Insight and comprehensive study of Ni-based catalysts supported on various metal oxides for CO₂ methanation

In this study, nickel supported on various metal oxides were prepared by simple impregnation and the performance for CO₂ methanation was tested. The oxide supports were all prepared by thermal decomposition of metal salts to provide comparable oxide properties such as surface area. Among the investigated oxides, nickel supported on CeO₂ and Y₂O₃ showed the highest CO₂ conversion of 90% at 320 °C with highest CH₄ selectivity of 99%. The order of catalyst activity (X_CO2@320°C) was reported: Ni/CeO₂ ~ Ni/Y₂O₃ > > Ni/La₂O₃ > Ni/ZrO₂ > Ni/Al₂O₃ > Ni/MgO > Ni/CaO > > Ni/MnO. The physicochemical properties of the catalysts were analyzed by TEM, BET, XRD, ICP, H₂-TPR, CO₂-TPD, H₂ chemisorption, TGA, Raman, and XPS. From the characterization results, the catalyst activity was independent to specific surface area of catalyst and crystallite size of Ni. The amount of oxygen vacancies and weak-to-medium basic sites exhibited major roles for enhancing catalyst activity. The CeO₂ and Y₂O₃ as reducible oxide supports not only provided abundant oxygen vacancies / basic sites, but also promoted Ni dispersion with appropriate interaction between metal and support, resulting in higher reducibility at low temperature. The reduction of catalyst at high temperature can significantly improve the performance of Ni supported on non-reducible MgO. However, the Ni/CeO₂ and Ni/Y₂O₃ reduced at high temperature suffered from coalescence of CeO₂ and Y₂O₃, though Ni crystallite sizes are well preserved from sintering.