A two-stage chemical looping approach is demonstrated for sustainable carbon-free hydrogen production through methane decomposition (CH4 → C + 2H2) combined with cyclic catalyst regeneration via the reverse Boudouard reaction (C + CO2 → 2CO). Ni-based spherical nanoparticle cluster, fabricated using a continuous aerosol-based synthetic approach, is developed for an effective cyclic catalysis of the above two chemical reactions.

In the first part, we utilized Ni-CeO2-Al2O3 catalyst materials to facilitate isothermal chemical looping reactions, maintaining a temperature of 600 °C throughout the process. Sufficiently high CO2 conversion rate for catalyst regeneration (in terms of TOFCO2, 36.09 h-1) and a stably high yield of hydrogen (in terms of CH4 conversion; TOFCH4, 39.62 h-1) are achievable. CeO2-incorporated samples generating whisker carbon after methane pyrolysis demonstrate a better activity for cyclic catalyst regeneration.

In the second part, we utilized Ni-Fe-Al2O3 catalyst material and modified the reaction parameters of the reverse Boudouard reaction as follows: (1) raised the reaction temperature to 700 ℃ (2) introduced oxygen to facilitate the gasification of carbon. These adjustments are anticipated to expedite the catalyst regeneration process effectively. Experimental results show that using the above methods, we can reduce the time required for the reverse Boudouard reaction (from 20 minutes to 10 minutes), achieving faster catalyst regeneration. The novelty of the work stands on developing high-performance dual functional catalyst material, by which the two-stage reactions can be promoted under a remarkably lower temperature (e.g., 600 °C). The proposed dual functional catalyst material and catalytic pathway in this study demonstrate significant advances for the chemical looping process of effective hydrogen production combined with cyclic catalyst regeneration via CO2 utilization, offering eco-friendly pathway for industrial applications.