Highly active NiO-CeO2 catalysts for synthetic natural gas production by CO2 methanation

Abstract NiO-CeO 2 mixed oxides were prepared by the soft-template method with nominal Ni/Ce molar ratios between 0.3 and 4.0. NiO and CeO 2 pure oxides were also prepared through the same procedure. A second series of NiO-CeO 2 mixed oxides (nominal Ni/Ce values = 0.3–1.5 mol mol −1 ) was synthesized by using the soft-templated ceria as the support and depositing Ni through incipient wetness impregnation. All samples were characterized by different techniques as to their chemical composition, structure, morphology, texture, and redox features. NiO nanocrystals of about 4 nm in size were obtained in the case of the soft‐templated samples, regardless of the Ni loading. Larger NiO nanocrystals (up to 20 nm in size) were formed by depositing Ni through the impregnation procedure. The catalytic performance was investigated in the CO 2 methanation reaction after mild reduction pretreatment (H 2 at 400 °C for 1 h). Catalytic testing was performed under atmospheric pressure, 300 °C, 72,000 cm 3  h −1  g cat −1 , and stoichiometric H 2 /CO 2 molar ratio. Pure NiO as well as the two NiO-CeO 2 mixed oxides series showed high CO 2 conversions (up to 87 mol%) together with CH 4 selectivity values close to 100 mol%. Despite the significantly different size (6–8 and 15–35 nm, respectively) of the Ni 0 nanocrystals originated by NiO reduction, comparable CO 2 conversion values were observed for the soft-templated and impregnated catalysts. The catalyst stability as well as the effect of reaction temperature, space velocity, and H 2 /CO 2 molar ratio were investigated on selected samples. The catalytic results were explained by taking into account that CO 2 and H 2 are activated on different phases.