High-resolution XPS and DFT investigations into Al-modified Phillips CrOx/SiO2 catalysts
High-resolution XPS and DFT investigations into Al-modified Phillips CrOx/SiO2 catalysts
复制标题
Al 改性 Phillips CrOx/SiO2 催化剂的高分辨率 XPS 和 DFT 研究
DOI：
10.1016/j.molcata.2015.01.020
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发表时间：
2015-05
影响因子：
--
通讯作者：
Liu, Boping
中科院分区：
文献类型：
--
作者：
He, Xuelian;Fang, Yuwei;Terano, Minoru;Liu, Boping
本文采用高分辨X射线光电子能谱（XPS）和乙烯聚合反应性能研究了Al改性对菲利普斯催化剂的影响。采用密度泛函理论（DFT）方法对反应机理进行了深入的研究.通过DFT计算证实了Cr 2p结合能（BE）的降低与Al改性使Cr的电子密度增加有关。铝改性菲利普斯催化剂的乙烯聚合活性得到提高。聚合物的分子量（MW）随着分子量分布（MWD）向低MW侧扩展而降低，这与密度泛函理论计算中链转移和链增长之间能垒差的减小相一致。通过从五重态能量表面经由最小能量交叉点（MECP）到三重态能量表面的自旋交叉，发现了经历金属络合物反应途径的引发步骤。模拟结果表明，铝改性对菲利普斯催化剂聚合活性的促进作用主要来源于铝改性铬活性位能垒降低的链引发反应。铝改性的催化剂在低分子量侧的短支链（SCBs）分布较少，可以预期聚合物的耐环境应力开裂性（ESCR）得到改善。
In this work, the effects of Al-modification on Phillips catalysts were investigated by high-resolution X-ray 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.
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影响因子：
1.5
作者：
A. Matta;Yanning Zeng;Toshiaki Taniike;M. Terano
通讯作者：
A. Matta;Yanning Zeng;Toshiaki Taniike;M. Terano
DOI：
10.1524/zpch.1999.208.part_1_2.274
发表时间：
1999
期刊：
Zeitschrift für Physikalische Chemie
影响因子：
--
作者：
G. Öhlmann
通讯作者：
G. Öhlmann
影响因子：
7.3
作者：
M. Mcdaniel;Eric D. Schwerdtfeger;M. D. Jensen
通讯作者：
M. Mcdaniel;Eric D. Schwerdtfeger;M. D. Jensen
影响因子：
3.7
作者：
Jane Estephane;E. Groppo;J. Vitillo;A. Damin;D. Gianolio;C. Lamberti;S. Bordiga;E. A. Quadrelli;J. Basset;G. Kervern;L. Emsley;G. Pintacuda;A. Zecchina
通讯作者：
Jane Estephane;E. Groppo;J. Vitillo;A. Damin;D. Gianolio;C. Lamberti;S. Bordiga;E. A. Quadrelli;J. Basset;G. Kervern;L. Emsley;G. Pintacuda;A. Zecchina
影响因子：
--
作者：
Bo-ping Liu;Yuwei Fang;M. Terano
通讯作者：
Bo-ping Liu;Yuwei Fang;M. Terano