Non-thermal Plasma Catalysis Research Articles

Reactive Blue Degradation in Aqueous Medium by Fe-Doping TiO<sub>2</sub> Catalytic Nonthermal Plasma

In this paper, Fe-doping TiO2 was introduced into a dielectric barrier discharge (DBD) process for catalytic nonthermal plasma (NTP) degradation of a mode organic pollutant reactive blue (KN-R). Plasma was generated in a DBD reactor; Fe-doping TiO2 was prepared by the sol-gel process. The catalytic-NTP oxidation reactions were studied under various conditions including the examination of the effects of initial pH, KN-R concentrations, and catalyst dose. Typical results indicated the synergy between plasma excitation of KN-R followed by the catalytic action of Fe-doping TiO2, which not only improved the conversion but also increased the mineralization efficiency. The determination of hydrogen peroxide and nitrate ions, and ultraviolet–visible absorption and Fourier transform infrared spectra analyses revealed that catalysts in a plasma system strengthen the mineralization of KN-R.

Performance of chlorobenzene removal in a nonthermal plasma catalysis reactor and evaluation of its byproducts

A nonthermal plasma catalysis reactor was developed as pretreatment technology for a biotrickling filter (BTF), which was adopted to enhance removal of poorly soluble and recalcitrant volatile organic compounds. The performance of this pretreatment process was evaluated under various technological parameters, including discharge voltage, initial concentration, and residence time. Experimental results show that the system afforded higher efficiency of removal and selectivity to CO2 compared with those obtained with the control plasma process at discharge voltages of 5–9kV and residence times of 3–15s. Increasing the discharge voltage and residence time increased the removal efficiency. The activity of catalysts followed the order CeO2/HZSM-5>CuO/MnO2>Ag/TiO2. Furthermore, the solubility and biodegradability of degradation products were examined and analyzed. The main products of chlorobenzene degradation were O3, COx, benzene derivatives, and nitrogenous organics. The amounts of nitrogenous byproducts and O3 concentration during the reaction decreased significantly in the plasma catalysis reactor. This pretreatment technology greatly enhanced the solubility and biodegradability of byproducts. The results provide fundamental data for a feasible plasma catalytic system used as pretreatment technology for a BTF.

Catalytic nonthermal plasma assisted co-processing of methane and nitrous oxide for methanol production

The objective of the present study is the direct conversion of potential greenhouse gases methane (CH4) and nitrous oxide (N2O) into value added products like methanol, syngas, etc. in a nonthermal plasma reactor operated under ambient conditions. Typical results indicated that co-processing of the reactants has an advantage of in-situ decomposition of N2O into N2 and atomic oxygen that favors methane partial oxidation to methanol. In order to improve the selectivity to methanol, plasma reactor was operated by integrating CuO/CeO2, NiO/CeO2 and Cu-Ni (5-5)/CeO2 catalysts. Among the studied catalysts, Cu-Ni (5:5wt%) supported on ceria showed the best selectivity of ∼36% to methanol.

Catalytic behavior and synergistic effect of nonthermal plasma and CuO/AC catalyst for benzene destruction

Nonthermal plasma-catalysis hybrid technology (NTP-C) operated at ambient temperature and pressure offers an innovative and effective approach to solving the problem of dilute volatile organic compounds pollution. Herein, the destruction of benzene (50–450 ppm) over an in-plasma NTP-C composite system was investigated. The AO x /active carbon (AO x /AC), AO x /3A molecular sieve (AO x /MS), and AO x /γ-Al2O3 (A = Fe, Ag, Zn, Mn, and Cu) catalysts were prepared by the incipient-wetness impregnation method. The destruction performances of NTP alone and NTP-C are compared under different reaction conditions, such as inlet reactant concentration, catalyst type, and energy density. AC exhibits the best benzene removal efficiency among three catalyst supports, and the performances of AO x /AC under different conditions follow the trend of CuO/AC > MnO/AC > MnO2/AC > Fe2O3/AC > AC > ZnO/AC > Ag2O/AC. The NTP with CuO/AC system exhibits the highest benzene elimination capability with almost 90.6 % inlet benzene removed at energy density of 70 and 270 J L−1. The strong adsorption ability of AC and the optimal catalytic ability of crystalline structure of CuO on the AC support may be contributed to the excellent performance of CuO/AC. It is found that the NO x by-product also can be well controlled over NTP-CuO/AC system. Additionally, the surface of CuO/AC is more slipperier and homogeneous with the reaction proceeding, indicating higher stability of CuO/AC.

Catalytic Non-Thermal Plasma Decomposition of Ethylene by Using ZrO2Nanoparticles

In the present work, ZrO2 nanoparticles loaded on glass wool (GW) were employed for catalytic and plasma-catalytic decomposition of ethylene. Unlike ZrO2 pellets, nanosized ZrO2 was found to exhibit catalytic activity for the decomposition of ethylene. Some carbon-containing by-products like CH4, C2H2, and HCHO were detected under room-temperature operation of the reactor. The formations of such unwanted by-products were suppressed and the conversion into CO2 was enhanced when the ZrO2 catalyst was combined with non-thermal plasma at high temperatures. The nanosized ZrO2 exhibited a stable decomposition performance during 80-h continuous operation, suggesting that it is able to withstand deactivation without substantial loss in its catalytic activity.

Synergistic effect of non-thermal plasma–catalysis hybrid system on methane complete oxidation over Pd-based catalysts

Abstract The complete oxidation of methane was carried out in a dielectric barrier discharge (DBD) quartz tube reactor where both catalyst and plasma were hybridized into one in-plasma catalysis system. The palladium-based catalysts such as Pd/Al2O3, Pd/SiO2, and Pd/TiO2 were used as oxidation catalyst. Input voltage of the plasma–catalyst reactor varied from 2 kVp-p to 4 kVp-p to investigate which input voltage offered the best circumstance for plasma–catalyst interaction. In the absence of catalyst, methane began to be oxidized to CO and CO2 even at room temperature, and the conversion increased with the increment of temperature and the input voltage since the active radicals were generated more abundantly under those conditions. However, large amount of CO were also produced in addition to CO2, especially at low temperature below 200 °C when plasma was only used. In the presence of both plasma and catalyst, methane was oxidized to produce mostly CO2 with low CO selectivity at room temperature, indicating that the complete oxidation was successfully performed with the aid of catalyst. The role of plasma was to oxidize CH4 to produce CO, which was subsequently oxidized to CO2 over catalyst at low temperature. Hence, in most cases, the methane conversion of plasma–catalysis hybrid system was almost equal to the summation of two separate systems. Interestingly, it was found that the synergistic effect of plasma–catalysis hybrid system on methane oxidation existed substantially only under specific condition. For example, 2 wt% Pd/Al2O3 presented higher methane conversion than the summation of conversion for catalyst only reaction and plasma only reaction when 4 kVp-p was applied.

Catalytic non-thermal plasma reactor for stripping the VOCs from air

Stripping of a mixture of volatile organic compounds containing dilute toluene, 1,4-dioxane and n-hexane from air was studied in a non-thermal plasma reactor operated in a dielectric barrier discharge configuration. Catalyst integration to plasma was carried out by depositing 5 wt% of MnOx and CoOx on the inner electrode, sintered metal fibres (SMF). Experimental results indicated that the removal efficiency of VOCs followed the order: toluene > n-hexane > 1,4-dioxane; and MnOx/SMF showed better performance compared to CoOx/SMF, probably due its ability for ozone decomposition leading to the formation of atomic oxygen. Water vapour further enhanced the performance that may be assigned due to the formation of OH radicals.

Catalytic performance of plasma catalysis system with nickel oxide catalysts on different supports for toluene removal: Effect of water vapor

The effect of water vapor on the performance of a combined non-thermal plasma catalysis (CPC) system with nickel oxide catalysts loaded on different supports was investigated. The catalysts NiO/γ-Al2O3, NiO/SBA-15 (Santa Barbara Amorphous-15), and NiO/TiO2 were prepared and their activities were tested in the absence and presence of water vapor. Complete destruction of toluene was achieved in the absence of water vapor at ambient temperature and pressure. The activities of catalysts for the toluene conversion in dry air decreased in the following order: NiO/γ-Al2O3>NiO/SBA-15>NiO/TiO2. The presence of water vapor in the feed stream had a significant negative impact on the performance of the CPC systems. This reduction in performance was primarily due to the quenching by water vapor of active species in the plasma and the competitive adsorption of water vapor on the catalyst surfaces. A novel in situ FTIR system was constructed and used to obtain in situ FTIR spectra of the reactive surfaces of the catalysts, revealing that the water molecules that adsorbed on the catalyst surfaces came from both water vapor present in the gas stream and from water vapor formed during the oxidation of toluene. H2O-TPD results indicated that the activation energies of water desorption from the catalysts decreased in the following order: NiO/γ-Al2O3>NiO/SBA-15>NiO/TiO2. The catalyst with lower water vapor desorption activation energy had higher resistance to water vapor. Therefore, the durability towards water vapor poisoning of these catalysts followed the order of: NiO/TiO2>NiO/SBA-15>NiO/γ-Al2O3.

Hydrogen production via decomposition of hydrogen sulfide by synergy of non-thermal plasma and semiconductor catalysis

Direct H2S decomposition induced by plasma with an aid of alumina-supported metal sulfide semiconductors (ZnS/Al2O3 and CdS/Al2O3) for the production of hydrogen was investigated in a dielectric barrier discharge (DBD) reactor. Effects of specific input energy (SIE), feed flow rate, metal sulfide loading, and added hydrogen on the performance of H2S decomposition were studied. With the aids of ZnS/Al2O3 and CdS/Al2O3, full conversion was obtained at reasonably low energy costs. The 100-h test runs indicated that both ZnS/Al2O3 and CdS/Al2O3 were stable in the course of H2S decomposition. A supported metal sulfide solid solution (Zn0.4Cd0.6S/Al2O3) exhibited higher performance than ZnS/Al2O3 and CdS/Al2O3, achieving full conversion at a reduced energy cost. The mechanism of the plasma-induced H2S decomposition with an aid of a semiconductor catalyst was tentatively proposed.

Catalytic non-thermal plasma reactor for mineralization of endosulfan in aqueous medium: A green approach for the treatment of pesticide contaminated water

An advanced oxidation process for the mineralization of a model pesticide endosulfan from aqueous medium has been developed by non-thermal plasma combined with cerium oxide catalysts. Plasma was generated in a dielectric barrier discharge reactor, whereas ceria was prepared by combustion synthesis and characterized by various physico-chemical techniques. Typical results indicated the synergy between plasma excitation of endosulfan followed by the catalytic action of cerium oxide, which not only improved the conversion, but also increased the mineralization efficiency, which was confirmed by a total organic carbon content analyzer and an infrared COx analyzer. Catalytic plasma approach showed a threefold increase in mineralization. Degradation followed first-order kinetics and rate of degradation is proportional to power input and reciprocal to initial endosulfan concentrations.

Catalytic non-thermal plasma reactor for the decomposition of a mixture of volatile organic compounds

The decomposition of mixture of selected volatile organic compounds (VOCs) has been studied in a catalytic non-thermal plasma dielectric barrier discharge reactor. The VOCs mixture consisting n-hexane, cyclo-hexane and p-xylene was chosen for the present study. The decomposition characteristics of mixture of VOCs by the DBD reactor with inner electrode modified with metal oxides of Mn and Co was studied. The results indicated that the order of the removal efficiency of VOCs followed as p-xylene > cyclo-hexane > n-hexane. Among the catalytic study, MnOx/SMF (manganese oxide on sintered metal fibres electrode) shows better performance, probably due to the formation of active oxygen species by in situ decomposition of ozone on the catalyst surface. Water vapour further enhanced the performance due to the in situ formation of OH radicals.

Non-thermal plasma catalysis of methane: Principles, energy efficiency, and applications

The reaction mechanism and energy efficiency analysis of non-thermal plasma assisted methane conversion are presented. Plasma catalysis is an innovative next-generation green technology that satisfies needs for energy and materials conservation, and environmental protection. Non-thermal plasma uniquely generates reactive species almost independently of reaction temperature. Those species initiate chemical reactions at remarkably lower temperatures than conventional thermochemical reactions. Low-temperature methane conversion is important because it minimizes exergy destruction accompanied by combustion of the initial feed, or production of high-temperature thermal energy, necessary for thermochemical methane reform. Non-thermal plasma has great flexibility to tune the process parameters so that energy and material consumption are minimized. This article explains aspects of plasma-assisted fuel reforming including arc plasma to non-thermal plasma. We specifically examine dielectric barrier discharge (DBD) as viable non-thermal plasma for practical fuel reforming. Second, the energy efficiency of non-oxidative methane conversion using DBD is analyzed. That energy efficiency determined by experimentation was 1%, although theoretical analysis suggested 8%, implying that DBD alone is invariably more inefficient. Finally, DBD-catalysts hybrid reaction is proposed and a synergistic effect between plasma-generated reactive species and catalysts is clarified, suggesting that vibrationally excited species are important for enhancing overall methane conversion efficiency with catalysts.

Catalytic Nonthermal Plasma Reactor for Dry Reforming of Methane

Co-processing of two greenhouse gases, methane and carbon dioxide, was carried out in a dielectric barrier plasma reactor. The influence of feed gas proportion on the performance of the plasma reactor was investigated, especially with an objective to increase the conversion of the reactants and selectivity to syngas. To understand the influence of the catalyst on dry reforming, 10–30% NiO/Al2O3 catalysts were prepared by a single-step combustion synthesis and various physicochemical techniques confirmed the formation of nanosized Ni particles. A total of 10% of the discharge volume was packed with Ni/Al2O3 catalysts in a packed-bed configuration. An interesting observation is the increased syngas selectivity on the addition of catalyst to plasma, and among the catalysts tested, 20% Ni showed a H2/CO ratio of 2.25 against 1.2 with a plasma reactor alone.

Combination of non-thermal plasma and heterogeneous catalysis for methane and hexadecane co-cracking: Effect of voltage and catalyst configuration

Co-cracking of methane and n-hexadecane is investigated over Mo–Ni/Al2O3 catalyst in a packed bed dielectric barrier discharge (DBD) plasma reactor. The effects of applied voltage and plasma-catalyst configuration are experimentally studied in terms of process energy efficiency and product composition. Hydrogen and gaseous hydrocarbon (methane, C2, C3 and C4 components) are obtained as the cracking product. Results show that combination of catalyst and plasma improves energy efficiency of hydrocarbons plasma conversion. The applied voltage has dominant effect on the catalytic-plasma cracking process and in-plasma catalysis configuration is more efficient compared with post-plasma catalysis. The highest energy efficiency is achieved the value of 194.44l/kWh for in-plasma configuration under highest applied voltage condition (11kV). In these conditions, the production rate and mole percent of hydrogen are obtained 107.66ml/min and 63.7%, respectively. The effect of catalyst deactivation is also investigated on the process variables.

Abatement of mixture of volatile organic compounds (VOCs) in a catalytic non-thermal plasma reactor

Total oxidation of mixture of dilute volatile organic compounds was carried out in a dielectric barrier discharge reactor with various transition metal oxide catalysts integrated in-plasma. The experimental results indicated the best removal efficiencies in the presence of metal oxide catalysts, especially MnOx, whose activity was further improved with AgOx deposition. It was confirmed water vapor improves the efficiency of the plasma reactor, probably due to the formation of hydroxyl species, whereas, in situ decomposition of ozone on the catalyst surface may lead to nascent oxygen. It may be concluded that non-thermal plasma approach is beneficial for the removal of mixture of volatile organic compounds than individual VOCs, probably due to the formation of reactive intermediates like aldehydes, peroxides, etc.

Decomposition of Trichloroethylene with Plasma-catalysis: A review

AbstractThe aim of this paper is to give a review of the research on the decomposition of trichloroethylene (TCE), a common industrial solvent, with combined use of non-thermal plasma and heterogeneous catalysis, i.e. plasma-catalysis. This air purification technique has been investigated over the last decade in an effort to overcome the disadvantages of non-thermal plasma treatment of waste air containing volatile organic compounds (VOCs). Some examples of different plasma technologies used for plasma-catalysis are given. These include the dielectric barrier discharge, the pulsed corona discharge and the atmospheric pressure glow discharge. In a plasma-catalytic hybrid system the catalyst can either be located in the discharge region or downstream of the plasma reactor. The mechanisms that drive both configurations are briefly discussed, followed by an extended literature overview of the removal of TCE with plasma-catalysis.

Catalytic non-thermal plasma reactor for abatement of toluene

A non-thermal plasma rector with a catalytic electrode made of sintered metal fibres (SMFs) was tested for the oxidative decomposition of a model VOC toluene. The input energy was varied in the range 160–295 J/l by varying the applied voltage between 12.5 and 22.5 kV at 200 Hz. Influence of various parameters like toluene concentration, SMF modification by Mn and Co oxides, input energy and ozone formation was studied. It has been observed that plasma catalytic approach is very effective for total oxidation of toluene at low input energy, especially at toluene concentration ≤250 ppm and SMF modification by transition metal oxides increased the performance of the reactor significantly. MnO x modification appears to be a better choice compared to CoO x, which may be attributed to the in situ decomposition of ozone leading to the formation of more reactive oxidants like atomic oxygen.

Novel catalytic non-thermal plasma reactor for the abatement of VOCs

A novel dielectric barrier discharge (DBD) reactor has been designed and tested for the abatement of diluted volatile organic compounds (VOCs) of different nature. The novelty of the DBD reactor is that a metallic catalyst made of sintered metal fibers (SMF) also acts as the inner electrode. The SMF electrodes modified with oxides of Ti, Mn and Co were efficient during the destruction of toluene, isopropanol (IPA) and trichloroethylene (TCE). Total oxidation of IPA was achieved at lower specific input energy (SIE) compared to toluene and TCE. Among the catalysts studied, MnOx/SMF showed the best performance, involving the formation of active oxygen species by in situ decomposition of ozone on the catalyst surface. The selectivity to CO2 as the total oxidation product during TCE destruction was improved up to ∼70% by modifying MnOx/SMF with TiO2.

Combination of non-thermal plasma and heterogeneous catalysis for oxidation of volatile organic compounds: Part 2. Ozone decomposition and deactivation of γ-Al2O3

The role of ozone was studied for two different configurations combining non-thermal plasma (NTP) and heterogeneous catalysis, namely the use of a gas phase plasma with subsequent exposure of the effluent to a catalyst in a packed-bed reactor (post-plasma treatment) and the placement of the catalyst directly in the discharge zone (in-plasma catalysis). Non-porous and porous alumina and silica were deployed as model catalysts. The oxidation of immobilised hydrocarbons, toluene as a volatile organic compound and CO as an inorganic pollutant were studied in both operational modes.While conversion and selectivity of hydrocarbon oxidation in the case of catalytic post-plasma treatment can be fully explained by the catalytic decomposition of O3 on γ-Al2O3, the conversion processes for in-plasma catalysis are more complex and significant oxidation was also measured for the other three materials (α-Al2O3, quartz and silica gel). It became obvious that additional synergetic effects can be utilised in the case of in-plasma catalysis due to short-lived species formed in the NTP.The capability of porous alumina for ozone decomposition was found to be correlated with its activity for oxidation of carbon-containing agents. It could be clearly shown that the reaction product CO2 poisons the catalytic sites at the γ-Al2O3 surface. The catalytic activity for O3 decomposition can be partially re-established by NTP treatment. However, for practical purposes the additional reaction pathways provided by in-plasma catalytic processes are essential for satisfactory conversion and selectivity.

Combination of non-thermal plasma and heterogeneous catalysis for oxidation of volatile organic compounds: Part 3. Electron paramagnetic resonance (EPR) studies of plasma-treated porous alumina

The effect of plasma processes inside the intra-particle volume of porous materials (especially Al2O3) was studied in order to evaluate the potential of the combination of non-thermal plasma (NTP) and in situ heterogeneous catalysis (plasma catalysis), for the improvement of efficiency and selectivity towards total oxidation of organic pollutants in gas cleaning applications. Electron paramagnetic resonance (EPR) spectroscopy was applied as an appropriate method to detect both the formation of radical species by the NTP as well as the initiation of structural changes to the catalyst.The presence of paramagnetic oxygen or hydroxyl species (O−, O2− or OH) could not be detected by EPR spectroscopy. The observed signal was not significantly influenced either by the type of atmosphere present during NTP treatment or by applying reducing agents to the sample after plasma treatment.However, by using non-porous and porous alumina (α- and γ-Al2O3) as model catalysts, the effect of NTP modifying the surface structure in the interior of a porous material could be clearly demonstrated. A paramagnetic species probably related to an AlOO aluminium peroxyl group was formed by NTP processes independently of the oxygen content of the gas atmosphere. It was not formed when the alumina sample was positioned in the off-gas flow of a plasma reactor, i.e. used in the post-treatment mode.The structure of the paramagnetic site was investigated by employing several spectroscopic tools (X- and Q-band EPR, electron spin echo envelope modulation [ESEEM] and EPR measurements after pre-deuteration).