| Manganese oxides are useful in heterogeneous catalysis as they are relatively inexpensive and abundant, and have a number of stable oxidation states. Typically, these catalysts are prepared by supporting the oxide on a suitable support material through impregnation techniques. The impregnation technique, while simple and convenient, can lead to micro-crystallite formation on the surface of the support especially at high metal loadings. Grafting loading techniques can be utilized to achieve highly dispersed surface active sites, which are uniform in composition and distribution. Here, the controlled deposition of manganese oxide sub mono-layers achieved through a grafting reaction between manganese alkoxides and gamma-alumina surface hydroxyl groups is reported. By optimizing reaction conditions, it was possible to use an ethanol solution of manganese(II) ethoxide to load up to 6.14 +/- 0.02% Mn on the alumina support. Additionally, the use of commercially available manganese(II) methoxide dissolved in methanol was used to load up to 3.87 +/- 0.05% Mn on the alumina support. Both values represent the highest reported manganese loadings achieved via grafting on gamma-alumina supports.;A number of techniques, including: TGA, XRD, XPS, EPR, UV/Vis, N 2 adsorption and TPR were used to characterize the surface structures and physical properties of grafted and impregnated gamma-alumina supported manganese oxide catalysts. Both loading techniques produced surfaces with a majority of supported manganese atoms in the Mn+3 oxidation state. Both catalyst synthesis techniques produced redox active materials with Mn+3/Mn+2 the most likely redox pair. However, the impregnated catalysts appeared to have a lesser extent of reduction, presumably due to the presence of Mn2O3 micro-crystallites.;The presence of supported manganese oxide limited thermally induced loss of support surface area, with the ethoxide grafted material limiting it the most. This is attributed to the impregnation and manganese methoxide grafting techniques producing multi-layers, micro-crystallites or oligomeric surface manganese oxides at the loadings investigated in this study, whereas the ethoxide grafting technique leads to a highly dispersed sub mono-layer of manganese oxide surface active sites at all achieved loadings. |
