Perovskite-type transition metal (TM) oxides are effective catalysts in oxidation and decomposition reactions. Yet, the effect of compositional variation on catalytic efficacy is not well understood. The present analysis of electronic characteristics of B-site substituted LaCoO 3 derivatives via in situ X-ray absorption spectroscopy (XAS) establishes correlations of electronic parameters with reaction rates: TM t 2g and e g orbital occupancy yield volcanotype or non-linear correlations with NO oxidation, CO oxidation and N 2 O decomposition rates. Covalent O 2p-TM 3d interaction, in ultra-high vacuum, is a linear descriptor for reaction rates in NO oxidation and CO oxidation, and for N 2 O decomposition rates in O 2 presence. Covalency crucially determines the ability of the catalytically active sites to interact with surface species during the kinetically relevant step of the reaction. The nature of the kinetically relevant step and of surface species involved lead to the vast effect of XAS measurement conditions on the validity of correlations.

We study 1s and 2p hard x-ray photoemission spectra (XPS) in a series of late transition metal oxides: Fe2O3 (3d 5 ), FeTiO3 (3d 6 ), CoO (3d 7 ) and NiO (3d 8 ). The experimental spectra are analyzed with two theoretical approaches: MO6 cluster model and local density approximation (LDA) + dynamical mean-field theory (DMFT). Owing to the absence of the core-valence multiplets and spin-orbit coupling, 1s XPS is found to be a sensitive probe of chemical bonding and nonlocal charge-transfer screening, providing complementary information to 2p XPS. The 1s XPS spectra are used to assess the accuracy of the ab-initio LDA+DMFT approach, developed recently to study the material-specific charge-transfer effects in core-level XPS.

The charge and spin-state evolution of manganese and cobalt in the LaMn 1−x Co x O 3 (x = 0.00, 0.25, 0.50, 0.75, and 1.00) perovskite nanoparticles have been studied with soft X-ray absorption spectroscopy. The results show a gradual increase in the average oxidation state of both Mn and Co ions with cobalt doping. The average valence of the LaMn 1−x Co x O 3 samples remains close to 3.0, with the Mn valence increasing from 3.1 to 4.0 and the Co valence increasing from 2.0 to 3.0. The symmetry of Mn and Co was determined using multiplet calculations. Calculating the intensity-area of the oxygen K pre-edge feature confirmed an increase in covalency with increasing Mn and Co oxidation state. The ground-state composition of Mn 3+ in LaMnO 3 , and Co 3+ in LaCoO 3 , was investigated, and it was found that Mn 3+ (D 4h) and Co 3+ (O h) are mainly in their low-spin state, with 10− 20% admixture of high-spin state contributions into a mixed spin ground state.

An in‐situ laboratory‐based X‐ray Absorption Near Edge Structure (XANES) Spectroscopy set‐up is presented, which allows performing long‐term experiments on a solid catalyst at relevant reaction conditions of temperature and pressure. Complementary to research performed at synchrotron radiation facilities the approach is showcased for a Co/TiO2 Fischer‐Tropsch Synthesis (FTS) catalyst. Supported cobalt metal nanoparticles next to a (very small) fraction of cobalt(II) titanate, which is an inactive phase for FTS, were detected, with no signs of re‐oxidation of the supported cobalt metal nanoparticles during FTS at 523 K, 5 bar and 200 h, indicating that cobalt metal is maintained as the main active phase during FTS.