Confinement of ultrasmall NiO nanoparticles into ordered and non-ordered mesoporous supports for CO₂ methanation

Introduction: Due to concern about global warming, researchers are focusing on green fuels obtained by reducing captured CO₂ (e-fuels) with green hydrogen. An important example among e-fuels is methane. Ni-based catalysts are currently among the most investigated systems used for CO₂ methanation due to their high activity and selectivity at relatively low temperatures and due to their low cost compared to catalysts based on noble metals. Ni is often paired with a supporter/promoter, like CeO₂.

Methods: In this work, nanocomposite catalysts consisting of a NiO or NiO/CeO₂ active phase dispersed onto mesostructured/mesoporous supports are presented. The use of such supports should allow fine dispersion of the active phase, reaching high activity levels with a low amount of Ni and Ce. To obtain NiO- and NiO/CeO₂-based nanocomposites, two different impregnation strategies are used: two-solvent (TS) impregnation and impregnation based on a self-combustion (SC) reaction. Various Ni:Ce ratios and chemically different mesostructured/mesoporous supports (SiO₂, Al₂O_3, and CeO₂) are studied. The catalysts are characterized with different techniques to determine their structural, textural, and morphological properties and tested for CO₂ methanation.

Results and conclusion: Regardless of the support, the SC method allows us to disperse both NiO and CeO₂ in the form of much smaller nanoparticles compared with the TS approach. The catalytic tests show a positive effect of CeO₂ as a promoter of CO₂ conversion; furthermore, the catalysts obtained via the SC impregnation process show a higher CO₂ conversion, presumably due to the higher dispersion of the active phase. The Ni:Ce ratio also has a remarkable effect on the performance. The effect of different types of support on the performance is also investigated. In particular, CeO₂ support is shown to promote the catalytic performance, achieving CO₂ conversions of >85 mol%, competing with the most promising systems reported in the literature.