Tuning Co2+ Spin State of Multicomponent Rock-salt Oxides for Efficient CO Catalytic Oxidation

The spin state of transition metal ions, specifically controlled by the electrons in antibonding orbital, is recognized as a descriptor for heterogeneous catalysts. However, the influence of spin state on the adsorption of CO molecular with two electrons in the highest occupied molecular orbital, has been overlooked. In this work, the Co 2+ spin states in multicomponent rock-salt oxides are regulated by increasing configurational entropy, demonstrating the impact of Co 2+ spin states on CO adsorption. The CO catalytic oxidation activity of as-synthesized rock-salt oxides exhibits a volcano-shaped relationship with the ratio of Co 2+ in high spin state to Co 2+ in low spin state. Mg 0.33 Co 0.33 Ni 0.33 O with this spin state ratio of 7.5 has the largest negative adsorption energy to CO molecular and exhibits the best catalytic activity. The findings on the relationship between the spin state of transition metal ions and reactant adsorption can contribute to the understanding of catalytic activity at the electronic level.