Confinement Effect of Zeolite Cavities on Methanol-to-Olefin

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The Confinement Effect of Zeolite Cavities on Methanol-to-Olefin Conversion: A DFT Study Xu Li, Qiming Sun, Yi Li, Ning Wang, Junran Lu, and Jihong Yu J. Phys. Chem. C, Just Accepted Manuscript • DOI: 10.1021/jp505696m • Publication Date (Web): 02 Oct 2014 Downloaded from http://pubs.acs.org on October 13, 2014

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The Journal of Physical Chemistry

The Confinement Effect of Zeolite Cavities on Methanol-to-Olefin Conversion: A DFT Study Xu Li, Qiming Sun, Yi Li,* Ning Wang, Junran Lu, and Jihong Yu* State Key Laboratory of Inorganic Synthesis and Preparative Chemistry, College of Chemistry, Jilin University, Qianjin Street 2699, Changchun 130012, PR China KEYWORDS: Methanol-to-olefin conversion, Side-chain mechanism, Zeolite cavity, spatial confinement, DFT

ABSTRACT. The confinement effect of zeolite cavities on the methanol-to-olefin (MTO) conversion is investigated through density functional theory (DFT) calculations. According to the side-chain mechanism, we select several hydrocarbon pool (HP) intermediates that may exist during the MTO conversion process and optimize their structures within the cluster models of zeolite cavities cha, lev, and lta, respectively. The transition states during methylation, deprotonation, methyl shift, and olefin-production are also located within these cavities. According to our results, all of the HP intermediates are stabilized in zeolite cavities, especially in cha and lta. Moreover, the cha cavity displays the lowest intrinsic free-energy barriers for all of the methylation and olefin-production steps, indicating its high MTO catalytic activity. We find that the differences in reaction barriers and reaction energies are highly related to the different confinement effects of zeolite cavities. In comparison with lev and lta, the cha cavity 1 ACS Paragon Plus Environment


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matches the dimensions of HP species very well, so it is able to provide the most suitable confinement to HP species. Our discovery will provide further understanding of the side-chain mechanism, which is important for finding new catalysts for MTO conversion.

INTRODUCTION

Zeolites are the most important solid catalysts in chemical industry because of their unique shape selectivity.1-4 Methanol-to-olefin (MTO) conversion over acidic zeolite catalysts has been an important non-petrochemical process to produce industrially demanding light olefins via natural gas, coal, or even biomass.5-7 The small-pore silicoaluminophosphate zeolite SAPO-34 has been used in industry as a highly selective catalyst for MTO conversion.8,9 The actual mechanism for MTO conversion over acidic zeolite has been considerably debated for a long time. So far, the hydrocarbon pool (HP) mechanism has been generally accepted, which was proposed by Dahl and Kolboe on the basis of their experimental studies.10 However, the HP mechanism is very complex;11-12 it depends on many factors, such as zeolite framework topology, framework composition, strength of acid site, pore openings, the shape of the pores, and the orientation of extra-framework species, etc. 13-17 Many studies have been conducted to investigate the mechanism of MTO conversion over zeolite catalysts. Through in-situ solid state MAS NMR spectroscopy, some important HP intermediates, such as the heptamethylbenzenium and hexamethylmethylenecyclohexadiene have been found in DNL-6, ZSM-5 and beta during MTO conversion. 18-20 According to the side-chain route, the formation of light olefins undergoes multiple steps of methylation, deprotonation, methyl shift, and side-chain elimination, producing a series of HP species (Figure 1). 21,22 At the beginning, hexamethylbenzene (Intermediate A) reacts with 2 ACS Paragon Plus Environment

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methanol in SN2 fashion to form heptamethylbenzenium (Intermediate B) and a water molecule; this is the first methylation step (Me1). Heptamethylbenzenium is then deprotonated (Dep1) to form hexamethylmethylenecyclohexadiene (Intermediate C), which may transform into Intermediate D through the second methylation step (Me2). Intermediate D may transform into Intermediates E and F through additional steps of deprotonation (Dep2) and methylation (Me3). The side-chains on Intermediates D and F may undergo several 1,2-methyl shift steps (Shift1–3 and Shift4–6) and turn into isomers D’ and F’, respectively. Ethylene and propylene are produced from Intermediates D’ and F’ through elimination steps (Elim1 and Elim2), respectively, closing the catalytic cycle. Water molecules play an important role during these catalytic cycles by passing protons between intermediates and zeolite frameworks.23

Figure 1. Side-chain route of HP mechanism for MTO conversion. 3 ACS Paragon Plus Environment


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Several types of zeolites have been tested as catalysts for MTO conversion. SAPO-34 containing cha cavities (11.6 Å × 10.6 Å; Figure 2a) has shown high selectivity in the production of light olefins.24,25 The 8-ring windows of the cha cavity allow the free diffusion of light olefins, and the space inside cha favors the formation of HP intermediates of specific size and shape.26,27 Other zeolites, such as SAPO-35 with lev cavities (10.1 Å × 9.7 Å; Figure 2b) and DNL-6 with lta cavities (11.9 Å × 11.9 Å; Figure 2c), have also been tested for MTO conversion.28,29 As compared to SAPO-34, SAPO-35 and DNL-6 have displayed different MTO catalytic performances. For instance, SAPO-35 can be deactivated more easily during MTO conversion.30 The distinct MTO catalytic performances of these zeolites might result from the different confinement effects of different zeolite cavities.31

Figure 2. Cluster models of (a) the cha cavity consisting of 36 T atoms, (b) the lev cavity consisting of 30 T atoms, and (c) the lta cavity consisting of 48 T atoms. Si atoms are shown in yellow, Al in purple, O in red, and H in white. Atoms calculated at the high ONIOM layer are shown as spheres. Among previous studies, theoretical calculations have provided an important insight into the mechanism of MTO conversion over acidic zeolite catalysts.32 Many theoretical studies have demonstrated that the framework topology decides the reactivity and selectivity of zeolites; their cavities provide the spatial room for the HP intermediates and transition states generated during 4 ACS Paragon Plus Environment

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MTO conversion.33 Through the QM/MM method, van Speybroeck and coworkers found that the activation energy for the methylation of polymethylbenzene was extremely low in the cha cavity (60.8 kJ/mol) than that in the channel intersections in zeolite MFI (161.7 kJ/mol).34 They also elucidated the effect of confined space on the growth of naphthalenic species in zeolites SAPO-34 and SSZ-13.35 Similarly, Iglesia and coworkers investigated the confinement effect on the selectivity of alkane-cracking and dehydrogenation in the pores of zeolite MOR.36 In this work, we employ the density functional theory (DFT) calculations to investigate the MTO catalytic cycle according to the HP mechanism. The confinement effect of different zeolite cavities, including the cha, lev, and lta cavities are evaluated assuming the same side-chain mechanism. Our theoretical calculations may provide a further insight into the confinement effect of zeolite cavities during the MTO conversion.

COMPUTATIONAL DETAILS

The cluster models of lev, cha and lta (Figures 2) were cut from the ideal silica structures of zeolites LEV, CHA, and RHO, which contain 30, 36 and 48 T atoms, respectively.37 One Brönsted acid site was considered for each cavity by replacing one Si atom by one Al. The locations of acid sites were chosen at the 8-ring window where methanol and light olefin molecules can diffuse easily. We tried several possible O atoms in the 8-ring windows and selected the ones with the best proton affinity as the acid sites for the following calculations. More details about the selection of the acid sites are shown in Figure S1 and Table S1 in the Supporting Information. The dangling bonds in all of these cluster models were saturated by H atoms. 5 ACS Paragon Plus Environment


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All the DFT calculations were carried out using the exchange-correlation functional B3LYP as implemented in the Gaussian 09 package.38 The B3LYP functional has been widely applied to investigate the catalytic reactions over zeolite clusters.39 Because the cavity models were too large for regular DFT calculations, we employed the 2-layer ONIOM method for all of our calculations.40 The SiO3–O–AlO2–OH–SiO3 cluster and HP species were in the high level, and the remaining framework atoms were in the low level. The cavity models and HP species were optimized together at ONIOM (B3LYP/6-31g(d,p):AM1) level. Transition states were confirmed through the intrinsic reaction coordinate (IRC) approach.41 The achievement of true energy minima and saddle points was checked by frequency calculations at the same level. Enthalpy, entropy, and free energy calculations were performed at 673 K. The single-point energy calculations were performed at ONIOM (B3LYP/6-31g(d,p):HF/6-31g(d)) level. Dispersion corrections were performed to the single-point energies according to the D3 method proposed by Grimme and coworkers.42

RESULTS AND DISCUSSION

Methylation and Deprotonation. Assuming the side-chain mechanism (Figure 1), generating ethylene requires two methylation (Me1 and Me2) and one deprotonation (Dep1) steps, and generating propylene requires one additional methylation (Me3) and one additional deprotonation (Dep2) steps. The calculated reaction barriers and reaction energies of these reaction steps within protonated cha, lev, and lta cavities are listed in Table 1 and Table 2, respectively. The optimized geometries of the transition states for the first methylation and the first deprotonation in different cavities are shown in Figure S2 in the Supporting Information.

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Table 1. Intrinsic Reaction Barriers (kcal/mol) for MTO Steps within Different Zeolite Cavities at 673 K Assuming the Same Side-Chain Mechanism.

Reaction Me1 Dep1 Me2 Shift1 Shift2 Shift3 Elim1 Dep2 Me3 Shift4 Shift5 Shift6 Elim2

cha ∆E 14.6 21.5 11.2 27.1 19.2 21.9 16.0 15.1 10.6 23.3 22.0 20.7 14.0

∆H 14.5 18.9 10.8 26.1 19.1 21.3 15.6 18.6 10.5 23.3 21.9 21.8 13.0

lev

∆G 18.5 30.2 15.0 30.8 17.7 23.2 19.2 21.7 16.1 17.3 21.1 17.7 17.2

−T∆S 4.0 11.3 4.2 4.7 -1.3 1.9 3.6 3.1 5.6 -6.0 -0.8 -4.1 4.2

∆E 28.9 14.2 13.2 14.0 15.4 21.9 19.6 28.1 23.7 21.2 15.1 16.0 16.2

∆H 28.4 10.9 14.0 24.6 15.3 21.3 18.6 36.5 24.7 19.4 14.4 15.7 14.0

∆G 33.9 26.4 19.7 23.4 14.0 24.8 23.7 47.3 30.9 24.2 17.4 17.4 21.5

lta −T∆S 5.5 15.5 5.7 -1.1 -1.3 3.5 5.1 10.8 6.2 4.8 3.0 1.8 7.5

∆E 20.2 16.1 17.2 17.3 19.5 26.2 17.6 9.3 17.4 25.6 23.6 15.2 13.3

∆H 19.7 14.0 17.8 16.7 18.9 25.6 18.2 7.3 17.7 24.4 23.3 15.1 12.7

∆G 27.1 21.6 20.6 15.9 21.4 29.4 26.5 14.2 24.3 26.3 22.7 13.8 20.3

−T∆S 7.4 7.6 2.8 -0.9 2.5 3.8 8.3 6.9 6.6 1.9 -0.6 -1.3 7.6

Table 2. Intrinsic Reaction Energies (kcal/mol) for MTO Steps within Different Zeolite Cavities at 673 K Assuming the Same Side-Chain Mechanism.

Reaction Me1 Dep1 Me2 Shift1 Shift2 Shift3 Elim1 Dep2 Me3 Shift4 Shift5 Shift6 Elim2

cha ∆E -2.5 16.7 -31.7 -6.9 2.8 -1.8 12.8 12.7 -34.3 2.5 3.7 -7.0 2.1

∆H -1.5 15.6 -30.9 -7.4 3.2 -1.4 14.1 15.0 -33.1 2.4 2.5 -5.4 2.8

lev

∆G 0.4 21.0 -33.0 -3.1 0.2 -2.5 7.2 15.2 -33.3 2.9 6.2 -11.8 0.1

−T∆S 1.9 5.4 -2.1 4.2 -3.0 -1.1 -6.9 0.2 -0.2 0.5 3.7 -6.4 -2.7

∆E 4.9 11.6 -14.1 -15.3 13.4 -19.5 15.8 21.0 -17.4 0.8 -6.3 4.5 -8.5

∆H 6.3 9.5 -23.3 -4.3 13.5 -18.6 14.9 31.0 -15.3 0.6 -6.3 4.1 -6.9

∆G 3.2 20.1 -19.1 -7.2 12.3 -24.0 19.5 34.8 -13.9 1.6 -6.7 1.5 -12.0

lta −T∆S -3.1 10.6 4.2 -2.9 -1.2 -5.4 4.6 3.8 1.4 1.0 -0.5 -2.7 -5.1

∆E -5.2 14.6 -13.9 -3.4 -7.3 7.5 13.1 9.7 -26.0 -0.4 5.9 -8.1 -1.0

∆H -4.5 12.8 -12.3 -4.5 -6.4 7.0 16.0 5.1 -24.3 -1.0 5.6 -7.4 0.4

∆G -0.2 15.6 -12.4 -3.5 -5.6 4.2 10.8 12.1 -19.9 0.1 6.3 -13.9 -2.8

−T∆S 4.3 2.8 -0.1 1.0 0.8 -2.8 -5.2 7.0 4.4 0.9 0.7 -6.5 -3.2



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For the transition states of the first methylation step (Me1), the Cm–Om breaking distances in methanol (cha, 2.14 Å, lev, 2.13 Å, lta, 2.14 Å) and the Cm–CHP forming distances between methanol and hexamethylbenzene (cha, 2.21 Å; lev, 2.24 Å, lta, 2.17 Å) are quite similar within different zeolite cavities (Table S2 in the Supporting Information). However, as shown in Table 1, the intrinsic free-energy barriers at 673K are quite different (cha, 18.5 kcal/mol; lev, 33.9 kcal/mol; lta, 27.1 kcal/mol). For the cha cavity, the zero-point-corrected energy barrier of 14.6 kcal/mol for the first methylation step is close to that reported by Van Speybroeck and coworkers (15.2 kcal/mol).34 The free-energy barriers of the second methylation step (Me2) follow the sequence of cha < lev < lta and those for the third methylation step (Me3) follow the sequence of cha < lta < lev. The free-energies of these methylation reactions show a slightly different trend (Table 2). For the first methylation reaction, the free-energies in cha and lta are generally the same, both of which are slightly lower than that of lev. The second and the third methylation steps in three cavities are all exothermic; the reaction free-energies of cha are much lower than those of lev and lta. All these results indicate that the methylation steps might take place more easily in cha than in the other two cavities. The first deprotonation step (Dep1) occurs between Intermediates B and C. As those in the first methylation step, the bond distances (Table S3 in the Supporting Information) involving H-shift in the first deprotonation step are similar in different cavities. However, different from the trend in the methylation steps, the intrinsic free-energy barriers for the first deprotonation step at 673 K follow the sequence of lta (21.6 kcal/mol) < lev (26.4 kcal/mol) < cha (30.2 kcal/mol). The second deprotonation step (Dep2) occur between Intermediates D and E. The intrinsic free-energy barriers for this step follow the sequence of lta (14.2 kcal/mol) < cha (21.7 kcal/mol)


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< lev (47.3 kcal/mol). The free-energies of the two deprotonation reactions show the same trend as their free-energy barriers. Both of the deprotonation steps are endothermic.

Olefin Production. In comparison with the direct-cracking mechanism, the concerted mechanism proposed by Van Speybroeck and co-worker is a lower-barrier pathway to yield olefins.22 According to this mechanism, Intermediates D and F turn into isomers D’ and F’ through methyl shift reactions (Shift1–3 and Shift4–6); D’ and F’ transform back into A through side-chain eliminations, producing ethylene (Elim1) and propylene (Elim2), respectively. Figure S2 shows the geometries of transition states of the elimination step within different zeolite cavities. The geometries of these transition states are similar among different cavities. To generate ethylene, the H1 atom in the methyl group is attracted by the water molecule, elongating the C1–H1 bond. With the assistance of the water molecule, the H1 atom shifts from C1 to Ow. The C2–CHP bond is then broken, and the ethylene molecule is eventually generated from Intermediate D’. Propylene is generated in a similar way (Table S4 in the Supporting Information). The intrinsic free-energy barriers for the two olefin-production steps within different zeolite cavities are shown in Table 1. For the ethylene-production reaction, the free-energy barriers follow the sequence of cha (19.2 kcal/mol) < lev (23.7 kcal/mol) < lta (26.5 kcal/mol); for the propylene-production reaction, the free-energy barriers follow the sequence of cha (17.2 kcal/mol) < lta (20.3 kcal/mol) < lev (21.5 kcal/mol). For both olefin-production reactions, cha exhibits the lowest intrinsic free-energy barriers, indicating that the olefin-production reactions happen more easily in the cha cavity. Moreover, the free-energy barriers of propylene-production reactions are generally lower than those of ethylene-production reactions, which agrees with the 9 ACS Paragon Plus Environment


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fact that propylene is the preferred product at the beginning of MTO conversion over SAPO-34 and SSZ-13.43 As shown in Table 2, the ethylene-production reactions in three cavities are all endothermic, whereas the propylene-production reactions are generally exothermic. This is probably because the Intermediate F’ for propylene-production is larger than Intermediate D’ for ethylene-production, which release more energies when its side-chain is eliminated within the limited space in zeolite cavities.

The Confinement Effect of Zeolite Cavities. It has been well accepted that zeolite cavities have important stabilization effects on HP intermediates.44 Van Speybroeck and coworkers found that the kinetics of zeolite-catalyzed reactions hinged on the balance between proper stablization of extra-framework intermediates and the resulting entropy losses.12 In this work, according to the side-chain mechanism, we have calculated several carbenium ions (Intermediates B, D, and F), neutral HP species (Intermediates A, C, and E), and the transition states during each reaction steps. The relative energies of these intermediates and transition states are shown in Table S5 and Figure S3 in the Supporting Information. According to our results, positively charged carbenium ions have lower relative energies within zeolite cavities than the neutral intermediates because of the host-guest electrostatic interactions. Moreover, as shown above, the cha cavity possesses the lowest intrinsic free-energy barriers for all of the methylation and olefin-production steps. Since the proton affinities of the acid sites in these cavities are similar (Table S1 in the Supporting Information), the differences in reaction barriers and energies might come from the different topologies of these cavities. Although cha, lev, and lta are all constructed by 4-, 6-, and 8-rings, their sizes are different. To study the dimensional match between zeolite cavities and HP species, we have calculated the 10 ACS Paragon Plus Environment

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void volumes45 of these cavities (Table S6 in the Supporting Information), the dimensions of HP species (Figure S4 in the Supporting Information), and the shortest H⋅⋅⋅O distances between HP species and zeolite cavities (Table S5 in the Supporting Information). The lev cavity (1074.98 Å3) is the smallest among all three cavities, which is built up by nine 4-rings, five 6-rings, and three 8-rings. As shown in Table S5 in the Supporting Information, the shortest H⋅⋅⋅O distances between HP species and lev range from 2.14 to 2.49 Å, most of which are shorter than 2.40 Å. This indicates that the HP species cannot translate or rotate freely in the limited void space of lev, therefore they are not well stabilized in lev. The mismatch between lev and HP species can be visualized in Figure 3, which shows the transition state for the first methylation step in lev. Dashed lines indicate the close contacts (< 3.0 Å) between HP species and zeolite cavities. The lta cavity (1720.34 Å3) is the largest among all three cavities, which is built up by twelve 4-rings, eight 6-rings, and six 8-rings. The shortest H⋅⋅⋅O distances between HP species and lta range from 2.40 Å to 3.64 Å, most of which are longer than 2.50 Å (Table S5 in the Supporting Information). This indicates that the HP species can translate or rotate freely in lta, therefore they can be better stabilized in lta than in lev. However, as shown in Figure 3, the close contacts between HP species and lta are quite rare, indicating that the HP species are not efficiently confined by the lta cavity. The cha cavity is built up by twelve 4-rings, two 6-rings, and six 8-rings. The cha cavity has a void volume of 1276.75 Å3, which is in between those of lev and lta. All of the HP species occupy the central region of the cha cavity. The shortest H⋅⋅⋅O distances between HP species and cha range from 2.30 Å to 2.51 Å, most of which are in between 2.35 Å and 2.45 Å (Table S5 in the Supporting Information). As shown in Figure 3, the cha cavity matches the dimensions of HP species very well. It provides not only enough void space for HP species to translate or rotate, but also suitable confinement strong enough to 11 ACS Paragon Plus Environment


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stabilize the HP species. The excellent dimensional match between cha and HP species might be the reason for the low reaction barriers in methylation and olefin-production steps. As a matter of fact, for any cavity and HP species, the best confinement effect may occur for when the shortest H⋅⋅⋅O distance between them is in between 2.35 Å and 2.45 Å (Table S5 in the Supporting Information). This model may be used for fast screening of potential MTO catalysts if they follow a similar side-chain mechanism.

Figure 3. The H⋅⋅⋅O distances (< 3.0 Å) between HP species and zeolite cavities during the first methylation step. In this study, we focus on the spatial confinement effects of zeolite cavities. To compare these effects among different cavities, we assume that the MTO reactions in all these cavities follow the same side-chain mechanism. In addition, we assume the acid sites are located in similar positions near the 8-ring windows within different cavities. On the basis of these assumptions, we found that the lev cavity should not exhibit good performance in MTO conversion. However, it has been reported that SAPO-35 with lev cavities might have good MTO reactivity under specific conditions.46 This might be because the MTO conversion in SAPO-35 undergoes a


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different reaction route, which requires more theoretical and experimental efforts to be unraveled.

CONCLUSION Through DFT calculations, we have studied the MTO conversion within cha, lta, and lev cavities assuming the same side-chain mechanism. The cha cavity exhibits the lowest intrinsic free-energy barriers for all of the methylation and olefin-production steps, which agrees well with the fact that SAPO-34 constructed by the cha cavities is one of the most widely used catalysts for MTO conversion. Further investigations show that the suitable confinement effect of the cha cavity might be the reason for such low reaction barriers. The lev and lta cavities are either too small or too large, providing too much or too little confinement to the HP species. Our theoretical calculations clearly demonstrate the essential role of the confinement of zeolite cavities during MTO conversion. Other zeolite cavities might be good candidate catalysts for MTO conversion following the side-chain route if they are able to provide suitable confinement to HP species like cha does.

ASSOCIATED CONTENT

Supporting Information Proton affinities for possible acid sites; selected bond distances in the optimized structures of transition states for methylation, deprotonation, and olefin-production steps; relative energies and the shortest H…O distances in HP species; dimensions of zeolite cavities and HP species. This material is available free of charge via the Internet at http://pubs.acs.org. 13 ACS Paragon Plus Environment


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AUTHOR INFORMATION Corresponding Author *E-mail [email protected]; Tel. +86-431-85168608; fax +86-431-85168608 (J.Y.). *E-mail [email protected]; Tel. +86-431-85168609 (Y.L.).

Notes The authors declare no competing financial interest.

ACKNOWLEDGMENT

We thank the State Basic Research Project of China (Grant Nos. 2011CB808703; 2014CB931802) and National Natural Science Foundation of China (Grant Nos. 91122029; 21273098; 21320102001). Y.L. thanks the support by Program for New Century Excellent Talents in University (NCET-13-0246).

REFERENCES

(1) Li, Y.; Yu, J. New Stories of Zeolite Structures: Their Descriptions, Determinations, Predictions, and Evaluations. Chem. Rev. 2014, 114, 7268-7316 (2) Smit, B.; Maesen, T. L. M. Molecular Simulations of Zeolites: Adsorption, Diffusion, and Shape Selectivity. Chem. Rev. 2008, 108, 4125-4184.


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Table of Contents Image



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Supporting Information

The Confinement Effect of Zeolite Cavities on Methanol-to-Olefin Conversion: A DFT Study Xu Li, Qiming Sun, Yi Li,* Ning Wang, Junran Lu, and Jihong Yu* State Key Laboratory of Inorganic Synthesis and Preparative Chemistry, College of Chemistry, Jilin University, Qianjin Street 2699, Changchun 130012, PR China


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Table S1. Proton Affinity (kcal/mol) for Different Possible Brönsted Acid Sites in Different Cavities. cha

lev

lta

Site

PA

Site

PA

Site

PA

Al1O2

294.94

Al1O2

295.29

Al1O1

300.79

Al1O3 Al1O4

295.12 296.69

Al1O4 Al2O2

297.38 295.29

Al1O2

297.28

Al2O5

297.38

Table S2. Selected Bond Distances (/Å) in Transition States for Methylation Steps within the cha, lev and lta Cavities. Bondsa Cm–Om Cm–CHP

cha TS_A-B 2.14 2.21

TS_C-D 1.99 2.28

lev TS_E-F 1.99 2.27

TS_A-B 2.13 2.24

lta

TS_C-D 1.97 2.32

TS_E-F 2.06 2.39

TS_A-B 2.14 2.17

TS_C-D 2.01 2.26

TS_E-F 2.02 2.22

a

Om and Cm denote the O and C atoms in methanol, respectively; CHP denote the C atoms in the HP intermediates, respectively.

Table S3. Selected Bond Distances (/Å) in Transition States for Deprotonation Steps within the cha, lev and lta Cavities. Bondsb Ow–HHP HHP–CHP

cha TS_B-C 1.23 1.41

TS_D-E 1.27 1.38

lev TS_B-C 1.24 1.40

lta TS_D-E 1.23 1.42

TS_B-C 1.27 1.37

TS_D-E 1.30 1.35

b

Ow denotes the O atom in the water molecule; HHP and CHP denote the H and C atoms in the HP intermediates, respectively.

Table S4. Selected Bond Distances (/Å) in Transition States for the Production of Ethylene and Propylene within the cha, lev and lta Cavities. Bondsc Ow–H1 H1–C1 C2–CHP

cha TS_D’-G 1.48 1.24 2.71

lev

TS_F’-G 1.50 1.24 3.07

TS_D’-G 1.43 1.28 2.68

lta TS_F’-G 1.44 1.27 3.11

TS_D’-G 1.53 1.22 2.67

TS_F’-G 1.53 1.22 2.97

c

Ow denotes the O atom in the water molecule; H1, HHP, C1, C2 and CHP denote the H and C atoms in the HP intermediates, respectively.



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Table S5. Relative Energies (kcal/mol), Enthalpies (kcal/mol), Free-Energies (kcal/mol), Entropies (kcal/mol), and the Shortest H…O Distances (Å) between HP Species and Zeolite Cavities at 673 K. Cavity Zeo+A+CH3OH(g) A+CH3OH TS_A-B B+H2O TS_B-C C+H2O C+CH3OH TS_C-D D+H2O TS_D-D1 D1+H2O TS_D1-D2 D2+H2O TS_D2-D' D'+H2O TS_D'-A A+C2H4 D+H2O TS_D-E E+H2O E+CH3OH TS_E-F F+H2O TS_F-F1 F1+H2O TS_F1-F2 F2+H2O TS_F2-F' F'+H2O TS_F'-A A+C3H6

cha E

H

G

0.0 -29.2 -14.6 -31.7 -10.2 -15.0 -9.1 2.1 -40.8 -13.7 -47.7 -28.6 -44.9 -23.0 -46.7 -30.7 -33.9 -40.8 -25.7 -28.1 -24.7 -14.1 -59.0 -35.7 -56.5 -34.5 -52.8 -32.1 -59.8 -45.8 -57.7

0.0 -29.0 -14.5 -30.5 -11.6 -14.9 -7.9 2.9 -38.8 -12.7 -46.2 -27.1 -43.0 -21.7 -44.4 -28.8 -30.3 -38.8 -20.2 -23.8 -22.8 -12.3 -55.9 -32.6 -53.5 -31.5 -50.9 -29.1 -56.3 -43.3 -53.5

0.0 -1.7 16.8 -1.3 28.9 19.7 28.0 43.0 -5.0 25.8 -8.1 9.6 -7.9 15.3 -10.4 8.8 -3.2 -5.0 16.7 10.2 17.1 33.2 -16.2 1.1 -13.3 7.8 -7.1 10.6 -18.9 -1.7 -18.8

lev −T∆S DH…O

0.0 27.3 31.3 29.2 40.5 34.6 35.9 40.1 33.8 38.5 38.1 36.7 35.1 37.0 34.0 37.6 27.1 33.8 36.9 34.0 39.9 45.5 39.7 33.7 40.2 39.3 43.8 39.7 37.4 41.6 34.7

2.50 2.48 2.50 2.46 2.37 2.40 2.51 2.39 2.45 2.32 2.30 2.49 2.31 2.45 2.43 2.52 2.43 2.45 2.44 2.43 2.38 2.41 2.38 2.50 2.46 2.34 2.37 2.37 2.43 2.34 2.32

lta

E

H

G

−T∆S

DH…O

E

H

G

−T∆S

DH…O

0.0 -23.9 5.0 -19.0 -4.8 -7.4 -6.8 6.4 -20.9 -6.9 -36.2 -20.9 -22.8 -0.9 -42.3 -22.7 -26.5 -20.9 7.2 0.1 2.6 26.3 -14.8 6.4 -14.0 1.2 -20.2 -4.2 -15.7 0.5 -24.2

0.0 -23.7 4.7 -17.4 -6.5 -7.9 -6.9 7.1 -30.2 -5.6 -34.5 -19.2 -21.0 0.3 -39.6 -21.0 -24.7 -30.2 6.3 0.8 3.3 28.0 -12.0 7.4 -11.4 3.0 -17.7 -2.0 -13.6 0.4 -20.5

0.0 4.9 38.8 8.1 34.5 28.2 26.2 45.9 7.1 30.5 -0.1 13.9 12.2 37.0 -11.8 11.9 7.7 7.1 54.4 41.9 44.4 75.3 30.5 54.7 32.1 49.5 25.3 42.8 26.8 48.3 14.8

0.0 28.6 34.1 25.5 41.0 36.1 33.1 38.8 37.3 36.1 34.4 33.1 33.2 36.7 27.8 32.9 32.4 37.3 48.1 41.1 41.1 47.3 42.5 47.3 43.5 46.5 43.0 44.8 40.4 47.9 35.3

2.42 2.32 2.35 2.31 2.27 2.29 2.19 2.26 2.26 2.27 2.46 2.30 2.26 2.30 2.49 2.46 2.40 2.26 2.28 2.17 2.38 2.14 2.16 2.15 2.16 2.23 2.24 2.26 2.20 2.39 2.31

0.0 -26.3 -6.1 -31.5 -15.4 -16.9 -22.9 -5.7 -36.8 -19.5 -40.2 -20.7 -47.5 -21.3 -40.0 -22.4 -26.9 -36.8 -27.5 -27.1 -28.6 -11.2 -54.6 -29.0 -55.0 -31.4 -49.1 -33.9 -57.2 -43.9 -58.2

0.0 -25.1 -5.4 -29.6 -15.6 -16.8 -21.6 -3.8 -33.9 -17.2 -38.4 -19.5 -44.8 -19.2 -37.8 -19.6 -21.8 -33.9 -26.6 -28.8 -25.6 -7.9 -49.9 -25.5 -50.9 -27.6 -45.2 -30.1 -52.6 -39.9 -52.2

0.0 -1.1 26.0 -1.3 20.3 14.3 10.5 31.1 -1.9 14.0 -5.4 16.0 -11.0 18.4 -6.8 19.7 4.0 -1.9 12.3 10.2 4.9 29.2 -14.9 11.4 -15.0 7.6 -8.7 5.1 -22.6 -2.3 -25.4

0.0 24.0 31.4 28.3 35.9 31.1 32.1 34.9 32.0 31.2 33.0 35.5 33.8 37.6 31.0 39.3 25.8 32.0 38.9 39.0 30.5 37.1 35.0 36.9 35.9 35.2 36.5 35.2 30.0 37.6 26.8

3.00 3.64 2.95 2.59 2.91 3.02 3.01 2.80 2.58 2.56 2.62 2.63 2.66 2.51 2.51 2.87 3.01 2.58 2.78 3.02 2.44 2.47 2.52 2.60 2.59 2.56 2.40 2.56 2.62 2.92 2.99


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Table S6. Dimensions of cha, lev, and lta Cavities. Cavity

cha

lev

lta

3.8×3.8 Å 1276.75 Å3

3.6×4.8 Å 1074.98 Å3

3.6×3.6 Å 1720.34 Å3

Dimension

Window Size Volumed

d: The void volume is calculated by the Material Studio software package.

Figure S1. Possible Brønsted acid sites in cha, lev, and lta. Atoms calculated at the high ONIOM layer are shown as spheres.



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Figure S2. Optimized transition states for the first methylation, deprotonation and elimination steps in cha, lev and lta.


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Figure S3. Free-energy profiles within different zeolite cavities at 673 K.

Figure S4. Dimensions of HP intermediates.


Confinement Effect of Zeolite Cavities on Methanol-to-Olefin

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