Operando Soft X-ray Absorption of LaMn 1- x Co x O 3 Perovskites for CO Oxidation.

We employed operando soft X-ray absorption spectroscopy (XAS) to monitor the changes in the valence states and spin properties of LaMn 1- x Co x O 3 catalysts subjected to a mixture of CO and O 2 at ambient pressure. Guided by simulations based on charge transfer multiplet theory, we quantitatively analyze the Mn and Co 2p XAS as well as the oxygen K-edge XAS spectra during the reaction process. The Mn sites are particularly sensitive to the catalytic reaction, displaying dynamics in their oxidation state. When Co doping is introduced ( x ≤ 0.5), Mn oxidizes from Mn 2+ to Mn 3+ and Mn 4+ , while Co largely maintains a valence state of Co 2+ . In the case of LaCoO 3 , we identify high-spin and low-spin Co 3+ species combined with Co 2+ . Our investigation underscores the importance to consider the spin and valence states of catalyst materials under operando conditions.