Article pubs.acs.org/IECR
Facile Synthesis and Catalytic Performance of Fe-Containing SilicaPillared Clay Derivatives with Ordered Interlayer Mesoporous Structure Shengjun Yang,† Guozheng Liang,*,† Aijuan Gu,*,† and Huihui Mao‡ †
Jiangsu Key Laboratory of Advanced Functional Polymer Design and Application, Department of Materials Science and Engineering, College of Chemistry, Chemical Engineering and Materials Science, Soochow University, Suzhou 215123, China ‡ State Key Laboratory of Chemical Resource Engineering, Beijing University of Chemical Technology, Beijing 100029, China ABSTRACT: A facile method was developed to synthesize a series of Fe-incorporated silica-pillared clays (denoted as Fe-SPCs) with various contents of Fe2O3. The synthesis was conducted under alkaline conditions using ethanol as the solvent containing the Fe source and dodecyl dimethyl benzyl ammonium chloride as the structure-directing agent. Characterization results showed that the Fe2O3 content of the Fe-SPCs was as large as 27.03 wt % and that all of the Fe-SPCs had a layered structure similar to that of the original SPC except that some silicone atoms in the tetrahedral coordination of the interlayered silica framework were replaced by Fe atoms. The Fe-SPCs showed excellent catalytic performance and reusability in the oxidative desulfurizations of both coking benzene and dibenzothiophene. A catalytical mechanism is proposed.
1. INTRODUCTION Increasing environmental concerns and legal requirements make deep desulfurization an important research subject in the field of green fuels.1−3 Oxidative desulfurization (ODS), a very promising process, is currently receiving growing attention because of its high desulfurization efficiency under mild conditions.4−6 The ODS process consists of two main steps, namely, the oxidation of sulfur compounds and subsequent purification; hence, the oxidant and its catalyst are the most important parameters determining the efficiency of the ODS process. Hydrogen peroxide (H2O2) is one of the most often used oxidant,7 and it has various catalysts. For use in the ODS process, heterogeneous catalysts consisting of transition metals (such as Mo, Co, V, Ti) on silicates, zeolites, molecular sieves, or mesoporous materials show high sulfur removal and reusability.8−11 Among the large variety of transition metals, Fe is special because of its innocuousness and low cost, and thus, Fe-containing porous silicates have been prepared and used as catalysts for the oxidation of benzene, alkane, and phenol.12−14 However, Fe-containing porous silicate has seldom been reported for use in the ODS process. Recently, a catalyst called Fe-MCM-41 was reported to be considerably active in the ODS process.15 Unfortunately, the synthesis of Fe-MCM-41 is complex (requiring a great deal of tetraethoxysilane and taking a long time); more importantly, the hexagonal structure of MCM-41 tends to be destroyed completely by steam at high temperature, but high temperature is necessary in petrochemical processes. Therefore, it is of great interest to develop new Fe-containing catalysts for ODS using a facile method. Pillared clay (PILC) is one of the most widely studied microporous materials.16 It is prepared by the intercalation of inorganic polyoxocation clusters that are thermally transformed into oxides grafted on to the clay layers, forming interlamellar galleries accessible to molecules.17 The introduction of © 2012 American Chemical Society
inorganic pillars into natural clay not only improves its resistance and stability and increases its microporosity, but also provides a larger surface area and greater accessibility to its acid sites (Brönsted and Lewis sites).18 Therefore, PILC shows great potential in many applications including catalysis, adsorption, and separation. To date, the most often used PILC has been silica-pillared clay (SPC) owing to its hydrophobicity and outstanding thermal stability.19 Recently, several metal-ion-doped SPCs, such as Ti-SPC,20 Al-SPC,21 and Ni/Co-SPC,22 have been synthesized. However, the synthesis of Fe-SPC has not been reported literature; in addition, when we used a nonpreswelling procedure reported in the literature to synthesize Fe-SPC, iron hydroxides are very easily formed and precipitated, leading to the failure of the preparation of Fe-SPC. Hence, the synthesis of Fe-SPC has its particular characteristics and is an interesting issue. This article presents a facile method for synthesizing Fe-SPC, according to which a series of Fe-SPCs with different contents of Fe2O3 were synthesized. In addition, the influence of the content of Fe2O3 on the structure and catalytic performance of the Fe-SPCs was studied in detail. The results showed that FeSPCs have high catalytic activity and reusability.
2. EXPERIMENTAL SECTION 2.1. Materials. Montmorillonite (MMT) with a basal (001) spacing of 14.7 Å and an anhydrous structural (layer) formula of [Si7.86Al0.14][Al2.84Fe0.30Mg0.86]O20(OH)4 was obtained from Inner Mongolia (Tianhong Mining Company, Chifeng City, China), and used as received. Dodecyl dimethyl benzyl Received: Revised: Accepted: Published: 15593
August 9, 2012 November 15, 2012 November 15, 2012 November 15, 2012 dx.doi.org/10.1021/ie3021413 | Ind. Eng. Chem. Res. 2012, 51, 15593−15600
Industrial & Engineering Chemistry Research
Article
2.6. Characterization. X-ray diffraction (XRD) was performed on a Rigaku D/Max 2500 VBZ+/PC diffractometer (Rigaku Company, Tokyo, Japan) using Cu Kα radiation at 40 kV and 50 mA in the range between 0.5° and 10° and Cu Kα radiation at 40 kV and 200 mA in the range between 3° and 90°. N2 adsorption isotherms were obtained using a Micromeritics ASAP 2000 instrument (Micromeritics, Norcross, GA). The samples were degassed at 115 °C for 12 h before measurement. The specific surface area (SBET) was estimated by the Brunauer−Emmett−Teller (BET) equation, and the radius distribution of the pores and mesopore analysis were obtained from the adsorption branch of the isotherm using the Barrett− Joyner−Halenda (BJH) method. Scanning electron microscopy (SEM) was performed using a S-4700 microscope (Hitachi, Tokyo, Japan) operated at 30 kV. Diffuse- reflectance (DR) UV−vis absorption spectra were recorded on a Cary 5-E spectrometer (Varian, Palo Alto, CA). X-ray photoelectron spectra (XPS) were obtained using an ESCALAB250 X-ray photoelectron spectrometer (Thermo Fisher Scientific, Essex, U.K.). Transmission electron microscopy (TEM) was performed using a JEOL-2100 transmission electron microscope (JEOL Ltd., Tokyo, Japan) at an accelerating voltage of 200 kV. X-ray fluorescence (XRF) analysis was performed on a Magix-601 X-ray fluorescence spectrometer (Philips, Tokyo, Japan). The quantitative results were used to analyze elements and calculate the heteroatom content of each sample. Fourier transform infrared (FTIR) spectra from 4000 to 400 cm−1 were recorded on a VECTOR 22 spectrometer (Bruker AXS, Karlsruhe, Germany) using a KBr disk.
ammonium chloride (C12DMBACl) (A.R.) was purchased from Tianjin Surfactants Company, Tianjin, China. Tetraethoxysilane (TEOS) (A.R.) and ammonia (25%) were obtained from Beijing Chemical Reagents Company, Beijing, China. Ferric nitrate (Fe(NO3)3 9H2O) (A.R.) was obtained from Shanghai Xinbao Fine Chemical Factory, Shanghai, China. Ethanol (99.7%) was purchased from Shanghai Zhengxin Chemical Factory, Shanghai, China. Coking benzene, a product of the coal coking process, that contained a thiopene concentration of 2183.3 ppm was obtained from Haibang Chemical Engineering Ltd., Lianyungang, China. 2.2. Synthesis of SPC. MMT (1.00 g) was added to 30 mL of water to form a clay suspension. C12DMBACl was dissolved in ethanol, and TEOS was added and stirred for 0.5 h to form a clear solution. The solution was then slowly dropped into the clay suspension (MMT/ C 1 2 DMBACl/TEOS/ethanol/water molar ratio of 1:2:30:1.2:250). After being stirred for 0.5 h, the mixture was filtered to remove the water and extra TEOS, and the product obtained was C12DMBACl/TEOS-intercalated clay. The interlamellar hydrolysis of this C12DMBACl/TEOSintercalated clay was conducted in an ammonia solution (pH 10). The reaction was conducted by dispersing C12DMBACl/ TEOS-intercalated clay (2.00 g) in an ammonia solution (50 mL) with stirring for 2 h at room temperature. The product was purified by filtration, dried in an oven at 90 °C, and subsequently calcined at 600 °C for 3 h (at a heating rate of 2 °C/min) to remove C12DMBACl. The prepared sample was denoted as SPC. 2.3. Synthesis of Fe-SPCs. MMT powder (1.00 g) was suspended in 30 mL of water to form suspension A. Fe(NO3)3·9H2O (X g) was added to a solution consisting of 2 mL of ethanol and 8 mL of TEOS to form suspension B, which was slowly dropped into suspension A, and stirred for 1 h to obtain a brown sol. Then, 3 mL of ammonia solution was slowly dropped into the sol. After being stirred for 3 h, the resultant mixture was filtered to obtain powders that were washed thoroughly with water, dried in an oven at 90 °C, and then calcined at 600 °C for 6 h using a programmed furnace (at a heating rate of 2 °C/min). The resultant product was denoted as Fe-SPC-X, where X = 1, 2, 3, 4 or 5. 2.4. Synthesis of the Control Sample. The control sample, denoted as Fe-SPC-c, was synthesized using the above process for Fe-SPC-X except that no ethanol was used. 2.5. Tests for Evaluating Catalytic Properties. First, 25.0 mL of coking benzene, 100 mg of Fe-SPC-X, and 0.5 mL of a 30% aqueous solution of H2O2 were blended with stirring at 50 °C for 60 min. Then, the Fe-SPC-X was separated from the oil by filtration and subjected to calcination at 300 °C for 1 h. The amount of sulfur remaining in the sample was determined on a GCMS-QP 2010 instrument (Shimadzu, Kyoto, Japan) with a capillary column (60 m in length). Dibenzothiophene (DBT) was dissolved in petroleum ether to give a model oil (sulfur content = 500 ppm) for ODS. A mixture of 25 mL of model oil, 100 mg of Fe-SPC-X, and 0.5 mL of a 30% aqueous solution of H2O2 were added to a threeneck glass flask with a water-bathed jacket , and stirred for 60 min at 50 °C. Then, the oxidized model oil was extracted three times with acetonitrile (total solvent-to-model oil volume ratio of 1:1). The amount of sulfur in the oil was determined on a model WK-2D microcoulometric integrated analyzer (Jiangsu Jiangfen Electroanalytical Instrument Co., Beijing, China). The used Fe-SPC-X was recovered by calcination at 300 °C for 1 h.
3. RESULTS AND DISCUSSION 3.1. Synthesis and Characterization of Fe-SPCs. Figure 1 shows pictures of suspensions of uncalcinated SPC and FeSPCs in water. The SPC suspension was white, whereas each Fe-SPC suspension was brown, with the color deepening as the content of Fe2O3 increased. On the other hand, all samples
Figure 1. Pictures of uncalcinated SPC and Fe-SPCs in water. 15594
dx.doi.org/10.1021/ie3021413 | Ind. Eng. Chem. Res. 2012, 51, 15593−15600
Industrial & Engineering Chemistry Research
Article
Figure 2. Small-angle XRD patterns of SPC and Fe-SPCs.
except Fe-SPC-c had a uniform distribution in water; however, there was a brown precipitate of iron hydroxide (marked by a red oval) at the bottom of the beaker containing the Fe-SPC-c suspension, indicating that the presence of alcohol plays a decisive role in the incorporation of Fe atoms. The structure of Fe-SPC includes morphological and chemical aspects. Figure 2 shows small-angle XRD patterns of SPC and Fe-SPCs. All of the samples had similar spectra, indicating that all of samples synthesized by this method had similar lamellar structures. Each curve has a refraction peak corresponding to a basal spacing of 3.2−3.5 nm; hence, the corresponding gallery height was around 2.2−2.5 nm (the thickness of a clay sheet is 0.96 nm), which is lager than that of MMT. This difference can be attributed to the intercalation of C12DMBACl during the synthesis of SPC and Fe-SPCs. On the other hand, the XRD line widths of all samples are similar, suggesting that the scattering domain size is not affected during the synthesis of the Fe-SPCs.23 In addition, no significant difference in the intensities among the refraction peaks for all samples was observed, meaning that the amount of Fe element used does not affect the layered structure of Fe-SPC.24 Figure 3 shows the wide-angle XRD patterns of MMT, SPC, and Fe-SPCs. Each spectrum shows the typical peaks of the trioctahedral subgroup of 2:1 phyllosilicates, including (110), (020), (004), (130), (200), (330), and (060) diffractions. Note that no diffraction line can be observed in Figure 3, indicating that the bulk iron oxide was highly amorphous. When more iron atoms were incorporated into the interlayered silica oxide framework, the sample did not exhibit any well-resolved diffraction peaks, reflecting the absence of any long-range ordering.25 The XRD patterns also show that these SPC samples still contained a small amount of quartz, but it did not show any catalytic or other negative effect on the ODS process. The detailed corresponding evidence and discussion are provided later in this article. FTIR spectroscopy has been extensively used to characterize inorganic materials such as molecular sieves and layered clays modified with transitional metals. Figure 4 shows FTIR spectra of SPC and the Fe-SPCs. With increasing content of Fe2O3, a slight red shift was found for the stretching vibration of the tetrahedral SiO4 or FeO4 unit (ca. 803 and 1080 cm−1),26,27
Figure 3. Wide-angle XRD patterns of SPC and Fe-SPCs.
Figure 4. FTIR spectra of SPC and Fe-SPCs.
indicating that heteroatoms were incorporated into the interlayered framework of SPC and M−O−Si bonds 15595
dx.doi.org/10.1021/ie3021413 | Ind. Eng. Chem. Res. 2012, 51, 15593−15600
Industrial & Engineering Chemistry Research
Article
formed.28−30 This is because Fe has a higher atomic weight than Si and the bond length of Fe−O is greater than that of Si− O, thus leading to a decrease in the vibration frequency.31 These analyses were further confirmed by the typical morphologies of SPC and the Fe-SPCs. As shown in the SEM images (Figure 5), all of samples were composed of
Figure 6. TEM images of SPC and Fe-SPCs.
Figure 7 presents representative N2 adsorption−desorption isotherms of the Fe-SPCs. The isotherms of the Fe-SPCs are
Figure 7. N2 adsorption−desorption curves of Fe-SPCs.
similar to those reported for SPC and SPC intercalates.32,33 According to the BDDT (Brunauer, Deming, Deming, and Teller) classification, the N2 isotherms of the Fe-SPCs can be assigned to be a combination of types I and IV,34 and they have a hysteresis loop corresponding to type B of Boer’s five types, indicating that the layered structure was preserved35 and that open slit-shaped pores formed in the region between interlayers.36 When the pressure was increased from a low to a medium value (P/P0 = 0.05−0.2), the N2 adsorption increased almost linearly, suggesting that these materials contained supermicropores and small mesopores with diameters between 1.4 and 2.0 nm.37 When the pressure was increased to a high value (P/P0 = 0.2−0.4), the adsorption was expected to jump because of capillary condensation in the mesopores;38 however, this phenomenon was not observed, indicating that the incorporation of iron led to a decrease in the order of the pores. The pore size distributions calculated by the BJH method using the adsorption branch are plotted in Figure 8, and the average pore sizes and volumes are summarized in Table 1. The average pore size of SPC was 2.1 nm, which was larger than those of Fe-SPC-1, Fe-SPC-2, and Fe-SPC-3, indicating that the incorporation of Fe led to a change in the interlayer framework.
Figure 5. SEM images of MMT, SPC, and Fe-SPCs.
plates, although the plates of the Fe-SPCs were slightly more numerous than those of SPC, suggesting that the platelets were almost unaffected by the hydrolysis. On the other hand, some small particles were observed around platelets of Fe-SPC-3, FeSPC-4 and Fe-SPC-5, demonstrating that some compounds were formed in the extralayer regions of the clays, especially when the content of Fe2O3 increased. The exact chemistry is analyzed in the subsequent discussion of UV−vis and XPS spectra. The morphologies of SPC and Fe-SPCs were also investigated by TEM technique, and the corresponding images are shown in Figure 6. Either SPC or Fe-SPC retains the morphology of its corresponding precursor, consisting of uniform layered structure. The scattering domain size is estimated to be 20−22 nm, which is in good agreement with the XRD results. The lattice with a d-spacing of 3 nm, corresponding to the (001) plane of SPC, is observed in the TEM image. Furthermore, the uniform gallery pores can be clearly observed between the dark layers. 15596
dx.doi.org/10.1021/ie3021413 | Ind. Eng. Chem. Res. 2012, 51, 15593−15600
Industrial & Engineering Chemistry Research
Article
Figure 9. DR UV−vis patterns of SPC and Fe-SPCs.
Figure 8. Pore size distributions of Fe-SPCs.
To obtain additional information about the chemical nature of the active species present in the Fe-SPCs, XPS curves were recorded and are provided in Figure 10. The appearance of the
These results are in good agreement with the N2 adsorption− desorption isotherms, and the value is closely related to the interlayer space height. This implies that the interlayer of C12DMBACl plays an important structure-directing role in the synthesis of the intercalated silica. Note that the peaks corresponding to the pore sizes smaller than 2 nm almost disappeared, especially for Fe-SPC-3, Fe-SPC-4, and Fe-SPC-5. When higher amounts of ferric nitrate were used to synthesize the Fe-SPCs, more Fe2O3 formed from the framework. This extragallery Fe2O3 occupied the spaces of gallery channels and increased the thickness of the pore walls, thus resulting in a significantly decreased number of micropores. Table 1 also shows that, as the content of Fe2O3 increased, the surface area and pore volume of the resultant Fe-SPC decreased, because of the packing of small metal particles on the surfaces and pores. To clearly investigate the position of Fe in the Fe-SPCs, DR UV−vis spectra were recorded, as shown in Figure 9. For the spectrum of SPC, there are very slight peaks (300−400 nm) attributable to FexOy or MgxOy clusters; however, the characteristic peaks belonging to isolated Fe3+ and Mg2+ appear at ca. 240−245 nm, reflecting that the cations of SPC were located mainly in the tetrahedral and octahedral positions of the clay.39 This result is different from the spectra of Fe-SPCs. Specifically, the presence of the peak at 257 nm indicates that Fe element was present as tetrahedrally coordinated Fe species in the framework. In addition, the appearance of the peaks at 415 and 510 nm suggests that there were octahedral Fe species or Fe2O3 out of the framework,40 and the Fe-SPCs with higher contents of Fe2O3 had more octahedral Fe species or Fe2O3 formed out of the framework.
Figure 10. XPS patterns of Fe-SPCs.
Fe 2p3/2 peak (at 712.5 eV) and the Fe 2p1/2 peak (at 726.1 eV) confirms the presence of tetrahedral coordination of Fe ions. Note that there is a shoulder peak at 721.2 eV, suggesting that some Fe ions existed in the state of octahedral coordination on the surfaces of the gallery pillars.41 From the preceding discussion, it can be stated that Fe was incorporated in the silica-framework between the interlayer regions of MMT, as shown in the Scheme 1. 3.2. Catalytic Performance. Each Fe-SPC was used as the catalyst for H2O2 in the ODS of DBT, and the reusability of the
Table 1. Structural Data of MMT, SPC, and Fe-SPCs sample
basal spacing (nm)
gallery height (nm)
surface area (m2/g)
pore volume (cm3/g)
pore size (nm)
content of Fe2O3 (wt %)
MMT SPC Fe-SPC-1 Fe-SPC-2 Fe-SPC-3 Fe-SPC-4 Fe-SPC-5
1.47 3.32 3.32 3.32 3.32 3.30 3.30
0.51 2.36 2.36 2.36 2.36 2.34 2.34
10 1156.2 614.9 442.3 337.8 378.5 321.9
0.05 0.72 0.67 0.53 0.46 0.39 0.30
7.2 2.1 1.8 1.8 2.0 − −
− − 6.37 12.30 17.53 22.47 27.03
15597
dx.doi.org/10.1021/ie3021413 | Ind. Eng. Chem. Res. 2012, 51, 15593−15600
Industrial & Engineering Chemistry Research
Article
Scheme 1. Schematic Structure of Fe-SPCs
which oxidize DBT to dibenzothiophene sulfone (DBTO2). DBTO2 can be extracted by acetonitrile easily, and oil desulfurization is achieved. Therefore, the catalytic performance is closely related to position of Fe in the Fe-SPCs. As discussed above, the active sites of oxidation are Fe species with tetrahedral coordination in the interlayer silica framework of SPC; hence, the catalytic activities are closely related to the structure of Fe-the SPCs. The extragallery Fe2O3 can be detected only when the content of Fe2O3 is higher than 17.53 wt %, in which case the deposited Fe2O3 covers some Fe species with tetrahedral coordination and hampers the active sites, leading to a decrease of the catalytic activity. From Table 2, it can be seen that the oxidation conversions of all of the Fe-SPCs (except Fe-SPC-5) after being recycled three times were still as high as 97.2%, indicating that these FeSPCs have excellent catalytic performance and recyclability. Note that the extragallery Fe2O3 particles also have some catalytic performance, but they tend to agglomerate during reaction and regeneration. The agglomeration reduces the specific surface area and blocks pores, thus leading to a greatly decreased catalytic performance. Because the agglomeration of the extragallery Fe2O3 in Fe-SPC-5 is obvious, the oxidation conversion of Fe-SPC-5 after it had been recycled three times sharply decreased from 91.2% to 83.1%. Similarly, the catalytic performance of SPC and the Fe-SPCs for H2O2 in the ODS of coking benzene was also measured. The corresponding results (Table 3) show that all of the FeSPCs had high conversions, but SPC did not. Moreover, the catalytic activity after three recycling runs was still as high as that during the first run, indicating that the Fe-SPCs have better
Fe-SPCs was also investigated. The results are summarized in Table 2. It can be seen that, unlike SPC, all of Fe-SPCs were Table 2. Conversions (%) Obtained in the Oxidation of DBT Using SPC and Fe-SPCs Recycled Different Numbers of Times cycle no.
SPC
Fe-SPC-1
Fe-SPC-2
Fe-SPC-3
Fe-SPC-4
Fe-SPC-5
1 2 3
0 − −
97.5 97.4 97.2
98.1 97.5 97.2
98.6 98.2 97.9
95.0 94.1 92.2
91.2 85.6 83.1
effective in the ODS of DBT and the conversion was related to the content of Fe2O3 in the Fe-SPC. Specifically, with increasing content of Fe2O3, the sulfur removal initially increased and then decreased. Fe-SPC-3 exhibited the highest sulfur removal. This phenomenon can be explained from the catalytic mechanism of Fe-SPCs in the ODS of DBT. Scheme 2 depicts a simple process for the oxidation of DBT. Specifically, tetrahedrally coordinated Fe species accept active oxygen from the oxidant (H2O2) to form Fe−OOH species, Scheme 2. Proposed Oxidation Mechanism of DBT
Table 3. Conversions (%) Obtained in the Oxidation of Coking Benzene Using SPC and Fe-SPCs Recycled Different Numbers of Times
15598
cycle no.
SPC
Fe-SPC-1
Fe-SPC-2
Fe-SPC-3
Fe-SPC-4
Fe-SPC-5
1 2 3
0 − −
>99 >99 >99
>99 >99 >99
>99 >99 >99
>99 >99 >99
>99 >99 >99
dx.doi.org/10.1021/ie3021413 | Ind. Eng. Chem. Res. 2012, 51, 15593−15600
Industrial & Engineering Chemistry Research
Article
(5) Mure, T.; Craig, F.; Zbigniew, R. Oxidation Reactivities of Dibenzothiophenes in Polyoxometalate/H2O2 and Formic Acid/H2O2 Systems. Appl. Catal. A: Gen. 2001, 219, 267. (6) Yu, G. X.; Lu, S. X.; Chen, H.; Zhu, Z. N. Oxidative Desulfurization of Diesel Fuels with Hydrogen Peroxide in the Presence of Activated Carbon and Formic Acid. Energy Fuels 2005, 19, 447. (7) Campos-Martin, J. M.; Capel-Sanchez, M. C.; Perez-Presas, P.; Fierro, J. L. G. Oxidative Processes of Desulfurization of Liquid Fuels. J. Chem. Technol. Biotechnol. 2010, 85, 879. (8) Garcia-Gutierrez, J. L.; Fuentes, G. A.; Hernandez-Teran, M. E.; Garcia, P.; Murrieta-Guevara, F.; Jimenez-Cruz, F. Ultra-deep Oxidative Desulfurization of Diesel Fuel by the Mo/Al2O3−H2O2 System: The Effect of System Parameters on Catalytic Activity. Appl. Catal. A: Gen. 2008, 334, 366. (9) Chica, A.; Gatti, G.; Moden, B.; Marchese, L.; Iglesia, E. Selective Catalytic Oxidation of Organosulfur Compounds with tert-Butyl Hydroperoxide. Chem.Eur. J. 2006, 12, 1960. (10) Caero, L. C.; Jorge, F.; Navarro, A.; Gutierrez-Alejandre, A. Oxidative Desulfurization of Synthetic Diesel Using Supported Catalysts Part II. Effect of Oxidant and Nitrogen Compounds on Extraction−Oxidation Process. Catal. Today 2006, 116, 562. (11) Shiraishi, Y.; Hirai, T.; Komasawa, I. Oxidative Desulfurization Process for Light Oil Using Titanium Silicate Molecular Sieve Catalysts. J. Chem. Eng. Jpn. 2002, 35, 1305. (12) Wącław, A.; Nowińska, K.; Schwieger, W. Benzene to Phenol Oxidation Over Iron Exchanged Zeolite ZSM-5. Appl. Catal. A: Gen. 2004, 270, 151. (13) Knops-Gerrits, P.; Verberckmoes, A.; Schoonheydt, R.; Ichikawa, M.; Jacobs, P. A. Alkane Oxidation by Dinuclear Iron Complexes in Hexagonal Mesoporous Solids. Microporous Mesoporous Mater. 1998, 21, 475. (14) Guo, J.; Al-Dahhan, M. Catalytic Wet Oxidation of Phenol by Hydrogen Peroxide Over Pillared Clay Catalyst. Ind. Eng. Chem. Res. 2003, 42, 2450. (15) Li, B. S.; Wu, K.; Yuan, T. H.; Han, C. Y.; Xu, J. Q.; Pang, X. M.. Synthesis, Characterization and Catalytic Performance of High Iron Content Mesoporous Fe-MCM-41. Microporous Mesoporous Mater. 2012, 151, 277. (16) Gil, A.; Korili, S. A.; Trujillano, R.; Vicente, M. A. A Review on Characterization of Pillared Clays by Specific Techniques. Appl. Clay Sci. 2011, 53, 97. (17) Letaïef, S.; Casal, B.; Aranda, P.; Martín-Luengo, M. A.; Hitzky, E. R. Fe-Containing Pillared Clays as Catalysts for Phenol Hydroxylation. Appl. Clay Sci. 2003, 22, 263. (18) Thomas, J. M.; Thomas, W. J. Principles and Practice of Heterogeneous Catalysts; Wiley-VCH: Weinheim, Germany, 1997. (19) Sampieri, A.; Fetter, G.; Bosch, P.; Bulbulian, S. Washing Effect on the Synthesis of Silica-Pillared Clays. J. Porous Mater. 2004, 11, 157. (20) Mao, H. H.; Li, B. S.; Li, X.; Yue, L. W.; Xu, J. Q.; Ding, B.; Gao, X. H.; Zhou, Z. Y. Facile Synthesis and Catalytic Properties of Titanium Containing Silica-Pillared Clay Derivatives with Ordered Mesoporous Structure through a Novel Intra-gallery Templating Method. Microporous Mesoporous Mater. 2010, 130, 314. (21) Mao, H. H.; Li, B. S.; Yue, L. W.; Wang, L. Y.; Yang, J. H.; Gao, X. X. Aluminated Mesoporous Silica-pillared Montmorillonite as Acidic Catalyst for Catalytic Cracking. Appl. Clay Sci. 2011, 53, 676. (22) Mao, H. H.; Li, B. S.; Li, X.; Liu, Z. X.; Ma, W. Mesoporous Nickel Containing Silica-Pillared Clays (Ni-SPC): Synthesis, Characterization and Catalytic Behavior for Cracking of Plant Asphalt. Catal. Commun. 2009, 10, 975. (23) Gardner, E.; Huntoon, K. M.; Pinnavaia, T. J. Direct Synthesis of Alkoxide-Intercalated Derivatives of Hydrotalcite-like Layered Double Hydroxides: Precursors for the Formation of Colloidal Layered Double Hydroxide Suspensions and Transparent Thin Films. Adv. Mater. 2001, 13, 1263. (24) Zhang, J. P.; Wang, L.; Wang, A. Q. Preparation and Properties of Chitosan-g-poly(acrylic acid)/Montmorillonite Superabsorbent
reusability. These results show that the Fe-SPCs have better catalytic performance and reusability for the ODS the organic sulfur compound in coking benzene than for DBT in oil. This can be explained from the catalyst mechanism. It is known that the conversion of catalytic oxidation is dependent on the size of pores and the molecular size of the sulfur compounds.42 The main organic sulfur compound in coking benzene is thiophene, which is much smaller than DBT; hence, thiophene can more easily enter the interlayer pores and contact the active sites than DBT. When the content of Fe2O3 in Fe-SPC is higher than 17.53 wt %, the reduced size of the interlayer pores makes it more difficult for DBT molecules to enter the pores, so as the content of Fe2O3 in the Fe-SPCs increased from 17.53 to 27.03 wt %, the catalytic oxidation conversion of DBT did not increase.
4. CONCLUSIONS Fe-SPCs with an ordered porous structure and different contents of Fe2O3 were synthesized using a facile method and characterized as mesoporous structures with uniform pores between the layers. The Fe-SPCs had a lamellar structure similar to that of the initial SPC. The amount of tetrahedral Fe incorporated into the silica in the interlayer space was correlated with the concentration of Fe in the TEOS/ethanol sol. An increased content of Fe2O3 led to a gradually reduced quality of pore structure and volume of pores. As the catalyst for H2O2 in the ODS of coking benzene or DBT, the Fe-SPCs exhibited almost 100% conversion, and the Fe-SPCs had better reusability for the ODS of the organic sulfur compound in coking benzene than for that of DBT in oil.
■
AUTHOR INFORMATION
Corresponding Author
*Tel.: +86 512 61875156. Fax: +86 512 65880089. E-mail:
[email protected] (A.G.),
[email protected] (G.L.). Notes
The authors declare no competing financial interest.
■
ACKNOWLEDGMENTS The authors thank the Natural Science Foundation of China (No. 51173123), the Priority Academic Program Development of Jiangsu Higher Education Institutions (PAPD), the Major Program of Natural Science Fundamental Research Project of Jiangsu Colleges and Universities (No. 11KJA430001), the Natural Science Funds of Universities of Jiangsu Province (No. 11KJB530001), and the Fundamental Research Funds for the Central Universities (No. ZY1224) for financially supporting this project.
■
REFERENCES
(1) Zhou, X. R.; Lv, S.; Wang, H.; Wang, X. N.; Liu, J. H. Catalytic Oxygenation of Dibenzothiophenes to Sulfones Based on FeIII Porphyrin Complex. Appl. Catal. A: Gen. 2011, 396, 101. (2) Sharipov, A. K.; Nigmatullin, V. R. Removal of Sulfur from Hydrotreated Diesel Fuel. Chem. Technol. Fuels Oils 2005, 41, 225. (3) Song, C. S.; Ma, X. L. New Design Approaches to Ultra-clean Diesel Fuels by Deep Desulfurization and Deep Dearomatization. Appl. Catal. B: Environ. 2003, 41, 207. (4) Jin, C. Z.; Wang, X. S.; Wang, Y.; Zhao, L. X.; Sun, D. A Titanium Containing Micro/Mesoporous Composite and Its Catalytic Performance in Oxidative Desulfurization. Microporous Mesoporous Mater. 2008, 111, 236. 15599
dx.doi.org/10.1021/ie3021413 | Ind. Eng. Chem. Res. 2012, 51, 15593−15600
Industrial & Engineering Chemistry Research
Article
Nanocomposite via in Situ Intercalative Polymerization. Ind. Eng. Chem. Res. 2007, 46, 2497. (25) Li, B. S.; Xu, J. Q.; Liu, J. J.; Zuo, S. L.; Pan, Z. Y.; Wu, Z. Y. Preparation of Mesoporous Ferrisilicate with High Content of Framework Iron by pH-Modification Method and Its Catalytic Performance. J. Colloid Interface Sci. 2012, 366, 114. (26) Araujo, A. S.; Jaroniec, M. Determination of the Surface Area and Mesopore Volume for Lanthanide-Incorporated MCM-41 Materials by Using High Resolution Thermogravimetry. Thermochim. Acta 2000, 345, 173. (27) Wu, C.; Kong, Y.; Gao, F.; Wu, Y.; Lu, Y. N.; Wang, J.; Dong, L. Synthesis, Characterization and Catalytic Performance for Phenol Hydroxylation of Fe-MCM-41 with High Iron Content. Microporous Mesoporous Mater. 2008, 113, 163. (28) Jiang, S. Y.; Kong, Y.; Wang, J.; Ren, X. Q.; Yan, Q. J. Synthesis, Characterization of Bimetallic Sn−Zn−MCM-41 and its Catalytic Performance in the Hydroxylation of Phenol. J. Porous Mater. 2006, 13, 341. (29) Takahashi, R.; Sato, S.; Sodesawa, T.; Kawakita, M.; Ogura, K. High Surface-Area Silica with Controlled Pore Size Prepared from Nanocomposite of Silica and Citric Acid. J. Phys. Chem. B 2000, 104, 12184. (30) Kong, Y.; Jiang, S. Y.; Wang, J.; Wang, S. S.; Yan, Q. J.; Lu, Y. N. Synthesis and Characterization of Cu−Ti−MCM-41. Microporous Mesoporous Mater. 2005, 86, 191. (31) Park, K. W.; Jung, J. H.; Seo, H. J.; Kwon, O. Y. Mesoporous Silica-Pillared Kenyaite and Magadiite as Catalytic Support for Partial Oxidation of Methane. Microporous Mesoporous Mater. 2009, 121, 219. (32) Li, B. S.; Mao, H. H.; Li, X.; Liu, Z. X.; Ma, W. Synthesis of Mesoporous Silica-Pillared Clay by Intragallery Ammonia-Catalyzed Hydrolysis of Tetraethoxysilane Using Quaternary Ammonium Surfactants as Gallery Templates. J. Colloid Interface Sci. 2009, 336, 244. (33) Gao, X. X.; Mao, H. H.; Lu, M. H.; Yang, J. H.; Li, B. S. Facile Aynthesis Route to NiO−SiO2 Intercalated Clay with Ordered Porous Structure: Intragallery Interfacially Controlled Functionalization Using Nickel−Ammonia Complex for Deep Desulfurization. Microporous Mesoporous Mater. 2012, 148, 25. (34) Brunauer, S.; Deming, L. S.; Deming, W. E.; Teller, E. On a Theory of the van der Waals Adsorption of Gases. J. Am. Chem. Soc. 1940, 62, 1723. (35) Choy, J. H.; Jung, H.; Han, Y. S.; Yoon, J. B.; Shul, Y. G.; Kim, H. J. New CoO−SiO2-Sol Pillared Clays as Catalysts for NOx Conversion. Chem. Mater. 2002, 14, 3823. (36) Yang, X. Y.; Li, Y.; Tendeloo, G. V.; Xiao, F. S.; Su, B. L. OnePot Synthesis of Catalytically Stable and Active Nanoreactors: Encapsulation of Size-Controlled Nanoparticles within a Hierarchically Macroporous Core@Ordered Mesoporous Shell System. Adv. Mater. 2009, 21, 1368. (37) Wei, L. M.; Tang, T.; Huang, B. T. Novel Acidic Porous Clay Heterostructure with Highly Ordered Organic−Inorganic Hybrid Structure: One-Pot Synthesis of Mesoporous Organosilica in the Galleries of Clay. Microporous Mesoporous Mater. 2004, 67, 175. (38) Zhang, H.; Pan, D. K.; Zou, K.; He, J.; Duan, X. A Novel Core− Shell Structured Magnetic Organic−Inorganic Nanohybrid Involving Drug-Intercalated Layered Double Hydroxides Coated on a Magnesium Ferrite Core for Magnetically Controlled Drug Release. J. Mater. Chem. 2009, 19, 3069. (39) Kumar, M. S.; Schwidder, M.; Grű net, W.; Brű ckner, A. On the Nature of Different Iron Sites and Their Catalytic Role in Fe−ZSM-5 DeNOx Catalysts: New Insights by a Combined EPR and UV/VIS Spectroscopic Approach. J. Catal. 2004, 227, 384. (40) Pérez-Ramirez, J.; Kumar, M. S.; Brű ckner, A. Reduction of N2O with CO over FeMFI Zeolites: Influence of the Preparation Method on the Iron Species and Catalytic Behavior. J. Catal. 2004, 223, 13. (41) Stefanis, A. D.; Kaciulis, S.; Pandolfi, L. Preparation and Characterization of Fe-MCM-41 Catalysts Employed in the Degradation of Plastic Materials. Microporous Mesoporous Mater. 2007, 99, 140.
(42) Zhao, X. S.; Lu, G. Q.; Millar, G. J. Advances in Mesoporous Molecular Sieve MCM-41. Ind. Eng. Chem. Res. 1996, 35, 2075.
15600
dx.doi.org/10.1021/ie3021413 | Ind. Eng. Chem. Res. 2012, 51, 15593−15600
