MethaneMethane pyrolysis is a promising technology for producing valuable hydrogenHydrogen and carbonCarbon without CO2 emission. Conventional solid metal catalysts are easily deactivated due to the coking and sintering. To circumvent these issues, molten saltsMolten salt are emerging as promising catalysts for methaneMethane pyrolysis due to various potential advantages. However, understanding of the molten-salt-mediated processes is still limited. This study investigates the methaneMethane conversion in the CaCl2–NiCl2 system, which shows a distinct behavior from the MgCl2–NiCl2, NaCl–KCl–NiCl2, and LiCl–NiCl2 systems. Our findings reveal that, instead of serving as a stable catalyst, the NiCl2 dissolved in CaCl2 was easily reduced to metallic Ni, which subsequently served as the catalyst for CH4 pyrolysis into carbonCarbon and H2. The NiCl2 dissolved in MgCl2, NaCl–KCl, or LiCl was also reduced by methaneMethane based on the presence of HCl in the exit gas, yet the methaneMethane conversion measured in those systems was much lower and more stable. Overall, the results presented in this study help clarify the reaction pathways and mechanisms of methaneMethane conversion in NiCl2-containing molten saltsMolten salt. Additionally, the thermodynamic calculations show the high stability of MnCl2, FeCl2, and CoCl2 in the presence of methaneMethane, making them worthy of further in-depth research as whole or as dopant species in molten saltMolten salt systems for CH4 pyrolysis.