Key Takeaways & Executive Findings
- •• • At 90 W input power and 200 mL/min inlet gas flow rate, single-pass CH4 conversion reaches 46.6% with H2 yield of 23.3%, demonstrating electron-driven cracking with limited Joule heating contribution. • • Increasing inlet gas flow rate from 200 to 800 mL/min raises reaction energy intensity by ~2.8 times, indicating enhanced convective heat transfer and shortened residence time that suppress deep CH4 cracking. • • BOLSIG+ calculations identify electron-induced vibrational excitation as the dominant CH4 activation pathway, where stepwise energy accumulation drives C–H bond dissociation. • • The overall CH4 cracking process is delineated into three stages: methane activation, radical evolution, and product formation, providing a mechanistic framework for optimizing DBD reactor design.
Abstract
Methane cracking driven by electric power holds significant promise in the context of the rapid development of renewable energy. The effects of carrier gas ratio, input power, and inlet gas flow rate on CH4 cracking performance were systematically investigated in a dielectric barrier discharge (DBD) reactor. The variation of temperature distribution and reaction energy intensity were also examined. The experimental results indicate that CH4 conversion and gaseous product formation are promoted by increasing the DBD input power or decreasing the inlet gas flow rate. At an input power of 90 W and an inlet gas flow rate of 200 mL/min, the single-pass CH4 conversion reaches 46.6%, with an H2 yield of 23.3%, demonstrating that CH4 cracking is governed by electron induced reactions. While the Joule heating from the inner and outer electrodes is relatively limited. The reaction energy intensity increases as the CH4 conversion decreases. When the inlet gas flow rate increases from 200 to 800 mL/min, the energy intensity rises by approximately 2.8 times, indicating that higher inlet gas flow rates enhance the convective heat transfer and shorten the gas residence time, thereby suppressing deep CH4 cracking. Moreover, BOLSIG+ calculations further reveal that CH4 activation is dominated by electron induced vibrational excitation, in which stepwise energy accumulation drives C–H bond dissociation. The energy transfer and species transformation pathways of overall CH4 cracking process, which comprises electron energy injection, vibrational excitation, stepwise dissociation, radical chain extension, and final product formation, can be summarized into three stages, i.e. methane activation, radical evolution, and product formation.
1. Introduction
Methane, the primary component of natural gas, coalbed methane, shale gas, and biogas, serves as both an energy carrier and a chemical feedstock. However, its chemical stability, due to a non-polar structure, poses significant challenges for efficient conversion. Conventional industrial routes, such as steam reforming, require high temperatures and pressures, leading to substantial energy consumption and CO2 emissions. The urgent need for decarbonization and the rapid growth of renewable electricity have intensified interest in electrified methane conversion technologies, particularly non-equilibrium plasma processes that can activate methane under mild conditions.
This study addresses the bottleneck of low energy efficiency and poor selectivity in plasma-driven methane cracking by systematically investigating the effects of key operational parameters in a dielectric barrier discharge (DBD) reactor. By correlating CH4 conversion, product yields, and reaction energy intensity with input power and gas flow rate, and by employing BOLSIG+ simulations to elucidate electron-driven activation mechanisms, this work provides critical insights for scaling up plasma-based methane conversion. The identification of vibrational excitation as the dominant activation pathway and the three-stage reaction scheme offer a rational basis for optimizing reactor design and process conditions to achieve economically viable hydrogen and carbon production.
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SUN Yiping, ZHAO Junning, ZHANG Yuanyuan, ZHANG Kai, ZHANG Dongke (2026). Reaction mechanisms and cracking performance of CH4 provoked by non-equilibrium plasma. Journal of Fuel Chemistry and Technology. https://doi.org/10.1016/S1872-5813(26)60690-1
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Frequently Asked Questions
What is the maximum single-pass CH4 conversion and H2 yield achieved in this DBD reactor, and under what conditions?
At an input power of 90 W and an inlet gas flow rate of 200 mL/min, the single-pass CH4 conversion reaches 46.6% with an H2 yield of 23.3%. These conditions represent the optimal balance for maximizing conversion and hydrogen production in the tested range.
How does the inlet gas flow rate affect reaction energy intensity and CH4 conversion, and what are the underlying mechanisms?
Increasing the inlet gas flow rate from 200 to 800 mL/min raises the reaction energy intensity by approximately 2.8 times. This is attributed to enhanced convective heat transfer and shortened gas residence time, which suppress deep CH4 cracking and reduce conversion efficiency.
What is the dominant electron-driven activation pathway for CH4 in the DBD plasma, as revealed by BOLSIG+ calculations?
BOLSIG+ calculations indicate that electron-induced vibrational excitation is the primary activation pathway. High-energy electrons accumulate energy in CH4 molecules through stepwise vibrational excitation, leading to C–H bond dissociation and subsequent radical reactions.
What are the three stages of the CH4 cracking process proposed in this study, and how do they contribute to product formation?
The three stages are: (I) methane activation via electron impact and vibrational excitation, (II) radical evolution involving stepwise dissociation and chain reactions, and (III) final product generation through radical recombination, yielding H2, C2 hydrocarbons, and higher hydrocarbons.
How does Joule heating from the electrodes influence the overall CH4 cracking performance?
Joule heating from the inner and outer electrodes is relatively limited compared to electron-driven reactions. The experimental results demonstrate that CH4 cracking is governed by electron-induced processes, with thermal effects playing a minor role.
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