Piovano Alessandro, Zarupski Jelena, Groppo Elena
Department of Chemistry, INSTM and NIS Centre, University of Torino, Via Giuria 7, 10125 Torino, Italy.
DPI, P.O. Box 902, 5600 AX Eindhoven, The Netherlands.
J Phys Chem Lett. 2020 Jul 16;11(14):5632-5637. doi: 10.1021/acs.jpclett.0c01665. Epub 2020 Jul 1.
In the field of Ziegler-Natta catalysis for olefin polymerization, carbon monoxide (CO) is used in the industrial practice to quench the reaction when it proceeds too fast, approaching critical levels for the plant safety. The quenching effect is explained as due to the reversible coordination of CO to the titanium active sites, but no direct evidence has been ever reported. In this work, we designed a series of experiments to monitor CO adsorption at variable temperatures on a model Ziegler-Natta catalyst by means of FT-IR spectroscopy. For the first time, we have been able to spectroscopically detect CO coordinated to alkylated Ti sites and the Ti-acyl species formed upon the subsequent insertion of CO into the Ti-alkyl bond, both in the absence and in the presence of the olefin monomer. In perspective, this has important implications for the characterization of the active sites in industrial Ziegler-Natta catalysts, even under working conditions.
在用于烯烃聚合的齐格勒-纳塔催化领域，工业实践中当反应进行过快接近工厂安全的临界水平时，会使用一氧化碳（CO）来终止反应。淬灭效应被解释为是由于CO与钛活性位点的可逆配位，但从未有过直接证据的报道。在这项工作中，我们设计了一系列实验，通过傅里叶变换红外光谱法监测在可变温度下CO在模型齐格勒-纳塔催化剂上的吸附情况。首次在有无烯烃单体的情况下，我们都能够通过光谱检测到与烷基化钛位点配位的CO以及CO随后插入钛-烷基键后形成的钛-酰基物种。从长远来看，这对于工业齐格勒-纳塔催化剂活性位点的表征具有重要意义，即使是在工作条件下。
