Ni-Catalysts Supported on N,B-Doped Graphene Aerogels for CO₂ Methanation

Methane synthesis from CO₂ hydrogenation is a promising approach for CO₂ recycling despite challenges such as nickel species loss and sintering. This study investigates reduced graphene aerogels (rGOA) doped with nitrogen (N-rGOA) and boron (B-rGOA) as supports for nickel-based CO₂ methanation catalysts. Boron doping (Ni/B-rGOA) improved Ni dispersion and increased the number of active sites through structural and electronic modifications. However, it exhibited slightly lower catalytic performance than nitrogen doping (Ni/N-rGOA), which is attributed to larger Ni particles and higher surface acidity, hindering CO₂ activation. ICP and XPS analyses revealed a higher Ni surface segregation in doped samples than in undoped Ni/rGOA. XPS also confirmed the presence of metallic Ni⁰ and Ni²⁺ species, with satellite peaks at 861 eV indicative of NiO. Boron doping modified the electronic structure of the carbon support, increasing Ni electron density and catalytic activity. TEM imaging showed well-dispersed Ni nanoparticles (5.9 to 7.3 nm) with no signs of aggregation. Among the tested catalysts, Ni/N-rGOA demonstrated superior CO₂ conversion and CH₄ selectivity, maintaining stable performance over 60 h of continuous operation. These findings underscore the potential of nitrogen-doped graphene aerogels as robust and efficient supports for the production of CO₂ methanation catalysts.