Sustainable ammonia synthesis:An in-depth review of non-thermal plasma technologies

Ammonia serves both as a widely used fertilizer and environmentally friendly energy source due to its high energy density,rich hydrogen content,and emissions-free combustion.Additionally,it offers convenient transportation and storage as a hydrogen carrier.The dominant method used for large-scale ammonia production is the Haber-Bosch process,which requires high temperatures and pressures and is energy-intensive.However,non-thermal plasma offers an eco-friendly alternative for ammonia synthesis,gaining significant attention.It enables ammonia production at lower temperatures and pressures using plasma technology.This review provides insights into the catalyst and reactor developments,which are pivotal for promoting ammonia efficiency and addressing existing challenges.At first,the reaction kinetics and mechanisms are introduced to gain a comprehensive understanding of the reaction pathways involved in plasma-assisted ammonia synthesis.Thereafter,the enhancement of ammonia synthesis efficiency is discussed by developing and optimizing plasma reactors and effective catalysts.The effect of other feeding sources,such as water and methane,instead of hydrogen is also presented.Finally,the challenges and possible solutions are outlined to facilitate energy-saving and enhance ammonia efficiency in the future.

Non-thermal plasma enhanced catalytic conversion of methane into value added chemicals and fuels

Plasma catalysis has recently gained increased attention for its application in gas conversion,notably in processes like the dry reforming of methane aimed at transforming them into valuable chemicals and fuels.As this field is still in its early developmental stages,there is a crucial necessity to explore the synergistic mechanism between plasma and catalysts.The optimization of catalysts is imperative to improve their selectivity and conversion rates for desired products in a plasma environment.Additionally,delving into microscale investigations of plasma characteristics,such as electron temperature and the density of energetic species,is essential to enhance the stability and activity of catalysts.This review examines recent advancements in various methane conversion techniques,encompassing Dry Reforming of Methane,Steam Methane Reforming,Pa rtial Oxidation of Metha ne,and Methane Decomposition utilizing non-thermal dielectric barrier discharge(DBD)plasma.The aim is to gain a deeper understanding of plasma-catalyst interactions and to refine catalyst selection strategies for maximizing the production of desired products such as syngas,oxygenates,or higher hydrocarbons.The review delves into the catalytic mechanisms that delineate the synergistic effects between DBD plasma and catalyst in each technology,shedding light on the role of diverse catalytic properties in activating methane molecules-a pivotal step in hybrid plasma-catalytic reactions.Various approaches employed by researchers in exploring suitable catalysts and optimal reaction conditions to bolster CH_(4) conversion rates and selectivity using DBD plasma are discussed.Additionally,the review identifies gaps in the realm of plasma catalysis,underscoring the necessity for further research to fully understand the underlying principles of plasma and catalyst which are not trivial to uncover.

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.

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.

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.

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.

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.

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.

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.

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.

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.

NOx storage and reduction assisted by non-thermal plasma over Co/Pt/Ba/γ-Al2O3 catalyst using CH_(4) as reductant

NOx storage and reduction(NSR)technology has been regarded as one of the most promising strategies for the removal of nitric oxides(NOx)from lean-burn engines,and the potential of the plasma catalysis method for NOx reduction has been confirmed in the past few decades.This work reports the NSR of nitric oxide(NO)by combining non-thermal plasma(NTP)and Co/Pt/Ba/γ-Al2O3(Co/PBA)catalyst using methane as a reductant.The experimental results reveal that the NOx conversion of NSR assisted by NTP is notably enhanced compared to the catalytic efficiency obtained from NSR in the range of 150°C–350°C,and NOx conversion of the 8%Co/PBA catalyst reaches 96.8%at 350°C.Oxygen(O_(2))has a significant effect on the removal of NOx,and the NOx conversion increases firstly and then decreases when the O_(2)concentration ranges from 2%to 10%.Water vapor reduces the NOx storage capacity of Co/PBA catalysts on account of the competition for adsorption sites on the surface of Co/PBA catalysts.There is a negative correlation between sulfur dioxide(SO_(2))and NOx conversion in the NTP system,and the 8%Co/PBA catalyst exhibits higher NOx conversion compared to other catalysts,which shows that Co has a certain SO_(2)resistance.

The Advantages of Non-Thermal Plasma for Detonation Initiation Compared with Spark Plug

In this paper,the characteristics of detonation combustion ignited by AC-driven non-thermal plasma and spark plug in air/acetylene mixture have been compared in a doubletube experiment system.The two tubes had the same structure,and their closed ends were installed with a plasma generator and a spark plug,respectively.The propagation characteristics of the flame were measured by pressure sensors and ion probes.The experiment results show that,compared with a spark plug,the non-thermal plasma obviously broadened the range of equivalence ratio when the detonation wave could develop successfully,it also heightened the pressure value of detonation wave.Meanwhile,the detonation wave development time and the entire flame propagation time were reduced by half.All of these advantages benefited from the larger ignition volume when a non-thermal plasma was applied.

Development of low power non-thermal plasma jet and optimization of operational parameters for treating dyes and emerging contaminants

Non-thermal plasma has emerged as an effective treatment system against the latest class of highly recalcitrant and toxic environmental pollutants termed emerging contaminants(ECs).In the present work,a detailed experimental study is carried out to evaluate the efficacy of a non-thermal plasma jet with two dyes,Rd.B and Met.Blue,as model contaminants.The plasma jet provided a complete dye decoloration in 30 min with an applied voltage of 6.5 kV_(p-p).·OH,having the highest oxidation potential,acts as the main reactive species,which with direct action on contaminants also acts indirectly by getting converted into H_(2)O_(2)and O_(3).Further,the effect of critical operational parameters viz,sample pH,applied voltage(4.5–6.5 kV_(p-p)),conductivity(5–20 mS cm^(-1)),and sample distance on plasma treatment efficacy was also examined.Out of all the assessed parameters,the applied voltage and sample conductivity was found to be the most significant operating parameters.A high voltage and low conductivity favored the dye decoloration,while the pH effect was not that significant.To understand the influence of plasma discharge gas on treatment efficacy,all the experiments are conducted with argon and helium gases under the fixed geometrical configuration.Both the gases provided a similar dye decoloration efficiency.The DBD plasma system with complete dye removal also rendered maximum mineralization of 73%for Rd.B,and 60%for Met.Blue.Finally,the system's efficiency against the actual ECs(four pharmaceutical compounds,viz,metformin,atenolol,acetaminophen,and ranitidine)and microbial contaminant(E.coli)was also tested.The system showed effectivity in the complete removal of targeted pharmaceuticals and a log2.5 E.coli reduction.The present systematic characterization of dye degradation could be of interest to large communities working towards commercializing plasma treatment systems.

Quality enhancement and microbial reduction of mung bean(Vigna radiata)sprouts by non-thermal plasma pretreatment of seeds

Mung bean(Vigna radiata)sprouts are widely consumed worldwide due to their high nutritional value.However,the low yield and microbial contamination of mung bean sprouts seriously reduces their economic value.This study investigates the effects of non-thermal plasma on the quality and microbial reduction of mung bean sprouts by pretreatment of seeds in water for different times(0,1,3 and 6 min).The quality results showed that short-time plasma treatment(1 and 3 min)promoted seed germination and seedling growth,whereas long-time plasma treatment(6 min)had inhibitory effects.Plasma also had a similar dose effects on the total flavonoid and phenolic contents of mung bean sprouts.The microbiological results showed that plasma treatment achieved a reduction of native microorganisms ranging from 0.54 to 7.09 log for fungi and 0.29 to 6.80 log for bacteria at 96 h incubation.Meanwhile,plasma treatment could also efficiently inactivate artificially inoculated Salmonella typhimurium(1.83–6.22 log)and yeast(0.53–3.19 log)on mung bean seeds.The results of seed coat permeability tests and scanning electron microscopy showed that plasma could damage the seed coat structure,consequently increasing the electrical conductivity of mung bean seeds.The physicochemical analysis of plasma-treated water showed that plasma generated various long-and short-lived active species[nitric oxide radicals(NO·),hydroxyl radicals(·OH),singlet oxygen(1O2),hydrogen peroxide(H_(2)O_(2)),nitrate(NO_(3)^(-)),and nitrite(NO_(2)^(-))]in water,thus the oxidizability,acidity and conductivity of plasma-treated water were all increased in a treatment timedependent manner.The result for mimicked chemical mixtures confirmed the synergistic effect of activity of H_(2)O_(2),NO_(3)^(-)and NO_(2)^(-)on bacterial inactivation and plant growth promotion.Taken together,these results imply that plasma pretreatment of mung bean seeds in water with moderate oxidizability and acidity is an effective method to improve the yield of mung bean sprouts and reduce microbial contamination.

Polysilicon Prepared from SiCl_4 by Atmospheric-Pressure Non-Thermal Plasma

Non-thermal plasma at atmospheric pressure was explored for the preparation of polysilicon from SiCl4. The power supply sources of positive pulse and alternating current （8 kHz and 100 kHz） were compared for polysilicon preparation. The samples prepared by using the 100 kHz power source were crystalline silicon. The effects of H2 and SiCl4 volume fractions were investigated. The optical emission spectra showed that silicon species played an important role in polysilicon deposition

Selective catalytic reduction of NO_(x) with NH_(3) assisted by non-thermal plasma over CeMnZrO_(x)@TiO_(2) core–shell catalyst

The presented work reports the selective catalytic reduction(SCR)of NO_(x) assisted by dielectric barrier discharge plasma via simulating marine diesel engine exhaust,and the experimental results demonstrate that the low-temperature activity of NH_(3)-SCR assisted by non-thermal plasma is enhanced significantly,particularly in the presence of a C_(3)H_(6) additive.Simultaneously,CeMnZrO_(x)@TiO_(2) exhibits strong tolerance to SO_(2) poisoning and superior catalytic stability.It is worthwhile to explore a new approach to remove NO_(x) from marine diesel engine exhaust,which is of vital significance for both academic research and practical applications.

Effect of indirect non-thermal plasma on particle size distribution and composition of diesel engine particles

To explore the effect of the gas source flow rate on the actual diesel exhaust particulate matter（PM）, a test bench for diesel engine exhaust purification was constructed, using indirect nonthermal plasma technology. The effects of different gas source flow rates on the quantity concentration, composition, and apparent activation energy of PM were investigated, using an engine exhaust particle sizer and a thermo-gravimetric analyzer. The results show that when the gas source flow rate was large, not only the maximum peak quantity concentrations of particles had a large drop, but also the peak quantity concentrations shifted to smaller particle sizes from 100 nm to 80 nm. When the gas source flow rate was 10L min^-1, the total quantity concentration greatly decreased where the removal rate of particles was 79.2%, and the variation of the different mode particle proportion was obvious. Non-thermal plasma（NTP） improved the oxidation ability of volatile matter as well as that of solid carbon. However, the NTP gas source rate had little effects on oxidation activity of volatile matter, while it strongly influenced the oxidation activity of solid carbon. Considering the quantity concentration and oxidation activity of particles, a gas source flow rate of 10L min^-1 was more appropriate for the purification of particles.