Catalytic Methane Pyrolysis in Molten Alkali Chloride Salts Containing Iron

Mixtures of molten iron-sodium-potassium chloride salts are found to be catalytic for methane pyrolysis. In a differential bubble column reactor, the apparent activation energy of the molten salt decreases from 301 kJ/mol for the eutectic NaCl-KCl to 171 kJ/mol for 3 wt % of iron-added as FeCl3. The solid carbon produced in the iron-containing salt mixture has a graphitic structure which is distinct from the more disordered carbon produced in the iron-free eutectic, suggesting a different solid carbon formation pathway. Results from H-D exchange investigations are consistent with a different reaction pathway for methane pyrolysis in the iron-containing NaCl-KCl melt than in the melt without Fe. The activity of the salt mixture was stable for over 50 h, producing molecular hydrogen and separable solid carbon. It is likely that the activity is due to the presence of Fe in molecular ions stabilized in the NaCl-KCl melt that facilitate the C-H bond activation in methane.