Tuning Ni/activated carbon catalysts through preparation methods for COx-free hydrogen generation

Hydrogen is considered a promising clean energy carrier for sustainable energy systems. Catalytic methane decomposition (CMD) provides a COx-free pathway for hydrogen production while simultaneously generating valuable carbon nanostructures. In this study, Ni-supported activated carbon (AC) catalysts were synthesized using three different preparation methods: wet impregnation (WI), sonicated wet impregnation (SWI), and hydrothermal (H) synthesis. The catalytic performance of the prepared catalysts (30Ni/AC) was evaluated in a fixed-bed reactor at 850 °C with 40% methane (CH 4 ) at a gas hourly space velocity (GHSV) of 12,000 mL/h.g cat . Structural and morphological properties of fresh and spent catalysts were investigated using XRD, SEM, TEM, EDX, and Raman spectroscopy. The hydrothermal catalyst exhibited the smallest Ni crystallite size (~ 20 nm) and the highest initial methane conversion (~ 77%), followed by the SWI catalyst (~ 73%). Both catalysts demonstrated higher hydrogen production rates and improved catalytic stability compared with the WI catalyst, which showed rapid deactivation due to larger crystallite size and carbon encapsulation. Structural analyses confirmed the formation of graphitic carbon nanotubes with varying degrees of crystallinity. Overall, the study highlights the strong influence of catalyst preparation method on metal dispersion, catalytic activity, and carbon quality during methane decomposition.