Pt／MgO体系中金属—担体相互作用的TPD和XPS研究

本文对铂担载于两种不同来源和制备历史的MgO上的体系(A:MgO 99.5%,BET表面积33m~2/g,B:MgO 99.999%,BET表面积9m~2/g)在低温(573K,LTR)和高温(773K HTR)还原后的H_2化学吸附、TPD和XPS等行为进行了考察。结果表明,体系A在HTR后发生了强相互作用,而B却未观察到类似的作用,A、B体系的LTR后和HTR后的脱附峰温基本一致,分别为388±5K,536±3K(LTR)和710±5K(HTR);来发现LTR和HTR后Pt4f_(7/2)的变化,也未发现表面杂质元素;A体系低温还原后的XPS较之B体系在533.5eV处多出了一个肩峰,可标识为表面OH基团。以上事实说明,所研究体系的金属—担体强相互作用与金属—担体间的电子转移,担体的迁移,高温还原后的储氢现象或生成的含氢物种等无关联关系,而表面OH的存在是所研究的体系产生强相互作用的可能原因。

A TPD AND XPS STUDY ON METAL SUPPORT INTERACTIONS IN Pt/MgO SYSTEMS

A study was made on Pt supported MgO systems of different origin and preparation history for their behavior in H_2 Chemisorption, TPD and XPS after low temperature reduetion(LTR, 573K) and high temperature reduction(ETR, 773K). The results show that system A (With a 99.5% pure MgO as support) enters to SMSI state after HTR While system B (With a 99.999% pure MgO as support) remains almost the same after HTR as compared with LTR. TPD peak temperatures after LTR and HTR were in fair agreement for both systems respectivly. No binding energy changes for Pt 4f_(7/2) were observed after LTR and HTR for system A and B, nor were the surface impurities by Auger scanning results. As compared with B, the XPS spectrum for A after LTR had an extra shoulder at 553.5eV which could be assigned to surface OH group. The results suggest that the SMSI for the systems studied may not be correlated with electron transfer between the metal and support, or with the support migration, or hydrogen storage and hydrogen containing species formation after HTR, but may be due to the presence of the surface OH group.