Mo/Mg/Al co-doped Fe catalysts for hydrogen production via methane decomposition: Experimental and DFT insights

Abstract

Among various thermocatalytic processes, methane decomposition over Fe-based catalysts has emerged as a sustainable route for hydrogen generation, offering a zero-carbon process and valuable carbon materials. However, Fe-based catalysts still suffer from incomplete reduction of active sites, poor structural stability, and ambiguous improving mechanisms. In this work, an efficient Mo‑promoted, MgAl2O4‑supported Fe catalyst was developed for catalytic methane decomposition to H2 production. The methane decomposition performance of Mo/Mg/Al co-doped Fe catalysts was investigated in a fixed bed reactor. In addition, the mechanism underlying the synergistic effects of Mo, Mg, and Al on methane decomposition was elucidated. The co-doped Fe catalysts with the molar ratio of Mo: Mg: Al = 2: 1: 1 exhibit the highest initial methane conversion of 94.5% at 850 °C. This catalyst mainly consists of Fe, MgAl2O4 and MoO3. The MgAl2O4 support generated by solid-solid reaction between MgO and Al2O3 inhibits the formation of inactive species and reinforces metal-support interactions, thereby enhancing stability. The addition of Mo further promotes the activation of Fe sites and adjusts their electronic configuration. With optimized loading, Mo significantly boosts methane conversion and hydrogen generation efficiency. The 0.8Mo-Fe2Mg4Al4 catalyst achieves an initial methane conversion of 94.5% and represents a 29.6% increase compared with the catalyst containing only Mg. Moreover, Mo stabilizes the spinel lattice, suppresses unfavorable solid solutions, and directs carbon deposition toward carbon nanotubes. Density functional theory calculation reveals that Mo enhances C-H bond activation and reduces reaction barriers, underpinning a dual effect of electronic modulation and structural stabilization. Overall, the results highlight the pivotal role of Mo in advancing Fe-based CMD catalysis and provide a foundation for the rational design of efficient hydrogen production catalysts.