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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experimental data continue to be obtained, and certain mechanistic concepts are being developed with the use of outdated models.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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2
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Liu S, Dun C, Chen J, Rao S, Shah M, Wei J, Chen K, Xuan Z, Kyriakidou EA, Urban JJ, Swihart MT. A General Route to Flame Aerosol Synthesis and In Situ Functionalization of Mesoporous Silica. Angew Chem Int Ed Engl 2022; 61:e202206870. [DOI: 10.1002/anie.202206870] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/10/2022] [Indexed: 11/10/2022]
Affiliation(s)
- Shuo Liu
- Department of Chemical and Biological Engineering University at Buffalo (SUNY) Buffalo NY 14260 USA
| | - Chaochao Dun
- The Molecular Foundry Lawrence Berkeley National Laboratory Berkeley CA 94720 USA
| | - Junjie Chen
- Department of Chemical and Biological Engineering University at Buffalo (SUNY) Buffalo NY 14260 USA
| | - Satyarit Rao
- Department of Chemical and Biological Engineering University at Buffalo (SUNY) Buffalo NY 14260 USA
| | - Mihir Shah
- Department of Chemical and Biological Engineering University at Buffalo (SUNY) Buffalo NY 14260 USA
| | - Jilun Wei
- Department of Chemical and Biological Engineering University at Buffalo (SUNY) Buffalo NY 14260 USA
| | - Kaiwen Chen
- Department of Chemical and Biological Engineering University at Buffalo (SUNY) Buffalo NY 14260 USA
| | - Zhengxi Xuan
- Department of Chemical and Biological Engineering University at Buffalo (SUNY) Buffalo NY 14260 USA
- RENEW Institute University at Buffalo (SUNY) Buffalo NY 14260 USA
| | - Eleni A. Kyriakidou
- Department of Chemical and Biological Engineering University at Buffalo (SUNY) Buffalo NY 14260 USA
| | - Jeffrey J. Urban
- The Molecular Foundry Lawrence Berkeley National Laboratory Berkeley CA 94720 USA
| | - Mark T. Swihart
- Department of Chemical and Biological Engineering University at Buffalo (SUNY) Buffalo NY 14260 USA
- RENEW Institute University at Buffalo (SUNY) Buffalo NY 14260 USA
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3
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Jin Y, Yang Y, Su C, Wang J, Wang Y, Liu B. Novel Imido‐Cr/Silica Ethylene Polymerization Catalysts Modified from the Phillips Catalyst. MACROMOL REACT ENG 2022. [DOI: 10.1002/mren.202200025] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
Affiliation(s)
- Yulong Jin
- Key Laboratory for Biobased Materials and Energy of Ministry of Education Guangdong Laboratory for Lingnan Modern Agriculture College of Materials and Energy South China Agricultural University Wushan Road 483 Guangzhou 510630 People's Republic of China
| | - Yang Yang
- Key Laboratory for Biobased Materials and Energy of Ministry of Education Guangdong Laboratory for Lingnan Modern Agriculture College of Materials and Energy South China Agricultural University Wushan Road 483 Guangzhou 510630 People's Republic of China
| | - Changzhi Su
- Liaoyang Petrochemical Research Center Petrochemical Research Institute of PetroChina Huoju Road 7 Liaoyang 111003 People's Republic of China
| | - Junrong Wang
- Liaoyang Petrochemical Research Center Petrochemical Research Institute of PetroChina Huoju Road 7 Liaoyang 111003 People's Republic of China
| | - Yongnian Wang
- Liaoyang Petrochemical Research Center Petrochemical Research Institute of PetroChina Huoju Road 7 Liaoyang 111003 People's Republic of China
| | - Boping Liu
- Key Laboratory for Biobased Materials and Energy of Ministry of Education Guangdong Laboratory for Lingnan Modern Agriculture College of Materials and Energy South China Agricultural University Wushan Road 483 Guangzhou 510630 People's Republic of China
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4
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Alzamly A, Bakiro M, Hussein Ahmed S, Siddig LA, Nguyen HL. Linear α-olefin oligomerization and polymerization catalyzed by metal-organic frameworks. Coord Chem Rev 2022. [DOI: 10.1016/j.ccr.2022.214522] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
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5
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Liu S, Dun C, Chen J, Rao S, Shah M, Wei J, Chen K, Xuan Z, Kyriakidou EA, Urban JJ, Swihart MT. A General Route to Flame Aerosol Synthesis and in situ Functionalization of Mesoporous Silica. Angew Chem Int Ed Engl 2022. [DOI: 10.1002/ange.202206870] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Affiliation(s)
- Shuo Liu
- University at Buffalo Chemical and Biological Engineering UNITED STATES
| | - Chaochao Dun
- Lawrence Berkeley National Laboratory: E O Lawrence Berkeley National Laboratory Molecular Foundry UNITED STATES
| | - Junjie Chen
- University at Buffalo Chemical and Biological Engineering UNITED STATES
| | - Satyarit Rao
- University at Buffalo Chemical and Biological Engineering UNITED STATES
| | - Mihir Shah
- University at Buffalo Chemical and Biological Engineering UNITED STATES
| | - Jilun Wei
- University at Buffalo Chemical and Biological Engineering UNITED STATES
| | - Kaiwen Chen
- University at Buffalo Chemical and Biological Engineering UNITED STATES
| | - Zhengxi Xuan
- University at Buffalo Chemical and Biological Engineering UNITED STATES
| | | | - Jeffrey J. Urban
- Lawrence Berkeley National Laboratory: E O Lawrence Berkeley National Laboratory Molecular Foundry UNITED STATES
| | - Mark T. Swihart
- University at Buffalo Chemical and Biological Engineering 308 Furnas Hall 14260-4200 Buffalo UNITED STATES
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6
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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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Werny MJ, Zarupski J, ten Have IC, Piovano A, Hendriksen C, Friederichs NH, Meirer F, Groppo E, Weckhuysen BM. Correlating the Morphological Evolution of Individual Catalyst Particles to the Kinetic Behavior of Metallocene-Based Ethylene Polymerization Catalysts. JACS AU 2021; 1:1996-2008. [PMID: 35574041 PMCID: PMC8611720 DOI: 10.1021/jacsau.1c00324] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/22/2021] [Indexed: 06/12/2023]
Abstract
Kinetics-based differences in the early stage fragmentation of two structurally analogous silica-supported hafnocene- and zirconocene-based catalysts were observed during gas-phase ethylene polymerization at low pressures. A combination of focused ion beam-scanning electron microscopy (FIB-SEM) and nanoscale infrared photoinduced force microscopy (IR PiFM) revealed notable differences in the distribution of the support, polymer, and composite phases between the two catalyst materials. By means of time-resolved probe molecule infrared spectroscopy, correlations between this divergence in morphology and the kinetic behavior of the catalysts' active sites were established. The rate of polymer formation, a property that is inherently related to a catalyst's kinetics and the applied reaction conditions, ultimately governs mass transfer and thus the degree of homogeneity achieved during support fragmentation. In the absence of strong mass transfer limitations, a layer-by-layer mechanism dominates at the level of the individual catalyst support domains under the given experimental conditions.
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Affiliation(s)
- Maximilian J. Werny
- Inorganic
Chemistry and Catalysis group, Debye Institute for Nanomaterials Science, Utrecht University, Universiteitsweg 99, 3584 CG Utrecht, The Netherlands
- Dutch
Polymer Institute (DPI), P.O. Box 902, 5600 AX Eindhoven, The Netherlands
| | - Jelena Zarupski
- Department
of Chemistry, INSTM and NIS Centre, University
of Torino, Via G. Quarello
15A, 10135 Torino, Italy
- Dutch
Polymer Institute (DPI), P.O. Box 902, 5600 AX Eindhoven, The Netherlands
| | - Iris C. ten Have
- Inorganic
Chemistry and Catalysis group, Debye Institute for Nanomaterials Science, Utrecht University, Universiteitsweg 99, 3584 CG Utrecht, The Netherlands
| | - Alessandro Piovano
- Department
of Chemistry, INSTM and NIS Centre, University
of Torino, Via G. Quarello
15A, 10135 Torino, Italy
- Dutch
Polymer Institute (DPI), P.O. Box 902, 5600 AX Eindhoven, The Netherlands
| | - Coen Hendriksen
- SABIC
Technology Center, Urmonderbaan 22, 6167 RD Geleen, The Netherlands
| | | | - Florian Meirer
- Inorganic
Chemistry and Catalysis group, Debye Institute for Nanomaterials Science, Utrecht University, Universiteitsweg 99, 3584 CG Utrecht, The Netherlands
- Dutch
Polymer Institute (DPI), P.O. Box 902, 5600 AX Eindhoven, The Netherlands
| | - Elena Groppo
- Department
of Chemistry, INSTM and NIS Centre, University
of Torino, Via G. Quarello
15A, 10135 Torino, Italy
- Dutch
Polymer Institute (DPI), P.O. Box 902, 5600 AX Eindhoven, The Netherlands
| | - Bert M. Weckhuysen
- Inorganic
Chemistry and Catalysis group, Debye Institute for Nanomaterials Science, Utrecht University, Universiteitsweg 99, 3584 CG Utrecht, The Netherlands
- Dutch
Polymer Institute (DPI), P.O. Box 902, 5600 AX Eindhoven, The Netherlands
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8
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Deng S, Liu Z, Liu B, Jin Y. Unravelling the Role of Al‐alkyl Cocatalyst for the VO
x
/SiO
2
Ethylene Polymerization Catalyst: Diethylaluminum Chloride Vs. Triethylaluminum. ChemCatChem 2021. [DOI: 10.1002/cctc.202001929] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Affiliation(s)
- Shiheng Deng
- Key Laboratory for Biobased Materials and Energy of Ministry of Education College of Materials and Energy South China Agricultural University Guangzhou 510630 P.R. China
- Guangdong Laboratory for Lingnan Modern Agriculture Guangzhou 510630 P.R. China
| | - Zhen Liu
- State Key Laboratory of Chemical Engineering School of Chemical Engineering East China University of Science and Technology Shanghai 200237 P.R. China
| | - Boping Liu
- Key Laboratory for Biobased Materials and Energy of Ministry of Education College of Materials and Energy South China Agricultural University Guangzhou 510630 P.R. China
- Guangdong Laboratory for Lingnan Modern Agriculture Guangzhou 510630 P.R. China
| | - Yulong Jin
- Key Laboratory for Biobased Materials and Energy of Ministry of Education College of Materials and Energy South China Agricultural University Guangzhou 510630 P.R. China
- Guangdong Laboratory for Lingnan Modern Agriculture Guangzhou 510630 P.R. China
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9
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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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10
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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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11
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Zanchin G, Piovano A, Amodio A, De Stefano F, Di Girolamo R, Groppo E, Leone G. NEt 3-Triggered Synthesis of UHMWPE Using Chromium Complexes Bearing Non-innocent Iminopyridine Ligands. Macromolecules 2021. [DOI: 10.1021/acs.macromol.0c02475] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Giorgia Zanchin
- CNR, Istituto di Scienze e Tecnologie Chimiche “Giulio Natta” (SCITEC), via A. Corti 12, I-20133 Milano, Italy
| | - Alessandro Piovano
- Dipartimento di Chimica, NIS Interdepartmental Research Center and INSTM Reference Center, Università degli Studi di Torino, Via G. Quarello 15A, I-10135 Torino, Italy
| | - Alessia Amodio
- Dipartimento di Chimica, NIS Interdepartmental Research Center and INSTM Reference Center, Università degli Studi di Torino, Via G. Quarello 15A, I-10135 Torino, Italy
| | - Fabio De Stefano
- Dipartimento di Scienze Chimiche, Università di Napoli “Federico II”, Complesso Monte S. Angelo, via Cintia, I-80126 Napoli, Italy
| | - Rocco Di Girolamo
- Dipartimento di Scienze Chimiche, Università di Napoli “Federico II”, Complesso Monte S. Angelo, via Cintia, I-80126 Napoli, Italy
| | - Elena Groppo
- Dipartimento di Chimica, NIS Interdepartmental Research Center and INSTM Reference Center, Università degli Studi di Torino, Via G. Quarello 15A, I-10135 Torino, Italy
| | - Giuseppe Leone
- CNR, Istituto di Scienze e Tecnologie Chimiche “Giulio Natta” (SCITEC), via A. Corti 12, I-20133 Milano, Italy
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12
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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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