Studies On Mesoporous CuO/Ce_1-x-y Zr_x RE_yO₂ Catalysts For CO Preferential Oxidation In Rich Hydrogen

Fuel cell is one of the most effective technologies to solve the energy crisis and environmental problems because of its high efficiency and environmental friendliness in the 21st century. Proton exchange membrane fuel cells （PEMFC） possess some good properties such as high energy density, low operation temperature, quick response and long lifetime, which make it having high potential to be applied in the moving energy system in future. Hydrogen-rich gas is a primary fuel source of PEMFC which normally contains about 1% CO, but the content of CO must be lower than 100 ppm, otherwise it will poison the Pt electrode. CO preferential oxidation （CO-PROX） is the most simple and effective method to reduce CO content to ppm level. The non-noble metal catalyst CuO/CeO2 is a CO preferential oxidation catalyst, which shows a good catalytic performance and has been paid much attention in recent years.The mesoporous CuO/CeO1-xZrxO2 catalysts prepared by the hydrothermal-impregnation method were studied in this paper. Some preparation conditions such as precipitatorts （NaOH and NH₃·H₂O solution）, the content of ZrO₂ in carrier, the loading amount of CuO, calcination temperature of supports and catalysts, the concentration of template agent, stirring time and effects of rare earth doping were investigated, and the influence of those preparation conditions to CO-PROX catalysts are analyzed in detail, with the consequence of some valuable conclusions.The results show that: the mesoporous CuO/m-CeO1-xZrxO2 catalysts can purify CO in H2-rich gas in a lower temperature range （95～175℃）, which have a comparable or higher catalytic activity than some noble metal catalysts and the similar catalysts reported in literature. NH₃·H₂O is more beneficial to catalysts having proper pore size and well-ordered mesopore structure than that of NaOH solution. Catalysts with high specific surface area and highly CuO dispersed prepared by adding ZrO₂, furthermore, catalytic performance and the ability of water resistance and carbon dioxide resistance improved. A lower loading amount of CuO can result in insufficient active sites, while the crystallized CuO will cover the active sites resulting in a lower catalytic activity when its loading amount is high. The optimized loading amount of CuO is dependent on the support preparation methods. The proper supports and calcination temperature for the catalysts can enhance the synergistic effect between CuO and Ce_1-xZr_xO₂. The reasonable concentration of template agent and stirring time are favorable to the refinement of pore diameter, and obtain a well-ordered pore structure. The species and quantities of the doped rare earth have an important effect on CuO/m-Ce_1-x-yZr_xRE_yO₂ catalysts structures and their properties.The investigation results show that the optimal preparation conditions are: precipitation agent is ammonia water, the content of ZrO₂ in carrier is 10wt%, the loading amount of CuO is 12wt%, calcination temperature of supports and catalysts are 400℃and 600℃respectively, the concentration of template agent is 0.10mol/L and stirring time is 4 hours. The 12%CuO/m-Ce0.9Zr0.1O2 catalyst exhibits favorable structural performance, catalytic performance, water resistance and carbon dioxide resistance, T50 is 69.5℃, T100 is 95℃, and temperature window is between 89.5 and 106℃. Doping the rare earth with larger ion radius can increase surface area, improve oxygen storage capacity, lower temperature reduction ability and thermal stability, and reinforce catalytic performance and water resistance and carbon dioxide resistance. The 12%CuO/m-Ce0.87Zr0.1Nd0.03O2 catalyst has the best catalytic activity, T50 is 69℃, T100 is 95℃, and temperature window is between 89 and 107℃.