Investigation of Mn-doping effects on the structural, morphological, thermal, and catalytic properties of Co3O 4 spinel nanoparticles towards CO oxidation

This study reports the synthesis of three sets of high-performance Mn-doped Co3O4 porous nanocrystals (PNCs) (5%Mn@Co3O4, 10%Mn@Co3O4, and 15%Mn@Co3O4) using a simple chemical co-precipitation method. These catalysts were then applied to the catalytic oxidation of carbon monoxide (CO). The investigation focused on the effects of Co2+ or Co3+ substitution by Mn2+ or Mn3+ within the Co3O4 matrix on various properties, including physiochemical characteristics, morphology, microstructure, reducibility, thermal stability, as well as their impact on catalytic performance. Comprehensive characterization techniques, including XRD, SEM, BET, XPS, H2-TPR, and DRIFT, were employed to elucidate the underlying factors responsible for effective CO oxidation. Compared to pure Mn3O4 and Co3O4, the Mn@Co3O4 PNCs catalyst exhibited a more controllable microstructure and a better dispersion of the active phase. The 5%Mn@Co3O4 catalyst demonstrated the highest activity, achieving 90% CO oxidation at 197 °C. This superior performance is attributed to its large specific surface area, excellent reduction capacity, and abundant oxygen species and vacancies. H2-TPR and XPS analysis provided further insights into the reaction mechanism. Density functional theory (DFT) calculations showed that the formation of oxygen bulk vacancies is more favorable for when Mn dopants occupy Co2+ sites. Overall, the chemical co-precipitation method offers a straightforward and cost-effective approach for producing Mn@Co3O4 catalysts suitable for CO abatement in exhaust and flue gases