摘要
首次用PASCA(化学分析正电子谱)及磁天平技术研究WO_3在_2γ-Al_2O_3表面的分散过程及γ-Al_2O_3的表面性质。结果表明:WO_3在γ-Al_2O_3表面最大单层分散量为0.120g WO_3/100m^2。这一结果只相当于文献报导理论值(0.189g WO_3/100m^2)的64％。还发现γ-Al_2O_3表面存在强和弱两类不同的中心:Sk和Sts,它们分别与WO_3作用生成不同稳定程度的“表面相互作用复合物”:WO_3-Sk和WO_3-Sts。提出γ-Al_2O_3表面可划分为两个区域:可吸附区A和隐蔽区S。这两个区域的比例大小既取决于γ-Al_2O_3本身的性质,也取决于吸附分子的性质及大小。WO_3首先吸附在可吸附区A中表面能最高的Sk中心上,然后再吸附到表面能较低的Sts中心,直到铺满整个可吸附区为止。
PASCA (Positron Annihilation Spectroscopy for Chemical Analysis) and magnetic measurements were used to study the dispersion process of WO3 on γ-Al2O3 surface.The results show that the maximum monolayer dispersion of WO3 (threshold) on y-Al2O3 is 0.120 g WO3/100m2, occupying 64% of the A12O3 surface, which is considerably lower than the reported value (0.189 g/100m2). It is also found that there exist two types of surface sites: the strong sites Sk (kink sites) and the weak sites Sts (terrace and step sites), which interact with WO3 resulting in the formation of 'surface interaction complexes'.WO3-Sk and WO3-Sts with different stabilities. The surface of γ-Al2O3 can be divided into two main areas: the adsorbable area (A), being absolutely important for molecular adsorption and catalytic reaction, and the shadowed area (S), being away from any catalytic reaction. The ratio of A to S area depends not only upon the properties of γ-Al2O3, but also the properties of the adsorbates.
