The Basic Research Of Performance Of Supported Copper-based Catalyst And Their Application In The Catalytic Reduction Of NO With CO

The burning of fossil fuels in motor vehicles meets the energy needs of society, while the release of a large number of pollutants has caused serious harm survival on atmosphere for human. Among them, the main harmful ingredients include:carbon monoxide (CO), nitrogen oxides (NO*), hydrocarbons (HC), soot particles and other toxic substances. How to effectively purify these pollutants has become an issue of lots of hot researches.Supported metal oxide catalysts are widely used in industrial and academic research. The investigation of the surface interaction between active components and promoter or support is significant to understand the nature of catalytic reactions and development the effective and practical catalysts. During my PhD period, the main research is involving in a series of supported copper oxide catalysts for catalyric reduction of NO by CO, which is one of the central reactions occurring in the three-way catalytic converters. Usually, there are two essential factors to affect the surface interaction between catalyst components, i.e., the intrinsic feature of active component (dispersion behavior, electrical structure) and the surface properties of support (redox, textural property). Tuning the surface interaction between active component and support is one of important strategies to improve catalytic properties. In this dissertation, we firstly prepared a series of copper oxide-based supported catalysts by changing the active component, support crystal structure, the addition method of promoter and the composition of mixed promoter. Then these catalysts were charaterizated by many technologies (BET, XRD, Raman, UV-vis DRS, TEM, XPS, TPR, in situ FTIR, and CO+NO model reaction) in order to study the role of each component and the catalytic performance in this model reaction, and establish the composition-structure-property relationship. The main results were shown as follows:1、The poor low-temperature (200-300℃) activity and N2selectivity of Cu-based catalysts for NO reduction by CO has driven us to further advance this process. The present work offered a simple but very promising strategy to achieve this goal by CO pretreating the binary CuO/MxOy/y-Al2O3(M=V, Mn, Fe, Co, Ni, Zn) catalysts to adjust the surface active sites. The results demonstrated that CO pretreatment significantly enhanced the low temperature NO conversion and N2selectivity of CuO/MxOy/γ-Al2O3, depending on the type of metal oxides. Among these catalysts, CO pretreated CuO/NiO/γ-Al2O3exhibited the highest activity/selectivity (i.e., about90%at200℃) and the excellent stability. The activity improvement probably resulted from the obtainment of more Cu+species, the decrease of apparent activation energy for NO conversion and the more favorable activation and dissociation of NO on the reduced surface, as evidenced by X-ray photoelectron spectroscopy (XPS) and in situ Fourier transforms infrared (FTIR) results.2、Acetic acid (HAc) aqueous was used as solvent in wetness impregnation to prepare CeO2modified γ-Al29O3support. With the help of HAc, the dispersion of CeO2on γ-Al2O3was significantly improved and the size of CeO2nanoparticles can be controlled through tuning the concentration of HAc aqueous. XPS analysis showed that the percentages of Ce3+in CeO2nanoparticles would vary with the size. Then we loaded CuO on the as-prepared Ce02-modified γ-Al2O3support and used NO reduction with CO as probe reaction to test the influences of impregnation solvent on the catalytic properties. The results demonstrated that the CuO/CeO2/y-Al2O3prepared in the solvent with volume ratio of20:1(H2O:HAc) had the highest activity in the NO+CO reaction. Combing the structural characterizations and catalytic performances, we thought that the size of the CeO2nanoparticles should be a key factor that affected the activities of Cu0/Ce02/y-Al2O3. CuO dispersed on CeO2nanoparticles with average size of ca.5nm should be the highest active sites for the NO+CO reaction.3、Three kinds of supported catalysts CuO/CeO2/γ-Al2O3with the same CuO/CeO2molar ratios for NO reduction by CO were prepared accurately by the stepwise impregnation (SI) and co-impregnation (CI) method, and characterized by XPS, TEM, UV-Vis etc.. Firstly, the CuO/CeO2/γ-Al2O3catalyst was obtained by impregnation Cu species and Ce species successively on γ-Al2O3support (CuO/CeO2/γ-Al2O3-SI and CeO2/CuO/γ-Al2O3-SI). We called this method stepwise impregnation. And another co-impregnated method was that Cu species and Ce species were supported onto the γ-Al2O3support simultaneously to get CuO/CeO2/γ-Al2O3catalyst (denoted as CuO/CeO2/γ-Al2O3-CI). The catalyst CuO/CeO2/γ-Al2O3-SI showed the best catalytic performance in all catalysts (CuO/CeO2/γ-Al2O3-SI, CuO/CeO2/γ-Al2O3-CI, CeO2/CuO/γ-Al2O3-SI). It suggested that the interaction between copper and cerium is critical to improve the catalytic performance. To our amazement is different impregnated strategies could lead to various catalytic performances resulting from interaction between active components and support, which was beneficial for us to design high efficiency catalysts in the future.