Hydrogen and carbon nanofibers synthesis by methane decomposition over Ni–Pd/Al2O3 catalyst

•Nanocrystaline gamma alumina with high surface area was used as catalyst support.•Effects of reaction temperature and palladium addition as prompter were studied.•Higher reaction temperature increased initial conversion and decreased stability.•SEM images show that morphology of produced carbon depends on reaction temperature.•50%Ni–15%Pd/Al2O3 catalyst showed promising catalyst lifetime.

Ni–Pd/Al2O3 catalysts were prepared and employed for the simultaneous production of COx-free hydrogen and carbon nanofibers via methane thermocatalytic decomposition. The results showed that the palladium addition to nickel catalyst improved the degree of reducibility and catalytic performance. Addition of palladium to nickel creates Ni–Pd alloy, which has the high activity for methane dissociation and increases the catalytic activity. The carbon diffusion in palladium is very faster than the diffusion in nickel. This leads to enhancing the rate of carbon diffusion and preventing the formation of encapsulating carbon, which increases the catalyst lifetime. Moreover, during the methane decomposition over Ni–Pd alloy, carbon nanofibers grow from several facets and form branched structure, which increases the rate of carbon migration and prevents the coverage of active sites. Scanning electron microscopy (SEM) analysis of the spent catalysts showed the formation of the intertwined filaments form carbon.

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