Investigation Of Solid-phase Method In Fabrication Of Metal-oxide Catalysts And Their Applications In Elimination Of CO Or/and NO

In the recent years, with the great development of economic and society, the diminishing petroleum reserves and deteriorating environment have held back further development of economic and even threatened human livings, and the design of new method for catalyst preparation becomes one of the most powerful ways to solve problems related to energy crisis and environment pollution. Generally, most of catalysts are prepared in aqueous phase, the resulting water pollution is always taken place and should be seriously considered. In contrast, water pollution can be totally avoided when the preparation is carried out in the absence of solvent. In this thesis, we put our focus on solid-phase method by choosing two kinds of widely used catalysts (supported catalysts and mixed oxide catalysts) and systematically investigate the advantages of solid-phase method. Moreover, with the assistance of various characterizations, we explore the influence of detailed synthetic parameters, study the possible formation process and correlate the connections between structure and performance of the prepared catalysts. The following presents research details:1. A series of highly loaded, well dispersed pore confined metal oxides (NiO, Co3O4, CeO2) was prepared by the solid-phase method with SBA-15 as support and nitrates as precursors. Characterizations of X-ray diffraction (XRD) and transmission electron microscopy (TEM) revealed that aggregation-free nanoparticles were obtained and N2 physisorption and TEM confirmed they were studded in mesopores. The influences of various synthetic parameters were exemplified with NiO, such as nickel loadings, calcination temperatures, different precursors and the present of mesopore. In addition, the effect of pore confinement on the thermal properties of guest species was also studied. Results indicated that, the particle sizes of NiO were almost not affected by the selected nickel loadings and calcination temperatures, while they were much influenced by the nature of nickel precursors and supports. The catalyst prepared from nickel acetate was consisted of many bulk NiO particles as the reason that it could not diffuse into the mesopores. The effect of pore confinement was reflected by the retard decomposition and aggregation of nickel nitrate and nanosized NiO. With assistance of investigation of the formation process, it was supposed the mobility of molten salt under thermal treatment played the key role in introduction of nickel species into the mesopores, while the viscosity of molten salt ensured the monodispersity of obtained nanoparticles. Finally, the catalytic applications of the prepared sample were evaluated in two model reactions:hydrodechlorination of chlorobenzene to benzene and decomposition of ammonia to pure hydrogen. The results showed as compared to conventional catalysts, the catalysts prepared by solid-phase method performed better activity, which indicated great potential of solid-phase method in reduction of pollution and production of energy.2. Chemically Bonded copper species with high loading (20 wt%) were firstly prepared by a solid-phase method with copper nitrate as precursor and SB A-15 as support, while in the same conditions most of copper were presented as bulk CuO when conventional wet impregnation method was used. The state of highly dispersed copper species was studied by characterizations such as X-ray diffraction, H2 temperature-programmed reduction (H2-TPR) and in-situ FT-IR, and it was assured that they formed by dehydroxylating with surface silanols of SBA-15 and presented as isolated copper dimmer. In addition, we also explored the influence of different silica supports and result showed it was pore structures rather than surface area of silica determined the effective bonding of copper, that was, due to the presence of capillary force, the unique pore structure of SBA-15 was advantageous for well diffusion of copper species, which in turn made the success bonding of high loaded copper.3. We prepared supported copper-ceria catalysts and investigated their catalytic performance in CO-PROX reaction. It was found that both the size of ceria and the effective contact between copper and ceria greatly influenced their performance, with catalysts derived from solid-phase method displayed the best performance for their smaller size and enhanced interactions between copper and ceria. Probably due to the diffusion limit exerted by SBA-15, the catalysts prepared with amorphous silica gel showed better activity than that with SBA-15 as a support.4. nickel-cerium mixed oxide catalysts were prepared by solid-phase method, and their catalytic performance in NO reduction by CO was also investigated. By comparing with conventional wet impregnation and coprecipitation method, we found the solid-phase derived NiO-CeO2 catalysts possessed several advantages: (l)The leaching of active species could be avoided with solid-phase method; (2) It was advantageous for solid-phase method to obtaining catalysts with high surface area, this was probably related with the evolved gases in the process of metal salt decomposition, this gases could create small pores on the catalyst surface; (3) the solid-phase method could enhance the interactions between nickel and ceria, as in the form of high dispersed NiO and doped Ni2+ in ceria. Just with these favoring properties, the catalysts prepared by solid-phase method got excellent activities in NO+CO reaction. Further exploring the effect of different nickel cerium ratios, it was found the best activity was achieved at Ni:Ce= 1:9, and larger or smaller ratios were not advantageous for the enhancement of catalytic activity.