文献类型：期刊文献

英文题名：Active Site Transformation During the Induction Period of Ethylene Polymerization over the Phillips CrOx/SiO2 Catalyst

作者：Zhong, Lei[1];Liu, Zhen[1];Cheng, Ruihua[1];Tang, Siyang[1];Qiu, Pengyuan[1];He, Xuelian[1];Terano, Minoru[2];Liu, Boping[1]

机构：[1]E China Univ Sci & Technol, State Key Lab Chem Engn, Shanghai 200237, Peoples R China;[2]Japan Adv Inst Sci & Technol, Sch Mat Sci, Nomi, Ishikawa 9231292, Japan

年份：2012

卷号：4

期号：6

起止页码：872

外文期刊名：CHEMCATCHEM

收录：;EI(收录号：20122215079959);WOS:【SCI-EXPANDED(收录号:WOS:000304441900023)】；

基金：We thank the National Natural Science Foundation of China (20774025), the Program of Introducing Talents of Discipline to Universities (B08021), and the Fundamental Research Funds for the Central Universities for financial support. We acknowledge Prof. Luigi Cavallo from the University of Salerno, Italy, for fruitful discussions and Dr. Brian Vicente from the University of California, Santa Barbara, for the valuable suggestions of English improvement.

语种：英文

外文关键词：adsorption; heterogeneous catalysis; metathesis; reaction mechanisms; spin crossover

摘要：In spite of the great importance of the Phillips catalyst in commercial polyethylene production and long-term research efforts, the initiation mechanism of polymerization still remains unclear. The effect of formaldehyde desorption on the active site transformation during the induction period of the Phillips catalyst is investigated over cluster models by using DFT. No reaction can be initiated over the cluster model coordinated with two formaldehyde molecules, owing to steric hindrance and electronic donation. The first reaction over cluster models, on which either one or no formaldehyde molecule is adsorbed, follows the metallacyclic mechanism into chromacyclopentane. Subsequent dimerization to 1-butene and metathesis to propylene and ethylene are more favorable over the cluster model adsorbed with one formaldehyde molecule. Only after a complete desorption of formaldehyde does further ring expansion to chromacycloheptane followed by 1-hexene formation become preferential. Spin state crossing from quintet diethyleneCrII complex to triplet chromacyclopentane with a spin acceleration effect is revealed.