镍负载硅酸铝催化剂上丙烯齐聚反应 Ⅲ.镍离子与丙烯分子的相互作用

Studies of Propylene Oligomerization over Ni (Ⅱ) Supported on Amorphous Aluminasilicate Catalyst Ⅲ. Interaction of Nickel Ions with Propylene Molecules

为了探明在Ni(Ⅱ)/SiO_2-Al_2O_3催化剂上丙烯齐聚反应诱导期的成因及活性中心的本质,考察了反应过程中镍离子与丙烯分子的相互作用,发现反应诱导期随着催化剂预抽空温度的升高而缩短,也随着丙烯预处理及反应温度的升高而缩短.用ESR、XPS法跟踪考察发现,随着丙烯在催化剂上反应的进行,首先Ni(Ⅱ)被丙烯还原成Ni(Ⅰ)离子.之后,丙烯与Ni(Ⅰ)配位形成不饱和配位离子,形成齐聚反应表面活性中间体,并且在反应过程中,二、三聚产物也可与Ni(Ⅰ)离子配位,形成三、四聚反应面活性中间体.结果表明在Ni(Ⅱ)/SiO_2-Al_2O_3催化剂上Ni(Ⅰ)离子是丙烯齐聚反应的活性中心。

To ascertain the cause of the formation of induction period in propylene oligomerization and the nature of active centers on nickel ions supported amorphous aluminasilicate catalyst (Ni-SA), the interaction of nickel ions with propylene molecules has been investigated with ESR, XPS measurements, in a closed recirculation apparatus. It was found that the induction period is shorted by increasing the pre-evacuation temperature and reaction temperature. ESR and XPS results show that Ni(II) has been reduced into Ni(I) by propylene, then Ni(I) ions form unsaturated complexes with propylene. It is suggested that the unsaturated complexes are active intermediates of propylene oligomerization. It is their formation that results in the elimination of the induction period. At the same time, the dimer or trimer coordinates to Ni (I) ions and forms the active intermediates of trimerization or tetramerization. The catalytically active centers are Ni(I) ions on Ni-SA catalyst.