Nickel supported on YSZ: The effect of Ni particle size on the catalytic activity for CO2 methanation

The catalytic conversion of carbon dioxide to synthetic CH4 was studied on five Ni/YSZ samples, with the same nickel loading (10 wt%) but different Ni particle size. The catalysts, prepared by different methods, were characterized combining morphological (BET, TEM), structural (XRD, in-operando XAS), electronic (XPS, in-operando XANES) analysis and H-2-TPR experiments. The results showed that catalytic activity and CH4 selectivity depended on size and morphology of Ni particles, and that type and amount of deposited carbon strongly depended on Ni-0 morphology. The kinetic measurements revealed that both H-2 and CO2 reactants were activated on Ni sites, and that YSZ support was not directly involved in the reaction mechanism. The most efficient catalyst was that prepared by wet impregnation with Ni(EDTA)(2-) complex due to the high Ni-0 dispersion. This catalyst showed low amount of carbon and remarkable stability over time on stream. In-operando XAS showed that it did not undergo deactivation by Ni-0 -> Ni2+ oxidation using high CO2 concentration, thus it is applicable in dynamic conditions like those typical in the energy storage from renewable sources process.