Preparation Of Mesoporous Ce_xZr_1-xO₂ Mixed Oxides And Catalytic Performances Of Cu-Based For CO Selective Oxidation In The H₂-rich

Ce_xZr_1-xO₂ are attracting much attention because of its unique redox properties and high oxygen storage capability, highly stability and low temperature catalytic activity . However, the low surface area makes this support less desirable in catalytic field because of low metal dispersion. Synthesizing mesoporous Ce_xZr_1-xO₂ ( m-Ce_xZr_1-xO₂ ) materials can increase their surface areas effectively. CuO/Ce_xZr_1-xO₂ catalysts, exhibiting high low temperature activity and selectivity for CO oxidation, are used for CO selective oxidation in the H2-rich gas and can remove the CO. In this paper, m-Ce_xZr_1-xO₂ with the high surface area and concentrative pore diameter distribution were successfully synthesized via polyol method. The influences of cerium and zirconium precursor concentration, PVP concentration, reaction time, calcination temperature, calcination time and Zr content on textural properties of m-Ce_xZr_1-xO₂ were investigated. CO selective oxidation in the H₂-rich gas was used as the probe reaction. CuO amount and calcination temperature and Zr content on the catalytic performances of CuO/m-Ce_xZr_1-xO₂ were studied. Physico-chemical properties, structure of the m-Ce_xZr_1-xO₂ and CuO-based catalysts were characterized by means of XRD, TEM, BET, TG, FT-IR, Raman, TPR and TPD.The m-Ce_0.5Zr_0.5O₂ materials were prepared with cationic-anionic mixed-surfactant assembly and polyol method. The results shown that the sample, synthesized by polyol method, had higher surface area and good reproducibihty, and the method was easy to operate.The effects of preparation conditions of polyol method on the surface area, pore distribution and thermal stability of m-Ce_0.5Zr_0.5O₂ was studied. The adding PVP is in favor of preventing the particles to agglomerate and sinter. Precursor concentration and reaction time influence chelate reaction between cerium zirconium and glycol. There is large effect of calcination temperature to structural properties of m-Ce_0.5Zr_0.5O₂, surface areas of samples is decreasing as the calcination temperature increasing. The specific surface area of prepared sample is 181m²/g, under the condition as: cerium and zirconium precursor concentration 0.04M, PVP concentration 0.16M, reaction time 7 h, calcination temperature 673K and calcination time 4 h.A series of m-Ce_xZr_1-xO₂ mixed oxides with different Zr content were synthesized by polyol method. The results showed that all samples were mesoporous cubic fluorite-structured Ce_xZr_1-xO₂ solution, had high surface areas (133-181 m²Â·g^-1) and concentrative pore diameter distribution (3.7-7.7 nm). The crystal structure, surface areas, pore performance and reduction property of m-Ce_xZr_1-xO₂ were related with Zr content. An increase of Zr content resulted in increasing surface areas and pore volumn,but lattice parameter was decreased.The influences of the CuO content and the calcination temperature on activity and selectivity of CuO/m-Ce_0.5Zr_0.5O₂ catalyst for the CO oxidation in the H₂-rich gas were investigated. Compared to non-mesoporous Ce_0.5Zr_0.5O₂ supported Cu based catalyst, CuO/m-Ce_0.5Zr_0.5O₂ catalyst was found to be effective catalysts for the CO oxidation, it can be explained by enlarged surface and high dispersion of CuO. The CuO content and the calcination temperature have great effect on CO oxidation, for a CuO/m-Ce_0.5Zr_0.5O₂ at calcined at 673K, 15% CuO content was sufficient for maximum activity, because there are stronger interaction between metal and support, more lattice defects, lower desorption temperature of CO and more active sites for the CO oxidation reaction.In m-Ce_xZr_1-xO₂(x=0.5-0.8) mixed oxides, the influences of coefficient x on performances of the supports and Cu based catalysts for the CO selective oxidation in the H₂-rich gas were investigated. The Cu based catalyst showed higher CO conversion and selectivity in H₂-rich gas when x=0.5, the CO conversion and selectivity of CuO/m-Ce_0.5Zr_0.5O₂ catalyst were 100 % and 96.2% at 383 K. By comparison of CuO/Ce_xZr_1-xO₂ (x=0.65-0.8) catalysts, CuO/m-Ce_0.5Zr_0.5O₂ catalyst had the strongest interaction between the activity component and the support, the highest dispersion, the most activity sites, the largest CO adsorption amount and the lowest desorption temperature of CO, all these were advantageous to the enhancement of catalyst activity.