Evolution of Ni-Mo/MgO during catalytic methane pyrolysis to produce base-growth nanotubes

Catalytic pyrolysis of methane is a promising approach for affordable hydrogen production without CO₂ emissions. While this process is thermodynamically appealing compared to steam reforming, the high stability of methane requires severe conditions, making catalyst stability challenging. Here, we report the behavior of a highly promising Ni-Mo/MgO catalyst, which greatly outperforms its Ni/MgO, Mo/MgO, and Ni-Mo/SiO₂ counterparts at atmospheric pressure. At 800°C, nearly 229 g of carbon nanotubes per gram of Ni are produced. We propose that this superior performance results from the phase evolution of the catalyst, which exsolves stable nickel catalyst particles under reaction conditions. We further reveal that molybdenum carbide formation reduces sintering and adheres the active catalytic particles to the support throughout the reaction, enabling catalyst reuse. Several characterization techniques (same-spot TEM, XPS, XRD, and Raman) are employed to examine catalyst morphology at every step, fostering a deeper understanding of its catalytic activity and stability.