Revisiting the identity of δ-MgCl2: Part II. Morphology and exposed surfaces studied by vibrational spectroscopies and DFT calculation
Revisiting the identity of δ-MgCl2: Part II. Morphology and exposed surfaces studied by vibrational spectroscopies and DFT calculation
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DOI：
10.1016/j.jcat.2020.04.017
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发表时间：
2020-07-01
影响因子：
7.3
通讯作者：
Groppo, Elena
中科院分区：
文献类型：
--
作者：
Piovano, Alessandro;D'Amore, Maddalena;Groppo, Elena
MgCl 2的活化是制备用于烯烃聚合的高性能齐格勒-纳塔（ZN）催化剂的重要步骤，其通过机械研磨原始MgCl 2或通过前体的化学转化来进行。根据所采用的活化方法，获得不同的纳米结构的无序和形态，这反过来又影响整体催化性能。在这项工作中，我们专注于δ-MgCl 2纳米颗粒的形态（即暴露表面的相对延伸），通过用振动光谱法研究一系列机械和化学活化的MgCl 2样品，通过建立一套全面的模型结构，（有序和无序）和相对表面，以突出纳米尺寸效应，并实现在原子水平上准确描述MgCl 2颗粒。我们发现，机械和化学活化促进了MgCl（2）表面暴露强酸性Mg 2+位点的表达，这些位点是主要参与催化的位点，以及表面间边缘的增加，这最近被认为是ZN催化剂立体选择性的主要原因。(C)2020爱思唯尔公司All rights reserved.
The activation of MgCl2 is an essential step for preparing performant Ziegler-Natta (ZN) catalysts for olefin polymerization, either by mechanical grinding of pristine MgCl2 or by chemical conversion of a precursor. Depending on the adopted activation process, different nanostructures are obtained in terms of disorder and morphology, which in turn influence the overall catalytic performance. In this work, we focused on the morphology of delta-MgCl2 nanoparticles (i.e. the relative extension of the exposed surfaces), by investigating with vibrational spectroscopies a series of mechanically and chemically activated MgCl2 samples, and by building up a comprehensive set of model structures (both ordered and disordered) and relative surfaces in order to highlight nanosizing effects and achieve an accurate description of MgCl2 particles at an atomistic level. We found that both mechanical and chemical activation promote the expression of MgCl(2 )surfaces exposing strongly acidic Mg2+ sites, which are those mostly involved in the catalysis, together with an increase of inter-surfaces edges, which have been recently considered as the main responsible for the ZN catalysts stereo-selectivity. (C) 2020 Elsevier Inc. All rights reserved.