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Highly ordered mesoporous MnO2 and Co3O4 are prepared by adopting an SBA-16-based nanocasting strategy under ultrasonic irradiation and characterized by means of numerous techniques. It is shown that the as-fabricated manganese and cobalt oxides possess well-ordered mesoporous architectures with polycrystalline pore walls. With the assistance of ultrasonic waves, the metal precursors can readily diffuse from the bulk solution to the inner pores of the silica template. The repeated four-step fabrication process, filling → filtration → washing → calcination, is beneficial for preventing the formation of manganese or cobalt oxide nanoparticles on the external surfaces of the template and facilitating more metal precursors to fill the mesopore channels of the template. After removal of the silica template by a 2 mol/L NaOH aqueous solution, the as-received highly ordered mesoporous MnO2 and Co3O4 exhibit a surface area of up to 266 and 313 m2/g, respectively, which is about 2−3 times higher than that reported in the literature. The mesoporous MnO2 and Co3O4 samples are more readily reduced at low temperatures and show much better catalytic performance for toluene complete oxidation than their bulk counterparts. The excellent performance of the mesoporous materials is ascribed to their ordered mesoporous structure, better reducibility, and high surface area.

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Mesoporous chromia with ordered three-dimensional (3D) hexagonal polycrystalline structures were fabricated at 130, 180, 240, 280, and 350 degrees C in an autoclave through a novel solvent-free route using KIT-6 as the hard template. The as-obtained materials were characterized (by means of X-ray diffraction, transmission electron microscopy, N(2) adsorption-desorption, temperature-programmed reduction, and X-ray photoelectron spectroscopy techniques) and tested as a catalyst for the complete oxidation of toluene and ethyl acetate. We found that with a high surface area of 106 m(2)/g and being multivalent (Cr(3+), Cr(5+), and Cr(6+)), the chromia (meso-Cr-240) fabricated at 240 degrees C is the best among the five in catalytic performance. According to the results of the temperature-programmed reduction and X-ray photoelectron spectroscopy investigations, it is apparent that the coexistence of multiple chromium species promotes the low-temperature reducibility of chromia. The excellent performance of meso-Cr-240 is because of good 3D mesoporosity and low-temperature reducibility as well as the high surface area of the chromia. The combustion follows a first-order reaction with respect to toluene or ethyl acetate in the presence of excess oxygen, and the corresponding average activation energy is 79.8 and 51.9 kJ/mol, respectively, over the best-performing catalyst.

A series of La(1-x)Sr(x)M(1-y)Fe(y)O(3) (M = Mn, Co; x = 0, 0.4; y = 0.1, 1.0) perovskite-type oxide catalysts have been fabricated via a strategy of citric acid complexation coupled with hydrothermal treatment. The materials are characterized by a number of analytical techniques. The oxidation of toluene is used as a probe reaction for the evaluation of catalytic performance. It is found that both La(0.6)Sr(0.4)FeO(3) and LaFeO(3) exhibit high activities. The partial substitution of manganese and cobalt with iron can significantly improve the catalytic performance of La(0.6)Sr(0.4)MnO(3) and La(0.6)Sr(0.4)CoO(3). At toluene/O(2) molar ratio = 1/200 and space velocity = 20,000 h(-1), the catalytic activity decreases in the sequence of La(0.6)Sr(0.4)Co(0.9)Fe(0.1)O(3) > La(0.6)Sr(0.4)FeO(3) > La(0.6)Sr(0.4)Mn(0.9)Fe(0.1)O(3) > LaFeO(3) > La(0.6)Sr(0.4)CoO(3) > La(0.6)Sr(0.4)MnO(3). Compared to the Fe-free counterparts, the La(0.6)Sr(0.4)Mn(0.9)Fe(0.1)O(3) and La(0.6)Sr(0.4)Co(0.9)Fe(0.1)O(3) catalysts are, respectively, 50 and 85 degrees C lower with regard to the temperature required for complete toluene oxidation. Toluene can be completely oxidized at 245 degrees C over La(0.6)Sr(0.4)Co(0.9)Fe(0.1)O(3). The excellent catalytic performance of La(0.6)Sr(0.4)Co(0.9)Fe(0.1)O(3) can be attributed to the presence of (i) Fe(3+)-O-Fe(4+) couples, (ii) a transition of electronic structure, and (iii) a trace amount of Co(3)O(4).