(688h) Exploring the Kinetic and Mechanism of Methane Decomposition to COx-Free Hydrogen and Carbon Nanotubes Using Ni-Mo/MgO As a Catalyst

The demand for high-efficiency, affordable, and environmentally friendly catalysts for converting methane into COx-free hydrogen and carbon nanotubes (CNTs) is an ongoing and critical research area. This study investigates the kinetics of methane conversion to high-quality and high-yield carbon nanotubes (CNTs) using a Ni-Mo/MgO catalyst under varying growth temperatures and H₂ flow rates. The underlying mechanism of the exsolution Ni segregation from the Mo carbide surface that evolves upon methane decomposition as a function of varying Ni: Mo ratio is discussed. Our findings show how the optimal ratio of Ni to Mo results in stabilized Ni clusters that nucleate multi-walled carbon nanotubes while minimizing catalyst deactivation. As a result, we found that the optimal ratio is 1:3 with a yield of 538% (Figure 1a), with the ideal Ni to Mo ratio differing with reaction temperature. The role of other promoters (Co) and co-reactants (H₂O, H₂) are also discussed. This behavior is explained in the context of a kinetic model, decoupling the carburization step, steady state rates, and deactivation rates due to metal particle encapsulation, where it is revealed that the presence of the MoC sink drastically reduces catalyst deactivation rates. The prepared catalysts were characterized using: XRD, BET, and TPR, while the as-deposited carbon materials were analyzed using XRD, TEM, and Raman spectra. Overall, our results demonstrate the kinetic importance of Ni particle size and Mo carbides on the stable formation of hydrogen from methane while co-producing high-quality CNTs (Figure 1b).