The influence of preparation method on the structure and redox properties of mesoporous Mn-MCM-41 materials

Mesoporous silica materials modified by manganese have been prepared using surfactants containing different numbers of carbon atoms. Manganese has been introduced by the direct hydrothermal (HT), template ion-exchange (TIE) and impregnation methods. Structural properties have been investigated by the nitrogen adsorption–desorption, X-ray diffraction (XRD) and FT-IR studies. Redox properties have been investigated by the temperature-programmed reduction method (TPR) and transient CO oxidation reaction. It has been found that structural properties are strongly related to the type of surfactant used, the amounts and the way of Mn introduction. Large distortion effects are observed for samples prepared by the TIE method. Reducibility of the samples containing different pore dimensions and Mn loadings, prepared by TIE method, are very similar. Manganese oxide species in the catalysts of narrow pores and containing small amounts of manganese obtained by the HT and impregnation methods show low reducibility. During CO oxidation reaction some deactivation processes are observed for catalysts prepared by different methods and containing small amounts of Mn. A slight increase in activity for catalysts containing larger amounts of manganese is observed after high temperature treatment. Such changes are attributed to the interaction of manganese with silica and changes of oxidation state during thermal treatment.