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Nifant'ev I, Komarov P, Sadrtdinova G, Safronov V, Kolosov N, Ivchenko P. Mechanistic Insights of Ethylene Polymerization on Phillips Chromium Catalysts. Polymers (Basel) 2024; 16:681. [PMID: 38475365 DOI: 10.3390/polym16050681] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/29/2024] [Revised: 02/28/2024] [Accepted: 02/29/2024] [Indexed: 03/14/2024] Open
Abstract
Silica-supported chromium oxide catalysts, also named Phillips chromium catalysts (PCCs), provide more than half of the world's production of high- and medium-density polyethylenes. PCCs are usually prepared in the Cr(VI)/SiO2 form, which is subjected to reductive activation. It has been explicitly proven that CO reduces Cr(VI) to Cr(II) species that initiate ethylene polymerization; ethylene activates Cr(VI) sites as well, but the nature of the catalytic species is complicated by the presence of the ethylene oxidation products. It is widely accepted that the catalytic species are of a Cr(III)-alkyl nature, but this common assumption faces the challenge of "extra" hydrogen: the formation of similar species under the action of even-electron reducing agents requires an additional H atom. Relatively recently, it was found that saturated hydrocarbons can also activate CrOx/SiO2, and alkyl fragments turn out to be bonded with a polyethylene chain. In recent years, there have been numerous experimental and theoretical studies of the structure and chemistry of PCCs at the different stages of preparation and activation. The use of modern spectral methods (such as extended X-ray absorption fine structure (EXAFS), X-ray absorption near-edge structure (XANES), and others); operando IR, UV-vis, EPR, and XAS spectroscopies; and theoretical approaches (DFT modeling, machine learning) clarified many essential aspects of the mechanisms of CrOx/SiO2 activation and catalytic behavior. Overall, the Cosse-Arlman mechanism of polymerization on Cr(III)-alkyl centers is confirmed in many works, but its theoretical support required the development of nontrivial and contentious mechanistic concepts of Cr(VI)/SiO2 or Cr(II)/SiO2 activation. On the other hand, conflicting experimental data continue to be obtained, and certain mechanistic concepts are being developed with the use of outdated models. Strictly speaking, the main question of what type of catalytic species, Cr(II), Cr(III), or Cr(IV), comes into polymerization still has not received an unambiguous answer. The role of the chemical nature of the support-through the prism of the nature, geometry, and distribution of the active sites-is also not clear in depth. In the present review, we endeavored to summarize and discuss the recent studies in the field of the preparation, activation, and action of PCCs, with a focus on existing contradictions in the interpretation of the experimental and theoretical results.
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Affiliation(s)
- Ilya Nifant'ev
- A.V. Topchiev Institute of Petrochemical Synthesis RAS, 29 Leninsky Pr., 119991 Moscow, Russia
- Department of Chemistry, M.V. Lomonosov Moscow University, 1-3 Leninskie Gory, 119991 Moscow, Russia
| | - Pavel Komarov
- A.V. Topchiev Institute of Petrochemical Synthesis RAS, 29 Leninsky Pr., 119991 Moscow, Russia
| | - Guzelia Sadrtdinova
- A.V. Topchiev Institute of Petrochemical Synthesis RAS, 29 Leninsky Pr., 119991 Moscow, Russia
- Faculty of Chemistry, National Research University Higher School of Economics, Myasnitskaya St. 20, 101100 Moscow, Russia
| | | | | | - Pavel Ivchenko
- A.V. Topchiev Institute of Petrochemical Synthesis RAS, 29 Leninsky Pr., 119991 Moscow, Russia
- Department of Chemistry, M.V. Lomonosov Moscow University, 1-3 Leninskie Gory, 119991 Moscow, Russia
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Groppo E, Rojas-Buzo S, Bordiga S. The Role of In Situ/ Operando IR Spectroscopy in Unraveling Adsorbate-Induced Structural Changes in Heterogeneous Catalysis. Chem Rev 2023; 123:12135-12169. [PMID: 37882638 PMCID: PMC10636737 DOI: 10.1021/acs.chemrev.3c00372] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/01/2023] [Indexed: 10/27/2023]
Abstract
Heterogeneous catalysts undergo thermal- and/or adsorbate-induced dynamic changes under reaction conditions, which consequently modify their catalytic behavior. Hence, it is increasingly crucial to characterize the properties of a catalyst under reaction conditions through the so-called "operando" approach. Operando IR spectroscopy is probably one of the most ubiquitous and versatile characterization methods in the field of heterogeneous catalysis, but its potential in identifying adsorbate- and thermal-induced phenomena is often overlooked in favor of other less accessible methods, such as XAS spectroscopy and high-resolution microscopy. Without detracting from these techniques, and while aware of the enormous value of a multitechnique approach, the purpose of this Review is to show that IR spectroscopy alone can provide relevant information in this field. This is done by discussing a few selected case studies from our own research experience, which belong to the categories of both "single-site"- and nanoparticle-based catalysts.
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Affiliation(s)
- Elena Groppo
- Department of Chemistry,
NIS Centre and INSTM, University of Torino, via Giuria 7, 10125 Turin, Italy
| | - Sergio Rojas-Buzo
- Department of Chemistry,
NIS Centre and INSTM, University of Torino, via Giuria 7, 10125 Turin, Italy
| | - Silvia Bordiga
- Department of Chemistry,
NIS Centre and INSTM, University of Torino, via Giuria 7, 10125 Turin, Italy
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Wang D, Zhou S, Liu Y, Kang X, Liu S, Li Z, Braunstein P. Controlling Polyethylene Molecular Weights and Distributions Using Chromium Complexes Supported by SNN-Tridentate Ligands. Macromolecules 2022. [DOI: 10.1021/acs.macromol.1c02351] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Dongqi Wang
- Key Laboratory of Biobased Polymer Materials, College of Polymer Science and Engineering, Qingdao University of Science and Technology, Qingdao 266042, China
| | - Shengmei Zhou
- Key Laboratory of Biobased Polymer Materials, College of Polymer Science and Engineering, Qingdao University of Science and Technology, Qingdao 266042, China
| | - Yongxin Liu
- Key Laboratory of Biobased Polymer Materials, College of Polymer Science and Engineering, Qingdao University of Science and Technology, Qingdao 266042, China
| | - Xiaohui Kang
- College of Pharmacy, Dalian Medical University, Dalian 116044, China
| | - Shaofeng Liu
- Key Laboratory of Biobased Polymer Materials, College of Polymer Science and Engineering, Qingdao University of Science and Technology, Qingdao 266042, China
| | - Zhibo Li
- Key Laboratory of Biobased Polymer Materials, College of Polymer Science and Engineering, Qingdao University of Science and Technology, Qingdao 266042, China
- College of Chemical Engineering, Qingdao University of Science and Technology, Qingdao 266042, China
| | - Pierre Braunstein
- Laboratoire de Chimie de Coordination, CNRS, CHIMIE UMR 7177, Université de Strasbourg, 4 rue Blaise Pascal, 67081 Cedex Strasbourg, France
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A New Insight into the Comonomer Effect through NMR Analysis in Metallocene Catalysed Propene- co-1-Nonene Copolymers. Polymers (Basel) 2019; 11:polym11081266. [PMID: 31370184 PMCID: PMC6723554 DOI: 10.3390/polym11081266] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/04/2019] [Revised: 07/22/2019] [Accepted: 07/22/2019] [Indexed: 11/16/2022] Open
Abstract
The "comonomer effect" is an intriguing kinetic phenomenon in olefin copolymerization that still remains without a detailed explanation. It typically relates to the rate of enhancement undergone in ethylene and propene catalytic polymerization just by adding small fractions of an alpha-olefin. The difficulty lies in the fact that changes caused by the presence of the comonomer in reaction parameters are so conspicuous that it is really difficult to pin down which of them is the primary cause and which ones are side factors with marginal contribution to the phenomenon. Recent investigations point to the modification of the catalyst active sites as the main driving factor. In this work, the comonomer effect in the metallocene copolymerization of propene and 1-nonene is analysed and correlated to the comonomer role in the termination of the chain-growing process. The associated termination mechanisms involved furnish most of chain-free active sites, in which the selective interaction of the comonomer was proposed to trigger the insertion of monomers. A thorough characterisation of chain-end groups by means of the 1H NMR technique allows for detailing of specific transfer processes, ascribed to comonomer insertions, as well as evidencing the influence of the growing chain's microstructure over the different termination processes available.
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Jiang B, Liu X, Weng Y, Fu Z, He A, Fan Z. Mechanistic study on comonomer effect in ethylene/1-hexene copolymerization with TiCl4/MgCl2 model Ziegler-Natta catalysts. J Catal 2019. [DOI: 10.1016/j.jcat.2018.11.034] [Citation(s) in RCA: 26] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
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Zheng Q, Zheng D, Han B, Liu S, Li Z. Chromium complexes supported by the bidentate PN ligands: synthesis, characterization and application for ethylene polymerization. Dalton Trans 2018; 47:13459-13465. [PMID: 30183787 DOI: 10.1039/c8dt02834f] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
Chromium-based complexes are among the most important catalysts in the field of ethylene polymerization and oligomerization. Heterogeneous Cr Phillips catalysts account for more than one-third of the commercialized high density polyethylene (HDPE). In this contribution, chromium complexes, LCrCl3 (Cr1-Cr4: L = 2,6-R1-4-R2-C6H2-N[double bond, length as m-dash]CH-C6H4-2-PPh2; Cr1: R1 = H, R2 = H; Cr2: R1 = Me, R2 = H; Cr3: R1 = iPr, R2 = H; Cr4: R1 = Ph2CH, R2 = iPr), have been synthesized and characterized by elemental analysis, ESI and IR spectroscopy. The molecular structures of Cr3 and Cr4 are defined by X-ray diffraction, revealing a distorted octahedral geometry around the chromium center in both structures. In the presence of an aluminum cocatalyst, complexes Cr1-Cr4 show moderate to high activities toward ethylene polymerization. The nature of the catalysts and various reaction conditions, such as the nature and the amount of cocatalyst, reaction time and temperature, are investigated in detail. The results show that the title complexes have good thermal stability and the substituents on the ligands significantly affect the catalytic properties. Particularly, complex Cr4 can produce HDPE with a high molecular weight up to 68.3 × 104 g mol-1 due to the suppression of the chain transfer/termination by the introduction of bulky Ph2CH groups.
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Affiliation(s)
- Quande Zheng
- Key Laboratory of Biobased Polymer Materials, Shandong Provincial Education Department; College of Polymer Science and Engineering, Qingdao University of Science and Technology, Qingdao 266042, China.
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Groppo E, Martino GA, Piovano A, Barzan C. The Active Sites in the Phillips Catalysts: Origins of a Lively Debate and a Vision for the Future. ACS Catal 2018. [DOI: 10.1021/acscatal.8b02521] [Citation(s) in RCA: 36] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Elena Groppo
- Department of Chemistry, NIS Centre and INSTM, University of Torino, Via Quarello 15/A, 10125 Torino, Italy
| | - Giorgia Antonina Martino
- Department of Chemistry, NIS Centre and INSTM, University of Torino, Via Quarello 15/A, 10125 Torino, Italy
| | - Alessandro Piovano
- Department of Chemistry, NIS Centre and INSTM, University of Torino, Via Quarello 15/A, 10125 Torino, Italy
| | - Caterina Barzan
- Department of Chemistry, NIS Centre and INSTM, University of Torino, Via Quarello 15/A, 10125 Torino, Italy
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The Effect of Al-Alkyls on the Phillips Catalyst for Ethylene Polymerization: The Case of Diethylaluminum Ethoxide (DEALE). Top Catal 2018. [DOI: 10.1007/s11244-018-1041-z] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/28/2022]
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Martino GA, Barzan C, Piovano A, Budnyk A, Groppo E. Tracking the reasons for the peculiarity of Cr/Al2O3 catalyst in ethylene polymerization. J Catal 2018. [DOI: 10.1016/j.jcat.2017.11.007] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
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Floryan L, Borosy AP, Núñez-Zarur F, Comas-Vives A, Copéret C. Strain effect and dual initiation pathway in CrIII/SiO2 polymerization catalysts from amorphous periodic models. J Catal 2017. [DOI: 10.1016/j.jcat.2016.11.037] [Citation(s) in RCA: 30] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/20/2022]
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Spectroscopic Methods in Catalysis and Their Application in Well-Defined Nanocatalysts. ACTA ACUST UNITED AC 2017. [DOI: 10.1016/b978-0-12-805090-3.00007-3] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register]
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