Controlled Preparation Of Porous Oxide-Supported Catalysts And Their Catalytic Performance For The Oxidation Of Carbon Monoxide And Toluene

In recent years, the atmospheric pollution in our country (especially in Beijing) has become more and more serious. It is highly required to control the emission of atmosphere pollutants. Carbon monoxide and volatile organic compounds (VOCs) are the main components of atmosphere pollutants. Catalytic oxidation is one of effective pathways for the removal of CO and VOCs, in which the key issue is the availability of high-performance catalysts. Therefore, it is of academic and practical significance to develop novel and high-performance catalytic materials that are used to remove CO and VOCs. Supported noble metal catalysts possess good low-temperature activities and strong anti-poisoning ability, whereas porous materials have high surface areas and easy transfer for reactant molecules. Hence, porous materials-supported noble metal catalysts are expected to perform well in the oxidation of CO and VOCs. Since performance of a supported noble metal catalyst is usually associated with several factors, such as size and shape of noble metal nanoparticles (NPs), chemical state of active noble metal species, nature of the support, interaction between noble metal NPs and support, preparation approach, and pretreatment condition, it is highly desirable to investigate the controlled preparation of supported noble metal catalysts and their catalytic properties for the removal of CO and VOCs. In this dissertation, solvothermal, colloidal crystal-templating, incipient wetness impregnation, and reduction methods were employed to prepare regularly morphological porous Co3O4 monodispersed microshpheres and three-dimensionally ordered meso-macroporous oxides (3DOM SiO2,3DOM Al2O3, and 3DOM CeO2-Al2O3) and their supported noble metal or transition-metal oxide nanocatalysts. A number of characterization techniques were used to determine the physicochemical properties of the materials, and their catalytic activities for the oxidative removal of typical atmospheric pollutants (e.g., carbon monoxide and toluene) were evaluated. By so doing, the "structure-performance" relationships of the catalysts were elucidated, the involved catalytic mechanisms were clarified, and the corresponding catalytic reaction kinetic equations were established. It is envisioned that the results obtained in the proposed project can provide a useful guidance on designing novel catalytic materials with high performance and developing the relevant catalytic technologies. The utilization of such novel and effective catalysts in eliminating the typical atmospheric pollutants at low temperatures can give rise to improvement in atmospheric environment quality. The main results of the investigations are as follows:(1) Porous cube-aggregated monodisperse Co3O4 microspheres and their supported gold (xAu/Co3O4 microsphere; x=1.6-7.4 wt%) NPs were prepared via the glycerol-assisted solvothermal and PVA-protected reduction routes, respectively. The Co3O4 displayed a porous cube-aggregated monodisperse microspherical morphology, and the sizes of Au NPs were in the range of 3.2-3.9 nm. Among the xAu/Co3O4 microsphere catalysts,7.4Au/Co3O4 microsphere possessed the highest Oads concentration and the best low-temperature reducibility, thus showing the highest catalytic activity for CO oxidation (T9o%=-8 ℃ at SV= 20,000 mL/(g h)) and toluene oxidation (T9o%= 250℃ at SV= 20,000 mL/(g h)). The xAu/Co3O4 microsphere catalysts exhibited an apparent activation energy of 40.7-53.6 kJ/mol for toluene oxidation and an apparent activation energy of 21.6-34.6 kJ/mol for CO oxidation. It is concluded that the excellent catalytic performance of 7.4Au/Co3O4 microsphere might be associated with its higher Oads concentration, better low-temperature reducibility, and stronger interaction between Au NPs and Co3O4 as well as the porous microspherical structure.(2) The 3DOM SiO2, zMnOx/3DOM SiO2, and yAu/zMnOx/3DOM SiO2 samples were prepared using the PMMA-templating, incipient wetness impregnation, and PVA-protected reduction methods, respectively. The yAu/zMnOx/3DOM SiO2 samples displayed a hierarchically 3DOM architecture (macropore diameter=180-200 nm and mesopore diameter=4-6 nm) and a surface area of 220-318 m2/g. MnOx NPs with a size of 18.7-25.7 nm and Au NPs with a size of 3.6-3.8 nm were uniformly dispersed on the surface of 3DOM SiO2. Among the yAu/zMnOx/3DOM SiO2 samples, 0.93Au/11.2MnOx/3DOM SiO2 possessed the highest Oads concentration and the best low-temperature reducibility, thus exhibiting the highest catalytic activity for toluene oxidation (T9o%= 255 ℃ at SV= 20,000 mL/(g h)). Based on the activity data and characterization results, it is concluded that the good performance of 0.93Au/11.2MnOx/3DOM SiO2 was associated with its higher Oads concentration, better low-temperature reducibility, and stronger interaction between Au and MnOx NPs as well as the unique bimodal macro-/mesoporous structure.(3) The 3DOM Al2O3,_yCo3O4/3DOM Al2O3, and xPt/yCo3O4/3DOM Al2O3 samples were prepared by adopting the PMMA-templating, incipient wetness impregnation, and PVA-protected reduction strategies, respectively. The xPt/yCo3O4/3DOM Al2O3 samples displayed a hierarchically 3DOM architecture (macropore diameter 180-200 nm and mesopore diameter= 4-6 nm) and a surface area of 94-100 m2/g. Co3O4 NPs with a size of 18.3 nm and Pt NPs with a size of 2.3-2.5 nm were well dispersed on the surface of 3DOM Al2O3. Among the xPt/yCo3O4/3DOM Al2O3 samples,1.3Pt/8.9Co3O4/3DOM Al2O3 possessed the highest Oads concentration and the best low-temperature reducibility, thus giving rise to the highest catalytic activity (T9o%= 160 ℃ at SV= 20,000 mL/(g h)) for toluene oxidation. It is concluded that the highly dispersed Pt NPs, high Oads concentration, good low-temperature reducibility, and strong interaction between Pt and CO3O4 NPs as well as hierarchically ordered macro-/mesoporous structure were responsible for the excellent catalytic performance of 1.3Pt/8.9Co3O4/3DOM Al2O3.(4) The 3DOM yCeO2-Al2O3 and xM/3DOM yCeO2-Al2O3 (M= Au, Ag, Pd, and Pt) samples were prepared using the PMMA-templating and PVA-protected reduction methods, respectively. The xM/3DOM yCeO2-Al2O3 samples showed a hierarchically 3DOM structure with a macropore diameter of 180-200 nm, a mesopore diameter of 4-6 nm, and a surface area of 102-108 m2/g. Noble metal NPs with a size of 3-4 nm were highly dispersed on the surface of 3DOM 26.9CeO2-Al2O3. Among the xM/3DOM 26.9CeO2-Al2O3 samples,0.27Pt/3DOM 26.9CeO2-Al2O3 possessed the highest Oads concentration and the best low-temperature reducibility, thus resulting in the highest catalytic activity for toluene oxidation (T9o%=198 ℃ at SV= 20,000 mL/(g h)). The introduction of water vapor to the feedstock could promote the oxidation of toluene. The apparent activation energies obtained over the xM/3DOM 26.9CeO2-Al2O3 samples were in the range of 46-100 kJ/mol. It is concluded that the higher Oads concentration, better low-temperature reducibility, and stronger interaction between Pt NPs and 3DOM 26.9CeO2-Al2O3 as well as the unique bimodal macro-/mesoporous structure were accountable for the good performance of 0.27Pt/3DOM 26.9CeO2-Al2O3.