Enhanced and stable methane decomposition in a triphasic system of Ni/coal-char catalyst and Na₂CO₃-NaCl eutectic molten salt

Na₂CO₃-NaCl eutectic molten salt is used to enhance Ni/CC catalyst for CMD. • 97.6% CH₄ conversion is obtained over 20 h under a counter-current gas flow system. • High and stable activity arises from a triple synergistic effect of the salt system. • The molten salt achieves >99% recovery via simple water washing and evaporation. • Besides H 2 , carbon products are graphitic spheres and thin graphitic sheets. Catalytic methane decomposition (CMD) is a promising route for low-CO ₓ hydrogen production, but conventional solid catalysts suffer from rapid deactivation due to carbon encapsulation and metal sintering. Herein, we develop a low-cost, robust gas-liquid-solid triphasic system by integrating a Ni/coal-char catalyst with a Na₂CO₃-NaCl eutectic molten salt (with an optimized mass ratio of 6:4 and counter-current operation). At 850 °C, this system achieves a stable methane conversion of 97.6% over 20 h, with no obvious deactivation. The exceptional performance originates from a triple synergistic effect of the eutectic salt: (i) mass transfer enhancement via counter-current operation, (ii) interface protection that suppresses Ni sintering and directs carbon growth toward value-added graphitic structures, and (iii) potential electronic modulation via Ni 2+ -CO₃ 2− coordination that facilitates CH 4 activation and conversion. Furthermore, the molten salt can be recovered almost completely (>99%, as determined by titration), with 94.1% methane conversion maintained after five cycles. This work provides a promising strategy toward industrial hydrogen production and deepens the mechanistic understanding of physical-chemical synergy in molten salt-mediated CMD systems. Download: Download high-res image (174KB) Download: Download full-size image