Methane Cracking for Hydrogen Production: A Review of Catalytic and Molten Media Pyrolysis

Abstract

Currently, hydrogen is mainly generated by steam methane reforming, with significant CO2 emissions, thus exacerbating the greenhouse effect. This environmental concern promotes methane cracking, which represents one of the most promising alternatives for hydrogen production with theoretical zero CO/CO2 emissions. Methane cracking has been intensively investigated using metallic and carbonaceous catalysts. Recently, research has focused on methane pyrolysis in molten metals/salts to prevent both reactor coking and rapid catalyst deactivation frequently encountered in conventional pyrolysis. Another expected advantage is the heat transfer improvement due to the high heat capacity of molten media. Apart from the reaction itself that produces hydrogen and solid carbon, the energy source used in this endothermic process can also contribute to reducing environmental impacts. While most researchers used nonrenewable sources based on fossil fuel combustion or electrical heating, concentrated solar energy has not been thoroughly investigated, to date, for pyrolysis in molten media. However, it could be a promising innovative pathway to further improve hydrogen production sustainability from methane cracking. After recalling the basics of conventional catalytic methane cracking and the developed solar cracking reactors, this review delves into the most significant results of the state-of-the-art methane pyrolysis in melts (molten metals and salts) to show the advantages and the perspectives of this new path, as well as the carbon products’ characteristics and the main factors governing methane conversion.

Experimental comparison of solar methane pyrolysis in gas-phase and molten-tin bubbling tubular reactors

“…Tin metal was selected as the molten medium based on its suitable physical properties, which were compatible with methane cracking conducted at temperatures typically ranging from 1000 to 1400°C. Melting and boiling temperatures (232°C and 2602°C, respectively [26]) are important in a pyrolysis process in bubble columns.…”

“…The liquid phase also impedes reactor clogging caused by carbon deposits on the hot walls. This alternative pathway is called molten media methane pyrolysis [26].…”

Production of COx-Free Hydrogen and Few-Layer Graphene Nanoplatelets by Catalytic Decomposition of Methane over Ni-Lignin-Derived Nanoparticles

“…The pressure drops then increased very quickly, reaching 537 mbar at 150 min TOS; the reactor was clogged and the CDM reaction was paused. The higher initial methane conversion of Ni/Al 2 O 3 catalyst could be attributed to the larger number of Ni sites [2,24]. However, because of high CDM activity, significant carbon deposits were formed over the catalyst and resulted in the reactor plugging.…”

Novel Hydrothermally Synthesized Strontium Telluride Nanoballs as an Efficient Electrocatalyst for Oxygen Evolution Reaction

“…Higher quantities of surface oxygen binding energy are required for OER activity. The telluride based material has received little attention for OER catalysis, despite its metallic nature [45]. As a result, metal tellurides have better electrical conductivity, mechanical strength, rate capability, and cycling stability due to their synergistic bene ts [46].…”