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. 2020 Apr 20;5(17):9707–9713. doi: 10.1021/acsomega.9b03984

Monomolecular Dehydration of Ethanol into Ethylene over H-MOR Studied by Density Functional Theory

Hongqiang Xia 1,*
PMCID: PMC7203697  PMID: 32391457

Abstract

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The framework effect of H-mordenite (H-MOR) zeolite on monomolecular dehydration of ethanol to ethylene has been simulated based on density functional theory. It is indicated that both the reaction mechanism and the activation energy barriers are significantly affected by the pore-confinement effect. In the 12-membered ring (12-MR), the energy barriers of the stepwise mechanism and the concerted mechanism are 35.0 and 42.4 kcal mol–1, respectively, suggesting that ethylene can be competitively formed through both pathways. While in the 8-membered ring (8-MR), the barrier of the concerted mechanism is 43.4 kcal mol–1, which is much lower than that of the stepwise mechanism with the ethoxy intermediate formation barrier of 53.7 kcal mol–1. Furthermore, the water molecule acts as the intermediate to stabilize the transition states (TSs) for both stepwise and concerted mechanisms and helps to transport protons during the reaction.

Introduction

Ethylene, one of the most important organic feedstock, has a great influence on global economic development. Compared with the traditional production of ethylene from petroleum hydrocarbons, it is much more economical and environmentally friendly to utilize bioethanol as a chemical resource. Several different kinds of catalysts have been developed to improve the ethylene yield from bioethanol dehydration and to reduce energy consumption for industrial applications. The most valuable catalysts are activated alumina and zeolites.1−5 The activated alumina exerts comparatively high activity and selectivity, but water existing in the reaction system usually leads to a significant reduction of the conversion of ethanol and deactivation of activated alumina; meanwhile, the reaction temperature is relatively high, which hinders its large-scale application in bioethanol conversion.6−8 Thus, researchers have devoted great concern to a more promising and commercially valuable class of catalysts, the zeolites, which have high hydrothermal stability and can catalyze reactions at lower temperatures.

ZSM-5 and MCM-41 zeolites are the frequently used catalysts for ethanol dehydration with high selectivity of ethylene at 240–300 °C.9−11 However, Takahara et al. further found that H-mordenite (H-MOR) has both the highest activity for dehydration of ethanol and selectivity for ethylene at 180 °C.12 Likewise, Busca et al. found that H-MOR has the highest catalytic activity and selectivity for ethylene at low ethanol conversion and temperature among the H-FER, H-MFI, H-MOR, H-Y, and H-HSY zeolites.3 Bhan et al. also reported that H-MOR can catalyze ethylene formation from ethanol at 95–133 °C rather than H-FER and H-MFI.13 The unique catalytic activity and selectivity of H-MOR at low temperature can be speculated to have relation with its two sets of channel structures, in which the pore-confinement effect and the Brønsted acid strength may have some influence on the reactivity of ethanol dehydration.

Understanding the reaction mechanisms and kinetics of ethanol dehydration to ethylene would be of great value in extending the development and application of biomass. The dehydration of a single ethanol molecule occurs through eliminating both the hydroxyl group and one H atom of the methyl group simultaneously. When there is no catalyst, this process is achieved by a four-centered transition state (TS) structure with an energy barrier of 72.0 kcal mol–1.14 When the ethanol molecule is protonated by an H+, the barrier is significantly decreased to 20.7 kcal mol–1.15 Moreover, when there are two ethanol molecules involved in the reaction, one ethanol acts as a proton transporter and simultaneously catalyzes the dehydration of another ethanol, which would lower the activation energy barrier to 55.4 kcal mol–1.

While in zeolites, the reaction mechanism of ethanol dehydration is more complicated. Brønsted acid sites in the Al-substituted zeolites provide the source of acidic protons to catalyze the dehydration of ethanol. It has been proposed that at first the ethanol molecule is adsorbed onto the Brønsted acid sites of the zeolite framework and then undergoes the dehydration process to generate ethylene, accompanied by the recovery of the Brønsted acid proton.5 It is generally believed that there are two mechanisms for the monomolecular dehydration of ethanol into ethylene, the carbocation mechanism, and the ethoxy intermediate (stepwise) mechanism (Scheme 1a). However, the corbocation mechanism is in dispute as the formation of the carbocation intermediate needs much higher energy to achieve the hydrogen transfer. Based on the carbocation mechanism, Nimlos et al. proposed the concerted reaction mechanism, in which the proton of Brønsted acid migrates to the O atom of ethanol and leads to the elimination of water; meanwhile, one H atom of ethanol is away from the β-C atom bonding with a neighboring electronegative skeleton O atom of the zeolite.16 As illustrated in Scheme 1b, the structure of TS contains an eight-membered ring, which would have much smaller strain energy than the four-centered TS and would lead to a significant decrease of the reaction activation energy barrier. Kondo and Haw studied the dehydration of ethanol on several zeolites with different pore sizes by IR spectroscopy and the NMR method and reported that the ethoxy species has high stability and can then decompose into ethylene.17−19 Moreover, the energy barrier for the decomposition of ethoxy species becomes larger in smaller-pored zeolites.

Scheme 1. Proposed Stepwise Mechanism (a) and Concerted Mechanism (b) for Monomolecular Dehydration of Ethanol.

Scheme 1

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To further understand the reaction mechanism of monomolecular ethanol dehydration to ethylene in the H-MOR zeolite, density functional theory (DFT) calculations were performed in this work. The concerted mechanism and the stepwise mechanism proceeding in the 12-membered-ring (12-MR) and the 8-membered-ring (8-MR) of the H-MOR zeolite are considered.

Computation Methods

As illustrated in Figure 1, the MOR zeolite contains two sets of channels, a 12-MR channel of 6.4 Å × 7.0 Å and an 8-MR channel of 2.6 Å × 5.7 Å. Sauer et al. have demonstrated that T4 inside the 12-MR and T3 inside the 8-MR are the preferred Al substitutional positions for the H-MOR zeolite,20,21 hence they are also adopted as the active sites in this work. The ONIOM approach giving consideration to both computational cost and accuracy would be appropriate to simulate the structures of the H-MOR zeolite.22,23 Thus, the two-layer ONIOM models of a 110T cluster containing an entire 12-MR and a 60T cluster containing an entire 8-MR were employed to simulate the confinement effect, as displayed in Figure 2. The terminal Si atoms were saturated by H atoms with a fixed bond length of 1.47 Å. For the 110T cluster, the high-level layer using the DFT method contains the ethanol molecule and an 8T cluster with the T4 site substituted by an Al atom (AlSi7O8H). In the literature, the high levels with 3T, 5T–8T, and even larger cluster models for zeolites have been studied,23 and for ethanol dehydration in H-ZSM-5, it has been proved that the high level beyond the 5T model does not significantly affect the barrier energies.16 On that basis and the unique channel structure of H-MOR, the 8T model was used as a high level to represent the active acid region. For the 60T model, the high-level DFT layer contains not only the ethanol molecule and the 8T cluster (AlSi7O8H), the atoms consisting of the 8-MR are also included (Si8O12), as these atoms are too close to the ethanol molecule. The ωB97XD functional and the 6-31G(d,p) basis set were adopted for the high level of the ONIOM models. It has been proved that the ωB97XD functional contains the long-range corrected functional, which can be accurate to describe the long-range weak dispersion interactions of the host–guest system compared with the traditional DFT functional.24−27 The other atoms were assigned to the lower layer and were treated by the AM1 method. Meanwhile, all of the atoms in the lower layer were frozen to keep the completeness of the zeolite framework with the intrinsic steric and electronic effects, and only the high DFT layer was optimized. For all optimized structures, vibrational frequency calculations were performed to verify reactants, TSs, and products. For the TSs, the presence of only one imaginary frequency is suitable, which should be consistent with the reaction directions of forward and reverse, and it also has been confirmed by the immediately following intrinsic reaction coordinate (IRC) calculations. All calculations were performed using the Gaussian 09 package.28

Figure 1.

Figure 1

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Structural diagram for the MOR framework with 12-MR and 8-MR channels (yellow for T atoms and red for O atoms).

Figure 2.

Figure 2

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Representations of the 12-MR and 8-MR channels of H-MOR zeolite by 110T and 60T cluster models using ONIOM methods.

The noncovalent interaction index approach developed by Johnson et al.29 was employed to visualize the noncovalent interactions of the adsorbed molecule and the zeolite framework. In this approach, the reduced density gradient (RDG), the electron density (ρ), and the second-largest eigenvalue (λ2) of ρ Hessian are the main indexes that can be used to distinguish the covalent and noncovalent interaction, as well as the H-bonding, weak van der Waals, and strong repulsive interaction. The Multiwfn software was used to obtain the values of RDG, ρ, and λ2.30

Results and Discussion

Brønsted Acid Strength of the 12-MR and 8-MR Channels

Generally, the acid strength of zeolites can significantly affect the reaction reactivity, including the dehydration of ethanol. Therefore, the intrinsic acid strength for H-MOR zeolite in different channels was evaluated using the deprotonation energy (DPE), and the smaller DPE value signifies the stronger acidity of the Brønsted acid.31−33 The DPE values for the T4 in the 12-MR and T3 in the 8-MR channels as well as the structural parameters are listed in Table 1, which are 299.9 and 306.4 kcal mol–1, respectively. Furthermore, the acid strength also can be inferred by the charge quantity of the acidic proton, with the stronger acidity corresponding to much more charge quantity of the acidic proton. As illustrated in Table 1, the value of qH for the 12-MR is larger than that for the 8-MR, which is conformed to the DPE value. Thus, the conclusion that the 12-MR has stronger Brønsted acid strength than the 8-MR of H-MOR zeolite can be reached, which agrees well with the reported literature.34,35

Table 1. DPEa, Charge, and Main Structural Parameters for the 12-MR and 8-MR Channels of H-MOR.

        bond length (Å)
 bond angle (deg)
channel DPE (kcal mol–1) qH qO Si–O Al–O O–H Si–O–Al
12-MR 299.9 0.352 –0.553 1.659 1.815 0.969 120.11
8-MR 306.4 0.330 –0.92 1.677 1.840 0.969 124.95
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a

DPE = Ezeolite– + EH – EH–zeolite, EH–zeolite, Ezeolite–, and EH represent the energy of zeolite with and without acidic proton, and an isolated proton, respectively.

Adsorption Properties of Ethanol Inside the 12-MR and 8-MR Channels

The most stable configuration and the main geometry parameters of ethanol adsorption inside the 12-MR and 8-MR channels are displayed in Figure 3. In the 12-MR, the lengths of the O–H bond are 1.051, 1.431, and 1.677 Å, respectively, suggesting the strong hydrogen bond interaction between the ethanol and the H-MOR framework. The calculated adsorption energy in the 12-MR is −28.5 kcal mol–1, which is very close to the experimental ethanol adsorption heat over H-ZSM-5.36,37 In the 8-MR, the distances of the acidic proton to the O atom of ethanol and the skeleton oxygen atom are 1.116 and 1.261 Å, respectively, which is similar to the situation in the 12-MR. However, the hydrogen atom of the hydroxyl group may have little interaction with the skeleton oxygen atom of the zeolite, due to the long distance of 2.239 Å between them. The steric-hindrance effect would lead to the hardly generation of a second hydrogen bond interaction. The diverse distance from the acidic proton to the O atom can be ascribed to the different Brønsted acid strength of the 8-MR and 12-MR channels. The stronger Brønsted acidity leads to the increasing distance between O10 and the acidic proton. Meanwhile, it clearly shows that one H atom of the methyl group is close to O5 of the 8-MR channel, with a distance of 2.398 Å. Another important difference is that the length of the C–C bond for the adsorbed ethanol in 8-MR shortens about 0.108 Å compared with that in 12-MR, and it can be predicted that the ethanol adsorbed in the 8-MR has a higher likelihood of further reactions. However, the calculated adsorption energy in the 8-MR is only −15.1 kcal mol–1, suggesting that the ethanol is preferred to be adsorbed in the 12-MR. It can be inferred that the confinement effect can significantly affect the adsorption properties.

Figure 3.

Figure 3

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Structures of the adsorbed ethanol molecule in the 12-MR and 8-MR channels of the H-MOR.

Concerted Mechanism of Ethanol Dehydration in 12-MR and 8-MR Channels

The TS structures of the ethanol dehydration following the concerted mechanism in the 12-MR and 8-MR channels are illustrated in Figure 4a. For the TS in the 12-MR, the distance from the O atom of ethanol to the acidic proton is only 0.973 Å, which is very close to 0.957 Å, the measured length of the O–H bond for water in experiment.38 However, the distance between the acidic proton and O10 is largely increasing to 1.847 Å. Meanwhile, the O–C bond of ethanol has cracked in the TS for the distance from the O atom to the α-C atom increasing to 2.377 Å. Moreover, one β-H of the methyl group is away from the β-C atom but approaches the O5 site of H-MOR with distances of 1.283 and 1.388 Å, respectively, which illustrates that the β-H atom would be transferred to the H-MOR zeolite and become an acidic proton. All of these changes of the bond length indicate the dehydration process of ethanol and the formation of ethylene. Finally, the acid proton at the O5 site would migrate back to the O10 site to regenerate the Brønsted acid. The activation energy barrier of ethanol dehydration to ethylene in the 12-MR through the concerted mechanism is 42.4 kcal mol–1.

Figure 4.

Figure 4

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Structures of TSs and relative Gibbs free energy profiles at 298 K for the concerted mechanism in the 12-MR and 8-MR channels of the H-MOR zeolite.

The TS in the 8-MR has similar changes in bond length to that in the 12-MR. The acidic proton gets away from the O10 (1.754 Å) and becomes closer to the O atom of ethanol (0.978 Å) to form an O–H bond. The β-H atom gets closer to the O2 (1.384 Å) but far away from the β-C of the methyl group (1.296 Å). During the reaction process, it also accompanies the migration of the acidic proton and the β-H atom. The activation energy barrier in the 8-MR for this reaction is 43.4 kcal mol–1. It can be inferred from the TS structures that the concerted mechanism would like to go through eight-atom-involved center structures both in the 8-MR and the 12-MR. The dehydration process occurs accompanied by the migration of β-H, leading finally to the formation of ethylene. As illustrated in Figure 4b, the reaction is slightly preferred to proceed in the 12-MR from the kinetics point of view. The different catalytic performance of the 12-MR and 8-MR channels would be associated with their Brønsted acid strengths. The stronger acid strength promotes the concerted mechanism to proceed more easily. But in thermodynamics, it would be preferred to proceed in the 8-MR with the reaction energy declining by 8.8 kcal mol–1 compared with that in the 12-MR channel. The structures of the product have been illustrated in Figure S1, indicating that the eliminated water has more interaction with the zeolite channel, which would benefit the reaction. Furthermore, it is also necessary to point out that the initial state of the reaction is the adsorbed ethanol in the H-MOR for both concerted and stepwise mechanisms, and the final state is the adsorbed water and ethylene in H-MOR. However, the adsorption configurations of the water and ethylene molecules with the H-MOR framework have a significant difference due to the different dehydration mechanisms, which leads to the different relative energies of the final states as illustrated in Figures 4 and 6.

Figure 6.

Figure 6

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Relative Gibbs free energy profiles at 298 K of the stepwise mechanism in the 12-MR and 8-MR channels of the H-MOR zeolite.

Stepwise Mechanism of Ethanol Dehydration in 12-MR and 8-MR Channels

Figure 5 displays all of the optimized structures and main geometry parameters for TS1, ethoxy intermediates, and TS2 involved in the stepwise mechanism. The first step is the formation of the ethoxy intermediate. For the TS1 in the 12-MR, the distance from α-C to the O atom enlarges to 2.164 Å, suggesting the cracking of the C–O bond of the adsorbed ethanol. The acidic proton is away from O10 with a distance of 2.220 Å simultaneously. Furthermore, the distances between α-C with O2 and O10 are 2.143 and 2.770 Å, respectively. All of these changes in the bond length indicate that the dehydration reaction occurs and leads to the formation of TS1 containing an ethyl carbocation. The zeolite framework would be of great help in stabilizing the carbocation. The energy barrier of this step is 35.0 kcal mol–1. Thus, it can be inferred that the formation of the ethoxy intermediate in the 12-MR would be much preferred to occur. It has been proved in experiment that the alkoxide species spread widely within the zeolite framework and has been proved to be more stable than the adsorbed complex.35 The ethoxy intermediate has the O2 and α-C atoms bonded with a bond length of 1.511 Å. Meanwhile, one H atom of water has a distance of 2.028 Å with O10. Thus, an eight-atom-involved center structure is also found in TS2, which is similar to the concerted mechanism. The distance between the H atom of water and the O10 atom has been shortened to 1.898 Å, together with one H atom of the methyl group getting closer to the O atom of water with a distance of 1.516 Å. It can be inferred that the eliminated water in the first step would like to participate in the next reaction and play a key role in the transport of hydrogen atoms. The C–O2 bond breaks with the distance enlarging to 2.333 Å; meanwhile, the C–C bond shortens to 1.394 Å, suggesting the formation of an ethylene molecule.

Figure 5.

Figure 5

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Structures of TSs and intermediates for the stepwise mechanism in the 12-MR and 8-MR channels of the H-MOR zeolite.

Figure 5 also illustrates the main structural parameters of TS1 in the 8-MR. The acidic proton is away from O10 with a distance of 2.112 Å but close to the O atom of ethanol with a distance of only 0.966 Å, which suggests that the acidic proton has been bonded with the O atom of ethanol to generate a water molecule. Meanwhile, it is notable that the distances from the O atom of ethanol to O10 and α-C are 2.510 and 2.635 Å, respectively, and the distances between O10 and α-C is 2.345 Å. These bond lengths indicate that there is a triangular ring structure constituted by the O atom of ethanol, O10, and α-C in TS1. It can be inferred from the changes in the bond length that in the first step of the stepwise mechanism, the breakage of the C–O bond of ethanol occurs accompanied by the elimination of water and the formation of an ethoxy intermediate. In the following reaction, the C–O10 bond breaks and the α-C is away from O10 with a distance of 3.192 Å. Meanwhile, the H atom of the methyl group would bond with O10 (1.394 Å). Furthermore, the O atom of water has a distance of 2.161 Å with α-C and 2.858 Å with a β-C atom, indicating that the water molecule would help to balance charge and stabilize the TS structure, which has also been proved in the literature.39−41 The decrease in the C–C bond length to 1.382 Å suggests the formation of an ethylene molecule.

The relative energy profiles for reactants, TSs, intermediates, and products of the stepwise mechanism are displayed in Figure 6. In the 12-MR, the activation energy barriers of the stepwise mechanism are 35.0 and 28.5 kcal mol–1, respectively. While in the 8-MR, the barriers are 53.7 and 45.4 kcal mol–1, respectively. Clearly, both in the 12-MR and 8-MR channels, the rate-determining step is the formation of an ethoxy intermediate, which is in line with the experimental result in the literature.42,43 In consideration of the experimental intrinsic activation energy with a value of 30.6 ± 2.4 kcal mol–1 in the 8-MR and 26.1 ± 7.9 kcal mol–1 in the 12-MR,42 38.5 ± 1.4 kcal mol–1 in the 12-MR18 for H-MOR, and the theoretical results ranging from 25.3 to 54.9 kcal mol–1 for ZSM-5,16,43−45 the energy profiles illustrated in Figures 4 and 6 can be regarded as reasonable, and most importantly, the tendencies are similar. Obviously, in the 12-MR, the ethanol molecule would prefer to react with zeolite to form an ethoxy intermediate at first, rather than directly decomposing into ethylene through the concerted mechanism. But considering the difference between them is only 7.4 kcal mol–1, it can be inferred that both mechanisms are existing. On the contrary, the ethanol molecule would like to directly decompose into ethylene rather than the formation of an ethoxy intermediate in the 8-MR channel. The isosurfaces of RDG in real space have been proved to successfully characterize the host–guest interactions in zeolite systems.46,47Figure 7 displays the isosurface plots of RDG for TSs of ethanol dehydration through the stepwise mechanism in the 12-MR and 8-MR of the H-MOR zeolite. Compared with the 12-MR, the TSs of the 8-MR show a much larger repulsive region, suggesting that the reaction system suffers much more repulsive interaction with the 8-MR channel. The pore-confinement effect of the H-MOR framework has a decisive impact on the reactivity, rather than the Brønsted acid strength.

Figure 7.

Figure 7

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Isosurface plots of RDG for the TSs of the stepwise mechanism in the 12-MR and 8-MR channels of the H-MOR zeolite.

Thus, it can be indicated that the dehydration reaction of monomolecular ethanol to ethylene is more likely to proceed through a stepwise mechanism in the 12-MR channel of the H-MOR zeolite.

Conclusions

Based on the DFT calculations, the monomolecular dehydration reaction mechanisms of ethanol to ethylene inside the 12-MR and 8-MR channels of H-MOR zeolite have been clarified. The pore-confinement effect has a decisive impact on the reactivity of the stepwise mechanism, while the Brønsted acid strength has little influence on both mechanisms. In the 12-MR, ethylene is preferably formed through the stepwise mechanism, but the concerted mechanism is also competitive. While in the 8-MR, the concerted mechanism is the favorable way to form ethylene. For both the concerted and stepwise mechanisms, the O atom of the ethanol molecule bonding to the acid proton leads to the elimination of water and the formation of ethylene or an ethoxy intermediate. The ethoxy intermediate can then decompose into ethylene. Furthermore, it is worth noting that the water molecule plays a crucial role in stabilizing TSs for both mechanisms. The water molecule also helps to transfer H atoms to regenerate the Brønsted acid proton in the stepwise mechanism.

Acknowledgments

This work was supported by the National Natural Science Foundation of China (No. 51806111), the National First-rate Discipline Construction Project of Ningxia (Chemical Engineering Technology (NXYLXK2017A04)), the China Postdoctoral Science Foundation (2015M572231), and the Key Research and Development Program in Ningxia (2019BDE03014).

Supporting Information Available

The Supporting Information is available free of charge at https://pubs.acs.org/doi/10.1021/acsomega.9b03984.

  • Optimized geometries of all of the TSs and intermediates involved in the concerted mechanism and the stepwise mechanism in the 8-MR and the 12-MR of H-MOR (PDF)

The author declares no competing financial interest.

Supplementary Material

ao9b03984_si_001.pdf (350.7KB, pdf)

References

  1. Li Y.-N.; Jin Z. S.; Yang W. M. Research status of dehydration of ethanol into ethylene over zeolite. Chem. Ind. Eng. Prog. 2009, 28, 67–72. [Google Scholar]
  2. Madeira F. F.; Gnep N. S.; Magnoux P.; Maury S.; Cadran N. Ethanol transformation over HFAU, HBEA and HMFI zeolites presenting similar Bronsted acidity. Appl. Catal., A 2009, 367, 39–46. 10.1016/j.apcata.2009.07.033. [DOI] [Google Scholar]
  3. Phung T. K.; Hernandez L. P.; Lagazzo A.; Busca G. Dehydration of ethanol over zeolites, silica alumina and alumina: Lewis acidity, Bronsted acidity and confinement effects. Appl. Catal., A 2015, 493, 77–89. 10.1016/j.apcata.2014.12.047. [DOI] [Google Scholar]
  4. Sun J.; Wang Y. Recent Advances in Catalytic Conversion of Ethanol to Chemicals. ACS Catal. 2014, 4, 1078–1090. 10.1021/cs4011343. [DOI] [Google Scholar]
  5. Zhang M. H.; Yu Y. Z. Dehydration of Ethanol to Ethylene. Ind. Eng. Chem. Res. 2013, 52, 9505–9514. 10.1021/ie401157c. [DOI] [Google Scholar]
  6. Roy S.; Mpourmpakis G.; Hong D. Y.; Vlachos D. G.; Bhan A.; Gorte R. J. Mechanistic Study of Alcohol Dehydration on gamma-Al2O3. ACS Catal. 2012, 2, 1846–1853. 10.1021/cs300176d. [DOI] [Google Scholar]
  7. Kostestkyy P.; Yu J. Y.; Gorte R. J.; Mpourmpakis G. Structure-activity relationships on metal-oxides: alcohol dehydration. Catal. Sci. Technol. 2014, 4, 3861–3869. 10.1039/C4CY00632A. [DOI] [Google Scholar]
  8. Fan D.; Dai D.-J.; Wu H.-S. Ethylene Formation by Catalytic Dehydration of Ethanol with Industrial Considerations. Materials 2013, 6, 101–115. 10.3390/ma6010101. [DOI] [PMC free article] [PubMed] [Google Scholar]
  9. Zhan N.; Hu Y.; Li H.; Yu D.; Han Y.; Huang H. Lanthanum-phosphorous modified HZSM-5 catalysts in dehydration of ethanol to ethylene: A comparative analysis. Catal. Commun. 2010, 11, 633–637. 10.1016/j.catcom.2010.01.011. [DOI] [Google Scholar]
  10. Ciftci A.; Varisli D.; Tokay K. C.; Sezgi N. A.; Dogu T. Dimethyl ether, diethyl ether & ethylene from alcohols over tungstophosphoric acid based mesoporous catalysts. Chem. Eng. J. 2012, 207–208, 85–93. 10.1016/j.cej.2012.04.016. [DOI] [Google Scholar]
  11. Varisli D.; Dogu T.; Dogu G. Silicotungstic acid impregnated MCM-41-like mesoporous solid acid catalysts for dehydration of ethanol. Ind. Eng. Chem. Res. 2008, 47, 4071–4076. 10.1021/ie800192t. [DOI] [Google Scholar]
  12. Takahara I.; Saito M.; Inaba M.; Murata K. Dehydration of ethanol into ethylene over solid acid catalysts. Catal. Lett. 2005, 105, 249–252. 10.1007/s10562-005-8698-1. [DOI] [Google Scholar]
  13. Chiang H.; Bhan A. Catalytic consequences of hydroxyl group location on the rate and mechanism of parallel dehydration reactions of ethanol over acidic zeolites. J. Catal. 2010, 271, 251–261. 10.1016/j.jcat.2010.01.021. [DOI] [Google Scholar]
  14. Sivaramakrishnan R.; Su M.-C.; Michael J. V.; Klippenstein S. J.; Harding L. B.; Ruscic B. Rate Constants for the Thermal Decomposition of Ethanol and Its Bimolecular Reactions with OH and D: Reflected Shock Tube and Theoretical Studies. J. Phys. Chem. A 2010, 114, 9425–9439. 10.1021/jp104759d. [DOI] [PubMed] [Google Scholar]
  15. Nimlos M. R.; Blanksby S. J.; Ellison G. B.; Evans R. J. Enhancement of 1,2-dehydration of alcohols by alkali cations and protons: a model for dehydration of carbohydrates. J. Anal. Appl. Pyrolysis 2003, 66, 3–27. 10.1016/S0165-2370(02)00103-1. [DOI] [Google Scholar]
  16. Kim S.; Robichaud D. J.; Beckham G. T.; Paton R. S.; Nimlos M.R. Ethanol Dehydration in HZSM-5 Studied by Density Functional Theory: Evidence for a Concerted Process. J. Phys. Chem. A 2015, 119, 3604–3614. 10.1021/jp513024z. [DOI] [PubMed] [Google Scholar]
  17. Kondo J. N.; Ito K.; Yoda E.; Wakabayashi F.; Domen K. An ethoxy intermediate in ethanol dehydration on bronsted acid sites in zeolite. J. Phys. Chem. B 2005, 109, 10969–10972. 10.1021/jp050721q. [DOI] [PubMed] [Google Scholar]
  18. Kondo J. N.; Nishioka D.; Yamazaki H.; Kubota J.; Domen K.; Tatsumi T. Activation Energies for the Reaction of Ethoxy Species to Ethene over Zeolites. J. Phys. Chem. C 2010, 114, 20107–20113. 10.1021/jp107082t. [DOI] [Google Scholar]
  19. Kondo J. N.; Yamazaki H.; Osuga R.; Yokoi T.; Tatsumi T. Mechanism of Decomposition of Surface Ethoxy Species to Ethene and Acidic OH Groups on H-ZSM-5. J. Phys. Chem. Lett. 2015, 6, 2243–2246. 10.1021/acs.jpclett.5b00846. [DOI] [PubMed] [Google Scholar]
  20. Brändle M.; Sauer J. Acidity differences between inorganic solids induced by their framework structure. A combined quantum mechanics molecular mechanics ab initio study on zeolites. J. Am. Chem. Soc. 1998, 120, 1556–1570. 10.1021/ja9729037. [DOI] [Google Scholar]
  21. Niwa M.; Suzuki K.; Katada N.; Kanougi T.; Atoguchi T. Ammonia IRMS-TPD study on the distribution of acid sites in mordenite. J. Phys. Chem. B 2005, 109, 18749–18757. 10.1021/jp051304g. [DOI] [PubMed] [Google Scholar]
  22. Dapprich S.; Komáromi I.; Byun K. S.; Morokuma K.; Frisch M. J. A new ONIOM implementation in Gaussian98. Part I. The calculation of energies, gradients, vibrational frequencies and electric field derivatives. J. Mol. Struct.: THEOCHEM 1999, 461–462, 1–21. 10.1016/S0166-1280(98)00475-8. [DOI] [Google Scholar]
  23. Chung L. W.; Sameera W. M. C.; Ramozzi R.; Page A. J.; Hatanaka M.; Petrova G. P.; Harris T. V.; Li X.; Ke Z.; Liu F.; Li H.-B.; Ding L.; Morokuma K. The ONIOM Method and Its Applications. Chem. Rev. 2015, 115, 5678–5796. 10.1021/cr5004419. [DOI] [PubMed] [Google Scholar]
  24. Chai J.-D.; Head-Gordon M. Long-range corrected hybrid density functionals with damped atom-atom dispersion corrections. Phys. Chem. Chem. Phys. 2008, 10, 6615–6620. 10.1039/b810189b. [DOI] [PubMed] [Google Scholar]
  25. Yi X.; Byun Y.; Chu Y.; Zheng A.; Hong S. B.; Deng F. Stability of the Reaction Intermediates of Ethylbenzene Disproportionation over Medium-Pore Zeolites with Different Framework Topologies: A Theoretical Investigation. J. Phys. Chem. C 2013, 117, 23626–23637. 10.1021/jp4089386. [DOI] [Google Scholar]
  26. Chu Y.; Li G.; Huang L.; Yi X.; Xia H.; Zheng A.; Deng F. External or internal surface of H-ZSM-5 zeolite, which is more effective for the Beckmann rearrangement reaction?. Catal. Sci. Technol. 2017, 7, 2512–2523. 10.1039/C7CY00377C. [DOI] [Google Scholar]
  27. Yi X.; Ding L.; Li G.; Liu Z.; Xia H.; Chu Y.; Zheng A.; Deng F. Insights into the reaction mechanism of propene H/D exchange over acidic zeolite catalysts from theoretical calculations. Catal. Sci. Technol. 2016, 6, 6328–6338. 10.1039/C6CY00757K. [DOI] [Google Scholar]
  28. Ortiz J. V.; Cioslowski J.; Fox D. J.. Gaussian 09, revision B.01; Wallingford CT, 2009.
  29. Johnson E. R.; Keinan S.; Mori-Sanchez P.; Contreras-Garcia J.; Cohen A. J.; Yang W. T. Revealing Noncovalent Interactions. J. Am. Chem. Soc. 2010, 132, 6498–6506. 10.1021/ja100936w. [DOI] [PMC free article] [PubMed] [Google Scholar]
  30. Lu T.; Chen F. W. Multiwfn: A multifunctional wavefunction analyzer. J. Comput. Chem. 2012, 33, 580–592. 10.1002/jcc.22885. [DOI] [PubMed] [Google Scholar]
  31. Brand H. V.; Curtiss L. A.; Iton L. E. Ab Initio Molecular Orbital Cluster Studies of the Zeolite ZSM-5. 1. Proton Affinities. J. Phys. Chem. A 1993, 97, 12773–12782. 10.1021/j100151a024. [DOI] [Google Scholar]
  32. Eichler U.; Brändle M.; Sauer J. Predicting Absolute and Site Specific Acidities for Zeolite Catalysts by a Combined Quantum Mechanics/Interatomic Potential Function Approach. J. Phys. Chem. B 1997, 101, 10035–10050. 10.1021/jp971779a. [DOI] [Google Scholar]
  33. Janik M. J.; Macht J.; Iglesia E.; Neurock M. Correlating Acid Properties and Catalytic Function: A First-Principles Analysis of Alcohol Dehydration Pathways on Polyoxometalates. J. Phys. Chem. C 2009, 113, 1872–1885. 10.1021/jp8078748. [DOI] [Google Scholar]
  34. Dominguez-Soria V. D.; Calaminici P.; Goursot A. Theoretical Study of Host-Guest Interactions in the Large and Small Cavities of MOR Zeolite Models. J. Phys. Chem. C 2011, 115, 6508–6512. 10.1021/jp108815r. [DOI] [Google Scholar]
  35. Chu Y. Y.; Han B.; Zheng A. M.; Yi X. F.; Deng F. Pore Selectivity for Olefin Protonation Reactions Confined inside Mordenite Zeolite: A Theoretical Calculation Study. J. Phys. Chem. C 2013, 117, 2194–2202. 10.1021/jp311264u. [DOI] [Google Scholar]
  36. Lee C.-C.; Gorte R. J.; Farneth W. E. Calorimetric study of alcohol and nitrile adsorption complexes in H-ZSM-5. J. Phys. Chem. B 1997, 101, 3811–3817. 10.1021/jp970711s. [DOI] [Google Scholar]
  37. Alexopoulos K.; Lee M.-S.; Liu Y.; Zhi Y.; Liu Y.; Reyniers M.-F.; Marin G. B.; Glezakou V.-A.; Rousseau R.; Lercher J. A. Anharmonicity and Confinement in Zeolites: Structure, Spectroscopy, and Adsorption Free Energy of Ethanol in H-ZSM-5. J. Phys. Chem. C 2016, 120, 7172–7182. 10.1021/acs.jpcc.6b00923. [DOI] [Google Scholar]
  38. Hasted J. B.Liquid Water: Dielectric Properties. In Water: A Comprehensive Treatise; Plenum Press: New York, 1972; Vol. 1. [Google Scholar]
  39. Shi F.-Q.; Li X.; Xia Y.; Zhang L.; Yu Z.-X. DFT Study of the Mechanisms of In Water Au(I)-Catalyzed Tandem [3,3]-Rearrangement/Nazarov Reaction/[1,2]-Hydrogen Shift of Enynyl Acetates: A Proton-Transport Catalysis Strategy in the Water-Catalyzed [1,2]-Hydrogen Shift. J. Am. Chem. Soc. 2007, 129, 15503–15512. 10.1021/ja071070+. [DOI] [PubMed] [Google Scholar]
  40. Liang Y.; Zhou H.; Yu Z.-X. Why Is Copper(I) Complex More Competent Than Dirhodium(II) Complex in Catalytic Asymmetric O–H Insertion Reactions? A Computational Study of the Metal Carbenoid O–H Insertion into Water. J. Am. Chem. Soc. 2009, 131, 17783–17785. 10.1021/ja9086566. [DOI] [PubMed] [Google Scholar]
  41. Xia Y.; Liang Y.; Chen Y.; Wang M.; Jiao L.; Huang F.; Liu S.; Li Y.; Yu Z.-X. An Unexpected Role of a Trace Amount of Water in Catalyzing Proton Transfer in Phosphine-Catalyzed (3 + 2) Cycloaddition of Allenoates and Alkenes. J. Am. Chem. Soc. 2007, 129, 3470–3471. 10.1021/ja068215h. [DOI] [PubMed] [Google Scholar]
  42. Chiang H.; Bhan A. Catalytic consequences of hydroxyl group location on the rate and mechanism of parallel dehydration reactions of ethanol over acidic zeolites. J. Catal. 2010, 271, 251–261. 10.1016/j.jcat.2010.01.021. [DOI] [Google Scholar]
  43. Xin H. C.; Li X. P.; Fang Y.; Yi X. F.; Hu W. H.; Chu Y. Y.; Zhang F.; Zheng A. M.; Zhang H. P.; Li X. B. Catalytic dehydration of ethanol over post-treated ZSM-5 zeolites. J. Catal. 2014, 312, 204–215. 10.1016/j.jcat.2014.02.003. [DOI] [Google Scholar]
  44. Zhou X.; Wang C.; Chu Y. Y.; Xu J.; Wang Q.; Qi G. D.; Zhao X. L.; Feng N. D.; Deng F. Observation of an oxonium ion intermediate in ethanol dehydration to ethene on zeolite. Nat. Commun. 2019, 10, 1961 10.1038/s41467-019-09956-7. [DOI] [PMC free article] [PubMed] [Google Scholar]
  45. Alexopoulos K.; John M.; Van der Borght K.; Galvita V.; Reyniers M. F.; Marin G. B. DFT-based microkinetic modeling of ethanol dehydration in H-ZSM-5. J. Catal. 2016, 339, 173–185. 10.1016/j.jcat.2016.04.020. [DOI] [Google Scholar]
  46. Sun W. M.; Di Felice R. Nature of the Interaction between Natural and Size-Expanded Guanine with Gold Clusters: A Density Functional Theory Study. J. Phys. Chem. C 2012, 116, 24954–24961. 10.1021/jp3079277. [DOI] [Google Scholar]
  47. Wang C.; Chu Y. Y.; Zheng A. M.; Xu J.; Wang Q.; Gao P.; Qi G. D.; Gong Y. J.; Deng F. New Insight into the Hydrocarbon-Pool Chemistry of the Methanol-to-Olefins Conversion over Zeolite H-ZSM-5 from GC-MS, Solid-State NMR Spectroscopy, and DFT Calculations. Chem. - Eur. J. 2014, 20, 12432–12443. 10.1002/chem.201403972. [DOI] [PubMed] [Google Scholar]

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