Dissociation Of CH Research Articles

Plasma-based global pathway analysis to understand the chemical kinetics of plasma-assisted combustion and fuel reforming

The Global Pathway Analysis (GPA) algorithm helps analyze the chemical kinetics of complex combustion systems by identifying important global reaction pathways connecting a source species to a sink species through various important intermediate species (i.e., hub species). The present work aims to extend GPA algorithm to plasma-assisted combustion and fuel reforming systems to identify the dominant global pathways in such systems at various conditions. In addition, the present study extends the ability of GPA algorithm to identify reaction cycles involving the excitation of high-concentration species (e.g., O2, N2, and fuel) to their vibrational and electronic states and the subsequent de-excitation to their ground state, based on their significance on the reactivity of plasma-assisted systems in terms of gas heating and radical production. Provisions are made in the GPA algorithm to evaluate the reactivity of identified reaction pathways and cycles based on the element-flux transfer (i.e., dominance), heat release, and radical production rate. The newly developed Plasma-based Global Pathway Analysis (PGPA) algorithm is then used to analyze the plasma-assisted combustion of ammonia and reforming of methane. The PGPA analyses elucidated the significance of vibrational-translational cycles on the reactivity of NH3/air mixtures. Further, analyses on the production of NO ascribed the early reforming of NH3 to N2 and H2 in impeding the production of NO during plasma-assisted NH3 ignition. Lastly, the enhanced reforming of CH4/N2 mixtures using plasma has been attributed to electron impact dissociation of CH4 when compared to thermal reforming. In contrast, conventional path-Flux analysis (PFA) was found to require significant manual effort and pre-analysis intuitions from expert knowledge, making it arduous to provide valuable insights into plasma chemistry. The user-friendly and automated nature of PGPA thus provides a valuable tool for assessing the kinetics of plasma-assisted systems helpful in analyzing and, further, a foundation in reducing plasma-assisted chemistry, without the needs of expert knowledge.

Dissociation and Adsorption of CH4 on Cu and Ag co-Doped Ni(111) Surface: A First Principle Study

Dissociation and Adsorption of CH4 on Cu and Ag co-Doped Ni(111) Surface: A First Principle Study

Synthesis of Heteroatom Pd-ZrOx Species on Zeolite for Complete Methane Oxidation

Realizing the potential benefits of nanoscale metal catalysts requires highly dispersed active sites and control of their local environment. Herein, we develop a catalyst synthesis route for manipulating the local environment of highly dispersed metal-active sites via the targeted deposition of Pd near highly dispersed ZrOx on ZSM-5 zeolite using electrostatic interactions. The formed heteroatom Pd-ZrOx in zeolite catalysts is characterized by scanning transmission electron microscopy (STEM), in situ infrared spectroscopy, temperature-programmed desorption (TPD) of O2, and temperature-programmed surface reaction (TPSR) of CH4. The combination of diverse characterization results demonstrates the heteroatom Pd-ZrOx species rendering a higher dispersion and lower oxygen coordination of Pd species, appropriately tuning the strength of Pd–O bonds, and providing abundant active oxygen species to accelerate the dissociation of CH4. Therefore, the catalytic performance of Pd species is effectively enhanced with the lowest temperature of 90% CH4 conversion decreasing from 390 °C (without ZrOx) to 340 °C. Our work provides a strategy of engineering to anchor highly dispersed noble metal species and regulate the local environment to tune catalytic properties.

Enhancing Coke Resistance of Mg1–xNixAl2O4 Catalysts for Dry Reforming of Methane via a Doping‐Segregation Strategy

AbstractDry reforming of methane (DRM) is an important reaction to utilize two greenhouse gases (CO2 and CH4) simultaneously and produce syngas (CO and H2) for the manufacture of downstream high‐value chemicals. One of the major obstacles to preventing the commercialization of Ni‐based catalysts in DRM is the serious coking problem. This work develops a doping‐segregation method to manipulate the active metal structure and metal‐support interaction of Mg1–xNixAl2O4 catalysts to enhance their coke resistance for DRM. The Mg1–xNixAl2O4 catalysts prepared via the sol‐gel method exhibit outstanding coke resistance: the coke deposition rate of supported catalyst Ni/MgAl2O4 is 326 times higher than that of the Mg0.7Ni0.3Al2O4 catalyst at 600 °C. The Ni structure and metal‐support interaction of Mg1–xNixAl2O4 catalysts have been systematically studied using various characterization. Combined with the temperature‐programmed surface reaction (TPSR) experiments, the enhanced coke resistance of Mg1–xNixAl2O4 catalysts is attributed to smaller Ni particles, higher Ni dispersion, and stronger metal‐support interaction, which significantly inhibit the direct dissociation of CH4 and promote the oxidation of formed coke. The findings of this work provide insights into the correlation between the enhanced coke resistance and the Ni structure of Mg1–xNixAl2O4 catalysts synthesized via the doping‐segregation strategy using spinel as the precursor, leading to a stable catalyst design for many dry reforming reactions.

The Adsorption Effect of Methane Gas Molecules on Monolayer PbSe with and without Vacancy Defects: A First-Principles Study.

In this paper, the adsorption effect of methane (CH4) gas molecular on monolayer PbSe with and without vacancy defects is studied based on first-principles calculations. The effects of the adsorption of methane molecular on monolayer PbSe and on the Se vacancy (VSe) and Pb vacancy (VPb) of monolayer PbSe are also explored. Our results show that methane molecules exhibit a good physical adsorption effect on monolayer PbSe with and without vacancy defects. Moreover, our simulations indicate that the adsorption capacity of CH4 molecules on monolayer PbSe can be enhanced by applying strain. However, for the monolayer PbSe with Vse, the adsorption capacity of CH4 molecules on the strained system decreases sharply. This indicates that applying strain can promote the dissociation of CH4 from VSe. Our results show that the strain can be used as an effective means to regulate the interaction between the substrate material and the methane gas molecules.

Preparing a Zr-Doped CeO2 Nanorod to Improve the Catalytic Performance of the Ni-Based Catalyst for Dry Reforming of Methane by Enhancing Oxygen Supply

Dry reforming of methane (DRM) is a feasible route to realize the resource utilization of greenhouse gases CO2 and CH4. The Ni-based catalyst is recognized as a potential catalyst for the industrialization of DRM. However, catalyst deactivation caused by carbon deposition is a challenge. Providing enough active oxygen species to accelerate the reaction between CHx (x = 0–3) and oxygen species is the key to inhibit coking. Ni-based catalysts loaded on a Zr-doped Ce1–xZrxO2 nanorod were prepared by a one-step hydrothermal method. Benefiting from lattice distortion caused by Zr doping, the Ni/Ce0.95Zr0.05O2 catalyst showed the best catalytic activity and stability. Compared with the Ni/CeO2 catalyst, the activation energy of CH4 and CO2 decreased by 20 and 22%, respectively. The 100 h stability test showed that the Ni/CeO2 catalyst was 10% deactivated, and the carbon deposition rate was 0.82 mgc·gcat·–1·h–1, while the Ni/Ce0.95Zr0.05O2 catalyst showed excellent stability. The extensive characterization of the catalysts indicated that the enhancement in DRM activity upon Zr doping could be attributed to the increase of oxygen vacancies and the improvement in lattice oxygen mobility. However, excessive Zr doping formed ZrO2 covering oxygen vacancies, resulting in decreased catalytic activity and stability. The results showed that lattice oxygen over the Ni/Ce0.95Zr0.05O2 catalyst not only participated in the oxidation of carbon intermediates but also contributed to the deep dissociation of CH4 over Ni through an oxygen-mediated dissociation pathway. Similarly, the redox cycle on the oxygen vacancies was also important for enhancing the CO2 adsorption activation to relieve the coking of the catalyst.

Effect of different valence metals doping on methane activation over La2O3(001) surface

La2O3 as a catalyst is used for oxidative coupling of methane (OCM) reactions due to its excellent stability and high C2 selectivity, but poor activity on methane dissociation limits its wide application. Different valence metals are doped on the La2O3(001) surface to improve the methane conversion activity, and the activation of methane on metal-doped La2O3(001) surfaces has been investigated via the density functional theory (DFT) calculations. The relationship between the valence states of doped metals and the methane conversion activities shows that doping low valence metals (Li, Na, K, Mg, Ca, Sr and Ba) and equivalent metals (Al, Ga, In) can significantly improve the conversion activity of methane. Among them, the activation energy of methane on the Li-La2O3(001) surface is the lowest, which is only 13.0 kJ/mol. However, doping of high valence metals (Zr, Nb, Re and W) cannot improve the CH4 dissociation activity. Furthermore, the relationships between surface oxygen vacancy formation energies, acid-base properties and the activation energies of CH4 have also been investigated. The results show that with the increase of metal valence state, the oxygen vacancy formation energy increases, while the dissociation activity of CH4 decreases. The introduction of alkali and alkaline earth metals increases the alkalinity of La2O3(001) surface, and the alkalinity of La2O3(001) doped with the alkali metal is stronger than that with the alkaline earth metal, exhibiting higher dissociation activity of CH4. Our research may provide a guide for improving methane conversion activity on La2O3 catalysts.

Highly dispersed Fe-decorated Ni nanoparticles prepared by atomic layer deposition for dry reforming of methane

Dry reforming of methane (DRM) is a sustainable chemical process that can simultaneously transform methane and carbon dioxide, which are generally considered greenhouse gases, into syngas with H2/CO ratio close to 1. The deposition of carbon on the active sites during long-period DRM tests will lead to severe deactivation of Ni-based catalysts. Thus, in this work, we proposed a series of uniformly dispersed Fe-decorated Ni/Al2O3 catalysts via atomic layer deposition (ALD) to solve this key issue. Modification with trace amounts of Fe (0.3–0.6%) had multiple effects on facilitating the CH4 dissociation on Ni0, improving the low-temperature catalytic activity, moderating the carbon species and accelerating coke oxidation. The sample denoted as 0.3%Fe/Ni/Al2O3 exhibited almost no activity loss in the 72 h test at 650 °C. The Fe-decorated Ni/Al2O3 structure achieved a balance between the enhancement of CH4 cracking and the elimination of coke. Furthermore, this advanced ALD approach of preparing uniform secondary metal nanoparticle-decorated catalysts provided guidance to other bimetallic systems, such as Pt/Ni, Mn/Ni, and Cu/Ni.

Microwave-assisted hydrothermal synthesis of Ru/CeO2 catalyst for efficient and stable low-temperature dry reforming of methane

As the widely applied catalysts in dry reforming of methane (DRM), Ni-based catalysts typically suffer from severe coke formation on the catalyst leading to the deactivation of the catalyst. Meanwhile, with great trends of reducing the operating temperature for DRM reactions, the Ni-based catalysts can’t exhibit comparable reactivity in low-temperature DRM reactions. To reduce coke formation and achieve better reactivity at low temperatures, a novel Ru/CeO2 catalyst was synthesized through a microwave-assisted hydrothermal method and exploited in a low-temperature DRM reaction in a fixed bed reactor. It exhibited comparable activity of above 58 % CH4 and 71 % CO2 conversion with above 0.85 H2/CO ratio for over 120 h at 600 °C. Moreover, it remained stable without obvious coke deposition on the catalyst after the long-term experiment. The characterizations by XRD, XPS, HAADF-STEM, FTIR and some temperature-programmed experiments indicated that microwave irradiation and the introduction of glucose played important roles in achieving great thermal stability and better DRM reactivity of Ru/CeO2. Ru, as the active metal compared with Ni, exhibited moderate CH4 dissociation ability leading to excellent coke resistance. The novel Ru/CeO2 catalyst with high DRM reactivity, simple synthesis method and great coke resistance in this work offers a new opportunity for the commercialization of low-temperature DRM reaction.

Deep insight of the influence of Pt loading content with catalytic activity on light-assisted dry reforming of methane

The photo-thermal-chemical transformation route that drives dry reforming of methane (DRM) reaction is a promising approach to fix solar energy into chemical energy. In this paper, by combining in situ DRIFTS experiments, the function of light was discovered, including enhancement in the catalysts' ability to activate reactant molecules, especially for the dissociation of CH4. In addition, the mechanism of DRM reaction is further ascertained. The rate-determining steps (RDS) of the reaction were confirmed to be CH4 dissociation and carbonate conversion steps, and increasing the Pt content to change the structure of catalysts might change the RDS from the above two RDS to CH4 dissociation and adsorption of CO2, so that affecting the characteristics of the reaction (the catalytic performance and stability). Hence, it possessed important theoretical and practical significance for the optimization of catalyst structure and the selection of optimal active component content to reduce the cost of industrialization.

Structural evolution of robust Ni3Fe1 alloy on Al2O3 in dry reforming of methane: Effect of iron-surplus strategy from Ni1Fe1 to Ni3Fe1

Bimetallic Ni−Fe alloy catalyst offers boosting effect for dry reforming of methane (DRM) by strong interaction between Ni and Fe. However, the facile segregation of iron species from the alloy particles remains an open challenge. Herein, in pursuit of a stable Ni−Fe alloy, Ni1Fe1/Al2O3 and Ni3Fe1/Al2O3 catalysts were developed by an evaporation-induced self-assembly method. Ni1Fe1/Al2O3 exhibited superior stability to Ni3Fe1/Al2O3 at 600 °C for 50 h. The structural evolution of Ni−Fe alloys existed on Ni1Fe1/Al2O3 and Ni3Fe1/Al2O3 in DRM, leading to the generation of Ni3Fe1/Al2O3 and Ni/Al2O3, respectively, where the equimolar alloy provided sufficient FeOx in the dealloying process. Compared to Ni3Fe1/Al2O3, Ni1Fe1/Al2O3 possessed smaller amounts of coke deposition with lower graphitization, which is beneficial to realloying of the segregated FeOx for Ni−Fe alloy. Furthermore, the two catalysts presented distinct pathways for coke deposition, where CO and CH4 dissociation concurrently occurred on Ni3Fe1/Al2O3, while only CH4 dissociation appeared on Ni1Fe1/Al2O3.

Effect of Ni NP morphology on catalyst performance in non-thermal plasma-assisted dry reforming of methane

Supported nickel nanoparticle catalysts, with differing nickel morphologies, were studied in the non-thermal-plasma-promoted dry reforming of methane. Catalysts with nickel particles containing a greater ratio of (111) lattice planes and surface structures in the nanoscale, i.e. dendritic and flake-like particles, showed higher conversions and yields (CH4 conversions of 65 % and 22 % and CO2 conversions of 43 % and 33 % respectively with H2 yields of 42 % and 34 % and CO yields of 31 % and 24 % respectively) than spherical analogues which had conversions of 26 % (CH4) and 16 % (CO2) and yields of 21 % (H2) and 11 % (CO). This is thought to be related to the favourability of (111) faces for CH4 dissociation and the potential for the formation of micro-discharges around their small surface features. All materials tested showed higher CH4 conversion and H2 production when compared with reactions carried out in the absence of a catalyst. The latter reactions showed a greater extent of competing side reactions, resulting in lower conversions and yields.

Selective Photocatalytic Conversion of Methane Induced by Lewis Acid–Base Pair on the Surface of In2O3/TiO2 Heterojunction Photocatalyst

The efficient catalytic conversion of light-driven methane (CH4) is still very challenging. Here, the surface-reconstructed In2O3/TiO2 heterojunction photocatalyst is successfully prepared by a two-step operation of ion exchange and calcination, and the efficient selective photocatalytic conversion of CH4 is achieved. In the absence of O2, the formation rates of ethane (C2H6) and hydrogen (H2) are 68.9 and 78.6 μmol h–1 g–1, respectively, which corresponds to the stoichiometric ratio. However, in the presence of O2 or water (H2O) as the oxidant, CH4 is converted to CO, and the CO formation rates are 113.2 and 94.4 μmol h–1 g–1, respectively. Our results show that the In3–O2– Lewis acid–base pair on the In2O3/TiO2 surface can realize the adsorption and activation of CH4. Moreover, the photogenerated hole-induced reactive oxygen centers (Ti4+O·–Ti4+OH– and Ti4+O2–Ti4+O·–) on the surface of In2O3/TiO2 are identified as the active species for inducing the dissociation of CH4 into ·CH3 radicals, which in turn are coupled into C2H6 by ·CH3. In contrast, in the presence of O2, the surface superoxide anion (O2–), surface ·O– radicals, and O22– anions are identified as the active species for inducing the oxidation of CH4 into CO.

Upgrading biogas into syngas via bi-reforming of model biogas over ruthenium-based nano-catalysts synthesized via mechanochemical method

The upgrading of biogas to value-added syngas via reforming of biogas is of great significance from the perspective of green carbon science. A series of Ru based nano-catalysts (Ru/MgO, Ru/La2O2CO3, Ru/CeO2) with relatively low Ru loading and high dispersion were successfully prepared by mechanochemical method, and applied in the bi-reforming of model biogas reaction. The representative catalysts were comprehensively characterized by XRD, N2 physical adsorption, ICP-OES, SEM, XPS, H2-TPR, CO2-TPD, HRTEM, FTIR of CO adsorption, TPSR, TG, and Raman spectroscopy, etc. Ascribed to the appropriate basicity of MgO, homogeneous Ru dispersion with ultra-small particle size, and strong interaction between Ru ultra-small nano particles and MgO support, Ru/MgO exhibit higher CO2 adsorption and activation, higher CH4 activation and dissociation, compared with Ru/La2O2CO3, Ru/CeO2, which facilitate the formation of active oxygen species and intermediate coke removal, thus enhance the resistance to coke deposition and sintering. At reaction conditions of T = 750 °C and weight hourly space velocity = 32,400 mLgCat−1 h−1, 0.5Ru/MgO catalyst exhibit satisfying catalytic activity (initial CH4/CO2 conversation rate of 87/48%) and superior stability (stable for 150 h) with negligible deactivation rates.

Efficiently Light-Driven Nonoxidative Coupling of Methane on Ag/NaTaO3: A Case for Molecular-Level Understanding of the Coupling Mechanism

Metal-decorated oxide semiconductors are overwhelming photocatalysts for nonoxidative coupling of methane (NOCM). However, the overall NOCM mechanism remains an unopened black box, which hinders the design of high-performance catalysts. Herein, we systematically studied a series of noble metal (Ag, Au, Pt, Pd, Cu, and Ni)-decorated oxides (NaTaO3, CaTiO3, LiNbO3, and TiO2) for NOCM. We proposed that the active sites for H abstraction and C–C coupling of CH4 are spatially separated. Specifically, NaTaO3 only completes the initial H abstraction of CH4 activation, while metal nanoparticles are responsible for the final C–C coupling. Noble metals dominate NOCM by significantly decreasing the energy barrier of CH4 dissociation and promoting C–C coupling. Among various metals, Ag is preferential for the weak adsorption of ·CH3 intermediates and subsequent metal-induced C–C coupling. This contributes to Ag/NaTaO3 the highest C2H6 yield of 194 μmol g–1 h–1 and stoichiometric H2 with 11.2% quantum efficiency. This work provides a molecular-level insight into the CH4 coupling mechanism on metal-decorated photocatalysts.

CH4 and CO2 conversion over boron nitride-supported Ni catalysts with B[sbnd]O defects in DBD plasma

Non-thermal plasma (NTP) combined with catalysts supplies a potential alternative to enable the CH4 and CO2 conversion to work at low temperatures. In this study, different Ni/BN catalysts were synthesized using modified wetness impregnation for CH4 and CO2 conversion in dielectric barrier discharge (DBD) plasma. Among, BN_IPA_Ni exhibited the highest catalytic performance with a CH4 conversion of 40.5%, a CO2 conversion of 26.6%, a H2 yield of 9.3% and a CO yield of 10.5%. The development of BO defects, which played a significant role in the size control of Ni particles to facilitate the dissociation of CH4 to form H*, is the key for the high catalysis activity and selectivity in this reaction. In addition, the BO defects of BN_IPA_Ni provide an efficient route to eliminate excess CHx species, which further inhibit the nucleation growth of carbon species to inert carbon.

CO2 coverage on Pd catalysts accelerates oxygen removal in oxy-combustion systems.

Oxy-combustion systems result in enriched CO2 in exhaust gases; however, the utilization of the concentrated CO2 stream from oxy-combustion is limited by remnant O2. CH4 oxidation using Pd catalysts has been found to have high O2-removal efficiency. Here, the effect of excess CO2 in the feed stream on O2 removal with CH4 oxidation is investigated by combining experimental and theoretical approaches. Experimental results reveal complete CH4 oxidation without any side-products, and a monotonic increase in the rate of CO2 generation with an increase in CO2 concentration in the feed stream. Density-functional theory calculations show that high surface coverage of CO2 on Pd leads to a reduction in the activation energy for the initial dissociation of CH4 into CH3 and H, and also the subsequent oxidation reactions. A CO2-rich environment in oxy-combustion systems is therefore beneficial for the reduction of oxygen in exhaust gases.

Plasma-assisted Ni catalysts: Toward highly-efficient dry reforming of methane at low temperature

Dry reforming of methane (DRM) reaction can convert primary greenhouse gases (CH4 and CO2) to value-added chemicals (H2 and CO), but generally suffers from harsh reaction conditions (>700 °C) and inevitable deactivation of catalysts. In this work, we report supported Ni catalysts based on a topotactic transformation process from the layered double hydroxides (NiZnAl−LDHs) precursors. Structural characterizations (XRD, HRTEM, CO chemisorption) verify a uniform distribution of Ni nanoparticles (∼7 nm) on the mixed metal oxides support with a high dispersion (denoted as Ni/MMO). With the assistance of non-thermal plasma (NTP), the optimal sample (Ni/MMO−S2) exhibits a good catalytic conversion of CH4 (∼69%) and CO2 (∼54%) at low temperatures (30–60 °C), which is comparable with the activity of thermocatalytic process at ∼650 °C without NTP. The energy efficiency of NTP-assisted catalysis process is an order of magnitude higher than that of thermocatalytic process at ∼650 °C and enhances by 80% relative to NTP-alone process at low temperatures. The Ni/MMO−S2 catalyst shows satisfactory stability after 600 min stability test, with a slight decrease in conversion (within ∼1%). In addition, a combined study including catalytic evaluations, operando OES, XAFS and XPS verifies that metallic Ni species acts as active center, which can promote the dissociation of CH4 and CO2 into highly reactive intermediate species with the assistance of NTP. This synergistic effect between plasma and Ni catalyst remarkably decreases the apparent activation energy by ∼50%, accounting for the high catalytic performance at low temperatures. This work demonstrates a promising synergistic catalysis strategy between plasma and catalysts at low temperatures, which can be extended to other reactions operated under harsh conditions.

A trinuclear cobalt complex, a new electrocatalyst for oxygen reduction to H2O2

• Reaction of amine-bis(phenolate) ligand (H 2 L) and Co(CH 3 CO 2 ) 2 gives a trinuclear cobalt complex, [L 2 Co 3 (CH 3 O)(CH 3 CO 2 ) 2 ]. • This complex can electro-catalyze oxygen reduction with almost 100% H 2 O 2 selectivity in 0.20 M KOH. • Catalytic activity can be attributed to the dissociation of CH 3 O - , allowing O 2 to bind. The reaction of 2-pyridylamino-N,N-bis(2-methylene-4,6-bimethyl)phenol (H 2 L) and Co(CH 3 CO 2 ) 2 affords a new trinuclear cobalt complex, [L-Co-μ(CH 3 CO 2 )-μ(CH 3 O)-Co-μ(CH 3 CO 2 )-μ(CH 3 O)-Co-L], which has been characterized by using physics-chemical and spectroscopic methods. Electrochemical investigations exhibit that this cobalt complex can serve as an electro-catalyst for oxygen reduction reaction (ORR). Under -0.4 V vs Ag/AgCl, the H 2 O 2 yield is almost 100% in 0.20 M KOH. Studies indicate that the dissociation of CH 3 O - group from the trinuclear cobalt complex makes empty positions on cobalt centres, amenable to binding to dioxygen (O 2 ) for the formation of H 2 O 2 or H 2 O.

Impact of the growth environment in inductively coupled plasma on the synthesis and morphologies of carbon nanohorns

The fabrication of carbon nanohorns (CNHs) from a methane precursor with argon in an inductively coupled plasma was recently demonstrated with a high production rate of ∼20 g/h by Casteignau et al. [Plasma Chem. Plasma Process. 42, 465 (2022)]. The presence of a promotor gas such as hydrogen was found to be important for the growth of CNHs, but the mechanisms at play remain unclear. Here, we study the impact of different promotor gases by replacing hydrogen with nitrogen and helium at different promotor:precursor (Pm:Pr) ratios, X:CH4 = 0.3–0.7 (X = H2 or N2, Ar, and He), and global flow rates FX+FCH4=1.7 and 3.4 slpm. The nature of the promotor gas is shown to directly influence the morphology and the relative occurrence of CNHs, graphitic nanocapsules (GNCs), and graphene nanoflakes. Using quantitative transmission electron microscopy, we show that CNHs are favored by an X:CH4 = 0.5, preferably with X = He or N2. With a lower total flow rate (1.7 slpm) of N2, even larger production rates and higher selectivity toward CNHs are achieved. Optical emission spectroscopy was used to probe the plasma and to demonstrate that the nature promotor gas strongly modulates the C2 density and temperature profile of the plasma torch. It is shown that CNHs nucleation is favored by high C2 density at temperatures exceeding 3500 K localized at the exit-end of the nozzle, creating a reaction zone with extended isotherms. H2 favors CH4 dissociation and creates a high C2 density but cools the nucleation zone, which leads to structures with a strong graphitic character such as GNCs.