A Mini-Review on Hydrogen and Carbon Production from Methane Pyrolysis by Molten Media

Under the background of carbon peaking and carbon neutrality, hydrogen as a clean and efficient energy carrier has received wide attention. The hydrogen production process of methane pyrolysis by molten media is regarded as one of the key technologies for hydrogen production in the future because it can produce high-purity H2 and carbon materials without producing CO2. In this article, the research progress of hydrogen production from methane pyrolysis by molten media in recent years (from 2017 to the present) is summarized, including liquid-phase catalysts and solid–liquid two-phase catalysts. In the liquid-phase catalyst section, the application of molten metals, molten salts, and molten metal–molten salt composites in methane pyrolysis is analyzed in detail, and their catalytic properties and reaction mechanisms are assessed. Molten metals have good methane pyrolysis activity, which is still limited by carbon pollution loss, and molten salts have good carbon cleaning ability but lack catalytic ability. Molten metal–molten salt composites combine efficient methane pyrolysis and high-purity carbon preparation but with high activation energy barriers. Then, the research progress of solid–liquid two-phase catalysts combining the interplay between molten media and solid catalysts is discussed. The combination of two-phase catalysts makes up for the limitation of liquid-phase catalysts, which can effectively reduce the activation energy barrier, but there are difficulties in industrialization. In addition, the economic feasibility of methane pyrolysis in molten media for hydrogen production is evaluated. The carbon materials market is the key to determining the economic benefits of the process. Finally, the challenges and prospects of the current research are summarized. Further reducing the activation energy barrier for methane pyrolysis by molten media and realizing the mass production of hydrogen and carbon materials combined with a two-phase catalytic system is the key to improving the economic efficiency of the process and achieving sustainable development.