摘要
应用FT-IR光谱及其差谱、DSC热分析以及催化选择性实验研究了不同配比的MoO_3-V_2O_5,MoO_3-TiO_2(锐钛矿型),MoO_3-WO_3和MoO_3-ZrO_2四种体系经不同温度焙烧后,界面过渡层非晶相分散的非单层结构及催化性能。FT-IR光谱及其差谱上出现了非晶相的特征吸收峰,并将其逐个与分子结构关联。DSC证明,在高于焙烧温度的升温扫描范围内(500～720℃),过渡层呈热介稳态,放热峰的出现与固熔体的形成及晶格畸变有关,但不存在表面及体相化学反应。以邻二甲苯选择性氧化制酸酐作为催化性能的反应探针,测定了转化率和选择性,表明非晶相分散的MoO_3和V_2O_5对反应有利,当配比处于分散阈值附近时选择性最佳。结合前文结果讨论了过渡层的非晶相分散机理和八面体非单层模型。
The non-crystalline dispersion on interfaces of MoOs-V2O5, MoO3-TiO2(anatase), MoO3-WO3 and MoO3-ZrO2 systems was studied by XRD and BET. XRD quantitative extrapolation indicates that there are the dispersed threshold values (maximum dispersion) of each component oxide on another surface, what is called 'both sides dispersed threshold value' of interface transition layer in this article. Exceeding threshold value, many of the extrapolated slops between residual crystalline and added crystalline are obviously less than 1; 'crystalline residual ratio' is intro-duced to describe and explain these smaller slopes. BET measurements show that specific surface areas of all samples are much smaller(<10m2/g) than that of carriers such as γ-Al2O3,etc. The above dispersed threshold values (0.34- 1.43g/100m2) from XRD are more than their monolayer dispersion capacities (0.088- 0.264g/100m2) calculated from a non-monolayer model proposed in this article. According to the model each component oxide is dispersed on another surface by ball octahedra (MeO6) which is closed-packed by sharing O atoms in a layer, and limited several of such layers are stacked up to form the non-monolayer dispersion on interface transition layer. The threshold values from XRD are much more especially than monolayer dispersion capacities from O= closed-packed model (0.117 g/100m2). To sum up, monolayer dispersion model is proved to be not suitable for binary oxide interface though it is suitable for MoO3/γ-Al2O3, etc. Parameters of non-monolayer model are calculated and listed.
