Surface Functionalization of Mesoporous Co3O4 and MnOx with Sodium for the Soot Oxidation Reaction

The synthesis, characterization, and catalytic evaluation of two different mesoporous transition metal oxides (m-Co3O4 and m-MnOx) for the soot oxidation reaction are reported. The effect of sodium addition on the soot oxidation was studied, finding that the optimal sodium load for enhancing the catalytic performance of cobalt and manganese oxides was 7 wt%. Structural, morphological, and textural properties were studied and characterized by X-ray diffraction (XRD), Raman spectroscopy (RS), scanning electron microscopy (SEM), and physical nitrogen adsorption/desorption curves. Moreover, inductively coupled plasma mass spectrometry (ICP-MS) and X-ray photoelectron spectroscopy (XPS) were performed to explore the chemical species present in the materials. The results show that either the 7Na/m-Co3O4 or 7Na/m-MnOx catalyst presented remarkable enhanced activity for the soot oxidation reaction, reaching 50% of soot conversion at 278 and 285 °C, respectively. The enhanced catalytic activity of these catalysts could be explained by the addition of the alkaline metal ion, which improved the soot/catalyst contact. Furthermore, the interaction between sodium and Co or Mn promoted the production of oxygen vacancies and, consequently, the mobility of lattice oxygen. The 7Na/m-Co3O4 catalyst showed resistance to deactivation for five cycles.