摘要
在甲醇氧化制甲醛的工业过程中,甲醇原料中含有的微量Fe(CO)_5以及反应设备因腐蚀产生的铁氧化物会使高活性的电解银催化剂中毒,导致甲醛选择性下降和副产物二氧化碳增加,从而降低催化剂的使用寿命.为了研究铁对上述反应的中毒机制,我们分别在实际催化剂(电解银)和模型催化剂[Ag(110)]表面对铁的中毒作用进行了原位模拟.本文报道了用XPS,LEED,SAES,SIMS和功函数测量等方法研究铁与银表面相互作用所得到的实验结果.
The silver catalyst surface poisoned by oxide iron causes the reduction of the catalyst selectivity for partial oxidation of methanol. The surface characteristics of the deactivated catalysts have been studied by XPS , SAES , SIMS and the measurement of work function. The results show that on the silver surface the iron exists in the form of oxidized iron species even in UHV condition. The oxidation state of iron increases with the poisoning degree from pure FeO to Fe3O4 and finally to Fe2O3. XPS and work function experiments confirm that with low coverage of iron, the Fe2+ cation interacts strongly with the silver atom via the coordinated oxygen. The electrons transfer from silver 3d to oxygen 2p and a strong bonding is formed between surface silver and coordinated oxygen(the maximum of dipole moment for Ag-O is 0.8 Debye). As being shown by SIMS, SEM and SAES, with the increasing of iron coverage, the multilayer occurrs, and then when heated to 480K the islands of oxide iron are found and the interaction between silver and oxygen disappears.
