Various nickel doping in commercial Ni–Mo/Al2O3 as catalysts for natural gas decomposition to COx-free hydrogen production

• We studied the natural gas catalytic decomposition to CO/CO2 free H2 and CNT.
• Commercial hydrotreating 5.2%Ni–10.96%Mo/Al2O3 was used as a principal catalyst.
• Increment of Ni doping (10–40wt %) enhanced the H2 and CNT productivity.
• The catalytic activity primarily depends on the isolated active Ni sites.
• TEM and TGA data of CNT were compatible with the catalytic performance.

Non-oxidative decomposition of natural gas to COx-free hydrogen production over commercial nickel-molybdate hydrotreating catalysts with different Ni loading from 5 to 40wt% were studied at 700 °C. The catalysts were characterized by XRD, BET, TEM, Raman spectroscopy and TG-DTA analysis. The catalytic decomposition activities showed that a tremendous hydrogen production (∼90%) was obtained over 20–40wt%Ni/Mo–Al2O3 catalysts. Moreover, all catalysts exhibited excellent durability up to 9 h with stable catalytic activity toward H2 production. Although the increase of Ni content reduces the catalyst surface area, the H2 productivity and longevity increases with increased Ni content, i.e., the catalytic decomposition activity primarily depends on the active Ni sites which overcompensates the surface deficiencies. TEM, TGA and XRD data of used catalysts indicated that a higher thermal stability and graphitization degree of multi-walled carbon nanotubes were obtained on all Ni containing catalysts. Higher metal loading produced carbon nanofibers beside CNTs due to increment of particle size and long reaction time.