Kinetic Analysis of the Decomposition Reaction of CH4 Injecting into Molten Slag

Kashiwaya, Yoshiaki; Watanabe, Masami

doi:10.2355/isijinternational.52.1394

Cited by 17 publications

(8 citation statements)

References 27 publications

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“…As a product of the first-step methane decomposition reaction, the concentration of CH 3 is the second highest, and it is active enough because of the existence of the dangling bond. , Besides, radical hydrogen (H*) could promote the decomposition of CH 4 to CH 3 (detailed possible routes where CH 4 decomposes into CH 3 can be seen in the SI). ,− For other carbon species, such as CH 2 , CH, and C, although they are also active enough, their concentrations are many orders of magnitude lower than that of CH 3 (see Figure S5 and the related text in the SI). From the above analysis, we conclude that gas-phase CH 3 is the dominating species during the graphene growth on the insulating surfaces as illustrated in Figure c.…”

Section: Resultssupporting

confidence: 80%

The Mechanism of Graphene Vapor–Solid Growth on Insulating Substrates

2021

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Wafer-scale single-crystal graphene film directly grown on insulating substrates via the chemical vapor deposition (CVD) method is desired for building high-performance graphenebased devices. In comparison with the well-studied mechanism of graphene growth on transition metal substrates, the lack of understanding on the mechanism of graphene growth on insulating surfaces greatly hinders the progress. Here, by using firstprinciples calculation, we systematically explored the absorption of various carbon species CH x (x = 0, 1, 2, 3, 4) on three typical insulating substrates [h-BN, sapphire, and quartz] and reveal that graphene growth on an insulating surface is dominated by the reaction of active carbon species with the hydrogen-passivated graphene edges and thus is less sensitive to the type of the substrate. The dominating gas phase precursor, CH 3 , plays two key roles in graphene CVD growth on an insulating substrate: (i) to feed the graphene growth and (ii) to remove excessive hydrogen atoms from the edge of graphene. The threshold reaction barriers for the growth of graphene armchair (AC) and zigzag (ZZ) edges were calculated as 3.00 and 1.94 eV, respectively; thus the ZZ edge grows faster than the AC one. Our theory successfully explained why the circumference of a graphene island grown on insulating substrates is generally dominated by AC edges, which is a long-standing puzzle of graphene growth. In addition, the very slow graphene growth rate on an insulating substrate is calculated and agrees well with existing experimental observations. The comprehensive insights on the graphene growth on insulating surfaces at the atomic scale provide guidance on the experimental design for high-quality graphene growth on insulating substrates.

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Section: Resultssupporting

confidence: 80%

The Mechanism of Graphene Vapor–Solid Growth on Insulating Substrates

2021

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“…Observing the flow rate of H 2 , found that there is high amount of H 2 in system. The study of Kashiwaya Y., and Watanabe M. reported that methane decomposition is reversible reaction in gas phase before CNTs growth 42 . Therefore, according to Le Chatelier’s principle, when the product quantity (H 2 ) increases, will prevent the dissociation of methane, resulting in fewer CNTs 43 , 44 .…”

Section: Resultsmentioning

confidence: 99%

Synthesis of MWCNTs by chemical vapor deposition of methane using FeMo/MgO catalyst: role of hydrogen and kinetic study

Chotmunkhongsin,

Ratchahat,

Chaiwat

et al. 2023

Sci Rep

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This study aims to investigate the role of hydrogen on CNTs synthesis and kinetics of CNTs formation. The CNTs were synthesized by catalytic chemical vapor deposition of methane over FeMo/MgO catalyst. The experimental results revealed that hydrogen plays an important role in the structural changes of catalyst during the pre-reduction process. The catalyst structure fully transformed into metallic FeMo phases, resulting in an increased yield of 5 folds higher than those of the non-reduced catalyst. However, the slightly larger diameter and lower crystallinity ratio of CNTs was obtained. The hydrogen co-feeding during the synthesis can slightly increase the CNTs yield. After achieving the optimum amount of hydrogen addition, further increase in hydrogen would inhibit the methane decomposition, resulting in lower product yield. The hydrogenation of carbon to methane was proceeded in hydrogen co-feed process. However, the hydrogenation was non-selective to allotropes of carbon. Therefore, the addition of hydrogen would not benefit neither maintaining the catalyst stability nor improving the crystallinity of the CNT products. The kinetic model of CNTs formation, derived from the two types of active site of dissociative adsorption of methane, corresponded well to the experimental results. The rate of CNTs formation greatly increases with the partial pressure of methane but decreases when saturation is exceeded. The activation energy was found to be 13.22 kJ mol−1, showing the rate controlling step to be in the process of mass transfer.

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“…Recent research has focused on enhancing hydrogen production by the direct thermocatalytic decomposition of methane to form elemental carbon and hydrogen as an attractive alternative to the conventional steam reforming process [4]. Thermodynamically, the reaction of CH4(g) → C + 2H2(g) can occur from 543°C, but kinetically, the reaction becomes dominant from 800°C without any catalyst [5]. Methane decomposition is a moderately endothermic reaction.…”

Section: Introductionmentioning

confidence: 99%

Production of Hydrogen Molecule from Methane Molecule Amplified with Excitation of Anti-Symmetric Modes of Vibration

ERDOĞAN

2023

Sakarya University Journal of Science

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Some factors, such as pressure and temperature, affect the rate of chemical reactions. In addition, the activation energy barrier must be overcome for the reaction to be initiated. It can be preferred to overcome this barrier by using catalysts and preheating. The catalyst ensures that it obtains the energy to react quickly by transferring it to the reactants. Similarly, the translational, vibrational, and rotational energy levels of reactants can be increased by preheating. According to the kinetic molecular theory of gases, preheating increases the kinetic energies of the gases and the speed of their collision, so the reaction takes place faster. This study theoretically investigates possible reactions of methane that can occur with the effect of only vibrational energy levels. The vibrational excitation of the molecules affects the reaction rates, and the activation barrier is overcome with lower energies. Using laser-based techniques makes the excitation of well-defined vibrational modes possible. This study investigated inelastic collisions of a methane molecule with well-characterized energy levels in infrared spectroscopy with some gases and the vibrational energy transfers that occur in these collisions. The methane molecule is the simplest form of a molecular structure consisting of more than three atoms of hydrogen atoms, which play an essential role in combustion chemistry. It shows that C⸺H stretch excitation increases the reaction rate of methane (CH4) molecules.

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Kinetic Analysis of the Decomposition Reaction of CH4 Injecting into Molten Slag

Cited by 17 publications

References 27 publications

The Mechanism of Graphene Vapor–Solid Growth on Insulating Substrates

The Mechanism of Graphene Vapor–Solid Growth on Insulating Substrates

Synthesis of MWCNTs by chemical vapor deposition of methane using FeMo/MgO catalyst: role of hydrogen and kinetic study

Production of Hydrogen Molecule from Methane Molecule Amplified with Excitation of Anti-Symmetric Modes of Vibration

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