Combination Of Non-thermal Plasma Research Articles

(Invited) Plasma Catalysis: An Emerging Electrification Technology for Sustainable Production of Fuels and Chemicals

The conversion of inert molecules (e.g., CO2, CH4, and N2) with strong chemical bonds for the synthesis of value-added synthetic fuels and platform chemicals has attracted significant interest. However, the activation of these molecules remains a great challenge as they are thermodynamically stable and require a significant amount of energy for activation. Non-thermal plasma (NTP) is an emerging and attractive technology for gas conversions under ambient conditions. The combination of NTP with heterogeneous catalysis has great potential to generate a synergistic effect from interactions between the plasma and catalysts, which can activate catalysts at low temperatures and improve the activity and stability of the catalysts, resulting in a remarkable increase in conversion, selectivity, and yield of end-products, as well as the energy efficiency of the process. Moreover, plasma processes can be switched on and off instantly, allowing for great flexibility in decentralised chemical production using renewable energy sources, particularly intermittent renewable energy. The potential of plasma-catalytic technologies for the synthesis of fuels and chemicals via various chemical processes such as CH4 activation, CO2 conversion, and ammonia synthesis will be discussed in this presentation.

Abstract 4780: Comparison of safety and efficacy outcomes with nonthermal plasma and tirapazamine in porcine skin and mouse melanoma models

Abstract A novel preclinical experimental therapy for various cancer types including melanoma is the combination of nonthermal plasma (NTP) and tirapazamine (TPZ) delivered in situ. This patented combination therapy delivers reactive oxygen species (ROS) and reactive nitrogen species (RNS) from the atmosphere that are activated and ionized with helium gas to create the state of matter known as plasma. The combination with the prodrug, TPZ, that only activates to become a ROS in hypoxic environments, shows synergistic targeting of cancer cells. In this study, we assayed the effects of the dual therapy on porcine skin, which is the closest model to represent human skin and is commonly used for testing drug therapy. The results demonstrated that porcine skin showed no significant cell killing with the therapy. We also compared the combination therapy in normal skin keratinocytes and 1205Lu cells derived from a melanoma metastasis to the lung. The cells were treated with NTP and TPZ and maintained in a hypoxic chamber. Four days following therapy the keratinocytes continued to grow in culture, whereas the melanoma cells expressing endogenous gap junctions, or overexpressed Cx43 gap junctions showed decreased viability. However, the melanoma cells with a dominant negative Cx43 mutant did not show this loss in viability. This confirms our previous report that gap junctions mediate the passage of derivatives of ROS to increase the extent of cell death. To determine the effects of NTP on regulating the lethal dose of TPZ, we performed IC50 curves for TPZ in the presence or absence of NTP in B16-F10 murine metastatic melanoma cells. We demonstrated a decrease in the IC50 from 28 μM without NTP to 17.4 μM with NTP. In further analysis, the effects of treating with NTP in the presence or absence of tissue culture media were compared. The results showed a highly significant increased efficacy of NTP in the absence of media. The combination therapy was more effective than each independent treatment. To further confirm the experimental analysis, we induced tumor formation with the B16-F10 cells in a syngeneic C57BL/6 mouse model. The tumors from mice that were untreated or treated with NTP or TPZ alone, showed a significant increase in tumor volume as compared to the tumors from mice receiving the combination treatment in situ. In comparison of the tumor growth rates, the control, NTP-, or TPZ-treated tumors had increased by approximately 350% by day 10, whereas the tumors in the mice that received the dual therapy only increased by an average of 70%. The results from these studies collectively implicate the combination of NTP and TPZ as a potential synergistic treatment for in situ melanomas that offer selectivity as compared to normal tissue. Citation Format: Matthew Yehl, Dominik Kucharski, Michelle Eubank, Xavier Ramadan, Ahmad Dianat, Bianca Pham, Timothy C. Hutcherson, Sandra Sexton, Shoshanna N. Zucker. Comparison of safety and efficacy outcomes with nonthermal plasma and tirapazamine in porcine skin and mouse melanoma models. [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 4780.

Degradation of chlorobenzene by non-thermal plasma coupled with catalyst: influence of catalyst, interaction between plasma and catalyst

Non-thermal plasma (NTP) is considered to be a promising technology for the removal of volatile organic compounds; however, its application is limited by low CO2 selectivity and undesirable by-products. To overcome these issues, this paper discusses the degradation of chlorobenzene (CB) in systems of NTP coupled with catalysts, and the influence of catalyst locations in the NTP was investigated. In addition, the interaction between plasma and catalyst was also explored. The results indicated that the degradability of CB was remarkably improved through the combination of NTP with catalysts, and the formation of ozone was effectively inhibited. The degradation efficiency increased from 33.9% to 79.6% at 14 kV in the NTP-catalytic system, while the ozone concentration decreased from 437 to 237 mg m−3, and the degradation efficiency of in plasma catalysis (IPC) systems was superior to that of the post plasma catalysis system, while the inhibition ability of ozone exhibited an opposing trend. In the IPC system, the degradation efficiency was 87.7% at 14 kV, while the ozone concentration was 151 mg m−3. Besides, the plasma did not destroy the pore structure and crystal structure of the catalyst, but affected the surface morphology and redox performance of the catalyst. Thus, NTP coupled catalytic system could improve the degradation performance of CB. Furthermore, the plasma discharge characteristics played a major role in the NTP synergistic catalytic degradation of CB. Finally, based on the experiment analysis results, the general reaction mechanism of CB degradation in an IPC reaction system was proposed.

Volatile organic compounds degradation by nonthermal plasma: a review.

Volatile organic compounds (VOCs) have posed a severe threat on both ecosystem and human health which thus have gained much attention in recent years. Nonthermal plasma (NTP) as an alternative to traditional methods has been employed to degrade VOC in the atmosphere and wastewater for its high removal efficiency (up to 100%), mild operating conditions, and environmental friendliness. This review outlined the principles of NTP production and the applications on VOC removal in different kinds of reactors, like single/double dielectric barrier discharge, surface discharge, and gliding arc discharge reactors. The combination of NTP with catalysts/oxidants was also applied for VOC degradation to further promote the energy efficiency. Further, detailed explanations were given of the effect of various important factors including input/reactor/external conditions on VOC degradation performance. The reactive species (e.g., high-energy electrons, HO·, O·, N2+, Ar+, O3, H2O2) generated in NTP discharge process have played crucial roles in decomposing VOC molecules; therefore, their variation under different parameter conditions along with the reaction mechanisms involved in these NTP technologies was emphatically explained. Finally, a conclusion of the NTP technologies was presented, and special attention was paid to future challenges for NTP technologies in VOC treatment to stimulate the advances in this topic.

Inactivation of airborne SARS-Co-V2 using NTP-UVGI hybrid process.

Indoor environments such as healthcare centers are known as one of the key centers in the outbreak of viral infectious diseases. In the present study, the pathogenic agents' treatment system (PATS) was designed by the combination of non-thermal plasma (NTP) with the ultraviolet germicidal irradiation (UVGI) processes. Then, the treatment efficiency of PATS was measured for the "SARS-Co-V2." The exhaled air of the confirmed case of "COVID-19" was considered as the viral source of "SARS-Co-V2" and directed to the upstream of PATS. The treatment process was done by passing directed air through two steps of treatment (NTP and UVGI). The treatment efficiency of PATS was measured by sampling at the sampling points (before and after the treatment process). According to the energy emission pattern (corona discharge, UV rays) in the designed system, during two steps, the high efficiency of treatment for the collected pathogens was achieved. Based on the real-time polymerase chain reaction (RT-PCR) results, the CT value was lower than 29 (CTs < 29), and after the treatment using PATS was upper than 40 (CTs > 40) confirming the highest removal efficiency of "SARS-Co-V2." Also, the treatment efficiency of each reactor in individual operation was at the optimum level. The findings suggested, the present PATS may eliminate the viral pathogens with hospital sources and also, be applicable in the other intensive care unit (ICU) wards with the same risk thus, significantly reducing the possible exposure risk of healthcare and sick companions, and preventing the outbreak of infectious diseases.

Treatment of organic wastewater by a combination of non-thermal plasma and catalyst: a review

Treatment of organic wastewater by a combination of non-thermal plasma and catalyst: a review

Abstract 1053: Combination therapy with nonthermal plasma and tirapazamine selectively targets glioblastoma cells and regulates the gap junction phenotype

Abstract Considering the side effects common to most chemotherapeutic agents, a novel approach was developed to selectively treat cancer by targeting the oxidative stress pathway which is induced in many tumor types. Our previous studies demonstrated that nonthermal plasma (NTP) selectively causes apoptotic cell death in melanoma cells while preserving the normal surrounding keratinocytes. The prodrug, tirapazamine, was shown to potentiate the effects of NTP while maintaining selectivity because tirapazamine only activates in hypoxic conditions, an environment common to many tumors. This patented combination therapy has an additive-to-synergistic effect on inducing apoptosis in melanoma. Previous studies have also demonstrated efficacy in a broad range of tumor cells including cervical carcinoma, colon cancer, and pancreatic adenocarcinoma. This report demonstrates for the first time that while NTP alone kills a targeted area of glioblastoma cells and tirapazamine alone kills most of the susceptible cells, the combination of NTP and tirapazamine kills all the cells throughout the tissue culture plate. The mechanism for the increase in the surface area of cell death was identified as the passage of reactive oxygen species (ROS) by intercellular communication through gap junctions. The IC50 dose of tirapazamine required to target several glioblastoma cell lines was less than that for melanoma cells. Through parameter optimization with varied plasma conditions and altered drug dosing, the selective killing of glioblastoma cells was achieved without affecting normal primary astrocytes. Primary astrocytes and glioblastoma cells were co-cultured to observe the effect on the optimal targeting dose of tirapazamine. Glioblastoma cells had an IC50 at hypoxia which was reduced as compared to astrocytes in their normoxia state. The Glioblastoma IC50 values were further decreased when co-cultured with astrocytes. This study documents an increase in the Connexin43 (Cx43) gap junction protein, upon treatment with NTP for both astrocytes and glioblastoma cells. However, treatment with tirapazamine alone ameliorates this effect in glioblastoma cells only and not in astrocytes. The combination therapy of NTP and tirapazamine increased this effect to levels comparable to the original expression levels. The regulation of Cx43 may reduce the metastatic potential of the glioblastoma cells while enabling the combination therapy to show efficacy both between glioblastoma cells and in the context of communication with astrocytes. By this mechanism, the astrocytes may act as conduits to transport ROS between pockets of glioblastoma cells. In summary, the results demonstrate that the novel combination therapy of NTP and tirapazamine is an effective method to selectively target glioblastoma cells with a potential for clinical applications with limited adverse reactions. Citation Format: Matthew Yehl, Andrew Nicolais, Samuel Gerardi, Ahmad Dianat, Olivia Kucharski, Timothy C. Hutcherson, Shoshanna N. Zucker. Combination therapy with nonthermal plasma and tirapazamine selectively targets glioblastoma cells and regulates the gap junction phenotype [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 1053.

Non-thermal plasma coupled with MOx/γ-Al2O3 (M: Fe, Co, Mn, Ce) for chlorobenzene degradation: Analysis of byproducts and the reaction mechanism

Chlorinated volatile organic compounds (VOCs) such as chlorobenzene pose serious human health and environmental risks, but are resistant to elimination techniques that are traditionally applied to Cl-free VOCs. Non-thermal plasma (NTP) offers a promising technique to decompose chlorobenzene, but its application remains limited owing to low COx selectivity and the generation of toxic byproducts. To address these problems, this study investigated chlorobenzene degradation in NTP coupled with MOx/γ-Al2O3 (M: Fe, Co, Mn, Ce) catalysts. The combination of NTP with MOx/γ-Al2O3 remarkably improved the removal efficiency (RE), mineralization rate (MR), Cl selectivity (SCl) and energy yield (EY) of chlorobenzene abatement, and decreased the production of residual O3. CoOx/γ-Al2O3 exhibited the best performance among these tested catalysts with higher RE, MR, SCl and EY by 26.06%, 25.52%, 33.03% and 2.41 g/kWh, respectively, at 510 J/L, compared with those of the NTP alone system. Several catalyst characterizations were applied to explore the relation between the catalyst characteristics and chlorobenzene abatement efficacy in NTP. The results indicate that the NTP catalytic oxidation of chlorobenzene strongly depends on the reducibility and acidity of the MOx/γ-Al2O3 samples, whereas the textural properties of the catalysts exert a limited influence on chlorobenzene degradation. High-resolution gas chromatography and high-resolution mass spectrometry analyses verified for the first time that PCDD/Fs were generated during chlorobenzene degradation in NTP catalytic reactions. A plausible decomposition mechanism of chlorobenzene in the NTP catalytic system is speculated according to the organic intermediates generated during chlorobenzene decomposition.

How activated carbon improves the performance of non-thermal plasma removing methyl ethyl ketone from a gas stream

The combination of non-thermal plasma (NTP), operated at room temperature and at atmospheric pressure in air and in combination with activated carbon filters offers a more efficient removal of VOCs from gas streams than each individual method alone. Efficiencies, synergies and mechanisms of this combination were investigated by means of comprehensive quantitative Fourier transform infrared spectroscopy analysis. Therefore, dry and wet synthetic air containing about 90 ppm of methyl ethyl ketone (MEK) were treated with non-thermal plasma (NTP) and an intentionally undersized activated carbon (AC) filter, separately and in combination. As a result, removal of about 50 % was achieved for NTP or AC alone but a removal close to 95 % was found for the combination. Ozone, generated by the NTP, was reduced by 55 % with the AC-filter. For the operation of the NTP with humid air, a decomposition of the pollutant on AC was observed even after the plasma was switched off. • Removal of MEK by non-thermal plasma (NTP) and activated carbon (AC) (each around 50 %). • Improved removal of MEK with combination of NTP and AC (close to 95 %). • Removal of MEK under humid conditions (even after NTP was switched off). • Reduced ozone production with use of AC (by 55 %).

C-dot doping for enhanced catalytic performance of TiO2/5A for toluene degradation in non-thermal plasma-catalyst system.

Non-thermal plasma (NTP) is gaining attention as a powerful tool to induce various reactions. The combination of NTP with catalysts has been successfully used to degrade volatile organic compounds (VOCs) for pollution control. In this study, a series of TiO2-C/5A catalysts, synthesized by carbon dots (C-dots) that decorate TiO2 by sol-gel and wetness impregnation methods, were incorporated with a dielectric barrier discharge (DBD) reactor in a single-stage structure to degrade toluene at atmospheric pressure and room temperature. A proton-transfer reaction mass spectrometer and a CO2 analyzer were used to monitor the concentration variations of organic by-products and CO2 online. The effects of input power, mass ratio of C-dots/TiO2 (TiO2/5A (0 wt%), TiO2-C1/5A (2.5 wt%), TiO2-C2/5A (5 wt%), TiO2-C3/5A (10 wt%)), gas flow rate, initial concentration of toluene on the toluene degradation efficiency, and CO2 selectivity were studied. The plasma-catalyst hybrid system could effectively improve the energy efficiency and reaction selectivity, attaining a maximum toluene degradation efficiency of 99.6% and CO2 selectivity of 83.0% compared to 79.5% and 37.5%, respectively, using the conventional plasma alone. Moreover, the generation of organic by-products also declined dramatically, averaging only half as much in plasma alone. The results also indicated that the appropriate amount of C-dot doping could greatly improve the catalyst efficiency in the hybrid plasma system. This is because the interaction between C-dots and TiO2 favors the formation of photoelectron holes and reduces the energy band gap and the recombination rate of photogenerated electron holes, which facilitates the generation of more active species on the catalyst surface, thereby leading to a more effective degradation reaction. These observations will provide guidance for the interaction studies between NTP and catalysts, not only for the exploration of new chemical mechanisms of aromatic compounds, but also for the screening of favorable materials for the desired reactions.

Synergy of NTP-La1-xAgxMn1-yCoyO3-δ Hybrid for Soot Catalytic Combustion at Low Temperature

Ag and Co co-doped La1-xAgxMn1-yCoyO3-δ perovskites were prepared by the citric acid sol–gel method. The maximum solubility of Ag+ in LaMnO3 decreased with the increase of Co doped in B-site, which lead to the exsolution of excess Ag+ from A-site of perovskite. The exsolution progress is more favorable to the formation of uniform and stable Ag nanoparticles on the perovskite substrate. The non-thermal plasma (NTP) assisted La1-xAgxMn1-yCoyO3-δ for soot catalytic combustion had been investigated under diesel exhaust gas conditions. When La1-xAgxMn1-yCoyO3-δ was utilized as the catalyst without NTP, the soot could hardly be oxidized at 200 °C. However, when La1-xAgxMn1-yCoyO3-δ was combined with NTP, the efficiency of soot removal was dramatically improved. The NTP-La0.5Ag0.5Mn0.8Co0.2O3-δ hybrid had the highest soot removal efficiency and CO2 selectivity. The combination of NTP and La1-xAgxMn1-yCoyO3-δ could form a synergistic catalytic effect, which significantly promoted the combustion of soot at low temperature. The results of characterization and experiments indicated that the synergistic catalytic performance depended on the coordination of short-living species in plasma, adsorbed oxygen and Ag nanoparticles on surface of La1-xAgxMn1-yCoyO3-δ. Based on these results, the reaction mechanism of plasma-catalyst hybrid for soot catalytic combustion was proposed.

Plasma Technology and Its Relevance in Waste Air and Waste Gas Treatment

Plasma technology is already used in various applications such as surface treatment, surface coating, reforming of carbon dioxide and methane, removal of volatile organic compounds, odor abatement and disinfection, but treatment processes described in this context do not go beyond laboratory and pilot plant scale. Exemplary applications of both non-thermal plasma and thermal plasma should underline the feasibility of scale-up to industrial application. A non-thermal plasma in modular form was built, which is designed for up to 1000 m³∙h−1 and was successfully practically tested in combination of non-thermal plasma (NTP), mineral adsorber and bio-scrubber for abatement of volatile organic components (VOCs), odorous substances and germs. Thermal plasmas are usually arc-heated plasmas, which are operated with different plasma gases such as nitrogen, oxygen, argon or air. In recent years steam plasmas were gradually established, adding liquid water as plasma gas. In the present system the plasma was directly operated with steam generated externally. Further progress of development of this system was described and critically evaluated towards performance data of an already commercially used water film-based system. Degradation rates of CF4 contaminated air of up to 100% where achieved in industrial scale.

Selective Catalytic Reduction of NO by NH3 Using a Combination of Non-Thermal Plasma and Mn-Cu/ZSM5 Catalyst

Dielectric barrier discharge (DBD) could generate non-thermal plasma (NTP) with the advantage of fast reactivity and high energy under atmosphere pressure and low-temperature. The presented work investigated the selective catalytic reduction (SCR) of nitric oxide (NO) using a combination of NTP and an Mn-Cu/ZSM5 catalyst with ammonia (NH3) as a reductant. The experimental results illustrate that the plasma-assisted SCR process enhances the low-temperature catalytic performance of the Mn-Cu/ZSM5 catalyst significantly, and it exhibits an obvious improvement in the NO removal efficiency. The reaction temperature is maintained at 200 °C in order to simulate the exhaust temperature of diesel engine, and the 10% Mn-8% Cu/ZSM5 catalyst shows the highest NO removal performance with about 93.89% at an energy density of 500 J L−1 and the selectivity to N2 is almost 99%. The voltage, frequency and energy density have a positive correlation to NO removal efficiency, which is positively correlated with the power of NTP system. In contrast, the O2 concentration has a negative correlation to the NO removal, and the NO removal efficiency cannot be improved when the NO removal process reaches reaction equilibrium in the NTP system.

Three-dimensional hollow urchin α-MnO2 for enhanced catalytic activity towards toluene decomposition in post-plasma catalysis

Complete oxidation of volatile organic compounds (VOCs) with high energy efficiency remains a challenge in post-plasma catalysis (PPC) due to insufficient adsorption towards gas and relatively low catalytic activity at room temperature. Three-dimensional (3D) hollow urchin α-MnO2 for post-plasma catalytic decomposition of toluene is demonstrated in this study. Hollow urchin catalyst assembled by well-defined one-dimensional (1D) α-MnO2 nanorods is prepared by a simple one-step hydrothermal method without any template. The toluene decomposition, CO2 selectivity and carbon balance over hollow urchin α-MnO2 reach up to ~100%, ~59% and ~81% at an SIE of 240 J L−1, which are 43%, 96% and 44% superior to that of non-thermal plasma (NTP) process, respectively. The combination of NTP with hollow urchin α-MnO2 also significantly promotes the energy efficiency by 64%, reaching 13.1 g kWh−1 at an SIE of 119 J L−1. Moreover, hollow urchin α-MnO2 exhibits higher catalytic activity for toluene decomposition and ozone conversion compared with solid urchin α-MnO2. The hollow structure with an enlarged contact surface area is expected to enhance adsorption towards gas and prolong the retention of gas on the catalyst surface. Furthermore, the fully exposed non-agglomerated 1D α-MnO2 nanorods can promote oxygen vacancy density and low-temperature reducibility, facilitating the adsorption and conversion of ozone into active oxygen species (~100% ozone conversion), which leads to the deep decomposition of toluene in PPC. This work explores a new concept in designing 3D hollow urchin nanoarchitecture as a novel catalyst for efficient plasma-catalytic gas purification.

Combination of non-thermal plasma and subsequent antibiotic treatment for biofilm re-development prevention.

The influence of non-thermal plasma (NTP) treatment on the prevention of antibiotic resistance of microbial biofilms was studied. Staphylococcus epidermidis and Escherichia coli bacteria and a yeast Candida albicans, grown on the surface of Ti-6Al-4V alloy used in the manufacture of prosthetic implants, were employed. Their biofilms were exposed to NTP produced by DC cometary discharge and subsequently treated with antibiotics commonly used for the treatment of infections caused by them: erythromycin (ERY), polymyxin B (PMB), or amphotericin B (AMB), respectively. All biofilms displayed significant reduction of their metabolic activity after NTP exposure, the most sensitive was S. epidermidis. The subsequent action of antibiotics caused significant decrease in the metabolic activity of S. epidermidis and E. coli, but not C. albicans, although the area covered by biofilm decreased in all cases. The combined effect of NTP with antibiotics was thus proved to be a promising strategy in bacterial pathogen treatment.

A Laboratory Study of Low-Temperature CO Removal from Mobile Exhaust Gas Using In-Plasma Catalysis

The combination of nonthermal plasma (NTP) with catalytic methods has been shown to improve catalyst light-off temperature via reactions among plasma discharge products and by-products. Thus, NTP may improve selectivity, process, and removal efficiency. In this study, NTP was combined with a catalytic film of mixed metal oxides (ceria-zirconia-gamma alumina layer) in the discharge zone to investigate low-temperature CO removal. Three different reactors having identical geometries were used: a plasma reactor, a catalytic reactor, and a hybrid plasma-catalytic reactor. The CO removal efficiency of 36.5% was achieved using hybrid plasma-catalytic reactor at 80 °C with 860 J/lit. The temperature and flow rate were found to have significant impacts (P-value ≤ 0.05), which is unexpected due to the key role of hydroxyl and active radicals induced by plasma discharge. Calculated synergy factor of about 2 signals call for further study on the hybrid properties of catalytic efficiency and plasma physics for optimal CO removal.

Highly selective conversion of H2S–CO2 to syngas by combination of non-thermal plasma and MoS2/Al2O3

The highly selective conversion of H2S–CO2 to syngas (a mixture of H2 and CO), which assisted by non-thermal plasma and MoS2/Al2O3 hybrid system, was obtained at low temperature and atmospheric pressure. The effects of reaction conditions, including the specific energy input (SEI), feed flow rate, feed gas composition (H2S/CO2 molar ratio), and MoS2 loading were carefully investigated. The 50-h-long runs indicate that MoS2/Al2O3 was stable in the course of simultaneous H2S–CO2 conversion into syngas with excellent reaction properties. High CO2 conversion (>60 %) and almost full H2S conversion (98–100 %) can be achieved. The non-thermal plasma combined with MoS2/Al2O3 offers a novel and energy-efficient strategy to produce syngas from concomitant H2S–CO2 acid gases with great value for detoxifying H2S and reducing CO2 emissions.

Non-thermal-plasma-activated de-NOx catalysis.

The combination of non-thermal plasma (NTP) with catalyst systems as an alternative technology to remove NOx emissions in the exhaust of lean-burn stationary and mobile sources is reviewed. Several factors, such as low exhaust gas temperatures (below 300°C), low selectivity to N2 and the presence of impurities, make current thermally activated technologies inefficient. Various hybrid plasma-catalyst systems have been examined and shown to have a synergistic effect on de-NOx efficiency when compared with NTP or catalyst-alone systems. The NTP is believed to form oxygenated species, such as aldehydes and nitrogen-containing organic species, and to convert NO to NO2, which improves the reduction efficiency of N2 during hydrocarbon-selective catalytic reduction reactions. The NTP has been used as a pretreatment to convert NO to its higher oxidation states such as NO2 to improve NOx reduction efficiency in the subsequent processes, e.g. NH3-selective catalytic reduction. It has been applied to the lean phase of the NOx storage to improve the adsorption capacity of the catalyst by conversion of NO to NO2 Alternatively, a catalyst with high adsorption capacity is chosen and the NTP is applied to the rich phase to improve the reduction activity of the catalyst at low temperature.This article is part of a discussion meeting issue 'Providing sustainable catalytic solutions for a rapidly changing world'.

Combined fast selective reduction using Mn-based catalysts and nonthermal plasma for NOx removal.

In this study, the concept of fast SCR for NO reduction with NH3 as reducing agent is realized via the combination of nonthermal plasma (NTP) with Mn-based catalyst. Experimental results indicate that 10% wt. Mn-Ce-Ni/TiO2 possesses better physical and chemical properties of surface, resulting in higher NO removal efficiency if compared with 10% wt. Mn-Ce/TiO2 and 10% wt. Mn-Ce-Cu/TiO2. Mn-Ce-Ni/TiO2 of 10% wt. achieves 100% NOx conversion at 150°C, while 10% wt. Mn-Ce/TiO2 and 10% wt. Mn-Ce-Cu/TiO2 need to be operated at a temperature above 200°C for 100% NOx conversion. However, NO conversion achieved with 10% wt. Mn-Ce-Ni/TiO2 is significantly reduced as H2O(g) and SO2 are introduced into the SCR system simultaneously. Further, two-stage system (SCR with DBD) is compared with the catalyst-alone for NOx conversion and N2 selectivity. The results indicate that 100% NOx conversion can be achieved with two-stage system at 100°C, while N2 selectivity reaches 80%. Importantly, NOx conversion achieved with two-stage system could maintain >95% in the presence of C2H4, CO, SO2, and H2O(g), indicating that two-stage system has better tolerance for complicated gas composition. Overall, this study demonstrates that combining NTP with Mn-based catalyst is effective in reducing NOx emission at a low temperature (≤200°C) and has good potential for industrial application.

Catalytic Removal of Volatile Organic Compounds

The degradation of air quality by the release of volatile organic compounds (VOCs) into the air particularly harms human health and our environment. [...]