Electronic parameters in cobalt-based perovskite-type oxides as descriptors for chemocatalytic reactions

Abstract

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.

Manipulating Surface Termination of Perovskite Manganate for Oxygen Activation

“…It is well known that the activation of surface lattice oxygen plays a key role in various oxygen related catalytic reactions for transition metal oxide catalysts. [46][47][48] The active lattice oxygen not only decreases the activation energy barrier of the transition from O 2 − species to important intermediate O 2 2− species in the activation process of oxygen molecule, but also improves the catalytic efficiency of lattice oxygen involved in the rection. [45,49,50] As displayed in Figure 6, in the O 2 dissociation pathway, the two steps for O 2 →O 2 − and O 2 2− → O − are exothermic reactions and the relative energy is negative, and they have only a small effect on the catalytic process.…”

Effect of dz2 orbital electron-distribution of La-based inorganic perovskites on surface kinetics of a model reaction

“…Recent studies have reported electronic parameters (e g orbital occupancy) of inorganic perovskites as the descriptor for catalytic activity in catalytic reactions. 7,14 The low surface areas obtained herein will not be used as sole descriptor for…”

“…Moreover, perovskites with an e g orbital filling and a number of oxygen vacancies can be used as oxygen evolution reduction (OER) catalysts. 3,14 There are a number of synthetic methods which can be used to synthesize perovskites including micro-emulsion, 15 soft template, 16 freeze-drying, 12 nanocasting (hard template), 17 and hydrothermal synthesis. 18 Perovskites synthesized by solgel method provide materials that are crystalline and with high purity when compared to other methods.…”

Composition and electronic structure of Mn3O4 and Co3O4 cathodes in zinc/air batteries: a DFT study

“…In this case the spin state is very sensitive to changes in the coordination geometry, e.g., Co-O length or Co-O-Co angle. Different to the cobalt, in manganese oxides Mn 3+ always remains in high-spin state (M S = 4µ B ) [18].…”