Research Of Catalytic Performance And Active Sites Over Inverse CeO₂/CuO And CuO/CeO₂Catalysts For Preferential Co Oxidation

Hydrogen has been considered to be the most potential strategic energy and clear energy in the21st century. The development of fuel cells is one of the ideal hydrogen conversion devices, which leads to the development of hydrogen storage technology. One of the most typical applications is the proton exchange membrane fuel cell (PEMFC). However, the0.5-1.0vol%CO in the hydrogen feed gas degrades the performance of the electrodes which are highly sensitive to the presence of even traces of CO. Hence, it is essential to keep the CO concentration below100ppm in the hydrogen. The preferential oxidation of CO is a simple and cost effective technique for performing this ultimate CO removal It is generally accepted that the CuO-CeO2catalysts have been investigated extensively in recent years from an economical point of view, and also have shown promising catalytic performance for the CO oxidation process.In this dissertation, a series of inverse CeO2/CuO catalysts was prepared in order to explore influences of the morphology of CuO supports and the precipitants on catalytic performance. Meanwhile, the nature of CO oxidation over the typical CuO/CeO2and inverse CeO2/CuO catalysts is also explored in order to search the active sites and investigate the decisive factors in this system. The crystalline structure and properties of the catalysts were characterized by XRD, H2-TPR, SEM, TEM/HRTEM, XPS, in situ XRD, Raman, in situ UV-VIS and N2adsorption-desorption techniques. The main contents of the thesis are as follows:1. The inverse CeO2/CuO catalysts with different-morphology supports were prepared using the precipitation-impregnation method and tested for CO preferential oxidation under different space velocity. The study shows that CO oxidation takes place at the interface of CeO2-CuO catalyst. The CeO2/CuO catalysts maintain their morphologies, structure and the length of periphery at the CeO2-CuO interface during the reaction. The two-dimensional and homogeneous petal morphology of support is most favorable for the formation of long periphery at the CeO2-CuO interface, therefore the CeO2supported on the CuO with petal morphology presents good catalytic activity.2. A series of inverse CeO2/CuO catalysts using different precipitants was prepared by the reverse microemulsion-impregnation method in order to investigate the influences of precipitants on catalytic performance. It is found that the CeO2/CuO catalysts using urea, NaOH and TMAH precipitants can maintain some amount of copper-ceria interfacial sites before185℃in the reaction, and the existence of H2offers an additional way to oxidize CO at low temperture because of the formation of hydroxyl groups (OH*).3. The CuO-CeO2catalysts were prepared via the surfactant-templated method aiming at comparing the traditional CuO/CeO2and inverse CeO2/CuO catalysts and finding the real reasons for the different catalytic performance. The study shows that there are two kinds of surface sites in the CuO-CeO2system, including CuO surface sites for CO chemisorption and CeO2surface sites with oxygen vacancies. The active sites for CO oxidation may be located on the contact interface of two-kind surface sites. The composition, content and BET surface area are three important factors for the CuO-CeO2catalysts if they are expected to achieve high activity and wide full CO conversion window. The Ce4Cu4and Ce4Cu1catalysts exhibite best resistance ability to H2O and CO2because of high BET surface area.