Unsupported NiO Nanoflowers for Enhanced Methane Activation and Direct Conversion to C2–C6 Hydrocarbons

This study compares unsupported NiO nanoflowers (NiEG) and ZrO2-supported NiO (25NiZ) for methane activation and hydrogenation, focusing on the impact of catalyst morphology. The NiEG catalyst demonstrated superior performance, achieving a high methane activation rate of 1.79 mol/(s·gNiO) and unique product selectivity. It produced ethylene and ethane at 503 K and higher hydrocarbons (C4–C6) at 593 K. Furthermore, the NiEG catalyst exhibited enhanced coke resistance, forming less-deactivating carbon nanotubes compared to the filamentous coke prevalent on the 25NiZ catalyst. We attribute this performance to the nanoflower morphology, which provides highly exposed and stable Ni sites that facilitate C-H cleavage and stabilize reaction intermediates.