Cooperative catalytic role of Co and Mn sites on LaCoₓMn₁₋ₓO₃ perovskite nanoparticles in CO and NO oxidation

Abstract

Perovskites have significant potential to improve efficiency, reduce the costs of conventional oxidation catalysts, and contribute to cleaner and more sustainable energy solutions. However, numerous structural factors influencing their catalytic performance are still a subject to debate. In this study, simple perovskite nanoparticles in the form of LaCoO3 (LC) and LaMnO3 (LM), as well as LaCoxMn1–xO3 (LCM)-mixed B-site perovskites with different B-site cations, were synthesized and their performances in CO oxidation and NO oxidation reactions were examined. The LaCo0.8Mn0.2O3 catalyst exhibited the highest catalytic activity in both CO and NO oxidation reactions, surpassing the 1 wt benchmark nanoparticle catalyst and other currently investigated perovskite nanoparticles. Co sites (predominantly Co3+) in the optimized LaCo0.8Mn0.2O3 catalyst were found to be enriched in electron density, while Mn sites (mostly in Mn4+ form) were found to be more electron deficient as opposed to LC and LM. LaCo0.8Mn0.2O3 not only released significantly greater amounts of oxygen and generated larger extents of oxygen vacancies than LC and LM under reducing conditions but also achieved this at favorably lower temperatures. In light of the current results, we report that Co sites in LCM operate as the main active site during both CO and NO oxidation by enabling stabilization and activation of O2 (ads), while Mn sites mainly serve as promoters by increasing the adsorption strength of CO (ads) and NO (ads) as well as facilitating oxygen vacancy formation and vacancy regeneration, where oxygen vacancies were also found to contribute particularly to the NO oxidation reaction within the currently investigated thermal window. These findings demonstrate that the electronic properties of LCM can be systematically tailored at the nanometer scale in a versatile manner to address different reactivity requirements of challenging catalytic reactions.