N2 H2 Research Articles

Enhanced photocatalytic organic pollutant degradation, H2 production and N2 fixation via a versatile zinc oxide-based nanocomposite: Synthesis, characterization and mechanism Insight

Developing highly efficient photocatalysts for visible light utilization is crucial for water purification, N2 fixation, and H2 generation. This work presents a novel α-Fe2O3/CeO2-ZnO heterostructure photocatalyst synthesized through a facile impregnation technique. The synthesized catalysts were characterized via XPS, TEM, SEM, XRD, BET, PL, EIS, Mott-schottky, etc. analyses. The optimized 25 wt% of α-Fe2O3/CeO2 on ZnO (25-FeCeZ) catalyst achieved 100 % ofloxacin (OFX) photodegradation under light irradiation within 90 min. The charge transfer pathway was investigated via optical analyses within the 25-FeCeZ. Experimental investigations elucidated the potential intermediates, four proposed OFX photodegradation pathways and photocatalytic mechanism. Scavenger experiments and ESR spectroscopy identified •O2–, •OH, and h+ as the primary reactive species. Furthermore, the degraded OFX solution exhibited lower overall toxicity compared to the initial solution, based on QSAR predictions and E. coli viability assays. The 25-FeCeZ catalyst displayed a significantly enhanced hydrogen production rate (2.57mmol g−1h−1) compared to pristine ZnO (0.09 mmol/g·h). Notably, the catalyst achieved an NH3 evolution rate of 335.80μmol g−1h−1 without additional sacrificial agents, which is 4.5 times greater than pure ZnO. Additionally, the optimised photocatalyst depicted a superb stability across all three photocatalytic processes. This study illustrates a promising approach for designing potent ZnO-based photocatalysts for diverse applications, including N2 fixation, H2 generation, and organic pollutant degradation under visible light irradiation.

Toward High-Performance Electrochemical Ammonia Synthesis by Circumventing the Surface H-Mediated N2 Reduction.

The rapid performance decay with potentials is a significant obstacle to achieving an efficient electrocatalytic N2 reduction reaction (eNRR), which is typically attributed to competition from hydrogen evolution. However, the potential-dependent competitive behavior and reaction mechanism are still under debate. Herein, we theoretically defined N2 adsorption, H mediation, and H2 evolution as three crucial regions along the potentials by revisiting the potential-dependent competitive adsorption between N2 and H on FeN4 and RuN4 catalysts. We revealed that the surface H-mediated mechanism makes eNRR feasible at low potentials but introduces sluggish reaction kinetics, showing a double-edged sword nature. In view of this, we proposed a new possibility to achieve high-performance NH3 synthesis by circumventing the H-mediated mechanism, where the ideal catalyst should have a wide potential interval with N2-dominated adsorption to trigger direct eNRR. Using this mechanistic insight as a new criterion, we proposed a theoretical protocol for eNRR catalyst screening, but almost none of the theoretically reported electrocatalysts passed the assessment. This work not only illustrates the intrinsic mechanism behind the low-performance dilemma of eNRR but also points out a possible direction toward designing promising catalysts with high selectivity and high current density.

One Iron for Two Iron Sites in a Metal–Organic Framework Toward Simultaneous N2−H2 Activation under Mild Conditions

AbstractIron‐based catalysts play an important role in the ammonia industry. As one of the most abundant iron minerals, Fe3O4 containing FeII and FeIII sites is widely distributed in the earth's crust and even on exoplanets, theoretically giving it both economic and catalytic potentials in ammonia synthesis. However, in the absence of specific active co‐catalyst and harsh conditions, Fe3O4 is impossible to achieve ammonia synthesis alone. Here, we designed to activate the relatively inert FeII and FeIII sites in Fe3O4 with a third FeIII site inlayed in a coordination framework (MIL‐101(Fe)) to achieve the unpresented multi‐site collaborative catalysis. In‐depth mechanism study confirmed the roles of three different Fe sites in N2 activation, H2 activation, and product transfer, respectively. Efficient N2−H2 activation to NH3 on the Fe3O4‐based catalytic system has been achieved at extremely mild conditions. Our research provides a theoretical basis and a new strategy for designing efficient non‐noble metal‐based ammonia synthesis catalyst with minimized energy consumption.

One Iron for Two Iron Sites in a Metal-Organic Framework Toward Simultaneous N2-H2 Activation under Mild Conditions.

Iron-based catalysts play an important role in the ammonia industry. As one of the most abundant iron minerals, Fe3O4 containing FeII and FeIII sites is widely distributed in the earth's crust and even on exoplanets, theoretically giving it both economic and catalytic potentials in ammonia synthesis. However, in the absence of specific active co-catalyst and harsh conditions, Fe3O4 is impossible to achieve ammonia synthesis alone. Here, we designed to activate the relatively inert FeII and FeIII sites in Fe3O4 with a third FeIII site inlayed in a coordination framework (MIL-101(Fe)) to achieve the unpresented multi-site collaborative catalysis. In-depth mechanism study confirmed the roles of three different Fe sites in N2 activation, H2 activation, and product transfer, respectively. Efficient N2-H2 activation to NH3 on the Fe3O4-based catalytic system has been achieved at extremely mild conditions. Our research provides a theoretical basis and a new strategy for designing efficient non-noble metal-based ammonia synthesis catalyst with minimized energy consumption.

Vacancy engineering of BiFeO3 perovskite for low-barrier electrochemical nitrogen fixation

Because of its environmental and intrinsic benefits, the nitrogen reduction reaction (NRR) using electrocatalysts has garnered significant attention. Engineering on the surface is commonly utilized to improve electrocatalytic activity by introducing atomic defects. In this study, we have developed a successful strategy to promote nitrogen activation by introducing oxygen vacancies into BiFeO3 perovskite. BiFeO3 with oxygen vacancies (denoted as VO-BiFeO3) possesses a high NH3 yield rate (89.3 μg h−1 mgcat−1) and Faradaic efficiency (FE) (13.5 %) at −0.40 V versus the reversible hydrogen electrode (RHE). According to density functional theory (DFT) calculations, the introduction of oxygen vacancies increases the binding capacity for nitrogen immobilization and reduces the energy barrier for the rate-determining step of NRR. Moreover, the analysis of the thermodynamic limiting potentials towards N2 reduction and H2 evolution demonstrates that VO-BiFeO3 has a higher selectivity for NRR than pristine BiFeO3.

Dual-comb spectroscopy of ammonia formation in non-thermal plasmas

Plasma-activated chemical transformations promise the efficient synthesis of salient chemical products. However, the reaction pathways that lead to desirable products are often unknown, and key quantum-state-resolved information regarding the involved molecular species is lacking. Here we use quantum cascade laser dual-comb spectroscopy (QCL-DCS) to probe plasma-activated NH3 generation with rotational and vibrational state resolution, quantifying state-specific number densities via broadband spectral analysis. The measurements reveal unique translational, rotational and vibrational temperatures for NH3 products, indicative of a highly reactive, non-thermal environment. Ultimately, we postulate on the energy transfer mechanisms that explain trends in temperatures and number densities observed for NH3 generated in low-pressure nitrogen-hydrogen (N2–H2) plasmas.

Promoted photocatalytic performances over Ti3+-B co-doped TiO2/BN with high carrier transfer and absorption capabilities driven by SWCNT addition

Recently, carbon nanotubes have been widely used as supporting materials for semiconductor photocatalysts due to their excellent electron and mass transportation. Herein, we prepared a novel SWCNT-decorated Ti3+-B co-doped TiO2/BN (STBN) photocatalyst with the presence of single-walled carbon nanotubes (SWCNTs) during the hybridization of BN and TiB2. The effects of SWCNTs on the structural and photocatalytic properties were investigated. Adding SWCNTs enables excellent multifunctional photocatalytic performances (N2 fixation, H2 production, and MO degradation) compared with the TBN synthesized in the previous study. Introducing SWCNTs reduces the transfer resistance and makes the photogenerated carriers transfer more efficiently, thereby improving photocatalytic activity. More defect sites provide extra adsorption sites for reactants and photogenerated electrons, significantly improving the system's photocatalytic activity. The enhanced photocatalytic mechanism of SWCNT-decorated hybrid catalysts was proposed at last.

Effect of gas atmospheres and SiO2 content on preparation and properties of SiO2–Si3N4 composite ceramics via nitridation of diamond-wire saw silicon waste powder

Composite ceramics are applied widely nowadays by combining superior properties of different ceramic materials. In this study, SiO2–Si3N4 composite ceramics with higher mechanical properties and lower dielectric constant were successfully fabricated by nitriding diamond-wire saw silicon waste. The effect of gas atmospheres (N2, NH3, N2–H2) and SiO2 content (0%, 10%, 20%, 30%, 40%) on the microstructure and properties of composite ceramics were studied. It shows that the synthesis of SiO2–Si3N4 composite ceramics can be obtained in the NH3 atmosphere, and it is inevitable to form the Si2N2O phase in N2 and N2–H2 mixture atmospheres. Furthermore, the shrinkage rate and dielectric constant of the ceramics decreased as SiO2 content increased from 0% to 40%. As for the porosity of the sintered ceramics, it first decreased and then increased, with a minimum of 1.73% at the SiO2 content of 20%. However, the flexural strength of the sintered ceramics was the inverse of the porosity, with a maximum of 160.72 MPa at the SiO2 content of 30%. For the sintered ceramic with 30% SiO2, the shrinkage rate, dielectric constant, porosity and flexural strength are 0.3%, 4.62, 1.97% and 160.72 MPa respectively. Thus, this study provides an environment-friendly and value-added approach to recycling photovoltaic waste and reducing the cost of the reactive sintering SiO2–Si3N4 composite ceramics with excellent mechanical and dielectric properties.

Mechanocatalytic Synthesis of Ammonia by Titanium Dioxide with Bridge-Oxygen Vacancies: Investigating Mechanism from the Experimental and First-Principle Approach.

Mechanochemical ammonia (NH3) synthesis is an emerging mild approach derived from nitrogen (N2) gas and hydrogen (H) source. The gas-liquid phase mechanochemical process utilizes water (H2O), rather than conventional hydrogen (H2) gas, as Hsources, thus avoiding carbon dioxide (CO2) emission duringH2 production. However, ammonia yield is relatively low to meet practical demand due to huge energy barriers of N2 activation and H2O dissociation. Here, six transition metal oxides (TMO) such as titanium dioxide (TiO2), iron(III) oxide (Fe2O3), copper(II) oxide (CuO),niobium(V) oxide(Nb2O5), zinc oxide (ZnO), and copper(I) oxide (Cu2O) are investigated as catalysts in mechanochemical N2 fixation. Among them, TiO2 shows the best mechanocatalytic effect and the optimum reaction rate constant is 3.6-fold higher than the TMO-free process. The theoretical calculations show that N2 molecules prefer to side-on chemisorb on the mechano-induced bridge-oxygen vacancies in the (101) crystal plane of TiO2 catalyst, while H2O molecules can dissociate on the same sites more easily to provide free H atoms, enabling an alternative-way hydrogeneration process of activated N2 molecules to release NH3 eventually. This work highlights the cost-effective TiO2 mechanocatalyst for ammonia synthesis under mild conditions and proposes a defect-engineering-induced mechanocatalytic mechanism to promote N2 activation and H2O dissociation.

Relaxation behavior of vibrationally excited N2(X1Σg + v″ = 6) collisions with H2

Relaxation behavior of vibrationally excited N2 (X1Σg + v″ = 6) induced by collisions with H2 has been investigated using coherent anti-Stokes Raman spectroscopy (CARS). The total pressure of the N2–H2 mixture was 500 Torr, and the molar ratios of H2 were 0.3, 0.4, 0.5, 0.6 and 0.8, respectively. The v″ = 6 vibrational state of the electronic ground-state manifold X1Σg + of N2 was selectively excited by overtone pumping, and the population evolution was monitored using CARS spectroscopy. The collisional deactivation rate coefficients of the excited state N2 (v″ = 6) with H2 and N2 are approximately 2.59 × 10−14 cm3s−1 and 1.04 × 10−14 cm3s−1 at 300 K, and 2.57 × 10−14 cm3s−1 and 0.54 × 10−14 cm3s−1 at 320 K, respectively. The relaxation rate coefficient of the N2–H2 collision was approximately 2.5 and 5 times that of the self-relaxation rate coefficient. The experimental results show that the population densities of the (1,2), (2,2), (3,5), and (3,6) levels of H2 have a maximum at 320 K, while the population densities of (2,3) and (2,4) show little change with increasing temperature. Simultaneously, the time-resolved CARS profiles of the vibrational levels v = 6,5,4 by preparing v = 6 of N2 also indicated that a near-resonant multi-quantum relaxation process occurred between N2–H2. The collision-induced population distribution of H2 was observed at molar ratios of 0.3, 0.4, 0.5, 0.6 and 0.8, respectively. The ro-vibrational population distribution of H2 after collision with N2 is given by the CARS signal intensity ratio, and the population of hydrogen molecules at v = 2, 3 vibrational states also provides strong experimental evidence for energy near-resonance collisions between N2–H2.

Study on pyrolysis mechanism of coal in hydrogen-rich atmosphere based on reactive molecular dynamics simulation

Due to the co-combustion of hydrogen-rich atmosphere and coal in power plants has a great influence on NOX emission, it has been studied by more and more researchers. Therefore, the study of the effect of hydrogen-rich atmosphere on coal pyrolysis mechanism provides a theoretical basis for subsequent application in power plants. In this paper, reaction molecular dynamics simulation is used to investigate the pyrolysis mechanism of Henan anthracite coal within the temperature range of 300–3600 K. The consistency between the activation energy, TG curve, and gas release characteristics derived from the ReaxFF simulation and the experimental results provides evidence for the validity of this method in investigating the pyrolysis mechanism of coal. Furthermore, the pyrolysis behavior of Henan anthracite coal in N2, H2, and NH3 atmospheres with varying temperatures are studied. The pyrolysis of Henan anthracite coal can be categorized into three distinct stages under varying atmospheric conditions, as revealed by the simulation findings. Compared with N2 pyrolysis atmosphere, H2 and NH3 pyrolysis atmospheres can reduce the release of CO, reduce the activation energy, promote the degree of pyrolysis and accelerate the pyrolysis process. NH3 atmosphere has more obvious influence on the coal pyrolysis process. Also, HCN (NOX precursor) generation reactions during pyrolysis are revealed in N2, H2 and NH3 atmosphere. H2 and NH3 pyrolysis atmospheres can increase the number of HCN generation reactions and change the distribution of HCN generation reactions. The analysis of HCN formation reaction shows that CN and H2CN are the main precursors of HCN.

Laser absorption spectroscopy for plasma-assisted thermochemical treatment. Part II.: Impact of the carbon and water contaminants on a low-pressure N2–H2 discharge

The density evolution of , , and molecules over time was monitored by laser absorption spectroscopy in a low pressure DC pulsed discharge in N2–H2 gas mixtures with addition of CH4 or O2. The discharge was maintained in an industrial-scale, active screen (AS) plasma nitrocarburizing (ASPNC) reactor with a steel AS. The measured species densities were analysed using a simplified kinetic model that includes three characteristic times for chemical processes in the ASPNC reactor. The shortest time (1–4 min) was associated with the gas residence time in the reactor, the middle one (about 20 min) was assigned to surface reactions on the AS and workload, whereas the largest one (about 3–5 h) was assigned to surface reactions on the cold reactor walls. The work highlights the importance of monitoring the gas composition during plasma nitrocarburizing processes in order to maintain defined treatment conditions and compensate for continuously changing chemical kinetics at the internal reactor surfaces.

Synthesis, Hirshfeld atom refinement of crystal structure, and Hirshfeld surface analysis of 5-ethoxycarbonyl-6-methyl-4-(2-(trifluoromethyl)phenyl)-3,4-dihydropyrimidin-2-(1H)-one formic acid monosolvate

We report the cyanamide-based multicomponent synthesis and crystal structure of the title compound, 5-ethoxycarbonyl-6-methyl-4-(2-(trifluoromethyl)phenyl)-3,4-dihydropyrimidin-2-(1H)-one which crystallized as a binary cocrystal with formic acid, C15H15F3N2O3·HCO2H (DHPM···FA). The molecular structure of the DHPM···FA heterosynthon was unequivocally confirmed using X-ray single crystal diffraction techniques and spectroscopic methods. X-ray diffraction analysis shows that this cocrystalline material crystallizes in the monoclinic space group P21/n, Z = 4 with the 3,4-dihydropyrimidin-2-(1H)-one ring in a twist-boat form attached to the ester and phenyl group in an s−cis/s−cis and sp−conformation, respectively. The molecular structure and crystalline packing are stabilized by intermolecular N2–H2∙∙∙O1, N1–H1∙∙∙O5, O4–H4A∙∙∙O1, C4–H4∙∙∙O5, C6–H6∙∙∙O3 and C16–H16∙∙∙O3 hydrogen bonds into a 3D supramolecular network R22(8). Furthermore, the Hirshfeld surface analysis confirms that the most important contributions for the crystal packing are the H∙∙∙O/O∙∙∙H (58.7%), C − H···C (17.8%), H∙∙∙H (30.4%) and H∙∙∙F/F∙∙∙H (18.3%) surface contacts.

Technical Challenges and Prospects in Sustainable Plasma Catalytic Ammonia Production from Methane and Nitrogen.

Ammonia is crucial for human life as an important ingredient for fertilizer, industrial and household chemicals, and is considered as a future fuel alternative and hydrogen storage molecule. There remain no viable alternatives to the energy-and capital-intensive Haber-Bosch (H-B) process. Efforts in the development of novel catalytic processes operated at milder conditions (low temperatures and ambient pressure), prominently electrochemistry and non-thermal plasma (NTP), and utilization of lower-cost H sources for ammonia formation than the ultrapure H2 have been witnessed in the last few years. Yet, limited progress from these routes has been made to date given unresolved low ammonia yield and technical challenges. Several rare works attempted to activate methane (CH4 ) and nitrogen (N2 ) by non-thermal plasma to produce ammonia and valued-added hydrocarbons have proven to be a promising research direction, rivalling the reaction between N2 and ultrapure H2 or water. The direct conversion of CH4 and N2 to ammonia is still at the beginning level, and it remains unclear that what extent these technologies must be improved to develop a commercial process. Toward this goal, this Perspective critiques current steps and miss-steps of sustainable plasma catalytic ammonia production from CH4 and N2 in terms of technology, plasma-catalyst synergy, mechanistic insights, and experimental protocols. We discuss mechanistic understandings of catalyst-promoted ammonia production and translate such discussions as well as key metrics achieved in the field into recommendations of feasible processes for ammonia and value-added hydrocarbons formation from CH4 and N2 .

THE EFFECT OF VARIATION OF WELDING CURRENT ON 6061 ALUMINUM PIPE ON MECHANICAL PROPERTIES AND MICRO STRUCTURE USING TIG WELDIN

Abstract
 TIG welding is a welding technique for connecting metals using tungsten rod electrodes and using noble gas as a protective gas which is exhaled on the weld metal to protect against contamination with the surrounding atmosphere. Aluminum metal is a metal that has a high affinity for absorbing H2, N2 and O2 in the air at high temperatures, so it is necessary to have a high purity protective gas during the welding process, because N2 H2 and O2 will cause a decrease in the corrosion resistance of the material. To find out the effect of the TIG welding process on the mechanical properties and microstructure, a study was carried out to determine the mechanical properties, namely hardness, and bending properties, as well as the microstructure found in aluminum after the tungsten inert gas welding process was carried out using current. different. In this study the welding process used the Tungsten Innert Gas process by varying the welding current, namely 100 A, 130 A and with a welding time of 2.5 seconds, 4.5 seconds, . So that from the welding parameters used, it will be known the effect of the welding parameters
 
 
 Keywords : Welding Current, Alumnium Metal, TIG welding

Crystal Engineering of Two Light and Pressure Responsive Physisorbents.

An emerging strategy in the design of efficient gas storage technologies is the development of stimuli-responsive physisorbents which undergo transformations in response to a particular stimulus, such as pressure, heat or light. Herein, we report two isostructural light modulated adsorbents (LMAs) containing bis-3-thienylcyclopentene (BTCP), LMA-1 [Cd(BTCP)(DPT)2 ] (DPT=2,5-diphenylbenzene-1,4-dicarboxylate) and LMA-2 [Cd(BTCP)(FDPT)2 ] (FDPT=5-fluoro-2,diphenylbenzene-1,4-dicarboxylate). Both LMAs undergo pressure induced switching transformations from non-porous to porous via adsorption of N2 , CO2 and C2 H2 . LMA-1 exhibited multi-step adsorption while LMA-2 showed a single-step adsorption isotherm. The light responsive nature of the BTPC ligand in both frameworks was exploited with irradiation of LMA-1 resulting in a 55 % maximum reduction of CO2 uptake at 298 K. This study reports the first example of a switching sorbent (closed to open) that can be further modulated by light.

Characterization of a DC glow discharge in N2–H2 with electrical measurements and neutral and ion mass spectrometry

The addition of small amounts of H2 were investigated in a DC glow discharge in N2, at low pressure (∼1 mbar) and low power (0.05–0.2 W cm−3). We quantified the electric field, the electron density, the ammonia production and the formation of positive ions for amounts of H2 varying between 0 and 5%, pressure values between 0.5 and 4 mbar, and currents between 10 and 40 mA. The addition of less than 1% H2 has a strong effect on the N2 plasma discharges. Hydrogen quenches the (higher) vibrational levels of N2 and some of its highly energetic metastable states. This leads to the increase of the discharge electric field and consequently of the average electron energy. As a result, higher quantities of radical and excited species are suspected to be produced. The addition of hydrogen also leads to the formation of new species. In particular, ammonia and hydrogen-bearing ions have been observed: N2H+ and NH4 + being the major ones, and also H3 +, NH+, NH2 +, NH3 +, N3H+ and N3H3 +. The comparison to a radiofrequency capacitively coupled plasma discharge in similar experimental conditions shows that both discharges led to similar observations. The study of N2–H2 discharges in the laboratory in the adequate ionization conditions then gives some insights on which plasma species made of nitrogen and hydrogen could be present in the ionosphere of Titan. Here, we identified some protonated ions, which are reactive species that could participate to the erosion of organic aerosols on Titan.

N2 Reduction versus H2 Evolution in a Molybdenum- or Tungsten-Based Small-Molecule Model System of Nitrogenase.

Molybdenum dinitrogen complexes have played a major role as catalytic model systems of nitrogenase. In comparison, analogous tungsten complexes have in most cases found to be catalytically inactive. Herein, a tungsten complex was shown to be supported by a pentadentate tetrapodal (pentaPod) phosphine ligand, under conditions of N2 fixation, primarily catalyzes the hydrogen evolution reaction (HER), in contrast to its Mo analogue, which catalytically mediates the nitrogen-reduction reaction (N2 RR). DFT calculations were employed to evaluate possible mechanisms and identify the most likely pathways of N2 RR and HER activities exhibited by Mo- and W-pentaPod complexes. Two mechanisms for N2 RR by PCET are considered, starting from neutral (M(0) cycle) and cationic (M(I) cycle) dinitrogen complexes (M=Mo, W). The latter was found to be energetically more favorable. For HER three scenarios are treated; that is, through bimolecular reactions of early M-Nx Hy intermediates, pure hydride intermediates or mixed M(H)(Nx Hy ) species.

Hydrotalcite-derived nickel–gallium alloy catalysts with enhanced resistance against metal sintering for methane decomposition

Catalytic methane decomposition is a promising way to convert methane into COx-free hydrogen and value-added carbon nanomaterials, but the development of a sintering-resistant catalyst is a challenge. In this study, Ni–Ga/Al2O3 alloy catalysts with different Ga/Ni atomic ratios were prepared from Ni3−xGaxAl (x = 0–1.2) hydrotalcite-like compounds (HTlcs) as precursors and tested for methane decomposition. Structural and physicochemical properties of the as-prepared and used catalysts were characterized by ICP, N2 physical adsorption, XRD, H2-TPR, H2 chemisorption, STEM-EDX, SEM, TEM, and Raman techniques. The results indicate that upon calcination at 500 °C, Ni–Ga–Al HTlcs are transferred to rock-salt Ni(Ga,Al)O oxide solid solutions, and reduction with H2 at 800 °C leads to single-phase and composition-uniform Ni–Ga alloy particles with an average crystal size of 8–10 nm. In catalytic methane decomposition at 600 °C, the alloying Ni with a suitable amount of Ga effectively enhances the catalyst life and carbon yield. Especially, Ni2.4Ga0.6Al shows the highest carbon yield of 61.1 g-C/g-cat, approximately 4.4 times that of the Ga-free Ni counterpart. Meanwhile, Ni–Ga alloying has a marked influence on the CNTs geometry, giving herringbone-like CNTs with small diameters and thin walls. It is gratifying to find that the Ni–Ga/Al2O3 catalyst exhibits good resistance against sintering under the adopted reaction condition, which accounts for the formation of uniform CNTs of smaller size. The findings provide guidelines for the control of carbon morphology and geometric size in methane decomposition.

Generation and decay of N2(A3Σu +) molecules in reacting CO2 and CH4 plasmas

Time-resolved number densities of N2(A3Σu +, v = 0, 1) molecules in diffuse ns pulse discharge plasmas in N2, N2–H2, N2–CH4, N2–CO2, and N2–CO2–CH4 are measured by tunable diode laser absorption spectroscopy (TDLAS). The first series of measurements is made in the discharge pulse bursts at a relatively low pulse repetition rate (3 kHz), when the N2(A3Σu +) generation and decay after individual discharge pulses is fully resolved. The second set of data is taken during a sequence of two pulse bursts generated at a higher pulse repetition rate (100 kHz), for different delay times between the first and second bursts. This approach is used to determine the effect of accumulation and decay of reacting species generated in the plasma, including N, H, and O atoms, CO molecules, and C2 hydrocarbon product species, on the rate of N2(A3Σu +) production and quenching. The effect of these species can be isolated since the rates of N2(A3Σu +) quenching by the initial reactant species (H2, CH4, and CO2) are slow. Comparison of the measurement results with the kinetic modeling predictions is used to obtain insight into the plasma chemical reaction kinetics. The results complement the measurements of N, H, O, and CO in high-pressure reacting plasmas, and help quantify the plasma chemical processes driven by the electron impact dissociation, electronic excitation, and reactive quenching of the excited electronic states. The present results may be used for the development and validation of higher fidelity kinetic models of reacting plasmas, incorporating state-specific electronic and vibrational energy transfer and chemical reactions.