The improved reactivity of manganese catalysts by Ag in catalytic oxidation of toluene

[Display omitted] ► Ag/Mn ratio of 1:3 is an appropriate ratio for high activity for toluene oxidation. ► Ag enters into MnO2 phase and leads the formation of Ag1.8Mn8O16 and Mn2O3. ► The ratios of Mn3+/Mn4+and Olatt/Osurf on the Mn catalyst are increased by Ag. ► The oxygen mobility and reducibility of manganese oxides are enhanced by Ag. ► The formation of benzaldehyde is closely related with lattice oxygen of the catalyst. The effects of Ag on Mn/SBA-15 catalysts have been investigated in the toluene catalytic oxidation. The reactivity of catalysts is related closely to the Ag/Mn molar ratio, and the sample with 1:3 of Ag/Mn molar ratio exhibits the highest reactivity for toluene oxidation, with a complete conversion at 260°C. Based on the characterization results, it is found that Ag enters into MnO2 phase, and the Ag1.8Mn8O16 mixed phase forms. Meanwhile Ag leads to parts of MnO2 being transformed into Mn2O3. The Ag/Mn molar ratio has a strong influence on the molar ratio of the surface Mn4+ to Mn3+ and surface adsorbed oxygen (Oads) to lattice oxygen (Olatt) through the interaction between silver and MnOx. The coexistence of MnO2, Mn2O3, Ag1.8Mn8O16, and the strong interactions between Ag and Mn species exhibit a good synergetic interaction, which promotes the reducibility of catalysts and the formation of abundant active lattice oxygen, thus increasing the catalytic activity of toluene oxidation. And the formation of intermediate benzaldehyde should be closely link with the lattice oxygen of the Mn based catalyst.