Robust α-NiMoO 4 /MoS 2 Catalysts for Low-Temperature Methane Pyrolysis: Synergistic Ni–Mo–S Interactions for Sustainable Hydrogen Production with Selective Carbon Nanotubes/Graphene

Catalytic methane decomposition (CMD) offers a promising route to CO2-free hydrogen and valuable carbon nanomaterials, but catalyst deactivation from carbon deposition remains a critical challenge. Herein, we report a scalable, low-waste sol–gel route to interface-engineered α-NiMoO4 and α-NiMoO4/MoS2 catalysts that enable stable CMD at 500 °C. Through precise calcination control (450–750 °C), we tailor phase composition and morphology: spherical α-NiMoO4/MoS2 nanoparticles (5–20 nm) dominate at 450–600 °C, while phase-pure α-NiMoO4 nanosheets form at 750 °C. The optimized α-NiMoO4/MoS2-450 °C catalyst (15 wt % Ni) delivers 26% CH4 conversion, a turnover frequency (TOF) of 0.61 s–1, a low apparent activation energy (Ea,app) of 43.27 kJ/mol and a hydrogen yield of 295.8 mmol g–1 h–1 at a reduced temperature of 500 °C (CH4/N2 = 12:18 mL/min). Notably, it maintains this performance for over 12 h-a 6-fold improvement over conventional Ni catalysts. Beyond hydrogen, the process valorizes the carbon byproduct into tailored nanostructures: highly graphitic carbon nanotubes (ID/IG = 1.03) from the nanosheet catalyst or few-layer graphene from the MoS2-containing nanoparticles. Mechanistic studies show that this selectivity originates from calcination-tuned metal–support interactions (MSI): MoS2 weakens Ni–support bonding, favoring graphene formation, whereas strong MSI in the pure spinel phase drives CNT growth through mixed tip- and base-growth mechanisms. Advanced characterization (H2-TPR, TEM, XPS) further demonstrates that synergistic Ni–Mo–S interactions not only weaken Ni–support bonding but also stabilize active Ni sites against aggregation and regulate carbon diffusion pathways. By directly correlating structural properties with catalytic performance, this work deepens the fundamental understanding of MSI effects in CMD and establishes a dual-functional catalysis strategy, where calcination-tuned interfaces simultaneously enhance hydrogen productivity and control nanocarbon selectivity. Together, these insights highlight a practical and scalable pathway for coproducing clean hydrogen and high-value carbon nanomaterials, bridging fundamental catalysis with sustainable energy solutions.