synthetic product gas containing H2, CO and CO2. The effect of residence time (0.95–2.82 s), plasma power (5–40 W), concentration (20–82 g/N m3), and temperature (ambient −400 °C) were investigated. It was demonstrated that the percentage removal of tar increased with increasing plasma power and residence time. 99%+ removal of toluene was observed at a plasma power of 40 W (the highest power used) and a residence time of 2.82 s (the highest residence time used). At ambient temperature, the toluene decomposition products include CO, lighter hydrocarbons, and solid residue. Unfortunately, at low temperatures, there was substantial solid residue formation. The synergetic effect of temperature and plasma was investigated to determine whether it could decrease residue formation. It was found that the solid residue completely disappeared at 400 °C. Furthermore, the selectivity and the yield of lower hydrocarbons increased with operating temperature. However, the yield of CO decreased due to the termination of radicals through the combination of CO and O at higher temperatures. Overall, this work demonstrates that toluene can be almost completely converted to smaller molecules by a DBD non-thermal plasma, and that a degree of control can be established by varying power, residence time and temperature, including eliminating the problem of solid residue formation.

Plasma-catalytic conversion of CO2 and CO2/H2O in a surface-wave sustained microwave discharge

The conversion of CO2 and CO2/H2O mixtures on a TiO2 supported NiO catalyst in a pulsed surface-wave sustained microwave discharge has been investigated. The influence of the catalyst preparation method (conventional calcination (in air or Ar) vs. Ar plasma-assisted decomposition) on the CO2 conversion and its energy efficiency has been studied. The results demonstrate that the Ar plasma-treated catalyst is more active compared to the conventional calcined one. The plasma-treated catalyst increases the CO2 conversion and its energy efficiency almost by a factor of two, compared to the plasma only assisted CO2 dissociation, while the conventional calcined catalysts affect the CO2 conversion rather insignificantly. The conversion of CO2 is found to be about 45% at 70Torr in pure CO2 with Ar plasma-treated catalyst, having an energy efficiency of 56%. In the case of CO2/H2O mixture, the CO2 conversion efficiency reaches 42% (energy efficiency is 52%) at 60Torr. The catalyst characterization shows that Ar plasma treatment may result in a higher density of oxygen vacancies and a comparatively uniform distribution of NiO on the TiO2 surface. 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/H2O mixture is proposed.

The plasma-assisted formation of Ag@Co3O4 core-shell hybrid nanocrystals for oxygen reduction reaction

In this study, Ag@Co3O4 core-shell hybrid nanocrystals are synthesized using a plasma discharge in water for oxygen reduction reaction in alkaline solutions. A detailed analysis via electron microscopy in combination with EDS elemental mapping conclusively verifies that the reactive oxygen species generated from the plasma-assisted decomposition of water molecules govern the phase structure of the nanocrystals. Under oxidizing conditions, the Co oxide, which is more stable than the Ag oxide, provides the driving force for the segregation and preferential oxidation of Co at the surface. This leads to the formation of the core-shell architecture. The electrochemical measurements for the oxygen reduction reaction reveal that the specific activities of the Ag@Co3O4 core-shell nanocrystals are ca. 5.2 and 2.6 times higher than those of the pure Ag and Ag-Co alloy nanocrystals. The enhanced catalytic performance is attributed to the combination of electronic and geometric effects, which facilitates the OO bond breaking and desorption for the oxygen reduction. The insights gain through this study may serve as a foundation to design better electrochemical oxygen reduction electrocatalysts.

Freestanding silicon nanocrystals with extremely low defect content

The future exploitation of the exceptional properties of freestanding silicon nanocrystals (Si NCs) in marketable applications relies upon our ability to produce large amounts of defect-free Si NCs by means of a low-cost method. Here, we demonstrate that Si NCs fabricated by scalable rf plasma-assisted decomposition of silane with additional hydrogen gas injected into the afterglow region of the plasma exhibit immediately after synthesis the lowest reported defect density, corresponding to a value of only about 0.002--0.005 defects per NC for Si NCs of 4 nm size. In addition, the virtually perfect hydrogen termination of these Si NCs yields an enhanced resistance against natural oxidation in comparison to Si NCs with nearly one order of magnitude larger initial defect density.

Plasma-assisted decomposition of gaseous propane to produce COx free hydrogen

In this study, we survey the alternative approach of using plasma technology to produce CO x free hydrogen. In a corona discharge reactor operating at atmospheric pressure, electrons were energized by an electric field to ionize propane and induce chemical reactions. A range of each test parameter was covered, namely the effect of power input in the range of 4.5–105 W and discharge time of 1, 2, 3, 4, 5 and 8.18 min. A 19% hydrogen content by volume was achieved at a power input of 102 W and discharge time of 8.18 min. Copyright , Oxford University Press.

Plasma enhanced catalytic reforming of biomass tar model compound to syngas

Direct thermal decomposition, plasma-assisted decomposition, catalytic steam reforming and plasma enhanced catalytic steam reforming of biomass tar using toluene as a model compound were comparatively studied. Plasma enhanced catalytic steam reforming showed the best performance. The introduction of a plasma to the catalytic reforming reaction accelerated the decomposition of toluene, while the co-existing Ni/SiO2 reforming catalyst, on the other hand, guided the reaction towards formation of CO and H2, realizing the highest toluene conversion, and the highest CO and H2 formation rates simultaneously.

Stable and color-tunable fluorescence from silicon nanoparticles formed by single-step plasma assisted decomposition of SiBr4

We describe a facile method to synthesize silicon nanoparticles through plasma-assisted decomposition of silicon tetrabromide, a novel precursor for gas phase synthesis. Raman spectroscopy, transmission electron microscopy, energy dispersive X-ray spectroscopy and Fourier transform infrared spectroscopy analyses demonstrate that the obtained silicon nanocrystals were covered with a silicon oxide layer. The nanoparticles can be easily dispersed in ethanol and the dispersion exhibited stable optical properties for over half a year, showing strong photoluminescence (PL) under ultraviolet irradiation with quantum yields of up to 24%. The PL properties of the nanoparticles were tolerant to hydrofluoric acid (HF) etching. The PL intensity of the nanoparticles was slightly enhanced after removal of the surface oxide layer via HF etching. Replacement of the surface oxide layer with a hydrogen-terminated surface after etching would be one of the possible reasons for this PL enhancement. In addition, we were able to tune the color of PL of the nanoparticles from dark-blue to greenish-yellow by changing the total pressure of the plasma chamber during synthesis. These results indicated that our method could provide us with a simple and practical method to produce silicon nanoparticles.

Thermocatalytic decomposition of natural gas over plasma-generated carbon aerosols for sustainable production of hydrogen and carbon

Thermocatalytic decomposition (TD) of natural gas (NG) is a promising CO 2-free approach to hydrogen production, however, the practical realization of the sustainable TD process faces significant technical challenges due to rapid deactivation of existing catalysts by carbon deposits. In this work, the authors report on TD of NG and methane over a new type of carbon-based catalyst: plasma-generated carbon aerosols. The carbon aerosols were produced by non-thermal plasma-assisted decomposition of NG at near-ambient conditions. The plasma-generated carbons exhibit highest catalytic activity for methane (or NG) decomposition among known carbon-based catalysts with a comparable surface area. The nanostructure of the plasma-generated carbons was characterized and found to be consistent with highly disordered (amorphous) carbon. It is demonstrated that the combination of the carbon aerosol generator with the TD reactor provides a means for sustainable production of hydrogen and carbon from NG with a relatively high energy efficiency.

Effect of air and oxygen content on the dielectric barrier discharge decomposition of chlorobenzene

Experiments were performed on the plasma-assisted decomposition of dilute concentrations of chlorobenzene in air/oxygen and argon/oxygen gas mixtures at atmospheric pressure using a coaxial geometry single dielectric barrier discharge for different oxygen concentrations and energy densities. The results show that the decomposition process requires higher energy densities using air mixtures compared to argon/oxygen mixtures and is not linearly dependent on the oxygen content for a given energy density. The main decomposition products detected in the offgas were carbon dioxide and carbon monoxide.

Decomposition of methylene chloride by electron beam and pulsed corona processing

Experiments on the plasma-assisted decomposition of dilute concentrations of methylene chloride in atmospheric-pressure N 2 and dry air streams by electron beam and pulsed corona processing are presented. This paper presents the first experimental evidence showing that the decomposition of methylene chloride in a non-thermal plasma at ambient gas temperature proceeds via reaction with nitrogen atoms. The decompositions is more efficient with energy deposition in electron beam generated plasmas because of the higher rate for electron-impact dissociation of N 2. In dry air mixture, the decomposition of methylene chloride is degraded substantially because the nitrogen atoms are consumed in the production of nitrogen oxides. At higher gas temperatures (300°C), the decomposition of methylene chloride in dry air is shown to proceed via reaction with oxygen atoms. The main products of methylene chloride decomposition in dry air mixtures are CO, CO 2, HCl, and probably Cl 2.

Chromium oxide films fabricated by Cr(CO) 6 chemical vapor deposition

Cr 2O 3 and ferromagnetic chromium dioxide have been fabricated by ultraviolet photolytic and plasma-assisted decomposition of Cr(CO) 6 in oxygen carrier gas. The photolysis process is surface mediated and proceeds by the sequential removal of (CO) groups. It yields different surface morphologies, and control of the substrate temperature is essential for optimum results. The plasma-assisted deposited films exhibit long-range ferromagnetic order and sufficient flatness to be utilized as a magneto-optic recording medium. The thermodynamic cycle of the plasma process was determined. Consequences for using such films are discussed.

Fabrication of ferromagnetic and antiferromagnetic chromium oxides by organometallic chemical vapor deposition

We have been able to fabricate CrO2 and Cr2O3 from ultraviolet photolytic and plasma-assisted decomposition of Cr(CO)6 in an oxygen carrier gas. The composition of these films is uniform in composition and contains little contamination. Using magneto-optic Kerr effect measurements, we have been able to demonstrate that the CrO2 films are ferromagnetic.

Influence of deposition conditions on sputter-deposited amorphous silicon

The electrical, optical, and photoelectronic properties of sputter-deposited amorphous silicon films have been systematically related to deposition parameters for the case of pure Ar sputtering gas in an rf diode system. Variation of the sputtering gas pressure from 25 to 150 mTorr controllably and reproducibly increases the film resistivity 3 to 4 orders of magnitude and significantly decreases optical absorption for photon energies ≲1.6 eV. Similar film property improvements can be realized through the use of large substrate-target spacings (∼10 cm) and substrate temperatures ≲500 °C. The film properties, however, are independent of deposition rate between 0.5 and 5 Å sec−1. The influence of gas pressure and substrate-target spacing has been linked to Ar bombardment of the growing film, which appears responsible for both high dangling-bond densities and incorporated gas. The influence of substrate temperature could result from annealing of collision-induced defects as the film grows, or from a decrease in the density of microvoids as reported by Paul et al. for amorphous germanium. The use of deposition conditions which minimize plasma interaction and maximize thermal reorganization results in remarkably good electrical and optical properties for nonhydrogenated amorphous silicon. Using the approach of Lewis et al. the addition of H2 to the Ar sputtering gas produces film properties which are further improved and quite similar to those observed for films prepared by plasma-assisted decomposition of silane.