Dynamic Surface Restructuring and Carbonate-Mediated Pathways in Perovskite-Catalyzed CO Oxidation Revealed by Operando Spectroscopy

In this work, we studied two perovskite-based catalysts, namely LaFeO₃ (LFO) and LaFe₀.₇₅Co₀.₂₅O₃ (LFCO), to reveal the reaction mechanism and disentangle the complex surface phenomena taking place during a seemingly simple CO oxidation reaction. Precise kinetic measurements and operando spectroscopy were employed to elucidate the interplay between the formation of surface intermediates and the transformations of the surface sites, leading to the occurrence of a frustrated phase transition that can potentially define the catalyst activity under different reaction conditions. Our work specifically highlighted the effect of partial cobalt substitution into the perovskite’s structure on improving the activity of the reference iron-containing lanthanum-based perovskite. In this regard, modulation-excitation spectroscopy coupled with phase-sensitive detection (MES-PSD) and near-ambient pressure X-ray photoelectron spectroscopy (NAP-XPS) were employed at different temperatures to elucidate the multifaceted role of cobalt in promoting the carbonate-mediated pathway for CO oxidation. For LFO, kinetic and theoretical analyses confirm a pure Mars-van Krevelen (MvK) mechanism mediated by bidentate carbonates, yielding low activity but high stability. In contrast, LFCO exhibits higher activity (despite slight deactivation) through a dual MvK/Langmuir-Hinshelwood (LH) pathway. Monodentate carbonates act as low-temperature and unstable intermediates, with LFCO accelerating carbonate-to-CO₂ conversion via enhanced surface oxygen mobility. The temperature also dictates mechanistic shifts: LH dominates below 170°C, while MvK prevails above this threshold. Additionally, operando NAP-XPS reveals this transition coincides with cobalt reduction, iron oxidation, and frustrated phase transitions that activate carbonate intermediates. In our catalytic systems, cobalt serves as the primary active site, while lanthanum stabilizes the perovskite structure and surface carbonates, and iron maintains charge balance. These findings demonstrate how composition and temperature govern dynamic surface restructuring and reaction pathways in perovskite catalysts.