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

Johannes Simböck,Simon Schönebaum,Regina Palkovits,M Ghiasi,Frank M F De Groot,Ulrich Simon

doi:10.1038/s41467-020-14305-0

Johannes Simböck, Simon Schönebaum + Show 4 more

Open Access

https://doi.org/10.1038/s41467-020-14305-0

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Journal: Nature Communications	Publication Date: Jan 31, 2020
Citations: 49	License type: open-access

Affiliation: RWTH Aachen University, Utrecht University

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 LaCoO3 derivatives via in situ X-ray absorption spectroscopy (XAS) establishes correlations of electronic parameters with reaction rates: TM t2g and eg orbital occupancy yield volcano-type or non-linear correlations with NO oxidation, CO oxidation and N2O 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 N2O decomposition rates in O2 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.

Highlights

Perovskite-type transition metal (TM) oxides are effective catalysts in oxidation and decomposition reactions
Information on covalent binding and band structure such as charge-transfer energy is accessible through combination of X-ray emission spectroscopy, X-ray photoelectron spectroscopy (XPS)[10,11] or X-ray absorption spectroscopy (XAS) at the O K-edge[12], and is relevant for catalysis when performed in near-ambient conditions
While these correlations are established in electrocatalysis, covalency and d-orbital occupancy have not been examined as descriptor in chemocatalysis in detail, with regard to implications of different reaction characteristics or the effects of variable Co oxidation or spin states[13]

Summary

Introduction

Perovskite-type transition metal (TM) oxides are effective catalysts in oxidation and decomposition reactions. Redox properties such as transition metal (TM) oxidation states, oxygen vacancy formation, or binding strength of reactants are commonly cited characteristics in the assessment of catalytic efficacy of perovskite-type oxides substituted with different TM1,7 These characteristics are a multifaceted expression of electronic states of the bulk and/or surface sites of the catalyst as Hwang et al.[5] recently emphasized by their correlation of TM 3dorbital occupancy with catalytic rates in the oxidation of NO, CO, or hydrocarbons. Charge-transfer energy was identified as relevant descriptor for trends in overpotential and other parameters for electrocatalytic efficacy as well[4] While these correlations are established in electrocatalysis, covalency and d-orbital occupancy have not been examined as descriptor in chemocatalysis in detail, with regard to implications of different reaction characteristics or the effects of variable Co oxidation or spin states[13]. The ideal descriptor may become comparable across different reactions, crystal structures, and catalyst compositions of TM oxides

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