Preparation Of Mesoporous Metal Oxides And Applied For CO Catalytic Oxidation

Catalytic CO oxidation has attracted considerable attentions because of its great values in fundamental research and many practical applications such as energy sources, environment, health and safety, and so on. Among the methods for CO elimination, catalytic oxidation has been recognized as one of the most effective pathways, in which catalyst is the key to achieving a high efficiency in CO removal. Although noble metal catalysts are catalytically more active at low temperature in comparison with the other metal oxides, the high cost, limited availability, and low resistance to halogens greatly restrict their large-scale application. Base metal oxides and their mixed oxides show good catalytic performance for CO catalytic oxidation, but most of possess lower surface areas and lack well-developed porous structure, which influence the improvement in catalytic activity. Therefore, it is of both theorectical and practical significance to develop transition metal oxide catalysts with high surface areas and highly porous structures. In this paper, we detailed study the CeO2 and they mixed oxides catalysts with different pore structures for CO catalytic oxidation. Their pore structures and physicochemical properties were characterized by XRD、BET、TEM、Raman、FTIR、XPS、H2-TPR techniques. The materials were evaluated for their catalytic activity in the CO oxidation reaction. The main results obtained in the investigations are as follows:1. Three kinds of CeO2 nano-materials with different pore structures, i.e., mesoporous, microporous and nanoparticle CeO2, were synthesized. Mesoporous CeO2(meso-CeO2) and microporous CeO2(micro-CeO2) were prepared by adopting the mesoporous silica KIT-6 and microporous high silica ZSM-5 as templates, respectively. And CeO2 nanoparticles(nano-CeO2) were synthesized by precipit ation method. The palladium loaded meso-CeO2, micro-CeO2 and nano-CeO2 supports were evaluated for the catalytic oxidation CO reaction. The Pd/meso-CeO2 exhibited the highest catalytic activity, and complete conversion temperature was about 50 oC for CO oxidation. According to the analysis, the good catalytic performance of Pd/meso-CeO2 is related not only to the large BET surface area, small particle size and 3D mesoporous structure, but also correlated to the active oxygen species on the surface of catalyst.2. Transition metal(Co, Cu, Fe)-doped CeO2 catalysts with the three-dimensional mesoporous channels have been synthesized through a nanocasting route using three-dimensional mesoporous silica KIT-6 as the template. All four catalysts exhibit high surface area(>120m2g-1) and ordered mesopore. he research results showed that the introduction of promoter(Co, Cu and Fe species) can effectively enhance the chemisorbed oxygen and oxygen vacancy concentration on the surface of metal-doped CeO2 catalysts. Compared with Co and Fe species, the Cu species have an obvious enhancement. The catalysts were evaluated for the catalytic oxidation CO reaction. The Cu-doped CeO2 catalyst exhibits a highest catalytic activity, and complete conversion temperature was about 55 oC for CO oxidation.3. By using mesoporous silica KIT-6 with different hydrothermal temperature as a template, Cu-doped CeO2 catalysts with different pore diameter were successfully prepared. When KIT-6-50(hydrothermal synthesis of mesoporous silica KIT-6 temperature was 50oC) and KIT-6-100(hydrothermal synthesis of mesoporous silica KIT-6 temperature was 100oC) were employed as the hard template, the uncoupled sub-framework Cu-doped CeO2 catalyst formed. When KIT-6-130(hydrothermal synthesis of mesoporous silica KIT-6 temperature was 130oC) was employed as the hard template, the coupled sub-framework Cu-doped CeO2 catalyst formed. Compared with the coupled sub-framework Cu-doped CeO2 catalyst, the uncoupled sub-framework Cu-doped CeO2 catalyst has higher surface area and more open system. Three catalysts were evaluated for the catalytic oxidation CO reaction. The Cu-doped CeO2 catalyst with KIT-6-50 as a template exhibited a highest catalytic activity, and complete conversion temperature was about 53 oC for CO oxidation. It can be concluded that the higher surface area and more open system are relatively conducive to the catalytic oxidation of CO.