Shaping the activity of neodymium modified silica supported nickel catalysts in CO2 methanation reaction

The influence of neodymium modifier on the performance of silica-supported nickel catalysts in CO 2 methanation, with molecular-level understanding of the occurred phenomena, was systematically investigated using TEM, TPR, TPD, in-situ DRIFTS and XPS. Catalysts containing 10 wt% Ni and 0–20 wt% Nd were obtained by a citric acid-assisted wet impregnation method. Studies revealed the formation of very small nickel nanoparticles (2–8 nm), which, depending on the Nd content, were partially covered with Nd 2 O 3 species. Even a very small amount of Nd improved activity, selectivity, and stability of catalysts in CO 2 methanation over a wide temperature range (200–500 °C). For catalysts with Nd content of 15 wt%, CO 2 conversion reached almost 60% at 300 °C with selectivity to methane close to 100%. The complex role of the modifier has been demonstrated. Its presence altered the electronic properties of the nickel crystallites, facilitating the activation of H 2 and weakening of C–O bonds in the resulting intermediate carbonyl groups, as well as the spillover of hydrogen atoms, thereby enhancing the partial reduction of the dispersed Nd 2 O 3 species and formation of associated hydroxyl groups. At the same time, Nd 2 O 3 promoted CO 2 activation through the formation of surface bicarbonate and carbonate species, and then further hydrogenation, leading first to intermediate formate species and finally methane. In addition, an introduction of Nd led to the increase in the durability of catalysts, likely through stabilization of oxygen-containing species and variation of surface hydroxyl chemistry, providing guidance for development of new Ni-based methanation catalysts.