In the context of global efforts to limit temperature rise to within 1.5°C, achieving net-zero greenhouse gas emissions has become a crucial goal for nations worldwide. Currently, over 70% of global greenhouse gas emissions come from the extraction, refining, transportation, and combustion of fossil fuels, making the transition to low-carbon energy urgent. Hydrogen, as a highly promising zero-emission energy carrier, plays a critical role in sectors that are difficult to electrify, such as heavy industry, space heating in cold regions, and heavy-duty transportation.
Globally, more than 75 million tons of pure hydrogen and 45 million tons of hydrogen-containing gas mixtures are produced annually, primarily for industrial raw materials. Among these, natural gas reforming is the most common method, accounting for about 75% of global hydrogen production. However, this process releases significant amounts of CO₂, producing "gray hydrogen" with 9-10 kg of CO₂ emissions per kg of hydrogen. To reduce carbon emissions, "blue hydrogen" has emerged, which involves natural gas reforming combined with carbon capture, utilization, and storage (CCUS) technology. However, this approach faces challenges such as high costs and complex transportation. Another method is water electrolysis, which produces "green hydrogen," but it currently accounts for less than 0.1% of global hydrogen production.
Figure 1. Potential Applications of Hydrogen in a Zero-Carbon Future.
In this context, methane pyrolysis for hydrogen production has gradually gained attention. This technology decomposes methane into hydrogen and solid carbon (CH₄ → C + 2H₂), producing no CO₂ emissions. The resulting hydrogen is called "turquoise hydrogen." Additionally, the solid carbon can be used in the production of rubber tires, coatings, or as a soil amendment, and even in the manufacture of carbon fiber and graphene, offering broad application prospects.
1 Catalytic Methane Pyrolysis
The reaction mechanisms of catalytic methane pyrolysis mainly include molecular adsorption and dissociative adsorption. In molecular adsorption, methane first adsorbs onto the catalyst surface and then gradually dissociates through a series of surface dehydrogenation reactions. In dissociative adsorption, methane directly dissociates upon adsorption at catalytic active sites, generating chemically adsorbed CH₃ and H fragments.
Figure 2.(a) Molecular Adsorption Mechanism; (b) Dissociative Adsorption Mechanism of Catalytic Methane Pyrolysis.
In terms of catalysts, metal catalysts such as Ni, Co, and Fe have attracted significant attention. Ni exhibits high initial activity but is prone to deactivation due to carbon deposition and poisoning; Co is expensive and toxic; Fe is relatively inexpensive, non-toxic, and stable. To enhance catalyst performance, researchers have explored combining different metals, such as Ni-Fe and Ni-Cu. Besides metal catalysts, carbon-based catalysts like activated carbon and carbon black are also used for methane pyrolysis, offering advantages such as resistance to carbon deposition, low cost, and sulfur poisoning.
Catalyst regeneration is also a critical aspect of catalytic methane pyrolysis. When the catalyst surface is covered with carbon and deactivated, O₂, H₂O, and CO₂ are commonly used to burn or gasify the carbon for catalyst regeneration.
2 Non-Catalytic Methane Pyrolysis
Non-catalytic methane pyrolysis requires temperatures exceeding 927°C due to the strong C-H bond. The reaction produces various products, such as H₂, C₂H₂, and C₂H₄, depending on temperature and residence time. The reaction mechanism generally involves radical reactions, with the primary step being the dissociation of methane into methyl radicals and hydrogen atoms.
Microwave methane pyrolysis is a non-catalytic method that uses microwaves as the heat source. Microwaves directly interact with the reaction medium, enabling volumetric heating with high energy transfer efficiency and the advantage that hydrogen does not absorb microwave radiation. Plasma methane pyrolysis is currently the most advanced methane pyrolysis technology, with a high level of maturity and successful demonstration at pilot scale.
Figure 3. Microwave-Driven Methane Decomposition.
Photothermal catalysis, as an emerging technology, shows potential in methane pyrolysis. Photothermal catalytic methane pyrolysis combines the synergistic effects of photocatalysis and thermal catalysis, utilizing light energy to excite catalysts and generate active sites while creating localized high temperatures, thereby achieving efficient methane decomposition into hydrogen and carbon at lower overall temperatures. Its core advantages include:
Reduced Energy Consumption: Replacing part of the thermal energy input with light energy, lowering the high temperatures required for traditional pyrolysis;
Enhanced Reaction Kinetics: The photothermal effect (light-to-heat conversion) and photogenerated charges (photocatalysis) jointly promote C-H bond breaking;
Controlled Product Selectivity: Light excitation can suppress side reactions (e.g., C₂+ hydrocarbon formation), improving H₂ purity.
Based on this, PerfectLight Technology has launched the PLR-RP/RT Series Photothermal/(Thermal) Catalytic Reaction Evaluation Systems, providing a platform for systematic research on photothermal/thermal catalytic reactions. The PLR-RP Series Photothermal Catalytic Reaction Evaluation System features innovative quartz column light-guiding and reactor designs, enhancing light source irradiation efficiency and catalyst light absorption area, meeting the needs of gas-solid phase reactions under photothermal synergistic catalysis. The PLR-RT Series Catalytic Reaction Evaluation System offers precise temperature and pressure control, ensuring repeatability of reactions, and real-time pressure and temperature monitoring to better replicate chemical reaction processes, meeting the needs of conventional gas-solid phase catalytic reactions. (Consultation Hotline: 400-1161-365)
Methane pyrolysis technology, as a promising hydrogen production method, can significantly reduce greenhouse gas emissions compared to traditional methods and offers advantages in integration with existing natural gas infrastructure. However, challenges remain in scaling up, market matching, cost, and policy. In the future, further research and innovation are needed to optimize catalyst design for improved anti-carbon deposition performance and lifespan, explore novel reactor designs for enhanced production efficiency, and develop high-value applications for carbon by-products. Simultaneously, governments and industries must work together to promote the large-scale commercial application of methane pyrolysis technology, contributing to the global goal of achieving net-zero emissions.
References：
Alireza Lotfollahzade Moghaddam, Sohrab Hejazi, Moslem Fattahi, Md Golam Kibria*, Murray J. Thomson*, Rashed AlEisad and M. A. Khan *，et al. Methane pyrolysis for hydrogen production:navigating the path to a net zero future. Energy Environ. Sci., 2025,18, 2747-2790.
