IR Spectroscopic Evidence for MoS 2 Morphology Change with Sulfidation Temperature on MoS 2 /Al 2 O 3 Catalyst

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Article

IR Spectroscopic Evidence for MoS2

Morphology Changewith Sulfidation Temperature on MoS

2

/Al2

O3

CatalystJianjun Chen, Vincent Labruyère, Francoise Mauge, Anne-

Agathe Quoineaud, Antoine Hugon, and Laetitia OlivieroJ. Phys. Chem. C, Just Accepted Manuscript • Publication Date (Web): 19 Nov 2014

Downloaded from http://pubs.acs.org on November 20, 2014

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1

IR Spectroscopic Evidence for MoS2 Morphology Change with

Sulfidation Temperature on MoS2/Al2O3 Catalyst

Jianjun Chen1, Vincent Labruyere

2, Francoise Mauge

1, Anne-Agathe Quoineaud

2, Antoine Hugon

2, Laetitia

Oliviero1*

1. Laboratoire Catalyse et Spectrochimie, ENSICAEN, Université de Caen Basse Normandie, CNRS, 6, bd du

Maréchal Juin, 14050 Caen, France

2. IFP Energies nouvelles, Rond-Point de l’Echangeur de Solaize, BP 3, 69360 Solaize, France

Abstract: Low temperature CO adsorption followed by IR spectroscopy (IR/CO)

characterization was used to depict the MoS2 morphology change with sulfidation temperature on

MoS2/Al2O3 catalyst. It is found that the morphology of MoS2 slabs on MoS2/Al2O3 catalyst under

typical sulfidation temperature range (573 to 723 K) is truncated triangle exposing both M-edge

and S-edge. Moreover, the IR/CO data indicates that the truncation degree (ratio of S-edge/M-edge)

of MoS2 slabs gradually increases with increasing sulfidation temperature. This finding is in lines

with Density Functional Theory (DFT) calculation on model catalyst, providing the IR evidence

of MoS2 morphology change with sulfidation temperature on Al2O3-supported catalyst. As a

further step, it is also found that the MoS2 morphology is strongly influenced by MoS2-Al2O3

interactions under the same sulfidation temperature.

Keywords: Hydrodesulfurization (HDS), Molybdenum disulfide (MoS2), Slab morphology, S- and

M- edges, truncation degree, CO adsorption.

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1 Introduction

Co (or Ni)-promoted MoS2/Al2O3 catalysts have been for many years the most important

hydrotreatment catalysts in petroleum refinery. The active phase of these catalysts is obtained by

sulfiding the oxidic precursors with a gas phase H2S/H2 mixture or a feedstock of organic sulfur

compound at the temperature range of 573 to 723 K 1. Sulfidation temperature, which is of crucial

importance to the hydrotreatment catalysts, has strong influences on the active phase structure and

catalytic performance of the Co (or Ni)-promoted MoS2/Al2O3 catalysts 2-4

.

With DFT (density functional theory) calculations Raybaud and co-workers 5, 6

recently made

an important progress in understanding the effect of sulfidation temperature on MoS2-based

catalysts. In their studies, they found that the morphology of MoS2 slabs, i.e. the relative

concentration of M-edge and S-edge exposed, is controlled by the pseudo chemical potential of

sulfur that is a function of sulfidation temperature and partial pressure ratio of H2S and H2

(PH2S/PH2). Therefore, it is expected according to these DFT calculations that variation of

sulfidation temperature may lead to morphology change of MoS2 slabs. This is of great importance

to the performance of Co(or Ni)-promoted MoS2/Al2O3 catalysts, as it is proposed that the Co(or Ni)

promoters have different affinity to M-edge and S-edge 7-10

, and that CoMoS sites located at

different edges have distinct intrinsic activity11-13

. Although the MoS2 morphology change with

PH2S/PH2 has been imaged by Lauritsen et al. 14

using STM (scanning tunneling microscopy) on

Au-supported MoS2 model catalyst prepared by a special procedure under ultra-high vacuum

(UHV) conditions, the direct experimental evidence of MoS2 change with sulfidation temperature

on MoS2/Al2O3 catalyst is still lacking. Moreover, the isolated character of Al2O3 makes STM

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investigation of MoS2 morphology change on Al2O3 support extremely difficult.

As a proven technique, low-temperature CO adsorption followed by infrared spectroscopy

(IR/CO) is intensively used to probe the edges sites of MoS2 slabs on MoS2/Al2O3 catalysts. It has

been observed by IR/CO that there are distinctly two different CO adsorption bands located at

~2110 and ~2070 cm-1

on MoS2 edges 15, 16

. Combining experimental infrared spectra and

theoretical DFT calculations, Travert et al. 17, 18

well established that the v(CO) bands located at

~2110 cm-1

and ~2070 cm-1

are respectively attributed to CO adsorption on M-edge and S-edge of

MoS2 slabs. These attributions correspond to monocarbonyl adsorption on 6 coordinated Mo atoms

with 50% S-coverage on M-edge and 100% S-coverage on S-edge. In addition, a quantitative

evaluation of the M-edge and S-edge concentrations on MoS2/Al2O3 catalysts can be obtained after

determination of the integrated molar extinction coefficient of CO adsorbed on each edge (ref.19

and Supplementary Information). Recently, this IR/CO technique has been used successfully to

characterize the effect of citric acid addition on MoS2 morphology of MoS2/Al2O3 catalysts

allowing the determination of the intrinsic activity of sites from each edge20

.

In this paper, we use IR/CO to investigate the MoS2 morphology change with sulfidation

temperature on MoS2/Al2O3 catalysts. For this purpose, two types of Mo/Al2O3 catalysts with

monolayer Mo loading were prepared by conventional impregnation in the presence and absence of

citric acid. Citric acid was used as chelating agent to reduce the slab-support interactions after

sulfidation 21, 22

, expecting a clearer IR spectroscopic evidence of MoS2 morphology change with

sulfidation temperature20, 23

. The objective of this study is to verify the DFT prediction on MoS2

morphology change with sulfidation temperature, bringing the experimental evidence of such

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morphology change on MoS2/Al2O3 catalyst, which was used as a base of industrial hydrotreatment

catalyst.

2 Experimental

2.1 Catalyst preparation

Two types of Mo/Al2O3 catalysts were prepared by an one-step pore volume impregnation

method in the presence or absence of citric acid (CA). The impregnation solutions were firstly

prepared with or without citric acid (CA, C6H8O7.H2O, PROLABO) and ammonium

heptamolybdate tetrahydrate (AHT, (NH4)6Mo7O24.4H2O, MERCK). Sequentially, the pretreated

γ-Al2O3 support (Sasol, specific surface area of 252m2

/g and pore volume of 0.84mL/g,

pre-calcined in air at 723K for 2 hours) was added into the solutions and strongly shaken for 2

hours. Finally the catalysts were dried at 383K for 3 hours. Note that these catalysts were not

calcined in order to keep the citric acid in its initial form. Hereinafter, the Mo/Al2O3 catalysts

prepared with and without CA are denoted as Mo(CA)/Al2O3 and Mo/Al2O3, respectively. The Mo

content was kept at 0.19 mmol per gram Al2O3 support (corresponding to monolayer Mo) for each

catalyst, and the molar ratio of CA/Mo is 2 for Mo(CA)/Al2O3 catalyst.

2.2 Infra Red (IR) spectroscopy characterization

The IR characterization was performed on a newly designed system called CellEx 24

. The

CellEx mainly consists of three parts: (i) a stainless steel reactor for catalyst sulfidation under

different temperature, pressure and gas phase; (ii) an IR cell equipped with a spectrometer for

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spectroscopic characterization; and (iii) a transfer connection between the reactor and IR cell for

transferring sample under protecting of inert gas. With the CellEx, the catalysts can be activated

under different conditions and sequentially in situ characterized by IR spectroscopy without any air

pollution.

2.2.1 Catalyst sulfidation

Catalyst sulfidation were performed in the stainless reactor of CellEx 24

. Catalyst sample was

firstly grounded and pressed into self-supporting pellet of ~8 mg/cm2 (precisely weighted). The

pellet was introduced into the reactor that was then evacuated to 1.33 Pa to remove the air. After

that the pellet was sulfided in a flow of 30 mL/min H2S/H2 (10%). The sulfidation temperature was

reached at 3 K/min and maintained for 2 hours. Sequentially, the pellet was flushed with Ar and

then cooled down to room temperature under Ar. Finally, the sulfided pellet was transferred under

Ar to the IR cell for IR characterization.

2.2.2 Low-temperature CO adsorption followed by IR spectroscopy (IR/CO)

After the above-described sulfidation, the catalyst was firstly evacuated in the IR cell under

vacuum at 623 K (or at the sulfidation temperature if the pellet was sulfided at temperature lower

than 623 K) and kept for 1 hour with the final pressure to 10-3

Pa. After evacuation, the catalyst was

cooled down by liquid nitrogen to 100K for CO adsorption. CO adsorption was performed by

introducing small calibrated doses (0.8852 cm3) of CO at different pressures (0.03 ~1.20 µmol of

CO) and finally with 133 Pa CO at equilibrium in the IR cell. IR spectra of adsorbed CO were

recorded with a Nicolet spectrometer (Nexus) equipped with a MCT detector with 256 scans and 4

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cm-1

resolution. For comparison, all the spectra presented were normalized to a sulfided catalyst

pellet of 5 mg/cm2.

The concentration of each type of edge sites was obtained after spectral decomposition

performed on Peakfit V4.12 using “Autofit peak II—Second derivative Methods”. In spectral

decomposition, the center and full width at half height (FWHH) of the generated peaks were

allowed varying in fixed small range. The molar extinction coefficient of CO adsorbed on M-edge

(εεεεM-edge) was determined in the IR cell by introducing small doses of CO onto the 623 K sulfided

Mo/Al2O3 catalyst at liquid nitrogen temperature (100 K). The molar extinction coefficient of CO

adsorbed on S-edge (εεεεS-edge) was determined by subtracting the contribution of M-edge from the

spectra obtained after introducing small doses of CO onto the 623 K sulfided Mo(CA)/Al2O3

catalyst at liquid nitrogen temperature (100 K). The determined εεεεM-edge and εεεεS-edge are 20±3

µmol-1

.cm and 35±9 µmol-1

.cm, respectively. Details for spectral decomposition, εεεεM-edge and εεεεS-edge

determination, and edge concentration calculation are given in Supplementary Information.

3 Results

2250 2200 2150 2100 2050 2000 1950

(2069)

CO/S-edge

Adso

rba

nce

(a

.u.)

Wavenumber (cm-1)

0.05

623K

573K

723K

(2111)

(2155)

(2189) (2065)

CO/Al3+

CO/OH

CO/M-edge

(2113)

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Figure 1: IR spectra of CO adsorbed (133 Pa at equilibrium, 100 K) on Mo/Al2O3 catalyst sulfided with 10% H2S/H2 at

different temperatures

The Mo/Al2O3 catalyst was sulfided with 10% H2S/H2 at different temperatures (573, 623, and

723 K) and then in situ characterized by IR/CO. The obtained IR spectra of CO adsorption (133 Pa

at equilibrium, 100 K) are shown in Figure 1. On the Mo/Al2O3 catalyst sulfided with different

temperature, a quite strong CO adsorption band located at ~2111 cm-1

is recorded, which is

attributed to CO adsorption on M-edge of MoS2 phase 17, 18, 25

. Another two bands located at ~2189

and ~2155 cm-1

are also observed, which are assigned to CO adsorption on Al2O3 support 17, 18, 25

.

In addition, a shoulder band at ~2065 cm-1

is also detected, which is associated to CO adsorption on

S-edge of MoS2 slabs 17, 18, 25

. With increasing sulfidation temperature, the υ(CO) band on M-edge

(band at ~2111 cm-1

) is gradually decreased while the shoulder band attributed to CO adsorption on

S-edge (band at ~2065 cm-1

) slightly becomes clearer.

Besides the CO adsorption band intensity, as shown in Figure 1, the CO adsorption band

position on M-edge and S-edge also varies with sulfidation temperature. When the sulfidation

temperature increases from 573 to 723 K, the CO adsorption band on M-edge is gradually

upward-shifted from 2111 to 2113 cm-1

and that on S-edge is shifted from 2065 to 2069 cm-1

. The

increase of sulfidation temperature also leads to an upward shift of the CO adsorption band on OH

groups indicating an increase of their Brønsted acidity which can be explained by a partial

deshydroxylation in accordance with the concomitant decrease of the associated band area26

.

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2250 2200 2150 2100 2050 2000 1950

(2183)

(2152)

(2064)

(2108)0.05

Ad

sorb

an

ce

Wavenumber

573K

623K

723K

CO/Al3+

CO/OH CO/M-edge

CO/S-edge

(2111) (2068)

Figure 2: IR spectra of CO adsorbed (133 Pa at equilibrium, 100 K) on Mo(CA)/Al2O3 catalyst sulfided with 10%

H2S/H2 at different temperatures

The same experiments were performed on the Mo(CA)/Al2O3 catalyst and the obtained IR

spectra of low-temperature CO adsorption (133 Pa at equilibrium, 100 K) on this catalyst are

shown in Figure 2. On the 573 K sulfided Mo(CA)/Al2O3 catalyst, the υ(CO) band on M-edge

(band at 2108 cm-1

) is recorded with high intensity with a broad width. Meanwhile, the υ(CO) band

on S-edge (band at 2064 cm-1

) is observed as an ill-defined shoulder. On this sample and for this

lower temperature, the CO adsorption band on Al3+

sites is much lower than for the other sample

and than for the higher sulfidation temperatures. It can be thus proposed that part of Al3+

sites are

covered by citric acid residuals after sulfidation at 573K. With increasing sulfidation temperature,

the intensity of υ(CO) band on M-edge is decreased whereas the CO adsorption band on S-edge

becomes more pronounced. On the 723 K sulfided sample, the intensity of the υ(CO) band on

S-edge is even higher than that on M-edge.

Like for Mo/Al2O3 catalyst, the υ(CO) band position on M-edge and S-edge also varies with

sulfidation temperature on Mo(CA)/Al2O3 catalyst. The CO adsorption band on M-edge is

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upward-shifted from 2108 to 2111 cm-1

and that on S-edge is shifted from 2064 to 2068 cm-1

with

increasing sulfidation temperature. Meanwhile, the CO adsorption band on OH groups is decreased

and upward shifted. Like proposed for the Mo/Al2O3 catalyst, it would indicate an increased

Brønsted acidity due to partial deshydroxylation 26

.

560 580 600 620 640 660 680 700 720 740

0

20

40

60

80

100

120

140

560 580 600 620 640 660 680 700 720 740

0

20

40

60

80

100

120

140

S-edge/M-edge

(A) Mo/Al2O

3

Ed

ge c

on

ce

ntr

ation

(µ

mo

l/g

cata

lyst)

Sulfidation temperature (K)

M-edge

S-edge

0.0

0.2

0.4

0.6

0.8

1.0

Ra

tio

of

S-e

dge

/M-e

dge

Ed

ge c

on

ce

ntr

ation

(µ

mo

l/g

cata

lyst)

Sulfidation temperature (K)

M-edge

S-edge

S-edge/M-edge

0.0

0.2

0.4

0.6

0.8

1.0

(B) Mo(CA)/Al2O

3

Ra

tio

of

S-e

dge

/M-e

dge

Figure 3: M-edge and S-edge site concentration detected by low-temperature CO adsorption (dash line) and the ratio of

S-edge/M-edge (solid line) on (A) Mo/Al2O3 and (B) Mo(CA)/Al2O3 catalyst sulfided with different temperature

The obtained IR spectra were further decomposed using the software Peakfit V4.12 and the

concentration of M-edge and S-edge was calculated after determining the molar adsorption

coefficient of CO adsorption on each edge (details in Supplementary Information). As shown in

Figure 3 (A), the concentration of M-edge detected by low-temperature CO adsorption on

Mo/Al2O3 catalyst declines with increasing sulfidation temperature. The concentration of S-edge

on this catalyst is much lower than that of M-edge. With increasing temperature, the S-edge

concentration first slightly decreases and then level off. Nevertheless, the concentration ratio of

S-edge/M-edge is steadily increased with sulfidation temperature.

Figure 3 (B) illustrates the M-edge and S-edge concentration as well as the S-edge/M-edge

ratio on Mo(CA)/Al2O3 catalyst sulfided at different temperature. Like that on Mo/Al2O3 catalyst,

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the M-edge and S-edge concentration declines with increasing sulfidation temperature. Meanwhile,

the S-edge/M-edge ratio is also increased with increasing temperature. In addition, on

Mo(CA)/Al2O3 catalyst the concentration of S-edge is strongly enhanced, which becomes

comparable with that of M-edge. Thus, the S-edge/M-edge ratio on this catalyst is much higher

than that on Mo/Al2O3 catalyst.

Considering that the ratio of M-edge and S-edge for a single MoS2 slab is in line with the

overall ratio of each edge detected by IR/CO, a schematic diagram of MoS2 morphology on

Mo/Al2O3 and Mo(CA)/Al2O3 catalyst was depicted in Figure 3. First, the present IR spectroscopic

data shows that the morphology of MoS2 phase on both Mo/Al2O3 and Mo(CA)/Al2O3 catalyst is

truncated triangle exposing both M-edge and S-edge. Secondly, the truncation degree of MoS2

slabs on Mo(CA)/Al2O3 catalyst is much higher than that on Mo/Al2O3 catalyst, indicating that

addition of citric acid leads to the MoS2 phase exposing relatively more S-edge, as previously

observed20

. Thirdly, the truncation degree of MoS2 slabs steadily increases with increasing

sulfidation temperature on both Mo/Al2O3 and Mo(CA)/Al2O3 catalyst, demonstrating that

sulfidation temperature influences the morphology of MoS2 slabs on Al2O3-supported catalysts.

4 Discussion

In this work, low-temperature CO adsorption followed by IR spectroscopy (IR/CO) was used

to probe the concentration of M-edge and S-edge sites on Mo/Al2O3 and Mo(CA)/Al2O3 catalyst

sulfide with different temperature. First of all, it is found that the concentration of M-edge and

S-edge sites decreases with increasing sulfidation temperature on both Mo/Al2O3 and

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Mo(CA)/Al2O3 catalyst (Figure 3). The decrease of M-edge and S-edge concentration detected by

CO adsorption can be attributed to the decrease in dispersion of MoS2 phase with increasing

sulfidation temperature. This is in agreements with previous studies with other techniques, such as

NO adsorption 3 and HRTEM (high resolution transmission electron microscopy) study.

2. To

further verify such results, TEM was also performed on the Mo/Al2O3 catalyst and a general

increase of slab length and stacking was observed by TEM (more details in Supplementary

Information).

Another result obtained from IR/CO characterization is that the ratio of S-edge/M-edge

steadily increases with increasing sulfidation temperature on both Mo/Al2O3 and Mo(CA)/Al2O3

catalyst (Figure 3). We consider this result as a strong indication of MoS2 morphology change with

sulfidation temperature on these two catalysts. This consideration is taken based on the statistic

assumption that the ratio of S-edge/M-edge on a single MoS2 slab is in line with the overall ratio of

each edge detected by CO adsorption. Moreover, this ratio is hardly affected by other MoS2

characteristics such as slab length and stacking, although these characteristics are also changed

with sulfidation temperature (ref.2, 3

and Supplementary Information).

It should be stressed that the fine structure of MoS2 edges is supposed to differ with sulfidation

temperature, which will also influence the CO adsorption on M-edge and S-edge. However, the

change of MoS2 edge fine structure with sulfidation temperature cannot result in the increase of

S-edge/M-edge ratio observed in this study. Indeed, previous studies 14, 27-29

proposed that the

sulfur and hydrogen coverage on MoS2 edges varies with a pseudo chemical potential of sulfur

(∆µS) that is a function of temperature and PH2S/PH2. For the sulfidation conditions used in our work,

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the ∆µS is then determined according to Ref. 30

and is reported in Table 1. It appears that the

chemical potential of sulfur corresponding to the sulfidation conditions used in this work only

varies in a small range: it decreases from -0,80 eV to -0.95 eV with increasing temperature from

573 to 723 K. In this range, the sulfur coverage on both M-edge and S-edge should stay constant

with 50% on both edges according to DFT calculations 5. Meanwhile, this decrease of chemical

potential of sulfur should lead to an increase of hydrogen coverage on MoS2 edges 14, 28

, which may

partially (together with decrease of MoS2 edge dispersion) account for the decrease of M-edge and

S-edge concentration detected by CO adsorption. However, several investigations suggested that H

adsorbs more strongly on S-edge than M-edge 31-34

, which will result in a more significant decrease

of CO adsorption intensity on S-edge than that on M-edge and cannot lead to the IR/CO result that

the ratio S-edge/M-edge steadily increases with increasing sulfidation temperature. Thus, the

increase of S-edge/M-edge ratio is a convincing evidence of MoS2 morphology change although

the fine structure of MoS2 edges such as hydrogen coverage may increase with sulfidation

temperature.

Table 1: MoS2 morphology revealed by IR/CO experiments and predicted by DFT calculations in the sulfidation

temperature range in this work

Catalysts/DFT Temperature range

(T, K)

∆µS range (1)

(eV)

MoS2 truncation degree

(S-edge/M-edge)

Mo/Al2O3 [523, 723] [-0.80, -0.95] [0.17, 0.35], increases with temperature

Mo(CA)/Al2O3 [523, 723] [-0.80, -0.95] [0.59, 0.75], increases with temperature

DFT(2) / [-0.80, -0.95] [0.30, 0.43], increases with temperature

(1). ∆µS: chemical potential of sulfur, calculated according to ref. 30;

(2). DFT (Density functional theory) calculations in ref. 5, 6;

In addition, the IR/CO result that MoS2 morphology varies with sulfidation temperature is in

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good agreements with DFT calculations 5, 6

. In the ∆µS range corresponding to the sulfidation

conditions of our work, the MoS2 morphology predicted by DFT calculations 5, 6

is compared with

our IR/CO results on Mo/Al2O3 and Mo(CA)/Al2O3 catalyst in Table 1. It appears that our IR/CO

results are essentially in line with DFT calculations 5, 6

in two aspects. First, DFT calculations 5, 6

predicted that under HDS sulfidation conditions, the morphology of MoS2 slab is a truncated

triangle exposing both M-edge and S-edge. Correspondingly, CO adsorption bands on both M-edge

and S-edge were unambiguously recorded on Mo/Al2O3 and Mo(CA)/Al2O3 catalyst in our IR/CO

study. Secondly, the increase of temperature from 573 to 723 K (this study) corresponds to a

decrease of ∆µS from -0.80 eV to 0.90 eV 30

. In this ∆µS range, DFT calculations predicted that the

truncation degree of MoS2 increases with decreasing ∆µS 5, 6

. Thus, both IR/CO study and DFT

calculations suggest that the MoS2 truncation degree (ratio of S-edge/M-edge) increases with

increasing sulfidation temperature in the range of 573 to 723 K.

Nevertheless, the precise MoS2 morphology revealed by IR/CO is not identical with that

predicted by DFT calculations 5, 6

. As shown in Table 1, the truncation degree (S-edge/M-edge ratio)

of MoS2 predicted by DFT is [0.30, 0.43], which is in-between the IR/CO results on Mo/Al2O3

catalyst [0.17, 0.35] and Mo(CA)/Al2O3 catalyst [0.59, 0.75]. Such difference between DFT and

IR/CO study can be tentatively explained by the fact that the MoS2-support interactions were not

taken into account in the DFT calculations in references5, 6

. However, further DFT studies35

have

included slab-support interaction but in the case of alumina, the estimated truncation degree was

not modified due to weak calculated interaction for slabs of length around 3 nm. Meanwhile, this

explanation is further supported by the IR/CO results that the truncation degree of MoS2 on

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Mo(CA)/Al2O3 catalyst is always higher than that on Mo/Al2O3 catalyst in accordance with

previous study20

. Therefore, the present results indicate that the MoS2 morphology is also strongly

influenced by MoS2-Al2O3 interactions. Such finding is in line with the recent STM study by

Lauritsen and co-workers 23

, in which it was found that the MoS2 slabs adopt different

morphologies on different supports (Au, graphite, and TiO2).

5 Conclusions

In conclusion, low-temperature CO adsorption followed by IR spectroscopy (IR/CO)

characterization was successfully used to depict the MoS2 morphology change with sulfidation

temperature on Mo/Al2O3 and Mo(CA) /Al2O3 catalyst. Within typical HDS sulfidation

temperature range (573 to 723 K), it is found that the MoS2 phase on Mo/Al2O3 and Mo(CA)

/Al2O3 catalyst exposes both M-edge and S-edge, and that the concentration of each edge detected

by CO adsorption decreases with increasing sulfidation temperature. More important, the IR/CO

results reveal that the ratio of S-edge/M-edge steadily increases with sulfidation temperature,

indicating that the MoS2 slab becomes more heavily truncated. This effect of sulfidation

temperature on MoS2 morphology is in good agreements with DFT predictions 5, 6

, verifying the

relevance of these DFT studies for Al2O3-supported catalysts. As a further step, the present IR/CO

data reveals that the MoS2 morphology is also strongly influenced by MoS2-Al2O3 interactions

under the same sulfidation temperature.

Acknowledgements

The French Ministry of Research is acknowledged for the Ph. D. grant of J. Chen. Yoann Levaque,

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Valérie Ruaux, and Philippe Bazin are greatly acknowledged for the technical support on IR

experiment. Perla Castillo-Villalon is greatly acknowledged for the help on catalyst preparation.

Supporting Information

Supporting Information Available: spectral decomposition, εM-edge and εS-edge determination, edge

concentration calculation and Transmission Electron Microscopy results are available free of

charge via the Internet at: http://pubs.acs.or

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TOC

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IR Spectroscopic Evidence for MoS 2 Morphology Change with Sulfidation Temperature on MoS 2 /Al 2 O 3 Catalyst