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

CTAB templated Ce0.8Zr0.2O2 (CZ), MnOx-Ce0.8Zr0.2O2 (Mn-CZ), CeO2 and MnOx 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 MnOx 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 MnOx. 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 MnOx serve as a source of the active oxygen from the CZ lattice, enhancing CO oxidation at high temperatures.