ARTICLE pubs.acs.org/EF
Adsorptive Removal of Thiophene by Cu-Modified Mesoporous Silica MCM-48 Derived from Direct Synthesis Jia-Hui Shan,†,‡ Le Chen,§ Lin-Bing Sun,‡ and Xiao-Qin Liu*,‡ †
School of Chemistry and Chemical Engineering, Nantong University, Nantong 226019, Jiangsu, China State Key Laboratory of Materials-Oriented Chemical Engineering, Nanjing University of Technology, Nanjing 210009, Jiangsu, China § Key Laboratory of Fine Petrochemical Engineering, Changzhou University, Changzhou 213164, Jiangsu, China ‡
ABSTRACT: A series of Cu-containing mesoporous MCM-48 molecular sieves (Cu-MCM-48) were prepared by the direct synthesis method and used as the adsorbents for desulfurization of model fuel. The samples were characterized by X-ray power diffraction, N2 adsorptiondesorption isotherms, BrunauerEmmettTeller specific surface area, transmission electron microscopy, inductively coupled plasma atomic emission spectrometry, and X-ray photoelectron spectroscopy. The results show that the Cu-MCM-48 adsorbent with a copper content up to 10 wt % can still retain the uniform mesoporous framework of MCM-48. The proposed direct synthesis method gives better Cu dispersion and a higher content of active component Cu+ in the support than the conventional incipient impregnation method. As a result, the desulfurization performance of these adsorbents is enhanced. The adsorption behaviors of thiophene on these molecular sieves were measured at 20 °C, and their adsorption capacities follow the order 10Cu-MCM-48 > 5Cu-MCM-48 > 10Cu/MCM-48 (synthesized by the incipient impregnation method) > 20Cu-MCM-48. The adsorption isotherms for thiophene fit the Langmuir model well.
1. INTRODUCTION The production of transportation fuels with a low sulfur concentration has been a major concern in the petroleum refining industry due to the increasingly stringent environmental regulations imposed by governments worldwide.1,2 The conventional hydrodesulfurization (HDS) process is a major desulfurization process in refineries worldwide. However, the HDS process is generally operated at high temperatures (>300 °C) and pressures (>4 MPa) with a high energy cost. It is very effective for the removal of thiols and sulfides, but not effective in removing thiophene derivatives, which constitute as much as 80% of the sulfur content in transportation fuels.35 To achieve the “no sulfur” specification, various methods, such as adsorptive desulfurization,610 biodesulfurization,1113 and oxidative desulfurization,14,15 have been explored to remove sulfur compounds from fuels. Among these methods, adsorptive desulfurization is one of the most promising ultradeep desulfurization methods because it can be operated at ambient conditions without using pressurized hydrogen gas. According to the reports of Yang’s group, transition metals (such as Ag+ and Cu+) on exchanged Y zeolite adsorbents exhibited a high sulfur adsorption capacity for thiophenic compounds via π-complexation under ambient conditions.16,17 Molecular orbital calculations showed that Cu+ (as that in CuY zeolite) formed stronger π-complexation bonding with the thiophenic compounds than Ag+ (in AgNO3).18,19 It has been proved that the formation of π-complexes between adsorbate molecules and cuprous ions is an essential step to remove thiophenic sulfur. Therefore, many reports have stated that cuprous species dispersed on various supports such as alumina,20,21 zeolite,8,2225 and carbon26 have been used as π-complexation adsorbents and are active in adsorptive desulfurization. A cheaper adsorption material such as r 2011 American Chemical Society
coal fly ash was reported recently. Ngamcharussrivichai et al.27 reported that they synthesized zeolites using Mae Moh coal fly ash, and their study suggested that the zeolites have potential for use as an adsorbent in the removal of refractory sulfur compounds. However, it was determined that pore diffusion limitation shows strong effects for desulfurization because of the large sizes of the thiophenic molecules.28 Thus, the aim of this work is to develop adsorbents with large pores to minimize diffusion limitation. Since the discovery of mesoporous silicas M41S, a series of mesoporous materials such as MCM-41 and SBA-15 have received much attention. Because of the high surface areas and large pore volumes, mesoporous silicas have been used as adsorbents or adsorbent supports. The incorporation of transition metals, such as Cu, Ag, and Pd, into M41S materials has been reported by many researchers. Wang et al.28 reported that metal halides supported on MCM-41 and SBA-15 mesoporous materials could adsorb sulfur compounds of jet fuel. Tian et al.29 introduced cupric species to SBA-15 by a solid-state grinding precursor and applied it to the adsorption of thiophene from model fuel. Chen et al.30 studied the removal of the thiophenic compounds from JP-5 jet fuel using AgNO3/MCM-41 and AgNO3/SBA-15. Ke et al.31 reported the use of Ce-MCM-41 as an adsorbent to remove thiophenic compounds from model fuels. These reports have shown that metal-containing ordered mesoporous molecular sieves could be more effective for adsorptive desulfurization than their mesoporous supports.2832 MCM-48, a member of the M41S mesoporous silica family,33,34 has attracted considerable attention because of its cubic array Received: March 28, 2011 Revised: June 13, 2011 Published: June 16, 2011 3093
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Energy & Fuels with a three-dimensional pore network, high surface area, narrow pore size distribution, and hydrothermal stability. The unique properties of MCM-48 make it promising for applications in processes including adsorption, ion exchange, catalysis, and so on. The preparation methods of metal-containing M41S materials may have important effects on their adsorption properties. The widely used methods for introducing metal include direct synthesis and post-treatment modification (for example, impregnation). A few works have reported that the incorporation of Cu to MCM-41 or SBA-15 by impregnation shows good desulfurization performance.30 However, to our knowledge, reports on adsorptive desulfurization using Cu-modified mesoporous silica MCM-48 are very scarce, if any. In this work, several Cu-modified MCM-48 adsorbents were prepared by the direct synthesis method. Their characteristics and adsorptive behaviors were compared with those prepared by the conventional incipient impregnation method.
2. EXPERIMENTAL SECTION 2.1. Materials. Thiophene (99%) was purchased from Acros Organics. Cetyltrimethylammonium bromide (CTAB) and tetraethyl orthosilicate (TEOS) were obtained from Aldrich. Cu(NO3)2 3 3H2O and isooctane of analytical reagent grade were provided by Shanghai Chemical. 2.2. Synthesis of MCM-48. Mesoporous silica MCM-48 was synthesized by the hydrothermal pathway.35 The template CTAB was dissolved in an aqueous solution of NaOH under stirring. After slight heating, to dissolve the surfactant, the silica source TEOS was added. The SiO2:Na2O:CTAB:H2O reactant ratio was 1:0.24:0.56:60. The resulting mixture was kept under stirring conditions for about 30 min at room temperature to homogenize the synthesis mixture. Subsequently the mixture was transferred into a Teflon-lined steel autoclave and kept at 110 °C for 72 h. The product was then filtered, washed with distilled water, and dried at 100 °C. The as-synthesized sample was then calcined at 550 °C for 6 h with a heating rate of 1 °C/min.
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Micromeritics ASAP2010 sorption analyzer. The pore size distribution curves were calculated from the desorption branch of the N2 adsorptiondesorption isotherm and the BarrettJoynerHalenda (BJH) formula. The samples were degassed at 150 °C under a vacuum before analysis. Transmission electron micrographs of the calcined samples were recorded by a JEOL JEM-2010 UHR transmission electron microscope with an acceleration voltage of 200 kV. A PerkinElmer Optima 2000 DV inductively coupled plasma atomic emission spectrometer was used to determine the total content of copper incorporated into the mesoporous silica MCM-48. The samples were dissolved with HF. Then the samples were dissolved in HNO3 and subsequently diluted as required. The X-ray photoelectron spectroscopy (XPS) analyses were conducted on a Physical Electronics PHI-550 spectrometer equipped with an Al KR X-ray source (hv = 1486.6 eV) at 10 kV and 35 mA. The typical base pressure was lower than 109 mbar. 2.6. Adsorption Experiments. Adsorptive desulfurization experiments were performed by a batch method under ambient conditions. The model fuel (20 mL), which consisted of thiophene and isooctane with a sulfur content of 11.74 mmol/L (corresponding to the concentration of 544 ppmw S), was mixed with the adsorbent (0.011.50 g) in a shaker apparatus operating for 4 h. The adsorption isotherm was obtained by varying the adsorbent mass in the process of adsorption. The liquid phase was then separated from the adsorbents by filtration, and the sulfur content of the treated model fuels was determined using a DL-2B-EE microcoulometer (Jiangyan Analytic Instruments Co., Ltd., China). The adsorbed amounts (normalized per adsorbent mass) were calculated by the following formula: Qi ¼
V ðC0 Ci Þ M
ð1Þ
where Qi is the amount of sulfur adsorbed on the adsorbent (mmol 3 g1), V is the volume of model fuel (L), M is the mass of the adsorbent used (g), and C0 and Ci are the initial and final sulfur concentrations in the model fuel (mmol 3 L1), respectively.
2.3. Synthesis of Cu-Modified MCM-48 by the Direct Synthesis Method. Cuprammonia solution composed of Cu(NO3)2
3. RESULTS AND DISCUSSION
and 25% aqueous ammonia was used as a copper precursor to load copper into the pores of MCM-48. Cu-modified MCM-48 prepared by the direct synthesis method, denoted as Cu-MCM-48, was synthesized following procedures similar to those of MCM-48, except the required Cu source, cuprammonia solution, which was added after the addition of TEOS. Before adsorption experiments, Cu-MCM-48 was calcined at 500 °C for 6 h in pure helium to promote autoreduction of Cu2+ species to Cu+.3639 The obtained samples were denoted as 5Cu-MCM-48, 10Cu-MCM-48, and 20Cu-MCM-48, where the numerals 5, 10, and 20 represent the mass percentage of copper in the samples.
3.1. XRD Characterization. The small-angle XRD patterns of MCM-48, 10Cu/MCM-48, and Cu-MCM-48 with different Cu contents are given in Figure 1A. MCM-48 has two intense diffraction peaks at 2θ of 2.5° and 3.0° indexed as (211) and (220) reflections, respectively, accompanied by three weak peaks resulting from (420), (332), and (431) reflections. With increasing Cu doping amount, the peak intensity of the (211) reflection was attenuated gradually, implying the degradation of the cubic ordered phase of MCM-48 with the introduction of the copper species. Moreover, the diffraction peaks of Cu-MCM-48 samples prepared by the direct synthesis method gradually shifted to lower 2θ angles with increasing Cu doping in comparison to those of MCM-48. For 5Cu-MCM-48 and 10Cu-MCM-48, the intense diffraction peaks are still observable, indicating the maintenance of the ordered cubic mesoporous structures. However, the ordered mesoporous structures cannot be obtained with a nominal Cu content of 20 wt % in this synthesis. 10Cu/MCM48 obtained by the incipient impregnation method exhibits poor order as shown in Figure 1A. The wide-angle XRD patterns of the samples are illustrated in Figure 1B. The patterns of 5Cu-MCM48 and 10Cu-MCM-48 samples are similar to that of pure siliceous MCM-48, and no crystalline CuO phase is observed, indicating that Cu is highly dispersed in MCM-48. However, in the case of 20Cu-MCM-48 and 10Cu/MCM-48, CuO
2.4. Synthesis of Cu-Modified MCM-48 by the Impregnation Method. For comparison, Cu-modified MCM-48 prepared by the impregnation method, denoted as Cu/MCM-48, was prepared by an incipient impregnation method. Cu/MCM-48 adsorbent was obtained by impregnating MCM-48 with an aqueous solution of copper nitrates. The impregnated adsorbent was air-dried overnight and calcined at 500 °C for 6 h in pure helium to promote autoreduction of Cu2+ species to Cu+. The loading amount of Cu was 10 wt %, and the obtained sample was denoted as 10Cu/MCM-48. 2.5. Characterization of the Samples. X-ray power diffraction (XRD) patterns of the samples were recorded on a Bruker D8 Advance diffractometer with a Cu KR monochromatized radiation source operated at 40 kV and 30 mA with a scan speed of 0.25 deg/s. The N2 adsorptiondesorption isotherms and BrunauerEmmett Teller (BET) specific surface area were measured at 196 °C on a
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Figure 1. (A) Small-angle and (B) wide-angle XRD patterns of the samples.
Table 1. Textural Properties of the Samples Cu mass
surface
total pore
contenta
area SBET
volume VP,BJH
pore size
(%)
(m2 3 g-1)
(cm3 3 g-1)
dP,BJH (Å)
MCM-48
0
795
0.88
25.0
5Cu-MCM-48
4.2
735
0.61
25.7
10Cu-MCM-48
9.1
565
0.53
32.8
10Cu/MCM-48
8.9
506
0.50
30.2
20Cu-MCM-48
16.3
346
0.32
35.5
sample
a
desorption
Acquired by inductively coupled plasma atomic emission spectroscopy.
diffraction peaks at 2θ of 36.2° and 38.8° are observed, indicating that Cu species in the channels are prone to migrate and agglomerate on the outer surface and form CuO, which may block the molecular sieve pores. This result suggests that the direct synthesis method gives a much higher dispersion capacity for Cu particles in the support than the conventional impregnation method. 3.2. Textural Properties of the Samples. Besides XRD, nitrogen physisorption is another method to characterize mesoporous materials, and the results are listed in Table 1. With increasing Cu content, the surface area and pore volume were attenuated gradually. Comparing the preparation methods, direct synthesis leads to samples with higher surface areas, as well as pore volumes and diameters, than the impregnation method. On the other hand, because some pores are plugged, the surface area of 20Cu-MCM-48 decreases drastically. Parts A and B of Figure 2 show N2 adsorptiondesorption isotherms and pore size distributions for MCM-48, 5Cu-MCM-48, 10Cu-MCM-48, and 10Cu/MCM-48. All these N2 adsorption isotherms show type IV adsorption isotherms (IUPAC) with an H1-type hysteresis loop due to capillary condensation, characteristic of mesoporous materials. By comparing the samples derived from direct synthesis and postmodification, it is obvious that 10Cu-MCM-48 possesses a high surface area and larger pore opening than 10Cu/MCM-48. The narrow and sharp pore size distribution curve of MCM-48, as depicted in Figure 2B, indicates uniform mesoporosity. However, the maximum pore size is enhanced as the Cu content increases. The excess Cu in the adsorbent causes the range of pore size distribution to broaden. These results are in good agreement with those observed from the XRD tests. 3.3. Transmission Electron Microscopy (TEM) Characterization. To compare the Cu particle distributions over MCM-48, TEM micrographs of the samples are presented in Figure 3. The ordered cubic structure of pure siliceous MCM-48 was observed
(Figure 3A). For 10Cu-MCM-48, which was prepared by the direct synthesis method, the structure of the mesoporous MCM48 support was not affected by the presence of Cu within the pores, and it still maintained the cubic structure (Figure 3B). The result shows that Cu particles are dispersed well and confined into the channels of MCM-48, and large metallic Cu particles are not observed on the 10Cu-MCM-48 sample. In contrast, for 10Cu/MCM-48, prepared by the impregnation method, Cu species (dark dotlike objects in Figure 3C) in the channels were prone to aggregate and agglomerate on the outer surface of MCM-48 to form bulk CuO. Meanwhile, it should be mentioned that we did observe small particles confined into the channels of MCM-48 in the 10Cu/MCM-48 sample, but the amount is much less than that in the 10Cu-MCM-48 sample. This remarkable difference in particle size and distribution of the two samples indicates that the direct synthesis method is superior to the impregnation method for obtaining highly dispersed Cu particles, in accord with the XRD results shown in Figure 1B. For the 20-Cu-MCM-48 sample, the CuO particles (dark dotlike objects in Figure 3D) were mainly located outside the mesopores and lead to pore clogging, as revealed by the XRD results shown in Figure 1B. 3.4. XPS Spectra. It is known that Cu+ is needed for π-complexation adsorption of aromatic sulfur compounds.39,40 However, Cu(I) is easily oxidized to Cu(II) by air, and Cu2+ cannot form π-complexation with sulfur compounds. Therefore, the adsorbent loses its sulfur selectivity and capacity after oxidization, so it is necessary to measure the valence state of Cu in 10Cu-MCM-48 and 10Cu/MCM-48 samples using XPS analysis. Figure 4 shows the Cu 2p3/2 spectra of the two samples. The Cu 2p3/2 spectrum of 10Cu-MCM-48 shifted to lower binding energy, suggesting that copper species are reduced to a lower valence state, and the peak of 10Cu-MCM-48 became sharper compared with that of 10Cu/MCM-48. The Cu 2p3/2 XPS spectra of the two samples are fitted by the XPS peak software and deconvolved into two peaks: one is for Cu 2p3/2+ at about 932.6 eV, and the other is assigned to Cu 2p3/22+ at about 934.4 eV, as shown in Figure 5 and Table 2. The fitting curve results demonstrate that the fraction of Cu+ in the total amount of copper is 67.4% for 10Cu-MCM-48 and 59.5% for 10Cu/ MCM-48, suggesting the concentration of Cu+ on the surface of 10Cu-MCM-48 is greater than that of 10Cu/MCM-48. This indicates that the direct synthesis method could enhance the concentration of Cu+ on the MCM-48 surface, which is favorable for adsorptive desulfurization. 3.5. Adsorption Equilibrium of Thiophene on the Adsorbents. To compare the adsorption abilities of 5Cu-MCM-48, 3095
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Figure 2. (A, left) N2 adsorptiondesorption isotherms and (B, right) BJH pore diameter distributions of the samples.
Figure 3. TEM images of the (A) MCM-48, (B) 10Cu-MCM-48, (C) 10Cu/MCM-48, and (D) 20Cu-MCM-48 samples.
Figure 4. Cu 2p3/2 XPS patterns of the samples.
10Cu-MCM-48, 20Cu-MCM-48, and 10Cu/MCM-48 for sulfur in the model fuel, the adsorption capacities of four adsorbent samples as a function of the equilibrium sulfur concentration are shown in Figure 6. It is clear that different adsorbents have significantly different sulfur adsorption capacities. 10Cu-MCM48 exhibits the highest adsorption capacity for thiophene, and the removal of thiophene over 10Cu-MCM-48 is more effective than that of 10Cu/MCM-48, which is closely related to the higher Cu+ amount in 10Cu-MCM-48 as shown in the foregoing XPS results. Moreover, the good mesoporous structure and the well-dispersed active species are also responsible for the excellent adsorptive desulfurization performance of 10Cu-MCM-48. The result is in agreement with the earlier observation from the 3096
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Figure 5. Peak fitting of Cu 2p3/2 of (A) 10Cu/MCM-48 and (B) 10Cu-MCM-48.
Table 2. XPS Fitting Data of the Cu 2p3/2 Region on the Surface of the Samples
The equilibrium expression of the Freundlich model is given by the following equation:
Cu 2p3/22+
Qi ¼ KF Ci 1=n
Cu 2p3/2+
sample
Eb (eV)
ri (%)
Eb (eV)
ri (%)
10Cu/MCM-48 10Cu-MCM-48
932.73 932.66
40.5 32.6
934.54 934.92
59.5 67.4
Figure 6. Adsorption isotherms of thiophene adsorbed on the samples (adsorbent mass, 0.011.5 g; model fuel volume, 20 mL; adsorption time, 4 h; adsorption temperature, 20 °C).
characterization of XRD, TEM, and XPS. 5Cu-MCM-48 shows lower adsorption performance than 10Cu-MCM-48; this may be due to the lower Cu doping amount. The worst sulfur adsorption capacity is on 20Cu-MCM-48 because of the blockage of channels by excessive CuO, which has been demonstrated by foregoing XRD and TEM characterization. Therefore, it is reasonable that the order of adsorption capacities for thiophene is 10Cu-MCM-48 > 5Cu-MCM-48 > 10Cu/MCM-48 > 20CuMCM-48. The Langmuir and Freundlich isotherm models were applied to experimental equilibrium data for the sample adsorptive desulfurization of thiophene. The equilibrium expression of the Langmuir model is given by the following equation: Qi ¼
Q 0 K L Ci 1 + K L Ci
ð2Þ
where Qi is the amount of adsorbed sulfur on the adsorbent (mmol 3 g1), Ci is the equilibrium concentration of sulfur in solution (mmol 3 L1), KL is the Langmuir adsorption constant (L 3 mmol1), Q0 is the maximum adsorption capacity (mmol 3 g1), and Q0KL is the relative affinity of the adsorbate toward the surface of the adsorbent.
ð3Þ
In this equation, KF and 1/n are the Freundlich constants characteristic of the system, indicating the adsorption capacity and intensity, respectively. The experimental equilibrium data and calculated values from isotherm models are given in Figure 7. It can be observed from Figure 7 that the adsorption isotherms of thiophene on the adsorbent samples can be described properly by the Langmuir and Freundlich models. The isotherm parameters, with R2 being the correlation coefficient given by the statistic software, are given in Table 3. From Table 3, it can be seen that the correlation coefficient R2 is about 0.99 for the Langmuir model and about 0.96 for the Freundlich model. The higher R2 values of the Langmuir model indicate that the Langmuir model is slightly more suitable for describing the adsorption equilibrium of adsorptive desulfurization of thiophene. The results in Table 3 show that the 10Cu-MCM-48 sample has maximum values of Q0 and KL for the Langmuir model, and this is in good agreement with the experimental results. The constants KF for the Freundlich model are shown in Table 3; it can be seen that the constant KF for thiophene adsorption on 10Cu-MCM-48 is larger than the others, indicating that 10CuMCM-48 has a larger adsorption capacity than the others. It can also be seen that the trend of KF is 10Cu-MCM-48 > 5Cu-MCM48 > 10Cu/MCM-48 > 20Cu-MCM-48, in good agreement with the experimental results. 3.6. Effect of Toluene on Adsorptive Desulfurization. It has been proved that there are large amounts of aromatics in transportation fuels,41 and aromatics such as benzene can strongly compete with thiophenic sulfur compounds by π-complexation adsorption. To clarify the influence of coexisting aromatic hydrocarbons on thiophene adsorption, the adsorption was carried out using the model fuel in the presence of 10 wt % toluene. It can be seen from Figure 8 that the thiophene uptake was 0.41, 0.56, 0.75, and 0.87 mmol 3 g1 on 20Cu-MCM-48, 10Cu/MCM-48, 5CuMCM-48, and 10Cu-MCM-48, respectively, after addition of toluene, which means the sulfur adsorption capacities decreased by 35.5%, 34.9%, 16.2%, and 11.3%, respectively. The results demonstrate that the effect of toluene on the adsorbents decreases in the order 20Cu-MCM-48 > 10Cu/MCM-48 > 5Cu-MCM-48 > 10Cu-MCM-48. Apparently, strong competitive adsorption of toluene takes place during thiophene adsorption with 20Cu-MCM-48 and 10Cu/MCM-48. The 10Cu-MCM-48 sample shows a higher selective adsorption performance for thiophene as 3097
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Figure 7. Langmuir and Freundlich isotherms of thiophene adsorbed on the samples (adsorbent mass, 0.011.5 g; model fuel volume, 20 mL; adsorption time, 4 h; adsorption temperature, 20 °C).
Table 3. Langmuir and Freundlich Isotherm Parameters for Various Samples Langmuir isotherm
Freundlich isotherm
sample
KL(L 3 mmol-1)
Q0 (mmol 3 g-1)
KLQ0
R2
KF
1/n
R2
20Cu-MCM-48
0.3329
0.9933
0.3307
0.9984
0.2822
0.4490
0.9769
10Cu/MCM-48 5Cu-MCM-48
0.4426 0.4106
1.4697 1.6905
0.6505 0.6941
0.9986 0.9928
0.5147 0.5547
0.3826 0.4061
0.9628 0.9696
10Cu-MCM-48
0.5376
1.9654
1.0566
0.9988
0.7530
0.3614
0.9547
’ AUTHOR INFORMATION Corresponding Author
*Phone: +86-25-83587178. Fax: +86-25-83587191. E-mail: liuxq@ njut.edu.cn.
Figure 8. Amount of thiophene adsorbed by the adsorbents in the thiophene/toluene system (adsorbent mass, 0.2 g; model fuel volume, 20 mL; adsorption time, 4 h; adsorption temperature, 20 °C).
compared with 10Cu/MCM-48, which indicates a better performance of the direct-synthesized sample.
4. CONCLUSIONS A series of Cu-functionalized mesoporous silicas MCM-48 with Cu content ranging from 5 to 20 wt % were synthesized by the direct synthesis method. In comparison with the impregnated sample, the direct-synthesized sample possesses a better mesoporous structure. Cu species can be well dispersed on 10CuMCM-48, while the crystalline phase of CuO is obvious on 10Cu/MCM-48. The 10Cu-MCM-48 sample has a surface area of 565 m2 3 g1, which is higher than that of the impregnated sample with the same Cu content (506 m2 3 g1). It is noticeable that the amount of active species Cu+ on the 10Cu-MCM-48 surface is higher than that on 10Cu/MCM-48. These factors are believed to be responsible for the good thiophene adsorption capacity of 10Cu-MCM-48 in the model fuel. The Cu-containing mesoporous silicas derived from direct synthesis may have potential applications in the adsorptive removal of thiophenic sulfur compounds in transportation fuels.
’ ACKNOWLEDGMENT We are deeply grateful for the financial support of the National Science Foundation of China (Grants 20976082 and 21006048), the Major Basic Research Project of the Natural Science Foundation of Jiangsu Province Colleges (Grant 08KJA530001), the Specialized Research Fund for the Doctoral Program of Higher Education of China (Grant 20093221120001), the Natural Science Foundation of Jiangsu Province Colleges (Grant 09KJB530004), and the Natural Science Foundation of Nantong University (Grant 09Z009). ’ REFERENCES (1) Zhou, D. H.; Wang, Y. Q.; He, N.; Yang, G. Acta Phys.-Chim. Sin. 2006, 22 (5), 542–547. (2) Velu, S.; Ma, X.; Song, C. Ind. Eng. Chem. Res. 2003, 42 (21), 5293–5304. (3) Dhar, G. M.; Srinivas, B. N.; Rana, M. S.; Maity, S. K. Catal. Today 2003, 86 (14), 45–60. (4) Hernandez-Maldonado, A. J.; Yang, R. T. AIChE J. 2004, 50 (4), 791–801. (5) Hernandez-Maldonado, A. J.; Yang, H. F.; Qi, G.; Yang, R. T. J. Chin. Inst. Chem. Eng. 2006, 37 (1), 9–16. (6) Sentorun-Shalaby, C.; Saha, S. K.; Ma, X. L.; Song, C. S. Appl. Catal., B 2011, 101 (34), 718–726. (7) Tang, K.; Hong, X.; Zhao, Y. H.; Wang, Y. G. Pet. Sci. Technol. 2011, 29 (8), 779–789. (8) Yang, R. T.; Hernandez-Maldonado, A. J.; Yang, F. H. Science 2003, 301, 79–81. (9) Xue, M.; Chitrakar, R.; Sakane, K.; Hirotsu, T.; Ooi, K.; Yoshimura, Y.; Feng, Q.; Sumida, N. J. Colloid Interface Sci. 2005, 285 (2), 487–492. 3098
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dx.doi.org/10.1021/ef200472j |Energy Fuels 2011, 25, 3093–3099
