Preparation Of Co/Ce Nanocomposites And Their Appilcation In Catalytic Elimination Of NO_x

With the serious problems resulted from air pollution,more and more concerns have been concentrated on the development of exhaust gas treatment and purification technology.Among various emission control technologys,selective catalytic reduction of NO（SCR）was considered as an efficient way to deal with the NO_x which is one of the main air pollutant.Therefore,it is of significance and has become a hot topic to develop efficient SCR catalysts,improve its application range and understand the catalytic process.In this thesis,different Co/Ce contained metal oxides composited catalysts were synthesized.And the catalytic reduction abilities of NO by C₃H₆ over the obtained catalysts were evaluated.Moreover,the relationship among the structure,physicalchemical properties and catalytic activities of the catalysts were also analyzed,which was helpful for understanding the influence factos on catalytic activities in the composited system.The main works are summarized as follows:1.CeO₂ porous nanospheres and a series of Co₃O₄/CeO₂ composites with high surface area were successfully prepared.The structural composition of as-prepared catalysts were characterized by X-ray powder diffraction（XRD）,Fourier transform infrared（FTIR）,scanning electron microscopy（SEM）,transmission electron microscope（TEM）and Brunauer-Emmett-Teller（BET）measurements.The catalytic abilities for NO reduction over these catalysts were also tested.The results showed that Co₃O₄/CeO₂ composites exhibited special Co-Ce synergistic effect compare with single oxides.10% Co₃O₄/CeO₂ exhibited the strongest synergistic effect and good stability during the reaction.Based on this,as-prepared catalysts were further characterized by temperatureprogrammed reduction（TPR）and X-ray photoelectron spectroscopy（XPS）measurements.It was found that the synergistic effect of Co₃O₄/CeO₂ catalysts resulted in the increase of the relative content of Co3+ species,which was in good consistent with the catalytic activity test results.Therefore,it was proposed that the Co3+ was the main active species in Co₃O₄/CeO₂ composites,and its relative contents in Co3+/Co²⁺ was related to the catalytic activities of the catalysts.2.CuO/CeO₂ composites were prepared via combination of CeO₂ with CuO.Influence of syhthesis methods,Cu loading,supports and elements modification of the samples on its catalytic activities were systematic discussed.The results showed that CuO/CeO₂ composites prepared by precipitate-hydrothermal method could form an even and compact mesoporous structure with interconnected pore channels,which could deepen the synergistic effect,also beneficial for the heterogeneous catalysis process.Compared with other supports,CeO₂ supported CuO could result in the formation of subnanometric（CuO）x clusters and Cu²⁺ in the octahedral coordination,which also led to the enhancement of catalytic activity.Based on this,W and Ca elements was added during the support preperation process.It was found that the addition of W and Ca to CeO₂ supports could affect its morphology and change the crystallinity of composites,which inhibits the synergistic effect of composit catalysts.3.Co,Cu dual active components was used to synthesize composited catalysts via different synthesis methods.One-step,two-step and three-step method was adopted to synthesize Co-Cu-Ce termary composite respectively.And the addition of second active component,the content of relative components and composite precursor was studied to improve the catalytic activity of catalysts.The results showed that the addition of Cu could improve the crystallinity of mesoporous termary composite,and the addition of Co could improve the catalytic activity at low temperature.Moreover,the termary composite catalysts prepared by different composite precursor exhibited the similar catalytic activities.These results provided experimental basis for design and development of new type of efficient catalyst.