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Proton Transfers Are Key Elementary Steps In Ethylene Polymerization On Isolated Chromium(III) Silicates
Murielle F Delley, Francisco Núñez-Zarur, Matthew P Conley, Aleix Comas-Vives, G. Siddiqi, S. Norsic, V. Monteil, O. Safonova, C. Copéret
Published 2014 · Chemistry, Medicine
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Significance The Phillips catalyst—CrOx/SiO2—produces 40–50% of global high-density polyethylene, yet several fundamental mechanistic controversies surround this catalyst. What is the oxidation state and nuclearity of the active Cr sites? How is the first Cr–C bond formed? How does the polymer propagate and regulate its molecular weight? Here we show through combined experimental (infrared, ultraviolet-visible, X-ray near edge absorption spectroscopy, and extended X-ray absorption fine structures) and density functional theory modeling approaches that mononuclear tricoordinate Cr(III) sites immobilized on silica polymerize ethylene by the classical Cossee–Arlman mechanism. Initiation (C–H bond activation) and polymer molecular weight regulation (the microreverse of C–H activation) are controlled by proton transfer steps. Mononuclear Cr(III) surface sites were synthesized from grafting [Cr(OSi(OtBu)3)3(tetrahydrofurano)2] on silica partially dehydroxylated at 700 °C, followed by a thermal treatment under vacuum, and characterized by infrared, ultraviolet-visible, electron paramagnetic resonance (EPR), and X-ray absorption spectroscopy (XAS). These sites are highly active in ethylene polymerization to yield polyethylene with a broad molecular weight distribution, similar to that typically obtained from the Phillips catalyst. CO binding, EPR spectroscopy, and poisoning studies indicate that two different types of Cr(III) sites are present on the surface, one of which is active in polymerization. Density functional theory (DFT) calculations using cluster models show that active sites are tricoordinated Cr(III) centers and that the presence of an additional siloxane bridge coordinated to Cr leads to inactive species. From IR spectroscopy and DFT calculations, these tricoordinated Cr(III) sites initiate and regulate the polymer chain length via unique proton transfer steps in polymerization catalysis.
This paper references
The state of Cr(VI) on the Phillips polymerization catalyst: III. The reaction between CrO3/silica and HCl
M. Mcdaniel (1982)
The state of Cr(VI) on the Cr/Silica polymerization catalyst
M. Mcdaniel (1981)
Metal and ligand K-edge XAS of organotitanium complexes: metal 4p and 3d contributions to pre-edge intensity and their contributions to bonding.
S. George (2005)
A Ciborska (2007)
Mechanistic Studies of Ethylene and α-Olefin Co-oligomerization Catalyzed by Chromium-PNP Complexes.
L. Do (2012)
A chromium catalyst for the polymerization of ethylene as a homogeneous model for the phillips catalyst.
Leonard A. MacAdams (2005)
Homogeneous Chromium Catalysts for Olefin Polymerization
K. Theopold (1998)
HREELS, TPD and XPS study of the interaction of water with the α-Cr2O3(001) surface
M. Henderson (2000)
α-Agostic Interactions and Olefin Insertion in Metallocene Polymerization Catalysts
R. Grubbs (1996)
NiO(111) and Cr2O3(111)
D Cappus (1993)
X-ray absorption spectroscopic and electrochemical studies of tris(catecholato(2-))chromate(V/IV/III) complexes.
A. Levina (2004)
Surface Chemistry and Spectroscopy of Chromium in Inorganic Oxides.
B. Weckhuysen (1996)
α‐Agostic Interactions and Olefin Insertion in Metallocene Polymerization Catalysts
R. Grubbs (1996)
Modeling metal-catalyzed olefin polymerization.
A. Rappé (2000)
Influence of dealumination and treatments on the chromium speciation in zeolite CrBEA
Konstantin Hadjiivanov (2009)
CHROMIUM ALLYLS ON SILICA : A STUDY OF STRUCTURE AND REACTIVITY
O. M. Bade (1998)
The state of Cr(VI) on the Phillips polymerization catalyst: II. The reaction between silica and CrO2Cl2
M. Mcdaniel (1982)
The structure of tris(1,1,1,5,5,5-hexafluoro-2,4-pentanedionato)aluminum(III) determined by gas phase electron diffraction
M. L. Morris (1979)
X-ray absorption edge determination of the oxidation state and coordination number of copper: application to the type 3 site in Rhus vernicifera laccase and its reaction with oxygen
L. S. Kau (1987)
Poisoning studies on chromium/silica. 2. Carbon monoxide
M. Mcdaniel (1991)
A Review of the Phillips Supported Chromium Catalyst and Its Commercial Use for Ethylene Polymerization
M. Mcdaniel (2010)
The surface chemistry of amorphous silica. Zhuravlev model
L. T. Zhuravlev (2000)
Nonclassical Metal Carbonyls
S. Strauss (2010)
A Systematic K-edge X-ray Absorption Spectroscopic Study of Cu(III) Sites
J. DuBois (2000)
Simulations of the structure and properties of amorphous silica surfaces
Jeanette M. Stallons (2001)
The active site for ethylene polymerization over chromium supported on silica
D. D. Beck (1981)
State of Chromium in CrSiBEA Zeolite Prepared by the Two-Step Postsynthesis Method: XRD, FTIR, UV−Vis, EPR, TPR, and XAS Studies
and Stanislaw Dzwigaj (2008)
Hydroxyl groups on oxide surfaces
V. Coustet (1997)
Ethylene-polymerization by surface supported Cr(IV) species: possible reaction mechanisms revisited by theoretical calculations
Rochus Schmid (2000)
Theoretical models of ethylene polymerization over a mononuclear chromium(II)/silica site
Øystein Espelid (2000)
Cocatalysts for metal-catalyzed olefin polymerization: activators, activation processes, and structure-activity relationships.
E. Chen (2000)
Mechanistic studies of the ethylene trimerization reaction with chromium-diphosphine catalysts: experimental evidence for a mechanism involving metallacyclic intermediates.
T. Agapie (2004)
Anna Ciborska (2007)
Catalysts for the living insertion polymerization of alkenes: access to new polyolefin architectures using Ziegler-Natta chemistry.
G. Coates (2002)
A XANES determination of the oxidation state of chromium in silicate glasses
A. J. Berry (2004)
Homoleptic Metal Carbonyl Cations of the Electron‐Rich Metals: Their Generation in Superacid Media Together with Their Spectroscopic and Structural Characterization
H. Willner (1997)
Silica-supported alkylidene complexes: their preparation, characterization and reactivity, especially towards olefins
M. Beaudoin (2002)
The state of Cr(VI) on the Phillips polymerization catalyst: IV. Saturation coverage
M. Mcdaniel (1982)
C-H bond activation in transition metal species from a computational perspective.
David Balcells (2010)
Ethylene insertion and .beta.-hydrogen elimination for permethylscandocene alkyl complexes. A study of the chain propagation and termination steps in Ziegler-Natta polymerization of ethylene
B. Burger (1990)
Synthesis and Characterization of Silica-Stabilized Chromium(IV) Alkylidene Complexes
Jamila Amor Nait Ajjou (1998)
Active Site Transformation During the Induction Period of Ethylene Polymerization over the Phillips CrOx/SiO2 Catalyst
L. Zhong (2012)
Organochromium(III) chemistry: a neglected oxidation state
K. Theopold (1990)
A Multiplet Analysis of Fe K-Edge 1s → 3d Pre-Edge Features of Iron Complexes
Tami E. Westre (1997)
Modeling CO and N2 adsorption at Cr surface species of Phillips catalyst by hybrid density functionals: effect of Hartree-Fock exchange percentage.
A. Damin (2009)
Molecular-Level Insight into Cr/Silica Phillips-Type Catalysts: Polymerization-Active Dinuclear Chromium Sites
Øystein Espelid (2002)
Mechanistic studies of olefin and alkyne trimerization with chromium catalysts: deuterium labeling and studies of regiochemistry using a model chromacyclopentane complex.
T. Agapie (2007)
Mechanism of Metal Oxide Nanoparticle Loading in SBA-15 by the Double Solvent Technique
J. V. D. Meer (2010)
Polymerization of ethylene by silica-supported dinuclear Cr(III) sites through an initiation step involving C-H bond activation.
Matthew P Conley (2014)
Theoretical analysis of co adsorption on the reduced Cr/silica system
Øystein Espelid (2002)
Nonclassical metal carbonyls . Progress in Inorganic Chemistry , ed
AJ Lupinetti (2001)
Hydroxyl groups on oxide surfaces: NiO(100), NiO(111) and Cr2O3(111)
D. Cappus (1993)
Theoretical Analysis of d–d Transitions for the Reduced Cr/Silica System
Øystein Espelid (2001)
This paper is referenced by
Tuning the Redox Chemistry of a Cr/SiO2 Phillips Catalyst for Controlling Activity, Induction Period and Polymer Properties
Maarten K. Jongkind (2020)
Acid-Base Pairs in Lewis Acidic Zeolites Promote Direct Aldol Reactions by Soft Enolization.
J. Lewis (2015)
Chapter 4 – Catalysis
Baron Peters (2017)
Silica-Supported Pentamethylcyclopentadienyl Ytterbium(II) and Samarium(II) Sites: Ultrahigh Molecular Weight Polyethylene without Co-Catalyst.
F. Allouche (2018)
Isostructural Molecular and Surface Mimics of the Active Sites of the Industrial WO3/SiO2 Metathesis Catalysts
V. Mougel (2015)
Selective propane dehydrogenation with single-site CoII on SiO2 by a non-redox mechanism
Bo Hu (2015)
Silica-Supported, Single-Site Sc and Y Alkyls for Catalytic Hydrogenation of Propylene
A. Getsoian (2017)
Eine Brücke zwischen industriellen und wohldefinierten Trägerkatalysatoren
C. Copéret (2018)
Reply to Peters et al.: Proton transfers are plausible initiation and termination steps on Cr(III) sites in ethylene polymerization
Murielle F Delley (2015)
Effect of Fluoride‐Modification on the Phillips Cr/SiO2 Catalyst for Ethylene Polymerization
Qiaoqiao Sun (2017)
Murielle F Delley (2020)
Highly Active Nonpromoted Hydrotreating Catalysts through the Controlled Growth of a Supported Hexagonal WS2 Phase
T. Alphazan (2014)
Grafting metal complexes onto amorphous supports: From elementary steps to catalyst site populations: Via kernel regression
S. Khan (2020)
Surface Organometallic Chemistry: Paving the Way Beyond Well-Defined Supported Organometallics and Single-Site Catalysis
C. Copéret (2017)
Deprotonation of coordinated ethylene may start Phillips catalysis
K. Theopold (2014)
Designed Surfaces for Active Catalysts
Satoshi Muratsugu (2017)
Olefin polymerization on Cr(III)/SiO2: Mechanistic insights from the differences in reactivity between ethene and propene
Murielle F Delley (2017)
Tracking the reasons for the peculiarity of Cr/Al2O3 catalyst in ethylene polymerization
Giorgia A. Martino (2018)
Understanding surface site structures and properties by first principles calculations: an experimental point of view!
Aleix Comas-Vives (2017)
Tricoordinate Organochromium(III) Complexes Supported by a Bulky Silylamido Ligand Produce Ultra-High-Molecular Weight Polyethylene in the Absence of Activators
H. Liu (2016)
Mechanism of Initiation in the Phillips Ethylene Polymerization Catalyst: Redox Processes Leading to the Active Site
C. Brown (2015)
Solid Lewis Acids Catalyze the Carbon–Carbon Coupling between Carbohydrates and Formaldehyde
S. V. D. Vyver (2015)
Amorphous SiO2 surface models: energetics of the dehydroxylation process, strain, ab initio atomistic thermodynamics and IR spectroscopic signatures.
Aleix Comas-Vives (2016)
New Concept of C–H and C–C Bond Activation via Surface Organometallic Chemistry
Manoja K Samantaray (2015)
The influence of functional groups on the ethylene polymerization performance of silsesquioxane-supported Phillips-type catalysts.
Ryuki Baba (2017)
Investigation of Catalytic Surfaces with Surface‐Enhanced Solid‐State NMR Spectroscopy
F. Blanc (2017)
Reexamining the evidence for proton transfers in ethylene polymerization
B. Peters (2015)
Bridging the Gap between Industrial and Well-Defined Supported Catalysts.
C. Copéret (2018)
Computational Studies of Chromium/Silica Catalysts
Z. Liu (2018)
Model systems in heterogeneous catalysis: towards the design and understanding of structure and electronic properties.
Q. Pan (2018)
Local Structures and Heterogeneity of Silica-Supported M(III) Sites Evidenced by EPR, IR, NMR, and Luminescence Spectroscopies.
Murielle F Delley (2017)
Single-Sites and Nanoparticles at Tailored Interfaces Prepared via Surface Organometallic Chemistry from Thermolytic Molecular Precursors.
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