Mesoporous Silica-Supported Manganese Oxides for Complete Oxidation of Volatile Organic Compounds: Influence of Mesostructure, Redox Properties, and Hydrocarbon Dimension

Manganese oxides supported on ordered mesoporous silicas and nonordered commercial silicas were comparatively studied in terms of physical properties and catalytic behavior in the complete oxidation of propane, <i>n</i>-decane, toluene, and <i>p</i>-cymene. Manganese oxides are well-dispersed on large-pore SBA-15, KIT-6, and commercial silicas, whereas they agglomerate on small-pore HMS and MCM-41. Mn/SBA-15 contains oxide species with the best reducibility, but its two-dimensional mesopores are significantly blocked. The alkane removal efficiency depends on the amount of accessible manganese oxides; therefore, the three-dimensional Mn/KIT-6 shows better performance than the pore-blocked Mn/SBA-15. In contrast, the ignition of aromatic hydrocarbons, which needs higher temperatures than alkanes, seems more strongly dependent on the reducibility, and Mn/SBA-15 shows the lowest ignition temperatures. Despite their much smaller surface areas, nonordered commercial silicas present significant advantages in the catalytic removal of large-molecule hydrocarbons due to the favorable mass transfer in the short mesopores within their thin particles