硅胶负载铬系催化剂催化乙烯聚合机理研究进展

Research progress in catalytic mechanism for silica gel supported chromium catalyst for ethylene polymerization

综述了商业应用最广泛的三种硅胶负载铬系催化剂的负载活化过程及其催化乙烯聚合机理,六价态的铬催化剂具有良好的催化活性,负载活化过程中,铬由较高价态被还原成具有较低活性的二价态,并提出铬物种在预活化与单体活化过程中的表面物理化学性质是该类催化剂研究的热点。硅胶负载铬系催化剂催化乙烯聚合制备高密度聚乙烯的机理遵循链引发、链增长和链转移;而催化乙烯低聚制备丙烯或1-丁烯的聚合机理为环内金属插入机理。

The supported activation process and polymerization mechanism of three most widely used commercial silica gel supported chromium catalysts are reviewed.Hexavalent chromium catalysts perform excellently in catalytic activity.During the supported process,chromium is reduced from a higher valence to a bivalent chromium with a lower activity.It is proposed that the surface physicochemical properties of chromium species in the process of pre activation and monomer activation has always been a research hotspot.The mechanism of ethylene polymerization with silica gel supported chromium catalysts to produce high-density polyethylene follows chain initiation,chain growth and chain transfer.The mechanism of catalytic ethylene oligomerization to produce propylene or butene is the intra-ring metal insertion.