Ethylene Epoxidation Catalyzed by a Cu38 Nanoparticle: A

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Ethylene Epoxidation Catalyzed by a Cu Nanoparticle: A Computational Study Chen-Chi Lee, and Hsin-Tsung Chen J. Phys. Chem. C, Just Accepted Manuscript • DOI: 10.1021/acs.jpcc.6b01181 • Publication Date (Web): 07 Mar 2016 Downloaded from http://pubs.acs.org on March 8, 2016

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The Journal of Physical Chemistry

Ethylene Epoxidation Catalyzed by a Cu38 Nanoparticle: A Computational Study

Chen-Chi Lee and Hsin-Tsung Chen*

Department of Chemistry, Chung Yuan Christian University, Chungli District, Taoyuan City 32023, Taiwan

*Corresponding author. E-mail address: [email protected] (H.-T.C.); Tel: +886-3-265-3324

1

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Abstract The reaction mechanisms of ethylene epoxidation on a Cu38 nanoparticle have been investigated by the first-principles calculations. The adsorption of C2H4 and O2 as well as the co-adsorption of O2-C2H4 were also examined. Our results show that C2H4 and O2 are likely to adsorb on the top (T) and hollow (H) sites with adsorption energies of −0.51 and −2.19 eV, respectively. The climbing image nudged elastic band method was carried out to illustrate the potential energy profile of the ethylene oxidation

reaction.

Both

epoxide

and

acetaldehyde

are

formed

by

the

Langmuir-Hinshelwood mechanism. The overall reaction for the formation of epoxide is predicted to be exothermic by 3.20 ~ 3.56 eV while it is exothermic by 3.83 ~ 4.31 eV for the formation of acetaldehyde. The Cu38 nanoparticle exhibits higher catalytic properties and selectivity for the epoxide formation compared to the Au38 nanoparticle.

2


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Introduction Epoxidation of alkene is an important heterogeneous catalytic process in industry because the product, epoxide, is a critical intermediate for chemical synthesis. To date, extensive studies have led to significant insights into the reaction mechanism for improving the selectivity of epoxide up to ~ 90% for the industry.1,2 Both adsorbed atomic O and molecular O2 are considered as the active species for the epoxidation reaction.3-5 Experimentally Ag surfaces have been used as the catalyst for the selectivity of epoxidation.6,7 The oxidation of ethylene is well-known to take place by the pathways of ethylene oxide (EO) and acetaldehyde (AA) formations. The oxometallacycle species has been demonstrated to be the important intermediate for both mechanisms experimentally7,8 and computationally.6,9,10 The selectivity of EO is found to be ~ 50% on the un-promoted Ag catalyst.11,12 While the EO selectivity can increase to ~ 90% by the additions of Cl and Cs.13 In addition, Lambert et al. have showed that the Cu (111) surface can enhance the EO selectivity experimentally.14,15 Torres et al. have performed theoretical studies to examine the better selectivity of EO on the Cu (111) surface.2,16 Wang et al. also reported that Cu-based materials are efficient catalysts for C3H6 epoxidation by molecular O2.5 Chen et al. have studied the ethylene epoxidation by adsorbed atomic O and molecular O2 on gold nanoparticle theoretically.17,18 They found that Au nanoparticles have the remarkable catalytic 3



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properties and are active and selective for ethylene epoxidation. However, to the best of our knowledge, there is no computational study on the reaction of C2H4 and O2 on the copper nanoparticle at molecular level. Therefore it is interesting to investigate the detailed mechanisms of C2H4 oxidation on the Cu nanoparticle and compare the catalytic behavior of Cu nanoparticle with Au nanoparticle. In this work, we report our recent computational studies on the detailed mechanisms of the C2H4 oxidation by O2 as well as the adsorption behaviors of C2H4 and O2 on Cu38 nanoparticle for understanding the catalytic behaviors of copper nanoparticle.

Computational Method The reaction mechanism of C2H4 with O2 on a Cu38 nanoparticle as well as the adsorption of C2H4 with O2 have been investigated by the spin-polarized density-functional theory (DFT)19 with the projector augmented wave (PAW) method and the plane-wave basis set with a cutoff energy of 400 eV. Calculations were performed by using the Vienna ab initio simulation package (VASP) program.20-24 The energy was obtained by the generalized gradient approximation (GGA)25 with PW91 exchange-correlation functional.26 The 25×25×25 Å3 cubic supercell was used to study the adsorption of C2H4 with O2 and the reaction of ethylene oxidation. The 4


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Brillouin zone with a Monkhorst-pack Γ point was performed for the calculations. In this study, the adsorption energy is calculated by the following equation

∆E ads = E total − E Cu38 − E molecule

(1),

where Etotal, ECu 38 and Emolecule represent the energy of adsorbed species on the Cu38 nanoparticle, the bare Cu38 nanoparticle and the gas-phase species, respectively. In addition, the coadsorption energy of C2H4 with O2 species was computed as

∆E coads = E total − E Cu 38 − E C 2 H 4 − E O2

(2).

The climbing image nudged elastic band (CINEB) method27,28 with creating at least eight images between the reactant and product was used to locate the transition states.

Result and Discussion As depicted in Figure 1, the Oh symmetric structure containing six square fcc(100)-like faces and eight hexagonal fcc(111)-like faces similar to Au38 nanoparticle was empoled.18,29,30 For the adsorption calculations, the C2H4 and O2 species were placed at several sites of the Cu38 nanoparticle which are top, T (on top of Cu atom); bridge, B (on the Cu-Cu bond); hollow, H (on the center of the square fcc(100)-like faces) and hcp, h (on the center of the trigonal plane of the hexagonal fcc(111)-like faces) sites of the nanocluster. For numbers, “1”, “2”, and “3” in Figure 1, denote different Cu atoms or Cu-Cu bonds of the nanoparticle. 5



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Adsorption and coadsorption of C2H4 and O2 on the Cu38 Nanoparticle. Optimizing stable structures of the C2H4 and O2 adsorbed on the various sites of Cu38 nanoparticle are illustrated in Figure 2 and Figure 3, respectively. The corresponding adsorption energies and some geometrical parameters are listed in Tables 1 and 2. The C2H4 can adsorb on the Cu38 nanoparticle via several isomeric structures. As shown in Figure 2, the C2H4-T3-η2 with “side-on” form via both C atoms binding to the top Cu atom of the square fcc(100)-like face is most stable one among the C2H4 adsorption. The adsorption energy is predicted to be −0.51 eV. The side-on C2H4-B3-µ2 structure on the bridge site of the square fcc(100)-like face with an adsorption energy of −0.41 eV is the second stable one. For the hexagonal fcc(111)-like face, the side-on C2H4-T1-η2 geometry with an adsorption energy of −0.49 eV is energetically the most favorable one. The next stable one is found to be the side-on C2H4-B1-µ2 configuration on the bridge site of the hexagonal fcc(111)-like faces with an adsorption energy of −0.34 eV. The C─C bonds in the π-bonded C2H4-T3-η2 and C2H4-T1-η2 structures are computed to be 1.374 and 1.370 Å which are slightly increasing compared to that (1.330 Å) of a calculated gas-phase C2H4. While the calculated C─C bonds in the di-σ-boned C2H4-B3-µ2 and C2H4-B1-µ2 structures both are 1.420 Å, see Table 1. The adsorption behaviors for C2H4 species on the Cu38 nanoparticle are similar to their counterparts in the Au38 nanoparticle.18 In addition, the Cu38 nanoparticle exhibits 6


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better catalytic ability compared to the C2H4 adsorbed on the Cu (111) surface due to the strong interaction (Eads= −0.74 ~ −0.99 eV for C2H4 adsorbed on the Cu38 nanoparticle and Eads = −0.06 ~ −0.10 eV for the Cu (111) surface).16 For the adsorption of O2 on the Cu38 nanoparticle, five and six stable configurations on the square fcc(100)-like face and hexagonal fcc(111)-like face are evaluated as illustrated in Figure 3. Table 2 lists their calculated adsorption energies and some geometrical parameters. The most stable adsorption geometry of O2 on the square fcc(100)-like face is located at H site forming O2-H-µ4-1 structure in which both O atoms of O2 are bridge at Cu-Cu bonds as depicted in Figure 3. The adsorption energy is predicted to be −2.19 eV and the O─O bond distance is calculated to be 1.509 Å. While the O2-h-µ2-1 structure adsorbed at h site of the hexagonal fcc(111)-like face with the adsorption energies of −1.51 eV and the O-O bond distance of 1.501 Å is energetically most favorable one. Compare to the C2H4 adsorption, the interactions between O2 and Cu38 nanoparticle are much stronger due to larger adsorption energy. To map out the reaction mechanism of ethylene epoxidation process, the coadsorption of C2H4 and O2 is also examined. The possible configurations and their related coadsorption energies are calculated and displayed in Figure 4 and Table 3, respectively. Three geometries of the square fcc(100)-like face and seven geometries of the hexagonal fcc(111)-like face are found as depicted in Figure 4. The 7



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coadsorption energies are calculated to be within −1.98 ~ −2.38 eV. One should note that the co-adsorbed O2 and C2H4 in the O2-T3-η1-C2H4-T3-η2, O2-B1-µ1-C2H4-T1-η2, and O2-h-µ2-C2H4-B1-µ2 configurations reacts each other forming OMME-like species. As summarized in Table 3, the coadsorption energies of O2-T3-η1-C2H4-T3-η2, O2-B1-µ1-C2H4-T1-η2, and O2-h-µ2-C2H4-B1-µ2 species are predicted to be −1.98, −2.38 and −2.00 eV, respectively. We believe that the intermediate OMME-like species would be the important precursor states for the formation of epoxide and exist on the catalyst during the epoxidation process.

Reaction mechanisms of C2H4 oxidation by molecular O2 on the Cu38 Nanoparticle. We examine the C2H4 oxidation reaction mechanisms on both square fcc(100)-like face and hexagonal fcc(111)-like face of the Cu38 nanoparticle. The reaction mechanisms are proposed by the following steps: C2H4(g) + O2(g) → C2H4(ads) + O2(ads) C2H4(ads) + O2(ads) → H2CC(H2)OO(ads) [OMME] H2CC(H2)OO(ads) → H2COCH2(ads) [ethylene oxide] + O(ads) H2CC(H2)OO(ads) → H3CC(H)O(ads) [acetaldehyde] + O(ads) The predicted potential energy profiles for C2H4 oxidation on the square fcc(100)-like face and hexagonal fcc(111)-like face are constructed in Figures 5 and 6 by 8


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performing the CINEB method. Figure 7 displays the calculated structures of transition states in the potential energy profiles for C2H4 oxidation. On the square fcc(100)-like face, the reaction takes place beginning from the C2H4 and O2 adsorption with adsorption energies of −0.51 and −1.44 eV. The C2H4(ads) and O2(ads) are therefore to form co-adsorbed O2-C2H4(ads) (O2-B3-µ2-C2H4-T3-η2) species which is 2.23 eV lower than the reactants in energy. In O2-C2H4(ads) co-adsorption, the O2(ads) is bidentately bound to two Cu atoms forming two O─Cu bonds (1.877 and 1.866 Å) and the C2H4(ads) is bound to one Cu atom forming two C─Cu bonds (2.152 and 2.146 Å) as seen in Figure 4. The co-adsorbed O2-C2H4(ads) in the O2-B3-µ2-C2H4-T3-η2 reacts each other to produce oxometallacycle-type species (OMME; O2-T3-η1-C2H4-T3-η2) by passing the TS1 (Ea = 0.53 eV) with an endothermicity of 0.25 eV. The bond distances of C─O and O─O in TS1 are calculated to be 1.826 and 1.462 Å. As shown in Figure 5, the formation products of ethylene oxide and acetaldehyde from the OMME species are found. The process of acetaldehyde formation is calculated to be highly exothermic by 2.33 eV with an energy barrier of 1.12 eV by overcoming TS2, whereas the process of ethylene oxide formation is less exothermic by 1.58 eV but only requires a very small energy barrier of 0.01 eV to pass TS3. In TS2, the bond distances of C─O and O─O are calculated to be 1.363 and 3.118 Å, respectively. The bond distances of C─O bond and O─O are 9



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computed to be 1.447 and 1.463 Å in the TS3. In summary, the overall reactions for the processes of acetaldehyde and ethylene oxide are predicted to be exothermicities of 4.31 and 3.56 eV, respectively, without any intrinsic barriers because of the calculated energies of all intermediates (O2-C2H4(ads) and OMME species) and transition states (TS1, TS2, and TS3) are below the reactants. Our calculations demonstrate that the ethylene oxide formation process is substantially favored on the square fcc(100)-like face of Cu38 nanoparticle due to the related low barrier (0.01 eV for the ethylene oxide formation and 1.12 eV for the acetaldehyde formation). Similar to the square fcc(100)-like face, the O2 and C2H4 molecule individually adsorbed on the hexagonal fcc(111)-like face with the adsorption energies of −0.34 and −1.44 eV, respectively. Then, the C2H4 and O2 are co-adsorbed on the Cu38 nanoparticle to form O2-C2H4

(ads)

species (O2-B1-µ2-C2H4-B1-µ2) with an

exothermicity of 2.03 eV. In O2-B1-µ2-C2H4-B1-µ2, both O2(ads) and C2H4(ads) are bidentately adsorbed on two Cu atoms of the hexagonal face as seen in Figure 4. The bond lengths of C─Cu bonds are computed to be 2.247 and 2.128 Å and the O─Cu bond lengths are computed to be 1.868 and 1.871 Å. The O2

(ads)

interacts with

C2H4(ads) in O2-B1-µ2-C2H4-B1-µ2 to proudce a oxometallacycle-type species (OMME; O2-B1-µ1-C2H4-T1-η2) by passing TS4 with an exothermicity of 0.35 eV. This process requires an energy barrier of 0.78 eV which is 0.25 eV more than that of square 10


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fcc(100)-like face. As depicted in Figure 6, the acetaldehyde formation from the OMME species, O2-B1-µ1-C2H4-T1-η2, is predicted to be exothermic by 1.45 eV with a high energy barrier of 1.64 eV by passing TS5, whereas the ethylene oxide formation is less exothermic by 0.82 eV but needs a small energy barrier (0.88 eV) to overcome TS6. The ethylene oxide formation process is also favorable on the hexagonal fcc(111)-like face. In conclusion, the square fcc(100)-like face active site has higher catalytic activity for both acetaldehyde and ethylene oxide formation process due to lower energy barriers. The selectivity of ethylene oxide is found to be higher on the square fcc(100)-like face due to the larger difference of the activation barrier between the epoxide and acetaldehyde formation. The difference of activation barrier is computed to be 1.17 and 0.76 eV for the square fcc(100)-like face and hexagonal fcc(111)-like face. In addition, the Cu38 nanoparticle exhibits higher catalytic properties and selectivity for the ethylene oxide formation compared to the Au38 nanoparticle due to the lower barriers (Ea = 0.01 eV on the square fcc(100)-like face of Cu38 nanoparticle and Ea = 0.78 eV for the Au38 nanoparticle) and larger difference of activation barrier (1.17 eV for the Cu38 nanoparticle and 0.45 eV for the Au38 nanoparticle).18

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Analysis of the Electronic State During C2H4 Oxidation Process. The predicted electronic local density of states (LDOS) for the O2 species (left panel), C2H4 species (right panel), and the d-projected electron density of the Cu atoms during C2H4 oxidation on the square fcc(100)-like face of Cu38 nanoparticle are plotted in Figure 8. The panels (a) and (g) in Figure 8 show the LDOS before the interaction between the O2 (C2H4) and the Cu38 nanoparticle; Figures 8b (8h) to 8f (8l) represent to the LDOS of adsorbed O2(ads) [adsorbed C2H4(ads)], co-adsorbed O2(ads)+C2H4(ads), OMME, ethylene oxide, and acetaldehyde, respectively. As shown in Figure 8(b), a broad overlap appears between the O2-p and Cu-d orbitals in 2.5 ~ −7.5 eV for the adsorbed O2 species on the nanoparticle. The C2H4-p electronic states coupling with Cu-d states is found above ~ −7.0 eV for the adsorbed C2H4 species (see Figures 8h). This calculated results indicate that the stronger interaction between the adsorbed molecules and the Cu nanoparticle. The LDOS of co-adsorbed O2(ads)+C2H4(ads) in Figures 8(c) and 8(i) is similar to the adsorbed O2(ads) or the adsorbed C2H4(ads). As the oxidation proceeds from the co-adsorbed O2(ads)+C2H4(ads) to OMME, the states of O2-p and Cu-d in Figure 8 (d) and the states of C2H4-s, C2H4-p and Cu-d states in Figure 8(j) apparently display stronger and broader hybridization for the adsorbed O2(ads) and C2H4(ads). The formation of C–O bond in OMME results in further interaction between adsorbed O2 (O2-p state) and adsorbed C2H4 (C2H4-s and 12


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C2H4-p states) species in the range of 0.0 ~ -8.0 eV as displayed in Figures 8 (d) and 8(j). Finally, the LDOS in Figures 8(e)-8(f) and 8(k)-8(l) for the reaction products are the combinations of the LDOS of the adsorbed ethylene oxide, acetaldehyde, and O adsorbates on the Cu38 nanoparticle.

Conclusion We have studied the adsorption and reaction of C2H4 and O2 on the Cu38 nanoparticle based on the spin-polarized first-principles calculations. The structures of C2H4-T3-η2 and O2-H-µ4-1 with adsorption energies of −0.51 and −2.19 eV are energetically most favorable ones for the adsorption of C2H4 and O2, respectively. The CINEB method is performed to calculate the potential energy profiles for the ethylene oxidation reaction on the Cu38 nanoparticle. The overall reaction for ethylene oxide formation is calculated to be exothermic by 3.56 eV on the square fcc(100)-like face and 3.20 eV on the hexagonal fcc(111)-like face while those are 4.31 and 3.83 eV for the acetaldehyde formation. The ethylene oxide formation is more favorable than the acetaldehyde formation on the Cu38 nanoparticle. In addition, the square fcc(100)-like face is more active and has higher selectivity for ethylene oxide formation than the hexagonal fcc(111)-like face. Compared to the Au38 nanoparticle, the Cu38 nanoparticle exhibits higher catalytic properties and selectivity for the ethylene oxide 13



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formation. The calculation results might provide useful information in the field of heterogeneous catalysis.

Acknowledgment. H.-T.C. is grateful to (1) Ministry of Science and Technology (MOST), Taiwan, under Grant Number MOST 104-2113-M-033-010 and MOST 103-2632-M-033-001-MY3 for the financial support, (2) National Center for High-performance Computing, Taiwan, for the computer time and facilities.

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Table 1. Calculated Adsorption Energies (in eV), Geometrical Parameters (Å) of Adsorbed C2H4 on Cu38 nanocluster species

Eads(eV)

dCu1-C1(Å)

dC1-C2(Å)

dC2-Cu2(Å)

C2H4-T3-η2

−0.51

2.165

1.374

2.165

C2H4-B3-µ2

−0.41

2.097

1.420

2.095

C2H4-T1-η1

−0.01

3.095

1.331

C2H4-T1-η2

−0.49

2.194

1.370

2.174

C2H4-T2-η2

−0.002

2.321

1.359

2.318

C2H4-B1-µ2

−0.34

2.094

1.420

2.104

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Table 2. Calculated Adsorption Energies (in eV), Geometrical Parameters (Å) of Adsorbed O2 on Cu38 nanocluster species

Eads(eV)

dCu1-O1(Å)

dO1-O2(Å)

O2-T3-η1

−0.61

1.945

1.304

O2-B3-µ1

−0.81

1.998, 1.984

1.354

O2-B3-µ2

−1.44

1.873

1.427

1.875

O2-H-µ4-1

−2.19

1.946

1.509

1.947

O2-H-µ4-2

−0.69

2.185, 2.177, 2.115, 2.216

1.371

O2-T1-η1

−0.69

1.961

1.311

O2-T2-η1

−0.24

2.064

1.296

O2-B1-µ1

−0.80

1.995, 1.992

1.343

O2-B1-µ2

−1.44

1.871

1.413

1.867

O2-h-µ2-1

−1.51

1.970, 1.968

1.501

1.902

O2-h-µ3-2

−0.49

2.019, 2.018, 2.154

1.365

18


dO2-Cu2(Å)

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Table 3. Calculated Coadsorption Energies (in eV), Geometrical Parameters (Å) of Co-Adsorbed C2H4-O2 on Cu38 nanocluster species

Ecoads(eV)

dCu1-O1(Å)

dO1-O2(Å)

dO2-C1(Å)

dC1-C2(Å)

dC2-Cu2(Å)

O2-T3-η1-C2H4-T3-η2(OMME)

−1.98

1.848

1.459

1.441

1.522

1.965

O2-B3-µ2-C2H4-T3-η2

−2.23

1.877

1.434

3.292

1.373

2.152

O2-B3-µ2-C2H4-B3-µ2

−2.10

1.871

1.431

3.189

1.395

2.164

O2-B1-µ2-C2H4-T1-η2

−2.17

1.874

1.432

3.154

1.373

2.175

O2-B1-µ1-C2H4-T1-η2(OMME)

−2.38

1.947

1.504

1.420

1.539

2.106

O2-B1-µ2-C2H4-B1-µ2

−2.03

1.871

1.432

3.333

1.375

2.247

O2-h-µ2-C2H4-T1-η2-1

−2.33

1.872

1.485

3.118

1.384

2.151

O2-h-µ2-C2H4-T1-η2-2

−2.25

1.982

1.492

3.116

1.370

2.175

O2-h-µ2-C2H4-B1-µ2-1

−2.15

1.937

1.517

3.064

1.380

2.117

O2-h-µ2-C2H4-B1-µ2(OMME)

−2.00

1.911

1.502

1.459

1.511

1.990

19



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Figure captions Figure 1. Schematic presentation for various adsorption sites on the hexagonal fcc(111)-like face and square fcc(100)-like face of the Cu38 nanoparticle. T1, T2, and T3 represent the top sites; B1, B2, and B3 represent the bridge sites; H represents the hole site; h represents the hcp site.

Figure 2. Calculated structures of adsorbed C2H4 on Cu38 nanoparticle. The bond lengths are given in angstroms. Figure 3. Calculated isomers of adsorbed O2 on Cu38 nanoparticle. The bond lengths are given in angstroms.

Figure 4. Calculated isomers of co-adsorbed C2H4 and O2 species on Cu38 nanoparticle. The bond lengths are given in angstroms. Figure 5. Calculated potential energy surface for the reaction of C2H4 and O2 on the hexagonal fcc(111)-like face of Cu38 nanoparticle. All energies (eV) are related to the isolated reactants. Figure 6. Calculated potential energy surface for the reaction of C2H4 and O2 on the square fcc(100)-like face of Cu38 nanoparticle. All energies (eV) are related to the isolated reactants. Figure 7. Geometrical illustration of transition states for the reactions on the hexagonal fcc(111)-like face and the square fcc(100)-like face of the Cu38 nanoparticle. The bond lengths are given in angstroms. Figure 8. The calculated electronic local density of states (LDOS) for the adsorbed O2 (left panel) and C2H4 (right panel) species, as well as the d-projected of the Cu atoms on the square fcc(100)-like face. Oa and Og represent the remaining oxygen atom adsorbed on the Cu38 and the oxygen atom of ethylene oxide or acetaldehyde.

20


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Page 21 of 29

2 B

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Figure 1.

21



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Figure 2.

22


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1.998 1.354 1.984

1.304 1.945

(a) O2-T3-

1

1.947 1.509

(b) O2-B3-

2.185

1.873 1

1.875

(c) O2-B3-

2

2.177 1.371

2.115

1.946

1.427

2.216

1.961 1.311

(d) O2-H- 4-1

(e) O2-H- 4-2

(f ) O2-T1-

1

1.296 2.064 1.995 (g) O2-T2-

1

1.902 1.970

1.501 1.968

(j) O2-h- 3-1

1.992 1.343

(h) O2-B1-

1

2.154 1.365 2.018 2.019 (k) O2-h- 3-2

Figure 3.

23


1.871

1.867

1.413 (i) O2-B1-

2


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Figure 4.

24


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Energy (eV)

Page 25 of 29

O2+C2H4 0 -0.51 O2+C2H4*

-0.86 TS2

-1.44 O2*+C2H4

-1.70 TS1 -2.23 O2*-C2H4*

-1.98

-1.97

O2*-C2H4*-OMME

TS3

-3.56 ethylene oxide -4.31 acetaldehyde

Reaction

Figure 5.

25


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy (eV)


Figure 6.

26


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1.826

1.462

2.000

1.442

1.872

3.118 1.363 1.931 1.912 1.477

TS2

TS1

2.215 2.139 1.909 1.375 1.318 TS4

1.521 1.833 1.805 1.235 2.909 TS5

Figure 7.

27


1.463 1.447 1.970 1.523 1.846 TS3

1.486 1.415 1.881 1.760 1.971 TS6


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Figure 8.

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Table of Contents: Energy (eV)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


29


Ethylene Epoxidation Catalyzed by a Cu38 Nanoparticle: A

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