Hydrothermal Templated Synthesis Of High Surface Area Ceria-zirconia Composite Oxides And Characterized

Cerium-zirconium mixed oxides as catalysts for three-way catalyst has attracted much interest. Improving the specific surface area and thermal stability are always hotspots for cerium-zirconium mixed oxides. In this dissertation, PEG-4000 and SDBS are used as templating agent to synthesize high specific surface area cerium-zirconium mixed oxides with mesoporous structure. The XRD, FT-IR, TEM, H₂-TPR and BET are used to characterize cerium-zirconium mixed oxides.Under the system that using PEG-4000 as templating agent, the influence of PEG-4000'content and temperature on specific surface area, the influence of pH value and the molar ratio of Ce/Zr on phase, thermal stability of samples are investigated. The BET results show that PEG-4000'content and temperature have great influence on specific surface area. Under the condition that the molar ratio of PEG-4000/([Ce]+[Zr]) is 0.3 and the temperature is 120℃, the prepared sample's specific surface area is of 146.7m²·g^-1 after calcination at 500℃for 2h. The XRD results show that the pH value has less influence on phase, but the crystallite size increases with the increase in pH value. On the contrary, the molar ratio of Ce/Zr has great influence on Ce_xZr_1-xO₂'s phase and when x＜0.5 there is no signal phase. The TEM results show that the prepared sample Ce_0.5Zr_0.5O₂ is of worm-like mesoporous structure. The FT-IR results show that PEG-4000 cooperated with inorganic precursor and the residual PEG-4000 can be removed by calcination at 500℃. The prepared sample holds poor thermal stability, the specific surface area decreased to 27m²·g^-1 and the pore collapsed dramatically after calcination at 800℃for 2h.Under the system that using SDBS as templating agent, the influence of SDBS's content on specific surface area, the influence of pH value on mesoporous structure and the sample's thermal stability are investigated. The BET results show that SDBS's content has great influence on specific surface area and when the micelle shape of SDBS is spheric the prepared sample's specific surface area is of 163.3 m².g^-1. The low-angle XRD results show that the condition which is weak acidic is in favor of forming MSU mesoporous structure. On the contrary, the condition which is alkaline is not in fovar of forming MSU mesoporous structure. The TEM results show that the sample of Ce_0.5Zr_0.5O₂ hold MSU worm-like mesopore. The FT-IR results show that SDBS cooperated with Ce(OH)₄ and Zr(OH)₄ latex. The sample possess excellent thermal stability and the specific surface are decreased to 62.4 m².g^-1 after calcination at 800℃for 2h. the H₂-TPR results show that the OSC and the reduce performance of low-temperature is related to specific surface area.