WYJAZDY I WYSTĄPIENIAWAKACJE 2008

Kanada, Vancuver, lipiec 2008Australia, Sydney, wrzesień 2008Słowacja, Strbske Pleso, wrzesień 2008

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WATOC 2008Sydney, September 14-19 2008

The World Association of Theoretical and Computational Chemists (WATOC) former: The World Association of

Theoretically Oriented Chemists.

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IX. PANNONIAN INTERNATIONAL SYMPOSIUM ON CATALYSIS

Strbske Pleso, Slovakia

8 - 12   Sept. 2008

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THEORETICAL MODELING OF SMART CATALYTIC ACTIVITY OF COPPER

CENTRES IN ZEOLITES: FROM ELECTRON DENSITY FLOW

TOWARDS ACTIVATION

Ewa BroclawikPawel Rejmak

Institute of Catalysis Polish Academy of Sciences

Pawel KozyraJoanna ZaluckaMariusz Mitoraj

Faculty of ChemistryJagiellonian University

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„Smart catalysis” – very selective, fine chemistry supported by transition metal

active centres in homogeneous, heterogeneous and enzymatic catalysis

Enzymatic activity: heme and nonheme iron centres (cytochromes, oxygenases etc.)

Zeolitic activity: exchanged transtion metal (Ag, Cu, Co) sites in zeolites (MFI, FAU, FER etc)

+

Al

H

Si

O

O

O

O

O

O O

–

Cu+, Ag+

FeIVO

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Methodologies for theoretical (QM) studies:

DFT modeling of stable structures, reaction intermediates and their physical properties for cluster models of zeolitic sites:

relatively cheap method, reliable results but neglect of long-range interactions, discrimination between different types of lattices, Si/Al ratio or specific metal siting hardly possible

QMPOT (Combined QM – Interatomic Potential Functions Method) –

entire framowk considered, main drawabcks of cluster modeling

eliminated but framework treated approximately (classical Force

Fields), extra parametrization required

Periodic models – in principle accurate for entire framowk but computationally demandingvarying Si/Al ratio or metal loading breaks strict periodicity

New theoretical concepts for interpretation – NOCV

(Natural Orbitals for Chemical Valence): analyzis of electron density flow accompanying catalytic event

SPECIATION OF COPPER SITES IN FAUJASITE (by interaction with CO probe)

Small cluster models are not useful to mimic various envirinments in different zeolites (e.g. FAU, mordenite, ferrierite, ZSM-5)

Local environments may be very similar but framework and site properties will differ QMPOT

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1) Periodic framework (O) - MM

2) Cluster (C) - QM

3) Link atoms (L)

Etot = EMM(O) + EQM(C+L) + E(O,C,L) = EMM(O) + EQM(C+L) – EMM(C+L) + ΔQM/MM(O,C,L) ≈ ≈ EMM(O) + EQM(C+L) – EMM(C+L)

(Eichler, U., Koelmel, C. M., Sauer, J. J. Comp. Chem. 1997, 18(4), 463)Sierka, M., Sauer, J. In: Yip., S. (Ed.), The Handbook of Materials Modelling, Part A Springer, Dordrecht, 2005, 241-258)

COMBINED QUANTUM MECHANIC – INTERATOMIC POTENTIAL FUNCTIONS METHOD (QMPot)

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Possible cationic (black) and crystallographic O positions (gray)(Smith., J. V. Adv. Chem. Ser. 1971, 101, 171)

Cu(I)-Y XRD and ND experiments indicate Cu(I) only in I’, II or II’ positions(Palomino, G. T., Bordiga, S., Zecchina, A., Marra, G. L., Lamberti, C. J. Phys. Chem. B 2000, 104, 8641)

theoretical positions (red) – stability: II≈I’ >> III(Rejmak, P., Sierka, M., Sauer, J. – w przygotowaniu)

Site I is not accessible for adsorbed molecules

FAUJAZITE (FAU)

Regular cell F-d3m, 192 atoms T and 384 O

FAU – high alumina contentX zeolite – Si/Al close to 1Y zeolite – Si/Al about 2-3

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The nearest environment of Cu+ ions in site II (2 Al atoms in para positions)

(A) free cluster(B) Force Field only(C) QMPot modelenvironment importance!!

2) The impact of embedding

4Al

Interaction of benzene with

Cu+, Ag+ i Na+ in ZSM-5 zeolite

Experiment: J. Załucka, P. Kozyra, J. Datka

Theory: M. Mitoraj, A. Michalak

environment importance accounted for

no microscopic insight into electronic processes/ charge flow

(need for new theoretical development)

Summary for QMPOT modeling:

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M7-Me-benzene (Me=Cu(I), Ag(I), Na(I))

Adsorption by 2 carbon atomsC=C variation, aromaticity diminished for Cu(I) and Ag(I)

6,5 kcal/mol 11,9 kcal/molEint = 19,2 kcal/mol

activation

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ΔQben Δcalc /cm-1 Δexp /cm-1

Cu+-M7-C6H6 0.012 -22 -13

Ag+-M7-C6H6 0.041 -11 -8

Na+-M7-C6H6 0.056 -2 -2

Mechanism of C=C activation??? Donation or backdonation???

Cu+-M7 Ag+-M7 Na+-M7before/after ΔQ

before/after ΔQ before

/after ΔQ

Benzene

0

+0.0120

+0.0410

+0.0560.012 0.041 0.0565

M+0.364

+0.0490.480

-0.0430.453

-0.1010.413 0.437 0.352

M7-0.364

-0.059

-0.48

+0.003

-0.453

+0.044-0.423-0.477 -0.409

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NOCV – Natural Orbitals for Chemical Valence(Mitoraj M., Michalak A., Organometallics, 26 (2007) 6576-6580)

NOCV are the eigenfunctions of a valence operator:

V i(ri) = i i(ri)

where:

V = 1/2(P – P0)

P – charge and bond order matrix for the molecule

P0 – charge and bond order matrix for promolecule– fragments

in the geometry of common system but noninteracting

i(ri) describes spatial distribution and character of elementary electron

density flows („channels”) i the share of a given “channel” in total density flow

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occupied „promolecular” orbitals

occupied molecular orbitals in composed system

“pairing property” of NOCV (rigorous proof by M. Radon):

relation between eigenvalues of V and expectation values of the molecular density

operator, P

•total electronic transfer may be decomposed into sum of separated transfers within pairs of coupled NOCV

•for each k, the transfer of νk electrons from ϕ−k to ϕ+k orbital is observed

•during this transfer the total number of electrons in (ϕ−k, ϕ+k ) pair remains equal exactly to two electrons

Now:

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NOCV – Natural Orbitals for Chemical Valence(Mitoraj M., Michalak A., Organometallics, 26 (2007) 6576-6580)

-i-i(ri)2+ii(ri)2 describes spatial distribution and character of elementary electron density flows

(„channels”) i the share of a given “channel” in total density flow

Decomposition of differential density flow:

ρ(r)molekule/cluster - ρ (r)fragment1 – ρ(r)fragment2

into elementary flow channels i(ri)

The method to discriminate between donation and backdonation

(even σ or π)!!

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Example: heme + CO

CO

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NOCV [M7-Cu+]-C6H6

-0.484*

-0.356*

-0.218*

-0.105*

yellow – electron outflow

green– electron inflow

donation

backdonation

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[Cu+-zeo]-C6H6

[Cu+-C6H6]-zeobond Cu-zeo

[Cu+]-[C6H6]

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NOCV [M7-Ag+]-C6H6

-0.160*

-0.266*

-0.217*

donation

backdonation

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[Ag+-zeo]-C6H6

[Ag+-C6H6]-zeo

[Ag+]-[C6H6]

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Vd Vbd Vd + Vbd Δcalc /cm-1 Δexp /cm-1

Cu+-M7-C6H6 0.46 0.70 1.16 -22 -13

Ag+-M7-C6H6 0.27 0.38 0.65 -11 -8

Na+-M7-C6H6 < 0.1 < 0.1 < 0.2 -2 -2

Both donation and backdonation correlate with C=C activation measured by IR frequency shifts

Total charge change does not correlate positively with C=C activation

Na+ - only electrostatic interaction, no activation

ΔQben

0.012

0.041

0.056

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CONCLUSIONS

Cluster DFT modeling:

open path to advanced calculations reasonable reproduction of experiment (for

justified model) rough understanding of physical nature of

the process

Combined QM/MM modeling:

environment importance accounted for detailed speciation/discrimination of sites statistical interpretation of experimental

results

New interpretative theoretical tools

microscopic insight into electronic processes/

charge flow

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Thank you for kind attention!

Acknowledgments

Polish State Committee for Scientific ResearchIR studies supported by grant NN204198733. Computational studies supported by: EU project Transfer of Knowledge TOK-CATA, contract MTKD-CT-2004-509832

grant N20418031/3999. grant PZB-KBN-116/T09/2004

Thanks to prof. J. Sauer and dr. M. Sierka (Humboldt University) for QMPOT code.