The Relationship Of Crystal Plane Sensitivity Of Au/CeO₂ Modified By Rare Earth Elements And Catatlytic Performance

CeO₂ as an important material, has earned intensive interest due to the high thermal stability and cycling easily between reduced and oxidized states（Ce3+andCe4+）. It has been probed for many different applications in a vary of fields, such as active component of three-way catalysts（TWC）, full cells, and the water-gas shift reaction.The catalytic of performance of CeO₂ depends largely on its particle size, morpholgy and surface structures. Cerium oxide as the supporter, active metal dispersion on the Ce based supports is affected by the morphology of supports and structure. In recent years, some research work about the relation between cerium oxide morphology, crystal and Au catalyst activity were done in our groups. In this thesis, the surface structures and the properties of Au/CeO₂ are investigated by incorporating the metal into the cerium oxide lattice; The interaction between gold and ceria is studied considering the incorporation of other element into ceria lattice; The catalytic performances for CO oxidation and light degradation of methylene blue are tested, which reveals that the morphology and exposed crystal plane of supports affect the structure of gold catalyst, such as chemical state, stability and catalytic activity. Some interesting results are listed as follows:1. On the basis of successful preparation of cerium oxide nanorods and nanopiece, a small amount of rare earth elements Zr are introduced into cerium oxide crystal phase structure. The structure and redox properties of catalysts are studied systematically by XRD, HRTEM, TEM, TPR, solid UV- Vis characterization techniques, and the results are listed that:（1） In the CO catalytic oxidation reaction, CeO₂ nanorod with exposed crystal faces {111} shows higher catalytic activity, compared to CeO₂ pieces with exposed crystal faces {110}; the loading of gold further improves the catalytic activity, and Au/CeO₂-rod also shows higher activity for CO oxidation than Au/CeO₂-piece, which suggests that catalytic performance of Au/CeO₂ is related to the crystal planes of surpport.（2） A small amount of Zr is introduced into cerium oxide nanorods structure, it is found that the introduction of Zr do not change the morphology of ceria nanorods, but preferred crystal plane changes and increases {110} crystal plane; Cerium oxide structure defects are increased and the surface oxygen oxidation reduction ability is enhanced due to the introduction of Zr.（3） Au/Ce-Zr-O₂ shows higher catalytic activity for CO oxidation, CO conversion about 90 % is obtained over Au/Ce0.98Zr0.02O₂ at room temperature.2. A series of Ce_1-x PrxO₂ nanometer pieces and Au/Ce_1-xPrxO₂-450 materials are prepared. The morphology and crystal characteristics of samples are studied. Their catalytic activities for degradation of methylene blue are tested in light. It is found that:（1） The catalytic activity is related to the content of Pr, Ce0.7Pr0.3O₂ pieces have highest activity for degradation of methylene blue, and methylene blue degradation rate is 80 % under the sunlight for 4 hours,（2） The loading of Au improves the methyl blue degradation activity, An increased about 10 % in methyl blue degradation activity is obtained over Au/Ce_1-xPrxO₂ compared to Ce_1-xPrxO₂. The high active under the sunlight is ascribed to the enhanced absorption in the visible area due to the introduction of Pr and the plasm effect of nanogold.