水蒸汽在Pd表面吸附的热力学

用密度泛函方法和相对论有效原子实势分别对PdOH2、PdOH 及PdO 的几何构型进行了优化, 得到PdOH2分子为Cs构型, Pd 与H2O 分子不在同一平面, RPdO=0.2283 nm; PdOH 分子为2A'态, RPdO=0.1965 nm, ROH=0.0968 nm, ∠PdOH=110.186°; PdO分子基态为3Π, RPdO=0.1858 nm. 根据电子-振动近似理论计算了不同温度下金属Pd与H2O、OH及游离态O原子反应的生成热力学函数, 导出了反应平衡压力随温度的变化关系, 分析认为水蒸汽引起Pd合金膜中毒是由于H2O分子的离解产物OH和O原子吸附在膜表面所致.

Thermodynamics of Water Adsorbed on Palladium Surface

The different structures of PdOH2, PdOH, and PdO were optimized by the relativistic effective core potential (RECP) and the density functional method B3LYP. The results showed that Pd and H2O of stable Pd-OH2 molecule were not in the same plane, and the bond length (R_PdO) was 0.2283 nm. For PdOH molecule, the ground state was 2A', the structure parameters RPdO, ROH, and ∠PdOH were 0.1965 nm, 0.0968 nm, and 110.186°, respectively; Theground state of PdO was 3Π, and the bond length was 0.1858 nm. Furthermore, the thermodynamic functions of PdOH2, PdOH, and PdO were also calculated according to electronic-vibration approximation, and based on this results, the relationship of the equilibrium pressures with temperatures was obtained. From the results, it was deduced that the poisoning effect of H2O was due to the adsorption of O and OH dissociated from H2O on palladium surface.