双浸渍法制备负载型钯催化剂

Double Impregnation Method Used in Preparing Supported Palladium Catalyst

本文通过Ｈ_２─Ｏ_２滴定、ＥＤＳ、ＩＣＰ─ＡＥＳ、ＴＰＲ、ＸＰＳ、ＩＲ等手段分析比较了在制备负载型钯催化剂中双浸渍法与常规浸渍法的优劣性．实验结果证明，与常规浸渍法相比，在较低含量下（如０．７ｗｔ％），双浸渍法制备的钯催化剂具有活性组分多集中于载体表面、分散度高、晶粒小的优点．这一方法中活性组分的固载机理是初始引入的ＥＤＴＡ与载体表面键合形成金属离子的络合中心．用钯盐溶液浸渍时，载体的吸附中心与络合中心同时作用．钯催化剂前身在较温和的条件下（＜１５０℃）可以被完全还原．显示出用双浸渍法制备高分散低含量的负载型贵金属催化剂具有良好的工业应用前景．

This paper presents a comparision of the double impregnation method (DI)with the conventional impregnation method (CI) for preparing supported palladium catalysts,Characterization of catalysts was performed using IR,TPR,H_2-O_2 titration,ICP,XPS and EDS.In comparision with CI catalysts,DI catalysts exhibited the merits of higher dispersion,smaller metal crystal and accumulation of most of the active ions on the surface of the support when the Pd content was low(e.g.0.7wt%).In DI method,the loading mechanism of active ion is that the EDTA introduced during the original im pregnation is bound by the carrier surface and it produces new metal ion complexing centers,independent of the normal centers already existing on the surface.The impregnation processes consist of normal and complexing impregnation taking place simultaneously.In addition,the Pd catalyst precursors could be reduced completely under mild condition(<150℃).Therefore there is a good prospect that supported Pd catalysts of low metal content may be prepared by DI method in an industrial scale.