Methane pyrolysis on NiMo/MgO catalysts: The significance of equimolar NiMo alloy resisting nanosize segregation during the reaction

As a perspective catalyst composition for methane non-oxidative decomposition/methane pyrolysis (CH4⇌C+2 H2) yielding clean hydrogen and only solid carbon, the combination of nickel and molybdenum on MgO support was investigated. With deliberately low Ni content and strong metal-support interaction, 7%Ni4%Mo/MgO and 7%Ni12%Mo/MgO catalysts and the monometallic references were prepared. Structural analysis was performed using TPR, XRD, TEM, XPS and Raman spectroscopy in reduced state and after methane decomposition test. Catalytic performance was investigated i) in a highly diluted CH4 flow in a fixed bed reactor under temperature ramp and ii) in 50% CH4/Ar using a horizontal reactor at 800 °C. Synergetic interaction of Mo and Ni was observed under both conditions. The results revealed that the deactivation was coupled with alloy segregation for the low Mo loading, while the more stable, non-segregating Mo/Ni∼1 composition of the individual metal particles in 7%Ni12%Mo/MgO sample resulted in good activity and high carbon nanotube yield. [Display omitted] •NiMo/MgO samples with Mo/Ni=1.2 and 0.4 were prepared by adsorption-precipitation.•Reduction resulted in alloyed NiMo particles in strong interaction with MgO.•In methane pyrolysis synergetic effect was observed, larger for Mo/Ni= 1.2.•During CNT formation alloyed NiMo particles segregated in samples with Mo/Ni=0.4.•The higher alloy stability in Mo/Ni=1.2 sample increased catalyst lifetime.