The Morphology And Size Effect For Catalytic Oxidation Of Toluene Over The Ce-based Metal Oxides

With the development of economy, the confliction between the development andenvironment became more and more prominent The air pollution was one of the most seriousproblems. The VOCs （volatile organic compounds） were the main air pollutants from theindustry. Catalytic oxidation was one of the most promising methods to degrade the VOCs tothe harmless CO₂and water. And the research emphasis of catalytic oxidation was thedevelopment of the catalysts.Ceria was an important rare-earth metal oxide with high oxygen storage capacity, whichwas extensively applied in the heterogeneous catalytic reactions. MnOx was one of the mostactive catalysts for VOCs oxidation. The mixed metal oxides were generally more active thanthe single metal oxide due to their synergistic effect between their structures. On account ofthese viewpoints, various shapes of Ce-based nanomaterials were prepared and theirmorphology-dependent catalytic activities were studied. Furthermore, the comparison ofcatalytic activities between the hollow and solid polyhedral MnOx have been done as well.The main contents and conclusions are as follows:（1） Ceria nanorods were synthesized through ultrasonic-assisited hydrothermal reactionmethod with cerium acetate and NaOH solution. The effect of synthetic conditionson the shape and yield of nanorods products, including the cerium source, the baseconcentration, the temperature and time of hydrothermal reaction and theultrasonication time, were discussed. And the optimal conditions were obtained.（2） The ceria nanopartiacles were obtained by the same route of nanorods with thecerium nitrate. The nanocubes were prepared by changing temperature and time ofthe reaction and the base concentration. Then, it was found that the nanorods werethe most active one since they mainly exposed the active planes （200）and（220）.（3）CeO₂nanorods with various aspect ratios were controllably synthesized. The lengthand diameter of CeO₂nanorods could be controlled by tuning the hydrothermalreaction time and the concentration of NaOH solution. The diameter was influencedonly by the concentration of NaOH solution. The length of the nanorods wasimpacted not only by the reaction time, but also by the concentration of NaOHsolution. The catalytic activities were related with the diameter of the nanorods.The smaller the diameter, the better the performance, and the samples with the similar diameter had the similar activity.（4） On the basis of the research on ceria nanorods, various content of Mn were addedinto ceria to form the nanorod-structured Mn-Ce mixed oxides. The best catalysthas been optimized. The effect of the active lattice oxygen and the stability of thecatalyst were both studied.（5） The mechanism for toluene oxidation has been deduced preliminarily through themeans of in situ FTIR.