Lamb M J, Apperley D C, Watson M J, Dyer P W
1Department of Chemistry, Durham University, South Road, Durham, DH1 3LE UK.
2Department of Chemistry, Centre for Sustainable Chemical Processes, Durham University, South Road, Durham, DH1 3LE UK.
Top Catal. 2018;61(3):213-224. doi: 10.1007/s11244-018-0891-8. Epub 2018 Jan 16.
Sequential treatment of a previously-calcined solid oxide support (i.e. SiO, γ-AlO, or mixed SiO-AlO) with solutions of Cr{N(SiMe)} (0.71 wt% Cr) and a Lewis acidic alkyl aluminium-based co-catalyst (15 molar equivalents) affords initiator systems active for the oligomerisation and/or polymerisation of ethylene. The influence of the oxide support, calcination temperature, co-catalyst, and reaction diluent on both the productivity and selectivity of the immobilised chromium initiator systems have been investigated, with the best performing combination (SiO, modified methyl aluminoxane-12 {MMAO-12}, heptane) producing a mixture of hexenes (61 wt%; 79% 1-hexene), and polyethylene (16 wt%) with an activity of 2403 g g h. The observed product distribution is rationalised by two competing processes: trimerisation via a supported metallacycle-based mechanism and polymerisation through a classical Cossee-Arlman chain-growth pathway. This is supported by the indirect observation of two distinct chromium environments at the surface of the oxide support by a solid-state Si NMR spectroscopic study of the Cr{N(SiMe)}/SiO pro-initiator.
用Cr{N(SiMe)}（0.71 wt% Cr）溶液和一种路易斯酸性烷基铝基助催化剂（15摩尔当量）对预先煅烧的固体氧化物载体（即SiO、γ-AlO或混合SiO-AlO）进行顺序处理，可得到对乙烯齐聚和/或聚合具有活性的引发剂体系。研究了氧化物载体、煅烧温度、助催化剂和反应稀释剂对固定化铬引发剂体系的生产率和选择性的影响，性能最佳的组合（SiO、改性甲基铝氧烷-12 {MMAO-12}、庚烷）产生己烯混合物（61 wt%；79% 1-己烯）和聚乙烯（16 wt%），活性为2403 g g h。观察到的产物分布可通过两个竞争过程来解释：通过负载金属环机制进行三聚和通过经典的科塞-阿尔曼链增长途径进行聚合。通过对Cr{N(SiMe)}/SiO预引发剂的固态Si NMR光谱研究，间接观察到氧化物载体表面存在两种不同的铬环境，这支持了上述观点。
