Alkane cracking in zeolites - CRM2

Outline◦ Haag-Dassau cracking mechanismLessons to draw from experimental resultsAlkane cracking in zeolites ◭ ◮ János Ángyán

Outline◦ Haag-Dassau cracking mechanismLessons to draw from experimental results◦ Alkane physisorption on zeolitesAlkane cracking in zeolites ◭ ◮ János Ángyán

Outline◦ Haag-Dassau cracking mechanismLessons to draw from experimental results◦ Alkane physisorption on zeolitesWhy is it important?Alkane cracking in zeolites ◭ ◮ János Ángyán

Outline◦ Haag-Dassau cracking mechanismLessons to draw from experimental results◦ Alkane physisorption on zeolitesWhy is it important?◦ Transition structuresAlkane cracking in zeolites ◭ ◮ János Ángyán

Outline◦ Haag-Dassau cracking mechanismLessons to draw from experimental results◦ Alkane physisorption on zeolitesWhy is it important?◦ Transition structuresOverview of some ab initio resultsAlkane cracking in zeolites ◭ ◮ János Ángyán

CarbocationsRRalkaniumionCRRH++H CRRRRAlkane cracking in zeolites ◭ ◮ János Ángyán

CarbocationsRRalkaniumionCRRH++H CRRRRcarbeniumionRCCR+HHC+CRRRRRRAlkane cracking in zeolites ◭ ◮ János Ángyán

CarbocationsRRalkaniumionCRRH++H CRRRRcarbeniumionRCCR+HHC+CRRRRRRAlkane cracking in zeolites ◭ ◮ János Ángyán

Alkane species in zeolitesR–HalkaneAlkane cracking in zeolites ◭ ◮ János Ángyán

Alkane species in zeolitesR–HalkanebifunctionalalkeneAlkane cracking in zeolites ◭ ◮ János Ángyán

Alkane species in zeolitesR–Halkanebifunctionalalkene+ H+Brønsted acidRcarbeniumAlkane cracking in zeolites ◭ ◮ János Ángyán

Alkane species in zeolitesR–Halkane+ H+ RH+2Brønsted acidalkaniumbifunctionalalkene+ H+Brønsted acidR+carbeniumAlkane cracking in zeolites ◭ ◮ János Ángyán

Alkane species in zeolitesR–Halkane+ H+ RH+2Brønsted acidalkaniumbifunctional−R’H / H 2alkene+ H+Brønsted acidR+carbeniumAlkane cracking in zeolites ◭ ◮ János Ángyán

Alkane species in zeolitesR–Halkane+ H+ RH+2Brønsted acidalkaniumbifunctionalLewisacid−H−R’H / H 2alkene+ H+Brønsted acidR+carbeniumAlkane cracking in zeolites ◭ ◮ János Ángyán

Alkane species in zeolitesR–Halkane+ H+ RH+2Brønsted acidalkaniumbifunctionalLewisacid−H−R’H / H 2alkene+ H+Brønsted acidR+carbeniumAlkane cracking in zeolites ◭ ◮ János Ángyán

Cracking mechanismsAlkane cracking in zeolites ◭ ◮ János Ángyán

Cracking mechanismsBimolecularAlkane cracking in zeolites ◭ ◮ János Ángyán

Cracking mechanismsBimolecularRHR 1 H+R 1R+beta-scissionalkeneAlkane cracking in zeolites ◭ ◮ János Ángyán

Cracking mechanismsBimolecularRHR 1 H+R 1R+beta-scissionalkene◦ in mono- and bifunctional catalystsAlkane cracking in zeolites ◭ ◮ János Ángyán

Cracking mechanismsBimolecularRHR 1 H+R 1R+beta-scissionalkene◦ in mono- and bifunctional catalysts◦ β-scission chain carrierAlkane cracking in zeolites ◭ ◮ János Ángyán

Cracking mechanismsBimolecularRHR 1 H+R 1R+beta-scissionalkene◦ in mono- and bifunctional catalysts◦ β-scission chain carrier◦ does not work in constrainedenvironmentAlkane cracking in zeolites ◭ ◮ János Ángyán

Cracking mechanismsBimolecularRHR 1 H+R 1R+beta-scissionalkene◦ in mono- and bifunctional catalysts◦ β-scission chain carrier◦ does not work in constrainedenvironmentAlkane cracking in zeolites ◭ ◮ János Ángyán

Cracking mechanismsBimolecularMonomolecularRHR 1 HRHR 1 H+RH 2+R 1R+H ++R 2beta-scissiondesorptionalkenealkene◦ in mono- and bifunctional catalysts◦ β-scission chain carrier◦ does not work in constrainedenvironmentAlkane cracking in zeolites ◭ ◮ János Ángyán

Cracking mechanismsBimolecularMonomolecularRHR 1 HRHR 1 H+RH 2+R 1R+H ++R 2beta-scissiondesorptionalkene◦ in mono- and bifunctional catalystsalkene◦ in monofunctional catalysts◦ β-scission chain carrier◦ does not work in constrainedenvironmentAlkane cracking in zeolites ◭ ◮ János Ángyán

Cracking mechanismsBimolecularMonomolecularRHR 1 HRHR 1 H+RH 2+R 1R+H ++R 2beta-scissiondesorptionalkene◦ in mono- and bifunctional catalysts◦ β-scission chain carrieralkene◦ in monofunctional catalysts◦ cracking or dehydrogenation◦ does not work in constrainedenvironmentAlkane cracking in zeolites ◭ ◮ János Ángyán

Cracking mechanismsBimolecularMonomolecularRHR 1 HRHR 1 H+RH 2+R 1R+H ++R 2beta-scissiondesorptionalkene◦ in mono- and bifunctional catalysts◦ β-scission chain carrier◦ does not work in constrainedenvironmentalkene◦ in monofunctional catalysts◦ cracking or dehydrogenation◦ at high T, medium-pore zeolites(ZSM-5)Alkane cracking in zeolites ◭ ◮ János Ángyán

Monomolecular cracking (Haag-Dessau) mechanismHH+H 3 CCCH 3CH 3Alkane cracking in zeolites ◭ ◮ János Ángyán

Monomolecular cracking (Haag-Dessau) mechanismHH+H 3 CCCH 3CH 3HH-exchangeH 3 CCCH 3CH 3 + H +Alkane cracking in zeolites ◭ ◮ János Ángyán

Monomolecular cracking (Haag-Dessau) mechanismdehydrogenationH 3 CCH 3C + + H 2CH 3HH+H 3 CCCH 3CH 3HH-exchangeH 3 CCCH 3CH 3 + H +Alkane cracking in zeolites ◭ ◮ János Ángyán

Monomolecular cracking (Haag-Dessau) mechanismCH 3dehydrogenationH 3 CC + + H 2CH 3HH 3 CCHCH 3CH 3+crackingH 3 CHC +CH 3+ CH 4HH-exchangeH 3 CCCH 3CH 3 + H +Alkane cracking in zeolites ◭ ◮ János Ángyán

Monomolecular cracking (Haag-Dessau) mechanismCH 3dehydrogenationH 3 CC + + H 2CH 3HH 3 CCHCH 3CH 3+crackingH 3 CHC +CH 3+ CH 4HH-exchangeH 3 CCCH 3CH 3 + H +Alkane cracking in zeolites ◭ ◮ János Ángyán

Product distribution of propane on HZSM-5Proton attacks on the central carbon atom:Kwaak, Schachtler, Haag, J. Catal. 149 (1994) 465.Alkane cracking in zeolites ◭ ◮ János Ángyán

Product distribution of propane on HZSM-5Proton attacks on the central carbon atom:CH 3CH 3CHHKwaak, Schachtler, Haag, J. Catal. 149 (1994) 465.Alkane cracking in zeolites ◭ ◮ János Ángyán

Product distribution of propane on HZSM-5Proton attacks on the central carbon atom:CH 3HCH 3+CHHKwaak, Schachtler, Haag, J. Catal. 149 (1994) 465.Alkane cracking in zeolites ◭ ◮ János Ángyán

Product distribution of propane on HZSM-5Proton attacks on the central carbon atom:CH 3HCH 3+CHHH 2 + C 3 H 637%Kwaak, Schachtler, Haag, J. Catal. 149 (1994) 465.Alkane cracking in zeolites ◭ ◮ János Ángyán

Product distribution of propane on HZSM-5Proton attacks on the central carbon atom:CH 3HCH 3+CHHH 2 + C 3 H 637%CH 4 + C 2 H 463%Kwaak, Schachtler, Haag, J. Catal. 149 (1994) 465.Alkane cracking in zeolites ◭ ◮ János Ángyán

Product distribution of propane on HZSM-5Proton attacks on the central carbon atom:CH 3HCH 3+CHHH 2 + C 3 H 6 CH 4 + C 2 H 437%63%Almost statistical cleavage of the alkanium ion.Kwaak, Schachtler, Haag, J. Catal. 149 (1994) 465.Alkane cracking in zeolites ◭ ◮ János Ángyán

Product distribution of i-butane on HZSM-5Proton attacks the tertiary carbon atom:CH 3CH 3CH 3+CHHOno, Kanae, J. Chem. Soc. Faraday Trans. 87 (1991) 663.Alkane cracking in zeolites ◭ ◮ János Ángyán

Product distribution of i-butane on HZSM-5Proton attacks the tertiary carbon atom:CH 3CH 3CH 3+CHHH 2 + C 4 H 833%Ono, Kanae, J. Chem. Soc. Faraday Trans. 87 (1991) 663.Alkane cracking in zeolites ◭ ◮ János Ángyán

Product distribution of i-butane on HZSM-5Proton attacks the tertiary carbon atom:CH 3CH 3CH 3+CHHH 2 + C 4 H 833%CH 4 + C 3 H 667%Ono, Kanae, J. Chem. Soc. Faraday Trans. 87 (1991) 663.Alkane cracking in zeolites ◭ ◮ János Ángyán

Product distribution of i-butane on HZSM-5Proton attacks the tertiary carbon atom:CH 3CH 3CH 3+CHHH 2 + C 4 H 833%CH 4 + C 3 H 667%Propene and methane formation is more prevalent than isobutene production.Ono, Kanae, J. Chem. Soc. Faraday Trans. 87 (1991) 663.Alkane cracking in zeolites ◭ ◮ János Ángyán

Product distribution of n-butane on HZSM-5Proton can attack on three different types of bonds:H H H HHCC C CHHHHHKranilla, Haag, Gates, J. Catal. 135 (1992) 115.Alkane cracking in zeolites ◭ ◮ János Ángyán

Product distribution of n-butane on HZSM-5Proton can attack on three different types of bonds:H H H HHCC C CHHHHHC 2 H 6 + C 2 H 417% 15%Kranilla, Haag, Gates, J. Catal. 135 (1992) 115.Alkane cracking in zeolites ◭ ◮ János Ángyán

Product distribution of n-butane on HZSM-5Proton can attack on three different types of bonds:H H H HHCC C CHHHHHCH 4 + C 3 H 2C 2 H 6 + C 2 H 420%17%17% 15%Kranilla, Haag, Gates, J. Catal. 135 (1992) 115.Alkane cracking in zeolites ◭ ◮ János Ángyán

Product distribution of n-butane on HZSM-5Proton can attack on three different types of bonds:H H H HHCC C CHHHHHCH 4 + C 3 H 2 C 2 H 6 + C 2 H 4 H 2 + C 4 H 820%17%17% 15%15% 17%Kranilla, Haag, Gates, J. Catal. 135 (1992) 115.Alkane cracking in zeolites ◭ ◮ János Ángyán

Product distribution of n-butane on HZSM-5Proton can attack on three different types of bonds:H H H HHCC C CHHHHHCH 4 + C 3 H 2 C 2 H 6 + C 2 H 4 H 2 + C 4 H 820%17%17% 15%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 ◭ ◮ János Ángyán

Product distribution of n-butane on HZSM-5Proton can attack on three different types of bonds:H H H HHCC C CHHHHHCH 4 + C 3 H 2 C 2 H 6 + C 2 H 4 H 2 + C 4 H 820%17%17% 15%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 ◭ ◮ János Ángyán

Monomolecular cracking mechanism: open questions◦ Activation energy?Alkane cracking in zeolites ◭ ◮ János Ángyán

Monomolecular cracking mechanism: open questions◦ Activation energy?◦ Nature of the transition structure(s)?Alkane cracking in zeolites ◭ ◮ János Ángyán

Monomolecular cracking mechanism: open questions◦ Activation energy?◦ Nature of the transition structure(s)?◦ Multiple reaction channels?Alkane cracking in zeolites ◭ ◮ János Ángyán

Monomolecular cracking mechanism: open questions◦ Activation energy?◦ Nature of the transition structure(s)?◦ Multiple reaction channels?◦ Effect of zeolite framework?Alkane cracking in zeolites ◭ ◮ János Ángyán

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 ◭ ◮ János Ángyán

Activation energiestransition structureEappZeOH + C Hn2n+2E adsE trueZeOH...C Hn 2n+2Experimental (apparent) activation energies should be corrected by adsorptionenergies to obtain intrinsic (true) activation energies.Alkane cracking in zeolites ◭ ◮ János Ángyán

n-hexane crackingApparent activation energies in different catalystsCatalystH-ZSM-5H-MORH-USYCDHYBabitz et al. Appl. Catal. A 179 (1999) 71.Alkane cracking in zeolites ◭ ◮ János Ángyán

n-hexane crackingApparent activation energies in different catalystsCatalystE ‡ appH-ZSM-5 149±8H-MOR 157±9H-USY 177±9CDHY 186±9Babitz et al. Appl. Catal. A 179 (1999) 71.Alkane cracking in zeolites ◭ ◮ János Ángyán

n-hexane crackingApparent activation energies in different catalystsCatalyst E ‡ app ∆H adsH-ZSM-5 149±8 −86±6H-MOR 157±9 −69±3H-USY 177±9 −50±3CDHY 186±9 −50±3Babitz et al. Appl. Catal. A 179 (1999) 71.Alkane cracking in zeolites ◭ ◮ János Ángyán

n-hexane crackingApparent activation energies in different catalystsCatalyst E ‡ app ∆H ads E ‡ trueH-ZSM-5 149±8 −86±6 235±14H-MOR 157±9 −69±3 226±12H-USY 177±9 −50±3 227±12CDHY 186±9 −50±3 236±12Babitz et al. Appl. Catal. A 179 (1999) 71.Alkane cracking in zeolites ◭ ◮ János Ángyán

n-hexane crackingApparent activation energies in different catalystsCatalyst E ‡ app ∆H ads E ‡ trueH-ZSM-5 149±8 −86±6 235±14H-MOR 157±9 −69±3 226±12H-USY 177±9 −50±3 227±12CDHY 186±9 −50±3 236±12Differences in apparent activation energies are due to adsorption energies!Babitz et al. Appl. Catal. A 179 (1999) 71.Alkane cracking in zeolites ◭ ◮ János Ángyán

n-hexane crackingApparent activation energies in different catalystsCatalyst E ‡ app ∆H ads E ‡ trueH-ZSM-5 149±8 −86±6 235±14H-MOR 157±9 −69±3 226±12H-USY 177±9 −50±3 227±12CDHY 186±9 −50±3 236±12Differences in apparent activation energies are due to adsorption energies!◦ intrinsic activation energy insensitive to acid strengthBabitz et al. Appl. Catal. A 179 (1999) 71.Alkane cracking in zeolites ◭ ◮ János Ángyán

n-hexane crackingApparent activation energies in different catalystsCatalyst E ‡ app ∆H ads E ‡ trueH-ZSM-5 149±8 −86±6 235±14H-MOR 157±9 −69±3 226±12H-USY 177±9 −50±3 227±12CDHY 186±9 −50±3 236±12Differences in apparent activation energies are due to adsorption energies!◦ intrinsic activation energy insensitive to acid strength◦ acid strengths of these zeolites are identicalBabitz et al. Appl. Catal. A 179 (1999) 71.Alkane cracking in zeolites ◭ ◮ János Ángyán

n-hexane crackingApparent activation energies in different catalystsCatalyst E ‡ app ∆H ads E ‡ trueH-ZSM-5 149±8 −86±6 235±14H-MOR 157±9 −69±3 226±12H-USY 177±9 −50±3 227±12CDHY 186±9 −50±3 236±12Differences in apparent activation energies are due to adsorption energies!◦ intrinsic activation energy insensitive to acid strength◦ acid strengths of these zeolites are identicalBabitz et al. Appl. Catal. A 179 (1999) 71.Alkane cracking in zeolites ◭ ◮ János Ángyán

n-alkane cracking in H-ZSM-5True activation energies seem to be independent of the chain lengthalkanepropanen-butanen-pentanen-hexaneNarbeshuber, Vinek, Lercher J. Catal. A 157 (1995) 338.Alkane cracking in zeolites ◭ ◮ János Ángyán

n-alkane cracking in H-ZSM-5True activation energies seem to be independent of the chain lengthalkane E ‡ app ∆H ads E ‡ truepropane 155 −43 198n-butane 135 −62 197n-pentane 120 −74 194n-hexane 105 −92 197Narbeshuber, Vinek, Lercher J. Catal. A 157 (1995) 338.Alkane cracking in zeolites ◭ ◮ János Ángyán

n-alkane cracking in H-ZSM-5True activation energies seem to be independent of the chain lengthalkane E ‡ app ∆H ads E ‡ true ∆H ads E ‡ truepropane 155 −43 198 -40 195n-butane 135 −62 197 -50 185n-pentane 120 −74 194 -60 180n-hexane 105 −92 197 -71 176unless one uses another set of adsorption energies...Narbeshuber, Vinek, Lercher J. Catal. A 157 (1995) 338.Alkane cracking in zeolites ◭ ◮ János Ángyán

n-alkane cracking in H-ZSM-5True activation energies seem to be independent of the chain lengthalkane E ‡ app ∆H ads E ‡ true ∆H ads E ‡ truepropane 155 −43 198 -40 195n-butane 135 −62 197 -50 185n-pentane 120 −74 194 -60 180n-hexane 105 −92 197 -71 176unless one uses another set of adsorption energies...Narbeshuber, Vinek, Lercher J. Catal. A 157 (1995) 338.Alkane cracking in zeolites ◭ ◮ János Ángyán

n-alkane cracking in H-ZSM-5True activation energies seem to be independent of the chain lengthalkane E ‡ app ∆H ads E ‡ true ∆H ads E ‡ truepropane 155 −43 198 -40 195n-butane 135 −62 197 -50 185n-pentane 120 −74 194 -60 180n-hexane 105 −92 197 -71 176unless one uses another set of adsorption energies...Narbeshuber, Vinek, Lercher J. Catal. A 157 (1995) 338.Alkane cracking in zeolites ◭ ◮ János Ángyán

Exprimental n-alkane adsorption energies0-20Eads (kJ/mol)-40-60-80-100-120-1400 2 4 6 8 10chain lengthVlugt, Krishna, Smit J. Phys. Chem. B 103 (1999) 1102.Alkane cracking in zeolites ◭ ◮ János Ángyán

VASP calculations◦ DFT with PW91 gradient correctionsAlkane cracking in zeolites ◭ ◮ János Ángyán

VASP calculations◦ DFT with PW91 gradient corrections◦ Ultrasoft pseudopotentials for C,H and OAlkane cracking in zeolites ◭ ◮ János Ángyán

VASP calculations◦ DFT with PW91 gradient corrections◦ Ultrasoft pseudopotentials for C,H and O◦ Cutoff energy 400 eVAlkane cracking in zeolites ◭ ◮ János Ángyán

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 ◭ ◮ János Ángyán

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 externaloptimizerAlkane cracking in zeolites ◭ ◮ János Ángyán

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 HessianAlkane cracking in zeolites ◭ ◮ János Ángyán

Transition states in chabazite optimized by VASPbond C 2 H 6 C 3 H 8 n-C 4 H a 10n-C 4 H b 10i-C 4 H 10CCCCHHOAlO(a) primary C–C bond(b) secondary C–C bondAlkane cracking in zeolites ◭ ◮ János Ángyán

Transition states in chabazite optimized by VASPbond C 2 H 6 C 3 H 8 n-C 4 H a 10n-C 4 H b 10i-C 4 H 10H1–O 2.97 2.62 3.01 3.25 2.94CCCCHHOAlO(a) primary C–C bond(b) secondary C–C bondAlkane cracking in zeolites ◭ ◮ János Ángyán

Transition states in chabazite optimized by VASPCCCCbond C 2 H 6 C 3 H 8 n-C 4 H a 10n-C 4 H b 10i-C 4 H 10H1–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 2.47HHOAlO(a) primary C–C bond(b) secondary C–C bondAlkane cracking in zeolites ◭ ◮ János Ángyán

Transition states in chabazite optimized by VASPCCHCHCbond C 2 H 6 C 3 H 8 n-C 4 H a 10n-C 4 H b 10i-C 4 H 10H1–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 2.79OAlO(a) primary C–C bond(b) secondary C–C bondAlkane cracking in zeolites ◭ ◮ János Ángyán

Transition states in chabazite optimized by VASPCCHCHCbond C 2 H 6 C 3 H 8 n-C 4 H a 10n-C 4 H b 10i-C 4 H 10H1–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 1.73OAlO(a) primary C–C bond(b) secondary C–C bondAlkane cracking in zeolites ◭ ◮ János Ángyán

Transition states in chabazite optimized by VASPCCHOAlCHOCbond C 2 H 6 C 3 H 8 n-C 4 H a 10n-C 4 H b 10i-C 4 H 10H1–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,theor215 180 185 155 150∆E ads 30 40 50 50 48E ‡ app,theor185 140 135 105 102(a) primary C–C bond(b) secondary C–C bondAlkane cracking in zeolites ◭ ◮ János Ángyán

Transition states in chabazite optimized by VASPCCHOAlCHOCbond C 2 H 6 C 3 H 8 n-C 4 H a 10n-C 4 H b 10i-C 4 H 10H1–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,theor215 180 185 155 150∆E ads 30 40 50 50 48E ‡ app,theor185 140 135 105 102E ‡ app,exp160 130 150 135 120(a) primary C–C bond(b) secondary C–C bondAlkane cracking in zeolites ◭ ◮ János Ángyán

Alkane cracking in zeolites ◭ ◮ János Ángyán

Ethane crackingT5 cluster calculations at MP2/6-31G(d) and BLYP/6-31G(d) levelBarrier in kJ/molMP2/6-31G(d) 308.6ZPE -8.4thermal effects -4.6long range effects -60.7total 226.5experimental 190-200Zygmunt, Curtiss, Zapol and Iton, J. Phys., Chem. B 104 (2000) 1944.Alkane cracking in zeolites ◭ ◮ János Ángyán

Ethane cracking215 kJ/mol(195 kJ/mol)75 kJ/molAlkane cracking in zeolites ◭ ◮ János Ángyán

Propane crackingAlkane cracking in zeolites ◭ ◮ János Ángyán

Propane cracking180 kJ/molAlkane cracking in zeolites ◭ ◮ János Ángyán

Propane cracking180 kJ/mol(190 kJ/mol)Alkane cracking in zeolites ◭ ◮ János Ángyán

Propane cracking180 kJ/mol(190 kJ/mol) 65 kJ/molAlkane cracking in zeolites ◭ ◮ János Ángyán

Isobutane dehydrogenationT5 cluster B3LYP/6-31G** and T3 cluster B3LYP/6-311** calculationsMilas and Nascimento Chem. Phys. Lett. 338 (2001) 67Alkane cracking in zeolites ◭ ◮ János Ángyán

Isobutane dehydrogenationT5 cluster B3LYP/6-31G** and T3 cluster B3LYP/6-311** calculationsCarbocation collapses directly, without alkoxide formationActivation energy: 223.5 kJ/mol (exp.: 172±6 kJ/mol)Milas and Nascimento Chem. Phys. Lett. 338 (2001) 67Alkane cracking in zeolites ◭ ◮ János Ángyán

Isobutane dehydrogenation∆E ‡ true(theor) = 190 kJ/mol∆E ‡ true(exp) = 172 kJ/molAlkane cracking in zeolites ◭ ◮ János Ángyán

Isobutane dehydrogenation: carbenium intermediateAlkane cracking in zeolites ◭ ◮ János Ángyán

Isobutane crackingAlkane cracking in zeolites ◭ ◮ János Ángyán

Isobutane crackingAlkane cracking in zeolites ◭ ◮ János Ángyán

Isobutane cracking∆E ‡ true(theor) = 150 kJ/mol∆E ‡ true(exp) = 170 kJ/molAlkane cracking in zeolites ◭ ◮ János Ángyán

n-butane: experimental activation energiesE ads = -62 kJ/molNarbeshuber, Vinek, Lercher J. Catal. A 157 (1995) 338.Alkane cracking in zeolites ◭ ◮ János Ángyán

n-butane: experimental activation energies80 kJ/molE ads = -62 kJ/molH/D exchangeNarbeshuber, Vinek, Lercher J. Catal. A 157 (1995) 338.Alkane cracking in zeolites ◭ ◮ János Ángyán

n-butane: experimental activation energies115 kJ/mol80 kJ/molE ads = -62 kJ/molH/D exchangedehydrogenationNarbeshuber, Vinek, Lercher J. Catal. A 157 (1995) 338.Alkane cracking in zeolites ◭ ◮ János Ángyán

n-butane: experimental activation energies115 kJ/mol135 kJ/mol80 kJ/molcrackingE ads = -62 kJ/molH/D exchangedehydrogenationNarbeshuber, Vinek, Lercher J. Catal. A 157 (1995) 338.Alkane cracking in zeolites ◭ ◮ János Ángyán

Cracking of n-butane: attack on primary C-C bondAlkane cracking in zeolites ◭ ◮ János Ángyán

Cracking of n-butane: attack on primary C-C bondAlkane cracking in zeolites ◭ ◮ János Ángyán

Cracking of n-butane: attack on primary C-C bond∆E ‡ true(theor) = 185 kJ/mol∆E ‡ true(exp) = 200 kJ/molAlkane cracking in zeolites ◭ ◮ János Ángyán

Cracking of n-butane: attack on secondary C-C bond∆E ‡ true(theor) = 155 kJ/mol∆E ‡ true(exp) = 185 kJ/molAlkane cracking in zeolites ◭ ◮ János Ángyán

Conclusions◦ reasonable agreement with available activation energy dataAlkane cracking in zeolites ◭ ◮ János Ángyán

Conclusions◦ reasonable agreement with available activation energy data◦ reliable determination of adsorption energies would be needed (dispersionforces)Alkane cracking in zeolites ◭ ◮ János Ángyán

Conclusions◦ reasonable agreement with available activation energy data◦ reliable determination of adsorption energies would be needed (dispersionforces)◦ complete mapping of multiple reaction pathwaysAlkane cracking in zeolites ◭ ◮ János Ángyán

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 ◭ ◮ János Ángyán

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 ◭ ◮ János Ángyán