Copper–manganese (Cu–Mn) mixed oxide catalysts were prepared by a coprecipitation technique from metal nitrates in aqueous solution using tetramethylammonium hydroxide (TMAH) as a pH regulator. The structures and properties of the mixed oxide catalysts were investigated by X-ray diffraction, extended X-ray absorption fine structure, X-ray photoelectron spectroscopy and H₂-TPR studies. Spinel-type mixed oxides were mainly formed in the Cu–Mn mixed oxides in which Cu and Mn species occupied both tetrahedrally and octahedrally coordinated sites. The occupancy of Cu and Mn in these sites depended on the Cu/Mn ratio. The average oxidation state of Cu was evaluated to be 2+ and was almost independent of the Cu/Mn ratio; reduced Cu species were also formed on the surface sites. By incorporation of Cu into Mn oxides, the average oxidation state of Mn increased both in the bulk sites and on the surface sites. The concentration of Mn on the surface sites was higher than that in the bulk sites. The Cu–Mn mixed catalysts exhibited higher activity than corresponding single-metal oxides at the reaction temperature range of 343–403 K. Formation of Cu–Mn spinel-type oxides gave rise to the increase in the catalyst surface area and the rate for CO oxidation normalized by surface area, and the Cu–Mn mixed oxides with the Cu/Mn molar ratio of 1 exhibited the highest activity for CO oxidation. CO-TPR studies revealed that in the temperature range of 343–403 K, the lattice oxygen at the first layer of the mixed oxides reacted with CO to form CO₂.

Gas-solid heterogeneous photooxidation of toluene over TiO₂ catalyst was studied to investigate the factors controlling the catalytic activities. The toluene photooxidation behavior on TiO₂ was strongly affected by the formation and oxidation behavior of intermediate compounds on TiO₂, and their accumulation decreased the reaction rate for toluene photooxidation. The formation and oxidation behavior of the byproduct compounds depended on the initial concentration of toluene and water vapor. In situ Fourier transform infrared (FTIR) studies revealed that water vapor promoted the cleavage of the aromatic ring and facilitated CO₂ formation. At the reaction temperature of 300 K, the deposition of Pt on TiO₂ suppressed CO formation, whereas catalytic activity was decreased due to the increase in the amount of intermediate compounds. On the other hand, Pt/TiO₂ showed higher activity than TiO₂ at 353 K, in spite of the increase of the intermediate compounds.

Catalytic oxidation of gaseous benzene using ozone over SiO₂-supported metal oxides (oxides of Mn, Fe, Co, Ni, and Cu) was performed at 343 K. The supported metal oxides were prepared from metal nitrates via impregnation followed by calcination at 873 K. X-ray diffraction studies revealed that aggregated metal oxides were formed on the supports. The quantities of the exposed metal oxides on SiO₂ were determined using temperature-programmed desorption of formic acid species adsorbed on the catalysts. The turnover frequencies (TOFs) for ozone decomposition and catalytic oxidation of benzene with ozone were also compared for the supported metal oxides. The TOFs for ozone decomposition with the supported metal oxides decreased in the order: Cu > Co ~ Ni > Fe > Mn. Conversely, the SiO₂-supported Mn oxide (Mn/SiO₂) catalyst exhibited the highest activity for catalytic oxidation of benzene with ozone and the highest efficiency for ozone utilization. FTIR studies revealed that benzene ring cleavage continuously proceeded on the Mn/SiO₂ catalyst, and oxygen-containing species, which were readily oxidized to CO₂ and CO in the presence of ozone, accumulated on the catalyst surface. The Fe-, Co-, Ni-, and Cu-oxides suffered from catalyst deactivation due to the build-up of by-product compounds, which was attributed to their low activity for oxidation of these substances. These results suggest that the most important steps in benzene oxidation with ozone on metal oxides are the formation and oxidation of by-product compounds. The higher activity of the Mn oxide catalyst for benzene oxidation is ascribed to the facile oxidation of these by-product compounds.