文献类型：期刊文献

英文题名：High-resolution XPS and DFT investigations into Al-modified Phillips CrOx/SiO2 catalysts

作者：Ma, Yue[1];Wang, Lisong[1];Liu, Zhen[1];Cheng, Ruihua[1];Zhong, Lei[1];Yang, Yun[1];He, Xuelian[1];Fang, Yuwei[2];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, Tatsunokuti, Ishikawa 9231292, Japan

年份：2015

卷号：401

起止页码：1

外文期刊名：JOURNAL OF MOLECULAR CATALYSIS A-CHEMICAL

收录：;EI(收录号：20151000610417);WOS:【SCI-EXPANDED(收录号:WOS:000352662400001)】；

基金：This work is financially supported by the National Natural Science Foundation of China (No. 20774025, No. 21104019 and No. 21274040), the Research Program of the State Key Laboratory of Chemical Engineering, the Fundamental Research Funds for the Central Universities and the Program of Introducing Talents of Discipline to Universities (B08021). We thank Prof. J.N. Harvey and Prof. T.J. Dudley for their kind suggestions to locate the minimum-energy crossing points (MECP) between two different potential energy surfaces and also PQ Corporation (USA) for the kind donation of the Phillips catalysts with or without Al-modification.

语种：英文

外文关键词：Phillips CrOx/SiO2 catalyst; Al-modification; X-ray photoelectron spectroscopy; Density functional theory; Spin-crossover

摘要：In this work, the effects of Al-modification on Phillips catalysts were investigated by high-resolution Xray photoelectron spectroscopy (XPS) and the performance in ethylene polymerization reactions. Density functional theory (DFT) method was used to achieve a deeper mechanistic understanding. The decreased Cr 2p binding energies (BE), related with an increase in electron density of chromium by Al-modification, have been confirmed by the DFT calculation. The ethylene polymerization activity over the Al-modified Phillips catalyst was increased. The molecular weight (MW) of polymer was decreased with the expansion of molecular weight distribution (MWD) to low MW side, which was in agreement with the decreased energy barrier difference between the chain transfer and chain propagation in DFT calculation. The initiation step undergoing a metallacycle reaction pathway was found through a spin crossover from the quintet energy surface via a minimum energy crossing point (MECP) to the triplet energy surface. Modeling results indicated that the promotion effect on polymerization activity from Al-modification for Phillips catalyst was mainly originated from the chain initiation reaction with lowered energy barrier for Al-modified Cr active sites. Improved environmental stress-crack resistance (ESCR) of polymer derived from the Al-modified catalyst could be expected from the less short chain branches (SCBs) distribution in the low MW side. (C) 2015 Elsevier B.V. All rights reserved.