Oxygen vacancy-dependent chemical intermediates on Ru/MnO catalysts dictate the selectivity of CO2 reduction

Structural dependence of the formation and transformation of the surface intermediates is the key to controlling the catalytic selectivity. Especially a highly controversial issue is whether formate species are spectator or active intermediates for CO2 reduction. Herein, the Ru/MnOx catalysts with different oxygen vacancy densities were developed to clarify these aspects. The high-defective RuMn-Ov showed high CH4 selectivity (i.e. 89.3 % for CH4 at 320 °C), while the low-defective RuMn-C mainly produced CO (i.e. 100 % for CO at 320 °C). By using multiple characterizations combined with theoretical modelling, it can be proved that the surface oxygen vacancies on MnOx induces the generation of the formate intermediate, followed by hydrogenated to methane via spillover H derived from Ru nanoparticle. Remarkably, the RuMn-C catalyst at high Ru loading (c.a. 5 wt%) without formate intermediates achieved over 93 % CO selectivity. The results give an instructive way to understand the selectivity regulation driven by response reaction pathways.