Unveiling the role of Metal-Support interactions in Ni catalysts for CO2-Free hydrogen and carbon nanotube production via methane pyrolysis

Abstract

As the demand for hydrogen (H2) production rises alongside the global push for net-zero CO2 emissions, methane pyrolysis (MP) has emerged as a promising technology for CO2-free H2 generation. Ni-based catalysts are widely studied for MP due to their ability to activate CH4 in the low reaction temperature, but rapid deactivation caused by carbon by-products remains a challenge. In this study, we investigated the role of metal-support interactions on the catalytic performance and carbon nanotube (CNT) production in MP. A series of NiO-supported alumina catalysts were synthesized via a one-step solution combustion synthesis method with controllable NiO nano-particle (NP) sizes and loading levels. The optimized catalyst exhibited an activation energy of 54.2 kJ/mol and remained active for up to 9 h. All catalysts in the series generated high quality CNTs as byproducts of MP, exhibiting controllable diameters and varying degrees of graphitization. Comprehensive analysis indicated no direct correlation between carbon yield and structural properties of catalysts such as NP size, surface area, dispersion or oxidation states. In contrast, hydrogen temperature-programmed reduction measurements revealed that the carbon yield was closely linked to the presence of beta 2-type NiO species associated with an Al-rich mixed oxide phase. Catalysts with higher amounts of beta 2-type NiO showed increased carbon production, likely driven by improved carbon diffusion at the Ni-Al2O3 interface. These results emphasize the importance of fine-tuning metal-support interactions to achieve optimal catalytic performance, enabling efficient H2 and CNT generation simultaneously during MP.