Effect of cobalt promotion on hydrotalcite-derived nickel catalyst for CO2 methanation

A series of cobalt-promoted Ni-Mg-Al hydrotalcite-derived catalysts were tested towards CO2 methanation reaction. The best among examined catalysts was the one with 1 wt% of cobalt in fresh hydrotalcite, obtaining 77% of CO2 conversion and 99% of CH4 selectivity at 300 °C. Above that temperature, the catalyst was working with-near-equilibrium parameters. It was also stable for up to 24 h on stream. Other cobalt-containing samples were likewise very active and selective during the time on stream. Due to the use of a low amount of cobalt (0.5–4 wt%) the Co-Ni alloy was not the subject of research – both materials formed probably solid solution of cobalt in the nickel matrix. Although the behavior of cobalt as a textural and electronic promoter was confirmed. Co was found to improve reducibility of nickel species, hydrogen uptake, and the acidic/basic properties by increasing the number of medium strength and strong basic sites. Tendency to sintering of nickel crystallites on cobalt-promoted catalysts was not confirmed in this study, however, with increased content of Co, bigger metal crystallites were formed under the reduction conditions.