预处理条件对Au/ZnO催化剂CO氧化性能的影响

Effects of Pretreatment Conditions on the Catalytic Performance of Au/ZnO Catalysts for CO Oxidation

采用沉积沉淀法制备了用于CO氧化的Au/ZnO催化剂,并用程序升温还原(TPR),X射线衍射(XRD)和透射电镜(TEM)技术对催化剂进行了表征.结果表明:采用沉积沉淀法可制备出高度分散的Au/ZnO催化剂;提高焙烧温度导致金颗粒聚集长大,样品经533,673,773K焙烧后金物种的颗粒尺寸分别为2.7,3.5,3.7nm.催化剂的TPR表征结果中发现部分还原态的金物种在室温就可被氧化,催化剂预先用流动空气处理可提高其氧化还原性,样品经多次氧化还原循环后,其氧化循环性能没有明显下降.CO的氧化反应结果表明,焙烧温度强烈影响催化剂对CO的氧化活性,533K焙烧后的催化剂活性最高.即使在反应气中含水3.1%(体积比)的湿气条件下,反应300h后,CO的转化率仍然保持在95%.

Au/ZnO catalysts were prepared by the deposition-precipitation （DP） method. Effects of calcination temperature and pretreatment conditions on the structure and the catalytic performance of Au/ZnO catalysts were investigated for CO oxidation. For the samples calcined in 533-773 K, no diffraction peak of gold species could be detected by XRD measurement. Transmission electron microscopy （TEM） observation revealed that the particle sizes of gold were 2.7, 3.5 and 3.7 nm respectively, for the catalysts calcined at 533, 673 and 773 K. Temperature-programmed reduction （H2-TPR） measurements further indicated that the pre-reduced gold species could be reoxidized at room temperature and the redox property of the catalyst could be enhanced through pretreatment with flowing air. However, its high redox properties still remained after several redox cycles. The result of CO oxidation on the catalytic behavior of the Au/ZnO catalysts was strongly influenced by the particle size and the surface area of the catalyst. The highly dispersed Au/ZnO catalyst with larger surface area and the least particle size can be prepared by the deposition-precipitation calcined at 533 K, resulting in the most promising activity and stability for CO oxidation. 95% CO conversion could be achieved after 300 h time-on-stream even though the feed gas contained 3.1 vol.% of water vapor.