Methanation of CO2 and CO by (Ni,Mg,Al)-Hydrotalcite-Derived and Related Catalysts with Varied Magnesium and Aluminum Oxide Contents

In the present study, the influence of the composition of Lewis basic (Mg,Al)Ox mixed oxide supports on CO2 and CO methanation performance of (Ni,Mg,Al)-hydrotalcite-derived catalysts is investigated. The hydrotalcite-derived and related precursors are synthesized by pH-controlled coprecipitation, calcination, and subsequent reduction. The catalysts with different supports prove suitability for CO2 and for CO methanation but display significant differences in respect to the temperature sensitivity of the reactions. The influence of the systematically varied support composition was studied by kinetic measurements, X-ray photoelectron spectroscopy (XPS), and in situ diffuse reflectance infrared Fourier transform (DRIFTS). Performance differences between CO2 and CO methanation were investigated for three different catalyst compositions. Different adsorption patterns in the DRIFTS measurements for these catalysts allow us to assign the increase in performance in the presence of magnesium oxide primarily to the enhancement of CO2 adsorption on the catalyst support. Temperature-dependent DRIFTS measurements display a correlation between the ratio of formate to carbonyl species on the catalyst surface and the activity of the catalyst in the case of magnesium-containing catalysts. The result suggests the role of CO as a key intermediate for CO2 methanation for magnesium-containing nickel hydrotalcite-derived catalysts. XPS measurements demonstrate that the magnesium content significantly affects the reducibility in the precursor material to generate the active component.