Highly active, selective and stable Ru/NiO-CeO2 catalyst for low-temperature CO2 methanation

Ni, Ru and CeO 2 -based bimetallic catalysts have been prepared and studied for low-temperature CO 2 methanation, optimizing both the composition and synthesis method. The most active catalyst obtained, with 1.6 % wt. Ru and 10 % wt. Ni, was synthesized by ruthenium impregnation on NiO-CeO 2 mixed oxide nanoparticles, which were prepared by reversed microemulsion. The onset reaction temperature is 190 °C and yields 26 μmol CH 4 ·s −1 ·g cat −1 at 250 °C and atmospheric pressure, with 100 % selectivity to CH 4 , being among the most active reported catalysts at low temperature. The high catalytic activity is attributed to the intimate contact between Ni and Ce cations on solid solution nanoparticles (7–8 nm), which promotes the creation of vacant sites for CO 2 chemisorption and dissociation, and further impregnation of ruthenium generates a synergy that facilitates low-temperature reducibility. In situ DRIFTS experiments confirmed that CeO 2 doping with Ni 2+ promotes CO 2 chemisorption, while ruthenium improves further hydrogenation of the surface carbon species. Isotopic 13 C 18 O 2 pulse experiments and NAP-XPS experiments with synchrotron radiation evidence that oxygen from CO 2 is retained on the catalyst upon dissociation, and that H 2 O evolves with catalyst oxygen. The Ce 3+ /Ce 4+ cations play the main role in this oxygen exchange process, Ni 2+ improves CeO 2 reduction and promotes the creation of oxygen vacancies where CO 2 is evenly chemisorbed and dissociated, and ruthenium is highly reduced to metal state under reaction conditions, which explains the effective dissociation of H 2 and fast hydrogenation of the surface carbon intermediates. • Bimetallic Ru/NiO-CeO 2 nanoparticles are more active than counterpart monometallic and non-nanoparticle catalysts. • Optimum balance between CO 2 chemisorption and hydrogenation of intermediate reactions • CO 2 is chemisorbed/dissociated on Ni 2+ -CeO 2 involving Ce 3+ /Ce 4+ redox cycles. • Ru 0 remains reduced under reaction conditions. • CO 2 exchanges oxygen atoms with the catalyst and hydrogenation to CH 4 occurs simultaneously.