New Cu2O -SiO2 Composite Aerogel-like Desulfurization Adsorbents

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Fuel Cells

New Cu2O -SiO2 Composite Aerogel-like Desulfurization Adsorbents with Different Molar Ratio of Si/Cu Based on #-complexation Shaobo Liu, Bo Zhang, Zhanqi Bai, Feifan Chen, Fang Xie, Jinbing Zhou, Yongkang Lu, Guangwu Miao, Jiamin Jin, and Zekai Zhang Energy Fuels, Just Accepted Manuscript • DOI: 10.1021/acs.energyfuels.8b02968 • Publication Date (Web): 16 Nov 2018 Downloaded from http://pubs.acs.org on November 18, 2018

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New Cu2O -SiO2 Composite Aerogel-like Desulfurization Adsorbents with Different Molar Ratio of Si/Cu Based on π-complexation

Shaobo Liu†, Bo Zhang⁎,†,‡, Zhanqi Bai‡, Feifan Chen†, Fang Xie†, Jinbing Zhou†, Yongkang Lu†, Guangwu Miao‡, Jiamin Jin‡, Zekai Zhang† †

Laboratory of Industrial Catalysis, College of Chemical Engineering, Zhejiang

University of Technology, 18 Chaowang Road, hangzhou 310014, China ‡

Zhejiang Chemical Research Institute Co., Ltd., 387 Tianmushan Road, Hangzhou

310007, China

ABSTRACT Cu2O-SiO2 composite aerogel-like adsorbents with different n(Si/Cu) were synthesized by a sol-gel method followed by drying under atmospheric pressure, and characterized by BET, XRD, SEM, H2-TPR, XRF and FT-IR means. Their adsorption performance for thiophene and benzothiophene in model fuels was investigated with equilibrium and breakthrough adsorption experiments, respectively. The results showed that Cu2O-SiO2 composite aerogel-like adsorbents exhibited an excellent desulfurization performance based on π-complexation between Cu(I) and thiophenics. The n(Si/Cu) of 1


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Cu2O-SiO2 had an obvious effect on their physical properties and consequently desulfurization performance. The BET surface area, pore size and pore volume decreased with the decrease of n(Si/Cu) (increase of Cu content). Only a part of Cu was incorporated into the materials. The more the Cu(I) and the higher the specific surface area, the larger the adsorption capacity was. Cu2O-SiO2-50 performed the best and breakthrough adsorption capacities for benzothiophene and thiophene were 5.78 mgS/gads. (0.90 mmol-S/mmol-Cu) and 4.76 mgS/gads. (0.74 mmol-S/mmol-Cu), respectively. The adsorption data can be well fitted by both the Langmuir and Freundlich adsorption isotherms. The effect of competitive adsorption of olefins or aromatics on the desulfurization performance of adsorbents was obviously weaker compared with the result in the literature. The spent Cu2O-SiO2 adsorbents can be well regenerated by benzene-n-heptane washing. The breakthrough adsorption capacity of thiophene on the first regenerated Cu2O-SiO2-50 was 71 % of that on fresh adsorbent.

KEYWORDS: sol-gel, aerogel, desulfurization, adsorption, π-complexation

1. INTRODUCTION As the combustion of fuel oils can emit SOx and particulates resulting in serious environmental pollutions, the sulfur content in fuels has been restricted through the more stringent environmental regulations all over the world.1-3 The Environmental Protection 2


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Agency (EPA) regulations in the United States, demand that the sulfur content in federal gasoline and diesel cannot exceed 10 and 15 ppmw by January 1st, 2017.4 On the other hand, Fuel cell stacks have ultra-low air pollutant emission and high system efficiency. The most fuel cell stacks use hydrogen as their fuel source. Onboard liquid fuel reforming can provide hydrogen for fuel cell APUs.5 However, the sulfur compounds in fuels are poisonous to the reforming and shift catalysts in the fuel processor and the electrode catalysts in fuel cell stacks. In general, sulfur content in the fuel needs to be reduced to less than 1 ppmw for proton exchange membrane fuel cell (PEMFC) and less than 10 ppmw for solid oxide fuel cell (SOFC).6-10 Desulfurization of fuels in refineries is usually achieved by traditional hydrodesulfurization technology (HDS). HDS is efficient in the removal of most sulfur compounds such as mercaptans, sulfides and disulfides from fuels, while less efficient for the removal of thiophene and its derivatives owing to their stable C-S bonds in the aromatic ring.11 In addition, HDS is not suitable for small stand alone and mobile fuel cell application for its harsh operation conditions of high temperature and pressure, as well as large volume of facilities and hydrogen recycling requirement.5, 12, 13 Thus, it is necessary to develop new ultra-deep desulfurization approaches. There are several approaches such as adsorptive desulfurization,14-17 oxidative desulfurization,18 extractive desulfurization,19 and biodesulfurization20,

21

being explored by researcher. Among them, adsorptive 3


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desulfurization (ADS) has been considered as a promising technology for ultra-deep desulfurization due to low energy consumption, low cost, environment-friendly and no need for hydrogen.15, 16 The choice of adsorbent is critical for the adsorption desulfurization technology. Suitable adsorbent should have high adsorption capacity and selectivity, as well as a good regeneration performance. For an efficient removal sulfur compounds from fuels, not only suitable pore structure but also highly dispersed adsorption active sites are required for the adsorbents. The nature of adsorption active centers determines the type of interaction between the adsorbate and the adsorbent. Two pairs of electrons lie in the S atom of thiophenics. One pair lies on the π-system (for aromaticity with six electrons) and the other lies in the ring plane.22 Therefore, thiophenics can act either as n-type donors by donating the lone pairs of electrons to the adsorbent (direct S–M (metal) interaction), or as p-type donors through the bonding of the π-electrons of the aromatic ring with the transition metal ion in the d-block with a suitable electron configuration (π-complexation). Typically, the transition metal ions are Cu+, Ag+, Pd2+ and Ni2+, etc. For example, Cu+ has an electronic configuration of 1s22s22p63s23p63d104s0, the 4s-orbital of Cu(I) can σ-bond with the π-molecular orbitals of thiophenics, simultaneously, 3d-orbitals of Cu(I) can feed back electron density to the antibonding π-orbital (π∗) of thiophenics.22-25 The stronger interaction of π-complexation compared with van der Waals force leads to the high 4


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selectivity, while it is also weak enough to be broken by the mild thermal and chemical treatment which is beneficial to the regeneration of adsorbent. Then, thiophene and thiophene derivatives could be selectively removed from fuels by the π-complexation adsorption. Yang and coworkers prepared a series of Y zeolite adsorbents based on π-complexation, which were modified by various transition metal ions such as Cu+, Ag+, Ni2+. These modified Y zeolite are capable of producing fuels with a total sulfur concentration of less than 1 ppmw, among which Cu(I)-Y performed the best.26-28 It was reported that Cu(I)Y zeolite could remove 0.55 mmol/g of thiophene, 0.83 mmol/g of benzothiophene from fuels with total sulfur content of 300 ppmw.28 Huang and coworkers prepared a new type of MOF-5/Cu (I) adsorbent by incorporating different amounts of CuCl into MOF-5, which exhibited a high desulfurization capacity.29 However, the severe diffusion resistance imposed by the micropores of Y zeolite and MOF-5 resulted in an inefficient remove of thiophene derivatives with a large molecular structure from fuels, which could not interact with adsorption active centers in the pores. On the other hand, the adsorption capacity of thiophenics on the π-complexation adsorbents can be reduced by the competitive adsorption of aromatic hydrocarbons and olefins in the real fuels for the similarity in molecular structures. The micropore-filling effect of microporous adsorbents can intensify the effect of above competitive adsorption. McKinley and coworker reported that the Ag(I)/SBA-15 adsorbent prepared by the 5


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impregnation method could effectively adsorb dibenzothiophene from model fuel.30 Neubauer et al. prepared Ag-Al2O3 mesoporous adsorbent by the impregnation method, which exhibited a good adsorption performance for thiophene(TP), benzothiophene(BT) and dibenzothiophene(DBT) from model Jet-A1.22 Wang et al. had impregnated CuCl and PdCl2 into MCM-41 and SBA-15 mesoporous materials, which could effectively remove sulfur compounds from jet fuel.31 Subhan and coworker found that mesoporous Cu-KIT-6 adsorbent exhibited an excellent adsorption performance for thiophene. Li et al. prepared Cu(I)-SBA-16 mesoporous molecular sieves by hydrothermal synthesis method, which had a good adsorption performance for dibenzothiophene (DBT) in model fuel.32 The poor dispersion of π-complexation centers on the above mesoporous adsorbents could be caused by the impregnation preparation method. Therefore, to develop various mesoporous materials contain highly dispersed π-complexation adsorption centers is desirable for upgrading the desulfurization adsorbents. Aerogel is a kind of solid materials with three-dimensional porous network through the formation of the mutual aggregate of nanoscale particles. It has been used widely as catalytic support and adsorbent due to its large surface area, high porosity and the nanoscale pore size.33,

34

In the preparation of aerogel-like adsorbents based on

π-complexation by the sol-gel method, the transition metals ions, whose content could be adjusted in a larger range, could be doped into the skeleton particles of aerogel-like 6


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material. Due to the high specific surface area and nanoscale skeleton particles of the aerogel-like materials, the doped transition metal ions could be sufficiently exposed and highly dispersed. At the same time, the diffusion resistance of macromolecular compounds could be significantly reduced because of the 3D mesoporous structure of aerogel-like materials during the adsorption process. In our previous works, the synthesized Ag2O-SiO2, NiO-SiO2, and Cu2O-SiO2 composite aerogel-like materials exhibited an excellent adsorption performance for thiophene and benzothiophene in model gasoline.35,

36

Ag2O-SiO2 performed the best, followed by Cu2O-SiO2 and

NiO-SiO2. However, the cost of Cu is lower compared with Ag, Cu2O-SiO2 would have a more prospect in the industrial application. The chemical composition of the aerogel-like materials could significantly affect their structural properties, subsequently influence their desulfurization performance. In this paper, Cu2O-SiO2 composite aerogel-like adsorbents with different Si/Cu molar ratios were synthesized a sol-gel method followed by drying under ambient pressure, and then applied in the adsorption of thiophene (TP) and benzothiophene (BT) from model gasoline. The influence of Si/Cu molar ratio for the structural properties and desulfurization performance of Cu2O-SiO2 composite aerogel-like materials were investigated, and the effect of competitive adsorption of aromatic hydrocarbons and olefins with thiophenics on desulfurization performance was also examined. In addition, because of the lower thermal stability of aerogel-like 7


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materials, the solve washing regeneration of Cu2O-SiO2 composite aerogel-like adsorbent was investigated. 2. EXPERIMENTAL 2.1. Materials. Copper(II) acetate monohydrate (99%), Thiophene (99%), Benzothiophene (97%)，Tetraethyl orthosilicate (TEOS, 98%) and Cyclohexene were purchased from the Aladdin Biochemical Technology Co., Ltd. (Shanghai, China). Ethanol (EtOH, 99.7%), n-hexane (97%), n-heptane (98.5%) and benzene (99.5%) were purchased from the Ling Feng Chemical Reagent Co., Ltd. (Shanghai, China). Quartz sand (25-50 mesh), and Ammonia solution (26%-25%) were purchased from the Sinopharm Chemical Reagent Co., Ltd. China. All the chemicals were used without further purification. 2.2. Adsorbents preparation. After copper acetate monohydrate (0.193, 0.143, 0.096, 0.048 g, respectively) was dissolved in 3 ml distilled water in a glass vial, 10 mL EtOH and 8 mL TEOS were added in above copper acetate solution under stirring. Then, the pH of mixed solution was adjusted to 2.5 by 1 mol/L HCl solution. Upon stirring for 90 minutes, a sol could be obtained. Subsequently, by drop-wise addition of 0.8 mol/L ammonia water, the pH of sol was adjusted to 6.5. An alcogel could be obtained for standing about 10 minutes. For strengthening the skeleton structure of the obtained alcogel, it was immersed in mixture liquid (40 mL EtOH and 10 mL TEOS) at 60 °C for 12 hours. Then, the removal of ethanol, water, acetic acid and other small organic molecules within 8


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the aged gel was carried out by immersing it in 50 mL of n-hexane. Subsequently, the exchange of n-hexane was performed twice in an interval of 12 h. After rinsing twice with 20 mL of n-hexane, the exchanged gel was dried at 80 ℃ for 2 h and immediately at 120 ℃ for 2 h. Then, CuO-SiO2 composite aerogel-like materials with different n(Si/Cu) were obtained. Finally, Cu2O-SiO2 composite aerogel-like materials was obtained by the reduction of the dried CuO-SiO2 aerogel-like materials in a gas mixture of H2/N2 (5 vol% H2) at 180 °C for 4 h to. The obtained sorbents were denoted to Cu2O-SiO2-n, where n represents the molar ratio of Si/Cu (n=37, 50, 74, 150, respectively). 2.3. Characterization. Temperature programmed reduction (H2-TPR) experiment was performed for CuO-SiO2-50 sample by a Micromeritics Autochem II 2920 analyzer equipped with a thermal conductivity detector (TCD). Prior to the H2-TPR test, the sample (c.a. 100 mg) was pretreated in Ar (20 mL/min) for 30 min at 160°C. After cooling to room temperature in argon atmosphere, the sample was flowed pass by the mixed gas of H2/Ar(10 vol % H2) at the flow rate of 30 ml/min. The temperature of sample was increased from room temperature to 300 °C with a heating rate of 10 °C/min. The alteration in H 2 content of the effluent was monitored by the TCD. The crystal structure of the samples was characterized by an X-ray diffraction (XRD) technique (XRD; D/MAX-IIIA, Rigaku, Japan) with Cu Kα radiation (40 kV and 200 mA) and data collection at 0.02°/min scan rate in the range 2θ of 10–80°. After evacuating the 9


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samples at 160 ℃ for 6 h, their nitrogen adsorption-desorption isotherms were measured at -196 °C with a surface area and porosity analyzer (Micromeritics ASAP 2010 V5.02). The specific surface areas of samples were calculated with the Brunauer-Emmett-Teller equation. The pore size distribution and pore volume of samples were obtained through the BJH method from desorption branch. The real content of Cu in the samples was determined

by

X-ray

fluorescence

Spectrometer

(XRF,

ARL

ADVANT’X

IntelliPowerTM 4200, ThermoFisher). The morphology of Cu2O-SiO2 materials was observed by an emission scanning electron microscopy (FE-SEM) analyzer (Model HITACHI S-4700(II)). 2.4. Model fuels. The model fuels of 10 mg-S/g containing thiophene (TP) or benzothiophene (BT) were made by dissolving TP or BT with n-heptane. Model fuels with different content of TP or BT (MF-1, MF-2, MF-3, MF-4, MF-5, MF-6, MF-7) was obtained by successively diluting the stock solution with n-heptane. A part of n-heptane in MF-2 model fuel was replaced by cyclohexene or benzene to obtain model fuel MF-8 or MF-9, respectively. Table 1 list the composition of model fuels.

10


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Table 1 Compositions of model fuels Thiophene

Benzothiophene

Cyclohexene

Benzene

N-heptane

（μg-S/g）

（μg-S/g）

(wt %)

(wt %)

(wt%)

MF-1

800

--

--

--

99.92

MF-2

1000

--

--

--

99.90

MF-3

1200

--

--

--

99.88

MF-4

1500

--

--

--

99.85

MF-5

1800

--

--

--

99.82

MF-6

2000

--

--

--

99.80

MF-7

--

1000

--

--

99.90

MF-8

1000

--

20

--

79.90

MF-9

1000

--

--

20

79.90

2.5. Batch experiments. Upon the reduction of the dried CuO-SiO2 materials with different n(Si/Cu) in a gas mixture of H2/N2 (5 vol% H2), the obtained Cu2O-SiO2 adsorbents were immediately applied in the desulfurization experiments. 0.1 g of Cu2O-SiO2 adsorbent was put into 1g of model fuel MF-1, MF-2, MF-3, MF-4, MF-5 and MF-6, respectively. The mixture of model fuel with adsorbent was well shaken for 12 h at 25 °C or 60 ℃, respectively, to obtain the complete equilibrium adsorption of TP over adsorbent. Then the adsorbent was separated from the mixture with a centrifuge. The content of TP remained in the filter was quantitatively analyzed by gas chromatography (GC, Agilent Technologies, 6890 N) equipped with a flame photometric detector (FPD). The equilibrium adsorption capacity (qe) was calculated as follows: qe =

(C0 -Ce )m 1000W

(1)

Where qe represents the equilibrium adsorption capacity (mgS/gads.), C0 represents 11


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the initial sulfur content in model fuels (mg-S/g), Ce represents the sulfur content of filter at adsorption equilibrium (mg-S/g), m represents the mass of the model fuel (g) and W represents the weight of the adsorbent (g). The equilibrium adsorption isotherms of the adsorbents at 25 oC or 60 oC were fitted with Langmuir and Freundlich equations, respectively. 2.6. Breakthrough adsorption experiments. The 1 g of freshly prepared Cu2O-SiO2 was filled into the middle of a vertical custom-made glass tube (length: 150 mm; internal diameter: 6 mm), in which the spare spaces were packed with quartz sand (25~50 mesh). Before adsorption test, the adsorbent bed was washed by n-heptane to remove any entrapped gas. At the ambient temperature and pressure, model fuel (MF-2 or MF-7) was fed into the adsorbent bed at a flow rate of 0.05 mL/min (liquid hourly space velocity (LHSV): 2 h-1) and the effluent was collected every 0.5 mL. The sulfur content in the effluent was measured by GC. The adsorption test was ended up until the sulfur content in the effluent became stable. The breakthrough adsorption curves were obtained by plotting the transient desulfurization ratio vs the cumulative volume of treated model fuel. Breakthrough adsorption capacities (qb) was calculated at the 99.9 % of desulfurization ratio threshold limit. The desulfurization ratio was obtained by formula (2). Desulfurization ratio (%) =

C0 -C ×100 C0

(2)

Where C0 represents the initial sulfur content in model fuels (μg-S/g), C represents 12


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the sulfur content of the effluent (μg-S/g). 2.7. Competitive adsorption experiment of benzene or cyclohexene. The competitive adsorption tests of benzene or cyclohexene to thiophene on the adsorbents were carried out by the model fuel MF-8 or MF-9 according to breakthrough adsorption experiments in 2.6. 2.8. Regeneration experiment. Due to the lower thermal stability of aerogel material, the regeneration of the saturated Cu2O-SiO2 adsorbent was performed by solvent washing. At room temperature and pressure, 10 mL benzene, used as a desorption agent, flowed through the saturated adsorbent bed for about 4 h. The sulfur content in the effluent was analyzed by GC equipped with an FPD. Subsequently, the adsorbent bed was washed with 20 mL n-heptane for about 8 h, at this time, the benzene content in the effluent did not change. The content of benzene in the effluent was detected by high performance liquid chromatography (HPLC, Agilent Technologies, 1220) equipped with ultraviolet detector (UVD, λ=254 nm). Then washed adsorbent was dried at 120 ℃ for 2 h and subsequently reduced in a gas mixture of H2/N2 (5 vol% H2) at 180 °C for 4 h. The breakthrough adsorption capacity was calculated after it was again subjected to a breakthrough adsorption experiment. The regeneration of adsorbent was repeated four times. 3. RESULTS AND DISCUSSION 3.1. Characterization. The H2-TPR profile of CuO-SiO2-50 sample is shown in 13


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Figure 1. By fitting with PeakFit software, it can be observed that the H2-TPR profile of CuO-SiO2-50 sample could be deconvoluted into two components. One, at the range between 160 and 240 °C and peaked at 228 °C, was belonged to the reduction of Cu(II) to Cu(I), and the second located in the range of 220 °C to 280 °C and peaked at 253°C, was assigned to the reduction of Cu(I) to Cu(0). Yang et al. also carried out the H2-TPR characterization of Cu-Y zeolite desulfurization adsorbent. They found that there are also two reduction temperature ranges, the first located at 130 °C~320 °C, and the other was between 200 °C and 500 °C, which were believed to attributed to the reductions of Cu(II) to Cu(I) and Cu(I) to Cu(0),24 respectively. Therefore, Cu2O-SiO2 samples could be obtained by reducing CuO-SiO2 aerogel-like adsorbents in the mixed gas of H2/Ar (10 vol% H2) at 180 °C for 4 h in this work. After the reduction, the color of sample changed from bluish green to white, also indicating the reduction of Cu(II) to Cu(I),37 namely CuO-SiO2 samples were reduced to Cu2O-SiO2 samples.

14


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Figure 1. H2-TPR profile of CuO-SiO2-50 sample The XRD patterns of Cu2O-SiO2 samples with different n (Si/Cu) are displayed in Figure 2. All the samples only have a wide peak at 2θ of 20–30°, due to the amorphous SiO2.38 However, it can be found that the characteristic diffraction peaks for copper oxides were not observed, indicating a high dispersion of the copper species in silica matrix, or too small crystal particles which were not detected.

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Figure 2. XRD patterns of Cu2O-SiO2 samples with different n(Si/Cu) and regenerated Cu2O-SiO2-50 sample

FT-IR spectra of SiO2 aerogels, fresh and regenerated Cu2O-SiO2-50 adsorbents are shown in Figure 3. For all sorbents, a large and broad band around at 3430 cm−1 are assigned to O-H stretching of water, surface and bridged hydroxyl groups, indicating the existence of a great amount of hydroxyl groups on the surface of aerogel-like material.22 The adsorption band at 1630 cm−1 is belonged to the deformational vibrations of adsorbed water molecules.32 The major bands at 1085 cm-1，804 cm-1 and 466 cm-1 are due to asymmetric stretching, symmetric stretching, and bending vibration of Si-O-Si, respectively.39 The peak near 960 cm-1 can be assigned to the stretching vibration of Si-OH, but also due to the Si-O-M bond in the SiO2-MOx (M=metal) composite oxides.40 Compared with SiO2 aerogels, no new infrared absorption bands appear in the FTIR 16


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spectrum of fresh Cu2O-SiO2-50 sample, however, the I1085/I960 decreases, which are 2.74 and 1.80, respectively, suggesting the formation of Si-O-Cu bond in the composite aerogel-like sample, which could affect the strength of the Si-O bond.

Figure 3. FTIR spectra of samples. a: SiO2 aerogel, b: fresh Cu2O-SiO2-50, c: regenerated Cu2O-SiO2-50 N2 adsorption–desorption isotherms of Cu2O-SiO2 samples with different n(Si/Cu) are shown in Figure 4. According to Brunauer-Deming-Deming-Teller (BDDT), the obtained isotherms of four samples are assigned to the type IV isotherm with a clear H2 hysteresis loop, which is typical of mesoporous materials of irregular structure.41 The physical properties and chemical composition of SiO2 aerogels and Cu2O-SiO2 adsorbents are listed in Table 2. Comparing with SiO2 aerogels, the specific surface area, pore size and pore volume of Cu2O-SiO2 samples dropped with the reduction of n(Si/Cu) (increase of Cu content), maybe attributed to the mismatch in the condensation rate 17


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between Si-O-Si and Si-O-Cu bonds and the effect of Cu(II) on the hydrolysis reaction of TEOS in the sol-gel process. However, for Cu2O-SiO2 samples, the BET surface area was still larger (600-700 m2/g), and the mean pore diameter was in between 2-5 nm. The real Cu content in samples detected by XRF, was much less than that introduced in the synthesis process. The actual incorporated rate of Cu in Cu2O-SiO2-150，Cu2O-SiO2-74， Cu2O-SiO2-50，Cu2O-SiO2-37 were 63 %，88 %，88% and 69%, respectively, relative to the added amount of Cu, namely 10~40% of added Cu did not enter into composite aerogel-like materials, maybe due to that the formation of the Si-O-Cu bonds is more difficult than that of Si-O-Si bonds.

Table 2. Physical properties and Cu content of SiO2 aerogel and Cu2O-SiO2 samples with different n(Si/Cu) Cu content (mmol/g)

SBET (m2/g)

V (cm3/g)

Daverage (nm)

--

881

1.5

6.9

0.08

0.05

700

0.6

3.5

Cu2O-SiO2-74

0.16

0.14

690

0.4

2.4

Cu2O-SiO2-50

0.24

0.21

635

0.4

2.5

Cu2O-SiO2-37

0.32

0.22

600

0.4

2.5

adsorbent

Add

XRF

SiO2

--

Cu2O-SiO2-150

18


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Energy & Fuels

Figure 4. N2 adsorption–desorption isotherms of Cu2O-SiO2 samples with different n(Si/Cu). The SEM images of Cu2O-SiO2 samples with different n(Si/Cu) are displayed in Figure 5a–d. All samples shown an aggregate of nanoscale particles of 20–50 nm, and the particle size distribution was uniform. No obvious changes were observed for the morphology structure of Cu2O-SiO2 samples with the decrease of n(Si/Cu), which were similar with that of the SiO2 aerogel reported.42, 43 This case indicates that the doping Cu could not significantly influence the intrinsic morphology of Cu2O-SiO2 samples.

19


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

Figure 5. SEM images of Cu2O-SiO2 samples (a) Cu2O-SiO2-37, (b) Cu2O-SiO2-50, (3) Cu2O-SiO2-74, (d) Cu2O-SiO2-150

3.2. The breakthrough adsorption experiment. Figure 6A displays the breakthrough adsorption curves of thiophene from model fuel MF-2 (thiophene: 1000 μg-S/g) over SiO2 aerogel, CuO-SiO2-50 and Cu2O-SiO2 with different n(Si/Cu), respectively. Figure 6B shows the breakthrough adsorption curves of thiophene and benzothiophene from model fuel MF-2 and MF-7 (benzothiophene: 1000 μg-S/g) over 20


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Energy & Fuels

Cu2O-SiO2-50 adsorbent, respectively. It can be seen from Figure 6A, the volumes of cumulative model fuel MF-2 treated over Cu2O-SiO2 adsorbents with different n(Si/Cu) are much more than that of the SiO2 aerogel and CuO-SiO2-50 before reaching the breakthrough point of thiophene. The volumes of model fuel MF-2 treated over SiO2 aerogel and CuO-SiO2-50 were small, only 2 and 2.5 mL, respectively, due to that the adsorption of thiophene on the two adsorbents was carried out by van der Waals force and interaction between surface hydroxyl groups and S atom in thiophene which were weaker.22 According to the results of BET, the specific surface area of Cu2O-SiO2 adsorbents was lower than that of SiO2 aerogel, indicating that the excellent desulfurization performance of Cu2O-SiO2 adsorbents is not mainly attributed to van der Waals forces and the interaction between hydroxyl groups and S atom in the thiophene. It was reported that Cu(I)Y, MOF-5/Cu(I), and CuCl/SBA-15 have an excellent adsorption performance for thiophenics from fuels, due to the π-complexation between Cu(I) and thiophenics.24, 29, 44 Therefore, compared with SiO2 aerogel and CuO-SiO2-50, the higher breakthrough adsorption capacities of thiophene over Cu2O-SiO2 adsorbents should be mainly attributed to the π-complexation between Cu(I) and thiophene. The n(Si/Cu) of Cu2O-SiO2 adsorbents had a significant effect on its desulfurization performance. The treated volume of model fuel MF-2 reduced in the order of Cu2O-SiO2-50 (7 mL) > Cu2O-SiO2-74 (6 mL) > Cu2O-SiO2-37 (5 mL) > Cu2O-SiO2-150 (4.5 mL), correspondingly, the breakthrough 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

adsorption capacity of thiophene was 4.76 mgS/gads., 4.08 mgS/gads., 3.4 mgS/gads. and 3.06 mgS/gads., respectively. Generally, the adsorption capacity of an adsorbent is related to its specific surface area and the amount of the adsorption active sites. The more the adsorption active sites and the higher the specific surface area, the larger the adsorption capacity is. The BET results showed that the specific surface area of Cu2O-SiO2 adsorbents decreased with the decrease of the n(Si/Cu) (the Cu(I) content increasing). Among Cu2O-SiO2 adsorbents with different n(Si/Cu), Cu2O-SiO2-50 had a higher specific surface area and more adsorption active sites (Cu(I)) at the same time, so the largest breakthrough adsorption capacity for thiophene. Although the specific surface of Cu2O-SiO2-74 was slightly bigger than that of Cu2O-SiO2-50, the obviously less Cu(I) content in the former compared with the latter resulted in its lower breakthrough adsorption capacity. For Cu2O-SiO2-150, the specific surface area was largest while Cu(I) content was lowest. However, for Cu2O-SiO2-37, the Cu(I) content was highest while the specific surface area was lowest. Thus, the breakthrough adsorption capacity of the above two adsorbents was low.

22


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Energy & Fuels

Figure 6. Breakthrough curves of thiophene from MF-2 (A) over different adsorbents and benzothiophene from MF-7 and thiophene from MF-2 (B) over Cu2O-SiO2-50 It can be found from Figure 6B that the breakthrough adsorption capacity for benzothiophene was greater than that for thiophene over Cu2O-SiO2-50. The cumulative volumes of treated MF-7 and MF-2 were 8.5 mL and 7 mL, correspondingly, the breakthrough adsorption capacitise for benzothiophene and thiophene were 5.78 mgS/gads. (0.90 mmol-S/mmol-Cu) and 4.76 mgS/gads. (0.74 mmol-S/mmol-Cu). This result could be attributed to a higher π-electron cloud density of benzothiophene compared to thiophene. A stronger π-complexation between Cu(I) and benzothiophene than that thiophene could be formed,45 when both of benzothiophene and thiophene can arrive at adsorption active sites due to the mesoporous structure of Cu2O-SiO2-50. After the adsorption over Cu2O-SiO2 adsorbents with different n(Si/Cu), the content of thiophene or benzothiophene in model fuels could be reduced to below the detection limit of GC-FPD (0.5 μg-S/g), which was satisfied with the requirement of fuel 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

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cells. Yang et al. reported that the breakthrough adsorption capacities of benzothiophene from JP-5 fuel over CuCl/SBA-15 and CuCl/MCM-41 mesoporous molecular sieves were 0.16 mmolS/gads. (0.030 mol-S/mol-Cu) and 0.31 mmolS/gads. (0.050 mol-S/mol-Cu), respectively,31 which were much lower than that over Cu2O-SiO2-50 in this work. These results indicated that Cu2O-SiO2-50 had an excellent desulfurization performance, maybe owing to the high dispersion of Cu(I) in Cu2O-SiO2-50. 3.3. Batch experiment. The adsorption isotherms describe the interaction between adsorbate molecules and adsorbent. The Langmuir isotherm equation assumes the monolayer adsorption on a surface containing a finite number of identical sites, and there is no molecular interaction. The linear Langmuir isotherm equation can be represented by the following equation: Ce 1 Ce = + qe KL qm qm

(3)

Where, qe (mgS/gads.) represents the amount adsorbed at equilibrium concentration Ce (mg-S/g), qm (mgS/gads.) represents the maximum amount of the adsorbate to form a complete monolayer coverage and KL (g/mg) represents the Langmuir parameter related to the adsorption affinity and can be obtained from the plot of Ce/qe versus Ce. The Freundlich isotherm equation is an empirical model and assumes a heterogeneous adsorbent surface with a nonuniform distribution of the heat of adsorption over the surface, where the stronger binding sites are occupied first and the adsorption 24


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Energy & Fuels

energy is exponentially decreased with the increase of cover degree. It can be linearly expressed by follows: 1 log(qe ) = log(KF ) + log(Ce ) n

(4)

Where, KF and 1/n represent the Freundlich constants related to adsorption capacity and adsorption intensity of adsorbent, respectively. The value of 1/n is a measure of surface heterogeneity, becoming more homogeneous as its value gets closer to one. The Freundlich constants can be obtained from the plot of log(qe) versus log(Ce). Here, two isotherm models of Langmuir and Freundlich were used to fit the adsorption experimental data of thiophene over Cu2O-SiO2 adsorbent with different n(Si/Cu) at 25 °C and 60 °C. The results are shown in Figures 7 and 8, and the various parameters are listed in Tables 3 and 4, respectively.

Figure 7. the Langmuir adsorption isotherms of thiophene over Cu2O-SiO2 adsorbents at 25 °C (A) and 60 °C (B).

25


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Figure 8. the Freundlich adsorption isotherms of thiophene over Cu2O-SiO2 adsorbents at 25 °C (A) and 60 °C (B). Table 3. The Langmuir adsorption constants of thiophene on Cu2O-SiO2 adsorbents at 25 °C and 60 °C Adsorbents

Cu2O-SiO2-37

Temperature (°C)

Constant

25

60

qm (mgS/g)

7.57

6.52

KL (g/mg)

1.4990

1.1246

0.9983

0.9806

qm (mgS/g)

12.03

10.24

KL (g/mg)

1.5689

1.1719

0.9965

0.9907

qm (mgS/g)

11.04

7.70

KL (g/mg)

1.3407

1.4135

0.99541

0.9975

qm (mgS/g)

7.68

6.39

KL (g/mg)

1.1605

1.0307

0.9942

0.9989

R2 Cu2O-SiO2-50

R2 Cu2O-SiO2-74

R2 Cu2O-SiO2-150

R2

26


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Energy & Fuels

Table 4. The Freundlich adsorption constants of thiophene on Cu2O-SiO2 adsorbents at 25 °C and 60 °C Adsorbents

Cu2O-SiO2-37

25

60

KF

4.4713

3.4198

1/n

0.4453

0.4911

2

0.9775

0.9791

KF

7.3342

5.4674

1/n

0.4894

0.5244

R2

0.9852

0.9797

KF

6.2630

4.4400

1/n

0.4969

0.4520

R2

0.9964

0.9959

KF

4.0179

3.1891

1/n

0.4838

0.5003

R2

0.9989

0.9958

R Cu2O-SiO2-50

Cu2O-SiO2-74

Cu2O-SiO2-150

Temperature (°C)

Constant

It can be seen from Table 3 and 4 that the R2 values of the Langmuir and Freundlich adsorption isotherms for various adsorbents are all greater than 0.97, indicating that the equilibrium adsorption data can be well fitted by both adsorption isotherms. The R2 values of the Langmuir adsorption isotherms were almost slightly higher than that of the Freundlich adsorption isotherms, that is, the equilibrium adsorption data were better fitted by the Langmuir isotherm model. The Langmuir parameter KL reflects the affinity of the adsorbent to adsorbate molecules. The larger the KL value, the better the adsorption. It can be found from Table 3 that for all adsorbents, the KL value at low temperature (25 °C) 27


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Page 30 of 49

was larger than that at high temperature (60 °C). In addition, the decrease of maximum monolayer adsorption capacity (qm) of thiophene with the increase of temperature indicated a better adsorption at the lower temperature, which was consistent with results in the literature,25, 35 because π-complexation could be broken by raising the temperature due to that it is a weaker chemical interaction compared with typical covalent bonds. At different adsorption temperatures, the qm of thiophene on adsorbents decreased following the order of Cu2O-SiO2-50 > Cu2O-SiO2-74 > Cu2O-SiO2-37 > Cu2O-SiO2-150, which agreed with the breakthrough adsorption capacity. It can be seen from Table 4 that the 1/n value of all adsorbents is significantly lower than 1, indicating that the energy distribution of active sites over the surface of the adsorbent was not uniform. 3.4. Isosteric adsorption heat. The isosteric adsorption heat can directly reflect the strength of the interaction between the adsorbent and the adsorbate molecules. The greater the adsorption heat, the stronger the interaction between the adsorbent and the adsorbate molecules is. As in many references,4, 36 the isosteric adsorption heat at constant surface coverage (qe=2 mgS/gads.) was calculated using the Clausius–Clapeyron equation (5) and adsorption isotherms at 25 °C and 60 °C, although the accuracy of which was not high enough.46 Assuming that the adsorption behavior of thiophene over Cu2O-SiO2 adsorbents follows the Langmuir isotherm, and the equilibrium data can be fitted by the equation (3) ∆H=-RT2 (

∂lnCe ) ∂T q 28


(5)

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Energy & Fuels

Where, Ce (ppmw) represents the equilibrium sulfur content at constant amount of thiophene adsorbed (q=2 mgS/gads.), T (K) is the adsorption temperature, and R is the universal gas constant. Isosteric adsorption heats of thiophene on Cu2O-SiO2 adsorbents with different n(Si/Cu) are list in Table 5. It can be seen that adsorption heats of thiophene on the adsorbents decreased in the order of Cu2O-SiO2-50 > Cu2O-SiO2-74 > Cu2O-SiO2-37 > Cu2O-SiO2-150, which was consistent with the maximum monolayer adsorption capacity (qm) and the breakthrough adsorption capacity of thiophene with n(Si/Cu) in the adsorbents. Yang et al. reported that the adsorption heat of thiophene on Cu(I)Y was 22.3 KJ/mol,47 which was higher than that on Cu2O-SiO2 adsorbents in this paper (-7.63 ~ -11.15 KJ/mol). Valla et al. had prepared the mesoporous molecular sieve (CuSAY) by the desiliconization or dealumination treatment for Cu(I)Y zeolite, and found that the adsorption heat of BT on CuSAY (-15.56 KJ/mol) was obvious less than that on Cu(I)Y (-41.94 KJ/mol).4 It was believed that the introduction of mesopores could lead to a decrease in the interaction strength between the adsorbent and BT, because the overlapping potentials originated from the surrounding walls of the micropores can exert a significant attraction force on the adsorbate molecules, which is called “micropore-filling effect”.4 In this paper, Cu2O-SiO2 adsorbents were mesoporous materials, therefore, the adsorption heat of thiophene on them was lower than that on 29


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Cu(I)Y reported in the literature.

Table 5. Isosteric adsorption heats of thiophene on Cu2O-SiO2 adsorbents with different n(Si/Cu)

a

Adsorbents

Cu2O-SiO2-37

Cu2O-SiO2-50

Cu2O-SiO2-74

Cu2O-SiO2-150

Hads. (KJ/mol)a

-9.13

-11.15

-10.09

-7.63

qe=2 mgS/gads. 3.5. Competitive adsorption of benzene and cyclohexene. Generally, there is

around 30 % aromatics and a certain amount of olefins in gasoline, and 20 % aromatics in diesel and jet fuels sometimes, whose content is much higher than that of thiophenics.48 For the application in the real fuels, the desulfurization performance of π-complexation adsorbents could be intensely reduced, due to the competitive adsorption of aromatics or olefins to thiophenic compounds owing to the similarity in molecular structures.49 The breakthrough curves of thiophene from model fuel MF-2, MF-8 and MF-9 over Cu2O-SiO2-50 adsorbent are shown in Figure.9. It can be found that, after the 20 wt% of cyclohexene (MF-8) or benzene (MF-9) present in the model fuel, the breakthrough of thiophene on Cu2O-SiO2-50 appeared earlier, the volumes of cumulative model fuel MF-8 and MF-9 was 3.5 ml and 4 ml, and the corresponding breakthrough adsorption capacity of thiophene was 2.38 mgS/gads. and 2.72 mgS/gads., respectively, which were 50 % and 57 % of that (4.76 mgS/gads.) with model fuel without cyclohexene and benzene (MF-2), respectively, due to the competitive adsorption of benzene and cyclohexene to thiophene. 30


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Energy & Fuels

Figure 9. Breakthrough curves of thiophene from model fuel MF-2, MF-8 and MF-9 over Cu2O-SiO2-50 adsorbent. Liu et al. had investigated the effect of competitive adsorption of toluene on the desulfurization performance of Cu(I)Y by model fuel containing 20 wt% of toluene, and found a decrease of 77.5% in the breakthrough adsorption capacity of thiophene (543 ppmw) compared with that using model fuel without toluene.50 Song et al. also found that the breakthrough adsorption capacity of thiophene on Cu(I)Y decreased by 49.2% and 63%, respectively, when only 0.7 wt% of toluene or cyclohexene was added to model fuel (0.142 mgTP/g).51 Yang et al. studied the adsorption of thiophene on Cu(I)-Y zeolite in a ternary solution of n-octane-benzene-thiophene (benzene: 20 wt%, thiophene: 300 ppmw), The results showed that the adsorption capacity of thiophene on Cu(I)-Y in ternary solution thiophene decreased from 0.74 mmolS/g to 0.13 mmolS/g, which was reduced to 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

17.6 %, compared with that in model fuel without benzene.28 Compared with the results in above literature (the date is list in Table 6), the effect of competitive adsorption of olefins or aromatics on the desulfurization performance of Cu2O-SiO2-50 adsorbent was obviously weaker in this paper, attributed to the no existence of micropore-filling effect in mesoporous Cu2O-SiO2-50 adsorbent. However, micropore-filling effect of microporous Cu(I)Y adsorbent could result in strengthening the competitive adsorption of benzene and cyclohexene molecules, although that the π-complexation between Cu(I) and thiophene is stronger than that between olefins or aromatics and Cu(I). Liu et al. reported that for the model fuel containing thiophene (564 ppmw) and 8 wt% toluene, the adsorption capacity of thiophene on CuCl/SBA-15 and CuCl/Al-SBA-15 dropped to 32% and 53% of that using model fuel without toluene, respectively.52 The effect of competitive adsorption of aromatics on the desulfurization performance for CuCl/SBA-15 and CuCl/Al-SBA-15 was more obvious than that on Cu2O-SiO2-50 adsorbent in this work. It could be explained that the three-dimensional mesoporous structure of Cu2O-SiO2-50 adsorbent is more favorable for reducing the diffusion resistance of the adsorbate molecules in the adsorbent compared with the SBA-15 mesoporous molecular sieve.

32


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Energy & Fuels

Table 6. Comparison of competitive adsorption of aromatic/olefins to thiophene on Cu2O-SiO2-50 with the results in the literature Adsorption capacity of thiophene

Ratio d

qwithoutb

qwithc

(%)

20 wt% benzene

4.76 mgS/g

2.38 mgS/g

57

20 wt% cyclohexene

4.76 mgS/g

2.72 mgS/g

50

20 wt% Toluene

0.40 mmol/g

0.09 mmol/g

22.5

0.7 wt% toluene

0.605 wt%

0.307 wt%

50.8

0.7 wt% cyclohexene

0.605 wt%

0.221 wt%

36.5

Cu(I)Y [Ref.28]

20 wt% benzene

0.74 mmolS/g

0.13 mmolS/g

17.6

CuCl/SBA-15 [Ref.52]

8 wt% toluene

0.16 mmolS/g

0.05 mmolS/g

32

8 wt% toluene

0.23 mmolS/g

0.12 mmolS/g

53

Adsorbent

Aromatic/olefinsa

Cu2O-SiO2-50 Cu(I)Y [Ref.50] Cu(I)Y [Ref.51]

CuCl/Al-SBA-15 [Ref.52] a

The content of aromatics and olefins in the fuel

b

The breakthrough adsorption capacity of thiophene in the fuel without aromatic/olefins

c

The breakthrough adsorption capacity of thiophene in the fuel with aromatic/olefins

d

qwith/qwithout

3.6. Adsorbent regeneration. The regeneration of adsorbent is of utmost importance for its practical applications. Because of the poor thermal stability of aerogel-like materials, the spent Cu2O-SiO2 adsorbent was regenerated by benzene-n-heptane solvent washing. The breakthrough adsorption capacities of thiophene on fresh and regenerated Cu2O-SiO2-50 were shown in Figure.10. After the first regeneration of spent Cu2O-SiO2-50, the breakthrough adsorption capacity of thiophene dropped to 71 % of the fresh adsorbent, and gradually decreased with the times of regeneration. However, after 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

four times of regeneration, the adsorption capacity was basically unchanged which was 43 % of the fresh adsorbent. Wang et al. had prepared Cu(I) or Pd(II) loaded on SBA-15 mesoporous molecular sieve as the π-complexation adsorbents for the removal of thiophene from the fuel. After the adsorbent was saturated, it was regenerated by benzene washing. The adsorption capacity of thiophene on the regenerated adsorbent recovered to 44% of the fresh adsorbent,31 which is significantly lower than that of Cu2O-SiO2-50 regenerated first time in this work. It indicates that Cu2O-SiO2 adsorbents had a good solvent washing regeneration performance.

Figure 10. Breakthrough adsorption capacity of thiophene on regenerated Cu2O-SiO2-50 adsorbent. In order to understand the reason for the decrease in adsorption capacity after the solvent washing regeneration for Cu2O-SiO2 adsorbents, the structural and physical properties of fresh and regenerated Cu2O-SiO2-50 were characterized and illustrated in 34


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Energy & Fuels

Figure 2 and Table 7. Figure 2 shows that XRD patterns of fresh and regeneration Cu2O-SiO2-50 was similar. From Table 7, It can be found that the specific surface area, pore volume and mean pore diameter of the regenerated Cu2O-SiO2-50 have not obviously changed compared with the fresh one. Combined the results of XRD and N2 adsorption–desorption, it can be deduced that the decrease in adsorption capacity of regenerated Cu2O-SiO2-50 for thiophene could not be attributed to the structural and textural changes of the adsorbent after the regeneration. The infrared spectrum of the regenerated Cu2O-SiO2-50 is also displayed in Figure 3. It can be found in Figure 3 that the infrared spectrum of the regenerated Cu2O-SiO2-50 was basically similar to that of fresh one, no new infrared absorption peaks belonging to the -CH2-, C-H or C-S bond are observed for the regenerated adsorbent. This result means that after regeneration by solvent washing, there was no residue of thiophene, benzene and n-heptane on the surface of the adsorbent, namely, these compounds was almostly rinsed off. At the same time, the I1080/I960 increased to 2.275, which is close to that of SiO2 aerogel, suggesting a decrease in the number of Si-O-Cu bonds in the adsorbent after the solvent washing regeneration. In addition, it can be seen the slight decrease in the intensity of band at 3430 cm-1, indicating a slight reduction of amount of surface O-H groups.32 The copper content in the fresh and regenerated Cu2O-SiO2-50 was analyzed by XRF and shown in Table 7. It can be found that the Cu content after regeneration reduced by 52%, suggesting a 35


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reduction in the number of adsorptive sites for the regenerated adsorbent. Thus, after the solvent washing regeneration for the spent adsorbent, the decrease in the adsorption capacity of thiophene could be mainly attributed to the losing of a part of Cu (I) which were only embedded or encapsulated in the adsorbent skeleton particles while not in the Si-O-Cu bonds. The slight decrease in the amount of surface O-H groups could also cause a little reduction for adsorption capacity.22 The less adsorption capacity of regenerated adsorbent was not caused by the covering of adsorption active centers by the residual benzene or thiophene. Table 7. Physical properties and Cu content of Cu2O-SiO2-50 adsorbents before and after regeneration Cu2O-SiO2-50 Cu (mmol/g)XRF SBET(m2/g) V(cm3/g) Daverage(nm) Fresh 0.21 635 0.44 2.7 Regenerated 0.10 627 0.42 2.7

4. CONCLUSION CuO-SiO2 composite aerogel-like samples were synthesized by sol-gel method and dried under ambient pressure, and then transformed to Cu2O-SiO2 composite aerogel-like adsorbents after the reduction in the mixed gas of H2/N2 (5 vol% H2), which were a kind of solid materials with three-dimensional porous network through the formation of the mutual aggregate of nanoscale particles. Cu2O-SiO2 adsorbents exhibited excellent adsorption performance for thiophenic compounds in the model fuels owing to the

36


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Energy & Fuels

π-complexation between Cu(I) and thiophenic compounds. For Cu2O-SiO2 adsorbents, only a part (60~90%) of Cu(I) were actually incorporated into the materials and the specific surface area, pore volume, and pore diameter decreased with the reduction of n(Si/Cu) (increase of Cu content), consequently leading to the changes in the desulfurization performance of Cu2O-SiO2 adsorbents with n(Si/Cu). The higher specific surface area and the greater the Cu content, the larger the adsorption capacity was. Among these adsorbents, Cu2O-SiO2-50 performed the best for it had the higher specific surface area and the greater Cu content at the same time. The equilibrium adsorption data of thiophene over Cu2O-SiO2 adsorbents can be well fitted by the Langmuir and Freundlich isotherm equations, the qm was bigger at the lower adsorption temperature. The change of maximum monolayer adsorption capacity agreed with the breakthrough adsorption capacity and adsorption heat with n(Si/Cu). The 3D mesoporous structure of Cu2O-SiO2 adsorbents could decrease the adsorption heat of thiophene and the effect of competitive adsorption of benzene and cyclohexene on its the desulfurization performance compared with results in the literature.4, 28, 50-52 Cu2O-SiO2 adsorbents had a good solvent washing regeneration performance, and the decrease in adsorption capacity after regeneration was mainly ascribed to the losing of Cu(I). Cu2O-SiO2 adsorbents prepared in this work is a promising desulfurization adsorbent.

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ACKNOWLEDGEMENT We are grateful to the financial supports from Natural Science Foundation of Zhejiang Province (grant no. LY17B070007).

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