Efficiency of manganese modified CTAB-templated ceria-zirconia catalysts in total CO oxidation

CTAB templated Ce_0.8Zr_0.2O₂ (CZ), MnO_x-Ce_0.8Zr_0.2O₂ (Mn-CZ), CeO₂ and MnO_x oxide catalysts were prepared by precipitation and tested in CO oxidation. Manganese was added to CZ oxide at the precipitation stage (Mn-CZ) or by impregnation of the precipitated CZ oxide with manganese salt (Mn-CZ IM). Despite the decrease in the specific surface area after modification with Mn, both Mn-modified catalysts showed the significant improvement in the catalytic performance. Mn-CZ IM exhibited better catalytic activity than Mn-CZ, which was explained by the different distribution of manganese in CZ found by the complex SEM-EDS, XRD, TPR, Raman spectroscopy, XPS, and EPR study. In Mn-CZ both Mn²⁺ and Mn³⁺ ions are incorporated into the CZ lattice and form particles of MnO_x phases uniformly distributed over the surface and in the bulk of CZ. In contrast, in Mn-CZ IM no manganese ions are embedded into the crystal lattice of CZ, while the surface of Mn-CZ IM comprises local areas mainly formed by CZ or MnO_x. Such arrangement provides the additional adsorption sites and the second redox pair (Mn³⁺/Mn²⁺) in addition to Ce³⁺/Ce⁴⁺, improving low-temperature efficiency, whereas the surface areas depleted with MnO_x serve as a source of the active oxygen from the CZ lattice, enhancing CO oxidation at high temperatures.