Exsolved LaNiRuO3 perovskite-based catalysts for CO2 methanation reaction†

Hydrogenation of CO₂ for methane formation is one of the thermodynamically favorable processes for reducing atmospheric CO₂ emissions. The present work demonstrates the synthesis and evaluation of LaNiRuO₃ perovskite-derived catalysts for CO₂ methanation in both supported and unsupported (bulk) forms. Specifically, two catalysts were prepared: (i) a Ru-substituted LaNiO₃ perovskite, LaNi_0.9Ru_0.1O₃, with 10 at% Ru and (ii) a supported version (30% LaNi_0.9Ru_0.1O₃/Al₂O₃). The catalysts were synthesized through controlled reduction conditions, and they were thoroughly characterized, before and after the exsolution process, using XRD, TEM, XPS, BET, H₂-TPR, and H₂-TPD techniques. The characterization results indicated that the exsolved LaNi_0.9Ru_0.1O₃/Al₂O₃ catalyst formed small Ni particles (∼6 nm), resulting in better dispersion (18%) while maintaining a high surface area (141 m² g⁻¹) and porosity. This catalyst demonstrated a 10% higher CO₂ conversion (77%) at a temperature lower by 50 °C (i.e. 400 °C) than the exsolved bulk LaNi_0.9Ru_0.1O₃ perovskite. Both catalysts exhibited over 90% selectivity for CH₄ in the 250–450 °C range. The enhanced catalytic performance of the exsolved LaNi_0.9Ru_0.1O₃/Al₂O₃ catalyst was attributed to the small Ni particle size, better dispersion, and the alumina support's high surface area and basic properties, facilitating the adsorption and dissociation of H₂ and CO₂. Further long-term stability tests at 400 °C and 25 000 mL g⁻¹ h⁻¹ (WHSV) over 54 h revealed that the exsolved LaNi_0.9Ru_0.1O₃/Al₂O₃ catalyst maintained a 70% CO₂ conversion, with the CH₄ yield and selectivity above 60% and 95%, respectively. Thus, supporting the perovskite catalyst on Al₂O₃ demonstrated a pronounced effect on the CO₂ conversion rate and CH₄ selectivity at lower temperatures along with ensuring the stability of catalyst over extended periods.