Computational Support for Phillips Catalyst Initiation via Cr-C Bond Homolysis in a Chromacyclopentane Site

Anthony Fong; Craig Vandervelden; Susannah L. Scott; Baron Peters

doi:10.1021/acscatal.7b03724

Computational Support for Phillips Catalyst Initiation via Cr-C Bond Homolysis in a Chromacyclopentane Site

Anthony Fong, Craig Vandervelden, Susannah L. Scott, Baron Peters

Research output: Contribution to journal › Article › peer-review

Abstract

Using density functional theory, we examine a possible homolysis initiation mechanism for the Phillips catalyst, starting from Cr^II sites exposed to ethylene. Spin-crossing in an abundant quintet bis(ethylene) Cr^II site leads to cycloaddition to form a chromacyclopentane site. One Cr-C bond then homolyzes to generate a tethered n-butyl radical: [Cr(CH₂)₃CH₂^•]. If the radical attaches to a nearby inorganic Cr site, it yields two alkylCr^III sites capable of Cossee-Arlman polymerization. The overall computed barrier for this initiation process is 132 kJ/mol, which is comparable to the 120 kJ/mol value that we estimated from reported initiation times in industrial reactors. Poisson statistics suggest that this mechanism could activate ∼35% of Cr sites on a commercial catalyst with a loading of 0.4 Cr/nm². Pairwise Cr grafting, amplification by complementary initiation reactions, or the creation of dangling bonds that form as the silica support fractures, might explain the apparent increase in per-site activity at lower Cr loadings.

Original language	English (US)
Pages (from-to)	1728-1733
Number of pages	6
Journal	ACS Catalysis
Volume	8
Issue number	3
DOIs	https://doi.org/10.1021/acscatal.7b03724
State	Published - Mar 2 2018
Externally published	Yes

Keywords

Phillips catalyst
density functional theory
homolysis
initiation
polymerization

ASJC Scopus subject areas

Catalysis
Chemistry(all)

Online availability

10.1021/acscatal.7b03724

Library availability

Discover UIUC Full Text

Cite this

@article{bcc8ebb12b0447febc0ab88b8616947e,

title = "Computational Support for Phillips Catalyst Initiation via Cr-C Bond Homolysis in a Chromacyclopentane Site",

abstract = "Using density functional theory, we examine a possible homolysis initiation mechanism for the Phillips catalyst, starting from CrII sites exposed to ethylene. Spin-crossing in an abundant quintet bis(ethylene) CrII site leads to cycloaddition to form a chromacyclopentane site. One Cr-C bond then homolyzes to generate a tethered n-butyl radical: [Cr(CH2)3CH2•]. If the radical attaches to a nearby inorganic Cr site, it yields two alkylCrIII sites capable of Cossee-Arlman polymerization. The overall computed barrier for this initiation process is 132 kJ/mol, which is comparable to the 120 kJ/mol value that we estimated from reported initiation times in industrial reactors. Poisson statistics suggest that this mechanism could activate ∼35% of Cr sites on a commercial catalyst with a loading of 0.4 Cr/nm2. Pairwise Cr grafting, amplification by complementary initiation reactions, or the creation of dangling bonds that form as the silica support fractures, might explain the apparent increase in per-site activity at lower Cr loadings.",

keywords = "Phillips catalyst, density functional theory, homolysis, initiation, polymerization",

author = "Anthony Fong and Craig Vandervelden and Scott, {Susannah L.} and Baron Peters",

note = "Funding Information: A.F., S.L.S., and B.P. were supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, under the Catalysis Science Initiative (No. DE-FG-02-03ER15467). C.V. was supported by the National Science Foundation (Award No. CBET-1605867). Publisher Copyright: {\textcopyright} 2018 American Chemical Society.",

year = "2018",

month = mar,

day = "2",

doi = "10.1021/acscatal.7b03724",

language = "English (US)",

volume = "8",

pages = "1728--1733",

journal = "ACS Catalysis",

issn = "2155-5435",

publisher = "American Chemical Society",

number = "3",

}

TY - JOUR

T1 - Computational Support for Phillips Catalyst Initiation via Cr-C Bond Homolysis in a Chromacyclopentane Site

AU - Fong, Anthony

AU - Vandervelden, Craig

AU - Scott, Susannah L.

AU - Peters, Baron

N1 - Funding Information: A.F., S.L.S., and B.P. were supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, under the Catalysis Science Initiative (No. DE-FG-02-03ER15467). C.V. was supported by the National Science Foundation (Award No. CBET-1605867). Publisher Copyright: © 2018 American Chemical Society.

PY - 2018/3/2

Y1 - 2018/3/2

N2 - Using density functional theory, we examine a possible homolysis initiation mechanism for the Phillips catalyst, starting from CrII sites exposed to ethylene. Spin-crossing in an abundant quintet bis(ethylene) CrII site leads to cycloaddition to form a chromacyclopentane site. One Cr-C bond then homolyzes to generate a tethered n-butyl radical: [Cr(CH2)3CH2•]. If the radical attaches to a nearby inorganic Cr site, it yields two alkylCrIII sites capable of Cossee-Arlman polymerization. The overall computed barrier for this initiation process is 132 kJ/mol, which is comparable to the 120 kJ/mol value that we estimated from reported initiation times in industrial reactors. Poisson statistics suggest that this mechanism could activate ∼35% of Cr sites on a commercial catalyst with a loading of 0.4 Cr/nm2. Pairwise Cr grafting, amplification by complementary initiation reactions, or the creation of dangling bonds that form as the silica support fractures, might explain the apparent increase in per-site activity at lower Cr loadings.

AB - Using density functional theory, we examine a possible homolysis initiation mechanism for the Phillips catalyst, starting from CrII sites exposed to ethylene. Spin-crossing in an abundant quintet bis(ethylene) CrII site leads to cycloaddition to form a chromacyclopentane site. One Cr-C bond then homolyzes to generate a tethered n-butyl radical: [Cr(CH2)3CH2•]. If the radical attaches to a nearby inorganic Cr site, it yields two alkylCrIII sites capable of Cossee-Arlman polymerization. The overall computed barrier for this initiation process is 132 kJ/mol, which is comparable to the 120 kJ/mol value that we estimated from reported initiation times in industrial reactors. Poisson statistics suggest that this mechanism could activate ∼35% of Cr sites on a commercial catalyst with a loading of 0.4 Cr/nm2. Pairwise Cr grafting, amplification by complementary initiation reactions, or the creation of dangling bonds that form as the silica support fractures, might explain the apparent increase in per-site activity at lower Cr loadings.

KW - Phillips catalyst

KW - density functional theory

KW - homolysis

KW - initiation

KW - polymerization

UR - http://www.scopus.com/inward/record.url?scp=85042943600&partnerID=8YFLogxK

UR - http://www.scopus.com/inward/citedby.url?scp=85042943600&partnerID=8YFLogxK

U2 - 10.1021/acscatal.7b03724

DO - 10.1021/acscatal.7b03724

M3 - Article

AN - SCOPUS:85042943600

SN - 2155-5435

VL - 8

SP - 1728

EP - 1733

JO - ACS Catalysis

JF - ACS Catalysis

IS - 3

ER -

Computational Support for Phillips Catalyst Initiation via Cr-C Bond Homolysis in a Chromacyclopentane Site

Abstract

Keywords

ASJC Scopus subject areas

Online availability

Library availability

Related links

Fingerprint

Cite this