サイエンティフィック・システム研究会 HPCミーティング2001

2001/11/02

Ziegler-Natta heterogeneous catalysis:a Car-Parrinello study
Kiyoyuki Terakuraa
Michele Parrinelloc, Mauro Boerob
cResearch Institute for Computational Sciences, Agency of Industrial Scienceand Technology (AIST), 1-1-1 Umezono, Tsukuba, Ibaraki 305-8568 ,Japanand Tsukuba Advanced Computing Center (TACC), Tsukuba, Ibaraki 3058568 ,JapancSwiss Center for Scientific Computing (CSCS), via Cantonale, Galleria 2,
CH-6928 Manno, Switzerland and ETH Hoenggerberg HCI, CH-8093
Zurich (Switzerland)
bJRCAT-ATP, 1-1-1 Higashi, Tsukuba, Ibaraki 305-0046, Japan

Outline¾ Main interests and computational details¾ MgCl2 (100), (110) and (104) active surfaces¾ TiCl4 and Ti2Cl6 catalytic species¾ Active centers and complex formation: stabilityproblems under real reaction conditions¾ α-Olefins polymerization: ethylene and propylene¾ The role of a donor phthalate (few notes)¾ Conclusions and perspectives (?)

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サイエンティフィック・システム研究会 HPCミーティング2001

2001/11/02

Main interests
 Ziegler-Natta (ZN) catalysis is by far the mostimportant industrial process in the production ofpolyolefins with high degree of stereoselectivity
 The reaction occurs at room temperature with avery high reaction rate and low amount of catalyst
 Experimental probes fail in recovering themicroscopic picture due to the very fast reaction
and the low percentage of active sites
 Quantum dynamical simulations can be a viable
tool to study in an unbiased way and on affordable
time scale active sites and the reaction pathway

Computational details
 Car-Parrinello molecular dynamics within BLYP

density functional approach Valence-core interaction described by normconserving Troullier-Martins pseudopotentials
with non-linear core corrections for Ti and Mg
 PW expansion of ψi(x) ：Ecut= 70 Ry
 Temperature control via Nose-Hoover thermostatchain Reaction path sampled within the Blue Moon
ensemble theory2

サイエンティフィック・システム研究会 HPCミーティング2001

2001/11/02

MgCl2 simulation cells: Surface (100), orthorombic, 32 formula units,17.673 x 14.560 x 28.000 A3
 Surface (110), monoclinic, 30 formula units,
19.095 x 12.522 x 28.000 A3a^b = 70.2o Surface (104), orthorombic, 48 formula units,14.560 x 21.711 x 28.000 A3

MgCl2 bulk crystal structureSpace group: R3m, a = 3.640 A, b = 17.673 A

3サイエンティフィック・システム研究会 HPCミーティング2001

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MgCl2 (100) surface
 Unrelaxed:

Mg-Cl = 2.526 A(exp. 2.530 A)
ClMgCl = 180o
 Reconstructed:

Mg-Cl = 2.442 A
2.635 A
∆E = 12.7 kcal/mol Mg

MgCl2 (104) surface
 Unrelaxed:

Mg-Cl = 2.526 A(exp. 2.530 A)
 Relaxed:

Mg-Cl = 2.421 A
2.597 A
ClMgCl = 162.1o∆E = 2.4 kcal/mol Mg

4サイエンティフィック・システム研究会 HPCミーティング2001

2001/11/02

MgCl2 (110) surface
 Unrelaxed:

Mg-Cl = 2.526 A
ClMgCl = 180o
 Relaxed:

Mg-Cl = 2.322 A
2.403 A
ClMgCl = 154o
∆E = 3.4 kcal/mol Mg

Molecular geometries of the catalysts

Ti2Cl6
Ti-Clbridge=2.44 A
TiClTi=93.7o

TiCl4
Ti-Cl=2.24 A
ClTiCl=109o5サイエンティフィック・システム研究会 HPCミーティング2001

2001/11/02

Deposition of the TiCl4 catalyst

Mononuclear Ti centers

Octahedral Ti 6-fold on
MgCl2 (110) surface as
proposed by Corradiniand co-workers.
Ebind= 40.3 kcal/mol

5-fold Ti site on MgCl2(110) surface obtained
from CPmd
Ebind= 29.4 kcal/mol[JACS 120, 2746 (1998)]

6サイエンティフィック・システム研究会 HPCミーティング2001

2001/11/02

Active mononuclear centers

Active Corradini center:
Active 5-fold center:removal of 1dangling Cl
substitution of a Cl with+ substitution of a Cl with a methyl group.
a methyl group.

Free energy calculation
 Select the reaction coordinate ξ to be monitored.

Our choice: ξ=|C1-Cα| (olefin-chain distance) Add to the Car-Parrinello lagrangean LCP theξ-ξ0)
constraint ξ: LCP DLCP+ λξ(ξ Compute the ensemble average < λξ > according
to the Blue Moon prescription
 Integrate the constraint force along the sampledpath7サイエンティフィック・システム研究会 HPCミーティング2001

2001/11/02

First insertion of ethylene

Main phases of the insertion¾ The π-complex (left), the transition state (center)and the final product (right)¾ Reaction coordinate: ξ = |C1-Cα|¾ The reaction is α-agostic assisted8サイエンティフィック・システム研究会 HPCミーティング2001

2001/11/02

Ethylene polymerization from mononuclear Ti

 ELF of the main steps of the ethylene insertion: the π-complex (right), the transition state (center) and the final
product (right). ELF=0: blue, ELF=1: red
 ELF is projected on the plane containing the C1 and C2
carbon atoms (grey) of the ethylene and Ti (purple).

Energetics ofthe reaction:

 Free (solid line) and total (dashed line) energy profiles for

the Corradini site (a) and for the 5-fold site (b)9サイエンティフィック・システム研究会 HPCミーティング2001

2001/11/02

Reorientation of the alkyl chain As a response to the incoming of a new olefin, thechain displaces spontaneously along the substrate.
The complex is dynamically stable.

Second insertion of ethylene

10サイエンティフィック・システム研究会 HPCミーティング2001

2001/11/02Second insertion of ethylene¾ π-complex (left), transition state (center) and finalproduct (right) in a single snapshot¾ Reaction is β-agostic assisted


JACS 120, 2746 (1998), Surf. Sci. 438, 1 (1999)

First insertion of propene The two possible π-complex enantiofaces for thefirst insertion of propene in the 5-fold active site
 The methyl group has to stay far from the support
to avoid steric repulsion11

サイエンティフィック・システム研究会 HPCミーティング2001

2001/11/02

First insertion of propene

 Transition state (left) and final product (right) for one of

the two enantiofaces. The other one would lead simply tothe mirror image. Insertion is α-agostic (Ha) assisted.
 Energy barrier: ∆F=10.8 kcal/mol (13.9 kcal/mol for theother enantioface).

Possible olefin orientations for propagation
Only (a) can give abarrierless complex
and a transition state
lower by ~7-8 kcal/
mol with respect to(b), (c) and (d).
The arrow indicatesthe position of thenearest Cl.

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サイエンティフィック・システム研究会 HPCミーティング2001

2001/11/02

Complexation of a second propene π-complex of a propene oriented as in (a). The chain

displaces along the substrate as in the case of ethylene.
 The insertion is α-agostic (Ha) also in the propagation

Propene polymerization from mononuclear Ti

The computed propene 1,2 insertion isIsotactic. The barrier is 10.5 kcal/mol(exp.9.5-12) with a final gain of 16.7
kcal/mol below the π-complex.
[JACS 122, 501 (2000)]
Cldangling-Mg = 3.03-3.22 A13

サイエンティフィック・システム研究会 HPCミーティング2001

2001/11/02

Complexation and insertion energies for
ethylene and propene

Ethylene
Propene(1,2)
Propene(2,1)

Insertion
Productπ-complex(kcal/mol) (kcal/mol) (kcal/mol)-8.4a,-6.5b +12.7a,+6.7b -5.8a,-23.3b-3.6b+10.5b-16.7b+5.6b+16.2b(-1.0)ba = Corradini site, b = 5-fold site

Binuclear Ti centers

Corradini’s Ti2Cl6 centeron MgCl2 (100) surface:
Mg-Cl(Ti)= 2.673 A (c)3.065 A (l)(supp)
Ti-Cl= 2.375 A
Ebind= 55.6 kcal/mol

Ti2Cl6 center on MgCl2(110) surface from CPmd:
Mg-Cl(Ti)= 2.995 A
Ti-Cl(supp)= 2.469 A
Ebind= 33.6 kcal/mol

14サイエンティフィック・システム研究会 HPCミーティング2001

2001/11/02Propene polymerization from binuclear Ti

 Singlet: disproportionation 2Ti(III) D Ti1(II) + Ti2(IV) with atotal energy gain of 55.8 kcal/mol. The binuclear site is
spontaneously destabilized.
 Final state: Ti1-Cα=2.273 A, Ti1-Cdangling=2.291 A
Ti1-Clsupport=2.630 A

Destabilized binuclear Ti center (triplet) Dissociation 2Ti(III) D Ti1(III)+Ti2(III) Final state 19.5 kcal/mol above the singlet
 Ti1-C1=3.033 A, Ti1-C2=2.595 A

J. Phys. Chem. A 105, 5096 (2001)

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サイエンティフィック・システム研究会 HPCミーティング2001

2001/11/02

Possible stable binuclear Ti species onMgCl2 (100) surface
 Ti atoms (yellow) trapped

below the active Ti2Cl6 on
top (~Terano’s islands)
 Gradual smoothing of thelattice mismatch between
Ti (yellow) and Mg (pink)

Active binuclear center on (110) Formation of π-complex

leads to a destabilization
with ∆Egain= 69.2 kcal/mol Ti1-C1= 2.185 A
Ti1-C2= 2.161 A
 Ti1(II) carrying weakly
bound to the support
 Ti2(IV): 5-fold site16サイエンティフィック・システム研究会 HPCミーティング2001

2001/11/02

Donor di-n-butyl phthalate Ability to coordinate to the support also in presence of Ti.

O1-O2 = 2.7-3.9 A (phthalates, diethers)
 Absence of secondary reactions with the catalyst
 Absence of secondary reactions with the Metal-C bond andthe growing polymer

Interaction of a donor with the support(100)

Mg1-Mg2(A)
3.674

Mg1-O1(A)
2.150

Mg2-O2(A)
2.246

Ebind(kcal/mol)
21.9

(110)

6.360

> 4.0

2.085

8.5

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サイエンティフィック・システム研究会 HPCミーティング2001

2001/11/02

Interaction of the donor with the active
Corradini center Ti-Mg1= 3.781 A, close to

Mg-Mg distance on (100) Mg1-O1= 2.203 A
Ti-O2 = 1.942 A
 Binding energy = 20.1
kcal/mol The center is poisoned bythe donor
 No interaction with 5-foldConclusions (and perspectives)
 The role and the relative importance of various

MgCl2 active surfaces has been investigated Interaction of Ti species with the support has beenstudied The polymerization reaction has been investigated
and the reaction pathway elucidated
 The problem of the stability of the active sites in arealistic system has been inspected The possible role of a donor phthalate has beenaddressed at a dynamical first principles level18

サイエンティフィック・システム研究会 HPCミーティング2001

2001/11/02

Acknowledgements Hosrt Weiss, BASF AG, Ludwigshafen (Germany) Stephan Hueffer, BASF AG (Germany) Yoshitada Morikawa, JRCAT-AIST (Japan) Akinobu Shiga, Sumitomo Co. (Japan)
 Shinichiro Nakamura, Mitsubishi Co. (Japan)
 Minoru Terano, JAIST, Hokuriku (Japan)

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