MoO3与不同载体的相互作用及其单层分散量的测定

用X光衍射研究了MoO_3/TiO_2,MoO_3/SiO_2和MoO_3/MgO等体系。结果表明,MoO_3在TiO_2胶表面呈密置单层分散,其最大分散量(阈值)与按密置单层模型计算的0.117克MoO_3/100米~2(即4.9 × 10~(18)Mo原子/米~2)相符。MoO_3在SiO_2胶表面呈单层分散但非密置单层,其分散阈值为 0.032克MoO_3/100米~2(即 1.4 × 10~(18)Mo原子/米~2)。MoO_3与MgO比较容易进行体相反应,在290℃即已有部分MgMoO_4形成,没有只形成表面单层分散的阶段,因此不存在表面分散阈值,还联系载体的酸碱性、化学键性质以及结构上的差异,对MoO_3/γ-Al_2O_3和上述体系进行了讨论和比较。     

WO3/钛铝胶体系的表面结构

WO_3/钛铝胶系列样品通过浸渍法制备. XRD 和XPS 测定结果表明WO_3单层分散在钛铝胶表面, 分散阈值为0.22 g WO_3/(100 m~2). 假定WO_3在钛铝胶表面按照密置单层模型分散, 其计算值为0.198 g WO_3/(100 m~2). 表明测定值与理论模型的计算值相接近. LRS测定表明: 当WO_3的载量低于0.082 g WO_3/(100 m~2钛铝胶)时, 只有四而体配位的钨存在; 当WO_3的载量超过0.082 g WO_3/(100 m~2钛铝胶)时, 钨主要以八面体配位存在. 同时, LRS的实验结果也表明, 550 ℃焙烧的WO_3/钛铝胶样品没有Al_2(WO_4)_3生成. 对高温焙烧条件下, Al_2(WO_4)_3的生成也进行了研究.     

用ISS研究负载型催化剂中活性组分与载体间的相互作用

Low energy (1.5 KeV) ISS is a surface sensitive technique for identification of element on the top layer of material. The energy losses of primary particle during the collision in low energy ISS technique are assumed to be completely kinetic, i.e. the electronic interaction energy transfer is generally small and will be neglected. In this paper, however, the electronic effect is measurable for certain supported oxide or halide catalysts by improved experimental technique. The shift of scatter- ing He~+ peak due to electronic effect is remarkable and different for Mo in MoO_3/TiO_2, MoO_3/γ-Al_2O_3, MoO_3/SiO_2 and Cu in CuO/γ-Al-2O_3, CuCl/γ-Al_2O_3. The corresponding “mass increment” was calculated by the binary collision approach. We find out that the “mass increment” may characterize the interaction between active component and carrier in supported catalysts. Thus, low energy ISS is not only a good tool for surface elemental analysis but also an effective probe for chemical information of surface species.