| A large number of volatile organic solvents, such as aromatics, alcohols, esters, ketones, etc., are emitted from industrial, transportation, and decoration activities. Most of volatile organic compounds (VOCs) are harmful to the atmosphere and human health. Therefore, the control of the VOCs emissions has gained much attention. Among the methods for VOCs elimination, catalytic oxidation has been recognized as one of the most effective pathways, in which catalyst is the key to achieving a high efficiency in VOCs removal. Although noble metal catalysts exhibit excellent low-temperature activities, they are expensive and thus their wide applications are limited. Base metal oxides and their mixed oxides show good catalytic performance for the oxidation of VOCs, but most of them possess lower surface areas and lack well-developed porous structure, which influence the improvement in low-temperature activity. Therefore, it is of both theorectical and practical significance to develope transition-metal oxide catalysts with high surface areas and highly porous structures. It has been demonstrated that transition-metal oxides, such as chromia, iron oxide, and cobalt oxide, perform well in catalyzing the oxidation of VOCs. In order to further enhance the catalytic performance, we investigated the templating strategies for the fabrication of mesoporous chromia, iron oxide, and cobalt oxide, characterized the physicochemical properties of these mesoporous materials by means of techniques, such as nitrogen adsorption-desorption (BET), X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), temperature programmed reduction (TPR), ultraviolet-visible (UV-vis) reflectance diffuse spectroscopy, and Fourier transform infrared (FT-IR) spectroscopy, thermogravimetric analysis (TGA), and differenctial scanning calorimetry (DSC). The catalytic activities of the materials were evaluated for the complete oxidation of typical VOCs, such as toluene, formaldehyde, methanol, acetone, and ethyl acetate. In addition, mesoporous samarium oxide and europium oxide were aslo synthesized and characterized. The main results obtained in the investigations are as follows:1. Three-dimensional (3D) ordered mesoporous chromia catalysts were fabricated using solvent-free thermal treatment and ultrasound-assisted impregnation methods with 3D ordered mesoporous silica (KIT-6) as hard template. The results show that the as-fabricated mesoporous chromia catalysts exhibited high specific surface areas (106?124 m2/g), 3D ordered mesoporous structures, excellent low-temperature reducibility, multiple-oxidation-state chromium coexistence, and high oxygen adspecies concentrations. The mesoporous chromia (meso-Cr-240) derived by the solvent-free thermal treatment method in autoclave at 240 oC performed the best for the oxidation of toluene and ethyl acetate under the conditions of space velocity = 20000 mL/(g h) and toluene or ethyl acetate concentration = 1000 ppm, the corresponding temperatures for achieving 90% conversion were 234 and 190 oC, and the apparent activation energy was 79.8 and 51.9 kJ/mol, respectively. The mesoporous chromia (meso-CR-400) obtained by the ultrasound-assisted impregnation method and after calcination at 400 oC showed the best catalytic performance for the oxidation of formaldehyde, acetone, and methanol; at a VOC conversion of 90% under the conditions of space velocity = 30000 mL/(g h) and VOC concentration = 500 ppm, the reaction temperature was 117, 124, and 130 oC, and the apparent activation energies were 45.6, 49.7, and 50.8 kJ/mol, respectively.2. The 3D ordered and wormhole-like mesoporous iron oxides were synthesized employing the vacuum impregnation and citric acid (CA)-assisted thermal decomposition methods with KIT-6 as hard template, respectively. It is shown that 3D ordered mesoporous iron oxide (Fe-KIT6-400) and wormhole-like mesoporous iron oxide (Fe-CA-400) obtained after calcination at 400 oC possessed the highest surface areas (113 and 165 m2/g, respectively). Among the as-synthesized catalysts, the Fe-CA-400 one exhibited the best low-temperature reducibility and the highest oxygen adspecies amount. Over the Fe-CA-400 catalyst under the conditions of space velocity = 20000 mL/(g h) and VOC (acetone or methanol) concentration = 1000 ppm, the temperatures required for a VOC conversion of 90% were 186 and 189 oC, respectively, and the corresponding apparent activation energies were 70.7 and 60.9 kJ/mol.3. The 3D ordered mesoporous cobalt oxides were prepared by the vacuum impregnation method with 3D mesoporous silica KIT-6 and SBA-16 as hard template. The results show that the pore structure of the as-prepared cobalt oxide was associated with that of the hard template. The surface areas of the mesoporous cobalt oxides were 118?121 m2/g. These mesoporous cobalt oxide materials possessed exceptional low-temperature recibility and rich oxygen adspecies. The mesoporous cobalt oxide derived with KIT-6 as hard template showed the best activity for the oxidation of toluene and methanol (i.e., the temperature at VOC conversion = 90% was 180 and 139 oC, respectively), and the corresponding apparent activation energies were 59.9 and 50.1 kJ/mol. 4. The samarium oxide and europium oxide nanoparticles and their mesoporous counterparts were generated by the surfactant-assisted and ultrasound-assisted impregnation (with KIT-6 as hard template) methods using nitrates of samarium and europium as metal source. It is shown that spherical Sm2O3 and Eu2O3 nanoparticles with surface areas of 44?49 m2/g were obtained using sodium dodecyl sulfate surfactant, whereas rod-like Sm2O3 and Eu2O3 nanoparticles with surface areas of 34?37 m2/g were prepared employing poly(N-vinyl-2-pyrrolidone) surfactant. The mesoporous Sm2O3 and Eu2O3 with surface areas of 134?166 m2/g were generated via the ultrasound-assisted impregnation route with KIT-6 as hard template. These nano-sized and mesoporous rare earth oxides displayed strong absorption in the ultraviolet region, such unique properties were associated with the particle morphologies and crystal structure of the materials.
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