Preparation Of Manganese, Cobalt Oxide Catalysts And Their Application In Catalytic Combustion

Manganese oxide becomes an in important transition metal oxide material due to its special physical and chemical properties. Manganses oxide is widely used in catalytic materials, electrochemical, ion exchange, adsorption and other fields. Manganese dioxide nanoparticles have excellent catalytic activity in the toluene combustion because of its large surface areas and good redox behaviros. In the preparation process, the calcination temperature will be affect the catalyst phase, crystallinity, surface area, etc. Therefore, it is of academica signigicance to investigate the catalytic properties of manganese dioxide prepared in different calcination temperatures. Among the transition metal oxide, cobalt oxide is an important functional material. Cobalt oxide have a wide range of applications in the field of catalytic matericals, electrochemical, magnetic and gas sensors due to its noval physicochemical properties and unique magnetic properties. Up to now, cobalt oxide with various morphologies have been aynthesized, such as nanoparticles, nanorods/ nanowires/ nanobelts/ nanotubes, nanocubes, nanospheres, nanospheres, nanosheets, urchin-like shape and so on. As far as we know, morphology of the materials have a great impact on their relative performance. Thus, it is of practical significance to investigate the catalytic properties of cobalt oxide with different morphologies. The main contents of this thesis can be summarized as follows:1. A series of MnO2 catalysts prepared in different calcination temperatures have been synthesized by a sol-gel process using KMnO4 and fumaric aicd as precursor, and the catalytic properties in the toluene combustion of these products have been investigated. Results show that MnO2 catalyst calcined at 450℃ (450-MnO2) is nanoparticles with tetragonal in crystal structure. With the increase of calcination temperature, Mn2O3 crystal phase gradually formed and the size of the nanoparticles gradually increasing, while the surface area became smaller and reduction performance at low temperature gradually decreased, resulting in catalyst activity is getting worse. Under the conditions of tolunen concentration=4 g/m3 and space velocity (SV)=20,000 h-1, each of catalysts performed well in the combustion of toluene. Especially,450-MnO2 catalyst exhibiting the best performance because of its larger surface area, lower hydrogen reduction temperature and homogeneous nanoparticles, and the total conversion temperature of toluene is 206 ℃. This catalyst kept high catalytic activity for toluene combustion during 48 h stability test, which indicated that the 450-MnO2 catalyst possess good stability.2. Different morphologies of Co(C03)0.5(OH)-0.11H2O precursors were prepared by solvothermal method with the cobalt nitrate as cobalt source, urea as homogeneous precipitation agent, PEG 600, PEG 400, and EG aqueous solution as solvent, respectively. After calcining the prepared Co(CO3)0.5(OH)·0.11H2O precursors at a certain temperature, Co3O4 with different morphologies were successfully synthesized. Moreover, it has been explored the catalytic properties in the dimethyl ether (DME) combustion of these Co3O4. Results show that it can be obtained urchin-like, rod-like, and wire-like Co3O4 with PEG 600, PEG 400, and EG aqueous solution as solvent, respectively. All of these Co3O4 possessed the spinel cubic structure. It is shown that the urchin-like Co3O4, rod-like Co3O4, and wire-like Co3O4 catalysts possessed a surface area of ca.69.43,55.87, and 76.78 m2/g, respectively. Under the conditions of DME/O2/He molar ratio=1/10/40, and space velocity = 30,000 h-1, urchin-like, rod-like, and wire-like Co3O4 catalysts exhibit excellent catalytic activity in the combustion of DME. The best-performing wire-like Co3O4 catalyst could effectively catalyze the DME combustion at lower temperatures (T10=141℃ and T90=152 ℃ at space velocity = 30,000 h-1) due to its larger surface area and better low-temperature reducibility.