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ALKANE CRACKING IN ZEOLITES: AN OVERVIEW OF RECENT MODELING RESULTS ALKANE CRACKING IN ZEOLITES: AN OVERVIEW OF RECENT MODELING RESULTS anos ´ Angy ´ an and Drew Parsons Institut f ¨ ur Materialphysik Universit ¨ at Wien Wien, Austria and Laboratoire de Chimie th ´ eorique Universit ´ e Henri Poincar´ e Vandoeuvre–l` es–Nancy Cedex, France Alkane cracking in zeolites anos ´ Angy ´ an
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Alkane cracking in zeolites - univ-lorraine.frcrm2.univ-lorraine.fr/pages_perso/Angyan/papers/talkwn.pdf · alkane cracking in zeolites: an overview of recent modeling results alkane

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Page 1: Alkane cracking in zeolites - univ-lorraine.frcrm2.univ-lorraine.fr/pages_perso/Angyan/papers/talkwn.pdf · alkane cracking in zeolites: an overview of recent modeling results alkane

ALKANE CRACKING IN ZEOLITES:

AN OVERVIEW

OF RECENT MODELING RESULTS

ALKANE CRACKING IN ZEOLITES:

AN OVERVIEW

OF RECENT MODELING RESULTS

Janos Angyan and Drew Parsons

Institut fur MaterialphysikUniversitat Wien

Wien, Austria

and

Laboratoire de Chimie theoriqueUniversite Henri Poincare

Vandœuvre–les–Nancy Cedex, France

Alkane cracking in zeolites JIN Janos Angyan

Page 2: Alkane cracking in zeolites - univ-lorraine.frcrm2.univ-lorraine.fr/pages_perso/Angyan/papers/talkwn.pdf · alkane cracking in zeolites: an overview of recent modeling results alkane

Outline

◦ Haag-Dassau cracking mechanism

Alkane cracking in zeolites JIN Janos Angyan

Page 3: Alkane cracking in zeolites - univ-lorraine.frcrm2.univ-lorraine.fr/pages_perso/Angyan/papers/talkwn.pdf · alkane cracking in zeolites: an overview of recent modeling results alkane

Outline

◦ Haag-Dassau cracking mechanismLessons to draw from experimental results

Alkane cracking in zeolites JIN Janos Angyan

Page 4: Alkane cracking in zeolites - univ-lorraine.frcrm2.univ-lorraine.fr/pages_perso/Angyan/papers/talkwn.pdf · alkane cracking in zeolites: an overview of recent modeling results alkane

Outline

◦ Haag-Dassau cracking mechanismLessons to draw from experimental results

◦ Alkane physisorption on zeolites

Alkane cracking in zeolites JIN Janos Angyan

Page 5: Alkane cracking in zeolites - univ-lorraine.frcrm2.univ-lorraine.fr/pages_perso/Angyan/papers/talkwn.pdf · alkane cracking in zeolites: an overview of recent modeling results alkane

Outline

◦ Haag-Dassau cracking mechanismLessons to draw from experimental results

◦ Alkane physisorption on zeolitesWhy is it important?

Alkane cracking in zeolites JIN Janos Angyan

Page 6: Alkane cracking in zeolites - univ-lorraine.frcrm2.univ-lorraine.fr/pages_perso/Angyan/papers/talkwn.pdf · alkane cracking in zeolites: an overview of recent modeling results alkane

Outline

◦ Haag-Dassau cracking mechanismLessons to draw from experimental results

◦ Alkane physisorption on zeolitesWhy is it important?

◦ Transition structures

Alkane cracking in zeolites JIN Janos Angyan

Page 7: Alkane cracking in zeolites - univ-lorraine.frcrm2.univ-lorraine.fr/pages_perso/Angyan/papers/talkwn.pdf · alkane cracking in zeolites: an overview of recent modeling results alkane

Outline

◦ Haag-Dassau cracking mechanismLessons to draw from experimental results

◦ Alkane physisorption on zeolitesWhy is it important?

◦ Transition structuresOverview of some ab initio results

Alkane cracking in zeolites JIN Janos Angyan

Page 8: Alkane cracking in zeolites - univ-lorraine.frcrm2.univ-lorraine.fr/pages_perso/Angyan/papers/talkwn.pdf · alkane cracking in zeolites: an overview of recent modeling results alkane

Outline

◦ Haag-Dassau cracking mechanismLessons to draw from experimental results

◦ Alkane physisorption on zeolitesWhy is it important?

◦ Transition structuresOverview of some ab initio results

Alkane cracking in zeolites JIN Janos Angyan

Page 9: Alkane cracking in zeolites - univ-lorraine.frcrm2.univ-lorraine.fr/pages_perso/Angyan/papers/talkwn.pdf · alkane cracking in zeolites: an overview of recent modeling results alkane

Carbocations

alkaniumion

C

R

R

R

R

HH ++

R

C

R

R

R

Alkane cracking in zeolites JIN Janos Angyan

Page 10: Alkane cracking in zeolites - univ-lorraine.frcrm2.univ-lorraine.fr/pages_perso/Angyan/papers/talkwn.pdf · alkane cracking in zeolites: an overview of recent modeling results alkane

Carbocations

alkaniumion

C

R

R

R

R

HH ++

R

C

R

R

R

carbeniumion

CC

C

R R

HR

R

H

+

+CC

C

R R

R R

Alkane cracking in zeolites JIN Janos Angyan

Page 11: Alkane cracking in zeolites - univ-lorraine.frcrm2.univ-lorraine.fr/pages_perso/Angyan/papers/talkwn.pdf · alkane cracking in zeolites: an overview of recent modeling results alkane

Carbocations

alkaniumion

C

R

R

R

R

HH ++

R

C

R

R

R

carbeniumion

CC

C

R R

HR

R

H

+

+CC

C

R R

R R

Alkane cracking in zeolites JIN Janos Angyan

Page 12: Alkane cracking in zeolites - univ-lorraine.frcrm2.univ-lorraine.fr/pages_perso/Angyan/papers/talkwn.pdf · alkane cracking in zeolites: an overview of recent modeling results alkane

Alkane species in zeolites

R–H

alkane

Alkane cracking in zeolites JIN Janos Angyan

Page 13: Alkane cracking in zeolites - univ-lorraine.frcrm2.univ-lorraine.fr/pages_perso/Angyan/papers/talkwn.pdf · alkane cracking in zeolites: an overview of recent modeling results alkane

Alkane species in zeolites

R–H

alkane

alkene

bifu

ncti

onal

Alkane cracking in zeolites JIN Janos Angyan

Page 14: Alkane cracking in zeolites - univ-lorraine.frcrm2.univ-lorraine.fr/pages_perso/Angyan/papers/talkwn.pdf · alkane cracking in zeolites: an overview of recent modeling results alkane

Alkane species in zeolites

R–H

alkane

alkene

bifu

ncti

onal

carbenium

+ HBrønsted acid

+ R

Alkane cracking in zeolites JIN Janos Angyan

Page 15: Alkane cracking in zeolites - univ-lorraine.frcrm2.univ-lorraine.fr/pages_perso/Angyan/papers/talkwn.pdf · alkane cracking in zeolites: an overview of recent modeling results alkane

Alkane species in zeolites

R–H

alkane

alkene

bifu

ncti

onal

carbenium

+ HBrønsted acid

+ R

RH2

alkanium

+ HBrønsted acid

+ +

+

Alkane cracking in zeolites JIN Janos Angyan

Page 16: Alkane cracking in zeolites - univ-lorraine.frcrm2.univ-lorraine.fr/pages_perso/Angyan/papers/talkwn.pdf · alkane cracking in zeolites: an overview of recent modeling results alkane

Alkane species in zeolites

R–H

alkane

alkene

bifu

ncti

onal

carbenium

+ HBrønsted acid

+ R

RH2

alkanium

+ HBrønsted acid

+ +

+

−R’H / H2

Alkane cracking in zeolites JIN Janos Angyan

Page 17: Alkane cracking in zeolites - univ-lorraine.frcrm2.univ-lorraine.fr/pages_perso/Angyan/papers/talkwn.pdf · alkane cracking in zeolites: an overview of recent modeling results alkane

Alkane species in zeolites

R–H

alkane

alkene

bifu

ncti

onal

carbenium

+ HBrønsted acid

+ R

RH2

alkanium

+ HBrønsted acid

+ +

+

−R’H / H2

−HLewis

acid

Alkane cracking in zeolites JIN Janos Angyan

Page 18: Alkane cracking in zeolites - univ-lorraine.frcrm2.univ-lorraine.fr/pages_perso/Angyan/papers/talkwn.pdf · alkane cracking in zeolites: an overview of recent modeling results alkane

Alkane species in zeolites

R–H

alkane

alkene

bifu

ncti

onal

carbenium

+ HBrønsted acid

+ R

RH2

alkanium

+ HBrønsted acid

+ +

+

−R’H / H2

−HLewis

acid

Alkane cracking in zeolites JIN Janos Angyan

Page 19: Alkane cracking in zeolites - univ-lorraine.frcrm2.univ-lorraine.fr/pages_perso/Angyan/papers/talkwn.pdf · alkane cracking in zeolites: an overview of recent modeling results alkane

Cracking mechanisms

Alkane cracking in zeolites JIN Janos Angyan

Page 20: Alkane cracking in zeolites - univ-lorraine.frcrm2.univ-lorraine.fr/pages_perso/Angyan/papers/talkwn.pdf · alkane cracking in zeolites: an overview of recent modeling results alkane

Cracking mechanisms

Bimolecular

Alkane cracking in zeolites JIN Janos Angyan

Page 21: Alkane cracking in zeolites - univ-lorraine.frcrm2.univ-lorraine.fr/pages_perso/Angyan/papers/talkwn.pdf · alkane cracking in zeolites: an overview of recent modeling results alkane

Cracking mechanisms

Bimolecular

R1H

R1

beta-scission

RH

alkene

++ R

Alkane cracking in zeolites JIN Janos Angyan

Page 22: Alkane cracking in zeolites - univ-lorraine.frcrm2.univ-lorraine.fr/pages_perso/Angyan/papers/talkwn.pdf · alkane cracking in zeolites: an overview of recent modeling results alkane

Cracking mechanisms

Bimolecular

R1H

R1

beta-scission

RH

alkene

++ R

◦ in mono- and bifunctional catalysts

Alkane cracking in zeolites JIN Janos Angyan

Page 23: Alkane cracking in zeolites - univ-lorraine.frcrm2.univ-lorraine.fr/pages_perso/Angyan/papers/talkwn.pdf · alkane cracking in zeolites: an overview of recent modeling results alkane

Cracking mechanisms

Bimolecular

R1H

R1

beta-scission

RH

alkene

++ R

◦ in mono- and bifunctional catalysts

◦ β-scission chain carrier

Alkane cracking in zeolites JIN Janos Angyan

Page 24: Alkane cracking in zeolites - univ-lorraine.frcrm2.univ-lorraine.fr/pages_perso/Angyan/papers/talkwn.pdf · alkane cracking in zeolites: an overview of recent modeling results alkane

Cracking mechanisms

Bimolecular

R1H

R1

beta-scission

RH

alkene

++ R

◦ in mono- and bifunctional catalysts

◦ β-scission chain carrier

◦ does not work in constrainedenvironment

Alkane cracking in zeolites JIN Janos Angyan

Page 25: Alkane cracking in zeolites - univ-lorraine.frcrm2.univ-lorraine.fr/pages_perso/Angyan/papers/talkwn.pdf · alkane cracking in zeolites: an overview of recent modeling results alkane

Cracking mechanisms

Bimolecular

R1H

R1

beta-scission

RH

alkene

++ R

◦ in mono- and bifunctional catalysts

◦ β-scission chain carrier

◦ does not work in constrainedenvironment

Alkane cracking in zeolites JIN Janos Angyan

Page 26: Alkane cracking in zeolites - univ-lorraine.frcrm2.univ-lorraine.fr/pages_perso/Angyan/papers/talkwn.pdf · alkane cracking in zeolites: an overview of recent modeling results alkane

Cracking mechanisms

Bimolecular

R1H

R1

beta-scission

RH

alkene

++ R

◦ in mono- and bifunctional catalysts

◦ β-scission chain carrier

◦ does not work in constrainedenvironment

Monomolecular

R1H

alkene

H+

desorption

+

+R2

RH

RH2

Alkane cracking in zeolites JIN Janos Angyan

Page 27: Alkane cracking in zeolites - univ-lorraine.frcrm2.univ-lorraine.fr/pages_perso/Angyan/papers/talkwn.pdf · alkane cracking in zeolites: an overview of recent modeling results alkane

Cracking mechanisms

Bimolecular

R1H

R1

beta-scission

RH

alkene

++ R

◦ in mono- and bifunctional catalysts

◦ β-scission chain carrier

◦ does not work in constrainedenvironment

Monomolecular

R1H

alkene

H+

desorption

+

+R2

RH

RH2

◦ in monofunctional catalysts

Alkane cracking in zeolites JIN Janos Angyan

Page 28: Alkane cracking in zeolites - univ-lorraine.frcrm2.univ-lorraine.fr/pages_perso/Angyan/papers/talkwn.pdf · alkane cracking in zeolites: an overview of recent modeling results alkane

Cracking mechanisms

Bimolecular

R1H

R1

beta-scission

RH

alkene

++ R

◦ in mono- and bifunctional catalysts

◦ β-scission chain carrier

◦ does not work in constrainedenvironment

Monomolecular

R1H

alkene

H+

desorption

+

+R2

RH

RH2

◦ in monofunctional catalysts

◦ cracking or dehydrogenation

Alkane cracking in zeolites JIN Janos Angyan

Page 29: Alkane cracking in zeolites - univ-lorraine.frcrm2.univ-lorraine.fr/pages_perso/Angyan/papers/talkwn.pdf · alkane cracking in zeolites: an overview of recent modeling results alkane

Cracking mechanisms

Bimolecular

R1H

R1

beta-scission

RH

alkene

++ R

◦ in mono- and bifunctional catalysts

◦ β-scission chain carrier

◦ does not work in constrainedenvironment

Monomolecular

R1H

alkene

H+

desorption

+

+R2

RH

RH2

◦ in monofunctional catalysts

◦ cracking or dehydrogenation

◦ at high T, medium-pore zeolites(ZSM-5)

Alkane cracking in zeolites JIN Janos Angyan

Page 30: Alkane cracking in zeolites - univ-lorraine.frcrm2.univ-lorraine.fr/pages_perso/Angyan/papers/talkwn.pdf · alkane cracking in zeolites: an overview of recent modeling results alkane

Monomolecular cracking (Haag-Dessau) mechanism

C

+H H

H3C CH3

CH3

Alkane cracking in zeolites JIN Janos Angyan

Page 31: Alkane cracking in zeolites - univ-lorraine.frcrm2.univ-lorraine.fr/pages_perso/Angyan/papers/talkwn.pdf · alkane cracking in zeolites: an overview of recent modeling results alkane

Monomolecular cracking (Haag-Dessau) mechanism

C

+H H

H3C CH3

CH3

H-exchangeH3C

H

C

CH3

CH3 + H+

Alkane cracking in zeolites JIN Janos Angyan

Page 32: Alkane cracking in zeolites - univ-lorraine.frcrm2.univ-lorraine.fr/pages_perso/Angyan/papers/talkwn.pdf · alkane cracking in zeolites: an overview of recent modeling results alkane

Monomolecular cracking (Haag-Dessau) mechanism

C

+H H

H3C CH3

CH3

H-exchangeH3C

H

C

CH3

CH3 + H+

CH3

dehydrogenationH3C

CH3

C+ + H2

Alkane cracking in zeolites JIN Janos Angyan

Page 33: Alkane cracking in zeolites - univ-lorraine.frcrm2.univ-lorraine.fr/pages_perso/Angyan/papers/talkwn.pdf · alkane cracking in zeolites: an overview of recent modeling results alkane

Monomolecular cracking (Haag-Dessau) mechanism

C

+H H

H3C CH3

CH3

H-exchangeH3C

H

C

CH3

CH3 + H+

CH3

dehydrogenationH3C

CH3

C+ + H2

crackingC +H3C

H

CH3

+ CH4

Alkane cracking in zeolites JIN Janos Angyan

Page 34: Alkane cracking in zeolites - univ-lorraine.frcrm2.univ-lorraine.fr/pages_perso/Angyan/papers/talkwn.pdf · alkane cracking in zeolites: an overview of recent modeling results alkane

Monomolecular cracking (Haag-Dessau) mechanism

C

+H H

H3C CH3

CH3

H-exchangeH3C

H

C

CH3

CH3 + H+

CH3

dehydrogenationH3C

CH3

C+ + H2

crackingC +H3C

H

CH3

+ CH4

Alkane cracking in zeolites JIN Janos Angyan

Page 35: Alkane cracking in zeolites - univ-lorraine.frcrm2.univ-lorraine.fr/pages_perso/Angyan/papers/talkwn.pdf · alkane cracking in zeolites: an overview of recent modeling results alkane

Product distribution of propane on HZSM-5

Proton attacks on the central carbon atom:

Kwaak, Schachtler, Haag, J. Catal. 149 (1994) 465.

Alkane cracking in zeolites JIN Janos Angyan

Page 36: Alkane cracking in zeolites - univ-lorraine.frcrm2.univ-lorraine.fr/pages_perso/Angyan/papers/talkwn.pdf · alkane cracking in zeolites: an overview of recent modeling results alkane

Product distribution of propane on HZSM-5

Proton attacks on the central carbon atom:

C

CH3

H H

CH3

Kwaak, Schachtler, Haag, J. Catal. 149 (1994) 465.

Alkane cracking in zeolites JIN Janos Angyan

Page 37: Alkane cracking in zeolites - univ-lorraine.frcrm2.univ-lorraine.fr/pages_perso/Angyan/papers/talkwn.pdf · alkane cracking in zeolites: an overview of recent modeling results alkane

Product distribution of propane on HZSM-5

Proton attacks on the central carbon atom:

C

CH3

H H

CH3H

+

Kwaak, Schachtler, Haag, J. Catal. 149 (1994) 465.

Alkane cracking in zeolites JIN Janos Angyan

Page 38: Alkane cracking in zeolites - univ-lorraine.frcrm2.univ-lorraine.fr/pages_perso/Angyan/papers/talkwn.pdf · alkane cracking in zeolites: an overview of recent modeling results alkane

Product distribution of propane on HZSM-5

Proton attacks on the central carbon atom:

C

CH3

H H

CH3H

+

H2 + C3H6

37%

Kwaak, Schachtler, Haag, J. Catal. 149 (1994) 465.

Alkane cracking in zeolites JIN Janos Angyan

Page 39: Alkane cracking in zeolites - univ-lorraine.frcrm2.univ-lorraine.fr/pages_perso/Angyan/papers/talkwn.pdf · alkane cracking in zeolites: an overview of recent modeling results alkane

Product distribution of propane on HZSM-5

Proton attacks on the central carbon atom:

C

CH3

H H

CH3H

+

H2 + C3H6

37%

CH4 + C2H4

63%

Kwaak, Schachtler, Haag, J. Catal. 149 (1994) 465.

Alkane cracking in zeolites JIN Janos Angyan

Page 40: Alkane cracking in zeolites - univ-lorraine.frcrm2.univ-lorraine.fr/pages_perso/Angyan/papers/talkwn.pdf · alkane cracking in zeolites: an overview of recent modeling results alkane

Product distribution of propane on HZSM-5

Proton attacks on the central carbon atom:

C

CH3

H H

CH3H

+

H2 + C3H6

37%

CH4 + C2H4

63%

Almost statistical cleavage of the alkanium ion.

Kwaak, Schachtler, Haag, J. Catal. 149 (1994) 465.

Alkane cracking in zeolites JIN Janos Angyan

Page 41: Alkane cracking in zeolites - univ-lorraine.frcrm2.univ-lorraine.fr/pages_perso/Angyan/papers/talkwn.pdf · alkane cracking in zeolites: an overview of recent modeling results alkane

Product distribution of i-butane on HZSM-5

Proton attacks the tertiary carbon atom:

C

CH3

H H

CH3CH3

+

Ono, Kanae, J. Chem. Soc. Faraday Trans. 87 (1991) 663.

Alkane cracking in zeolites JIN Janos Angyan

Page 42: Alkane cracking in zeolites - univ-lorraine.frcrm2.univ-lorraine.fr/pages_perso/Angyan/papers/talkwn.pdf · alkane cracking in zeolites: an overview of recent modeling results alkane

Product distribution of i-butane on HZSM-5

Proton attacks the tertiary carbon atom:

C

CH3

H H

CH3CH3

+

H2 + C4H8

33%

Ono, Kanae, J. Chem. Soc. Faraday Trans. 87 (1991) 663.

Alkane cracking in zeolites JIN Janos Angyan

Page 43: Alkane cracking in zeolites - univ-lorraine.frcrm2.univ-lorraine.fr/pages_perso/Angyan/papers/talkwn.pdf · alkane cracking in zeolites: an overview of recent modeling results alkane

Product distribution of i-butane on HZSM-5

Proton attacks the tertiary carbon atom:

C

CH3

H H

CH3CH3

+

H2 + C4H8

33%

CH4 + C3H6

67%

Ono, Kanae, J. Chem. Soc. Faraday Trans. 87 (1991) 663.

Alkane cracking in zeolites JIN Janos Angyan

Page 44: Alkane cracking in zeolites - univ-lorraine.frcrm2.univ-lorraine.fr/pages_perso/Angyan/papers/talkwn.pdf · alkane cracking in zeolites: an overview of recent modeling results alkane

Product distribution of i-butane on HZSM-5

Proton attacks the tertiary carbon atom:

C

CH3

H H

CH3CH3

+

H2 + C4H8

33%

CH4 + C3H6

67%

Propene and methane formation is more prevalent than isobutene production.

Ono, Kanae, J. Chem. Soc. Faraday Trans. 87 (1991) 663.

Alkane cracking in zeolites JIN Janos Angyan

Page 45: Alkane cracking in zeolites - univ-lorraine.frcrm2.univ-lorraine.fr/pages_perso/Angyan/papers/talkwn.pdf · alkane cracking in zeolites: an overview of recent modeling results alkane

Product distribution of n-butane on HZSM-5

Proton can attack on three different types of bonds:

C C CCH

H H H H

H

HHHH

Kranilla, Haag, Gates, J. Catal. 135 (1992) 115.

Alkane cracking in zeolites JIN Janos Angyan

Page 46: Alkane cracking in zeolites - univ-lorraine.frcrm2.univ-lorraine.fr/pages_perso/Angyan/papers/talkwn.pdf · alkane cracking in zeolites: an overview of recent modeling results alkane

Product distribution of n-butane on HZSM-5

Proton can attack on three different types of bonds:

C C CCH

H H H H

H

HHHH

C2H6 + C2H4

17% 15%

Kranilla, Haag, Gates, J. Catal. 135 (1992) 115.

Alkane cracking in zeolites JIN Janos Angyan

Page 47: Alkane cracking in zeolites - univ-lorraine.frcrm2.univ-lorraine.fr/pages_perso/Angyan/papers/talkwn.pdf · alkane cracking in zeolites: an overview of recent modeling results alkane

Product distribution of n-butane on HZSM-5

Proton can attack on three different types of bonds:

C C CCH

H H H H

H

HHHH

C2H6 + C2H4

17% 15%17%20%

CH4 + C3H2

Kranilla, Haag, Gates, J. Catal. 135 (1992) 115.

Alkane cracking in zeolites JIN Janos Angyan

Page 48: Alkane cracking in zeolites - univ-lorraine.frcrm2.univ-lorraine.fr/pages_perso/Angyan/papers/talkwn.pdf · alkane cracking in zeolites: an overview of recent modeling results alkane

Product distribution of n-butane on HZSM-5

Proton can attack on three different types of bonds:

C C CCH

H H H H

H

HHHH

C2H6 + C2H4

17% 15%17%20%

CH4 + C3H2 H2 + C4H8

15% 17%

Kranilla, Haag, Gates, J. Catal. 135 (1992) 115.

Alkane cracking in zeolites JIN Janos Angyan

Page 49: Alkane cracking in zeolites - univ-lorraine.frcrm2.univ-lorraine.fr/pages_perso/Angyan/papers/talkwn.pdf · alkane cracking in zeolites: an overview of recent modeling results alkane

Product distribution of n-butane on HZSM-5

Proton can attack on three different types of bonds:

C C CCH

H H H H

H

HHHH

C2H6 + C2H4

17% 15%17%20%

CH4 + C3H2 H2 + C4H8

15% 17%

In spite of different number of equivalent bonds, each product is formed withthe same probability.

Kranilla, Haag, Gates, J. Catal. 135 (1992) 115.

Alkane cracking in zeolites JIN Janos Angyan

Page 50: Alkane cracking in zeolites - univ-lorraine.frcrm2.univ-lorraine.fr/pages_perso/Angyan/papers/talkwn.pdf · alkane cracking in zeolites: an overview of recent modeling results alkane

Product distribution of n-butane on HZSM-5

Proton can attack on three different types of bonds:

C C CCH

H H H H

H

HHHH

C2H6 + C2H4

17% 15%17%20%

CH4 + C3H2 H2 + C4H8

15% 17%

In spite of different number of equivalent bonds, each product is formed withthe same probability.Larger activation entropy for external bonds compensatesfor the smaller activation energy for internal bonds.

Kranilla, Haag, Gates, J. Catal. 135 (1992) 115.

Alkane cracking in zeolites JIN Janos Angyan

Page 51: Alkane cracking in zeolites - univ-lorraine.frcrm2.univ-lorraine.fr/pages_perso/Angyan/papers/talkwn.pdf · alkane cracking in zeolites: an overview of recent modeling results alkane

Monomolecular cracking mechanism: open questions

◦ Activation energy?

Alkane cracking in zeolites JIN Janos Angyan

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Monomolecular cracking mechanism: open questions

◦ Activation energy?

◦ Nature of the transition structure(s)?

Alkane cracking in zeolites JIN Janos Angyan

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Monomolecular cracking mechanism: open questions

◦ Activation energy?

◦ Nature of the transition structure(s)?

◦ Multiple reaction channels?

Alkane cracking in zeolites JIN Janos Angyan

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Monomolecular cracking mechanism: open questions

◦ Activation energy?

◦ Nature of the transition structure(s)?

◦ Multiple reaction channels?

◦ Effect of zeolite framework?

Alkane cracking in zeolites JIN Janos Angyan

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Monomolecular cracking mechanism: open questions

◦ Activation energy?

◦ Nature of the transition structure(s)?

◦ Multiple reaction channels?

◦ Effect of zeolite framework?

◦ Alternative mechanisms?

Alkane cracking in zeolites JIN Janos Angyan

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Activation energies

E

ZeOH + C H

transition structure

ZeOH...C H

app

trueEadsE

E

ZeOH + C H

transition structure

ZeOH...C H

app

trueEadsE

n 2n+2

2n+2n

Experimental (apparent) activation energies should be corrected by adsorp-tion energies to obtain intrinsic (true) activation energies.

Alkane cracking in zeolites JIN Janos Angyan

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n-hexane cracking

Apparent activation energies in different catalysts

Catalyst

H-ZSM-5

H-MOR

H-USY

CDHY

Babitz et al. Appl. Catal. A 179 (1999) 71.

Alkane cracking in zeolites JIN Janos Angyan

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n-hexane cracking

Apparent activation energies in different catalysts

Catalyst E‡app

H-ZSM-5 149±8

H-MOR 157±9

H-USY 177±9

CDHY 186±9

Babitz et al. Appl. Catal. A 179 (1999) 71.

Alkane cracking in zeolites JIN Janos Angyan

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n-hexane cracking

Apparent activation energies in different catalysts

Catalyst E‡app ∆Hads

H-ZSM-5 149±8 −86±6

H-MOR 157±9 −69±3

H-USY 177±9 −50±3

CDHY 186±9 −50±3

Babitz et al. Appl. Catal. A 179 (1999) 71.

Alkane cracking in zeolites JIN Janos Angyan

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n-hexane cracking

Apparent activation energies in different catalysts

Catalyst E‡app ∆Hads E‡

true

H-ZSM-5 149±8 −86±6 235±14

H-MOR 157±9 −69±3 226±12

H-USY 177±9 −50±3 227±12

CDHY 186±9 −50±3 236±12

Babitz et al. Appl. Catal. A 179 (1999) 71.

Alkane cracking in zeolites JIN Janos Angyan

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n-hexane cracking

Apparent activation energies in different catalysts

Catalyst E‡app ∆Hads E‡

true

H-ZSM-5 149±8 −86±6 235±14

H-MOR 157±9 −69±3 226±12

H-USY 177±9 −50±3 227±12

CDHY 186±9 −50±3 236±12

Differences in apparent activation energies are due to adsorption energies!

Babitz et al. Appl. Catal. A 179 (1999) 71.

Alkane cracking in zeolites JIN Janos Angyan

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n-hexane cracking

Apparent activation energies in different catalysts

Catalyst E‡app ∆Hads E‡

true

H-ZSM-5 149±8 −86±6 235±14

H-MOR 157±9 −69±3 226±12

H-USY 177±9 −50±3 227±12

CDHY 186±9 −50±3 236±12

Differences in apparent activation energies are due to adsorption energies!◦ intrinsic activation energy insensitive to acid strength

Babitz et al. Appl. Catal. A 179 (1999) 71.

Alkane cracking in zeolites JIN Janos Angyan

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n-hexane cracking

Apparent activation energies in different catalysts

Catalyst E‡app ∆Hads E‡

true

H-ZSM-5 149±8 −86±6 235±14

H-MOR 157±9 −69±3 226±12

H-USY 177±9 −50±3 227±12

CDHY 186±9 −50±3 236±12

Differences in apparent activation energies are due to adsorption energies!◦ intrinsic activation energy insensitive to acid strength

◦ acid strengths of these zeolites are identical

Babitz et al. Appl. Catal. A 179 (1999) 71.

Alkane cracking in zeolites JIN Janos Angyan

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n-hexane cracking

Apparent activation energies in different catalysts

Catalyst E‡app ∆Hads E‡

true

H-ZSM-5 149±8 −86±6 235±14

H-MOR 157±9 −69±3 226±12

H-USY 177±9 −50±3 227±12

CDHY 186±9 −50±3 236±12

Differences in apparent activation energies are due to adsorption energies!◦ intrinsic activation energy insensitive to acid strength

◦ acid strengths of these zeolites are identical

Babitz et al. Appl. Catal. A 179 (1999) 71.

Alkane cracking in zeolites JIN Janos Angyan

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n-alkane cracking in H-ZSM-5

True activation energies seem to be independent of the chain length

alkane

propane

n-butane

n-pentane

n-hexane

Narbeshuber, Vinek, Lercher J. Catal. A 157 (1995) 338.

Alkane cracking in zeolites JIN Janos Angyan

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n-alkane cracking in H-ZSM-5

True activation energies seem to be independent of the chain length

alkane E‡app ∆Hads E‡

true

propane 155 −43 198

n-butane 135 −62 197

n-pentane 120 −74 194

n-hexane 105 −92 197

Narbeshuber, Vinek, Lercher J. Catal. A 157 (1995) 338.

Alkane cracking in zeolites JIN Janos Angyan

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n-alkane cracking in H-ZSM-5

True activation energies seem to be independent of the chain length

alkane E‡app ∆Hads E‡

true ∆Hads E‡true

propane 155 −43 198 -40 195

n-butane 135 −62 197 -50 185

n-pentane 120 −74 194 -60 180

n-hexane 105 −92 197 -71 176

unless one uses another set of adsorption energies...

Narbeshuber, Vinek, Lercher J. Catal. A 157 (1995) 338.

Alkane cracking in zeolites JIN Janos Angyan

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n-alkane cracking in H-ZSM-5

True activation energies seem to be independent of the chain length

alkane E‡app ∆Hads E‡

true ∆Hads E‡true

propane 155 −43 198 -40 195

n-butane 135 −62 197 -50 185

n-pentane 120 −74 194 -60 180

n-hexane 105 −92 197 -71 176

unless one uses another set of adsorption energies...

Narbeshuber, Vinek, Lercher J. Catal. A 157 (1995) 338.

Alkane cracking in zeolites JIN Janos Angyan

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n-alkane cracking in H-ZSM-5

True activation energies seem to be independent of the chain length

alkane E‡app ∆Hads E‡

true ∆Hads E‡true

propane 155 −43 198 -40 195

n-butane 135 −62 197 -50 185

n-pentane 120 −74 194 -60 180

n-hexane 105 −92 197 -71 176

unless one uses another set of adsorption energies...

Narbeshuber, Vinek, Lercher J. Catal. A 157 (1995) 338.

Alkane cracking in zeolites JIN Janos Angyan

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Exprimental n-alkane adsorption energies

-140

-120

-100

-80

-60

-40

-20

0

0 2 4 6 8 10

Eads

(kJ/

mol

)

chain length

Vlugt, Krishna, Smit J. Phys. Chem. B 103 (1999) 1102.

Alkane cracking in zeolites JIN Janos Angyan

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VASP calculations

◦ DFT with PW91 gradient corrections

Alkane cracking in zeolites JIN Janos Angyan

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VASP calculations

◦ DFT with PW91 gradient corrections

◦ Ultrasoft pseudopotentials for C,H and O

Alkane cracking in zeolites JIN Janos Angyan

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VASP calculations

◦ DFT with PW91 gradient corrections

◦ Ultrasoft pseudopotentials for C,H and O

◦ Cutoff energy 400 eV

Alkane cracking in zeolites JIN Janos Angyan

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VASP calculations

◦ DFT with PW91 gradient corrections

◦ Ultrasoft pseudopotentials for C,H and O

◦ Cutoff energy 400 eV

◦ Structural optimizations (residual forces < 0.02 )

Alkane cracking in zeolites JIN Janos Angyan

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VASP calculations

◦ DFT with PW91 gradient corrections

◦ Ultrasoft pseudopotentials for C,H and O

◦ Cutoff energy 400 eV

◦ Structural optimizations (residual forces < 0.02 )

◦ Transition states optimized by using QMPot (Sierka & Sauer) as externaloptimizer

Alkane cracking in zeolites JIN Janos Angyan

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VASP calculations

◦ DFT with PW91 gradient corrections

◦ Ultrasoft pseudopotentials for C,H and O

◦ Cutoff energy 400 eV

◦ Structural optimizations (residual forces < 0.02 )

◦ Transition states optimized by using QMPot (Sierka & Sauer) as externaloptimizer

◦ Order of critical points verified by the calculation of Hessian

Alkane cracking in zeolites JIN Janos Angyan

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Transition states in chabazite optimized by VASP

C

H

O

Al

O

H

C C

C

bond C2H6 C3H8 n-C4Ha10 n-C4Hb

10 i-C4H10

(a) primary C–C bond(b) secondary C–C bond

Alkane cracking in zeolites JIN Janos Angyan

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Transition states in chabazite optimized by VASP

C

H

O

Al

O

H

C C

C

bond C2H6 C3H8 n-C4Ha10 n-C4Hb

10 i-C4H10

H1–O 2.97 2.62 3.01 3.25 2.94

(a) primary C–C bond(b) secondary C–C bond

Alkane cracking in zeolites JIN Janos Angyan

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Transition states in chabazite optimized by VASP

C

H

O

Al

O

H

C C

C

bond C2H6 C3H8 n-C4Ha10 n-C4Hb

10 i-C4H10

H1–O 2.97 2.62 3.01 3.25 2.94H1–C1 1.23 1.20 1.20 1.25 1.14H1–C2 1.25 1.32 1.33 1.27 1.58C1-C2 1.96 2.08 2.12 2.47 2.47

(a) primary C–C bond(b) secondary C–C bond

Alkane cracking in zeolites JIN Janos Angyan

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Transition states in chabazite optimized by VASP

C

H

O

Al

O

H

C C

C

bond C2H6 C3H8 n-C4Ha10 n-C4Hb

10 i-C4H10

H1–O 2.97 2.62 3.01 3.25 2.94H1–C1 1.23 1.20 1.20 1.25 1.14H1–C2 1.25 1.32 1.33 1.27 1.58C1-C2 1.96 2.08 2.12 2.47 2.47H2–C2 1.09 1.11 1.10 1.10 1.10H2–O’ 2.23 2.14 3.44 2.31 2.79

(a) primary C–C bond(b) secondary C–C bond

Alkane cracking in zeolites JIN Janos Angyan

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Transition states in chabazite optimized by VASP

C

H

O

Al

O

H

C C

C

bond C2H6 C3H8 n-C4Ha10 n-C4Hb

10 i-C4H10

H1–O 2.97 2.62 3.01 3.25 2.94H1–C1 1.23 1.20 1.20 1.25 1.14H1–C2 1.25 1.32 1.33 1.27 1.58C1-C2 1.96 2.08 2.12 2.47 2.47H2–C2 1.09 1.11 1.10 1.10 1.10H2–O’ 2.23 2.14 3.44 2.31 2.79Al–O 1.74 1.74 1.74 1.73 1.73Al–O’ 1.73 1.74 1.72 1.73 1.73

(a) primary C–C bond(b) secondary C–C bond

Alkane cracking in zeolites JIN Janos Angyan

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Transition states in chabazite optimized by VASP

C

H

O

Al

O

H

C C

C

bond C2H6 C3H8 n-C4Ha10 n-C4Hb

10 i-C4H10

H1–O 2.97 2.62 3.01 3.25 2.94H1–C1 1.23 1.20 1.20 1.25 1.14H1–C2 1.25 1.32 1.33 1.27 1.58C1-C2 1.96 2.08 2.12 2.47 2.47H2–C2 1.09 1.11 1.10 1.10 1.10H2–O’ 2.23 2.14 3.44 2.31 2.79Al–O 1.74 1.74 1.74 1.73 1.73Al–O’ 1.73 1.74 1.72 1.73 1.73E‡true,theor 215 180 185 155 150∆Eads 30 40 50 50 48E‡app,theor 185 140 135 105 102

(a) primary C–C bond(b) secondary C–C bond

Alkane cracking in zeolites JIN Janos Angyan

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Transition states in chabazite optimized by VASP

C

H

O

Al

O

H

C C

C

bond C2H6 C3H8 n-C4Ha10 n-C4Hb

10 i-C4H10

H1–O 2.97 2.62 3.01 3.25 2.94H1–C1 1.23 1.20 1.20 1.25 1.14H1–C2 1.25 1.32 1.33 1.27 1.58C1-C2 1.96 2.08 2.12 2.47 2.47H2–C2 1.09 1.11 1.10 1.10 1.10H2–O’ 2.23 2.14 3.44 2.31 2.79Al–O 1.74 1.74 1.74 1.73 1.73Al–O’ 1.73 1.74 1.72 1.73 1.73E‡true,theor 215 180 185 155 150∆Eads 30 40 50 50 48E‡app,theor 185 140 135 105 102E‡app,exp 160 130 150 135 120

(a) primary C–C bond(b) secondary C–C bond

Alkane cracking in zeolites JIN Janos Angyan

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Alkane cracking in zeolites JIN Janos Angyan

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Ethane cracking

T5 cluster calculations at MP2/6-31G(d) and BLYP/6-31G(d) level

Barrier in kJ/molMP2/6-31G(d) 308.6ZPE -8.4thermal effects -4.6long range effects -60.7total 226.5experimental 190-200

Zygmunt, Curtiss, Zapol and Iton, J. Phys., Chem. B 104 (2000) 1944.

Alkane cracking in zeolites JIN Janos Angyan

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Ethane cracking

215kJ/mol

(195kJ/mol)75kJ/mol

Alkane cracking in zeolites JIN Janos Angyan

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Propane cracking

Alkane cracking in zeolites JIN Janos Angyan

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Propane cracking

180kJ/mol

Alkane cracking in zeolites JIN Janos Angyan

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Propane cracking

180kJ/mol

(190kJ/mol)

Alkane cracking in zeolites JIN Janos Angyan

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Propane cracking

180kJ/mol

(190kJ/mol) 65kJ/mol

Alkane cracking in zeolites JIN Janos Angyan

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Isobutane dehydrogenation

T5 cluster B3LYP/6-31G** and T3 cluster B3LYP/6-311** calculations

Milas and Nascimento Chem. Phys. Lett. 338 (2001) 67

Alkane cracking in zeolites JIN Janos Angyan

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Isobutane dehydrogenation

T5 cluster B3LYP/6-31G** and T3 cluster B3LYP/6-311** calculations

Carbocation collapses directly, without alkoxide formation

Activation energy: 223.5 kJ/mol (exp.: 172 ±6 kJ/mol)

Milas and Nascimento Chem. Phys. Lett. 338 (2001) 67

Alkane cracking in zeolites JIN Janos Angyan

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Isobutane dehydrogenation

∆E‡true(theor) = 190 kJ/mol ∆E‡

true(exp) = 172 kJ/mol

Alkane cracking in zeolites JIN Janos Angyan

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Isobutane dehydrogenation: carbenium intermediate

Alkane cracking in zeolites JIN Janos Angyan

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Isobutane cracking

Alkane cracking in zeolites JIN Janos Angyan

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Isobutane cracking

Alkane cracking in zeolites JIN Janos Angyan

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Isobutane cracking

∆E‡true(theor) = 150 kJ/mol ∆E‡

true(exp) = 170 kJ/mol

Alkane cracking in zeolites JIN Janos Angyan

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n-butane: experimental activation energies

Eads= -62kJ/mol

Narbeshuber, Vinek, Lercher J. Catal. A 157 (1995) 338.

Alkane cracking in zeolites JIN Janos Angyan

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n-butane: experimental activation energies

Eads= -62kJ/mol

80kJ/mol

H/D exchange

Narbeshuber, Vinek, Lercher J. Catal. A 157 (1995) 338.

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n-butane: experimental activation energies

Eads= -62kJ/mol

80kJ/mol

H/D exchange

115kJ/mol

dehydrogenation

Narbeshuber, Vinek, Lercher J. Catal. A 157 (1995) 338.

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n-butane: experimental activation energies

Eads= -62kJ/mol

80kJ/mol

H/D exchange

115kJ/mol

dehydrogenation

135kJ/mol

cracking

Narbeshuber, Vinek, Lercher J. Catal. A 157 (1995) 338.

Alkane cracking in zeolites JIN Janos Angyan

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Cracking of n-butane: attack on primary C-C bond

Alkane cracking in zeolites JIN Janos Angyan

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Cracking of n-butane: attack on primary C-C bond

Alkane cracking in zeolites JIN Janos Angyan

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Cracking of n-butane: attack on primary C-C bond

∆E‡true(theor) = 185 kJ/mol ∆E‡

true(exp) = 200 kJ/mol

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Cracking of n-butane: attack on secondary C-C bond

∆E‡true(theor) = 155 kJ/mol ∆E‡

true(exp) = 185 kJ/mol

Alkane cracking in zeolites JIN Janos Angyan

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Conclusions

◦ reasonable agreement with available activation energy data

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Conclusions

◦ reasonable agreement with available activation energy data

◦ reliable determination of adsorption energies would be needed (dispersionforces)

Alkane cracking in zeolites JIN Janos Angyan

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Conclusions

◦ reasonable agreement with available activation energy data

◦ reliable determination of adsorption energies would be needed (dispersionforces)

◦ complete mapping of multiple reaction pathways

Alkane cracking in zeolites JIN Janos Angyan

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Conclusions

◦ reasonable agreement with available activation energy data

◦ reliable determination of adsorption energies would be needed (dispersionforces)

◦ complete mapping of multiple reaction pathways

◦ future calculations on “true” catalysts (QM/MM methods)

Alkane cracking in zeolites JIN Janos Angyan

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Conclusions

◦ reasonable agreement with available activation energy data

◦ reliable determination of adsorption energies would be needed (dispersionforces)

◦ complete mapping of multiple reaction pathways

◦ future calculations on “true” catalysts (QM/MM methods)

Alkane cracking in zeolites JIN Janos Angyan