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C: Surfaces, Interfaces, Porous Materials, and Catalysis

Hydrogenation of Cyclohexene on the M/Pt (111) and Pt/M/Pt (111) (M=Fe, Co, Ni, Cu) Surfaces from a Systematic DFT Study Hong-Yan Ma, and Gui-Chang Wang J. Phys. Chem. C, Just Accepted Manuscript • DOI: 10.1021/acs.jpcc.8b02848 • Publication Date (Web): 02 Jul 2018 Downloaded from http://pubs.acs.org on July 12, 2018

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The Journal of Physical Chemistry

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The Hydrogenation of Cyclohexene on the M/Pt (111) and Pt/M/Pt (111)

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(M=Fe, Co, Ni, Cu) Surfaces from a Systematic DFT Study

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Hong-Yan Ma 1, Gui-Chang Wang 2,*

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(1 RenAi college of Tianjin University, Tianjin 301636, P. R. China;

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Tianjin Key Lab of Metal and Molecule-based Material Chemistry; Collaborative Innovation Center of

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Chemical Science and Engineering (Tianjin), Nankai University, Tianjin 300071, P. R. China)

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College of Chemistry and the

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* Corresponding author: Gui-Chang Wang Telephone: +86-22-23503824 (O)

E-mail address: [email protected]

Fax: +86-22-23502458

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ACS Paragon Plus Environment

The Journal of Physical Chemistry 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

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Abstract:

The hydrogenation of cyclohexene on the M/Pt (111), Pt/M/Pt (111) (M=Fe, Co, Ni, Cu),

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Pt (111) and Ni (111) surfaces has been studied using density functional theory (DFT) calculation. The

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low hydrogenation barriers could explain high hydrogenation reactivity of the Pt/M/Pt (111) sandwich

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structure. The Pt/Cu/Pt (111) surface may be an efficient catalyst for speeding up cyclohexene

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hydrogenation, due to its high standard turnover frequency (TOF°). However, the experimental results

6

showed the opposite: almost no cyclohexane was detected on the Pt/Cu/Pt (111). The possible reason

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is the Pt-Cu alloy formed on the topmost layer of the Pt/Cu/Pt (111) actually influences the

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hydrogenation process, meaning the chemical property of the so-called Pt/Cu/Pt (111) might be

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sensitive to the surface Pt coverage. Besides, on the basis of a volcano-type relationship between the

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TOF° and the co-adsorption energy of the cyclohexene and the hydrogen atoms, similar sandwich

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structures on which the corresponding adsorption energy is in the range of -0.4~ -1.6 may possess

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excellent hydrogenation reactivity.

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1. Introduction

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Bimetallic catalysts have aroused the researchers’ attention 1-24, because they often have excellent

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reactivity and enhanced selectivity. For example, the reactivity of the Au/Pt (100) surface was much

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higher than the clean Pt (100) as accelerating cyclohexene dehydrogenated to benzene 1-2. In addition,

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the Au-Pd and Pt-Sn bimetallic catalysts showed distinguished selectivity in the hydrogenation of

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butadiene into butene 3-5. Likewise, the Pt-Co, Pt-Fe and Ni-Fe catalysts exhibited large 2-methylfuran

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yield in the hydrodeoxygenation of furfural 6-7. Thus, the Pt-based bimetallic alloys are widely used.

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From an ecnomic point of view, to dilute or replace the precious metals should be encouraged. For

9

instance, the Pt-Cu single-atom alloys have been found not only active in C-H bond scission but also

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coke-resistant even at 0.01monolayer surface Pt coverage 8.

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Cyclohexene has been widely used in organic synthesis and petroleum extraction. And there are

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several competitive pathways for cyclohexene, such as isomerization, hydorgenation, dehydorgenation

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and decompositon. We are interested in the hydrogenation of cyclohexene, not only because it is an

14

important reaction in petroleum industry, but also the aboundent research data that is needed for

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analyzing and comparing the reactivity of the catalysts related. Cyclohexene hydrogenation has been studied from both experimental and theoretical aspects 11-13,

16 17

25-28

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surface vibrational spectroscopy via sum frequency generation and 0.39 eV was calculated as the

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apparent activation energy of hydrogenation on the basis of the Arrhenius plot 27. Bratlie et. al had

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investigated the conversion of benzene to cyclohexane on Pt (111) and found a similar apparent

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activation energy of 0.44 eV 28. Compared with the Pt (111), the Pt-supported bimetallic catalysts

22

exhibit more notable hydrogenation reactivity, especially the Pt/M/Pt (111) (M=Fe, Co, Ni) subsurface

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monolayer on which a low-temperature hydrogenation pathway of cyclohexene was found by the

. Between 300 and 400 K, only hydrogenation of cyclohexene was observed on the Pt (111) by

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temperature-programmed desorption (TPD)11. The catalytic property of such subsurface monolayer

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structure seems to be unusual. Similar hydrogenation reaction pathways were present on both the Ni/Pt

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(111) and Co/Pt (111) surface monolayers at 200~230 K 12-13. In fact, the surface monolayer and

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subsurface monolayer are two sorts of monolayer bimetallic surfaces, and they are usually prepared by

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depositing monolayer of one metal on a single crystal substrate of another metal. Which metal enriches

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the surface region is crucial as it could improve or restrain the desirable reactions. It may be predicted

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according to the surface segregation energies 29-30. More importantly, the preparation condition of the

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catalysts is also important. For example, Fe preferred to diffuse into the subsurface region at 300~ 850

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K, whereas Fe moved to the Pt (111) bulk above 850 K 11.

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The special property of the Pt/M/Pt (111) sandwich structure was attributed to the influence of the 31

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subsurface atoms, and d-band of the surface Pt was broadened and it moved to lower energy

,

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resulting in weaker interaction with the adsorbed species. This is reasonable but not enough. Based on

13

a combination of DFT and energetic span model, we want to investigate the chemical behavior of M/Pt

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(111) and Pt/M/Pt (111) (M=Fe, Co, Ni, Cu) with the hydrogenation of cyclohexene as the probe

15

reaction. The DFT calculations concentrate on optimizing structures, searching for the transitional

16

state (TS) and electronic structure analysis. What is more, the Turnover Frequency (TOF) of the

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hydrogenation will be estimated to decide the sequence of the catalytic activity.

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2. Computational details The results were obtained from the Vienna ab initio simulation package (VASP)

32-33

. The

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generalized gradient approximation (Perdew–Wang 91 34) and the projector-augment wave (PAW)

22

scheme

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cutoff of 400 eV and a 3×3×1 Monkhorst-Pack grid 37 have been applied for the bulk calculation. The

35-36

were used to describe the exchange–correlation energy and electron-ion interaction. A

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bimetallic surfaces were modeled with a p (3×3) unit cell (see Figure 1), containing four layers of

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metal atoms and a vacuum region around 11.5 Å. The Spin polarizations and dipole correction scheme

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were included. The influence of Monkhorst-Pack grid, plane wave cutoff and vacuum region on the

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adsorption energy are listed in Table S1. For the gas phase molecules calculations, a 15 × 15 × 15 Å3

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cubic unit cell and a 1×1×1 Monkhorst-Pack grid have been used. The Gaussian smearing method with

6

a broadening 38 of 0.1 eV was performed for ionic relaxations calculation. The M/Pt (111) and Pt/M/Pt

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(111) (M=Fe, Co, Ni, Cu) structures were built by substituting Pt atoms with M atoms. The M/Pt (111)

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slabs were ended with M, and the Pt/M/Pt (111) slabs were terminated with Pt. Only two topmost

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layers were permitted to relax, the others were frozen until the force acted on all relaxed atoms was

10

smaller than 0.03 eV/Å. The DFT optimized Pt-Pt distance of 2.82 Å was used not only for the Pt (111)

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and the M/Pt (111) and Pt/M/Pt (111) systems, owing to the contraction or expansion of lattice of the

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bimetal surface 39-40. The Ni-Ni distance of 2.49 Å was used for the Ni (111).

13

14 15

Figure 1 Models used in the DFT calculations. Figure 1A and Figure 1B shows top and site view of

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the (3×3) (1/9 ML) cell for the Ni/Pt (111) and Pt/Ni/Pt (111). The blue balls denote Pt atom, while the

17

green ones denote Ni atom.

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The adsorption energy has been calculated as: E ads,M =E M/surface －E surface －E M . DFT-D2 method 41

20

was used for van der Waals correction. The TSs are searched by the nudged elastic band (NEB) 42 ,

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with a series of four images along the given elementary step. A quasi-Newton algorithm was adopted

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to further optimize the approximate transition states by reducing residual forces below 0.05 eV/ Å. At

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last, the TSs were examined by verifying the existence of the only one normal mode combined with a

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pure imaginary frequency. The activation energy (E a ) is the difference between the energy of the initial

5

state (IS) and the transition state (TS): E a =E TS －E IS . When van der Waals correction is considered, the

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E a on each surface decreases about 0.10 eV (Table S2). The effect of van der Waals correction on the

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barrier is less obvious than on the adsorption energy, which is in agreement with the results on the

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toluene 43.

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3. Results and discussion

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This paper has been divided into three sections. The adsorption energies of the species involved

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in the hydrogenation of cyclohexene are discussed firstly. Secondly, the kinetic studies of the

13

cyclohexene reactions are presented to discuss the activity of the bimetallic surfaces. Finally, the

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standard turnover frequency (TOF°) is supplied to evaluate the efficiency of a catalyst system.

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3.1 The adsorption of the cyclohexene and other intermediates on the M/Pt (111), Pt/M/Pt (111)

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(M= Fe, Co, Ni, Cu), Pt (111) and Ni (111) surfaces.

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The adsorption of cyclohexene on Pt (111) has been investigated by different methods 11, 44-45. The

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di-σ bonded cyclohexene is the most favorable adsorption mode with the adsorption energy of -0.87

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eV (see Table 1). Theπadsorption mode are favored on all the surfaces except the Pt(111)(see Support

20

Figure S 1). The cyclohexenyl (C 6 H 11 ) is adsorbed with a strong C-M σ bond (M= Fe, Co, Ni, Cu, Pt)

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on these surfaces. The bridge sites are the favorite sites for the cyclohexenyl, and the corresponding

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adsorption energies are between -1.75 and -2.51 eV. In contrast, the physisorbed cyclohexane is found

23

on all the surfaces and the adsorption energies are about -0.27~ -0.55 eV. As a result, the adsorption 6


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strength on the same surface is in the trend of C 6 H 11 > C 6 H 10 > C 6 H 12 .

2 3

Table 1 The terms of energy decomposition of the adsorption energies on the M/Pt (111), Pt/M/Pt (111)

4

(M=Fe, Co, Ni, Cu), Ni (111) and Pt (111) surfaces (eV). Metal surface Fe/Pt(111) Co/Pt(111)

Ni/Pt(111)

Cu/Pt(111)

Pt/Fe/Pt(111)

Pt/Co/Pt(111)

Pt/Ni/Pt(111)

Pt/Cu/Pt(111)

Pt(111)

Ni(111)

Pt/Ni(111)

Pt 4 Cu 5 /Pt(111)

Species

E ads

E dis(molecular)

E dis(surface)

E int

C 6 H 12 C 6 H 11 C 6 H 10 C 6 H 12 C 6 H 11 C 6 H 10 C 6 H 12 C 6 H 11 C 6 H 10 C 6 H 12 C 6 H 11 C 6 H 10 C 6 H 12 C 6 H 11 C 6 H 10 C 6 H 12 C 6 H 11 C 6 H 10 C 6 H 12 C 6 H 11 C 6 H 10 C 6 H 12 C 6 H 11 C 6 H 10 C 6 H 12 C 6 H 11 C 6 H 10 C 6 H 12 C 6 H 11 C 6 H 10 C 6 H 12 C 6 H 11 C 6 H 10 C 6 H 12 C 6 H 11 C 6 H 10

-0.55 -2.36 -1.10 -0.31 -2.22 -0.74 -0.34 -2.25 -1.00 -0.27 -1.75 -0.55 -0.33 -1.85 -0.66 -0.33 -1.97 -0.69 -0.32 -2.27 -0.67 -0.34 -2.28 -0.69 -0.39 -2.49 -0.87 -0.35 -1.94 -0.56 -0.43 -2.51 -1.25 -0.64 -2.47 -0.95

0.27 0.52 1.20 0.27 0.51 1.43 0.28 0.49 0.42 0.28 0.48 0.14 0.28 0.39 0.12 0.28 0.39 0.02 0.28 0.21 0.18 0.28 0.36 0.24 0.28 0.40 1.92 0.26 0.43 0.22 0.28 0.14 1.66 0.02 0.44 1.91

0.21 0.36 0.31 0.20 0.31 0.37 0.21 0.36 0.41 0.20 0.34 0.21 0.11 0.24 0.11 0.13 0.26 0.13 0.11 0.38 0.11 0.20 0.49 0.12 0.31 0.65 0.77 0.30 0.46 0.51 0.24 0.70 0.39 0.29 0.54 0.60

-1.03 -3.24 -2.61 -0.78 -3.04 -2.54 -0.83 -3.1 -1.83 -0.75 -2.57 -0.90 -0.72 -2.48 -0.89 -0.74 -2.62 -0.84 -0.71 -2.86 -0.96 -0.82 -3.13 -1.05 -0.98 -3.54 -3.56 -0.91 -2.83 -1.29 -0.95 -3.35 -3.30 -0.95 -3.45 -3.46

5 6

The adsorption strength of the same molecule (C 6 H 10 , C 6 H 11 and C 6 H 12 ) follows the order of

7

M/Pt (111) > Pt (111) > Pt/M/Pt (111) (M= Fe, Co, Ni, Cu), which is consistent with the findings of

8

Humbert and Chen 11. In addition, the furfural binding energies were calculated to be: Co/Pt (111)> Pt

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(111)> Pt/Co/Pt (111) 6. The similar consequence could be explained from two sides. On the one hand,

2

the position of the surface d-electron bands is a crucial factor determining the adsorption property of

3

simple adsorbates 46. When theε d gets close to the Fermi level, the more active the metal becomes.

4

For example, we get a linear relationship between the adsorption energy of hydrogen atom and the

5

occupied d-band center (ε d ) of the bimetallic surfaces (see Figure 2). On the other hand, for the

6

complex adsorbate such as benzene

7

adsorption. In fact no linear relationship had been found between the adsorption energy of cyclohexene

8

and theε d of the surfaces we studied.

47

and naphthalene 48 the molecule orbital also impacts on the

9

10 11

Figure 2 The linear relationship between the adsorption energy of hydrogen and the d-band center (ε

12

d)

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Note: the adsorption energy of hydrogen has been calculated according to: E ads =E co-adsorpiton －0.5×

14

E H2(g) －E clean surface .

of the M/Pt (111), Pt/M/Pt (111) (M=Fe, Co, Ni, Cu), Ni(111) and Pt(111) surfaces.

15 16

The decomposition of adsorption energy could provide a deep insight into the essence of

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adsorption. The adsorption energy is considered to be made up of two parts: E dist and E inter . E dist

18

reveals the distortion of the molecule and the metal, thus it contains E dist(molecule) and E dist(surface) . Both 8


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E dist(molecule) and E dist(surface) are calculated as the energy difference between in the isolated state and in

2

adsorption mode. The other part (E inter ) is connected with the binding energy to the metal, and it is

3

calculated by this equation: E ads =E dist(molec) +E dist(surf) +E inter . The results of the adsorption

4

decomposition are show in Table 1.

5

Take the system of cyclohexene adsorbed on the M/Pt (111) as an example, to further understand

6

the factors that influence the distortion of the molecules and the metal surfaces, the geometric data and

7

the projected densities of states (PDOS) are presented in Table 2, Figure 3 and Figure 4. E dist(surf) is

8

related to the change of the distance between the two topmost metal layers in the situation of the clean

9

surface and the cyclohexene adsorbed system. The dd1 represents this change in Table 2, and the

10

positive value shows the corresponding distance becomes larger than on the clean surface. The order

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of the dd1 is Ni/Pt (111)>Co/Pt (111)>Fe/Pt (111)>Cu/Pt (111), in agreement with the sequence of

12

E dist(surface) .

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Table 2 Geometric details of cyclohexene adsorption on the M/Pt (111) (M=Fe, Co, Ni, Cu) surfaces E dis(surface) /eV d1st layer-2nd layer (clean slab)/Å d1st layer-2nd layer (after adsorption)/Å dd1/Å E dis(molecular) /eV dC=C(in gas phase)/Å dC=C(after adsorption)/Å dd2/Å dd3/Å

Fe/Pt(111) 0.31 2.041

Co/Pt(111) 0.37 1.987

Ni/Pt(111) 0.41 1.984

Cu/Pt(111) 0.21 2.138

2.087

2.043

2.055

2.136

0.046 1.20

0.056 1.43

0.071 0.42

-0.002 0.14

1.444 0.102 1.833

1.451 0.109 1.723

1.404 0.062 2.071

1.373 0.031 2.376

1.342

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Note: dd1 is the average variation of the distances between the two uppermost metal layers relative to

16

the clean relaxed surface. dd2 is the difference of the C=C length of the cyclohexene beween in gas

17

phase and in the adsorption geometry. dd3 is the distance between the C=C bond and the top metal

18

layer in the adsorption geometry.

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Figure 3 The changes of the PDOS on the sum of the d z2 , d xz and d yz orbitals on the first layer of the M/Pt (111) surface (M=Fe, Co, Ni, Cu).

5 6 7

Figure 4 The changes of the PDOS on the P z orbitals of the carbons of the cyclohexene molecule adsorbed on the M/Pt (111) surface (M=Fe, Co, Ni, Cu)

8 9

After adsorption the density of the state on the 3d orbitals of the M/Pt (111) surfaces could be

10

altered, especially the d z2 ,d xz and d yz orbitals. The changes of the PDOS on the sum of the d z2 , d xz and

11

d yz orbitals on the first layer of the M/Pt (111) surface is revealed in Figure 3, calculated by 10


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subtracting the PDOS on the clean surface from the PDOS on the surface distorted as in the adsorption

2

case. The negative value means decrease of the densitiy of state in comparation with the clean surface,

3

while the positive means increase of the densitiy of state. At the Fermi level, the more obvious the

4

variation of the density of the state is, the larger the E dist(surface) is. For instance, a sharp and broad peak

5

at the Fermi level is found on the Ni/Pt (111) surface, which forms a striking contrast to the situation

6

that only a little changes at the Fermi level on the Cu/Pt (111) surface (see Figure 3), and the

7

E dist(surface) is 0.41 and 0.21 eV on the Ni/Pt(111) and the Cu/Pt(111), respectively.

8

The E dist(molecule) is also linked to the geometry data. The C=C bond of the cyclohexene elongates

9

during interacting with the metal surfaces. In the relax gas-phase the C=C bond length is 1.342 Å.

10

After adsorption the C=C bond length is increased by 0.03~0.1 Å. The differences of the C=C length

11

beween the cyclohexene in gas phase and in the adsorption geometry are listed in Table 2(see dd2).

12

Besides, the average distances between the the C=C bond and the first metal layer in the adsorption

13

mode are also listed (see dd3). It is noticed that when the C=C bond is lenthened and the C=C bond

14

moves toward the metal surface, the E dist(molecule) usually gets larger.

15

Figure 4 represents the changes of the PDOS on the P z orbitals of the carbons of the cyclohexene

16

molecule. This is obtained by subtracting the PDOS of cyclohexene molecule in gas phase from the

17

PDOS of cyclohexene molecule distorted in the adsorption structure. The interacations between the

18

molecule and the support cause the fluctuation of the electronic density. The occupied π

19

cyclohexene orbitals probably interact with the d z2 , d xz and d yz orbitals of the first metal layer, thus

20

pushing the bonding contributions to lower energies and the antibonding ones to high energies

21

sometimes above the Fermi level. Meanwhile, the posibile interactions betweent the emptyπ *

22

molecular orbitals and the occupied d orbitals of the metal surface lead to thisπ* orbital filled in a

23

measure and the related densitiy of state increased. Consistent with the above discussions, a positive 11



Page 12 of 38

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peak is found just the above the Fermi level, and its position is 2.80, 2.67, 3.52 and 4.06 eV on the

2

Fe/Pt(111), Co/Pt(111), Ni/Pt(111) and Cu/Pt(111), respectivly.

3

What is more, E dist(molecule) has been found to be closely related to the energetic gap between the

4

highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO)47-48.

5

In Figure 4 the positions of the peaks that are the nearest to the Fermi level may refer to the HOMO

6

(the peak below the Fermi level) and the LUMO (the peak above the Fermi level). The gaps for the

7

cyclohexene in the adsorption geometries are 3.56, 3.34, 4.37 and 4.87 eV on the Fe/Pt(111),

8

Co/Pt(111), Ni/Pt(111) and Cu/Pt(111), respectivly, which could be correlated with the distortion

9

energies: 1.20, 1.43, 0.42 and 0.14 eV on the the Fe/Pt(111), Co/Pt(111), Ni/Pt(111) and Cu/Pt(111),

10

respectivly. The severe distortions of the cyclohexene on the Fe/Pt(111) and the Co/Pt(111) surfacce

11

indicate a better electronic interaction between the orbitals of the molecule and the d orbitals of the

12

surface layer. Consequently, the E inter for the cyclohexene on the Fe/Pt(111) (-2.61eV) and the

13

Co/Pt(111) (-2.54 eV) is more negetive than on the Ni/Pt(111) (-1.83 eV) and Cu/Pt(111) (-0.90 eV),

14

suggesting a close conection between the E inter and the E dist(molecule).

15

The adsorption energy is the end product of the E dist and the E int , so a strong interaction

16

sometimes does not give rise to a strong adsorpion. For example, the E inter of C 6 H 10 is -3.56 and -1.83

17

eV on the Pt(111) and Ni/Pt(111) respectively, whereas the corresponding E ads of C 6 H 10 is -0.87 and

18

-1.00 eV. Actually, the energy cost by the molecule distortion could not be neglected. The E dist(molecule)

19

of C 6 H 10 on the Pt (111) is 1.50 eV more than that on the Ni/Pt(111) (see Table 1), which could be

20

responsible for the lower E ads on the Pt (111). According to the E inter , we can divide the surfaces into

21

two groups: strong interaction on the M/Pt(111), Pt(111) and Ni(111), moderate interaction on the

22

Pt/M/Pt(111) (M=Fe, Co, Ni, Cu). Such moderate interaction has been suggested as the reason for the

23

high hydrogenation activity of the sandwiches structures 11. 12


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3.2 Thermodynamic stability of the M/Pt(111) and Pt/M/Pt(111) surfaces (M=Fe, Co, Ni, Cu)

3

The Pt/M/Pt(111) sandwich structure is thermodynamically more stable than the M/Pt(111)

4

structure no matter when the surface is clean (in vaccum) or adsorbed by the species including

5

hydrogen, C 6 H 10 , C 6 H 11 and C 6 H 12 . The segregation energy (E seg,vacuum ) is the energy needed to move

6

the subsurface admetal to the surface of the host metal in vacuum. And it could be expressed as:

7

E seg,vacuum ＝E M/Pt(111) －E Pt/M/Pt(111) . When E seg,vacuum is negative enough, the metal (M) deposited on the

8

host (Pt(111)) will segregate to the surface to produce the M/Pt(111) surface monolayer structure.

9

Otherwise, the surface layer will be the Pt and the Pt/M/Pt(111) subsurface alloy will be formed. The

10

values of E seg,vacuum in Table 3 are all positive, indicating the Pt/M/Pt(111) is more stable than

11

M/Pt(111) structures under vaccum condition, which corresponds with the calculated results 49-50.

12 13

Table 3 Calculated surface segregation energies under vacuum (E seg,vacuum ), the difference in the

14

adsorption energy of the same adsorbate between on the M/Pt (111) and on the Pt/M/Pt (111) (M=Fe,

15

Co, Ni, Cu) surfaces (ΔE ads ) and the sum of E seg,vacuu and ΔE ad ( E seg, ads ) (unit is eV) Surface pair E seg,vacuum ΔE H (4/9) E seg,H (4/9) ΔE H (8/9) E seg,H (8/9) ΔE C6H10 E seg,C6H10 ΔE C6H11 E seg,C6H11 ΔE C6H12 E seg,C6H12

Fe/Pt(111) Pt/Fe/Pt(111) 8.48 -2.89 5.59 -4.88 3.60 -0.44 8.04 -0.51 7.97 -0.22 8.26

Co/Pt(111) Pt/Co/Pt(111) 6.93 -1.88 5.05 -3.57 3.36 -0.05 6.88 -0.25 6.68 0.02 6.95

Ni/Pt(111) Pt/Ni/Pt(111) 5.52 -2.30 3.22 -4.31 1.21 -0.33 5.19 0.02 5.54 0.05 5.57

Cu/Pt(111) Pt/Cu/Pt(111) 3.15 0.41 3.56 0.61 3.76 0.14 3.29 0.53 3.68 0.07 3.22

Cu/Pt(111) Cu 5 Pt 4 /Pt(111) 9.71 0.97 1.68 1.70 11.41 0.40 10.11 0.72 10.43 0.37 10.08

16 17

The surface compnents that bond strongly to the adsorbates might move to the uppermost layer,

18

thus the surface composition could be changed. For example, the Pd 3 Pt@Pd 3 Cr core–shell structures

19

are thermodynamic favored at 1/4 monolayer O, but the Pd 3 Cr@Pd 3 Pt core–shell structures are stable 13



Page 14 of 38

1

under the cacuum condition 51. To test the influence of the adsorbate, we calculate the segregation

2

energy(E seg,ads ) under adsorbate environment. E seg, ads can be expressed as: E seg, ads ＝E seg,vacuum＋ΔEads.

3

ΔE ads is calculated as: ΔE ads ＝E ads,M/Pt(111) －E ads,Pt/M/Pt(111) . E ads,M/Pt(111) or E ads,Pt/M/Pt(111) presents the

4

adsorption energy of the same adsorbate on the M/Pt(111) or the Pt/M/Pt(111) surface. Similar to the

5

E seg,vacuum , a positive value of E seg, ads means the Pt/M/Pt(111) structure is more stable. On the contrary,

6

a negative value suggests the M/Pt (111) is thermodynamically favorable. In the present of 4/9 or 8/9

7

monolyaer H, although the ΔE ads is negetive, implying the bonding of hydrogen to the M is stronger

8

than to the Pt, the combination of E seg,vacuum and ΔE ads is still positive, because the E seg,vacuum controls

9

the segregation tendency. Therefore, the hydrogen will not induce M segreated to the surface unless at

10

much higher H coverage, which is in agreement with the literature49-50. The adsorption of C 6 H 10 ,

11

C 6 H 11 and C 6 H 12 could not inflenece the stability of the Pt/M/Pt (111) structures either. And the trend

12

of the E seg,ads is Pt/Fe/Pt (111)> Pt/Co/Pt (111)> Pt/Ni/Pt (111)>Pt/Cu/Pt (111), whereas the position

13

of the occupied surface d-electron bands of the clean surfaces is just reverse: Pt/Cu/Pt (111)> Pt/Ni/Pt

14

(111)> Pt/Co/Pt (111)> Pt/Fe/Pt (111), implying the E seg,ads is related to the occupied d-band centers of

15

the pure ingredients that form the bimetallic surfaces 49.

16

It had been reported that the Cu-Pt surface alloy was preferred no matter depositing Cu on a Pt 52-53

17

(111) or depositing Pt on a Cu (111) substrate

. Besides, the Cu-Pt alloy composition has been

18

found sensitive to many factors such as the initial amount of solute metal and the annealing

19

temperature. For example, Barrett et al. estimated the Pt concentration in surface layer as 0.40, 0.50

20

and 0.05 at 0.40, 2.10 and 4.20 initial Cu monolayer (ML) respectively, when the Cu/Pt (111) was

21

annealed at 573 K 52. Another example is Belkhou et al. found the concentration of Pt in the top layer

22

of the Pt/Cu (111) was 0.25 at 588 K, whereas 0.13 at 623 K 53. The structure and the composition of

23

the alloy interior are more complex contrasted with the surface layer. There are two possible structures 14


Page 15 of 38 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


1

for the interior of the Cu/Pt (111) alloy: Cu 50 Pt 50 (L1 1 )and Cu 75 Pt 25 (L1 2 ). The former has an alternate

2

of pure Cu and pure Pt atomic layer, whereas a homogeneous phase is formed on the latter structure.

3

The Cu 50 Pt 50 was suggested to be the preferred structure for the Cu/Pt (111) bulk, due to the quickly

4

formed Cu 50 Pt 50 phase and the limited initial Cu amount 52.

5

Considering the calculations may give useful information, we build a series of models:

6

Pt x Cu 8-x /Pt 8-x Cu x /Pt (111)(x=1, 2, 3, 4, 5, 6, 7, 8) on the assumption that the Cu atoms only diffuse to

7

the subsurface layer to simplify the calculations (the corresponding structures are shown in Support

8

Figure S 2). For the Pt x Cu 8-x /Pt 8-x Cu x /Pt(111) alloy, the E seg,vacuu is calculated as : E seg,vacuum ＝

9

E Cu/Pt(111) －E

PtxCu8-x/Pt8-xCux/Pt(111)

and the values of E seg,vacuu are shown in Table 4. All the E seg,vacuum is

10

positive, so the Pt-Cu surface alloys are more stable than the Pt/Cu(111) monolayer in vaccum.

11

Besides, the E seg,vacuum becomes larger with the increasing concentration of Pt in the surface layer,

12

implying the Pt/Cu/Pt(111) is thermodynamically more stalbe than the Pt-Cu surface alloy. According

13

to

14

Pt x Cu 8-x /Pt 8-x Cu x /Pt(111)> Pt/Cu(111), demenstrating the the Pt-Cu surface alloys is in a metastable

15

state to a certain extent. Actually, the formation of the surface alloy is attributed to the interuption of

16

the dissolution in the surface area.

the

calcaulted

segregation

energies,

the

thermal

stability

order

is:

Pt/Cu/Pt(111)>

17

Above all, the Pt/M/Pt(111) subsurface structure and Pt/M(111) monolayer structure are two ideal

18

conditions. When preparing these surfaces, the biggest difference is the temperture at which the M is

19

deposited on the Pt(111). For exmple, based on the Cu/Pt Auger electron spectrometer (AES) ratio, the

20

Cu/Pt(111) surface was observed to be relatively stable up to 550 K above which the AES ratio

21

deminished steadily 11. As a result the Cu/Pt(111) monolayer and the Pt/Cu/Pt(111) subsurface were

22

prepared at 300 and 600 K 11, respectively. Moreover, the deposited M atoms may diffuse to the bulk

23

of the Pt(111) at high temperture. Therefore, it is hard to avoid the difference between the actual 15



Page 16 of 38

1

situation of the M/Pt(111) and Pt/M/Pt(111) catalysts and our calculated models, which may arouse in

2

the contradictions between the experimental results and the theoretical results.

3 4

3.3 Cyclohexene hydrogenation on the M/Pt (111) and Pt/M/Pt (111) (M=Fe, Co, Ni, Cu), Pt(111) and

5

Ni (111) surfaces

6

In this section, the detailed reaction mechanisms of the cyclohexene converted to cyclohexane

7

will be illustrated. The energetic data for each elementary step and the corresponding transition state

8

structures are displayed in Figure 5. The species (C 6 H 10 , C 6 H 11 and C 6 H 12 ) of the most stable

9

adsorption mode and the co-adsorption systems with the lowest energy are used to search for the

10

transition states.

16


Page 17 of 38


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 1 58 59 60 17



Page 18 of 38

1

Figure 5 Possible pathways of cyclohexene hydrogenation to cyclohexane at 2/9 H coverage on the Fe/Pt (111)(A),

2

Co/Pt(111)(B), Ni/Pt(111)(C), Cu/Pt(111)(D), Pt/Fe/Pt(111)(E), Pt/Co/Pt(111)(F), Pt/Ni/Pt(111)(G), Pt/Cu/Pt(111) (H),

3

Ni(111) (I) and Pt(111)(J) surfaces.

4 5

3.3.1 Cyclohexene hydrogenation on the Pt (111), Ni (111), Pt/Ni (111), Ni/Pt (111) and Pt/Ni/Pt (111)

6

surfaces

7

The reaction of cyclohexene on the Pt (111) and Ni (111) was intensively studied 11-12, 25-28. The 27-28

8

conversion of cyclohexene to cyclohexane was detected at around 400 K on the Pt (111)

9

Furthermore, at the pressure of about 10-5 Torr two small desorption peaks of cyclohexane were

10

observed between 150 K and 250 K in the presence of co-adsorbed hydrogen and cyclohexene on the

11

Pt(111) 11. On the contrary, almost no cyclohexane was found on the Ni (111) under similar reaction

12

conditions 12. In the light of these findings, it is easy to conclude the Pt (111) surface is more active

13

than the Ni (111) on promoting cyclohexene hydrogenation to cyclohexane. In our calculations, the

14

activation energies for the two elementary steps (C 6 H 10 +H=C 6 H 11 and C 6 H 11 +H=C 6 H 12 ) are 0.87,

15

1.04 eV on the Pt (111) and 1.16, 0.89 eV on the Ni (111). The step with the highest barrier is

16

considered as the key step. The barrier of the key step on the Pt (111) is lower than on the Ni (111) by

17

only 0.1 eV, which seems not enough causing such difference of hydrogenation activity between the Pt

18

(111) and the Ni (111) as viewed from the dynamics. In fact, the rate determining states will be

19

confirmed by the AUTOF program 54 in section 3.4, which could provide the convincing explanation.

20

.

It seems that both the Ni/Pt (111) and the Pt/Ni/Pt (111) show high activity according to the 11-12

21

TPD results

: a sharp peak of the cyclohexane that was produced by the cyclohexene

22

hydrogenation was found at 231 and 203 K on the Ni/Pt (111) and the Pt/Ni/Pt (111) surface,

23

respectively. But the Pt/Ni/Pt(111) structure should be more active in comparison with the Ni/Pt(111),

24

because barriers of two hydrogenation steps are 0.51 and 0.81 eV on the Pt/Ni/Pt(111), whereas 0.61 18


Page 19 of 38 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


1

and 1.19 eV on the Ni/Pt (111). As we have mentioned in section 3.2, due to the segregation of Pt 55-56

2

the upmost layer of the Ni/Pt (111) bimetallic may be almost the pure Pt layer. Thus, it is the Pt atoms

3

that take part in cyclohexene hydrogenation on the so-called Ni/Pt (111) surface.

4

The conclusion could be arrived at that the Ni/Pt (111), the Pt/Ni/Pt (111) and the Pt/Ni (111)

5

may exhibit similar chemical property on account of the same Pt-enriched top layer. For example, it

6

had been observed the Pt/Ni (111) and the Ni/Pt (111) showed analogous activity in the cyclohexene

7

hydrogenation 12: the activity of the Pt/Ni (111) and the Ni/Pt (111) were estimated to be 0.004 and

8

0.002 molecules per metal atom. And the activity of the Pt/Ni/Pt (111) was calculated to be 0.03

9

molecules per metal atom using the same method 11. The hydrogen barriers on the Pt/Ni (111) are also

10

calculated: 0.86 and 0.74 eV. The corresponding transition state structures are displayed in Support

11

Figure S 3. On the basis of the barriers of the key step, the reactivity of the three Ni-Pt bimetallic

12

catalysts is in the order of Pt/Ni/Pt(111)>Pt/Ni(111)>Ni/Pt(111), in good agreement with the sequence

13

obtained from experiments 11-12 .

14

3.3.2 Cyclohexene hydrogenation on the M/Pt (111) and Pt/M/Pt (111) (M=Fe, Co) surfaces

15

The reaction pathway of cyclohexene hydrogenation to cyclohexane had been observed at 221

16

and 166 K on the Fe/Pt (111) and Co/Pt (1111), respectively 11, 13. The migration of the Pt atoms from

17

the interior toward the surface is expected to be responsible for this phenomenon. At first, the

18

hydrogenation barriers of the key step on the Co/Pt (111) and the Fe/Pt (111) are 1.14 and 1.41 eV,

19

implying the hydrogenation process is hindered. Secondly, the Fe and Co atoms prefer to stay in the

20

interior of the Pt (111) in the light of the calculated surface segregation energies in section 3.2, which

21

could be attested by the stable Pt/M/Pt (111) (M=Fe, Co) structures at high temperatures using AES

22

11,13

23

. The sandwich structures of the Pt/M/Pt (111) (M=Fe, Co) should be the potential catalyst when 19



Page 20 of 38

1

accelerating cyclohexene hydrogenated to cyclohexane, especially the Pt/Co/Pt (111). The

2

hydrogenation barriers of the key step are 0.84 and 0.92 eV on the Pt/Co/Pt (111) and the Pt/Fe/Pt

3

(111), respectively. The Pt/Co/Pt (111) is clearly more active than the Pt/Fe/Pt (111), in accordance

4

with the TPD results that the cyclohexane peak turned up at 187 and 180 K on the Pt/Fe/Pt (111) and

5

Pt/Co/Pt (111) when the hydrogen atoms were pre-dosed with the cyclohexene

6

activity of catalyzing cyclohexene to cyclohexane was estimated to be 0.006 on the Pt/Co/Pt (111)

7

surface and 0.005 on the Pt/Fe/Pt (111) surface, using cyclohexane peak area ratios 11.

8

3.3.3 Cyclohexene hydrogenation on the Cu/Pt (111) and Pt/Cu/Pt (111) surfaces

11

. Moreover, the

9

We have calculated the hydrogenation barriers of cyclohexene on the Cu/Pt (111) and the

10

Pt/Cu/Pt (111) surfaces. The key step is the first hydrogen step (C 6 H 10 +H=C 6 H 11 ) on both surfaces.

11

The barriers of the key step are 1.31 and 0.74 eV on the Cu/Pt (111) and the Pt/Cu/Pt (111),

12

respectively. So the reactivity order is Pt/Cu/Pt (111) >Cu/Pt (111). However, the TPD experiments

13

showed a very small peak of the cyclohexane that was produced by the cyclohexene and the

14

pre-adsorbed hydrogen on the Cu/Pt (111) and the Pt/Cu/Pt (111) surfaces 11. And the activity of the

15

Pt/Cu/Pt (111) was even regarded as 0.00 on the ground of the cyclohexane TPD peak area ratios 11.

16

The Pt/Cu/Pt (111) may be an excellent hydrogenation catalyst according to our results. This conflict

17

may be attributed to the phenomenon that the Cu-Pt surface alloys were formed.

18

We speculate the surface Pt atoms take positive effect on promoting the cyclohexene

19

hydrogenation, owing to the lower hydrogenation barrier on the Pt/Cu/Pt (111) compared with the

20

Cu/Pt (111). For the Pt/Cu/Pt (111) structure, the actual topmost layer is composed by not only Pt but

21

also Cu, leading to a decrease of the hydrogenation activity. However, an increase of the

22

hydrogenation activity is presented on the Cu/Pt (111) structure.

23

To verify the effect of the surface Pt, we build a 3 × 3 super cell (see Support Figure S 3) to 20


Page 21 of 38 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


1

model the Pt 4 Cu 5 /Pt (111) surface alloy, supposing about half monolayer Pt has segregated to the

2

surface. The cyclohexene and other intermediates prefer to bond with the surface Pt atoms rather than

3

Cu atoms on the Pt 4 Cu 5 /Pt (111) surface alloy (see Figure S 1). Only the surface Pt atoms take part in

4

the hydrogenation path (see Support Figure S 3). The barrier of the key hydrogenation step is 0.97 eV,

5

between the barrier (0.74 eV) on the Pt/Cu/Pt (111) and the barrier (1.31 eV) on the Cu/Pt (111). This

6

indicates the hydrogenation reactivity of the Pt 4 Cu 5 /Pt (111) is lower than Pt/Cu/Pt (111), but higher

7

than Cu/Pt (111). The activity of the Cu-Pt bimetallic catalysts might be sensitive to the concentration

8

of the surface Pt, thus the real composition in the surface layer of the Pt/Cu/Pt (111) or the Cu/Pt (111)

9

structure could be crucial. But how to get this needs further research.

10

11 12

Figure 6 The PDOS on d orbitals on the uppermost layer of the clean Cu/Pt (111), Pt 4 Cu 5 /Pt (111) and

13

Pt/Cu/Pt (111) surface (A). The PDOS on d orbitals of the Pt/Cu/Pt (111) surface layer while the

14

surface is clean and after adsorbed by hydrogen atoms (B).

15 16

The PDOS on d orbitals on the uppermost layer of the clean Cu/Pt (111), Pt 4 Cu 5 /Pt (111) and

17

Pt/Cu/Pt (111) surface is demenstrated in Figure 6A, and the origin is the Fermi level. At fist, the

18

highest densitiy of the state is observed on the Cu/Pt (111) surface layer, due to the filled d-band of Cu

19

element. Secondly, the width of the d-band is 4.56, 5.09 and 5.69 eV on the Cu/Pt (111), Pt 4 Cu 5 /Pt

20

(111) and Pt/Cu/Pt (111), respectively, because the 6d orbitals are usually more expansive than the 4d

21



Page 22 of 38

1

orbitals. Forthermore, the occupied d-band center of the Cu/Pt (111) and Pt 4 Cu 5 /Pt (111) is almost the

2

same:-1.94 eV. For the Pt/Cu/Pt (111) the occupied d-band center is -2.11 eV, meaning the Pt/Cu/Pt

3

(111) is less reactive. The d-band center and the band width are closely connected: when the d band

4

width of the surface atom increases, the d band shifts down 46. Although the Cu/Pt (111) and Pt 4 Cu 5 /Pt

5

(111) have similar occupied d-band center, the chemical beheviors are different. For instance, the

6

adsorption energies of the same adsorbat are more exothermic on the Pt 4 Cu 5 /Pt (111)(see Table 1). The

7

modification of the valence band caused by Pt 5d-Cu3d hybridisation was observed in the experiments

8

53

9

(111) and the Pt 4 Cu 5 /Pt (111) are shown in Figure 6 B. The changed d obtials on the Pt-Cu surface

10

alloy may enhance the energy overlap between d states and adsorbate orbitals, therefore the interaction

11

with the adsorbate is strengthened.

. And the diffference in the density of states just below the Fermi level between on the clean Cu/Pt

12 13

3.4 Effect of the pre-covered hydrogen on the cyclohexene hydrogenation

14

It had been noticed that more hydrogenated products were formed on condition that the hydrogen

15

atoms were pre-adsorbed 13, 57-58. To make clear the influence of the surface hydrogen, we increase the

16

coverage of pre-adsorbed hydrogen from 2/9 to 4/9 (4/9 is close to the estimated saturation coverage 11)

17

and find most of the hydrogenation barriers are decreased (see Figure 7). For example, at 2/9 H

18

coverage the barriers for the key steps are 1.41, 1.14, 0.92, 0.84 eV on the Fe/Pt (111), Co/Pt (111),

19

Pt/Fe/Pt (111) and Pt/Co/Pt (111), respectively. At 4/9 H coverage the corresponding barriers are

20

decreased to 1.01, 0.70, 0.91, 0.63 eV. Besides, the hydrogen atoms adsorbed near the olefin carbon

21

are most likely participant in the hydrogenation. If adsorbed more hydrogen atoms, the amount of the

22

hydrogen atoms that are able to interact with the nearby olefin carbon could be larger, thus the

23

probability of the hydrogenation is increased. This might explain the reason why the Pt (111) showed 22


Page 23 of 38 1 2 1 3 4 5 2 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


certain hydrogenation reactivity under reaction pressure of 10 Torr of cyclohexene and 100 Torr of hydrogen 27 but poor reactivity under the press of about 10-5 Torr 11.

23


The Journal of Physical Chemistry 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 1 60 24


Page 24 of 38

Page 25 of 38 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


1

Figure 7 Possible pathways of cyclohexene hydrogenation to cyclohexane at 4/9 H coverage on the Fe/Pt (111)(A),

2

Co/Pt(111)(B), Ni/Pt(111)(C), Cu/Pt(111)(D), Pt/Fe/Pt(111)(E), Pt/Co/Pt(111)(F), Pt/Ni/Pt(111)(G), Pt/Cu/Pt(111) (H),

3

Ni(111) (I) and Pt(111)(J) surfaces.

4 5

The electronic structure of the surface is changed after the hydrogen atoms are adsorbed. Figure 5

6

B shows the PDOS on d orbitals of the Pt/Cu/Pt (111) surface layer when the surface is clean and

7

adsorbed by chydrogen atoms at 4/9 ML. After adsorption, the occupied d band center shifts from

8

-2.11 to -2.41eV, and the d band width increases from 5.69 to 7.33 eV. This results in a weaker

9

interaction with the adsorbate. For instance, the adsorption energy of cyclohexene is -0.69 and -0.41

10

eV on the clean Pt/Cu/Pt (111) and 4/9H Pt/Cu/Pt (111) surfaces. The weakly bonded adsorbate may

11

be more reactive sometimes. Wang et al. found that weaker adsorption on the Pt 1 /Cu(111) accouts for

12

the splendid selectivity and catalytic activity of Pt 1 /Cu (111) surface for formic acid dehydrogenation

13

to hydrogen 59.

14

It is noteworthy that the order of the catalytic activity of the bimetallic surface is obtained by

15

comparing the hydrogenation barrier of the key step at the same H coverage. The “artificially” fixed

16

hydrogen coverage brings about two opposite results. For one thing, it allows us to objectively

17

distinguish the efficiency of the catalysts without considering the conditions of the reaction. For

18

another, our judgments on the catalysts may deviate from the experimental results.

19

We try to estimate the saturated hydrogen coverage on the Pt/M/Pt (111) and M/Pt (111) surfaces

20

under the condition of 273.15 K and the standard pressure. This temperature and pressure will be used

21

in the next section. The chemical potential (μ) of H in gas phase is obtained as half of gas H 2 (μ H =

22

-0.18 eV), on the basis of the thermochemical data 60. The saturated hydrogen coverage is calculated

23

according to the hypothesis the adsorption equilibrium will be reached when the adsorption energy of

24

hydrogen is equal to -0.18 eV 58. The equilibrium concentration of hydrogen is regarded as 4/9 on the

25



Page 26 of 38

1

Pt/M/Pt (111) (M=Fe, Co, Ni, Cu), Cu/Pt (111), Pt (111) and Ni (111), because the corresponding

2

adsorption energy is close to -0.18 eV. Whereas, the adsorption energy of hydrogen is -0.63, -0.53 and

3

-0.66 eV at 8/9 H coverage on the Fe/Pt (111), Co/Pt (111) and Ni/Pt (111), respectively, implying the

4

the equilibrium H concentration may be more than one monolayer. At high hydrogen coverage, the

5

M-ended surface maybe more stable than the Pt-ended surface, due to the stronger M-H bond (M=Fe,

6

Co, Ni). But the reaction mechanisms of cyclohexene hydrogenation on the subsurface H are not

7

obtained in our work. What is more, the H coverage in the TPD experiments is suggested as 40-50% of

8

the saturation coverage 11. Consequently, the real H coverage on the Pt/M/Pt (111) (M=Fe, Co, Ni, Cu),

9

Cu/Pt (111), Ni (111) and Pt (111) may be more close to 2/9. The actual H coverage could be more

10

than 4/9 for the case on the M/Pt (111) (M=Fe, Co, Ni), the calculated results at 4/9 is still meaningful

11

and will be used in the next section.

12 13 14

3.5 The standard Turnover frequencies of the hydrogenation reactions We apply the AUTOF program that is based on the energetic span model to estimate the Turnover . The TOF could be a measure of turnovers and its unit is s−1. The TOF changes

54

15

Frequency (TOF)

16

with the temperature and the concentrations of reactants. The standard turnover frequency (TOF°) 61 is

17

considered to be more applicable to judge the efficiency of a catalyst system, because all the factors

18

that influence the TOF are declared: the TOF° is measured at the standard concentration of reactants

19

and products (or 10 5 Pa in case of gases) at 273.15 K.

20

The free energy profiles should be provided in order to calculate the TOF°. At first, the standard

21

chemical potential (μ∃) of hydrogen, cyclohexene and cyclohexane in gas phase at 273.15 K can be

22

obtained from the thermochemical data 60. The changes of the free energy induced by mixing are

23

ignored. The functional relation between the standard entropy (S∃) and the temperature could be 26


Page 27 of 38 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


1

computed in the light of the data 60. The difference of the standard chemical potential (Δμ∃) between 0

2

and 273.15 K can be calculated asΔμ∃=－ ∫

3

0.69 and 0.70 eV. The reference state corresponds to the gas phase cyclohexene, hydrogen and clean

4

surface at 273.15 K under standard pressure. According to the calculated adsorption energies, the

5

reaction heats and barriers, we determine the positions of the initial states, transition states and the

6

final states (shown in Figure 8).

273.15

0

S ∃(T)dT. The calculatedΔμ C6H10 ∃ andΔμ C6H10 ∃ is

7

8 9

Figure 8 The free energy profiles of cyclohexene hydrogenation to cyclohexane on the Pt/M/Pt (111),

10

M/Pt (111) (M=Fe, Co, Ni, Cu), Ni(111) and Pt (111) at 2/9 H coverage (left) and at 4/9 H coverage

11

(right). The subscript of “ad” means the adsorbed states in the figure.

12 13

For the gaseous species, the translational entropy is approximately taken as the most important 62

14

contribution

. But for the surface reactions, the contributions of translation and rotation are often

15

neglected due to the frustrated adsorption configurations

16

calculated according to the harmonic normal mode approximation 64. Table S 2 demonstrates that there

17

is almost no difference in the hydrogenation barriers between the situation when the entropy effect is

18

adopted and the situation without entropy effect. Actually, for many surface reactions entropy change

19

could be ignorable

20

when steam methane reforming at 800°C

63

. The contribution from vibration can be

62, 65

, except at high temperature. For example, the entropic effect is significant 66

. Besides, the Table S 2 also lists the zero point energy

27



Page 28 of 38

1

corrections to the activation energy. And the difference between the non-zero point energy corrected

2

and zero point energy corrected barriers are less than 0.05 eV, implying the impact of zero point

3

energy corrected may be neglected.

4

In the energetic span theory, the TOF° depends on the effective reaction barriers (E a eff). Figure 9

5

A shows a linear relationship between the E a eff and the lg(TOF°). The E a eff is the energy difference

6

between the TOF determining transition state (TDTS) and the TOF determining intermediate (TDI).

7

How to identify the TDTS and TDI is shown in reference

8

different on different surfaces. For instance, at 2/9 H coverage the TDTS is TS C6H11+H and TS C6H10+H

9

on the Pt (111) and Cu/Pt (111) surfaces, respectively. But the TDI is (C 6 H 10(ad) +2H (ad) ) on both

10

59

. The TDTS and the TDI are usually

surfaces.

11

It is obvious that the smaller E a eff is followed by the higher TOF°. In other words, the TOF° could

12

become larger on condition that the pre-covered H could diminish the E a eff. For example, the TDTS is

13

TS C6H10+H and the TDI is (C 6 H 10(ad) +2H (ad) ) at 2/9 H coverage on the Ni (111), and the E a eff and TOF°

14

is 1.36 eV and 4.6e-13 s-1. At 4/9 H coverage, the TDTS and TDI are still refer to the TS C6H10+H and

15

(C 6 H 10(ad) +2H (ad) ), but the E a eff is reduced to 1.03 eV which leads to higher TOF° of 5.0e-7 s-1.

16

However, the increased H concentration not always brings about an increase in the TOF°. The TOF° at

17

4/9 H coverage is 9 orders of magnitude lower than 2/9 H coverage on Pt/Cu/Pt (111), because the E a eff

18

at 4/9 H coverage is 0.54 eV higher than at 2/9 H coverage.

19

28


Page 29 of 38 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


1 2

Figure 9 The linear correlation between the lg(TOF°) and the E a eff and the lg(TOF°) (A). The

3

relationship between the lg(TOF°) and the co-adsorption energy of the cyclohexene and hydrogen

4

atoms on the M/Pt(111), Pt/M/Pt(111) (M=Fe, Co, Ni, Cu), Ni(111) and Pt(111) (B). The black means

5

at 2/9 H coverage, and the red means at 4/8 H coverage.

6

Note: At 2/9 H coverage the E ads is calculated as: E ads =E co-adsorpiton －E H2(g) －E clean surface . At 4/9 H

7

coverage, E ads =E co-adsorpiton －E H2(g) －E 2H adsorbed surface .

8 9

A volcano-type relationship is found between the TOF° of cyclohexene hydrogenation and the

10

co-adsorption energy of the cyclohexene and hydrogen atoms on the surfaces we have studied. The

11

Pt/Ni/Pt (111) structure manifests high activity on the basis of Figure 9 B. Such kind of sandwich

12

structures may be efficient in promoting cyclohexene hydrogenation, when the corresponding

13

adsorption energy is between -0.4 and -1.6 eV. The Pt/Ni/WC surface has been found more active than

14

the Pt/Ni/Pt (111) when accelerating cyclohexene hydrogenation

15

of the cyclohexene on the Pt/Ni/WC is around -0.45 eV

16

above. This coincides with our prediction and indicates such volcano-type relationship might be

17

helpful for designing potential hydrogen catalysts.

67

. Moreover, the adsorption energy

67

, approximately in the range mentioned

18 19

4. Conclusions

20

The adsorption of the stable intermediates involved in cyclohexene hydrogenation and the

21

hydrogenation pathways on the M/Pt (111), Pt/M/Pt (111) (M=Fe, Co, Ni, Cu), Pt (111) and Ni (111) 29



Page 30 of 38

1

have been investigated by periodic DFT calculations. Our calculations reveal that the adsorption

2

strength roughly follow this order: M/Pt (111) > Pt (111) >Ni (111) > Pt/M/Pt (111) (M= Fe, Co, Ni,

3

Cu). The thermodynamic stability of the clean surface is Pt/M/Pt (111)>M/Pt (111). But this sequence

4

could be reversed if the adsorbate interacts stongly with the M. The pre-adsorbed hydrogen atoms

5

could stablize the M/Pt(111) structures at high concentration. In this condition, the electronic

6

environmental of the surface layer will be changed, which indirectly affects the adsorption strength of

7

the adsorbates. Moreover, the pre-adsorbed hydrogen atoms could also influence the E a eff that is the

8

dominant factor controlling the TOF. Above all, the volcano-like relationship between the TOF° and

9

the co-adsorption energy of the hydrogenation reactants could supply some clues for designing the

10

Pt-based sandwich structure catalysts: it may be a potential hydrogen catalyst, in case the

11

corresponding adsorption energy is within -0.4~-1.6 eV.

12 13

Supporting Information

14

The Supporting Information is available free of charge via the Internet at http://pubs.acs.org.

15

Influence of the K-points, vacuum and plane wave cutoff, The van der Waals corrections, entropy

16

effect and zero point energy corrections to the activation energy, Configurations of the adsorbates,

17

models of Pt x Cu 8-x /Pt 8-x Cu x /Pt (111) (x=1, 2, 3, 4, 5, 6, 7, 8) and pathways on the Pt/Ni (111) and

18

Pt 4 Cu 5 /Pt (111).

19 20 21

Acknowledgements This work was supported by the National Natural Science Foundation of China (Grants No.

22

20273034，20673063). The work was carried out at National Supercomputer Center in Tianjin, and

23

the calculations were performed on TianHe-1(A).

24 30


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1

References and Notes

2

[1] Sachtler, J. W. A.; Van Hove, M. A.; Biberian, J. P.; Somorjai, G. A. Enhanced reactivity of

3

ordered monolayers of gold on Pt (100) and platinum on Au (100) single-crystal surfaces. Phys. Rev.

4

Lett. 1980, 45, 1601–1603.

5

[2] Ma, H. Y.; Shang, Z. F.; Xu, W. G.; Wang, G. C. Cyclohexene dehydrogenation to produce benzene

6

on nAu/Pt(100) and nPt/Au(100) (n = 0, 1, 2) surfaces from a first-principles study. J. Phys. Chem. C

7

2012, 116, 9996–10008.

8

[3] Vigné, F.; Haubrich, J.; Loffreda, D.; Sautet, P.; Delbecq, F. Highly selective hydrogenation of

9

butadiene on Pt/Sn alloy elucidated by first-principles calculations J. Catal. 2010, 275, 129–139.

10

[4] Kolli, N. E.; Delannoy, L.; Louis, C. Bimetallic Au–Pd catalysts for selective hydrogenation of

11

butadiene: Influence of the preparation method on catalytic properties. J. Catal. 2013, 297, 79–92.

12

[5] Loffreda, D.; Michel, C.; Delbecq, F.; Sautet, P. Tuning catalytic reactivity on metal surfaces:

13

Insights from DFT. J. Catal. 2013, 308, 374–385.

14

[6] Jiang, Z.; Wan, W.; Lin, Z.; Xie. J.; Chen, J.G. Understanding the role of M/Pt (111)(M= Fe, Co,

15

Ni, Cu) bimetallic surfaces for selective hydrodeoxygenation of furfural. ACS Catal. 2017,

16

7, 5758–5765.

17

[7] Wang. C.; Luo, J.; Liao, V.; Lee J. D.; Onn, T. M.; Murray, C. B.; Gorte, R. J. A comparison of

18

furfural hydrodeoxygenation over Pt-Co and Ni-Fe catalysts at high and low H 2 pressures.Catal. Today,

19

2018, 302, 73–79.

20

[8] Marcinkowski, M. D.; Darby, M. T.; Liu, J.; Wimble, J. M.; Lucci, F. R.; Lee, S.; Michaelides, A.;

21

Flytzani-Stephanopoulos, M.; Stamatakis, M; Sykes, E. C. H. Pt/Cu single-atom alloys as

22

coke-resistant catalysts for efficient C – H activation. Nature Chem. 2018, 10, 325–332.

23

[9] Peck, J. W.; Koel, B. E. Selective dehydrogenation of 1, 3-cyclohexadiene on ordered Sn/Pt (111) 31



Page 32 of 38

1

surface alloys. J. Am. Chem. Soc. 1996, 118, 2708–2717.

2

[10] Ma, H. Y.; Wang, G. C. Theoretical study of 1, 3-cyclohexadiene dehydrogenation on Pt (1 1 1),

3

Pt 3 Sn/Pt (1 1 1), and Pt 2 Sn/Pt (1 1 1) surfaces. J. Catal. 2011, 281, 63–75.

4

[11] Humbert, M. P.; Chen, J. G.Correlating hydrogenation activity with binding energies of hydrogen

5

and cyclohexene on M/Pt(111) (M = Fe, Co, Ni, Cu) bimetallic surfaces. J. Catal. 2008, 257, 297–306.

6

[12] Khan, N. A.; Zellner, M. B.; Murillo, L. E.; Chen, J. G.A comparison of similarities and

7

differences in the activities of Pt/Ni(111) and Ni/Pt(111) surfaces. Catal. Lett. 2004, 95, 1–6.

8

[13] Khan, N. A.; Murillo, L. E.; Chen, J. G. Observation of novel low-temperature hydrogenation

9

activity on Co/Pt(111) surfaces. J. Phys. Chem. B 2004, 108, 15748–15754.

10

[14] Dupont, C.; Jugnet, Y.; Loffreda, D. Theoretical evidence of PtSn alloy efficiency for CO

11

oxidation. J. Am. Chem. Soc. 2006, 128, 9129–9136.

12

[15] Stassi, J. P.; Zgolicz, P. D.; de Miguel, S. R.; Scelza, O. A. Formation of different promoted

13

metallic phases in PtFe and PtSn catalysts supported on carbonaceous materials used for selective

14

hydrogenation. J. Catal. 2013, 306, 11–29.

15

[16] Zhang, H.; Watanabe, T.; Okumura, M.; Haruta, M.; Toshima, N. Crown jewel catalyst: How

16

neighboring atoms affect the catalytic activity of top Au atoms? J. Catal. 2013, 305, 7–18.

17

[17] Sun, J.; Karim, A. M.; Zhang, H.; Kovarik, L.; Li, X. S.; Hensley, A. J.; McEwen, J. S.; Wang, Y.

18

Carbon-supported bimetallic Pd–Fe catalysts for vapor-phase hydrodeoxygenation of guaiacol. J.

19

Catal. 2013, 306, 47–57.

20

[18] Han, S.; Evans, E. J. Jr; Mullen, G. M.; Mullins, C. B. H 2 O-improved O 2 activation on the Pd–Au

21

bimetallic surface. Chem. Commun., 2017, 53, 3990–3993.

22

[19] Collinge, G.; Kruse, N.; McEwen, J. S. Role of Carbon monoxide in catalyst reconstruction for

23

CO hydrogenation: first-principles study of the composition, structure, and stability of Cu/Co(101̅2) as 32


Page 33 of 38 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


1

a function of CO pressure. J. Phys. Chem. C 2017, 121, 2181–2191.

2

[20] Esan, D. A.; Trenary, M. Selective hydrogenation of acrolein to propanal on a pseudomorphic

3

Pt/Ru(001) bimetallic surface. Top Catal, 2017,1–10.

4

[21] Zhang, M.; Yao, R.; Jiang, H.; Li, G.; Chen Y. Catalytic activity of transition metal doped Cu(111)

5

surfaces for ethanol synthesis from acetic acid hydrogenation: a DFT study. RSC Adv., 2017, 7,

6

1443–1452.

7

[22] Chen, H.; He, D.; He, Q.; Jiang, P.; Zhou, G.; Fu. W. Selective hydrogenation of p

8

–chloronitrobenzene over an Fe promoted Pt/AC catalyst. RSC Adv., 2017, 7, 29143–29148.

9

[23] Singh, J. A.; Yang, N.; Liu, X.; Tsai, C. Stone, K. H.; Johnson, B.; Koh, A. L.; Bent, S. F.

10

Understanding the active sites of CO hydrogenation on Pt–Co catalysts prepared using atomic layer

11

deposition. J. Phys. Chem. C 2018, 122, 2184–2194.

12

[24] Ro. I.; Aragao. I. B.; Chada, J. P.; Liu, Y.; Rivera-Dones, K. R.; Ball, M. R.; Zanchet, D.;

13

Dumesic, J. A.; Huber, G. W. The role of Pt-Fe x O y interfacial sites for CO oxidation. J. Catal. 2018,

14

358, 19–26.

15

[25] Tsai, M.C.; Friend, C.M.; Muetterties, E.L. Dehydrogenation processes on nickel and platinum

16

surfaces. conversion of cyclohexane, cyclohexene, and cyclohexadiene to benzene. J. Am. Chem.

17

Soc. 1982, 104, 2539–2543.

18

[26] Papp, C.; Denecke, R.; Steinrück, H. P. Adsorption and reaction of cyclohexene on a Ni(111)

19

surface. Langmuir, 2007, 23, 5541–5547.

20

[27] Su, X.; Kung, K.; Lahtinen, J.; Shen, R. Y.; Somorjai, G. A. Cyclohexene dehydrogenation and

21

hydrogenation on Pt(111) monitored by SFG surface vibrational spectroscopy: different reaction

22

mechanisms at high pressures and in vacuum. Catal. Lett. 1998, 54, 9–15.

23

[28] Bratlie, K. M.; Montano, M. O.; Flores, L. D.; Paajanen, M.; Somorjai, G. A. Sum frequency 33



Page 34 of 38

1

generation vibrational spectroscopic and high-pressure scanning tunneling microscopic studies of

2

benzene hydrogenation on Pt(111). J. Am. Chem. Soc., 2006, 128, 12810–12816.

3

[29] Ruban, A. V.; Skriver, H. L.; Nørskov, J. K. Surface segregation energies in transition-metal

4

alloys. Phys. Rev. B 1999, 59, 15990–16000.

5

[30] Nilekar, A. U.; Ruban, A. V.; Mavrikakis, M. Surface segregation energies in low-index open

6

surfaces of bimetallic transition metal alloys. Surf. Sci. 2009, 603, 91–96.

7

[31] Kitchin, J. R.; Nørskov, J. K.; Barteau, M. A.; Chen, J. G. Modification of the surface electronic

8

and chemical properties of Pt(111) by subsurface transition metals. J. Chem. Phys. 2004, 120,

9

10240–10246.

10

[32] Kresse, G.; Furthmüller, J. Efficiency of ab-initio total energy calculations for metals and

11

semiconductors using a plane-wave basis set. Comput. Mater. Sci. 1996, 6, 15–50.

12

[33] Kresse, G.; Furthmüller, Efficient iterative schemes for ab initio total-energy calculations using a

13

plane-wave basis set. Phys. Rev. B 1996, 54, 11169–11186

14

[34] Perdew, J.P.; Wang, Y. Accurate and simple analytic representation of the electron-gas correlation

15

energy. Phys. Rev. B 1992, 45, 13244–13249.

16

[35] Kresse, G.; Joubert, D. From ultrasoft pseudopotentials to the projector augmented-wave method.

17

Phys. Rev. B 1999, 59, 1758–1775.

18

[36] Blöchl, P. E. Projector augmented-wave method. Phys. Rev. B 1994, 50, 17953–17979.

19

[37] Monkhorst, H. J.; Pack, J. D. Special points for brillouin-zone integrations. Phys. Rev. B 1976, 13,

20

5188–5192.

21

[38] Elsässer, C.; Fähnle, M.; Chan, C. T.; Ho, K. M. Density-functional energies and forces with

22

Gaussian-broadened fractional occupations. Phys. Rev. B 1994, 49, 13975–13978.

23

[39] Kitchin, J. R.; Khan, N. A.; Barteau, M. A.; Chen, J. G.; Yakshinskiy, B.; Madey, T. E. Elucidation 34


Page 35 of 38 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


1

of the active surface and origin of the weak metal–hydrogen bond on Ni/Pt(1 1 1) bimetallic surfaces:

2

a surface science and density functional theory study. Surf. Sci. 2003, 544, 295–308.

3

[40] Gauthier, Y.; Schmid, M.; Padovani, S.; Lundgren, E.; Buš, V.; Kresse, G.; Redinger, J.; Varga, P.

4

Adsorption sites and ligand effect for CO on an alloy surface: A direct view. Phys. Rev. Lett. 2001, 87,

5

036103(4).

6

[41] Grimme, S. Semiempirical GGA–type density functional constructed with a long-range dispersion

7

correction. J. Comput. Chem. 2006, 27, 1787–1799.

8

[42] Henkelman, G.; Jonsson, H. Improved tangent estimate in the nudged elastic band method for

9

finding minimum energy paths and saddle points. J. Chem. Phys. 2000, 113, 9978–9985.

10

[43] Trinh, Q. T.; Nguyen, A. V.; Huynh, D. C.; Pham, T. H.;Mushrif, S.H. Mechanistic insights into

11

the catalytic elimination of tar and the promotional effect of boron on it: first-principles study using

12

toluene as a model compound. Catal. Sci. Technol.2016, 6, 5871–5883.

13

[44] Rodriguez, J. A.; Campbell, C. T. Probing ensemble effects in surface reactions. 3. Cyclohexane

14

adsorption on clean and bismuth-covered platinum (111). J. Phys. Chem. 1989, 93, 826–835.

15

[45] Lytken, O.; Lew, W.; Campbell, C. T. Catalytic reaction energetics by single crystal adsorption

16

calorimetry: hydrocarbons on Pt (111). Chem. Soc. Rev., 2008, 37, 2172–2179.

17

[46] Hammer, B.; Nørskov, J. K. Theoretical surface science and catalysis—calculations and concepts.

18

Adv. Catal. 2000, 45, 71–129.

19

[47] Morin, C.; Simon, D.; Sautet, P. Chemisorption of benzene on Pt (111), Pd (111), and Rh (111)

20

metal surfaces: a structural and vibrational comparison from first principles. J. Phys. Chem. B 2004,

21

108, 5653–5665.

22

[48] Morin, C.; Simon, D.; Sautet, P. Trends in the chemisorption of aromatic molecules on a Pt (111)

23

surface: benzene, naphthalene, and anthracene from first principles calculations. J. Phys. Chem. B 35



Page 36 of 38

1

2004, 108, 12084–12091.

2

[49] Menning, C.A.; Chen, J.G. General trend for adsorbate-induced segregation of subsurface metal

3

atoms in bimetallic surfaces. J. Chem. Phys. 2009,130, 174709.

4

[50] Greeley, J.; Mavrikakis, M. Alloy catalysts designed from first principles. Nature Mater. 2004, 3,

5

810–815.

6

[51] Trinh, Q.T.; Yang, J.; Lee, J.Y.; Saeys, M. Computational and experimental study of the Volcano

7

behavior of the oxygen reduction activity of PdM@PdPt/C (M= Pt, Ni, Co, Fe, and Cr) core–shell

8

electrocatalysts. J. Catal., 2012, 291, 26–35.

9

[52] Barrett, N. T.; Belkhou, R.; Thiele, J.; Guillot, C. A core-level photoemission spectroscopy study

10

of the formation of surface alloy CuPt (111): comparison with PtCu (111). Surf. Sci. 1995, 331–333,

11

776–781.

12

[53] Belkhou, R.; Barrett, N. T.; Guillot, C.; Fang, M.; Barbier, A.; Eugène, J.; Carrière, B.; Naumovic,

13

D.; Osterwalder, J. Formation of a surface alloy by annealing of Pt/Cu(111). Surf. Sci. 1993, 297,

14

40–56.

15

[54] Uhe, A.; Kozuch, S.; Shaik, S. Automatic analysis of computed catalytic cycles. J. Comput. Chem.

16

2011, 32, 978–985.

17

[55] Deckers, S.; Offerhaus, S.; Habraken, F.; van der Weg, W. Initial growth and surface alloy

18

formation of Pt on Ni(111). Surf. Sci. 1990, 237, 203–212.

19

[56] Gauthier, Y.;

20

alloy surfaces: structure and composition in relation to some catalytic properties. Surf. Sci. 1985, 162,

21

342–347.

22

[57] Hwu, H. H.; Eng, J., Jr.; Chen, J. G. Ni/Pt (111) bimetallic surfaces: unique chemistry at

23

monolayer Ni coverage. J. Am. Chem. Soc. 2002, 124, 702–709.

Baudoing, R.; Joly, Y.; Rundgren, J.; Bertolini, J. C.; Massardier, J. Pt x Ni 1− x (111)

36


Page 37 of 38 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


1

[58] Fan, C.; Zhu, Y. A.; Zhou, X. G.; Liu, Z. P. Catalytic hydrogenation of benzene to cyclohexene on

2

Ru (0 0 0 1) from density functional theory investigations. Catal. Today 2011, 160, 234–241.

3

[59] Wang, Y. F.; Li, K.; Wang, G.C. Formic acid decomposition on Pt 1 /Cu (111) single platinum

4

atomcatalyst: Insights from DFT calculations and energetic span modelanalysis. Appl. Surf. Sci. 436,

5

2018, 631–638.

6

[60] Barin, I. Thermochemical Data of Pure Substances; VCH Verlag, Weinheim, 1995.

7

[61] Kozuch, S.; Martin, J. M. L. “Turning over” definitions in catalytic cycles. ACS Catal. 2012, 2,

8

2787–2794.

9

[62] Gu, X.-K.; Liu, B.; Greeley, J. First-principles study of structure sensitivity of ethylene glycol

10

conversion on platinum. ACS Catal. 2015, 5, 2623−2631.

11

[63] Trinh, Q. T.; Chethana, B. K.; Mushrif, S. H. Adsorption and Reactivity of Cellulosic Aldoses on

12

Transition Metals. J. Phys. Chem. C 2015, 119, 17137−17145.

13

[64] Gokhale, A. A.; Kandoi, S.; Greeley, J. P.; Mavrikakis, M.; Dumesic, J. A. Molecular-level

14

descriptions of surface chemistry in kinetic models using density functional theory. Chem. Eng. Sci.

15

2004, 59, 4679–4691.

16

[65] Liu, B.; Greeley, J. Decomposition pathways of glycerol via C-H, O-H, and C-C bond scission on

17

Pt(111): A density functional theory study. J. Phys. Chem. C 2011, 115, 19702–19709.

18

[66] Blaylock, D. W.; Ogura, T.; Green, W. H.; Beran, G. J. O. Computational investigation of

19

thermochemistry and kinetics of steam methane reforming on Ni(111) under realistic conditions. J.

20

Phys. Chem. C 2009, 113, 4898–4908.

21

[67] Humbert, M. P.; Menning, C. A.; Chen, J. G. Replacing bulk Pt in Pt–Ni–Pt bimetallic structures

22

with tungsten monocarbide (WC): Hydrogen adsorption and cyclohexene hydrogenation on

23

Pt–Ni–WC. J. Catal. 2010, 271, 132–139. 37



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