Synthesis of Titanium Modified Three-Dimensional KIT-5 Mesoporous

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Catalysis and Kinetics

Synthesis of Titanium Modified Three-dimensional KIT-5 Mesoporous Support and Its Application of the Quinoline Hydrodenitrogenation Qian Meng, Aijun Duan, Kebin Chi, Zhen Zhao, Jian Liu, Peng Zheng, Bo Wang, Cong Liu, Di Hu, and Yuanzheng Jia Energy Fuels, Just Accepted Manuscript • DOI: 10.1021/acs.energyfuels.9b00520 • Publication Date (Web): 29 Apr 2019 Downloaded from http://pubs.acs.org on May 2, 2019

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Energy & Fuels

1

Synthesis

of

Titanium

Modified

Three-dimensional

KIT-5

2

Mesoporous Support and Its Application of the Quinoline

3

Hydrodenitrogenation

4

Qian Meng,† Aijun Duan,*,† Kebin Chi,‡ Zhen Zhao,† Jian Liu,† Peng Zheng,† Bo

5

Wang,† Cong Liu,† Di Hu,† and Yuanzhen Jia†

6

† State

7

P. R. China.

8

‡ Petrochemical

Key Laboratory of Heavy Oil Processing, China University of Petroleum, Beijing, 102249,

Research Institute, PetroChina Company Limited, Beijing 102206, PR China.

1

ACS Paragon Plus Environment

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ABSTRACT:

10

A series of Ti-KIT-5 materials with different ratios of Si/Ti were synthesized, and

11

employed as the supports to prepare the NiMo catalysts. All the modified supports

12

and catalysts were measured by means of small and wide angle XRD, N2 isothermal

13

absorption-desorption, FT-IR, XPS, Py-IR and HRTEM techniques. The small angle

14

XRD and N2 analysis characterization proved that the modified Ti-KT-x materials

15

maintained the orderly mesoporous structure, and displayed the larger pore size than

16

the pure support. Additionally, results from the FT-IR and XPS spectra demonstrated

17

that Ti species were successfully embedded into the framework of KIT-5 material. It

18

was noted that the introduction of suitable Ti species increased the amount of acid

19

sites and promoted well distribution of the active metals. The hydrodenitrogenation

20

performances of the NiMo/Ti-KT-x catalysts were evaluated under the reaction

21

conditions of 4 MPa, 10 h-1 and different temperatures ranging from 340 oC to 400 oC.

22

The modified NiMo/Ti-KIT-5 catalysts showed the higher catalytic activities than

23

NiMo/KIT-5 catalyst, which was attributed to the larger pore size, more acid sites and

24

sulfide active metal species. Moreover, the NiMo/Ti-KT-20 catalyst showed the

25

highest hydrodenitrogenation efficiencies (81.56 %).

26

KEYWORDS:

27

Hydrodenitrogenation

Three-dimensional

support;

2


Ti

modified

catalyst;

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Energy & Fuels

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1. INTRODUCTION

29

Hydrotreating technology has always been a very important method for converting

30

inferior fuels into high-valued products based on the removal of the impurities (sulfur,

31

nitrogen and metal) under the H2 pressure.1-5 In the hydrotreating process of oil

32

feedstock, the existence of nitrogen-containing compounds not only hinders the

33

removal of sulfur due to the competitive adsorption of nitrogen and sulfur compounds

34

on the acidic active sites, resulting in the deactivation and poisoning of catalysts, but

35

also produces refractory NOx pollutants after combustion in engine.6-7 Therefore, deep

36

removal of the nitrogen-containing compounds by hydrodenitrogenation is of

37

significance for ultraclean fuel production, in which the use of highly active

38

hydrogenation catalysts is the keynote of the hydrotreating technology.

39

Traditional hydrogenation catalysts are the Mo or W based catalysts promoted by

40

the Ni(Co) atoms.8-9 Recently some new active components, including Ni2P, MoP and

41

RuP, have been gradually applied to the hydrodenitrogenation study.10-14 However,

42

their application are greatly restricted by the poor stability, complex preparation

43

process and high-price, etc. Consequently the traditional Mo or W based catalysts are

44

still used extensively. In order to improve the catalytic efficiency, the development of

45

new carriers is the focus of scientific research.

46

Al2O3 as traditional hydrogenation carrier, with the advantage of low-price and

47

excellent mechanical properties, has been extensively used in industries.15-16

48

However, the limitations of wide pore distribution and single Lewis acid sites restrict 3


Energy & Fuels 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

49

the improvement of hydrogenation activity, which requires synergistic contribution of

50

B and L acids. Since MCM-41 material was discovered,17-19 mesoporous materials

51

with high specific surface area (800-1000 m2/g), open and adjustable pore size (2-50

52

nm) and easily modulated properties, attracted extensive attention from researchers.20

53

Nevertheless, the weak hydrothermal stability and less acid sites are obviously

54

disadvantageous to their application in catalytic process. Two main measures are

55

taken to improve their properties: one is the preparation of meso-microporous

56

composite materials with the incorporating of acidic zeolite precursors into the

57

framework of mesoporous materials.21-24 Zhang et al. reported the synthesis of

58

Beta-SBA-15 composite material and used it as the catalyst support for

59

dibenzothiophene hydrodesulfurization.21 The activity results showed that the

60

NiMo/Beta-SBA-15 catalyst had the higher HDS efficiencies in comparison with the

61

reference NiMo/Beta and NiMo/SBA-15 catalysts, which were ascribed to the

62

synergistic effect of the superior pore structure and large amounts of acid sites. Wu

63

et.al prepared the novel ZSM-5-KIT-6 composite materials via the enwrapping

64

method, and the catalytic performance of corresponding NiMo catalysts were

65

evaluated in the HDS reaction of 4, 6-DMDBT.22 Compared with the reference

66

catalysts, the NiMo/ZSM-5-KIT-6 displayed the highest HDS efficiencies, moreover,

67

the conversion of 4,6-DMDBT over the composite catalyst was two times higher than

68

that of NiMo/Al2O3 catalyst, which was related to the superior diffusion from the

69

hierarchical channel and the excellent Brønsted acid sites. 4


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Energy & Fuels

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Another way is the preparation of heteroatom doped mesoporous materials,25-31

71

including Al3+, Ti4+ and Zr4+. The introduction of heteroatoms can change the acidity

72

properties of catalysts resulting from the different sizes and coordination numbers of

73

Si and heteroatoms. Furthermore, the metal modification could modulate the

74

interaction between support and active metals. Guo et.al explored the effect of Al, Zr

75

and Ti modification on the MCM-41 supports in quinoline hydrodenitrogenation

76

reaction.25 The evaluation results showed that the modified NiW/MCM-41-X (X=Al,

77

Zr and Ti) catalysts had the higher HDN activities than the pure NiW/MCM-41

78

catalyst resulting from the incorporation of Al, Zr and Ti metals increasing the

79

amount of acid sites and the dispersion of Ni and W species. Boahene et.al prepared a

80

series of modified Ti-HMS materials with different Si/Ti ratios of 20, 40 and 80, and

81

applied to support NiPMo for the light gas oil hydrotreating.26 The activity data

82

illustrated that the modified HMS-Ti supported NiPMo catalysts exhibited the higher

83

HDS and HDN catalytic performance than the reference NiMo/HMS catalyst prepared

84

by the convention preparation method, which was associated with the outstanding

85

structural properties of the modified supports and promoting the well dispersion of

86

active metals. Biswas et al. studied the effect of different loadings and preparation

87

methods (the direct and post synthesis) on the modified Zr-SBA-15 supported NiMo

88

catalysts in the hydrodesulfurization and hydrodenitrogenation of heavy gas oil.30 In

89

view of the activity results, it was found that the NiMo/Zr-SBA-15 catalysts

90

synthesized by two methods displayed the higher efficiencies than NiMo/SBA-15 5


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91

catalyst. Among all the modified catalysts, the NiMo/Zr-SBA-15 (23 wt%, post

92

synthesis) had the best catalytic performance, which was linked with the synergetic

93

effect of excellent pore structure properties, higher zirconia loading, better dispersion

94

of active metals (Mo and Ni) and more acid sites. Ledesma et al. studied the catalytic

95

performance of indole over Ir/SBA-15 catalysts modified with Ti species, and the F

96

and Al elemental species were also introduced to improve the acidities of catalysts.31

97

The activity evaluation data illustrated that the Ir/AlTi-SBA-15 catalyst exhibited the

98

highest catalytic activity, which was attributed to Ti species incorporation leading to

99

the significant reduction of the size of Ir crystallites, and Al species modification

100

bringing more acid sites, especially Brønsted acid sites.

101

KIT-5 material was firstly synthesized by Kleitz et al. with F127 (EO106PO70EO106,

102

Mw =125 000) as the template in the weak acid system.32 Because of high surface area

103

(about 1000 m2/g) and pore volume (0.8-0.9 cm3/g), large pore size (7-10 nm) and

104

three-dimensional channel, it was extensively applied in large molecule catalysis.24,

105

33-34

106

hydrodenitrogenation reaction.

Thus, KIT-5 material would be convinced to be the potential candidate for the

107

In order to promote its reaction performance, a series of Ti-KIT-5 samples with the

108

different atomic ratios of Si/Ti (10, 20, 40, 60) were prepared via the direct synthesis

109

method. Moreover, the corresponding NiMo/Ti-KIT-5 catalysts prepared with the

110

stepwise impregnation method were evaluated in the quinoline hydrodenitrogenation

111

under the conditions of H2 pressure of 4 MPa, H2/hydrocarbon of 400 ml/ml, WHSV 6


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Energy & Fuels

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of 10 h-1 and different reaction temperatures ranging from 340 oC to 400 oC.

113

Furthermore, based on the information from XRD, N2 absorption-desorption, SEM,

114

TEM and Py-IR, the relationship between structure properties and reactive activities

115

was discussed in detail to provide guidance for the development of highly-efficient

116

catalysts.

117

2. EXPERIMENT

118

2.1 Synthesis of KIT-5 and Ti-KIT-5 supports

119

The pure KIT-5 material was synthesized according to the method reported in the

120

literature.23,32 The detailed steps were as follows: 5.0 g of F127 (EO106PO70EO106) was

121

well dissolved in 250 ml of 0.5 M HCl with stirring for 3-4 h at 45 oC; then 25.0 g of

122

TEOS were added into the solution and stirring continuously for 24 h at the same

123

temperature. Afterwards, the white suspension were transferred into the Teflon bottle

124

and kept heating for 24 h at 100 oC. The sample was collected by filtrating, drying at

125

100 oC for 12 h in air, and calcining for 6 h at 550 oC, and denoted as KIT-5.

126

The preparation procedure for Ti-KIT-5-x (x represents the ratio of Si/Ti: 10, 20,

127

40, 60) samples were described as follows: firstly, 5.0 g of F127 and 25.0 g of TEOS

128

were added into 250 ml of 0.5 M HCl, and stirring continuously to form a

129

well-distributed solution; secondly, different amounts of Ti source (Tetrabutyl

130

Titanate, 98 %) were added into the above solution with stirring for 24 h at the same

131

temperature. Finally, the mixture were transferred into the autoclave and heated

7


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statically for 24 h at 100 oC. Then the white solid were obtained by filtrating, drying,

133

and calcining for 6 h at 550 oC, and denoted as Ti-KT-x (x = 10, 20, 40, 60).

134

2.2 Preparation of catalysts

135

The corresponding NiMo/Ti-KT-x catalysts were prepared by the two-step

136

incipient-wetness impregnation method. The loading of MoO3 (12 wt% ) and NiO (3

137

wt%) were successively impregnated on the carriers. After each impregnation, the

138

as-prepared catalysts were dried for 12 h at 100 oC, and calcined for 6 h at 550 oC.

139

Finally, the obtained catalysts were denoted as NiMo/Ti-KT-10, NiMo/Ti-KT-20,

140

NiMo/Ti-KT-40, NiMo/Ti-KT-60 and NiMo/KIT-5, respectively.

141

2.3 Characterization of supports and catalysts

142

Small angle and wide angle X-ray diffraction (XRD) spectra were measured

143

between 0.5-4o and 5-60o on the Bruker D8 advance system with Cu kα (40 KV, 50

144

mA).

145

With the Micromeritics Tristar 3020 porosimetry instrument, the N2 adsorption

146

characterization was performed. The specific surface area and pore distribution

147

derived from the absorption branch were obtained by the Brunauer-Emmett-Teller

148

(BET)

149

morphologies of all the samples were observed by the scanning electron microscopy

150

(SEM) spectra with the Quanta 200F instrument, and the channel properties of

151

supports were recorded on a JEOL JEM 2100 apparatus. Additionally, the surface

and

the

Barrett-Joyner-Halenda

(BJH)

methods,

8


respectively.

The

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Energy & Fuels

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contents of Ti species were tested using the SEM-EDS analyses on the Quanta 200F

153

instrument.

154

Fourier transform infrared (FTIR) spectra of the samples were recorded at the

155

wavenumber length of 400-4000 cm-1 using the DIGILAB FTS-3000 instrument. The

156

analysis of acid distribution and amounts of the samples were performed on a

157

MAGNAIR 560 spectrophotometer using pyridine as the probe molecule.

158

The oxidized catalysts were tested by the Raman spectra with a Renishaw Invia

159

Raman spectrometer using the He/Cd laser of 325 nm. Furthermore, the X-ray

160

photoelectron spectra (XPS) of all the sulfided catalysts were performed with the

161

Thermo Fisher K-Alpha spectrometer.

162

The MoS2 morphologies over the sulfided catalysts were observed via the

163

high-resolution transmission electron microscopy technique (HRTEM) using the

164

Philips Tecnai G2 F20 STWIN microscope at the accelerating voltage of 300 kV.

165

According to the statistical results of MoS2 phases derived from 400 stacking layers,

166

the average length and stacking number of MoS2 stacking layers of all the sulfided

167

catalysts were acquired.

168

2.4 Catalytic activity measurement

169

The hydrodenitrogenation (HDN) activities of the series NiMo/Ti-KT-x catalysts

170

were evaluated with a fixed-bed reactor. 1.0 g of fresh catalyst, previously crushed

171

into 40-60 mesh, was loaded into the hollow reaction tube. Quartz sand was used to

172

dilute the catalyst in the process of hydrogenation reaction to distribute the feedstock 9


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Page 10 of 42

173

fluid uniformly and to make the heat transfer evenly in the catalyst bed. The catalyst

174

was presulfided in situ for 4 h at 360 oC with the 2.5 wt% CS2 solution (cyclohexane

175

as the solvent). After that, the hydrodenitrogenation reaction with quinoline as the

176

reactant (dissolving in cyclohexane, N content of 500 ppm) was carried out under the

177

conditions of the pressure of 4.0 MPa, H2/hydrocarbon of 400 ml/ml, different

178

temperatures of 340-400 oC and the confined WHSV of 10 h-1.

179

After the above reaction, the nitrogen contents of reactants and products were

180

detected on a RPP-2000 SN sulfur and nitrogen instrument with the injection quantity

181

of 20 μg/ml. Additionally, the detailed compounds distribution of the products was

182

also investigated using the Thermo-Finnigan Trace DSQ GC-MS apparatus with a

183

HP-5MS column. The HDN efficiencies of various catalysts were calculated based on

184

Equation (1), in which the nitrogen contents of the feedstock and products were

185

defined as Nf and Np, respectively.

186

HDN(%) =

(𝑁𝑓 ― 𝑁𝑝) 𝑁𝑓

× 100%

(1)

187

The pseudo-first-order kinetics should be applied to deal with the reaction results of

188

quinoline hydrodenitrogenation according to the research of other scholars,25,41 and

189

the rate constant defined as k (mol g-1 h-1) could be calculated with the equation (2), in

190

which m and F represent the mass of catalyst (g) and feeding rate of reactant molecule

191

(mol h-1), respectively.

192

𝑘𝐻𝐷𝑁 =

𝐹 1 ln ( ) 𝑚 1―𝑥

(2)

10


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Energy & Fuels

193

𝑓𝑀𝑜 =

194

𝑛𝑖 =

𝑀𝑜𝑒𝑑𝑔𝑒 𝑀𝑜𝑡𝑜𝑡𝑎𝑙

𝑡

=

∑𝑖 = 1(6𝑛𝑖 ― 6)

(3)

𝑡

∑𝑖 = 1(3𝑛2𝑖 ― 3𝑛𝑖 + 1)

𝐿 + 0.5 6.4

(4)

195

The fMo, representing the number of Mo atoms on the edge surface, is usually

196

calculated with the fraction of Mo atoms on the edge to the total Mo atoms over MoS2

197

stacking layers based on Equation (3), where t means the total number of MoS2

198

stacking layers deriving from 20 photographs (including 400 stacking slabs).

199

Meanwhile in Equation (4), the number of Mo atoms the edge of MoS2 stacking layers

200

(ni) is calculated with the average length of MoS2 stacking layers (L).35 Additionally,

201

the turn-over frequency (TOF) reflecting the number of quinoline molecules reacted

202

per second and per Mo atom located on the edges of MoS2 stacking slabs, could be

203

derived from the equation (5).

204

TOF =

205

3. RESULTS

206

3.1 XRD characterization

𝐹×𝑥 𝑛𝑀𝑜 × 𝑓𝑀𝑜

(5)

207

Figure 1 shows the small angle XRD patterns of a series of Ti-KT-x supports. As

208

shown in Figure 1, the KIT-5 sample has two diffraction peaks located at about 0.7°

209

and 0.8°, corresponding to the (111) and (200) reflections associated with the

210

three-dimensional face-centered cubic Fm3m symmetry structure.23,32 Similar to pure

211

KIT-5 material, the Ti-KT-x (x>10) display the same strong diffraction peaks

212

indicating the relatively high mesoporous order. However, the peak intensity of the 11


Energy & Fuels

213

Ti-KT-10 support is comparatively weak, confirming that the introduction of

214

excessive Ti species slightly decrease the orderliness of mesopores. Furthermore,

215

comparing with the KIT-5 and Ti-KT-10 materials, the peak positions of the Ti-KT-x

216

(x>10) shift to the low angle, meaning that they possess the larger unit cell

217

parameter.23,32

111 200 Intensity/a.u

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

Page 12 of 42

a b c d e 1

2

2 theta, degree

3

4

218 219

Figure 1. Small angle XRD patterns of Ti-KT-x materials: (a) KIT-5, (b) Ti-KT-60, (c) Ti-KT-40,

220

(d) Ti-KT-20, (e) Ti-KT-10.

221

In order to study the distribution of Ti species, wide angle XRD are performed to

222

characterize the Ti-KT-x materials, and the results are shown in Figure S1. It is found

223

from Figure S1 that all the samples present the broad diffraction peak at about 24o

224

ascribed to the amorphous silica.35-37 When the less Ti species (x=60, 40) are

225

introduced into the mesoporous KIT-5 materials, there are no diffraction peaks

226

belonging to the TiO2 crystal phases, confirming that the Ti species are well dispersed

227

on the Ti-KT-60 and Ti-KT-40 supports. Nevertheless, with the introduced Ti species 12


Page 13 of 42

228

increasing (x=20, 10), the peaks attributed to the TiO2 anatase phase are observed at

229

25.5o, 37.9o and 47.9o,28,37 moreover, the peak intensities gradually increase.

230

3.2 N2 analysis technique characterization

B

-1

)

A b c d e

0.0

a

dV/dD(cm-3g-1nm-1)

a

Volume adsorped (mg L

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

Energy & Fuels

b c d e

0.2

0.4

0.6

0.8

0

1.0

20

40

231

60

80

100

Diameter(nm)

Relative pressure(P/Po)

232

Figure 2. N2 adsorption-desorption isothermals (A) and pore size distributions (B): (a) KIT-5,

233

(b) Ti-KT-60, (c) Ti-KT-40, (d) Ti-KT-20, (e) Ti-KT-10.

234

The nitrogen absorption-desorption techniques are used to analyze pore properties

235

of the Ti-KT-x materials, and the results are displayed in Figure 2. From Figure 2(A),

236

the pure KIT-5 and modified Ti-KT-x materials possess the type IV isothermals with

237

the typical H2 hysteresis loops at the P/Po values between 0.4 and 0.8, indicating the

238

existence of the cage-type mesoporous structure.23,34 Furthermore, it can be found

239

from Figure 2(B), all the samples have relatively concentrated pore distribution.

240

Table 1.

Pore structural properties of Ti-KT-x materials.

Samples

Sta(m2·g-1)

Smicb(m2·g-1)

Smesb(m2·g-1)

Vtc(cm3·g-1)

Vmicd(cm3·g-1)

Vmese(cm3·g-1)

df(nm)

KIT-5

931

240

691

0.85

0.14

0.71

7.8

Ti-KT-6 0

914

222

692

0.91

0.13

0.78

9.7

13


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Ti-KT-4 0 Ti-KT-2 0 Ti-KT-1 0

Page 14 of 42

880

194

686

0.88

0.11

0.77

9.4

827

163

664

0.90

0.06

0.84

9.3

791

146

645

0.75

0.04

0.71

8.1

241

a

242

pressure of 0.98;

243

Calculated using the BJH method from the adsorption branch.

Calculated by the BET method; d

b

Calculated by the t-plot method;

Calculated using the t-plot method;

e

c

Obtained at a relative

Calculated using the BJH method;

f

244

Additionally, the detailed pore structure data are listed in Table 1. From Table 1,

245

the modified Ti-KT-x (x>10) materials exhibit larger pore sizes than those of the pure

246

KIT-5 material, since the atomic radius of Ti4+ (0.061 nm) embedded into the

247

mesoporous framework is larger than that of Si4+ (0.040 nm) and leading to cell

248

amplification.27,28 However, comparing with the pure KIT-5 material, the modified

249

Ti-KT-x materials have the smaller microporous specific surface areas and volumes,

250

especially the Ti-KT-20 (32.1 % and 57.1 % decrements in surface area and volume)

251

and Ti-KT-10 (39.2 % and 71.4 % decrements in surface area and volume); while

252

their mesoporous specific surface areas and volumes are basically the same, indicating

253

that introducing more Ti species would lead to the blockage of micropore.27,28,36

14


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254

3.3 FT-IR characterization of the materials

-1

-1

460 cm

806 cm

-1

950 cm

Transmittance (a.u.)

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

Energy & Fuels

1078 cm

b -1 1636 cm -1

960 cm

400

600

800

1000

1200

1400

1600

wavenumber(cm-1)

255 256

a -1

Figure 3. FT-IR spectra of the supports: (a) KIT-5, (b) Ti-KT-40.

257

Figure 3 shows the FT-IR results of the Ti-KT-40 and pure KIT-5 samples. From

258

Figure 3, the peaks ascribed to the symmetric and asymmetric stretching vibrations of

259

Si-O-Si bond are observed at 460 cm-1, 806 cm-1 and 1078 cm-1, respectively.23, 36 The

260

peak centered at 1636 cm-1 is caused by the silanol group on the surface.38 For the

261

pure KIT-5 material, the weak peak presented at 950 cm-1 is attributed to the vibration

262

of Si-O- of Si-OH,36 while the incorporation of Ti species makes the peak move

263

toward high wavenumber (960 cm-1), which is caused by the synergetic effect of the

264

Si-OH and Si-O-Ti groups,23,37,38 indicating that the Ti species were incorporated into

265

the framework of KIT-5 material.

266

3.4 SEM of the materials

267

The modified Ti-KT-x samples are characterized by the SEM technique to study 15


Energy & Fuels 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

268

the morphologies, and the results are shown in Figure S3. It is clearly seen from

269

Figure S3 that the pure KIT-5 consists of irregularly concentrated particles with the

270

smooth surface. In contrast with KIT-5 sample, the Ti-KT-40 sample has an

271

agglomerated phase of the large particles, which is attributed to the incorporation of

272

Ti species partly hindering the orderly arrangement of inorganic silicon species in the

273

synthesis condition.23 Furthermore, with the Ti species increasing, it is clearly

274

observed that the Ti-KT-20 sample has super large pore (2-5 μm).

275

3.5 SEM-EDS elemental mapping

276

To measure the distribution of Ti species, the Ti-KT-40 sample is characterized

277

with the EDS elemental mapping technology, and the images are displayed in Figure

278

S4. It is clearly observed from the photograph that Ti species are well dispersed on the

279

Ti-KT-40 sample. Meanwhile the EDS results collected through the entire picture are

280

presented in Figure S4, demonstrating that the as-synthesized Ti-KT-40 support has

281

the similar Si/Ti ratio to the origin system.

282

3.6 TEM of the materials

283

The channel properties of various Ti-KT-x samples are surveyed by the TEM

284

spectra, and shown in Figure S5. The KIT-5 support has the highly ordered channel,

285

and the clearly visible (111) crystal surface confirming the three-dimensional

286

face-centered cubic Fm3m symmetry structure.32,37 It is observed from Figure S5 that

287

when less Ti species (x=60, 40, 20) are embedded into the KIT-5 materials, the 16


Page 16 of 42

Page 17 of 42

288

modified samples can retain orderly mesoporous channel well. However, with the

289

embedded Ti species increasing, the mesoporous channel of Ti-KT-10 sample is

290

destroyed slightly. Furthermore, the TiO2 crystallite are very clear over Ti-KT-10

291

sample in Figure S5, and there are no TiO2 crystallite over other modified samples

292

(x>10) proving the well dispersion of Ti species. The results of TEM spectra are

293

consistent with XRD characterization.

294

3.7 Raman of the catalysts

-1

954 cm

a Intensity/a.u

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

Energy & Fuels

b -1

396 cm

-1

524 cm

-1

642 cm

c d e

200

295

400

600

800

1000

1200

Wavenumber/cm-1

296

Figure 4. Raman spectra of the series of Ti-KT-x supports: (a) NiMo/KIT-5, (b) NiMo/Ti-KT-60,

297

(c) NiMo/Ti-KT-40, (d) NiMo/Ti-KT-20, (e) NiMo/Ti-KT-10.

298

The Ti-KT-x samples of Raman spectra are tested to characterize the coordination

299

state of active metals and the dispersion of Ti species,27,28,36,37 and displayed in Figure

300

4. All the samples exhibit the broad signals at 954 cm-1 belonging to the high

301

coordination polymolybdate clusters such as Mo8O266-.35,36 Meanwhile it is observed

302

from Figure 4 that the modified NiMo/Ti-KT-x catalysts have the higher peak 17


Energy & Fuels 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

303

intensity than the pure NiMo/KIT-5 catalyst resulting from the incorporation of Ti

304

species enhancing the dispersion of Mo species.27,28,36 Moreover, the peak intensity of

305

NiMo/Ti-KT-20 catalyst is higher than other modified catalysts, which is favorable to

306

the quinoline hydrodenitrogenation reaction. Furthermore, when incorporating the less

307

Ti species into KIT-5 material, there is no bulk TiO2 crystalline appearing over

308

Ti-KT-60 material, indicating that Ti species are well dispersed on the support.

309

However, with the Ti species increasing (x NiMo/Ti-KT-40 (7.1 %) >

333

NiMo/Ti-KT-10 (6.1 %) > NiMo/Ti-KT-60 (5.3 %).

19


Energy & Fuels

(A)

(B)

5+

Mo (5/2), (3/2)

Mo (5/2), (3/2)

2-

S

240

235

230

225

5+

6+

4+

Intensity/a.u.

Mo (5/2), (3/2)

Mo (5/2), (3/2)

Mo (5/2), (3/2)

2-

S

240

220

235

B.E.(eV)

225

220

(D) 5+

Mo (5/2), (3/2)

Mo (5/2), (3/2)

6+

Mo (5/2), (3/2)

2-

S

240

235

230

225

220

5+

6+

Mo (5/2), (3/2)

Mo (5/2), (3/2)

Mo (5/2), (3/2)

Mo (5/2), (3/2)

Mo (5/2), (3/2)

2-

S

240

235

B.E.(eV)

(E)

4+

5+

4+

Intensity/a.u.

6+

Intensity/a.u.

230

B.E.(eV)

(C)

230

225

220

B.E.(eV) 4+

Mo (5/2), (3/2)

2-

S

240

334

4+

Mo (5/2), (3/2)

Intensity/a.u.

6+

Intensity/a.u.

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

Page 20 of 42

235

230

225

220

B.E.(eV)

335

Figure 5. XPS spectra of the series sulfided NiMo/Ti-KT-x catalysts: (A) NiMo/KIT-5,

336

(B) NiMo/Ti-KT-60, (C) NiMo/Ti-KT-40, (D) NiMo/Ti-KT-20, (E) NiMo/Ti-KT-10.

337

The Mo 3d XPS results of various sulfided NiMo/Ti-KT-x catalysts are presented

338

in Figure 5, in which the Mo 3d spectra consist of three well-resolved contributions.

339

The two peaks presented at 229.0 ± 0.1 eV and 232.1 ± 0.1 eV, with a fixed

340

intensity ratio of 3 : 2, are corresponding to Mo 3d5/2 and 3d3/2 in the Mo4+ state

341

(MoS2).23 Moreover, the peak intensity is closely related to the hydrogenation activity

342

of the catalyst. The vi,ration peaks corresponding to Mo 3d5/2 and 3d3/2 spectra of 20


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Energy & Fuels

343

Mo6+ are observed at 232.4 ± 0.1 eV and 235.5 ± 0.1 eV, indicating that part of

344

Mo species after sulfuration still exist in the form of oxidation state.35-37 The weak

345

signals centered at 230.1 ± 0.1 eV and 233.2 ± 0.1 eV result from the 3d5/2 and

346

3d3/2 spectra of Mo5+ (MoOxSy).35,37,38 Additionally, the signal attributed to the S 2s

347

curves is found at 226.4 eV.

348

Table 2.

XPS fitting results of Mo 3d spectra of various sulfided NiMo/Ti-KT-x catalysts.

Mo4+ Catalysts

Mo5+

Mo6+

SMob,

ar.%a

ar.%

ar.%

ar.%

ar.%

ar.%

(229.0 eV)

(232.1 eV)

(230.1 eV)

(233.2 eV)

(232.4 eV)

(235.5 eV)

NiMo/KIT-5

32.6

21.1

2.8

1.8

25.0

16.7

53.7

NiMo/Ti-KT-60

33.1

23.9

3.3

2.2

22.5

15.0

57.1

NiMo/Ti-KT-40

37.2

24.8

2.8

2.0

19.9

13.3

62.0

NiMo/Ti-KT-20

41.2

27.4

0.8

0.5

18.1

12.0

68.6

NiMo/Ti-KT-10

42.4

17.3

4.2

2.9

19.9

13.3

59.7

349

a

%

Ar.% means the area percentage of XPS peak; b SMo=Mosulfidation= Mo4+/( Mo4++ Mo5++ Mo6+).

350

The XPS fitting results obtained by means of the deconvolution are listed in Table

351

2, in which the ratio of Mo4+ species to all the Mo species is defined as the sulfidation

352

degree of Mo species. It is worth pointing out that the modified NiMo/Ti-KT-x

353

catalysts have the higher sulfidation than NiMo/KIT-5 catalyst, since the introduction

354

of Ti species modulates the interaction between supports and active metals, thereby

355

enhancing the dispersion of active metals.36,40 With the embedded Ti species

356

increasing, the sulfuration degree of the NiMo/Ti-KT-x catalysts enhances firstly and

357

then decreases. The sulfuration degree of all the sulfided catalysts is in accordance 21


Energy & Fuels 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

358

with the order: NiMo/Ti-KT-20 (68.6 %) > NiMo/Ti-KT-40 (62.0 %) >

359

NiMo/Ti-KT-10 (59.7 %) > NiMo/Ti-KT-60 (57.1 %) > NiMo/KIT-5 (53.7 %).

360

The Ni 2p XPS spectra of sulfided NiMo/Ti-KT-x catalysts is shown in Figure S10,

361

in which it is composed of three well-revolved peaks located at around 854.1 ± 0.1

362

eV, 856.2 ± 0.1 eV and 862.1 ± 0.1 eV, belonging to NiS, NiMoS and NiO

363

species,27,36 respectively. The detailed fitting results of all the sulfided catalysts are

364

summarized in Table S2. The sulfidation degree of Ni species is calculated by using

365

the proportion of sulfided Ni species accounting for the total Ni species. It is worth

366

noting that the NiMoS percentage enhances with the increase of Ti species (x > 10),

367

confirming that the incorporation of Ti species is conducive to the formation of

368

NiMoS phase.27,36 The amounts of NiMoS phases over various sulfided

369

NiMo/Ti-KT-x change with the following order: NiMo/Ti-KT-20(69.1 %) >

370

NiMo/Ti-KT-40(67.0 %) > NiMo/Ti-KT-10(64.3 %) > NiMo/Ti-KT-60(62.7 %) >

371

NiMo/KIT-5(56.1 %). This is consistent with the results of Mo 3d XPS, indicating

372

that moderate amount of Ti species can promote the formation of active phase,

373

therefore facilitate the HDN reaction.

22


Page 22 of 42

Page 23 of 42

374

3.9 Py-IR of the catalysts

A

B L+B

L

B

a b c d

L

L+B

L

B

a

Absorbance, a.u.

L Absorbance, a.u.

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

Energy & Fuels

b c d e

e 1400

375

1450

1500

1550

1600

1650

1700

1400

1450

1500

Wavelength, nm

1550

1600

1650

1700

Wavelength, nm

376

Figure 6. Py-IR spectra of various catalysts at (A) 200 oC and (B) 350 oC: (a) NiMo/KIT-5, (b)

377

NiMo/Ti-KT-60, (c) NiMo/Ti-KT-40, (d) NiMo/Ti-KT-20, (e) NiMo/Ti-KT-10.

378

In order to assess the effect of Ti species addition on the acidic properties of

379

catalysts, a series of NiMo/Ti-KT-x catalysts are detected by the Py-IR technique, and

380

the results are displayed in Figure 6. The adsorbed pyridine molecules are degased at

381

200 oC and 350 oC, while the former represents the total acid amounts of the catalysts,

382

and the latter reflects the medium and strong acid amounts.23 The signals presented at

383

about 1450 cm-1 and 1611 cm-1 are assigned to Lewis acid; while the signal centered

384

at about 1543 cm-1 is caused by Brønsted acid. Furthermore, the peak attributed to

385

Lewis and Brønsted acid is also observed at about 1490 cm-1.35-37 As shown in Figure

386

6, the NiMo/KIT-5 catalyst has only the Lewis acid, while the modified

387

NiMo/Ti-KT-x catalysts possess Lewis and Brønsted acids simultaneously.

388 389 23


Energy & Fuels 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

390

Table 3.

Page 24 of 42

Acidities amounts over NiMo/Ti-KT-x catalysts measured by pyridine. Acid amount (200 °C)/mmol·g-1

Acid amount (350 °C)/mmol·g-1

L

B

L+B

L

B

L+B

NiMo/KIT-5

44.7

0

44.7

14.6

0

14.6

NiMo/Ti-KT-60

48.9

3.1

52.0

17.6

1.5

19.1

NiMo/Ti-KT-40

58.6

5.0

63.6

23.5

1.9

25.4

NiMo/Ti-KT-20

66.2

6.6

72.8

26.8

2.4

29.2

NiMo/Ti-KT-10

70.4

7.1

77.5

30.8

3.5

34.3

Sample

391

The detailed acid data of all the catalysts are summarized in Table 3. It is found

392

from Table 3, the NiMo/KIT-5 catalyst has the minimal amounts of total acid (44.7

393

mmol·g-1) and medium and strong acid (14.6 mmol·g-1) in contrast with the modified

394

NiMo/Ti-KT-x catalysts. Furthermore, the total acid, and the medium and strong acid

395

amounts of the modified catalysts enhance gradually with the Ti species increasing.

396

The total acidity (200 oC) and the middle strong acidity (350 oC) amounts of all the

397

catalysts are arranged with the sequence: NiMo/Ti-KT-60 (52.0 mmol·g-1, 19.1

398

mmol·g-1) < NiMo/Ti-KT-40 (63.6 mmol·g-1, 25.4 mmol·g-1) < NiMo/Ti-KT-20 (72.8

399

mmol·g-1, 29.2 mmol·g-1) < NiMo/Ti-KT-10 (77.5 mmol·g-1, 34.3 mmol·g-1).

24


Page 25 of 42 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

400

Energy & Fuels

3.10 HRTEM of the sulfided catalysts

(a)

(b)

(c)

(d)

(e)

401 402

Figure 7. HRTEM micrographs of the sulfided catalysts: (a) NiMo/KIT-5, (b) NiMo/Ti-KT-60,

403

(c) NiMo/Ti-KT-40, (d) NiMo/Ti-KT-20, (e) NiMo/Ti-KT-10.

404 405 406 407 25


Energy & Fuels 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

408

Table 4.

Page 26 of 42

HRTEM characterization of the sulfided NiMo/Ti-KT-x catalysts.

Catalyst

Lav(nm)

Nav

fMo

NiMo/KIT-5

5.41

4.23

0.17

NiMo/Ti-KIT-5-60

4.85

3.51

0.21

NiMo/ Ti-KIT-5-40

4.34

3.41

0.23

NiMo/ Ti-KIT-5-20

4.07

3.09

0.27

NiMo/ Ti-KIT-5-10

4.19

2.90

0.24

409 410

HRTEM characterization is performed to investigate the morphology and

411

dispersion of MoS2 phases formed over a series of sulfided NiMo/Ti-KT-x

412

catalysts,23,35 and the representative micrographs of the various sulfided catalysts are

413

displayed in Figure 7. It is found from Figure 7 (a) to (e) that the MoS2 slabs are

414

clearly observed. And based on 20 photographs containing 400 stacking layers, the

415

average length and number of MoS2 stacking layers are listed in Table 4.27 The data in

416

Table 4 displays that the NiMo/Ti-KT-x catalysts have the shorter length, and the less

417

numbers of MoS2 stacking layers comparing with NiMo/KIT-5 catalyst, which is

418

ascribed to the incorporation of Ti species enhancing the interaction between the

419

carriers and the active metals.36,40 Furthermore, the average length of the MoS2

420

stacking layers over all the catalysts follow the order: NiMo/KIT-5 >

421

NiMo/Ti-KT-60 > NiMo/Ti-KT-40 > NiMo/Ti-KT-10 > NiMo/Ti-KT-20. Moreover,

422

the average number of the MoS2 stacking layers over the series sulfided

423

NiMo/Ti-KT-x catalysts change in the following order: NiMo/Ti-KT-10 < 26


Page 27 of 42

424

NiMo/Ti-KT-20 < NiMo/Ti-KT-40 < NiMo/Ti-KT-60 < NiMo/KIT-5. The fMo in

425

Table 4, representing the ratio of the Mo atoms amounts located on the edge of MoS2

426

crystallites to all the Mo atoms, is applied to describe the dispersion of Mo species on

427

the sulfided catalysts. With the Ti species increasing, the fMo values of all the sulfided

428

NiMo/Ti-KT-x catalysts are in accordance with the order: NiMo/KIT-5

443

NiMo/Ti-KT-40 > NiMo/Ti-KT-10 > NiMo/Ti-KT-60 > NiMo/KIT-5, which could be

444

ascribed to the incorporation of Ti species bringing the suitable acid sites and high

445

sulfidation of active metals. Remarkably, the NiMo/Ti-KT-20 catalyst has the highest

446

HDN efficiencies (81.56 %) at the reaction temperature of 400 oC, which is about 1.57

447

times higher than that of NiMo/KIT-5 (52.05 %) under the same conditions.

448

Furthermore, the NiMo/Ti-KT-20 exhibits the higher catalytic performance than

449

NiMo/Al2O3

450

NiMo/Ti-KT-20 catalyst derives from the synergetic effect of large pore diameter and

451

ordered pore channel, high specific surface area, high sulfidation, suitable acidity and

452

moderate stacking degree of MoS2 phases.

catalysts.

The

excellent

hydrodenitrogenation

activity

of

453

The reaction network of quinoline hydrogenation is shown in Figure S11,41-45 and

454

the removal of N atoms is carried out via the two routes: one is the aromatic

455

intermediates pathway of: Q → THQ1 → OPA → PB; the other is the saturated

456

intermediates pathway of: Q → DHQ → PCHA → PCH + PCHE. The product

457

component of quinoline hydrogenation over all the catalysts is presented in Table 5. It

458

is

459

hydrodenitrogenation over different NiMo/Ti-KT-x catalysts are very high, greater

460

than 95.5%. Concluding the high contents of THQ1 and THQ5 with the low content

461

of quinoline, it is deduced that the conversion of quinoline to THQ1 or THQ5 by the

clearly

observed

from

Table

5

that

the

28


conversions

of

quinoline

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

Energy & Fuels

462

hydrogenation is very fast, while the further reaction of hydrogenation or the breakage

463

of C-N bond is relatively slow, which is consistent with previous reports.41,42 And

464

with the addition of Ti species, the content of THQ1 and THQ5 decrease significantly,

465

indicating that the introduction of Ti species enhances the hydrogenation and

466

accelerates the breakage of C-N bond.

467

Table 5.

Products selectivity of the series NiMo/Ti-KT-x catalysts in quinoline HDN. NiMo/Ti-KT-1

Selectivity (%)

NiMo/KIT-5

NiMo/Ti-KT-60

NiMo/Ti-KT-40

NiMo/Ti-KT-20

PCH

20.92

26.82

36.28

42.89

31.23

PCHE

8.48

9.17

11.04

10.87

11.87

PB

12.77

14.80

18.23

18.99

16.13

DHQ

9.66

8.44

7.21

5.52

8.04

THQ5

20.16

17.58

10.08

6.44

13.22

OPA

7.13

5.22

3.15

2.72

3.51

Q

4.17

3.48

2.62

2.24

3.12

THQ1

16.71

14.49

11.17

10.34

12.20

PCH/PB

1.64

1.81

2.00

2.24

1.93

0

468 469

The PCH and PB generally represent the selectivity of saturated intermediates

470

pathway and aromatic intermediates pathway, respectively. As shown in Table 5, and

471

the PCH selectivity is much higher than PB on the series NiMo/Ti-KT-x catalysts,

472

demonstrating that the saturated intermediates pathway is the main route, which is

473

consistent with the previous researches.41,42 The PCH/PB ratio of the serious 29


Energy & Fuels 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

Page 30 of 42

474

NiMo/Ti-KT-x catalysts is higher than that of NiMo/KIT-5, illustrating that doped Ti

475

species enhance the selectivity of the saturated intermediates pathway. As the

476

embedded Ti species increase, the PCH/PB ratio of various catalysts firstly increases,

477

and then decreases. Moreover, it changes with the order: NiMo/Ti-KT-20 (2.24) >

478

NiMo/Ti-KT-40 (2.00) > NiMo/Ti-KT-10 (1.93) > NiMo/Ti-KT-60 (1.81) >

479

NiMo/KIT-5 (1.64). Among all the NiMo/Ti-KT-x catalysts, the NiMo/Ti-KT-20 has

480

the highest PCH/PB ratio, which is ascribed to the following factors: (1) high specific

481

surface area and pore volume; (2) open three-dimensional channel and abundant

482

intergranular pores; (3) more embedded Ti species, which brings more acid sites and

483

high sulfidity degree. Additionally, the kHDN and TOF values of various

484

NiMo/Ti-KT-x catalysts are consistent with the below order: NiMo/Ti-KT-20 (3.94 ×

485

10-4 mol g-1 h-1, 10.60 × 10-1 h-1) > NiMo/Ti-KT-40 (2.59 × 10-4 mol g-1 h-1, 8.60 ×

486

10-1 h-1) > NiMo/Ti-KT-10 (1.87 × 10-4 mol g-1 h-1, 7.49 × 10-1 h-1) > NiMo/Ti-KT-60

487

(1.49 × 10-4 mol g-1 h-1, 6.94 × 10-1 h-1) > NiMo/KIT-5 (1.26 × 10-4 mol g-1 h-1, 5.820

488

× 10-1 h-1).

489

Table 6.

Rate constants and TOF values of different NiMo/Ti-KT-x catalysts for quinoline HDN

490

at 380 oC. Catalyst

kHDN(10-4 mol g-1 h-1)

TOF (10-1 h-1)

NiMo/KIT-5

1.26

5.82

NiMo/Ti-KT-5-60

1.49

6.94

NiMo/ Ti-KT-5-40

2.59

8.60

30


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

Energy & Fuels

NiMo/ Ti-KT-5-20

3.94

10.60

NiMo/ Ti-KT-5-10

1.87

7.49

491 492

4. DISCUSSION

493

The catalytic activities of various NiMo/Ti-KT-x catalysts are closely connected with

494

the structural properties, the sulfidation of active species, acidities and the

495

morphologies of MoS2 active phases.

496

The pore structural properties greatly affect the diffusion of reactants and products

497

in channel and the distribution of active metals (Mo and Ni species) over the supports.

498

It can be noted from Figure 1 and Figure 2 that the modified Ti-KT-x materials still

499

maintain the relatively orderly mesoporous channels. Considering the pore data in

500

Table 1, the Ti-KT-20 support has the high specific surface area (827 m2·g-1) and

501

volume (0.90 cm3·g-1), and large pore size (9.3 nm), which effectively promote the

502

transfer of quinoline and its hydrogenation products.

503

The sulfided species of catalysts have a significant effect on the catalytic activities,

504

which is closely connected with the dispersion of active metals and the interaction

505

between the supports and active metals (MSI). Generally speaking, the moderate

506

interaction is conductive to the dispersion of active metals. The incorporated Ti

507

species can enhance the interaction of the mesoporous silica and promote the

508

dispersion of active metals, which is confirmed by the Raman spectra. As shown in

509

Figure 4, the peaks ascribed to the high coordination polymolybdate species of 31


Energy & Fuels 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

510

modified NiMo/Ti-KT-x catalysts are relatively intensifier than that of the

511

NiMo/KIT-5 catalyst. The peak of the high coordination polymolybdate species of the

512

NiMo/Ti-KT-20 is relatively intensifier than other catalysts. Furthermore, the Ti

513

species, especially Ti3+, as the electronic promoters, enhance the sulfidation of Mo

514

and Ni species. The NiMo/Ti-KT-20 catalyst with the largest percentage of Ti3+

515

species (7.5 %) displays the highest sulfuration of Mo species (68.6 %) and Ni species

516

(70.1 %), which facilitate the hydrodenitrogenation reaction.

517

The acid properties, especially the existence of B acid, are the important factors for

518

catalytic activities and product selectivity. The pure NiMo/KIT-5 catalyst possesses

519

very few Lewis acid (44.7 mmol·g-1) and lack of B acid. By incorporating Ti atoms

520

into the framework of KIT-5 material, the amount of acid sites of the catalysts

521

increase significantly due to the difference of coordination number between silica and

522

titanium. Combining the data in Table 3 and Figure 8, it is clearly observed that the

523

modified NiMo/Ti-KT-x catalysts with more acid sites displayed the higher

524

hydrodenitrogenation efficiencies than NiMo/KIT-5 catalyst. Especially, the

525

NiMo/Ti-KT-20 catalyst with the suitable amounts of total acid sites (72.8 mmol·g-1)

526

and B acid sites (6.6 mmol·g-1) has the highest hydrodenitrogenation activities

527

(80.56 %) under the reaction condition, simultaneously possesses the highest PCH/PB

528

ratio, demonstrating that appropriate amount of acid sites are favorable for the

529

cleavage of C-N bond.

530

Additionally, the catalytic activities of NiMo/Ti-KT-x catalysts depend on the 32


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Energy & Fuels

531

structure of MoS2 active phase. It is clearly noted from Table 4, the Ti species

532

addition is linearly related to the distribution of MoS2 active phases. With the Ti

533

species increasing, the average stacking lengths and stacking numbers of MoS2

534

gradually decrease due to the enhanced interaction between active metals and

535

supports. Among all the catalysts, the NiMo/Ti-KT-20 catalyst with the shorter length

536

(4.07 nm), and the suitable number (3.09) of MoS2 stacking layers reveals more brim

537

and edge sites, and displays the highest catalytic performance.

538

Above all, the excellent hydrodenitrogenation activity of NiMo/Ti-KT-20 catalyst

539

could ascribe to the synergistic effect of its high surface area and pore volume, open

540

three-dimensional channel, the highest sulfidation, suitable amount of acid sites and

541

moderate distribution of MoS2 stacking layers. Meanwhile the NiMo/Ti-KT-20

542

catalyst has the maximum kHDN (3.94 × 10-4 mol g-1 h-1) and highest selectivity of

543

PCH/PB (2.24).

544

5. CONCLUSION

545

A series of Ti-KT-x samples with different ratios of Si/Ti were prepared by the direct

546

synthesis method, and the modified Ti-KT-x (x>10) materials retained the orderly

547

mesoporous structure. Meanwhile the characterization results of FT-IR and XPS

548

spectra revealed that the Ti species were successfully embedded into the framework

549

of KIT-5 material, and when the ratio of Si/Ti was less than 60, TiO2 crystallite

550

appeared on the surface of supports. The Ti-KT-20 sample with more Ti loading

551

possessed relatively high surface area (827 m2·g-1) and pore volume (0.90 cm3·g-1), 33


Energy & Fuels 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

552

open and orderly three-dimensional channel (9.3 nm).

553

The NiMo/Ti-KT-20 catalyst exhibited the highest reaction performance in

554

quinoline hydrodenitrogenation, and had the maximum kHDN (3.94 × 10-4 mol g-1 h-1)

555

and TOF (10.60 × 10-1 h-1), which was attributed to the highest sulfidation (68.6 %),

556

suitable acid sites and MoS2 stacking layers.

557

ASSOCIATED CONTENT

558

Supporting Information

559

The Supporting Information is available.

560

Wide angle XRD patterns of the series Ti-KT-x materials (Figure S1), UV-Vis DRS

561

spectras of different materials (Figure S2), SEM spectra of different materials (Figure

562

S3), SEM-mapping image and EDS elemental mapping analysis of Ti-KT-40 material

563

(Figure S4), TEM spectra of the series Ti-KT-x materials (Figure S5), Sizes

564

distribution of TiO2 particles on the Ti-KT-10 material (Figure S6), H2-TPR technique

565

of the series NiMo/Ti-KT-x catalysts (Figure S7), XPS spectra (O 1s) of the sulfided

566

catalysts (Figure S8), XPS spectra (Ti 2p) of the sulfided NiMo/Ti-KT-20 catalyst

567

(Figure S9), Ni 2p XPS spectra of the sulfided NiMo/Ti-KT-x catalysts (Figure S10),

568

HDN reaction network of quinoline (Figure S11), Quinoline HDN results with time

569

on stream over NiMo/Ti-KT-20 catalyst (Figure S12), XPS fitting results of Ti 2p

570

spectra of the sulfided NiMo/Ti-KT-x catalysts (Table S1), XPS fitting results of Ni

571

2p spectra of the sulfided NiMo/Ti-KT-x catalysts (Table S2) and Ti content of the

572

series modified Ti-KT-x materials by ICP method (Table S3). 34


Page 34 of 42

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Energy & Fuels

573

AUTHOR INFORMATION

574

Corresponding Author

575

*Tel: 86-10-89732290. E-mail: [email protected].

576

Notes

577

The authors declare no competing financial interest.

578

ACKNOWLEDGEMENTS

579

This work was financially supported by the National Natural Science Foundation of

580

China (No. 21676298, 21878330, U1463207 and 21503152), CNPC Key Research

581

Project and KLGCP (GCP201401).

582

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and

its

high

isomerization

performance

38


for

hydrodesulfurization

of

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41


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254x190mm (96 x 96 DPI)


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Synthesis of Titanium Modified Three-Dimensional KIT-5 Mesoporous

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