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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experimental data continue to be obtained, and certain mechanistic concepts are being developed with the use of outdated models.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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Monwar M, Cruz C, Barr J, McDaniel M. Ethylene polymerization by hydrocarbon-reduced Cr/silica catalyst. J Catal 2021. [DOI: 10.1016/j.jcat.2020.10.019] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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Cr[CH(SiMe3)2]3/SiO2 catalysts for ethene polymerization: The correlation at a molecular level between the chromium loading and the microstructure of the produced polymer. J Catal 2021. [DOI: 10.1016/j.jcat.2020.12.022] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
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Jongkind MK, Meirer F, Bossers KW, ten Have IC, Ohldag H, Watts B, van Kessel T, Friederichs N, Weckhuysen BM. Influence of Metal-Alkyls on Early-Stage Ethylene Polymerization over a Cr/SiO 2 Phillips Catalyst: A Bulk Characterization and X-ray Chemical Imaging Study. Chemistry 2021; 27:1688-1699. [PMID: 32729972 PMCID: PMC7898848 DOI: 10.1002/chem.202002632] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/30/2020] [Revised: 07/22/2020] [Indexed: 12/03/2022]
Abstract
The Cr/SiO2 Phillips catalyst has taken a central role in ethylene polymerization since its invention in 1953. The uniqueness of this catalyst is related to its ability to produce broad molecular weight distribution (MWD) PE materials as well as that no co-catalysts are required to attain activity. Nonetheless, co-catalysts in the form of metal-alkyls can be added for scavenging poisons, enhancing catalyst activity, reducing the induction period, and tailoring polymer characteristics. The activation mechanism and related polymerization mechanism remain elusive, despite extensive industrial and academic research. Here, we show that by varying the type and amount of metal-alkyl co-catalyst, we can tailor polymer properties around a single Cr/SiO2 Phillips catalyst formulation. Furthermore, we show that these different polymer properties exist in the early stages of polymerization. We have used conventional polymer characterization techniques, such as size exclusion chromatography (SEC) and 13 C NMR, for studying the metal-alkyl co-catalyst effect on short-chain branching (SCB), long-chain branching (LCB) and molecular weight distribution (MWD) at the bulk scale. In addition, scanning transmission X-ray microscopy (STXM) was used as a synchrotron technique to study the PE formation in the early stages: allowing us to investigate the produced type of early-stage PE within one particle cross-section with high energy resolution and nanometer scale spatial resolution.
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Affiliation(s)
- Maarten K. Jongkind
- Inorganic Chemistry and CatalysisDebye Institute for Nanomaterial ScienceUtrecht UniversityUniversiteitsweg 993584 CGUtrechtThe Netherlands
| | - Florian Meirer
- Inorganic Chemistry and CatalysisDebye Institute for Nanomaterial ScienceUtrecht UniversityUniversiteitsweg 993584 CGUtrechtThe Netherlands
| | - Koen W. Bossers
- Inorganic Chemistry and CatalysisDebye Institute for Nanomaterial ScienceUtrecht UniversityUniversiteitsweg 993584 CGUtrechtThe Netherlands
| | - Iris C. ten Have
- Inorganic Chemistry and CatalysisDebye Institute for Nanomaterial ScienceUtrecht UniversityUniversiteitsweg 993584 CGUtrechtThe Netherlands
| | - Hendrik Ohldag
- Advanced Light Source, MicroscopyLawrence Berkeley National Laboratory1 Cyclotron RoadBerkeleyCA94720USA
- Department of Materials Science and EngineeringStanford University450 Serra MallStanfordCA943505USA
- Department of PhysicsUniversity of California Santa Cruz1156 High StreetSanta CruzCA95064USA
| | - Benjamin Watts
- Laboratory for Synchotron Radiation—Condensed Matter (LSC)Paul Scherrer Institute (PSI)Forschungsstrasse 1115232VilligenSwitzerland
| | - Theo van Kessel
- Technology and Innovation DepartmentSABICUrmonderbaan 226167 RDGeleenThe Netherlands
| | - Nic. Friederichs
- Technology and Innovation DepartmentSABICUrmonderbaan 226167 RDGeleenThe Netherlands
| | - Bert M. Weckhuysen
- Inorganic Chemistry and CatalysisDebye Institute for Nanomaterial ScienceUtrecht UniversityUniversiteitsweg 993584 CGUtrechtThe Netherlands
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Jongkind MK, van Kessel T, Velthoen MEZ, Friederichs N, Weckhuysen BM. Tuning the Redox Chemistry of a Cr/SiO 2 Phillips Catalyst for Controlling Activity, Induction Period and Polymer Properties. Chemphyschem 2020; 21:1665-1674. [PMID: 32539171 PMCID: PMC7496818 DOI: 10.1002/cphc.202000488] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/07/2020] [Revised: 06/12/2020] [Indexed: 11/06/2022]
Abstract
The Cr/SiO2 Phillips catalyst has taken a central role in ethylene polymerization ever since its discovery in 1953. This catalyst is unique compared to other ethylene polymerization catalysts, since it is active without the addition of a metal-alkyl co-catalyst. However, metal-alkyls can be added for scavenging poisons, enhancing the catalyst activity, reducing the induction period and altering polymer characteristics. Despite extensive research into the working state of the catalyst, still no consensus has been reached. Here, we show that by varying the type of metal-alkyl co-catalyst and its amount, the Cr redox chemistry can be tailored, resulting in distinct catalyst activities, induction periods, and polymer characteristics. We have used in-situ UV-Vis-NIR diffuse reflectance spectroscopy (DRS) for studying the Cr oxidation state during the reduction by tri-ethyl borane (TEB) or tri-ethyl aluminum (TEAl) and during subsequent ethylene polymerization. The results show that TEB primarily acts as a reductant and reduces Cr6+ with subsequent ethylene polymerization resulting in rapid polyethylene formation. TEAl generated two types of Cr2+ sites, inaccessible Cr3+ sites and active Cr4+ sites. Subsequent addition of ethylene also revealed an increased reducibility of residual Cr6+ sites and resulted in rapid polyethylene formation. Our results demonstrate the possibility of controlling the reduction chemistry by adding the proper amount and type of metal-alkyl for obtaining desired catalyst activities and tailored polyethylene characteristics.
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Affiliation(s)
- Maarten K. Jongkind
- Inorganic Chemistry and CatalysisDebye Institute for Nanomaterial ScienceUtrecht UniversityUniversiteitsweg 993584 CGUtrechtThe Netherlands
| | - Theo van Kessel
- SABICTechnology and Innovation DepartmentUrmonderbaan 226167RD GeleenThe Netherlands
| | - Marjolein E. Z. Velthoen
- Inorganic Chemistry and CatalysisDebye Institute for Nanomaterial ScienceUtrecht UniversityUniversiteitsweg 993584 CGUtrechtThe Netherlands
| | - Nic. Friederichs
- SABICTechnology and Innovation DepartmentUrmonderbaan 226167RD GeleenThe Netherlands
| | - Bert M. Weckhuysen
- Inorganic Chemistry and CatalysisDebye Institute for Nanomaterial ScienceUtrecht UniversityUniversiteitsweg 993584 CGUtrechtThe Netherlands
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Martino GA, Piovano A, Barzan C, Rabeah J, Agostini G, Bruekner A, Leone G, Zanchin G, Monoi T, Groppo E. Rationalizing the Effect of Triethylaluminum on the Cr/SiO 2 Phillips Catalysts. ACS Catal 2020. [DOI: 10.1021/acscatal.9b04726] [Citation(s) in RCA: 12] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Giorgia A. Martino
- Department of Chemistry, NIS Centre and INSTM, University of Torino, via G. Quarello 15A, 10135 Torino, Italy
| | - Alessandro Piovano
- Department of Chemistry, NIS Centre and INSTM, University of Torino, via G. Quarello 15A, 10135 Torino, Italy
| | - Caterina Barzan
- Department of Chemistry, NIS Centre and INSTM, University of Torino, via G. Quarello 15A, 10135 Torino, Italy
| | - Jabor Rabeah
- Leibniz Institute for Catalysis at the University of Rostock (LIKAT), Albert-Einstein-Str. 29, D-18059 Rostock, Germany
| | - Giovanni Agostini
- Leibniz Institute for Catalysis at the University of Rostock (LIKAT), Albert-Einstein-Str. 29, D-18059 Rostock, Germany
| | - Angelika Bruekner
- Leibniz Institute for Catalysis at the University of Rostock (LIKAT), Albert-Einstein-Str. 29, D-18059 Rostock, Germany
| | - Giuseppe Leone
- CNR, Istituto di Scienze e Tecnologie Chimiche “Giulio Natta” (SCITEC), via A. corti 12, I-20133 Milano, Italy
| | - Giorgia Zanchin
- CNR, Istituto di Scienze e Tecnologie Chimiche “Giulio Natta” (SCITEC), via A. corti 12, I-20133 Milano, Italy
| | - Takashi Monoi
- R&D Division, Japan Polychem Corporation, 1-1 Marunouchi 1-chome, Chiyoda-ku, 100-8251 Tokyo, Japan
| | - Elena Groppo
- Department of Chemistry, NIS Centre and INSTM, University of Torino, via G. Quarello 15A, 10135 Torino, Italy
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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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