Article pubs.acs.org/EF
Removal of Dibenzothiophene with Composite Adsorbent MOF-5/ Cu(I) Wei Dai,*,† Jue Hu,† Limei Zhou,† Shuang Li,‡ Xin Hu,† and He Huang*,‡ †
College of Chemistry and Life Sciences, Zhejiang Normal University, Zhejiang Jinhua 321004, People’s Republic of China College of Biotechnology and Pharmaceutical Engineering, Nanjing University of Technology, Nanjing 210009, People’s Republic of China
‡
ABSTRACT: A new type of composite adsorbent, MOF-5/Cu(I), was prepared by MOF-5 doped with different amount of CuCl using a spontaneous monolayer dispersion technique. These new composite adsorbents were characterized by X-ray diffraction, thermogravimetric analysis, electrondispersion X-ray scope, and N2 adsorption, respectively. The desulfurizaion performance of the prepared adsorbents was evaluated by the selective adsorption of dibenzothiophene from the simulated oils in a fixed-bed breakthrough column at room temperature. From the obtained breakthrough curves, both the breakthrough capacity and the saturation capacity of the adsorbents for sulfur element were determined. The results show that MOF-5/Cu(I) exhibited high desulfurization capacities, which are superior to those reported previously in the literature. In addition, these novel composite adsorbents possessed good durability and affinities for the adsorption of dibenzothiophene in the presence of aromatic components and moisture. The saturated composite adsorbent MOF-5/Cu(I) can be regenerated with nitrogen atmosphere sweeping at 623 K for 4 h. About 97% of the desulfurization capacity was recovered after regeneration. materials have been investigated during the past decade.5−8 However, most commercial fuels are composed of about 20−30 wt % aromatic components and 70−80 wt % aliphatic components. The aromatic components and thiophenic sulfur compounds have similar affinity toward the adsorbent; therefore, there is a competitive adsorption between them, which may lead to invalidation of the adsorptive purification method. The number of materials exhibiting permanent nanoporosity has rapidly expanded in recent years, due in large part to the discovery of metal−organic frameworks (MOFs) and coordination polymers, etc.9,10 MOFs are more versatile for application-oriented tailoring than activated carbons and zeolites. The major applications currently being considered for these compounds focus on gas storage, catalysis, and separations, as carriers for nanomaterials and drug delivery.11−13 For these applications, their high surface areas and unique pore structures are likely to offer many potential advantages over existing compounds. Recently, MOFs have been used to remove thiophenic compounds from model fuels, which represent a type of alternative adsorbents that can be potentially used in the cost-effective production of low-sulfur fuels by selective adsorption.13−15 However, the study about the thiophenic compounds adsorption by MOFs is still scarce.16,17 Especially, no attempts have been made to remove the thiophenic sulfur compounds by using π-complexation MOFs adsorbents. Among all kinds of MOFs, a typical and common representative is MOF-5, originally synthesized in 1999,18 which consists of Zn4O6+-clusters as metal centers and benzene-1,4-dicarboxylate as linkers forming a cubic network.
1. INTRODUCTION Sulfur-containing compounds are widely known contaminants in petroleum and in fuels. Removal of these compounds before commercial use is extremely important because of environmental protection and catalyst poisoning issues.1,2 Therefore, deep desulfurization of transportation fuels becomes an urgent task presently, and many efforts have been dedicated to it. Today, the most commonly used process for the removal of organic sulfur compounds from crude oil is the hydrodesulfurization (HDS) reaction, which involves catalytic conversion of various sulfur compounds to hydrogen sulfide in the presence of hydrogen. However, hydrodesulfurization technology is relatively ineffective for deep desulfurization to ppm levels, because the double bonds of olefins and aromatic hydrocarbons contained in fuels are more reactive than those of thiophenic sulfur compounds such as a typical representative of dibenzothiophene (DBT) in the hydrogenation reaction. In the HDS process, the thorough removal of thiophenic sulfur compounds will result in the decrease in fuel quality and the increase in cost.3,4 Hence, removing thiophenic sulfur compounds from fuels becomes the key to the deep desulfurization project. The selective adsorption of sulfurcontaining compounds seems particularly promising in deep desulfurization. This approach is an attractive research field owing to advantages of being less energy intensive, easy to regenerate, having fast adsorption/desorption kinetics, and having low cost of solid adsorbent. In particular, adsorption of thiophenic sulfur compounds using the adsorbent with the function of π-complexation has attracted more attention because it has moderate operation conditions and avoids the use of hydrogen. Such adsorbents contain some metal ions such as Ag+ or Cu+, which are dispersed on the surface of the substrate.5 Various types of adsorbents such as zeolites, activated carbons, metal oxides, and other mesoporous © 2013 American Chemical Society
Received: December 13, 2012 Revised: January 25, 2013 Published: January 25, 2013 816
dx.doi.org/10.1021/ef3020662 | Energy Fuels 2013, 27, 816−821
Energy & Fuels
Article
mmol Cu(I) in 1 g of substrate. For instance, MOF-5/3Cu(I) means doping 3 mmol of Cu(I) into 1g of MOF-5. 2.2. Desulfurization of Sorbents. Three simulated oils were prepared using benzene (99.8%, Sigma-Aldrich) as the representative of aromatic oil (ARO) and n-octane (99.8%, Sigma-Aldrich) as the representative of aliphaticoil (ALO), and the mixture of 80 wt % noctane and 20 wt % benzene was used to represent the mixed oil (MIO). DBT (>99%, Sigma-Aldrich) was used as the representative of sulfur contaminants. The content of sulfur element in the simulated oils for ARO, ALO, and MIO are 760 ppm, 760 ppm, and 190 ppm, respectively. The desulfurization performance of adsorbents was tested on the basis of breakthrough curves. Experiments to collect the breakthrough curves were performed in a vertical quartz column of length 300 mm and inner diameter of 10 mm with a glass grid for supporting the adsorbent. The sorbents were loaded into the adsorption column inside a glovebox to avoid contact with air. The testing oil was pumped up with a mini creep pump (BT01-YZ1515). Prior to each adsorption measurement, the adsorbent was activated by being heating to 473 K and maintained for 2 h in nitrogen stream. After cooling to room temperature (298 K) in a nitrogen stream, the sorbent was consolidated by light tapping. The adsorption experiments were carried out at 298 K and atmospheric pressure. First, the fixed bed was flushed downward with sulfur-free n-octane or benzene at a flow rate of 1 cm3/min for 30 min, and then the feed was switched to the simulated oils containing different contents of thiophene with unchanged flow rate. Samples were taken regularly to examine the sulfur content in the simulated oils until saturation was reached. The total sulfur content in the simulated oils was determined with a gas chromatograph (GC-7890) equipped with a flame photometric detector and an EC-5 capillary column (length = 40 m; i.d. = 0.32 m). Sulfur concentrations were determined from the calibrated sulfur standard curves. Breakthrough curves were obtained by plotting the transient sulfur concentration versus the cumulative fuel volume. The concentration was normalized with the total sulfur content in the feed, and the cumulative fuel volume was normalized with the volume of the adsorbent bed. The normalized sulfur adsorption capacity of an adsorbent was calculated with the following eq 1 and 2:
Due to its good thermal stability and its well-defined structures, it therefore may be favorable for the selective capture of thiophenic sulfur compounds. The question is how to prepare the MOF-5 composite adsorbents containing metal ions? As a conventional πcomplexation adsorbents preparation method, the impregnation technique has been extensively used to introduce d-block metals ions such as Ag+, Cu+, Ni2+, and Zn2+ into zeolites, activated carbon, and porous silica materials.5−7 However, there are two intrinsic disadvantages for the impregnation method: (1) the lack of uniform distribution of active species because of the forced condensation of metal precursors on the support surface during the drying process and (2) limited activity because of the restrained amount of active metals deposited on support surface. Xie and his co-workers19 have develped a new doping technique (i.e., spontaneous monolayer dispersion technique), which suggests that a great many salts can disperse spontaneously onto the surfaces of supports to form a thermodynamically stable monolayer or submonolayer. The utmost dispersion capacity is called dispersion threshold. Only when the amount of salt exceeds its threshold on a support, the surplus oxide or salt can exist as a separate crystalline state or amorphous phase. In this case, organic thiophenic sulfur molecules may interact with the active metal sites and thus were effectively captured. Therefore, the new π-complexation MOFs materials containing metal ion seem to be promising in deep desulfurization. The main objective of the present work is dedicated to the adsorptive desulfurization of dibenzothiophene from model fuel by π-complexation adsorbent MOF-5/Cu(I). To achieve the goal, MOF-5/Cu(I) was prepared by modification of MOF-5 with different amount of CuCl using the above-mentioned spontaneous monolayer dispersion technique. Commercial oil products contain different portions of aromatic components; therefore, three simulated oils with different amounts of aromatic components were prepared in this study, that is, 100 wt % aromatic component (ARO), 20 wt % aromatic component (MIO), and 100 wt % aliphatic component (ALO). The desulfurization behavior of the novel MOF-5/Cu(I) composite adsorbents was investigated and compared.
qb =
⎛ vρxi ⎞ ⎜ ⎟t 100 ⎝ m ⎠b
qs =
⎛ vρxi ⎞ ⎜ ⎟ ⎝ m ⎠
∫0
ts
(1)
[1 −
ct ] dt × 100 ci
(2)
where qb is the breakthrough capacity per unit mass of adsorbent, %; qs is the saturation capacity of unit mass of adsorbent, %; v is the flow rate of oil, cm3/min; ρ is the fuel density, g/cm3; ci is the initial sulfur content, ppm; ct is the sulfur content of the oil passing through the bed at time t, ppm; m is the mass of adsorbent in the column, g; xi is the content of sulfur element in the simulated oils, %; tb is the breakthrough time, min; ts is the saturation time when ct/ci = 1, min.
2. EXPERIMENTAL SECTION 2.1. Preparation of MOF-5/Cu(I). The MOF-5 support was prepared by the method following the detailed description given in the literature.20 In a typical reaction, terephthalic acid (5.10 g, 30 mmol) and Zn(NO3)2·6H2O (12.16 g, 40 mmol) were dissolved in DMF (400 mL). Freshly distilled triethylamine (16.0 g, 160 mmol) was added dropwise into the above solution under strong stirring at room temperature. The mixture was stirred for 3 h at room temperature. The precipitate was isolated by filtration, washed with DMF (2 × 40 mL) followed by dry ether (2 × 40 mL), and dried under vacuum. Then, the MOF-5 was obtained as white powder. The MOF-5 was heated at 423 K under vacuum overnight in order to remove present solvents, moisture, and other volatile components. Then, the MOF-5 was cooled to room temperature for surface modification. According to a previous study on the method of loading CuCl,19,21 a defined quantity of CuCl (99+%, Sigma-Aldrich) was mixed with the MOF-5 powder and the mixture was placed inside a quartz reactor. The temperature was raised slowly to 673 K in a nitrogen atmosphere and maintained at the temperature for 2 h. Then, the reactor was cooled in the nitrogen atmosphere to room temperature, and the MOF-5/Cu(I) composite adsorbent was obtained. Special care was taken to avoid exposure of the materials to air. The resulting sorbents are referred to as MOF-5/nCu(I), where n corresponds to the loading number of
3. RESULTS AND DISCUSSION 3.1. Properties of MOF-5/Cu(I). Specific surface areas and pore volumes were determined by N2 adsorption at 77 K using a Micromeritics ASAP2020 gas adsorption analyzer. The specific surface areas were calculated using the Brunauer− Emmett−Teller (BET) equation by assuming the section area of nitrogen molecule to be 0.162 nm2.22 The total pore volumes were determined as the volume of liquid nitrogen adsorbed at a relative pressure of 0.99.23 The pore size distributions were determined using the density funtional theory (DFT) method for slit-shaped pores.24 The nitrogen adsorption isotherms and the pore size distribution curves of MOF-5, MOF-5/2Cu(I), MOF-5/3Cu(I), and MOF-5/4Cu(I) at 77 K are shown in Figures 1 and 2, respectively. Clearly, all these samples show type I adsorption isotherms according to the IUPAC classification.24 The BET surface area and the total pore 817
dx.doi.org/10.1021/ef3020662 | Energy Fuels 2013, 27, 816−821
Energy & Fuels
Article
Figure 3. XRD analysis for MOF-5 samples before and after loading Cu(I).
Figure 1. Adsorption isotherms of N2 at 77 K on samples of MOF-5 before and after loading Cu(I).
Thermal gravimetric analysis (TGA) was measured from a Netzsch STA 449 C thermal graphic analyzer from 25 to 600 °C with a heating rate of 10 K/min in N2, Figure 4 shows the
Figure 2. Pore size distribution of MOF-5 samples before and after loading Cu(I).
volume of MOF-5 are 1876 m2/g and 0.51 cm3/g, respectively. After loading different levels of Cu(I), the BET surface area and total pore volume of composite sorbents decreased compared with MOF-5 with 1557 m2/g and 0.41 cm3/g in MOF-5/ 2Cu(I), 1243 m2/g and 0.33 cm3/g in MOF-5/3Cu(I), and 929 m2/g and 0.26 cm3/g in MOF-5/4Cu(I), respectively. The pore size distributions calculated by density functional theory (DFT) prove that the pore size of MOF-5 and MOF-5/Cu(I) ranges from 1 to 2 nm. X-ray diffraction (XRD) data were recorded from a Bruker D8 Advance X-ray Diffractometer with Cu Kα radiation (λ = 1.542 Å). Scanning electron microscopy images were obtained from a scanning electron microscope (Philips PW 3040/60) operated at 20 kV. Prior to the observation, the sample was sputter-coated with a gold layer to increase their conductivity. Figure 3 shows the XRD patterns of MOF-5 before and after loading different contents of Cu(I). The XRD pattern of MOF5 matches that reported in the literature.25,26 After CuCl was loaded onto MOF-5, the strong diffraction peaks of CuCl appeared at the higher angle of 29°, 32°, and 48°, respectively, compared with the pure MOF-5. Simultaneously, it can be observed that some peaks shift to the higher angle when Cu(I) is doped into the MOF-5.
Figure 4. TGA of MOF-5 under nitrogen atmosphere.
weight loss of MOF-5 with increasing the furnace temperature. A weight loss of about 19.2% was observed between 50 and 200 °C, which could be attributed to the removal of moisture and solvent molecules. From 200 to 400 °C, no obvious mass loss can be found, which demostrated the superior thermodynamic stability of MOF-5 up to 400 °C. Further increasing the temperature to 500 °C lead to the weight loss of 40% and then no mass loss can be found when temperature was further increased to 600 °C. Since the MOF-5 is stable up to 400 °C, which is higher than the softening point of CuCl, spontaneous monolayer dispersion technique can be used in loading Cu(I) into the MOF-5 substrate to form the MOF-5/Cu(I) composite sorbents. MOF-5 and MOF-5/3Cu(I) were tested by electron dispersion X-ray scope (EDS). As shown in Table 1, the copper element composition of MOF-5/3Cu(I) is 18.2 wt %. 3.2. Desulfurization Capacity of MOF-5/Cu(I) Adsorbents. Dibenzothiophene breakthrough curves of MOF-5 and MOF-5 with various Cu(I) loading levels were recorded and shown in Figure 5 for ALO, Figure 6 for ARO, and Figure 7 for MIO. For all three simulated oils, MOF-5/Cu(I) sorbents 818
dx.doi.org/10.1021/ef3020662 | Energy Fuels 2013, 27, 816−821
Energy & Fuels
Article
Table 1. Element Composition of MOF-5 Samples Before and After Loading Cu(I) Resulting from EDS Analysis elemental analysis, wt % sample
Cu
Cl
Zn
C
H
O
total
MOF-5 MOF-5/3Cu(I)
0 18.2
0 2.7
33.6 26.1
37.1 29.5
1.8 1.1
27.5 22.4
100 100
Figure 7. Breakthrough curves of dibenzothiophene in the mixed oil over MOF-5 and MOF-5/Cu(I) at room temperature.
capacity of MOF-5/3Cu(I) than MOF-5/2Cu(I). While if more Cu(I) were introduced into the support, it may block the pore and leads to the increase of the diffusion resistance during the mass transfer reactions, which actually can decrease the amount of accessible active Cu(I) sites to form the πcomplexation with DBT, and thus, the sorbent with higher Cu(I) loading (MOF-5/4Cu(I)) shows a smaller sulfur uptake capacity than that with lower Cu(I) loading (MOF-5/3Cu(I)). Therefore, among all the samples, MOF-5/3Cu(I) shows the highest desulfurization capacity. Another thing that should be noted is that MOF-5/Cu(I) sorbents have better desulfurization performance for ALO than for ARO. For example, the maximal breakthrough capacity and saturation capacity of the MOF-5/3Cu(I) are 9.42 and 10.94 wt % for ALO, while the corresponding values reduce to 3.96 and 4.84 wt % for ARO with respect to the sulfur element. Although the capacity decreased, the adsorbent still shows better desulfurization performance than those previously reported.5,21 The breakthrough capacities of the adsorbents in this work are summarized in Table 2, together with those of a number of sorbents reported previously.5,21 Breakthrough capacities for some of the MOF-5/Cu(I) sorbents were comparable or superior to those of activated carbons, zeolites, and SBA-15 reported previously.6−8,21 On the other hand, the MOF-5/Cu(I) composite adsorbents show much stronger durability in desulfurization with the presence of the dissolved water. In order to test the effect of moisture in the oil on the desulfurization capacity of the sorbents, water-saturated simulated oil was prepared as follows: Simulated MIO oil containing 80 wt % n-octane, 20 wt % benzene, and DBT (190 ppm sulfur element) was mixed and thoroughly agitated with distilled water and the mixture sat until distinct oil and water phases appear, the water-saturated simulated oil can be obtained after getting rid of the water phase. The DBT breakthrough curves were then collected using dry and water-saturated simulated oil (MIO), respectively, and the results are shown in Figure 8. The breakthrough and saturation capacity of the MOF-5/3Cu(I) adsorbent for the sulfur element are 6.16 and 6.82 wt % in the dry oil, but the corresponding values reduced to 5.63 and 6.01 wt % in the water-saturated oil. Although the capacity decreased 8.61% and 11.88%, respectively, for breakthrough and saturation capacity with the presence of water in the oil, these performances are
Figure 5. Breakthrough curves of dibenzothiophene in the aliphatic oil over MOF-5 and MOF-5/Cu(I) at room temperature.
Figure 6. Breakthrough curves of dibenzothiophene in the aromatic oil over MOF-5 and MOF-5/Cu(I) at room temperature.
adsorbed more DBT than MOF-5 due to the π-complexation reaction, but the uptake amounts are not proportional to the loading amount of Cu(I). This nonlinear response could be a consequence of variations in the structure and composition of domains on the MOF-5/Cu(I) surface or inaccessibility to the active Cu sites for some domains. Shapes of the curves can provide qualitative information about the strength of adsorption. For example, the steeper slopes for the MOF-5/ Cu(I) sorbents suggested their stronger interactions with DBT than MOF-5 does. It was found that after loading 2 mmol/g Cu(I), the sulfur uptake capacity of MOF-5/2Cu(I) was significantly increased in comparison with the MOF-5, which is due to π-complexation between DBT and Cu (I). Further increasing the Cu (I) doping level increases the amount of the active Cu (I) sites, which results in the better desulfurization 819
dx.doi.org/10.1021/ef3020662 | Energy Fuels 2013, 27, 816−821
Energy & Fuels
Article
Table 2. Sulfur Capacity of Different Composite Adsorbents at Ambient Temperature and Pressurea ALO
a
ARO
MIO
adsorbent
BC, wt %
SC, wt %
BC, wt %
SC, wt %
BC, wt %
SC, wt %
MOF-5 MOF-5/2Cu(I) MOF-5/4Cu(I) MOF-5/3Cu(I) zeolite-Y/Cu(I) A.C./Cu(I) SBA-15/Cu(I)
2.11 5.89 8.45 9.42 5.50 2.65 6.48
5.05 8.59 9.99 10.94 7.54 6.15 8.52
1.58 3.34 3.61 3.96 0.61 1.12 1.14
2.80 4.17 4.49 4.84 1.73 3.91 3.92
1.94 4.57 5.63 6.16 0.70 1.61 0.95
3.79 5.22 6.16 6.82 1.41 2.06 2.11
ref this this this this 5 21 21
work work work work
BC: breakthrough capacity, wt %. SC: saturation capacity, wt %.
recovered its original pink color. The DBT breakthrough curves of regenerated MOF-5/3Cu(I) were then collected again with the three types of simulated oil, and the results are shown in Figure 9. The sulfur uptake capacities of the regenerated
Figure 8. Breakthrough curves of DBT in the MIO feed over the MOF-5/3Cu(I) adsorbent at room temperature. (1) water-saturated; (2) without water; (3) MOF-5/3Cu(I) packed together with FCCs.
still much better than the sorbents reported previously.6,7 To avoid the loss of desulfurization capacity caused by water, a layer of high surface area carbons made from Finger Citron residue27(FCCs) was put on the top of MOF-5/3Cu(I), then dibenzothiophene breakthrough curve were tested using the water-saturated oil. By this way, the dissolved water in the oil could be adsorbed by the layer of activated carbon before the oil contacts with the MOF-5/3Cu(I). Excluding the amount of DBT adsorbed by activated carbon, the breakthrough and saturation adsorption capacity of MOF-5/3Cu(I) were calculated to be 6.01 and 6.81 wt %, respectively, which is quite close to the adsorption capacities of the adsorbent in the dry oil. Therefore, the effect of dissolved water on the adsorption capacity of the MOF-5/Cu(I) adsorbent can be easily eliminated by adding an extra layer of activated carbon sorbents. 3.3. Regeneration Tests of the Composite Adsorbent MOF-5/Cu(I). The adsorbed DBT could not be removed from the MOF-5/Cu(I) materials by purging with sulfur-free noctane. However, DBT can elute from MOF-5 during a similar purge. Preliminary experiments also indicated that regeneration of the MOF-5/Cu(I) sorbents required high temperature treatment. These results are consistent with strong interactions between DBT and adsorption sites on the MOF-5/Cu(I) sorbents but relatively weak interactions between DBT and MOF-5. The π-complexation adsorption mechanism has been proposed for the adsorption of organosulfur compounds.5,6 The color of MOF-5/3Cu(I) is black when it is saturated with DBT. After the nitrogen sweeping at 623 K for 4 h. MOF-5/3Cu(I)
Figure 9. Breakthrough curves of DBT over the regenerated composite adsorbent MOF-5/3Cu(I). 1, 2 and 3: initial breakthrough curves in ARO, MIO and ALO, respectively. 1′, 2′, and 3′: the breakthrough curves in ARO, ALO, and MIO after regeneration, respectively.
adsorbent in these oils are 3.78%, 5.90%, and 10.2% for breakthrough capacity and 4.69%, 6.63%, and 10.71% for saturation capacity, which are almost 97% of the initial values. Actually, we have run six cycles to test the regeneration performance of MOF-5/3Cu(I). Results show that about 97% of the sulfur capacity can be recovered after six cycles of reaction indicating its good recyclability and stability.
4. CONCLUSION The π-complexation adsorbents MOF-5/Cu(I) prepared using spontaneous monolayer dispersion technique were more effective in the preferential adsorption of DBT from ALO, ARO, and MIO model oils than MOF-5. The desulfurization capacities of MOF-5/Cu(I) composite sorbents are comparable to or superior to those reported previously in the literature. Stronger durability in the presence of aromatic components and moisture was also observed, and the effect of dissolved water on the adsorption capacity of the adsorbent can be easily eliminated using a layered column of activated carbon at the top of MOF-5/Cu(I) sorbents. Besides the high desulfurization capacity, MOF-5/Cu(I) sorbents can be easily regenerated by nitrogen sweeping and about 97% of the sulfur uptake capacity 820
dx.doi.org/10.1021/ef3020662 | Energy Fuels 2013, 27, 816−821
Energy & Fuels
Article
(25) Muller, M.; Hermes, S.; Kahler, K.; van den Berg, M. W. E.; Muhler, M.; Fischer, R. A. Chem. Mater. 2008, 20, 4576−4587. (26) Nishihara, Y.; Takemura, M.; Mori, A.; Osakada, Kohtaro. J. Organomet. Chem. 2001, 620, 282−286. (27) Dai, W.; Liu, Y.; Su, W.; Hu, G.; Deng, G.; Hu, X. Adsorpt. Sci. Technol. 2012, 30, 183−191.
was recovered after regeneration. With further development including the optimization of strategies of sorbent regeneration, these adsorbents could be used in the adsorption of organosulfur compounds from oil products such as gasoline or diesel.
■
AUTHOR INFORMATION
Corresponding Authors
*Fax: +86-579-82282531. Tel:+86-579-82282269. E-mail:
[email protected]. *Fax: +86-25-83172094. Tel: +86-25-83172101. E-mail:
[email protected]. Notes
The authors declare no competing financial interest.
■
ACKNOWLEDGMENTS This work was supported by the National Basic Research Program of China (973 Program) (2009CB724700) and the Natural Science Foundation of China (21106136).
■
REFERENCES
(1) Avidan, A.; Klein, B.; Ragsdale, R. Hydrocarbon Process. 2001, 80, 47−53. (2) Knudsen, K. G.; Cooper, B. H.; Topsoe, H. Appl. Catal. A 1999, 189, 205−215. (3) Song, C. Catal. Today 2003, 86, 211−263. (4) Ali, S. H.; Hamad, D. M.; Albusairi, B. H.; Fahim, M. A. Energy Fuels 2009, 23, 5986−5994. (5) Yang, R. T.; Hernandez-Maldonado, A. J.; Yang, F. H. Science 2003, 301, 79−81. (6) Yang, R. T.; Hernandez-Maldonado, A. J. Ind. Eng. Chem. Res. 2003, 42, 123−129. (7) Takahashi, A.; Yang, F. H.; Yang, R. T. Ind. Eng. Chem. Res. 2002, 41, 2487−2496. (8) Liu, F.; Xue, S.; Cao, L.; Chi, Y.; Zhang, T.; Xue, D. J. Phys. Chem. C 2007, 111, 7396−7402. (9) Rowsell, L.C. J.; Yaghi, O. M. Microporous Mesoporous Mater. 2004, 73, 3−14. (10) Ma, S.; Zhou, H. Chem. Commun. 2010, 46, 44−53. (11) Millward, A. R.; Yaghi, O. M. J. Am. Chem. Soc. 2005, 127, 17998−17999. (12) Cychosz, K. A.; Wong-Foy, A. G.; Matzger, A. J. J. Am .Chem. Soc. 2008, 130, 6938−6939. (13) Blanco-Brieva, G.; Campos-Martin, J. M.; Al-zahrani, S. M.; Fierro, J. L. G. Global Nest J. 2010, 12, 296−304. (14) Liu, B.; Zhu, Y.; Liu, S.; Mao, J. J. Chem. Eng. Data 2012, 57, 1326−1330. (15) Khan, N. A.; Jun, J. W.; Jeong, J. H.; Jhung, S. H. Chem. Commun. 2011, 47, 1306−1308. (16) Khan, N. A.; Jhung, S. H. Angew. Chem., Int. Ed. 2012, 51, 1198−1201. (17) Peralta, D.; Chaplais, G.; Simon-Masseron, A.; Barthelet, K.; Pirngruber, G. D. Energy Fuels 2012, 26, 4953−4960. (18) Li, H.; Eddaoudi, M.; O’Keeffe, M.; Yaghi, O. M. Nature 1999, 402, 276−279. (19) Xie, Y.; Tang, Y. Adv. Catal. 1990, 37, 1−43. (20) Dai, W.; Zhuang, H.; Lu, X.; Han, M.; Zheng, Y. J. Fuel Chem. Technol. 2010, 38, 626−630. (21) Dai, W.; Zhou, Y.; Li, S.; Li, W.; Su, Wei.; Sun, Yan.; Zhou, Li. Ind. Eng. Chem. Res. 2006, 45, 7892−7896. (22) Barrett, E. P.; Joyner, L. G.; Halenda, P. P. J. Am. Chem. Soc. 1951, 73, 373−385. (23) Gregg, S. J.; Sing, K. S. W. Adsorption, Surface Area, and Porosity; Academic Press: London, 1982. (24) Daguerre, E.; Guillot, A.; Py, X. Carbon 2000, 38, 59−64. 821
dx.doi.org/10.1021/ef3020662 | Energy Fuels 2013, 27, 816−821
