Stoichiometric (LaCoO3) vs. Non-stoichiometric (LaCo0.9O3−δ) perovskite catalysts for CO oxidation: Kinetics and reaction models

Abstract

This study compares the catalytic activity of CO oxidation over two perovskite catalysts: stoichiometric LaCoO₃ and non-stoichiometric LaCo_0.9O_3−δ. Through catalytic activity and kinetic analysis, we aim to propose a strategy for designing efficient non-stoichiometric perovskite catalysts. The non-stoichiometric LaCo_0.9O_3−δ catalyst exhibits superior activity in CO oxidation compared to the stoichiometric LaCoO₃ catalyst. X-ray photoelectron spectroscopy (XPS) and Oxygen-temperature programmed desorption (O₂-TPD) results reveal an enrichment of adsorbed oxygen species, which are crucial for CO oxidation reactions, on the surface of non-stoichiometric LaCo_0.9O_3−δ. This suggests that non-stoichiometric composition effectively generates oxygen vacancies on the catalyst surface, facilitating the formation of adsorbed oxygen species. Interestingly, a higher apparent activation energy is observed for the LaCo_0.9O_3−δ compared to the LaCoO₃, while the reaction orders of CO are 1.0 and − 1.5 for the LaCoO₃ and the LaCo_0.9O_3−δ, respectively. Based on these findings, we conclude that the LaCoO₃ follows the Mars-van Krevelen mechanism, utilizing lattice oxygen at high temperatures, while the LaCo_0.9O_3−δ operates via the Langmuir-Hinshelwood mechanism at lower temperatures due to its enriched adsorbed oxygen species. This underscores non-stoichiometry as an efficient catalyst design strategy for enhancing catalytic activity of perovskites in various oxidation reactions where adsorbed oxygen species play a crucial role.