CO₂ methanation on γ-Al₂O₃ nanoparticles from waste aluminium: Effect of Ba promoter on sulfur impurities

The inferior activity of γ-Al₂O₃ (GAL1) from the waste aluminium for CO₂ methanation was improved using Ba promoter. Ba promoted CO₂ conversion to ∼82% with 100% methane selectivity at 400 °C (Ni-Ba/GAL1), compared to ∼10% conversion without Ba (Ni/GAL1). Acid digestion of waste aluminium formed residual Al₂(SO₄)₃ at ∼0.5% atomic weight, forming the detrimental NiAl₂O₄ under reaction conditions. Ba inhibited NiAl₂O₄ formation by producing BaAl₂O₄, increasing Ni-Ba/γ-Al₂O₃ stability for 50 h at 400 °C. In-situ DRIFTS analysis revealed that NiAl₂O₄ caused CO₂ methanation via CO₂ dissociation into CO, followed by high temperature hydrogenation to CH₄. Ba promotes catalytic activity and stability of alumina with sulfur impurities by maintaining Ni^o oxidation states to catalyze CO₂ hydrogenation to formate at low temperatures, producing a high methane yield. In addition to transforming waste aluminium into a valuable material, investigation on γ-Al₂O₃ catalytic activity expands its potential use as a catalyst for CO₂ methanation.