CuY core-shell structure for the

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Materials and Interfaces

Alkali-treatment of silicalite-1/CuY core-shell structure for the adsorption desulfurization of dimethyl disulfide from methyl tert-butyl ether Chao Yang, Xuan Meng, Dezhi Yi, Zhiming Ma, Naiwang Liu, and Li Shi Ind. Eng. Chem. Res., Just Accepted Manuscript • DOI: 10.1021/acs.iecr.8b06463 • Publication Date (Web): 04 Jan 2019 Downloaded from http://pubs.acs.org on January 11, 2019

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Industrial & Engineering Chemistry Research

1

Alkali-treatment of silicalite-1/CuY core-shell structure for the

2

adsorption desulfurization of dimethyl disulfide from

3

methyl tert-butyl ether

4

Chao Yang, Xuan Meng, Dezhi Yi, Zhiming Ma, Naiwang Liu, Li Shi*

5

State Key Laboratory of Chemical Engineering,

6

East China University of Science and Technology, Shanghai 200237, China

7

E- mail: [email protected]

8

Abstract: NaOH treated silicalite-1/CuYOH core-shell composites were synthesized at

9

the mass ratio of tetraethyl orthosilicate (TEOS)/ tetrapropylammonium hydroxide

10

(TPAOH)/ ethanol/ H2O/ CuY=20 g (0.096 molar):19 g (0.0234 molar):17 g (0.369

11

molar):87 g (4.8293 molar):5 g to achieve the selective adsorption desulfurization of

12

dimethyl disulfide (DMDS) from methyl tert-butyl ether (MTBE). As the core zeolite,

13

CuY was obtained by Cu2+ ion-exchange on NaY. After alkali treatment, NaY zeolite

14

was provided with more loading positions for silicalite-1 crystals owing to the

15

desilication effect of NaOH. Results showed that the core-shell YOH-CuCl2 displayed

16

the best performance in desulfurizing DMDS from MTBE with a sulfur adsorption

17

capacity of 37.073 mgs/gadsorbent for the sake of its significant mass gain and compact

18

silicalite-1 coatings. The preparation of silicalite-1/CuYOH core-shell composites and

19

the shape selective adsorption mechanism of desulfurizing DMDS on these core-shell

20

composites were expounded.

21

Key words: Desilication; silicalite-1/CuY core-shell composites; selective adsorption

22

desulfurization; Methyl tert-butyl ether; Dimethyl disulfide.

23

1. Introduction

24

An increasing concern about lowering sulfur content in liquid fuels has been the

25

focus issue on environmental pollution due to detrimental environmental impacts

26

caused by the emission of sulfur oxides,1, 2 among which the SO2 is considered the

27

chief element leading to acid rain and ozone depletion, as well as some serious

28

diseases such as eye and throat irritation and heart disease.3, 4 Consequently, more and

29

more countries have put into effective measures in restricting sulfur content in

ACS Paragon Plus Environment

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

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gasoline and diesel fuel at a low level (< 10 ppm S).5-8

31

Methyl tert-butyl ether (MTBE) as a gasoline additive agent has been widely

32

applied based primarily on its good octane-enhancing property.9 As was known that

33

MTBE was produced by the reaction of methanol and isobutene (isobutene was

34

contained in C4-fractions). However, besides the isobutene, there are various kinds of

35

sulfur compounds especially the dimethyl disulfide (DMDS).10 When using this C4

36

stream to produce MTBE, DMDS in the products would reach more than 45 ppm,11

37

which will cause toxic effects when inhaled or absorbed by skin as well as release

38

oxygen (SOx) emissions after being burned. The imposition of increasingly stringent

39

environmental standards on sulfur content of gasoline and diesel fuels has made it

40

highly urgent to develop new strategies for handling with this kind of needs.6, 10, 12-15

41

Catalytic hydrodesulfurization (HDS), distillation desulfurization (DDS), and

42

adsorption desulfurization (ADS) are the major methods that have been used in

43

desulfurization of MTBE.16-22 Generally, HDS is carried out with Co-Mo/A12O3 or

44

Ni-Mo/A12O3 etc. as the catalysts at 300-400 °C and 3-7 MPa of H2. However,

45

besides this harsh operating conditions, HDS can not also meet the current deep

46

desulfurization requirements and is always accompanied by the loss of octane number

47

of MTBE. Meanwhile, despite DDS can acquire deep desulfurization, it needs huge

48

energy consumption and inevitably causes the loss of MTBE. Whereas, among these

49

technologies proposed for the deep desulfurization (< 10 ppm S), ADS appears to be a

50

promising technology which can be carried out at atmospheric temperature and low

51

pressure with a simple operation and low energy consumption as well as no hydrogen

52

and catalyst requirements.14, 23-25

53 54

Scheme. 1. Structure of (1) DMDS and (2) MTBE.


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55

So far, various types of adsorbents have been reported for the desulfurization in

56

liquid fuels: activated carbons (ACs), alumina, modified composite oxide, zeolites,

57

mesoporous silica and metal-organic frameworks (MOF).26-28 However, when

58

desulfurizing DMDS from MTBE by adsorption, a strong competitive adsorption

59

between MTBE and DMDS on π-complex adsorbents would occur.19, 29 As a matter of

60

fact, DMDS and MTBE were adsorbed on these absorbents by π-complexation of

61

metal-S.19, 30, 31 Combining with the structure of DMDS and MTBE shown in Scheme.

62

1, the methyl and tert butyl are both electron donating groups, and the electron

63

donating ability of tert butyl is better than that of methyl. As a result, the

64

electronegativity of O in MTBE is weakened more than S in DMDS, leading to a

65

smaller electronegativity gap between S and O. When they form metal-S and metal-O,

66

it does not make much difference. In MTBE solution, the MTBE was much more than

67

DMDS; the contact probability between adsorbents and MTBE is absolutely much

68

more than that of DMDS. Thus, for DMDS, MTBE comes into being a strong

69

competitive adsorption on these π-complexation adsorbents.32 Yang and co-workers

70

had confirmed that the sulfur adsorption capacity of the π-complex adsorbents would

71

sharply decrease in the presence of MTBE and even completely lose within large

72

amounts of MTBE.14, 23 Thus, the selective adsorption for organosulfur compounds

73

still remains as a great challenge. To meet the selectivity requirements, special

74

attention has been given to improve the interaction between the S-compounds and

75

modified adsorbents via π-complexation, van der Waals’ interaction, electrostatic

76

interaction, and (or) reactive chemisorption.29,

77

zeolite and its modified one had been proved to be promising materials to meet this

78

requirement in adsorptive desulfurization extensively.39-41 The unit cell of NaY zeolite

79

consisted of 18 four-membered rings, 4 six-membered rings and 4 twelve-membered

80

rings. The diameter of the main channel entrance with twelve-membered ring was

81

0.8-0.9 nm. The maximum diameter of the main hole (or super cage) was about 1.25

82

nm with a volume of about 0.850 nm3, providing NaY a possibility to store DMDS.

32-38

Researches suggested that Y

83

Lv et al.42 studied the adsorptive separation of DMDS from liquefied petroleum

84

gas by different zeolites, and concluded that 5 wt% Ag2O/NaY showed the highest



85

breakthrough sulfur capacity reaching up to 87.86 mgs/gadsorbents, and the direct S-Ag(I)

86

interaction played an important role in the evidently improved adsorption ability and

87

selectivity; Wakita et al.41 investigated the removal of dimethyl sulfide and

88

t-butylmercaptan in the city gas by using NaY, NaX, Hβ zeolite. They found that the

89

adsorption site of NaY was the Na+ in the supercage with a maximum sulfur capacity

90

to be 1.1 mmols/gadsorbents of DMS on NaY;

91

to remove DMDS from C4 hydrocarbon mixture and claimed that ion-exchanged

92

zeolites were favorable adsorbents with high capacity in removal of DMDS from gas

93

hydrocarbon mixture at ambient conditions. Results showed that the best sulfur

94

capacity was 8.70 mgs/gadsorbents, when β zeolite with a SiO2/Al2O3 ratio of 25

95

contented 10 wt% of Cu(I); Zhao et al.43 aimed at the removal of DMDS from MTBE

96

by using ZSM-5 zeolites. Investigation showed that both the pore structure and acidity

97

played important roles in determining the sulfide adsorption process and

98

CLD-modified ZSM-5 zeolite exhibited an optimal DMDS adsorption capacity to be

99

8.24 mgs/gadsorbents. Our research group also tried many efforts in desulfurizing DMDS.

100

Dezhi Yi et al.11, 44 used silver-modified bentonite and liquid-phase ion exchanged

101

NaY with Cu2+, Ni2+, Co2+ and Ce3+ to remove DMDS from n-octane solution and

102

concluded that multilayer intermolecular forces and S-M bonds played important roles

103

in desulfurization process. In these studies, we had got a good understanding that the

104

organic sulfur (DMDS) in mixtures could be removed by adsorption on zeolites

105

including NaY, ZSM-5 or β loaded with different metal ions (Cu2+, Ag+, Ni2+ etc.).

106

However, all these research did not give a solution to a question that when there were

107

substances in the mixture that could initiate competitive adsorption effects with

108

DMDS, such as MTBE, and that’s why the silicalite-1/CuYOH core-shell composites

109

were synthesized and studied in this research.

Lee et al.10 used ion-exchanged zeolites

110

Silicalite-1 as the high-silica zeolites, actually pure silicon owning the same

111

topological structure as ZSM-5 only without aluminum, contained ten-membered

112

rings with a basic structural unit made up of eight five-membered rings; and the

113

maximum aperture was less than 0.6 nm, which provided silicalite-1 a shape

114

selectivity to allow DMDS to pass by only. In the present study, considering that NaY


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115

zeolite had a high sulfur adsorption capacity; and silicalite-1 owned a higher shape

116

selectivity. We coated the Cu2+ ion-exchanged NaY (CuY) with an silicalite-1 shell

117

(pure silica crystal) to form a silicalite-1/CuY core-shell composite to achieve

118

selective adsorption desulfurization. Zhao et al.45 had successfully synthesized

119

core-shell structured composite molecular sieves comprising mono-dispersed

120

nano-zeolite Y as cores and ordered silica as shells. In order to provide a better

121

growing environment on the surface of NaY, before ion exchange with Cu2+, NaY

122

zeolite was treated by 0.5 mol/L aqueous NaOH solution; by desilication effects,46, 47

123

NaY zeolites were provided with an enlarged out-surface area, producing more

124

loading positions for silicalite-1 crystals. In this paper, different copper ion source

125

(CuCl2, Cu(NO3)2 and CuSO4) were used to synthesize silicalite-1/CuY core-shell

126

composites. Moreover, these adsorbents were characterized by Scanning electron

127

microscopy (SEM), Transmission electron microscope (TEM), X-ray diffraction

128

(XRD), ICP-OES, EDS measurements, Fourier transform infrared spectra (FT-IR),

129

and N2 adsorption-desorption. Selective adsorption mechanism of silicalite-1/CuY

130

core-shell composites was also discussed based on these experimental data and

131

characterization analysis.

132

2. Experimental

133

2.1. Material preparation

134

The NaY zeolites (Si/Al = 2.4) with a industrial grade were provided by

135

Wenzhou Catalyst Factory. Analytically pure sodium hydroxide (NaOH), copper

136

chloride (CuCl2), copper nitrate (Cu(NO3)2), copper sulfate (CuSO4), ethanol (EtOH),

137

tetraethyl orthosilicate (TEOS) and 25 % tetrapropylammonium hydroxide (TPAOH)

138

solution were obtained from Shanghai Tansoole Company. Deionized water was used

139

throughout the experiments.

140

2.2. Alkaline treatment of NaY

141

NaY zeolites were added into 0.5 mol/L aqueous NaOH solution (1g NaY : 30

142

mL NaOH solution), then this solid-liquid system was kept at 25 °C and persistently

143

stirred for 1 h to keep a full mix.48 The separation of this slurry was carried out by two

144

different methods to collect the alkaline treated NaY zeolites:49 filtration (maximum



145

pore size of filter paper to be 15-20 μm) and centrifugation (6000 r/min for 30 min);

146

then the alkaline treated NaY zeolites were washed thoroughly with hot deionized

147

water and dried at 120 °C. The alkaline treated NaY was denoted as NaYOH.

148

2.3. Synthesis of CuYOH, silicalite-1 and CuYOH core-shell composites

149

2.3.1. Preparation of CuYOH zeolites

150

CuYOH zeolites were prepared through liquid phase ion-exchange by modifying

151

NaYOH zeolites with different Cu2+ resources (CuCl2 (aq), Cu(NO3)2 (aq), CuSO4 (aq))43, 44,

152

50

153

liquid ratio of 1 g: 20 ml); after a 24 h-stirring in the water bath at 90 °C, the mixture

154

was separated by suction filter; then washed with enough deionized water, dried at

155

120 °C overnight, and finally calcined in air at 450 °C for 6 h. The modified NaYOH

156

were denoted as YOH-CuCl2, YOH-Cu(NO3)2 and YOH-CuSO4, respectively.

157

2.3.2. Synthesis of CuYOH core-shell composite molecular sieves

: proper amount of NaYOH zeolites were added into 0.5 mol/L Cu2+ solution (solid to

158

In this study, a sol-gel coating process with TPAOH as the template was

159

conducted to synthesize the silicalite-1/CuYOH core-shell structured composite

160

molecular sieves:51

161

The silicalite-1 coatings were synthesized from silicalite-1 shell precursor

162

solution consisting of TEOS (silica source), TPAOH (template or structure-directing

163

agent) and EtOH, as well as deionized water with a mass ratio of TEOS/ TPAOH/

164

ethanol/ H2O=20 g:19 g:17 g:87 g (0.096: 0.0234: 0.369: 4.8293 in molar ratio). In

165

this process, TEOS was added dropwise and stirred for 2 h at room temperature to

166

sufficiently hydrolyze TEOS into deionized water; then 5 g CuYOH was added to form

167

a homogeneous suspension. This suspension was transferred into an autoclave; after a

168

hydrothermal synthesis being carried out at 180 °C for 24 h, silicalite-1/CuYOH

169

core-shell structured composites were collected by suction filtration, washed

170

thoroughly with deionized water, dried at 120 °C overnight, and finally calcined in air

171

at 550 °C for 6 h. The core-shell CuYOH composite molecular sieves were denoted as

172

CSYOH-CuCl2, CSYOH-Cu(NO3)2 and CSYOH-CuSO4, respectively.

173

2.3.3 Preparation of silicalite-1 and NaYOH core-shell composites

174

Silicalite-1 was prepared at the same mass ratio of TEOS/ TPAOH/ ethanol/ H2O


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175 176


=20 g:19 g:17 g:87 g with the same synthetic method only without adding CuYOH. Alkaline treated NaY core-shell composites were prepared in the same operation

177

process with only changing CuYOH into NaYOH, denoted as CSNaYOH.

178

2.4. DMDS adsorption experiments

179

2.4.1. Static adsorption tests

180

In order to obtain the sulfur adsorption capacity of each adsorbent, the static

181

adsorption tests were conducted. The static adsorption tests were carried out by

182

adding 0.2 g adsorbent into a 20 mL MTBE solvent with DMDS as the solute (sulfur

183

content: 748.52 mg/L) in an 30 ml airtight container standing at room temperature for

184

24 h. After a full adsorption, a TS-3000 fluorescence sulfur tester was used to analyze

185

the concentration of sulfur before and after the static tests.11,

186

adsorption capacity of the adsorbent was calculated as follow:

187

Sulfur adsorption capacity (mgs/gadsorbent) = (748.52- Ct)×20/0.2;

188

where the Ct (mg/L) was the sulfur concentration of MTBE solution after static tests.

189

2.4.2. Dynamic adsorption tests

44, 52

The sulfur

190

To acquire the dynamic active data of each adsorbent, they were filled into a

191

fixed bed flow reactor at 0.1 MPa and 25 °C, with a weight hourly space velocity of 5

192

h-1 to evaluate their adsorption desulfurization rate. In this process, a quartz column

193

(length: 250 mm; internal diameter: 6 mm) was needed, in the middle of which about

194

0.89 g adsorbent samples (20-40 mesh) were fixed; while the spare spaces up and

195

down were filled with quartz sand (20-40 mesh) to keep the adsorbents from being

196

washed away by the MTBE solution, which was pumped into the fixed-bed flow

197

reactor at a flow rate of 6 mL/h (sulfur content: 286.13 mg/L). The export sulfur

198

content was analyzed by a TS-3000 fluorescence sulfur tester every 30 min.

199

2.5. Characterization of materials

200 201 202 203 204

Scanning electron microscopy (SEM) images were recorded on a Hitachi S-3400 microscope working at 15 KV acceleration voltage with a magnification of 1-20 K. Transmission electron microscope (TEM) images were conducted on a JEM-2100 working at 200 KV with a magnification of 2-1500 K. A X-ray Diffraction (XRD) was applied to characterize the crystal structures of



205

these silicalite-1/NaYOH (CuYOH) core-shell composites in powder state, which was

206

performed by a D8 Advance polycrystalline diffractometer equiped with Cu Kα

207

radiation (40 KV, 100 mA) over the range from 10° to 75° in a step of 0.02°.

208

Fourier transform infrared spectra (FT-IR) was collected with a Magna-IR550

209

spectrometer (Nicolet Company) by mixing the adsorbent sample powder with the

210

dried KBr in an appropriate mass ratio (1:100). And the finely ground adsorbents were

211

pressed into a self-supporting wafer with a diameter of about 10 mm.

212

To obtain the surface area and pore volume of the adsorbents, a JW-BK200C

213

instrument was used by adsorbing nitrogen at -196 °C on 150 mg of sample, which

214

must be previously degassed at 300 °C for at lest 2 h under high vacuum atmosphere.

215

The BET surface area (St), total pore volume (Vt), micropore volume (Vmic) could be

216

calculated by nitrogen isotherms.

217

Additionally, in order to verify the element distribution of different adsorbents

218

(variation of silicon and aluminum after alkali treatment and core-shell experiment)

219

and the actual Cu2+ loading amount, EDS and ICP-OES measurements (total copper

220

in solid sample) were conducted via a TEAMEDS and Agilent 725 ICP-OES.

221

3. Results and discussion

222

3.1. Mass gain of NaYOH and NaYOH/CuYOH after coating silicalite-1.

14 12

in theory after filtration after centrifugation


120 100

8

80

6

5g

60

4.653 4.76

40

2

20

0 NaYOH

225

140

mass gain (%)

mass gain (g)

10

4

223 224

160

Mass gain (%)

16

Mass gain (g)

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 8 of 34

CSNaYOH

CSYOH - CuCl2

CSYOH - Cu(NO3)2

CSYOH - CuSO4

0

Figure. 1. Mass gain of NaY after NaOH treatment and NaYOH/CuYOH after coating silicalite-1.

In this research, we aimed at synthesizing a kind of core-shell composite with


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226

NaYOH or CuYOH as the core zeolite and silicalite-1 as the coating to realize the

227

selective adsorption of DMDS from MTBE solution. Obviously, compared with

228

NaYOH or CuYOH, the synthesized core-shell composites were definitely heavier, and

229

after being treated by NaOH, the NaYOH were certainly lighter. In this study, two

230

different methods were tried to collect NaYOH and core-shell structured composites:

231

filtration (maximum pore size of filter paper to be 15-20 μm) and centrifugation (6000

232

r/min for 30 min). As shown in Figure. 1, 5 g NaY zeolites decreased to 4.653 g after

233

NaOH treatment collected by filtration, owing to the desilication effects of NaOH (aq)

234

on siliceous molecular sieves including Y and ZSM-5;46, 47 and the removed silicon

235

would generate Si(OH)4 (aq) dissolving in water solvent. Meanwhile, NaOH (aq)

236

could also smash the NaY zeolites into smaller particles, which could be easily

237

filtered out with water through the filter paper, making the mass gain from

238

centrifugation slightly higher than that from filtration.

239

When NaYOH and CuYOH were coated with silicalite-1 by hydrothermal synthesis,

240

according to the mass ratio (TEOS/ TPAOH/ ethanol/ H2O/ NaYOH (or CuYOH) = 20

241

g:19 g:17 g:87 g:5 g), the mass gain of NaYOH and CuYOH zeolites should be a

242

constant value in theory shown as the blue area or line. After centrifugation, the mass

243

gain of NaYOH and CuYOH zeolites were almost all close to that of theory. In contrast,

244

the red area or line showed that after filtration, the mass gain had decreased a lot.

245

Based on this phenomenon, we assumed that a certain number of silicalite-1 crystals

246

did not grow on the external surface of NaYOH or CuYOH zeolites, but formed a

247

homogeneous nucleation in the solution, and these silicalite-1 crystals made no

248

contribution to the external surface modification of the NaYOH or CuYOH zeolites.53

249

Generally, these silicalite-1 crystals produced by homogeneous nucleation were very

250

small in size, which could be easier to pass filter paper, leading to a difference mass

251

gain between centrifugation and filtration. In addition, with the change of different

252

Cu2+ resources from CuCl2, Cu(NO3)2 to CuSO4, the mass gain of CuYOH was

253

successively reduced. However, the mass gain showed on the the red area or line also

254

suggested that more silicalite-1 crystals had been successfully coated on NaYOH and

255

CuYOH surface, forming a silicalite-1 shell around. In this research, the core-shell



256

composites by filtration were investigated.

257

3.2. XRD patterns of adsorbents.

258

In the mass gain analysis, we believed that the silicalite-1 crystals had been

259

coated on NaYOH and CuYOH surface. In order to confirm this conclusion, X-ray

260

diffraction patterns were conducted to identify the mineralogical structure of these

261

adsorbents. As shown in Figure. 2, the characteristic peaks at 2θ=15.64° and 23.64°

262

were considered the feature peaks of NaY zeolite.44 Figure. 2 (2) made it clear that

263

after being treated by NaOH, all the characteristic peaks of the Y molecular sieve was

264

retained. Figure. 2 (3)-(5) suggested that after being modified by Cu2+, CuYOH also

265

maintained the same characteristic peaks of Y zeolites. However, both NaOH

266

treatment and Cu2+ modification would decrease the crystallinity of NaY, due to the

267

framework defects caused by desilication effects and Cu2+ modifying process.

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 10 of 34

10

15

20

25

30

35

(5)

(10)

(4)

(9)

(3)

(8)

(2)

(7)

(1)

(6) 40 10

15

20

25

30

35

40

2-Theta (degrees)

268 269 270 271

Figure. 2. X-ray diffraction patterns of NaY, silicalite-1, NaYOH /CuYOH and NaYOH /CuYOH with silicalite-1 shell: (1) NaY, (2) NaYOH, (3) YOH-CuCl2, (4) YOH-Cu(NO3)2, (5) YOH-CuSO4, (6) silicalite-1, (7) CSNaYOH, (8) CSYOH-CuCl2, (9) CSYOH-Cu(NO3)2, (10) CSYOH-CuSO4.

272

After being coated by silicalite-1, the XRD patterns of the NaYOH or CuYOH with

273

silicalite-1 shell showed the same diffraction peaks as Y zeolite, suggesting that the

274

crystalline of Y zeolite framework was retained during the coating process;45 and the

275

intensity of the Y zeolite characteristic peaks were further decreased, which were

276

mostly ascribed to the coating process of diluted zeolites as the mesoporous shell and

277

the weak shielding effects of mesoporous shells on X-rays.45 Compared with parent


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278

NaY, and silicalite-1 crystal, there was a great distinction in the X-ray diffraction

279

patterns of the core-shell structured NaYOH or CuYOH, but the same feature peaks of

280

both NaY and silicalite-1 crystal were preserved. The most intense peaks of MFI-type

281

material, especially between 2θ=22-25° indicated that the silicalite-1 shell was

282

successfully coated on the surface of NaYOH and CuYOH.54

283

3.3. SEM and TEM images of NaY, NaYOH, CuYOH and the core-shell composites (b)

(a)

2 um

1 um

2

(c)

(d)

0.5 um

0.5 um

284 285

Figure. 3. SEM images of (a) NaY, (b) NaYOH, (c) CSNaYOH, (d) CSYOH-CuCl2.

(a)

(b)

100 nm

(c)

100 nm

(d)

200 nm

286 287

200 nm

Figure. 4. TEM images of (a) NaY, (b) YOH-CuCl2, (c) CSNaYOH, (d) CSYOH-CuCl2.

288

The SEM images in Figure. 3 (a) and (b) displayed the overall morphology of

289

NaY zeolites before and after NaOH treatment. Images showed that the parent NaY

290

zeolites presented a regular shape; however, after being treated by NaOH, besides the

291

corrosion on the surface, NaY zeolites were broken into smaller and irregular particles.

292

Compared with the parent NaY zeolites, it was obvious that the outer surface area of

293

NaYOH was significantly improved, which was beneficial for coating silicalite-1 shell

294

owing to more attachment points being produced. Figure. 3 (c) and (d) exhibited the



Page 12 of 34

295

morphology of core-shell composites CSNaYOH, and CSYOH-CuCl2, respectively; and

296

the significant silicalite-1 coating could be obviously observed. Compared with our

297

previous work,49 the NaYOH and YOH-CuCl2 zeolites were coated more completely.

298

For the sake of a more intuitive understanding of core-shell structure, TEM was

299

conducted and TEM images were shown in Figure. 4. The parent NaY zeolite in

300

Figure. 4 (a) exhibited a relatively smooth surface. Correspondingly, as depicted in

301

Figure. 4 (b), after being treated by NaOH and ion exchanged by Cu2+ (CuCl2),

302

considerable quantity of broken and smaller molecular sieve particles were observed;

303

meanwhile, Cu2+ was found to be well dispersed in molecular sieves by ion exchange

304

method. Figure. 4 (c) and (d) presented the core-shell structure of CSNaYOH and

305

CSYOH-CuCl2, respectively; results showed that a clearly and fully coated silicalite-1

306

shell was formed around the Cu2+ modified NaY zeolite. At this point, the core-shell

307

system was finally confirmed.

308

3.4. Element distribution analysis of different adsorbents.

309

Table. 1. Variation of silicon and aluminum after alkali treatment and core-shell experiment. Sample

Si (mg/g)

Al (mg/g)

Si/Al

NaY NaYOH YOH-CuCl2 CSY-CuCl2 CSYOH-CuCl2

28.3 25.2 24.4 28.4 35

11.3 11.9 11.5 8.1 6.8

2.41 2.04 2.05 3.38 4.96

310 311

To validate the element distribution and content of different adsorbents, EDS and

312

ICP-OES measurements were conducted and shown in Table. 1 and Figure. 5. In this

313

research, the Si/Al (mole ratio of Si to Al) of parent NaY zeolite was 2.4. By

314

comparison, the value of ICP was very close to 2.4 (2.41, ICP), owing to that ICP

315

tested the Si/Al within the whole sample, and the value of EDS displayed a deviation

316

to be 2.52 for the sake of detecting the surface of samples only. After alkaline

317

treatment, an obvious decline of Si/Al (2.04) with a basically unchanged aluminum

318

content was observed, indicating that some of the element Si in NaY zeolite were

319

removed after alkaline treatment;46, 47 when combined with EDS (2.04), it could draw

320

a conclusion that the vast majority of these removed Si came from the surface of NaY


Page 13 of 34 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


321

zeolite; and the absence of silicon would inevitably leave many vacancies and enlarge

322

the out surface area of NaY zeolites. (a)

(b)

(c)

(d)

323 324

Figure. 5. EDS analysis of (a) NaY, (b) YOH-CuCl2, (c) CSY-CuCl2, (d) CSYOH-CuCl2.

325

By liquid phase ion-exchange with CuCl2, the Si/Al of NaYOH showed no big

326

difference (2.05). After coating Y-CuCl2 and YOH-CuCl2 with silicalite-1, the Si/Al of

327

the as-made core-shell composites were improved clearly to be 3.38 (3.43) and 4.96

328

(4.77), respectively. Combining the SEM and TEM images, it was further confirmed

329

that silicalite-1 was successfully coated on NaY zeolite; meanwhile, comparing the

330

Si/Al of CSY-CuCl2 and CSYOH-CuCl2, more Si were detected, indicating that the

331

alkaline treatment had played an important role in coating process by providing more

332

loading positions for silicalite-1 crystals.

333

3.5. Textural properties of adsorbents.

334

The textural properties of these as-made core-shell structures were conducted by

335

virtue of N2 adsorption-desorption isotherms. As could be seen in Figure. 6, no

336

obvious hysteresis loop and notable plateau at high relative pressure (> 0.4) were

337

observed on NaY zeolites, which could be considered belonging to type-I, suggesting

338

that NaY zeolite possessed mainly a microporous property.55 However, after being



339

treated by NaOH, the N2 adsorption-desorption isotherms of NaYOH and CuYOH were

340

situated between type-I and type-Ⅳ, indicating that NaYOH and CuYOH showed both

341

microporous and mesoporous properties. 250

3

Volume adsorbed (cm /g)

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 14 of 34

200

400 NaY NaYOH YOH-CuCl2 YOH-Cu(NO3)2 YOH-CuSO4

Silicalite-1 CSNaYOH CSYOH-CuCl2 CSYOH-Cu(NO3)2 CSYOH-CuSO4

350 300

150

250 200

100

150 50 100 0

0.0 0.2 0.4 0.6 0.8 1.0

50

0.0

0.2

0.4

0.6

0.8

1.0

Relative Pressure (P/P0)

342 343

Figure. 6. N2 adsorption-desorption isotherms of different adsorbents (displaced along the y-axis).

344

Table. 2. Structural properties of NaY, silicalite-1, NaYOH, CuYOH and core-shell structures. Adsorbents

St (m2/g)

Smicro (m2/g)

Smeso (m2/g)

Vt (cm3/g)

Vmic (cm3/g)

Da (nm)

Dmic (nm)

NaY Silicalite-1 NaYOH YOH-CuCl2 YOH-Cu(NO3)2 YOH-CuSO4 CSNaYOH CSYOH-CuCl2 CSYOH-Cu(NO3)2 CSYOH-CuSO4

786.27 489.21 704.32 572.56 525.11 401.32 624.51 546.23 445.68 411.47

754.24 471.68 629.05 493.30 458.25 337.87 544.29 507.22 385.62 335.35

32.02 17.54 75.27 79.27 66.86 63.45 80.23 39.01 60.06 76.12

0.38 0.35 0.42 0.37 0.31 0.27 0.39 0.36 0.32 0.28

0.29 0.20 0.26 0.24 0.23 0.19 0.26 0.24 0.21 0.17

1.81 2.06 2.20 2.10 2.21 2.42 2.19 2.21 2.40 2.49

0.84 0.65 0.86 0.84 0.83 0.85 0.85 0.85 0.85 0.85

345 346

St: total surface area; Smicro: surface area of micropores; Smeso: surface area of mesopores; Vt: total pore volume; Vmic: microporous pore volume; Da: average pore size; Dmic: microporous pore size.

347

Table. 2 further displayed the structural properties of these adsorbents. The total

348

surface area of NaY zeolite was 786.27 m2/g, in which the surface area of micropores

349

occupied a leading position reaching 95.93% of 754.24 m2/g, in accordance with the

350

BJH pore size distributions showed in Figure. 7. After NaOH treatment, the total


Page 15 of 34

351

surface area of NaYOH had dropped down to 704.32 m2/g, owing to the desilication

352

effects of NaOH on NaY zeolites, during which a large number of micropores had

353

disappeared from 754.24 to 629.05m2/g, while the surface area of mesopores had

354

increased from 32.02 to 75.27 m2/g. With further modification by Cu2+, the the

355

surface area of CuYOH zeolites would be reduced synchronously; but the micropores

356

still held the most proportion ( Table. 2 and Figure. 7).

357

As to silicalite-1 crystals, according to the N2 adsorption-desorption isotherms,

358

silicalite-1 was situated between type-I and type-Ⅳ, indicating that silicalite-1 owned

359

both microporous and mesoporous properties. Similar to NaY zeolites, in silicalite-1,

360

the surface area of micropores also occupied a leading position reaching 96% of the

361

total surface area. The most important property of silicalite-1 in this research was that

362

the microporous pore size was only 0.65 nm much lower than that of NaY (0.84 nm),

363

NaYOH (0.86 nm), and CuYOH zeolites (0.84, 0.83, and 0.85 nm), providing

364

silicalite-1 shell a capacity of shape selective adsorption; as a matter of fact, to some

365

certain, the smaller the micropore size was, the better the shape selecting function

366

would be. NaY Silicalite-1 NaYOH YOH- CuCl2 YOH- Cu(NO3)2 YOH- CuSO4 CSNaYOH CSYOH-CuCl2 CSYOH-Cu(NO3)2 CSYOH-CuSO4

0.035

1.0

0.030

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

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


0.8

0.025 0.020

0.6

0.015 0.010

0.4

0.005 0.000

0.2

0.0

367 368

2

0

2

4

4

6

8

6

Pore width (nm)

10

12

14

8

10

Figure. 7. BJH pore size distributions of different adsorbents.

369

In addition, as the core, the total pore volume of NaYOH zeolites had increased

370

from 0.383 to 0.423 cm3/g owing to the desilication effects of NaOH, which provided



Page 16 of 34

371

a large enough volume to store the adsorbed substances (DMDS). Even after being

372

coated by silicalite-1 shell, the total pore volume of these core-shell composites was

373

still remained considerable, insuring a relatively large sulfur adsorption capacity. All

374

in all, the shape selective property of silicalite-1 shell and the large sulfur adsorption

375

capacity of the core zeolites (NaYOH and CuYOH) made these core-shell composites

376

appreciable adsorbents for removing DMDS from MTBE.

377

3.6. FT-IR spectra of adsorbents.

378

In order to detect the shape selective adsorption function of these synthesized

379

core-shell composites, the FT-IR spectra after the adsorption of DMDS in MTBE on

380

different zeolites were recorded and shown in Figure. 8. Owing to the fierce

381

competitive adsorption between MTBE and DMDS elaborated in introduction, almost

382

no DMDS could be detected on NaY, NaYOH or CuYOH zeolites. As could be seen,

383

compared with the core-shell composites, no bonds locating at 1228 cm-1 were

384

observed, which was determined as the stretching vibration of C-S.49 However, via

385

physical intermolecular force and other interactions, both the stretching vibration of

386

C-S and the stretching vibration of C-O-C (1108 cm-1) were presented on silicalite-1

387

crystals, suggesting that DMDS and MTBE could be both absorbed on silicalite-1. (a) (b)

1108 1010

1228 C-S

(c) (d) (e) (f) (g) (h) (i) (j) C-O-C

1620 H-OH

1950 1800 1650 1500 1350 1200 1050 900

750

600

450

-1

wavenumbers (cm )

388 389 390 391

Figure. 8. FT-IR spectra recorded after the adsorption of DMDS in MTBE on different zeolites: (a). NaY, (b). silicalite-1 crystal, (c). NaYOH, (d). YOH-CuCl2, (e). YOH-Cu(NO3)2, (f). YOH-CuSO4, (g). CSNaYOH, (h). CSYOH-CuCl2, (i). CSYOH-Cu(NO3)2, (j). CSYOH-CuSO4.

392

By the way, after the silicalite-1 was coated on NaYOH or CuYOH zeolites to form


Page 17 of 34 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


393

core-shell composites, the stretching vibration of C-S could also be detected,

394

indicating that these core-shell composites possessed the capacity to adsorb DMDS

395

from MTBE. This phenomenon could be explained by two reasons: one was that the

396

stretching vibration of C-S on core-shell composites came from the DMDS adsorbed

397

on silicalite-1 crystals; the other was that silicalite-1 as the coating might own a

398

shape-selection characteristic of molecular scale between DMDS and MTBE, leading

399

to that the DMDS passed through the passageway in silicalite-1 crystals and finally

400

was adsorbed by the core zeolites. These two possibilities would be confirmed by

401

their final active adsorption data analysis.

402

3.7. Cu2+ loading amount in different absorbents

403

Table. 3. Cu2+ source and their loading amounts in NaYOH zeolites and core-shell composites. Cu2+ source

Concentration (mol/L)

Loading capacity in theory (mg/g)

In CuYOH zeolite (mg/g)

In core-shell composites (mg/g)

CuCl2 Cu(NO3)2 CuSO4

0.5 0.5 0.5

82.29 82.29 82.29

4.6 3.4 1.7

4.3 2.9 1.5

404

405 406

Scheme. 2. Structure of (1) Cu-S and (2) Cu-O.

407

In our previous study,49 we had proved that after been modified by Cu2+, Cu2+

408

could form Cu-S to adsorb DMDS by π-complexation19, 30, 31 as shown in Scheme. 2.

409

In theory, the larger the loading amount of Cu2+ was, the more DMDS could be

410

adsorbed. Table. 3 displayed Cu2+ loading amount in different absorbents. Results

411

showed that Cu2+ loading amount from CuCl2 reached the maximum quantity both in

412

CuYOH and core-shell composites, which provided the core zeolites more active



413

centers for adsorption of DMDS. However, Cu-O could also be formed at the

414

presence of MTBE; and unfortunately, the formation of Cu-O was easier than Cu-S;

415

and that was why there was a fierce competitive adsorption between DMDS and

416

MTBE on π-complexation adsorbents without shape selective function.

417

3.8. Desulfurization performances of the core-shell zeolites.

418

3.8.1. Static active data analysis To prove if silicalite-1 as the coating could selectively adsorb DMDS from

420

MTBE, the sulfur adsorption capacities of DMDS in MTBE solution on different

421

absorbents were obtained by static adsorption activity tests. As shown in Figure. 9,

422

after adsorption, silicalite-1 coating played a crucial role in adsorption of DMDS. mgs/gadsorbent

mg/L Raw material sulfur concentration：748.52 789.92

742.34

792.72

846.32 830.22

37.073

32.985 30.56

26.468

792.13

748.52

483.86 377.79

0

418.67

442.92

0.618 -4.42 -9.78 -8.17

-4.14

a

b

c

d

e

-4.361

f

g

h

i

j

Sulfur adsorbtion capacity (mgs/gadsorbent)

419

Sulfur content after adsorbtion (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

Page 18 of 34

423 424 425 426

Figure. 9. Sulfur content after adsorption and sulfur adsorption capacity of DMDS in MTBE on different absorbents: a. NaY, b. silicalite-1 crystal, c. NaYOH, d. YOH-CuCl2, e. YOH-Cu(NO3)2, f. YOH-CuSO4, g. CSNaYOH, h. CSYOH-CuCl2, i. CSYOH-Cu(NO3)2, j. CSYOH-CuSO4.

427

In this study, the raw material sulfur concentration was 748.52 mg/L. Results

428

showed that after static adsorption, on the one hand, adsorbents without silicalite-1

429

coating, such as NaY, NaYOH and CuYOH, presented a poor desulfurization

430

performance; however, considering the fierce competition effects between DMDS and

431

MTBE on these π-complexation adsorbents,32 the sulfur content after adsorption being

432

increased higher than the raw one could be well explained. Besides, from the results

433

of adsorption, the order of adsorption capacity was CuYOH > NaYOH > NaY. That was

434

because when formed the π-complexation with sulfur atoms the π-complexation


Page 19 of 34 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


435

capacity of Cu2+ was stronger than Na+; meanwhile, after NaOH treatment, the

436

content of Na+ in NaYOH would be inescapably more than that of NaY, leading to a

437

lager adsorption capacity of NaYOH than NaY; especially, the YOH-CuCl2 put up the

438

best adsorption capacity of -9.78 mgs/gadsorbents, followed by YOH-Cu(NO3)2, and

439

YOH-CuSO4. On the other hand, adsorbents with silicalite-1 coating, like CSNaYOH,

440

CSYOH-CuCl2, CSYOH-Cu(NO3)2, and CSYOH-CuSO4, exhibited a significant capacity

441

in desulfurization of DMDS from MTBE. And the order of adsorption capacity of

442

these core-shell composites was in accord with the uncoated ones. It was noted that

443

silicalite-1 crystals as the adsorbents alone did not performed well with only a low

444

adsorption capacity of 0.618 mgs/gadsorbents, indicating a selective adsorption of DMDS

445

from MTBE for silicalite-1 crystals.

446

When silicalite-1 crystals were coated as the shell around the core zeolites (NaY,

447

NaYOH and CuYOH), the selective adsorption capacity of DMDS from MTBE could

448

be dramatically improved. As Figure. 9 depicted, after being coated, the sulfur

449

adsorption capacity of YOH-CuCl2 raised from -9.78 to 37.073 mgs/gadsorbents;

450

YOH-Cu(NO3)2 and YOH-CuSO4 also showed a substantial upgrade, owing to the fact

451

that when coating CuYOH with silicalite-1, the silicalite-1 shell could prevent MTBE

452

from migrating into the core zeolites, permitting only DMDS to pass by and CuYOH as

453

the core would adsorb DMDS, holding back it from migrating out.

454

3.8.2. Dynamic active data analysis

455

After the static adsorption activity tests, we also tried the dynamic tests to further

456

evaluate the desulfurization performances of these as-made adsorbents. They were

457

fixed into a quartz column reactor with a particle size of 20-40 mesh. The export

458

samples were collected every half an hour; and the breakthrough curves of different

459

adsorbents were shown in Figure. 10. Similarly, adsorbents with and without

460

silicalite-1 coating displayed a remarkable difference in desulfurization performance.

461

As could seen, with the elapse of time, the desulfurization performances of the

462

adsorbents overall showed a downward trend. For NaY, NaYOH and CuYOH zeolites,

463

as a result of the competitive adsorption and no silicalite-1 shell, exhibited poor

464

performances in the whole process of desulfurization. Throughout the tests, the



465

desulfurization rate of NaY, NaYOH and CuYOH zeolites were all along negative,

466

suggesting none desulfurization capacity of these adsorbents. 100

Desulfurization rate of DMDS(%)

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 34

80

NaY Silicalite-1 NaYOH YOH- CuCl2 YOH- Cu(NO3)2 YOH- CuSO4 CSNaYOH CSYOH-CuCl2 CSYOH-Cu(NO3) CSYOH-CuSO4

60 40 20 0 -20 0

467 468 469

1

2

3

4

Time (h) Figure. 10. Breakthrough curves of NaY, NaYOH, silicalite-1, CuYOH and silicalite-1/CuYOH core-shell structured composites adsorbing DMDS in MTBE solution.

470

As to silicalite-1, the breakthrough curve of in Figure. 10 confirmed that

471

silicalite-1 crystal could selectively adsorb DMDS from MTBE to a certain extent.

472

After being coated, the desulfurization rate of CSNaYOH, CSYOH-CuCl2,

473

CSYOH-Cu(NO3)2, and CSYOH-CuSO4 were remarkably improved; within 2.5 h, all

474

the core-shell structured CuYOH zeolites could 100% remove DMDS from MTBE,

475

and CSNaYOH also kept this level for about 1.5 h. All in all, the CSYOH-CuCl2 still

476

displayed the best performance, for which more than 80% desulfurization rate could

477

be achieved and kept for about 4.5 hours. However, beyond 3.5 h, the desulfurization

478

rate of the core-shell composites would sharply decline, indicating that the adsorbents

479

would soon came into the end of their active life.

480

3.9. Mechanism analysis

481

Based on the explorations above of these core-shell structured composites, and in

482

order to discuss the synthesis and application process more intuitively of these

483

as-made zeolites, Figure. 11 was presented. As could be seen, the parent NaY zeolites

484

(Si/Al = 2.4) possessed a relatively glossy surface; and after being treated by 0.5

485

mol/L NaOH solution, as the silicon in the lattice of NaY zeolites was removed and


Page 21 of 34 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


486

transferred into Si(OH)4, the surface of NaY zeolites became full of bumps and

487

hollows, leading to a lager apparent surface area, which could provide more loading

488

positions for silicalite-1 crystals. Si/Al = 2.4 : Si + Si(OH)4 (aq)

: Al

NaOH

superfluous

fragmentized

treatment

NaY

treatment

Cu2+ exch

NaY

addin ion TE ange

silicalite-1 crystal

g OS

multilayer monolayer

silicalite-1 crystals grow silicalite-1 crystals encase

silicalite-1 crystals grow

NaY zeolite ad

along the surface

on the surface

sorption ex perimen

0.65 nm

t MTBE

DMDS DMDS in

a

MTBE solution

dsor

DMDS was adsorbed into core CuY by Cu-S while MTBE was held back outside

489 490 491 492

Figure. 11. Preparation of CuYOH zeolites and the growth of silicalite-1 coating by both monolayer and multilayer on the surface of CuYOH; as well as the DMDS adsorption mechanism on core-shell structured composites in MTBE.

493

However, the overdose treatment of NaOH including concentration and

494

processing time would break NaY zeolites into smaller fragments, which was

495

considered disadvantageous to the growth of silicalite-1 shell on NaY zeolites. After

496

being modified by Cu2+, the shell precursor solution with TEOS as the silica source

497

and TPAOH as the template was prepared to form the silicalite-1 coating through a

ptio n



498

sol-gel coating process. Owing to the larger out surface area, the silicalite-1 crystals

499

would be easily coated on NaY zeolites, grow along the surface and finally

500

completely cover NaY zeolites to form the silicalite-1 shell.

501

In the process of adsorbing DMDS from MTBE, combined with BET analyse,

502

the average micro pore size was 0.6496 nm; meanwhile the maximum molecule size

503

of DMDS was 0.37 nm and MTBE was 0.74 nm.56, 57 When core-shell structured

504

composites contacted DMDS and MTBE simultaneously, DMDS could diffuse

505

rapidly in the microporous channels of silicalite-1 shell; however, owing to the larger

506

size and the branched structure, the diffusion of MTBE would be inevitably limited.

507

DMDS diffused into the core-shell structured composites would be fixed by Cu-S

508

bonds and stored inside, leading to the enrichment of DMDS on the core CuYOH

509

zeolites and the decreased concentration of DMDS in MTBE solution. Ultimately, the

510

purpose of selectively desulfurizing DMDS from MTBE was achieved.

511

4. Conclusion

512

In this research, we have tried to present an effective method for growing a

513

clearly and fully coated silicalite-1 shell on NaY zeolites. Results showed that after

514

NaOH treatment, the Si/Al of NaY had decreased from 2.4 to 2.04; and the absence of

515

silicon would inevitably leave many vacancies and enlarge the out surface area of

516

NaY zeolites. After coating silicalite-1, the Si/Al of CSY-CuCl2 and CSYOH-CuCl2

517

were improved to 3.38 and 4.96, respectively, indicating that the alkaline treatment

518

did play an positive role in coating process by providing more loading positions for

519

silicalite-1 crystals. Besides, as the core, after being ion exchanged by Cu2+, CuYOH

520

had shown a better adsorption capacity than NaY and NaYOH to store more organic

521

sulfurs (DMDS) by the active adsorption centers (Cu2+) via Cu-S bonds between

522

DMDS and copper ions. After being coated with silicalite-1, by shape selectivity of

523

silicalite-1 shell and adsorption centers in CuYOH core, the silicalite-1/CuYOH

524

core-shell structured composites had performed well in desulfurizing DMDS from

525

MTBE, among which the CSYOH-CuCl2 performed the best sulfur adsorption capacity

526

of 37.073 mgs/gadsorbent; and more than 90% desulfurization rate could be achieved and

527

kept for about 4.3 hours with a sulfur content of 286.13 mg/L.


Page 22 of 34

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528 529

Acknowledgments

530

Project financially supported by the National Science Foundation for Young

531

Scientists of China (No. 21706065); the Open Project of State Key Laboratory of

532

Chemical Engineering (SKL-ChE-18C02); China Postdoctoral Science Foundation

533

(NO.2017M621389), Shanghai Sailing Program (NO.18YF1406300), and Explore

534

and Research Foundation for Youth Scholars of Ministry of Education of China (NO.

535

222201814011).

536

Reference

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[1] Habimana, F., Shi, D., and Ji, S. Synthesis of Cu-BTC/Mt composites porous materials and their performance in adsorptive desulfurization process. Appl. Clay Sci. 2018, 152, 303-310. [2] Moreira, A. M., Brandão, H. L., Hackbarth, F. V., Maass, D., Souza, A. A. U. D., and S. M. A. Guelli U. de Souza. Adsorptive desulfurization of heavy naphthenic oil: equilibrium and kinetic studies. Chem. Eng. Sci. 2017, 17, 223-231. [3] Chen, X., Shen, B., Sun, H., and Zhan, G. Ion-exchange modified zeolites x for selective adsorption desulfurization from claus tail gas: experimental and computational investigations. Micropor. Mesopor. Mat. 2017, 261. 227-236. [4] Darake, S., Hatamipour, M. S., Rahimi, A., and Hamzeloui, P. So2 removal by seawater in a spray tower: experimental study and mathematical modeling. Chem, Eng. Res. Des. 2016, 109, 180-189. [5] Li, D. Crucial technologies supporting future development of petroleum refining Industry. Chinese J. Catal. 2013, 34, 48-60. [6] L. Wang, L. Zhao, C. Xu, Y. Wang, and J. Gao. Screening of active metals for reactive adsorption desulfurization adsorbent using density functional theory. Appl. Surf. Sci. 2016, 399, 440-450. [7] Chen, X., Zhu, K., Ahmed, M. A., Wang, J., and Liang, C. Mössbauer spectroscopic characterization of ferrites as adsorbents for reactive adsorption desulfurization. Chinese J. Catal. 2016, 37, 727-734. [8] M. Tang, L. Zhou, M. Du, Z. Lyu, X.-D. Wen, X. Li, and H. Ge, A novel reactive adsorption desulfurization Ni/Mn0 adsorbent and its hydrodesulfurization ability compared with Ni/ZnO. Catal. Commun. 2015, 61, 37-40. [9] Armor, J. N. Environmental catalysis. Appl. Catal., B 1992, 1, 221-256. [10] Lee, J., Beum, H. T., Ko, C. H., Park, S. Y., Park, J. H., Kim, J. N., Chun, B. H., and Kim, S. Y. Adsorptive Removal of Dimethyl Disulfide in Olefin Rich C4 with Ion-Exchanged Zeolites. Ind. Eng. Chem. Res. 2011, 50, 6382-6390. [11] Dezhi Yi, Huan Huang, Xuan Meng, and Li Shi. Desulfurization of Liquid Hydrocarbon Streams via Adsorption Reactions by Silver-Modified Bentonite. Ind. Eng. Chem. Res. 2013, 52, 6112-6118. [12] B. pawelec, R.M. Navarro, J. Miguel Cameos-Martin, and J. L. G. Fierro, Towards near zero-sulfur liquid fuels: a perspective review. Catal. Sci. Technol. 2011, 1, 23-42.



568 569 570 571 572 573 574 575 576 577 578 579 580 581 582 583 584 585 586 587 588 589 590 591 592 593 594 595 596 597 598 599 600 601 602 603 604 605 606 607 608 609 610 611

[13] A. Stanislaus, A. Marafi, and M. S. Rana. Recent advances in the science and technology of ultra low sulfur diesel (ULSD) production. Catal. Today 2010, 153, 1-68. [14] Hernandez-Maldonado A. J., and Yang R. T. New sorbents for desulfurization of diesel fuels via π-complexation. AICHE J. 2004, 50, 791-801. [15] Huan Huang, Dezhi Yi, Yannan Lu, Xiaolin Wu, Yunpeng Bai, Xuan Meng, and Li Shi. Study on the adsorption behavior and mechanism of dimethyl sulfide on silver modified bentonite by in situ FTIR and temperature programmed desorption. Chem. Eng. J. 2013, 225, 447-455. [16] Shahadat Hussain A. H. M., and Tatarchuk B. J. Mechanism of hydrocarbon fuel desulfurization using Ag/TiO2-Al2O3 adsorbent. Fuel Process Technol. 2014, 126, 233-242. [17] Tian F. P.; Shen Q. C.; Fu Z. K.; Wu Y. H.; and Jia C. Y. Enhanced adsorption desulfurization performance over hierarchically structured zeolite Y. Fuel Process Technol. 2014, 128, 176-182. [18] Teymouri M, Samadi-Maybodi A, Vahid A, and Miranbeigi A. Adsorptive desulfurization of low sulfur diesel fuel using palladium containing mesoporous silica synthesized via a novel in-situ approach. Fuel Process Technol. 2013, 116, 257-264. [19] A. J. Hernández-Maldonado, F. H. Yang, G. Qi, and R. T. Yang. Desulfurization of transportation fuels by π-complexation sorbents: Cu(I)-, Ni(II)-, and Zn(II)-zeolites. Appl. Catal., B 2005, 56, 111-126. [20] Meng, X., Huang, H., Weng, H., and Shi, L. Ni/ZnO-based Adsorbents Supported on Al2O3, SiO2, TiO2, ZrO2: A Comparison for Desulfurization of Model Gasoline by Reactive Adsorption. Bull Korean Chem. Soc. 2012, 33, 3213-3217. [21] Saleh, T. A.; Danmaliki, G. I.; Shuaib, T. D. Nanocomposites and hybrid materials for adsorptive desulfurization. In Applying Nanotechnology to the Desulfurization Process in Petroleum Engineering; Saleh, T. A., Ed.; IGI Global: Hershey, PA, USA, 2016; pp 129-153, DOI: 10.4018/978-1-4666-9545-0.ch004. [22] Peralta D, Chaplais G, Simon-Masseron A, Barthelet K, and Pirngruber GD. Metal-organic framework materials for desulfurization by adsorption. Energ. Fuel. 2012, 26, 4953-4960. [23] Hernández-Maldonado A. J., and Yang R. T. Desulfurization of transportation fuels by adsorption. Catal. Rev. 2004, 46, 111-150. [24] Salem ABSH, and Hamid H, S. Removal of sulfur compounds from naphtha solutions using solid adsorbents. Chem. Eng. Technol. 1997, 20, 342-347. [25] Palomino J. M.; Tran D. T.; Kareh A. R.; Miller CA; Gardner JMV; Dong H. Zirconia-silica based mesoporous desulfurization adsorbents. J. Power Sources 2015, 278, 141-148. [26] Tang, X. L., Qian, W., Hu, A., Zhao, Y. M., Fei, N. N., and Shi, L. Adsorption of thiophene on Pt/Ag-supported activated carbons prepared by ultrasonic-assisted impregnation. Ind. Eng. Chem. Res. 2011, 50, 9363-9367. [27] Ryzhikov, Andrey, Igor Bezverkhyy, and Jean-Pierre Bellat. Reactive adsorption of thiophene on Ni/ZnO: Role of hydrogen pretreatment and nature of the rate determining step. Appl. Catal., B 2008, 84, 766-772. [28] Sentorun-Shalaby, C., Saha, S. K., Ma, X., and Song, C. Mesoporous-molecular-sievesupported nickel sorbents for adsorptive desulfurization of commercial ultra-low-sulfur diesel fuel. Appl. Catal., B 2011, 101, 718-726. [29] Hernández-Maldonado, Arturo J., and Ralph T. Yang. Desulfurization of Commercial Liquid Fuels by Selective Adsorption via π-Complexation with Cu (I)-Y Zeolite. Ind. Eng. Chem.


Page 24 of 34

Page 25 of 34 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

612 613 614 615 616 617 618 619 620 621 622 623 624 625 626 627 628 629 630 631 632 633 634 635 636 637 638 639 640 641 642 643 644 645 646 647 648 649 650 651 652 653 654 655


Res. 2003, 42, 3103-3110. [30] A. J. Hernández-Maldonado; F. H. Yang; G. S. Qi; R. T. Yang. Sulfur and nitrogen removal from transportation fuels by π-complexation. J. China Ind. Chem. Eng. 2006, 37, 9-16. [31] Y. Li, F. H. Yang, G. Qi, and R. T. Yang. Effects of oxygenates and moisture on adsorptive desulfurization of liquid fuels with Cu(I)Y zeolite. Catal. Today 2006, 116, 512-518. [32] Chen, H., Wang, Y., Yang, F. H., and Yang, R. T. Desulfurization of high-sulfur jet fuel by mesoporous π-complexation adsorbents. Chem. Eng. Sci. 2009, 64, 5240-5246. [33] Shan G, Zhang H, Liu H, and Xing J. π-complexation studied by fluorescence technique: application in desulfurization of petroleum product using magnetic π-complexation sorbents. Sep. Sci. Technol. 2005, 40, 2987-2999. [34] Wardencki W, and Staszewski R. Dynamic adsorption of thiophenes, thiols and sulphides from n-heptane solutions on molecular sieve 13X. J. Chromatogr A. 1974, 91, 715-722. [35] Salem ABSH. Naphtha desulfurization by adsorption. Ind. Eng. Chem. Res. 1994, 33, 336-3340. [36] Khan N. A., Hasan Z., and Jhung S. H. Ionic liquids supported on metal-organic frameworks: remarkable adsorbents for adsorptive desulfurization. Chem. Eur. J. 2014, 20, 376-380. [37] Triantafyllidis K. S., and Deliyanni E. A. Desulfurization of diesel fuels: adsorption of 4,6-DMDBT on different origin and surface chemistry nanoporous activated carbons. Chem. Eng. J. 2014, 236, 406-414. [38] Ji F, Li C, Tang B, Xu J, Lu G, and Liu P. Preparation of cellulose acetate/zeolite composite fiber and its adsorption behavior for heavy metal ions in aqueous solution. Chem. Eng. J. 2012, 209, 325-333. [39] Huang Huan, Salissou M. Nour, Yi Dezhi, Meng Xuan, and Shi Li. Study on Reactive Adsorption Desulfurization of Model Gasoline on Ni/ZnO-HY Adsorbent. China Pet. Process Pe. 2013, 15, 57-64. [40] S. Satokawa, Y. Kobayashi, and H. Fujiki. Adsorptive removal of dimethysulfide and t-butylmercaptan from pipeline natural gas fuel on Ag zeolites under ambient conditions. Appl. Catal., B 2005, 56, 51-56. [41] H. Wakita, Y. Tachibana, and M. Hosaka. Removal of dimethyl sulfide and t-butylmercaptan from city gas by adsorption on zeolites. Micropor. Mesopor. Mat. 2001, 6, 237-247. [42] Lidan Lv, Jie Zhang, Chongpin Huang, Zhigang Lei, and Biaohua Chen. Adsorptive separation of dimethyl disulfide from liquefied petroleum gas by different zeolites and selectivity study via FT-IR. Sep. Purif. Technol. 2014, 125, 247-255. [43] Ya-wei Zhao; Ben-xian Shen; Hui Sun. Chemical Liquid Deposition Modified ZSM-5 Zeolite for Adsorption Removal of Dimethyl Disulfide. Ind. Eng. Chem. Res. 2016, 55, 6475-6480. [44] Dezhi Yi, Huan Huang, Xuan Meng, and Li Shi. Adsorption-desorption behavior and mechanism of dimethyl disulfide in liquid hydrocarbon streams on modified Y zeolites. Appl. Catal., B 2014, 148, 377-386. [45] Lv Y., Qian X., Tu B. and Zhao D. Generalized synthesis of core-shell structured nano-zeolite@ordered mesoporous silica composites. Catal. Today 2013, 204, 2-7. [46] Verboekend D. and Pérez-Ramírez J. Desilication mechanism revisited: highly mesoporous all-silica zeolites enabled through pore-directing agents. Chem. Eur. J. 2011, 17, 1137-1147. [47] Groen, J. C., Peffer, L. A., Moulijn, J. A., and Pérezramírez, J. Mechanism of hierarchical porosity development in MFI zeolites by desilication: the role of aluminium as a



656 657 658 659 660 661 662 663 664 665 666 667 668 669 670 671 672 673 674 675 676 677 678 679 680 681 682 683 684 685 686 687 688 689 690 691 692 693 694 695 696 697 698 699

pore-directing agent. Chem. Eur. J. 2005, 11, 4983-4994. [48] Shen B, Qin Z, Gao X, Lin F, Zhou S, Shen W, Wang B, Zhao H, and Liu H. Desilication by Alkaline Treatment and Increasing the Silica to Alumina Ratio of Zeolite Y. Chinese J. Catal. 2012, 33, 152-163. [49] Chao Yang, Xuan Meng, Dezhi Yi, Zhiming Ma, Naiwang Liu, and Li Shi. Cu2+ modified silicalite-1/NaY structure for the adsorption desulfurization of dimethyl disulfide from methyl tert-butyl ether. Ind. Eng. Chem. Res. 2018, 57, 9162-9170. DOI: 10.1021/acs.iecr.8b01211. [50] H. Xie, D. Yi, L. Shi, and X. Meng. High Performance of CuY Zeolite for Catalyzing Acetylene Carbonylation and the Effect of Copper Valence States on Catalyst. Chem. Eng. J. 2017, 313, 663-670. [51] X. F. Qian, B. Li, Y. Y. Hu, G. X. Niu, D. Y. H. Zhang, R. C. Che, Y. Tang, D. S. Su, A. M. Asiri, and D.Y. Zhao. Chem. Eur. J. 2012, 18, 931-939. [52] X. Liu, D. Yi, Y. Cui, L. Shi, and X. Meng. Adsorption desulfurization and weak competitive behavior from 1-hexene over cesium-exchanged Y zeolites (CsY). J. Energy Chem. 2018, 27, 271-277. [53] Van Vu, Dung; Miyamoto, Manabu; Nishiyama, Norikazu; Ichikawa, Satoshi; Egashira, Yasuyuki; Ueyama, Korekazu Catalytic activities and structures of silicalite-1/H-ZSM-5 zeolite composites. Micropor. Mesopor. Mat. 2008, 115, 106-112. [54] Bouizi, B. Y.; Diaz, I.; Rouleau, L.; Valtchev, V. P. Core-Shell Zeolite Microcomposites. Adv. Funct. Mater. 2005, 15, 1955-1960. [55] J. C. Groen, LAA Peffer, J. A. Moulijn, and J. Pérez-Ramı́Rez. On the introduction of intracrystalline mesoporosity in zeolites upon desilication in alkaline medium. Micropor. Mesopor. Mat. 2004, 69, 29-34. [56] Li, L.; Quinlivan, P.; Knappe, D. Effects of activated carbon surface chemistry and pore structure on the adsorption of organic contaminants from aqueous solution. Carbon 2002, 40, 2085-2100. [57] Bondi, A. van der Waals volumes and radii. J. Phys. Chem. 1964, 68, 441-451.


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Page 27 of 34 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

700 701 702


TOC graphic

silicalite-1 coating

: Si : Al Cu2+ exchange

NaOH, aq

encrusting

NaY

Si: Al=2.4

Si: Al=2.04

Coating growth

0.65 nm Adsorption

MTBE

DMDS

703


experiment

Si: Al=4.96


Scheme. 1. Structure of (1) DMDS and (2) MTBE.

Scheme. 2. Structure of (1) Cu-S and (2) Cu-O.

14 12



mass gain (%)

mass gain (g)

160 140 120

Mass gain (%)

16

Mass gain (g)

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 28 of 34

10

100

8

80

6

5g

60

4

4.653 4.76

40

2 0

20 NaYOH

CSNaYOH

CSYOH - CuCl2

CSYOH - Cu(NO3)2

CSYOH - CuSO4

0

Figure. 1. Mass gain of NaY after NaOH treatment and NaYOH/CuYOH after coating silicalite-1.


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


Intensity (a.u.)

Page 29 of 34

10

15

20

25

30

35

(5)

(10)

(4)

(9)

(3)

(8)

(2)

(7)

(1)

(6) 40 10

15

20

25

30

35

40

2-Theta (degrees) Figure. 2. X-ray diffraction patterns of NaY, silicalite-1, NaYOH /CuYOH and NaYOH /CuYOH with silicalite-1 shell: (1) NaY, (2) NaYOH, (3) YOH-CuCl2, (4) YOH-Cu(NO3)2, (5) YOH-CuSO4, (6) silicalite-1, (7) CSNaYOH, (8) CSYOH-CuCl2, (9) CSYOH-Cu(NO3)2, (10) CSYOH-CuSO4.

(a)

(b)

(c)

(d)

Figure. 3. SEM images of (a) NaY, (b) NaYOH, (c) CSNaYOH, (d) CSYOH-CuCl2.

(a)

(b)

(c)

(d)

Figure. 4. TEM images of (a) NaY, (b) YOH-CuCl2, (c) CSNaYOH, (d) CSYOH-CuCl2.



(a)

(b)

(c)

(d)

Figure. 5. EDS analysis of (a) NaY, (b) YOH-CuCl2, (c) CSY-CuCl2, (d) CSYOH-CuCl2.

250

3

Volume adsorbed (cm /g)

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 34

200

400

NaY NaYOH YOH-CuCl2 YOH-Cu(NO3)2 YOH-CuSO4

Silicalite-1 CSNaYOH CSYOH-CuCl2 CSYOH-Cu(NO3)2 CSYOH-CuSO4

350 300

150

250 200

100

150 50

0

100

0.0 0.2 0.4 0.6 0.8 1.0

50

0.0

0.2

0.4

0.6

0.8

1.0

Relative Pressure (P/P0) Figure. 6. N2 adsorption-desorption isotherms of different adsorbents (displaced along the y-axis).


Page 31 of 34

NaY Silicalite-1 NaYOH YOH- CuCl2 YOH- Cu(NO3)2 YOH- CuSO4 CSNaYOH CSYOH-CuCl2 CSYOH-Cu(NO3)2 CSYOH-CuSO4

0.035

1.0 3 -1 -1 dV/dD (cm g nm )

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


0.030

0.8

0.025 0.020

0.6

0.015 0.010

0.4

0.005 0.000

0.2 0.0

0

2

2

4

4

6

8

10

12

6

14

8

Pore width (nm)

10

Figure. 7. BJH pore size distributions of different adsorbents.

(a) (b)

1108 1010

1228 C-S

(c) (d) (e) (f) (g) (h) (i) (j) C-O-C

1620 H-OH

1950 1800 1650 1500 1350 1200 1050 900 -1

wavenumbers (cm )

750

600

450

Figure. 8. FT-IR spectra recorded after the adsorption of DMDS in MTBE on different zeolites: (a). NaY, (b). silicalite-1 crystal, (c). NaYOH, (d). YOH-CuCl2, (e). YOH-Cu(NO3)2, (f). YOH-CuSO4, (g). CSNaYOH, (h). CSYOH-CuCl2, (i). CSYOH-Cu(NO3)2, (j). CSYOH-CuSO4.


742.34

792.72

846.32 830.22

32.985

748.52 483.86 377.79

0.618

0

-4.42

-4.14

b

30.56

26.468

792.13

-9.78 -8.17

d

c

e

418.67

442.92

-4.361

g

f

h

j

i

Sulfur adsorbtion capacity (mgs/gadsorbent)

37.073

Raw material sulfur concentration：748.52 789.92

Page 32 of 34

mgs/gadsorbent

mg/L

a

Figure. 9. Sulfur content after adsorption and sulfur adsorption capacity of DMDS in MTBE solution on different absorbents: a. NaY, b. silicalite-1 crystal, c. NaYOH, d. YOH-CuCl2, e. YOH-Cu(NO3)2, f. YOH-CuSO4, g. CSNaYOH, h. CSYOH-CuCl2, i. CSYOH-Cu(NO3)2, j. CSYOH-CuSO4.

100

Desulfurization rate of DMDS(%)

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

Sulfur content after adsorbtion (mg/L)


NaY Silicalite-1 NaYOH YOH- CuCl2 YOH- Cu(NO3)2 YOH- CuSO4 CSNaYOH CSYOH-CuCl2 CSYOH-Cu(NO3) CSYOH-CuSO4

80 60 40 20 0

-20 0

1

2

Time (h)

3

4

Figure. 10. Breakthrough curves of NaY, NaYOH, silicalite-1, CuYOH and silicalite-1/CuYOH core-shell structured composites adsorbing DMDS in MTBE solution.


Page 33 of 34

Si/Al = 2.4 : Si + Si(OH)4 (aq)

: Al

NaOH

superfluous

fragmentized

treatment

treatment

NaY

NaY silicalite-1 crystal multilayer monolayer

silicalite-1 crystals grow silicalite-1 crystals encase

silicalite-1 crystals grow

NaY zeolite

along the surface

adsorption

experiment

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


on the surface

0.6496 nm

MTBE

DMDS DMDS in MTBE solution

a DMDS was adsorbed into core CuY by Cu-S while MTBE was held back outside

Figure. 11. Preparation of CuYOH zeolites and the growth of silicalite-1 coating by both monolayer and multilayer on the surface of CuYOH; as well as the DMDS adsorption mechanism on core-shell structured composites in MTBE. Table. 1. Variation of silicon and aluminum after alkali treatment and core-shell experiment. Sample

Si (mg/g)

Al (mg/g)

Si/Al

NaY NaYOH YOH-CuCl2 CSY-CuCl2 CSYOH-CuCl2

28.3 25.2 24.4 28.4 35

11.3 11.9 11.5 8.1 6.8

2.41 2.04 2.05 3.38 4.96



Page 34 of 34

Table. 2. Structural properties of NaY, silicalite-1, NaYOH, CuYOH and core-shell structures. Adsorbents

St (m2/g)

Smicro (m2/g)

Smeso (m2/g)

Vt (cm3/g)

Vmic (cm3/g)

Da (nm)

Dmic (nm)

NaY Silicalite-1 NaYOH YOH-CuCl2 YOH-Cu(NO3)2 YOH-CuSO4 CSNaYOH CSYOH-CuCl2 CSYOH-Cu(NO3)2 CSYOH-CuSO4

786.27 489.21 704.32 572.56 525.11 401.32 624.51 546.23 445.68 411.47

754.24 471.68 629.05 493.30 458.25 337.87 544.29 507.22 385.62 335.35

32.02 17.54 75.27 79.27 66.86 63.45 80.23 39.01 60.06 76.12

0.38 0.35 0.42 0.37 0.31 0.27 0.39 0.36 0.32 0.28

0.29 0.20 0.26 0.24 0.23 0.19 0.26 0.24 0.21 0.17

1.81 2.06 2.20 2.10 2.21 2.42 2.19 2.21 2.40 2.49

0.84 0.66 0.86 0.84 0.83 0.85 0.85 0.85 0.85 0.85

St: total surface area; Smicro: surface area of micropores; Smeso: surface area of mesopores; Vt: total pore volume; Vmic: microporous pore volume; Da: average pore size; Dmic: microporous pore size. Table. 3. Cu2+ source and their loading amounts in NaYOH zeolites and core-shell composites. Cu2+ source

Concentration (mol/L)

Loading capacity in theory (mg/g)

In CuYOH zeolite (mg/g)

In core-shell composites (mg/g)

CuCl2 Cu(NO3)2 CuSO4

0.5 0.5 0.5

82.29 82.29 82.29

4.6 3.4 1.7

4.3 2.9 1.5


CuY core-shell structure for the

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