Vapor and Molten Mg-Based Catalysts for Methane Activation

Methane (CH4) pyrolysis using molten catalysts offers a promising route for COx-free, clean hydrogen (H2) production. We used density functional theory to investigate the catalytic activity of molten magnesium, molten zinc, and a molten Zn/Mg alloy. We find that molten Mg and Zn exhibit substantial catalytic activity, with methane activation barriers ranging from 165 to 181 and 138 to 192 kJ/mol, respectively. In contrast, their vapors show much higher barriers (338 kJ/mol for Mg and 336 kJ/mol for Zn). Alloying Mg and Zn in a 1:1 ratio yields activation barriers of 177 to 190 kJ/mol, comparable to those of pure molten Mg. The performance of molten Mg, Zn, and Mg-Zn is competitive with that of other molten metal catalysts. We have found that a carbon atom inserted in molten Mg migrates to the surface, whereas in molten Zn and in the Mg–Zn alloy, the carbon atom prefers to be located inside the melt.