Highly selective and stable Ni/La-M (M=Sm, Pr, and Mg)-CeO₂ catalysts for CO₂ methanation

In the study presented herein, nickel catalysts supported on CeO₂ and, for the first time in the literature, on La₂O₃-Sm₂O₃-CeO₂, La₂O₃-Pr₂O₃-CeO₂ and La₂O₃-MgO-CeO₂ were prepared and evaluated for the reaction of CO₂ methanation. The carriers were prepared through a sol-gel microwave assisted method and the catalysts were obtained following wet impregnation. The physicochemical properties of the catalysts prior to reaction were determined through H₂-TPR, H₂-TPD, Raman spectroscopy, XRD, CO₂-TPD, N₂ physisorption-desorption, XPS and TEM. The spent catalysts, after the time-on-stream experiments were further characterised using TEM and TGA. It was shown that the simultaneous incorporation of La³⁺, Pr³⁺ and La³⁺, Sm³⁺ into the crystal structure of cerium oxide created higher population of oxygen vacant sites. Moreover, the co-presence of La³⁺, Mg²⁺ and La³⁺, Pr³⁺ into the CeO₂ increased the plethos of moderate basic sites. These physicochemical properties increased the rate of CO₂ methanation reaction at relatively low temperatures. Furthermore, it is argued that the addition of La³⁺ stabilized the Ni active sites via the probable formation of a new compound (La-O-Ni) on the catalyst surface or synergetic catalytic centers at the interfacial area improving the catalytic properties (activity and stability). Finally, the catalytic performance tests revealed that the addition of La³⁺ mainly improved the conversion of CO₂ and yield of CH₄ for the Ni/La-Mg-Ce and Ni/La-Sm-Ce samples. The rCO₂ and X_CO2 values at 300 °C followed the order Ni/La-Sm-Ce >> Ni/La-Mg-Ce > Ni/La-Pr-Ce > Ni/Ce.