Dual of CaO and MgO doped highly dispersed and stable Ni on ZrO₂ for CO₂ methanation

The conversion of carbon dioxide (CO₂) to methane has gained significant attention owing to its potential for integration with renewable hydrogen. However, achieving both low-temperature activity and high-temperature stability remains a challenge, primarily because of the sintering of Ni-based catalysts. This study introduces Ni-MgO-CaO/ZrO₂ catalyst for CO₂ methanation, a formulation not previously reported. We conducted an extensive theoretical (DFT) and experimental analysis, providing a thorough examination of the structural, catalytic activity, and stability relationships across undoped, single-doped, and dual-doped catalysts. A series of Ni-MgO-CaO-ZrO₂ catalysts were prepared and systematically evaluated by optimizing the Ca: Mg ratios and calcination temperature; the NiMgO₁-CZ catalyst Ca: Mg = 1: 1 calcined at 550 °C achieved 75 % CO₂ conversion with 100 % CH₄ selectivity at 250 °C, outperforming other tested compositions. The NiMgO-CZ catalyst featured highly dispersed Ni NPs within the CaO-MgO framework, ensuring both high activity and robust stability. Long-term stability tests conducted over 100 h revealed minimal particle growth (3.6 % for NiMgO₁-CZ compared to 34 % for Ni-CaO/ZrO₂) and only a mere 1 % decline in CO₂ conversion at 350 °C following prolonged testing at 550 °C. DFT calculations further confirmed that incorporating MgO to CaO-doped Ni/ZrO₂ enhanced sintering resistance attributed to the effective confinement of the Ni NPs by Ni-MgO at the CaO-MgO interface, thereby ensuring long-term performance. Additionally, carbon deposition was negligible for all CaO- and MgO-doped catalysts, with only Ni/ZrO₂ showing a slight deposition.