硅胶菲利普斯催化剂的重要性学习分析揭示了乙烯聚合活性与接枝亲和力之间的权衡关系

IF 3.3 3区 化学 Q2 CHEMISTRY, PHYSICAL The Journal of Physical Chemistry C Pub Date : 2024-10-29 DOI:10.1021/acs.jpcc.4c05331
Changhae Andrew Kim, Armin Shayesteh Zadeh, Baron Peters
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摘要

由于二氧化硅载体的无定形结构,乙烯聚合的单原子 Cr/SiO2 催化剂(即 Phillips 催化剂)的许多方面仍然是个谜。以前的计算研究曾研究过单个位点或少量位点集群模型的各种机理,但没有研究过无定形二氧化硅板坯模型上位点集合的位点平均动力学。本研究采用重要性学习算法来探测菲利普斯催化剂的结构异质性。通过这种方法,我们获得了与多项实验研究定量一致的位点平均动力学。此外,我们还证明了催化速率与接枝概率是反相关的,并研究了调节这种权衡的结构特征。我们的研究结果解释了为什么只有一部分铬原子在乙烯聚合中具有活性,以及为什么在更高温度下煅烧会产生更活跃的催化剂。此外,我们还发现贝尔-埃文斯-波兰尼(BEP)关系并不能解释菲利普斯催化剂中由于应变对中间体和过渡态的不同影响而产生的位点间活性变化。
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Ethylene Polymerization Activity vs Grafting Affinity Trade-off Revealed by Importance Learning Analysis of In Silico Phillips Catalyst
Many aspects of the single-atom Cr/SiO2 catalyst for ethylene polymerization, i.e., the Phillips catalyst, remain enigmatic due to the amorphous structure of the silica support. Previous computational studies have examined various mechanisms on cluster models of a single site or a small collection of sites, but none have examined the site-averaged kinetics for the ensemble of sites on a slab model of amorphous silica. This work uses the importance learning algorithm to probe the structural heterogeneities of the Phillips catalyst. In this way, we obtain site-averaged kinetics in quantitative agreement with several experimental studies. Moreover, we show that the catalytic rates are anticorrelated with the grafting probabilities and examine the structural features which modulate this trade-off. Our results explain why only a fraction of the Cr atoms appear to be active in ethylene polymerization and why calcination at higher temperatures yields more active catalysts. Furthermore, we show that the Bell–Evans–Polanyi (BEP) relation does not explain the site-to-site activity variations in the Phillips catalyst due to different influences of strain on the intermediates and the transition states.
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来源期刊
The Journal of Physical Chemistry C
The Journal of Physical Chemistry C 化学-材料科学:综合
CiteScore
6.50
自引率
8.10%
发文量
2047
审稿时长
1.8 months
期刊介绍: The Journal of Physical Chemistry A/B/C is devoted to reporting new and original experimental and theoretical basic research of interest to physical chemists, biophysical chemists, and chemical physicists.
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