Recent advances in non-thermal plasma(NTP)catalysis towards C1 chemistry

C1 chemistrymainly involves the catalytic transformation of C1molecules(i.e.,CO,CO2,CH4 and CH3OH),which usually encounters thermodynamic and/or kinetic limitations.To address these limitations,non-thermal plasma(NTP)activated heterogeneous catalysis offers a number of advantages,such as relatively mild reaction conditions and energy efficiency,in comparison to the conventional thermal catalysis.This review presents the state-of-the-art for the application of NTP-catalysis towards C1 chemistry,including the CO2 hydrogenation,reforming of CH4 and CH3OH,and water-gas shift(WGS)reaction.In the hybrid NTP-catalyst system,the plasma-catalyst interactions aremultifaceted.Accordingly,this reviewalso includes a brief discussion on the fundamental research into themechanisms of NTP activated catalytic C1 chemistry,such as the advanced characterisation methods(e.g.,in situ diffuse reflectance infrared Fourier transform spectroscopy,DRIFTS),temperatureprogrammed plasma surface reaction(TPPSR),kinetic studies.Finally,prospects for the future research on the development of tailor-made catalysts for NTP-catalysis systems(which will enable the further understanding of its mechanism)and the translation of the hybrid technique to practical applications of catalytic C1 chemistry are discussed.

Sustainable Ammonia Synthesis from Nitrogen and Water by One-Step Plasma Catalysis

Sustainable ammonia synthesis at ambient conditions that relies on renewable sources of energy and feedstocks is globally sought to replace the Haber-Bosch process.Here,using nitrogen and water as raw materials,a nonthermal plasma catalysis approach is demonstrated as an effective powerto-chemicals conversion strategy for ammonia production.By sustaining a highly reactive environment,successful plasma-catalytic production of NH_(3) was achieved from the dissociation of N_(2) and H_(2)O under mild conditions.Plasma-induced vibrational excitation is found to decrease the N_(2) and H_(2)O dissociation barriers,with the presence of matched catalysts in the nonthermal plasma discharge reactor contributing significantly to molecular dissociation on the catalyst surface.Density functional theory calculations for the activation energy barrier for the dissociation suggest that ruthenium catalysts supported on magnesium oxide exhibit superior performance over other catalysts in NH_(3) production by lowering the activation energy for the dissociative adsorption of N_(2) down to 1.07 eV.The highest production rate,2.67 mmol gcat.^(-1) h^(-1),was obtained using ruthenium catalyst supported on magnesium oxide.This work highlights the potential of nonthermal plasma catalysis for the activation of renewable sources to serve as a new platform for sustainable ammonia production.

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 CO_(2) 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 NTPcatalytic 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 k V,while the ozone concentration was151 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.

Is a catalyst always beneficial in plasma catalysis? Insights from the many physical and chemical interactions

Plasma-catalytic dry reforming of CH_(4)(DRM) is promising to convert the greenhouse gasses CH_(4) and CO_(2) into value-added chemicals, thus simultaneously providing an alternative to fossil resources as feedstock for the chemical industry. However, while many experiments have been dedicated to plasma-catalytic DRM, there is no consensus yet in literature on the optimal choice of catalyst for targeted products,because the underlying mechanisms are far from understood. Indeed, plasma catalysis is very complex,as it encompasses various chemical and physical interactions between plasma and catalyst, which depend on many parameters. This complexity hampers the comparison of experimental results from different studies, which, in our opinion, is an important bottleneck in the further development of this promising research field. Hence, in this perspective paper, we describe the important physical and chemical effects that should be accounted for when designing plasma-catalytic experiments in general, high-lighting the need for standardized experimental setups, as well as careful documentation of packing properties and reaction conditions, to further advance this research field. On the other hand, many parameters also create many windows of opportunity for further optimizing plasma-catalytic systems.Finally, various experiments also reveal the lack of improvement in plasma catalysis compared to plasma-only, specifically for DRM, but the underlying mechanisms are unclear. Therefore, we present our newly developed coupled plasma-surface kinetics model for DRM, to provide more insight in the underlying reasons. Our model illustrates that transition metal catalysts can adversely affect plasmacatalytic DRM, if radicals dominate the plasma-catalyst interactions. Thus, we demonstrate that a good understanding of the plasma-catalyst interactions is crucial to avoiding conditions at which these interactions negatively affect the results, and we provide some recommendations for improvement. For instance, we believe that plasma-catalytic DRM may benefit more from higher reaction temperatures,at which vibrational excitation can enhance the surface reactions.

Research on degradation mechanism of trichlorobenzene and Hg^(0) by nonthermal plasma catalysis

Aiming at mercury and dioxin in fire coal gas as research objects,nonthermal plasma(NTP)catalytic technology was used to investigate the degradation effect of operating condition parameters on mixed pollutants in mixed flue gas condition,and to explore the synergistic degradation of Hg0and TCB(1,2,3-trichlorobenzene,TCB)under mixed flue gas conditions.The research results showed that the conversion efficiency of mercury and TCB increased with the additional output of voltage,and decreased with the increase of the gas flow rate.Under optimal reaction conditions:voltage=17 k V,frequency=300 Hz,gas flow rate=21 min^(-1),the conversion efficiency of Hg^(0)and TCB reached the highest 91.4%and 84.98%,respectively.In the NTP catalytic system,active free radicals played an important role in the synergistic conversion of mercury and TCB,which have a competitive effect,to make the conversion efficiency of mixed pollutants lower than a single substance.In the mixed flue gas condition,the mixed gas has an inhibitory effect on the synergistic conversion of mercury and TCB.Kinetic modeling of NTP catalytic synergistic reaction was established.Under three conditions of TCB,mercury and TCB,mixed simulated flue gas,the NTP catalytic technology showed a quasi-firstorder kinetic reaction for the degradation of TCB.According to the synergistic effect of NTP and composites,the transformation and degradation of TCB mainly included two processes:TCB and ring opening,and Hg^(0)was finally oxidized to Hg^(2+).

Catalysis Conversion Methane into C_(2) Hydrocarbons via Electric Field Enhanced Plasma

In this paper the effect of catalyst and carrier in electric field enhanced plasma on methane conversion into C2 hydrocarbons was investigated. Methane coupling reaction was studied in the system of continuous flow reactor on Ni, MoO3, MnO2 catalysts and different ZSM-5 carriers. The per pass conversion of methane can be as high as 22%, the selectivity of ethylene can be as high as 23.8%, of acetylene 60.8%, of ethane 5.4% and of total C2 hydrocarbons was more than 90%. ZSM-5-25 was the better carrier and MnO2 was the better active component. The efficiency of energy was as high as 7.81%.

Simultaneous removal of NO and SO_2 from dry gas stream using non-thermal plasma

In order to investigate the feasibility of sequential removal NO and SO2 using non-thermal plasma and adsorbent simultaneously, the removal of NO and SO2 from dry gas stream （NO/SO2/N2/O2） with very little O2 using non-thermal plasma was investigated using a coaxial dielectric barrier discharge. Comparative experiments were carried out in the dry gas stream with and without Ar respectively at O2 concentration of 0.1%. The results showed that NO could be removed remarkably and it would be enhanced in the presence of Ar in the dry gas stream. It seems that SO2 could not be removed unless there is Ar in the dry gas stream. The mechanism of removal of NO and SO2 in the dry gas stream was discussed.

Synergistic removal of nitrogen monoxide by non-thermal plasma and catalyst simultaneously

An experimental system of De-NO with plasma-catalyst（Cu zeolite） was established to investigate the differences between De- NO with plasma-catalyst and De-NO only with plasma, to provide the instruction for selecting appropriate catalyst and operating condition, The characteristics of De-NO with plasma and De-NO with plasma-catalyst were investigated comparatively by experiments. The experimental results show that De-NO with plasma-catalyst has high NO removal rate; Cu zeolite is an effective catalyst which can promote NO removal rate in plasma remarkably; De-NO with plasma-catalyst should be operated at low temperature and the temperature has opposite effects on the function of catalvst and plasma; water vapor and O2 can increase the NO removal rate.

Application of in-plasma catalysis and post-plasma catalysis for methane partial oxidation to methanol over a Fe_2O_3-CuO/γ-Al_2O_3 catalyst

Methane partial oxidation to methanol （MPOM） using dielectric barrier discharge over a Fe2O3-CuO/γ-Al2O3 catalyst was performed.The multicomponent catalyst was combined with plasma in two different configurations,i.e.,in-plasma catalysis （IPC） and post-plasma catalysis （PPC）.It was found that the catalytic performance of the catalysts for MPOM was strongly dependent on the hybrid configuration.A better synergistic performance of plasma and catalysis was achieved in the IPC configuration,but the catalysts packed in the discharge zone showed lower stability than those connected to the discharge zone in sequence.Active species,such as ozone,atomic oxygen and methyl radicals,were produced from the plasma-catalysis process,and made a major contribution to methanol synthesis.These active species were identified by the means of in situ optical emission spectra,ozone measurement and FT-IR spectra.It was confirmed that the amount of active species in the IPC system was greater than that in the PPC system.The results of TG,XRD,and N2 adsorption-desorption revealed that carbon deposition on the spent catalyst surface was responsible for the catalyst deactivation in the IPC configuration.

Study on purification technology of polyacrylamide wastewater by non-thermal plasma

In this work,non-thermal plasma has been applied to treat polyacrylamide(PAM)wastewater.We have investigated the in fluence of the rule of PAM wastewater initial pH,solution concentration and discharge time,discharge voltage on chemical oxygen demand(COD)degradation rate.At the same time,the effect of pH and discharge time on the viscosity removal rate of PAM solution was also studied.Then,the effect of pH on the viscosity removal rate of 1.0g 1^-1 PAM solution was studied separately.Through orthogonal test,the factors affecting the COD degradation rate of PAM wastewater were determined as follows:discharge time>discharge voltage>solution concentration>wastewater initial pH.1'he COD highest removal rate of PAM wastewater reached 85.74%,when the optimal conditions are as follows:discharge voltage 40 kV,discharge time 5 h,solution concentration 1.0 g 1^-1,pH 1.5.This research provides some basic data and new theoretical basis for PAM wastewater purification.

Non-thermal Plasma Suppresses Bacterial Colonization on Skin Wound and Promotes Wound Healing in Mice

The present study evaluated the effect of non-thermal plasma on skin wound healing in BalB/c mice.Two 6-mm wounds along the both sides of the spine were created on the back of each mouse（n=80） by using a punch biopsy.The mice were assigned randomly into two groups,with 40 animals in each group：a non-thermal plasma group in which the mice were treated with the non-thermal plasma;a control group in which the mice were left to heal naturally.Wound healing was evaluated on postoperative days（POD） 4,7,10 and 14（n=5 per group in each POD） by percentage of wound closure.The mice was euthanized on POD 1,4,7,10,14,21,28 and 35（n=1 in each POD）.The wounds were removed,routinely fixed,paraffin-embedded,sectioned and HE-stained.A modified scoring system was used to evaluate the wounds.The results showed that acute inflammation peaked on POD 4 in non-thermal plasma group,earlier than in control group in which acute inflammation reached a peak on POD 7,and the acute inflammation scores were much lower in non-thermal group than in control group on POD 7（P0.05）.The amount of granular tissue was greater on POD 4 and 7 in non-thermal group than in control group（P0.05）.The re-epithelialization score and the neovasularization score were increased significantly in non-thermal group when compared with control group on POD 7 and 10（P0.05 for all）.The count of bacterial colonies was 103 CFU/mL on POD 4 and 20 CFU/mL on POD 7,significantly lower than that in control group（109 CFU/mL on POD 4 and 1012 CFU/mL on the POD 7）（P0.05）.It was suggested that the non-thermal plasma facilitates the wound healing by suppressing bacterial colo-nization.

Sterilization of Staphylococcus Aureus by an Atmospheric Non-Thermal Plasma Jet

An atmospheric non-thermal plasma jet was developed for sterilizing the Staphylococcus aureus （S. aureus）. The plasma jet was generated by dielectric barrier discharge （DBD）, which was characterized by electrical and optical diagnostics. The survival curves of the bacteria showed that the plasma jet could effectively inactivate 10 6 cells of S. aureus within 120 seconds and the sterilizing efficiency depended critically on the discharge parameter of the applied voltage. It was further confirmed by scanning electron microscopy （SEM） that the cell morphology was seriously damaged by the plasma treatment. The plasma sterilization mechanism of S. aureus was attributed to the active species of OH, N 2 ＋ and O, which were generated abundantly in the plasma jet and characterized by OES. Our findings suggest a convenient and low-cost way for sterilization and inactivation of bacteria.

Recent progress on non-thermal plasma technology for high barrier layer fabrication

This review describes the application of non-thermal plasma（NTP） technology for high barrier layer fabrication in packaging area.NTP technology is considered to be the most prospective approaches for the barrier layer fabrication over the past decades due to unpollution,high speed,low-costing.The applications of NTP technology have achieved numerous exciting results in high barrier packaging area.Now it seemly demands a detailed review to summarize the past works and direct the future developments.This review focuses on the different NTP resources applied in the high barrier area,the role of plasma surface modification on packaging film surface properties,and the deposition of different barrier coatings based on NTP technology.In particular,this review emphasizes the cutting-edge technologies of NTP on interlayer deposition with organic,inorganic for multilayer barriers fabrication.The future prospects of NTP technology in high barrier film areas are also described.

Deposition of stain resistance coating by non-thermal plasma brush application to dental whitening

A non-thermal plasma brush is employed to deposit stain-resistant SiO2-like coatings on resin composite fillings and bovine teeth.With post-treating by plasma,the hardness of the coating increases from H to 8H and the water contact angle decreases from 98.8° to 61.7°.The Fourier transform infrared spectroscopy (FTIR) results show that,after plasma post-treating,the Si-O-Si and Si-OH bonds of the coating increase.Scanning electron microscope (SEM) images show the coatings to be uniform,without cracks.The coatings present outstanding performance in a stain resistance test both on resin composite and bovine teeth.Being easy to handle and less time consuming than traditional methods,with a body-friendly temperature and material,this plasma brush provides a promising in-situ coating method on patient teeth in dental clinics.

Experimental Study on Indoor Air Cleaning Technique of Nano-Titania Catalysis Under Plasma Discharge

In this study, a new technique of air cleaning by plasma combined with catalyst was proposed, which consisted of electrostatic precipitation, volatile organic compounds （VOCs） decomposition and sterilization. A novel indoor air purifier based on this technique was adopted. The experimental results showed that formaldehyde decomposition by the plasma-catalyst hybrid system was more efficient than that by plasma only, Positive discharge was better than negative discharge in formaldehyde removal. Meanwhile, the outlet concentration of ozone byproduct was effectively reduced by the nano-titania catalyst.

Analysis of the microstructure and elemental occurrence state of residual ash-PM following DPF regeneration by injecting oxygen into non-thermal plasma

Particulate matter(PM)capture tests were carried out on clean diesel particulate filters(DPFs)under different loads(25%,50%,75%and 100%).DPFs were regenerated by a non-thermal plasma(NTP)injection device.Raman spectroscopy and x-ray photoelectron spectroscopy were used to investigate changes in the microstructure and element occurrence state of the sediment in DPF channel before and after regeneration.The order of the PM samples decreased before NTP treatment as the load increased;the amorphous carbon content was high,and the oxidationactivity was higher.After NTP treatment,the carbon atoms at the edge of the microcrystalline structure in the ash-PM samples were oxidized,and the structure was reorganized;in addition,the amorphous carbon content decreased,and the structure was more diversified.Before NTP,the C element of PM samples was the main component,and the content of the O element was relatively low.The C element occurred in the form of C–C,C–OH,and O–C=O functional groups,and O atoms were mainly combined with C–O.After NTP,the content of Na,P,S,Ca,and other inorganic elements in ash-PM samples was prominent because C atoms were removed by NTP active substances.There were two forms of S element occurrence(SO42-and SO32-);the proportion of SO42-was approximately 40%,and the proportion of SO32-was approximately60%.Study of the microstructure and element occurrence of the residues in the DPF channels improved our understanding of the mechanism of the low-temperature regeneration of DPFfrom NTP.

Efficiency of Removing Sulfur Dioxide in the Air by Non-Thermal Plasma Along with the Application of the Magnetic Field

The non-thermal plasma created by high voltage pulsed power supply can be used to remove sulfur dioxide in the air, but how to increase the removing efficiency is not clear. It is novel to apply the magnetic field in removing SO2 as discussed in this paper. The mechanisms of removing sulfur dioxide by non-thermal plasma along with the application of the magnetic field are analyzed, and the related factors affecting the removal efficiency, such as the magnitude of pulsed voltage, the polarity of the pulse, the layout of the discharge electrode, especially the magnetic field are experimentally investigated. It can be concluded that the purification efficiency is improved significantly by applying the magnetic field.

Mechanism and Kinetics Analysis of NO/SO_2/N_2/O_2 Dissociation Reactions in Non-Thermal Plasma

The kinetics mechanism of the dissociation reactions in a NO/SO2/N2/O2 system was investigated in consideration of energetic electrons＇ impacts on a non-thermal plasma. A model was derived from the Boltzmann equation and molecule collision theory to predict the dissociation reaction rate coefficients. Upon comparison with available literature, the model was confirmed to be acceptably accurate in general. Several reaction rate coefficients of the NO/SO2/N2/O2 dissociation system were derived according to the Arrhenius formula. The activation energies of each plasma reaction were calculated by quantum chemistry methods. The relation between the dissociation reaction rate coefficient and electron temperature was established to describe the importance of each reaction and to predict relevant processes of gaseous chemical reactions. The sensitivity of the mechanism of NO/SO2/N2/O2 dissociation reaction in a non-thermal plasma was also analysed.

Improvement of Polytetrafluoroethylene Surface Energy by Repetitive Pulse Non-Thermal Plasma Treatment in Atmospheric Air

Improvement of polytetrafluoroethylene surface energy by non-thermal plasma treatment is presented, using a nanosecond-positive-edge repetitive pulsed dielectric barrier discharge generator in atmospheric air. The electrical parameters including discharging power, peak and density of micro-discharge current were calculated, and the electron energy was estimated. Surface treatment experiments of polytetrafluoroethylene films were conducted for both different applied voltages and different treating durations. Results show that the surface energy of polytetrafluoroethylene film could be improved to 40 mJ/m2 or more by plasma treatment. Surface roughness measurement and surface X-ray photoelectron spectroscopy analysis indicate that there are chemical etching and implantation of polar oxygen groups in the sample surface treating process, resulting in the improvement of the sample surface energy. Compared with an AC source of 50 Hz, the dielectric barrier discharges generated by a repetitive pulsed source could provide higher peak power, lower mean power, larger micro-discharge current density and higher electron energy. Therefore, with the same applied peak voltage and treating duration, the improvement of polytetrafluoroethylene surface energy using repetitive pulsed plasma is more effective, and the plasma treatment process based on repetitive pulsed dielectric barrier discharges in air is thus feasible and applicable.

Investigation of non-thermal atmospheric plasma for the degradation of avermectin solution

Increasing concern with regard to food safety in the presence of pesticide residues(PRs) on the surface of agricultural products has resulted in the rapid development of practical degrading technologies for corresponding PRs. In this paper, an unconventional method of degrading pesticides, non-thermal atmospheric plasma(NTAP), was proposed to degrade the avermectin(AVM) in aqueous solution. Optical emission spectroscopy shows that NTAP, consisting of filamentary streamers, contains a variety of reactive oxygen species(ROS) that may interact with AVM. The high-performance liquid chromatography(HPLC)-MS/MS results indicate that the efficiency of AVM degradation seriously depends on multiple operation parameters of the NTAP,including the applied voltage, treatment time and gas flow rate. The maximum degradation rate of AVM was observed to be 97.47% after 240 s exposure under NTAP with an applied voltage of 18 kV and gas flow rate of 1 l min-1. Molecular dynamics simulation based on a reactive force field for the interaction between O(ground state atomic oxygen) and AVM was performed to analyze the underpinning mechanisms. The simulation result shows the possible pathways of the NTAPgenerated O degrading AVM by destroying the glycosyl group or fracturing the ester group.