Thermocatalytic decomposition of methane to COx-free hydrogen and carbon over Ni–Fe–Cu/Al2O3 catalysts

•Nanocrystalline gamma alumina with high surface area was used as catalyst support.•Effects of iron and copper as promoter in nickel catalysts were investigated.•Increasing in reaction temperature increased the methane conversion.•Morphology of the produced carbon depends on the reaction temperature.•50%Ni-10%Fe-10%Cu/Al2O3 showed promising catalytic stability.

The catalytic performance of 50%Ni-10% Fe-n% Cu/Al2O3 (n = 0, 5, 10, 15) catalysts was studied to produce COx-free hydrogen and carbon nanofibers via methane thermocatalytic decomposition. X-ray diffraction (XRD) studies revealed the formation of NiFe2O4 and NixCu(1−x)O species in calcined samples and before catalytic tests. Moreover, Ni–Fe and Ni–Cu alloys were observed in the reduced catalysts. Addition of iron or copper to nickel catalyst improved the catalytic performance. Promoting effect of iron for nickel catalyst in methane decomposition was due to enhance of carbon diffusion rate and preventing the formation of encapsulating carbon. However, the addition of iron decreased the reducibility of nickel catalyst. Furthermore, copper increased methane adsorption and improved both the reducibility and nickel dispersion on the catalyst surface. Moreover, high affinity of copper with graphite structure prevented the generation of encapsulating carbon on the nickel surface and hindered the catalyst deactivation. Results revealed the significant improvement in the catalytic performance of the promoted catalysts at temperature higher than 700 °C.

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