不同方法制备的CeO2载体对CuO/CeO2催化剂水煤气变换活性和稳定性的影响

摘要

分别采用沉淀法(A),水热法(B)和柠檬酸溶胶-凝胶法(C)制备了三种CeO2材料,并以其为载体采用沉积-沉淀法制备了CuO/CeO2催化剂.运用N2物理吸附、粉末X射线衍射(PXRD)、原位粉末X射线衍射(in situ PXRD)、氢气-程序升温还原(H2-TPR)和循环伏安法(CV)等技术对其进行了表征,考察了不同方法制备的CeO2载体对CuO/CeO2水煤气变换(WGS)催化剂的结构、氧化-还原性能、催化活性和稳定性的影响.结果表明,它们的催化活性和稳定性顺序都是CuO/CeO2-A＞CuO/CeO2-B＞CuO/CeO2-C.联系表征结果,CuO/CeO2催化剂的活性与催化剂中CuO的颗粒度、CuO的微观应力和中等大小且与二氧化铈相互作用的CuO的数量等有关,而这些因素很大程度上受CeO2载体本身的热稳定性的影响.根据CV中扫描次数的增加,Cu2+←→Cu0氧化还原峰面积减小,推断CuO/CeO2催化剂在一定条件下氧化还原是不可逆的,这可能是其在反应气氛下经受温度循环之后活性降低的原因.%Three CeO2 materials Were prepared with precipitation(A),hydrothermal route(B)and citrate sol-gel(C)methods,and then used as the support of CuO/CeO2 catalysts,which were prepared by a deposition-precipitation method and examined with respect to their catalytic activities for the water-gas shift(WGS)reaction.The effect of the CeO2 support prepared with different methods on the structural properties,redox properties,catalytic activities and stabilities of the CuO/CeO2 catalysts for the WGS reaction was studied in detail using N2 physics adsorption(Brunauer-Emmett-Teller,BET),powder X-ray diffraction(PXRD),in situ PXRD,H2-temperature programmed reduction(H2-TPR)and cyclic voltammetry(CV).Results indicate that both the catalytic activities and stabilities of the as-synthesized CuO/CeO2 catalysts are CuO/CeO2-A＞CuO/CeO2-B＞CuO/CeO2-C Characterization results show that catalytic activities of the CuO/CeO2 catalysts ale closely related to the crystal size of CuO particles,the microsuain value for CuO,and the amount of moderate size copper oxides(crystalline)that interacted with celia.These factors depend greatly on the thermal stabilities of the CeO2 supports.CV results suggest that the peak area of Cu2+←→Cu0 redox reaction decreased from the first to the second cycle,indicating that the electrode reaction is irreversible and this might be a reason for the observed deactivation of CuO/CeO2 catalysts after the temperature cycle.