甲醇在Pd(Ⅲ)面上的吸附和热解离  

THE ADSORPTION AND THERMAL DECOMPOSITION OF CH_3OH ON Pd(111) SURFACE

作　　者：蒋致诚[1] R.J.Levis N.Winograd 

机构地区：[1]中国科学院兰州化学物理研究所 [2]宾夕法尼亚州立大学化学系

出　　处：《分子催化》1990年第1期1-12,共12页Journal of Molecular Catalysis(China)

摘　　要：用XPS和静态SIMS研究了110～600K温度范围内甲醇在Pd(111)面上的吸附和解离表面化学反应。实验结果表明,甲醇在Pd(111)面上的热解离反应途径依赖于其初始暴露量。在110K低温下,暴露量为1.5L时达到单层饱和吸附。在此暴露量以下,甲醇在表面的热解离占主导地位,其解离的中间吸附物种有CH_3ads、CH_3Oads和H_2Oads。这表明在Pd(111)面上,不仅甲醇中O-H键,而且C-O键也被活化。而在初始暴露量大于1.5L时,甲醇从表面的热脱附趋于主导地位。Pd(111)面上相对稳定的中间吸附物种CH_3ads的存在可能有助于理解Pd催化剂在合成CH_3OH、CH_4、CH_3OCH_3和CH_3CH_3反应中的催化作用机理。We have recently reported the first XPS and SSIMS observations suggesting that CH3OH adsorbed at 110 K on clean Pd(111) surface with an initial exposure of 1.5 L dissociates upon heating at both the C-O and O-H bonds. In this paper, we expand that discussion by examining the nature of the initial CH3OH layer and the formation of thermal decomposition intermediates on the surface. In brief, CH3OH and its deuterated analogs ( CD3OH, CH3OD and CD3OD ) were adsorbed on atomically clean Pd(111) surface at low temperature ( 110 K ). The XPS method was utilized to provide surface concentration with limited chemical specificity while the SSIMS analysis in combination with labeling experiments yielded more detailed carbon-containing surface fragments as the substrate temperature was raised from 110 K to 600 K. The key results obtained in our experiments are as follows: At 110 K, the sticking coefficient of CH3OH adsorption on Pd(111) is near unity.The careful analysis of the changes of the binding energy and FWHM of XPS Cls peak and the appearance of the(CH3OH)n H + SIMS signal for multi-aggregated CH3OH the first monolayer chemisor-ption is completed at CH3OH exposure of 1.5 L. Above 1.5 L exposure, the physisorbed multilayer is formed on the surface. The thermal decomposition reaction pathway of CH3OH on Pd(111) is strongly dependent on the initial CH3OH exposure. For the saturation CH3OH exposure of 1.5 L or less, the thermal decomposition, rather than thermal desorption, is the dominant reaction on the surface upon heating the substrate from 110 K to near 400 K. At 110 K and 1.5 L exposure of CH3OH, the single Cls XPS peak at 286.2 eV and the presence of molecular CH3OH related cracking pattern ( CH3OHH+ CH2OH+ and CH3+) show that only molecular CH3OH is present on the surface. Upon heating the substrate to 175-300 K, the single Cls peak splits into a doublet ( Eb value 285.9 eV and 284.2 eV ) with approximately equal intensity while keeping approximately the same total area as that of the s

关 键 词：甲醇 吸附 热解离 钯催化剂 

分 类 号：O623.411[理学—有机化学] O643.36[理学—化学]