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Influence of Au promoter on hydrodesulfurization activity of thiophene

over sulfided AuNi/SiO2 bimetallic catalysts

Zhanghuai Suo *, Aihua Lv, Hongying Lv, Mingshan Jin, Tao He

Institute of Applied Catalysis, Yantai University, 32 Qingquan Road, Yantai City, Shandong Province 264005, PR China

a r t i c l e i n f o

Article history:

Received 4 November 2008Received in revised form 12 January 2009

Accepted 15 January 2009

Available online 20 January 2009

Keywords:

Gold

Nickel

Silica

Bimetallic catalyst

Thiophene

Hydrodesulfurization

a b s t r a c t

AuNi/SiO2 bimetallic catalysts with high performance on hydrodesulfurization (HDS) were prepared

through consecutive impregnation route. The activities of the catalysts with different metal loading were

estimated by thiophene HDS. The activity is affected by nickel and gold loadings as well as the catalyst

pretreatment. It is found the presence of Au can partly inhibit the formation of nickel sulfide phase

and significantly increase the HDS activity of Ni/SiO2 catalyst. The sulfided catalysts show higher activity

than reduced or oxidized catalysts. Synergetic effect between gold and nickel species is preferable for

high activity with low metal loadings.

2009 Elsevier B.V. All rights reserved.

1. Introduction

Sulfur in transportation fuels remains one of major sources of

air pollution. With increasing emphasis on environmental protec-

tion, strict legislation has been imposed on sulfur level in diesel

[14]. Therefore, it is urgent for refiners and scientists to develop

new HDS catalysts with high activity and selectivity.

In order to find catalysts for HDS of fuel with high activity and

selectivity, many researches have been performed during the two

decades [57]. Using of noble metal-based catalyst is particularly

interesting due to their high performance in HDS [810]. Using

gold in catalysis was inspired by the finding of its high activity

through Harutas work for low-temperature CO oxidation [11].

Gold has advantages of its strong affinity to sulfur compounds

and good sulfur tolerance [1214]. Based on the knowledge, Vene-

zia et al. [15,16] applied gold catalyst in hydrodesulfurization,claiming that the beneficial effect of gold was present in supported

AuPd bimetallic HDS catalyst. The recent work of these authors

also reported the influence of gold promoter on HDS activity over

supported cobalt catalyst [17]. The result shows that the AuCo

bimetallic catalyst promotes thiophene HDS activity as compared

with the monometallic cobalt catalyst.

Herein, Au promoted Ni catalyst was applied in HDS reaction for

the first time. The aim of present work is to show the influence of

gold promoter on HDS of thiophene activity over supported nickel

and the synergetic effect between gold and nickel species are also

addressed.

2. Experimental

2.1. Preparation of catalysts

Ni/SiO2 catalysts with Ni loading of 1.0, 2.5, 5.0, 7.5, and 10wt%

respectively, were prepared by incipient wetness impregnation of

SiO2 (Qingdao Ocean Chemical Co., Ltd.; SSA = 420.7 m2/g;

dP = 4.88 nm) with an aqueous solution of nickel nitrate followed

by drying overnight at 100 C and calcination inair for 4 h at400 C.

1%Au/SiO2 catalyst was prepared by incipient wetness tech-

nique using aqueous solution of chloroauric acid (HAuCl43H2O).

After impregnating overnight and drying for 5 h at 60 C, the sam-

ple immersed in dilute ammonia solution to remove chloride ionsadsorbed on the surface and then dried at 60 C for 5 h. Finally, the

sample was calcined in air at 400 C for 4 h. The actual loading of

Au is 0.98%, as determined by AAS.

AuNi/SiO2 catalysts were prepared by consecutive impregna-

tion method. The Ni/SiO2 samples obtained were used to impreg-

nate with gold salt solution to obtain AuNi/SiO2 catalysts as in

preparation procedure of Au/SiO2.

2.2. Characterization of catalysts

The surface areas and pore volumes were determined with

NOVA 3000e automatic analyzer by low-temperature nitrogen

1566-7367/$ - see front matter 2009 Elsevier B.V. All rights reserved.doi:10.1016/j.catcom.2009.01.019

* Corresponding author. Tel.: +86 0535 6902514; fax: +86 0535 6902233.

E-mail address: zhsuo@ytu.edu.cn (Z. Suo).

Catalysis Communications 10 (2009) 11741177

Contents lists available at ScienceDirect

Catalysis Communications

j o u r n a l h o m e p a g e : w w w . e l s e v i e r . c o m / l o c a t e / c a t c o m

mailto:zhsuo@ytu.edu.cnhttp://www.sciencedirect.com/science/journal/15667367http://www.elsevier.com/locate/catcomhttp://www.elsevier.com/locate/catcomhttp://www.sciencedirect.com/science/journal/15667367mailto:zhsuo@ytu.edu.cn

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adsorption using the BET and the BJH equations, respectively. The

crystalline phases of all samples were identified by X-ray diffrac-

tion (XRD) in a Shimadzu-6100 diffractometer using Cu Ka radia-

tion. Standard JCPDS files were employed to identify the phases.

The H2-TPR profiles of sulfided Ni/SiO2 and sulfided AuNi/SiO2samples were obtained using 10% H2/N2 gases from room temper-

ature up to 900 C with heating rate of 20 C/min. The Ni 2p and Au

4f XPS studies of sulfided Ni/SiO2

and sulfided AuNi/SiO2

samples

were performed in a VG ESCALAB 210 X-ray photoelectron spec-

trometer. The binding energy was determined utilizing Si 2p line

as a reference with energy of 103.4 eV.

2.3. HDS activity

The HDS activities of thiophene over all samples were tested in

a continuous flow fix-bed microreactor. The feed gases are 1 vol%

thiophene in hexane with liquid hourly space velocity (LHSV) of

3.6 h1 and H2 flow rate of 50 ml/min. The reaction operates at

atmospheric pressure and reaction temperature of 340 C. Prior

to the catalytic activity evaluation, the catalysts were sulfided

in situ at 340 C for 4 h in a continuous stream of 3 vol% CS2/hex-

ane. The activity was determined after 60 min on stream. The reac-

tion products were analyzed by on line gas chromatography with

FID detector and a graphitized carbon black column.

3. Results and discussion

The textural properties of sulfided Ni/SiO2 and sulfided AuNi/

SiO2 catalysts are listed in Table 1. It is shown that the surface

areas and pore volumes of all samples decrease with increasing

Ni loading, while the average pore diameter changes slightly. On

the other hand, addition of gold to supported nickel catalyst makes

the surface area and the pore volume decrease. However, the aver-

age pore diameter of nickel catalyst does not change distinctly

with addition of gold, which agrees with the result of Venezia

et al. [17]. This is due to their different chemistry of synthesis,

which may result in the partial coating of Ni/SiO2 surface by Au

or blocking of large pore of SiO2.

The XRD diffraction lines of nickel sulfide phase can not be

found in sulfided Ni/SiO2 samples with Ni loadings of 2.5% and be-

low. For the samples with higher Ni loadings, the diffraction lines

at 2h = 21.1, 31.5, 38.7, 50.6 and 55.7 are attributed to nickel

sulfide (Ni3S2) phase according to JCPDS standard (300863), being

in agreement with the result from Le et al. [18]. XRD patterns of

sulfided 1%AuNi/SiO2 catalysts are presented in Fig. 1. Metallic

gold phase is observed for all samples, indicating that Au0 is main

phase after the samples were calcined in air at 400 C for 4 h. The

diffraction lines of nickel sulfide are difficult to be observed in all

gold-containing samples except for 1%Au10%Ni/SiO2 catalyst,

suggesting the presence of gold can partly inhibit the formation

of nickel sulfide phase.H2-TPR profiles of oxidized Ni/SiO2, Au/SiO2 and oxidized Au

Ni/SiO2 samples show that no reduction in Au/SiO2 sample occurs

between 25 C and 800 C. The reduction peak of Ni/SiO2 sample

appeared at 429 C was attributed to the reduction of NiO phase.

When metallic Au was added to Ni/SiO2, the maximum reduction

temperature was increased to 454 C, leading to the conclusion

that the presence of Au increases the reduction of NiO phase. This

can be explained that stronger NiO bond in AuNi/SiO2 catalysts

results in higher reduction temperature. Chin et al. found that

addition of Au significantly reduced the total amount of H2 chem-

isorbed on AuNi/MgAl2O4 catalysts [19].

There are two reduction peaks in the TPR profiles of sulfided Ni/

SiO2 and sulfided AuNi/SiO2 catalysts (Fig. 2). For sulfided Ni/SiO2

the low-temperature peak (Tmax 250 C) is attributed to the super-ficial reduction of sulfur with anionic vacancies and the high-tem-

perature peak (Tmax 357 C) arises from the reduction of the bulk

sulfides [20,21]. With the inclusion of gold in the sulfided Ni/

SiO2, the two maximum reduction peaks decrease to 226 C and

338 C, respectively, indicating that the presence of Au is prefera-

ble for the reduction of nickel sulfide phase, being in agreement

with Yuans work on co-impregnated NiAu/SiO2 [22].

Table 1

Textural property of sulfided Ni/SiO2 and sulfided AuNi/SiO2 catalysts.

Catalyst sample SBET (m2/g) Vp (cm

3/g) Rp (nm)

1%Ni/SiO2 392.5 1.01 4.85

0.5%Au1%Ni/SiO2 380.6 0.97 3.30

1%Au1%Ni/SiO2 366.9 0.92 3.30

1.5%Au1%Ni/SiO2 351.0 0.86 3.30

2.5%Ni/SiO2 385.7 0.90 3.32

1%Au2.5%Ni/SiO2 355.3 0.88 3.29

5%Ni/SiO2 372.8 0.89 3.32

1%Au5%Ni/SiO2 333.9 0.88 3.31

7.5%Ni/SiO2 363.8 0.86 3.29

1%Au7.5%Ni/SiO2 319.1 0.83 3.28

10%Ni/SiO2 355.4 0.84 3.27

1%Au10%Ni/SiO2 304.5 0.76 3.24

10 20 30 40 50 60 70 80

Intensity/a.u.

2 Theta / o

5%Ni/SiO2

1%Au-5%Ni/SiO2

7.5%Ni/SiO2

1%Au-7.5%Ni/SiO2

10%Ni/SiO2

1%Au-10%Ni/SiO2

Ni3S

2Au

0

Ni3S

2

Ni3S

2Au

0

Ni3S

2

Fig. 1. XRD patterns of sulfided Ni/SiO2 and sulfided AuNi/SiO2 catalysts.

50 100 150 200 250 300 350 400 450

sulfided Au-Ni/SiO2

H2consumption

TemperatureoC

sulfided Ni/SiO2

226oC 338

oC

250oC

357oC

Fig. 2. H2-TPR profiles of sulfided 7.5%Ni/SiO2 and sulfided 1%Au7.5%Ni/SiO2catalysts.

Z. Suo et al. / Catalysis Communications 10 (2009) 11741177 1175

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The Ni 2p XPS spectra of sulfided Ni/SiO2 and sulfided AuNi/

SiO2 samples are shown in Fig. 3. For sulfided Ni/SiO2, the binding

energies of Ni 2p1/2 and Ni 2p3/2 are 873.7 eV and 855.0 eV, which

are attributed to Ni2+ species [18]. For sulfided AuNi/SiO2 they are

shifted to 872.5 eV and 854.3 eV due to the perturbation of gold to

nickel. The negative shift is identifiable of low-valence nickel spe-

cies which is superior to the formation of surface sulfide. It can be

concluded from its XRD and XPS results that NiO is the main phaseon the surface of Ni/SiO2 and AuNi/SiO2, meanwhile, nickel sulfide

phase is the main phase in the bulk of sulfide Ni/SiO 2 and AuNi/

SiO2. The binding energies of Au 4f5/2 and Au 4f7/2 appear at

87.1 eV and 83.8 eV, respectively, for sulfided AuNi/SiO2, which

are attributed to metallic gold, indicating that metallic gold pres-

ent in surface and bulk of the catalyst along with its XRD and

TPR results.

The HDS activities of Au/SiO2, Ni/SiO2 and AuNi/SiO2 samples

were evaluated in order to estimate the influence of Au promoter

on the nickel catalyst. The activity of Au/SiO2 is found to be low

although thiophene conversion increases from 2.9% at 0.5% Au

loading to 6.8% at 1.5% Au loading. As shown in Fig. 4, the activity

of sulfided Ni/SiO2 changes greatly with Ni loading, thiophene con-

version is 6.1% at 1% Ni loading and amounts to 32.6% at 7.5% Niloading. Due to the presence of Au, sulfided AuNi/SiO2 gives high-

er HDS activity than Ni/SiO2. For example, 36.5% conversion of thi-

ophene is obtained when addition of 1%Au to sulfided 1% Ni/SiO2.

For sulfided AuNi/SiO2 catalyst, the HDS activity is found to be

sensitive to its chemical state. The sulfided catalyst shows higher

activity than the oxidized or the reduced catalysts. On the other

hand, the activity is also affected by sulfidation temperature and

sulfidation time of AuNi/SiO2 catalyst. When sulfidation temper-

ature increases from 250 C to 450 C, thiophene conversion is

found to increase from 45.2% to 60.4% and the activity is increased

to maximum at sulfidation for 2 h.

When Au is added to Ni/SiO2, the elevated activity is found. The

improvement is more notable at Ni loading of 5% or lower, as

shown in Fig. 4. Their dependences of HDS activities on Au loading

are also found. These results show that the synergy effect between

gold and nickel is significant for HDS activity with low Ni loadings.

This view can be supported by the work of Pinzn et al. using Pt

Mo bimetallic HDS catalysts, in which the enhanced HDS activities

are due to an improved dispersion of the active species on the sup-

port, which was reached at low metal contents and a specific atom-

ic ratio [23]. There is an increase of Nisulfide dispersion at low

loadings and this would be supported by the shift of the XPS sig-

nals of Ni in the presence of Au, as given by Venezia et al. [17]. Chin

et al also provided some consistent evidences of a significant inter-

action between gold atoms and reduced Ni crystallites on AuNi/

MgAl2O4 [19].

4. Conclusions

This work shows the potential uses of gold promoter on HDS

over sulfided Ni/SiO2 catalyst. It is found that the presence of Au

inhibits the formation of nickel sulfide. NiO is the main phase on

the surface, while the main nickel sulfide phase exists in the bulk

of sulfide Ni/SiO2 and AuNi/SiO2. Moreover, the HDS activity of

the bimetallic AuNi catalyst is sensitive to its reduction tempera-

ture of the sulfur species and chemical state. The sulfided catalysts

show higher activity than the oxidized and the reduced catalysts.Further, the synergy effect between gold and nickel is more signif-

icant for HDS activity of the catalysts with low metal loadings.

Acknowledgements

This work was financially supported by the National Science

Foundation of China (NSFC NO. 20473070).

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