Investigation of Mn-doping effects on the structural, morphological, thermal, and catalytic properties of Co3O4 spinel nanoparticle catalysts for CO oxidation

This study reports the synthesis of three sets of high-performance manganese (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 used for the catalytic oxidation of carbon monoxide (CO). This investigation focused on the effects of Co²⁺ or Co³⁺ substitution by Mn²⁺ or Mn³⁺ within the Co₃O₄ matrix on various properties of the PNCs, including their physicochemical characteristics, morphology, microstructure, reducibility, thermal stability, and their impact on the catalytic performance. Comprehensive characterization using techniques such as X-ray diffraction (XRD), scanning electron microscopy (SEM), Brunauer–Emmett–Teller (BET) analysis, X-ray photoelectron spectroscopy (XPS), Hydrogen-Temperature Programmed Reduction and (H₂-TPR), was employed to elucidate the factors responsible for effective CO oxidation. Compared to pure Mn₃O₄ and Co₃O₄, the Mn@Co₃O₄ PNCs catalysts exhibited a more controllable microstructure and 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 analyses provided further insights into the reaction mechanism. Density functional theory calculations showed that the formation of bulk oxygen vacancies is more favorable when Mn³⁺ is substituted at the Co²⁺ sites. Overall, the chemical coprecipitation method offers a straightforward and cost-effective approach for producing Mn@Co₃O₄ catalysts suitable for CO abatement in exhaust and flue gases.