- Email: [email protected]
Phosphotungstic acid anchored on amine-functionalized MIL-101: An effective catalyst for the direct esterification of 1-butene to sec-butyl acetate
Journal of the Taiwan Institute of Chemical Engineers 99 (2019) 201–206
Contents lists available at ScienceDirect
Journal of the Taiwan Institute of Chemical Engineers journal homepage: www.elsevier.com/locate/jtice
Phosphotungstic acid anchored on amine-functionalized MIL-101: An effective catalyst for the direct esterification of 1-butene to sec-butyl acetate Lulu Yan, Jundong Xu, Tingting Duan, Bingbing Zhao, Yu Fan∗ State Key Laboratory of Heavy Oil Processing, China University of Petroleum, Beijing 102249, PR China
a r t i c l e
i n f o
Article history: Received 6 October 2018 Revised 19 March 2019 Accepted 30 March 2019 Available online 9 April 2019 Keywords: Phosphotungstic acid Ethylenediamine grafted MIL-101 Charge interaction Dispersion Olefin esterification
a b s t r a c t This article proposes a novel strategy for enhancing the dispersion and stability of supported H3 PW12 O40 (HPW) via the charge interaction between HPW anions and amino groups originating from ethylenediamine (ED) grafted on the unsaturated metal sites of MIL-101. Due to its larger specific surface area and pore volume as well as stronger interactions between HPW and the carrier, the as-prepared catalyst exhibited a higher sec–butyl acetate (SBAC) yield for the direct esterification of olefins than did the catalyst prepared by the encapsulation of HPW in the mesoporous cages of MIL-101. In addition, the HPW content incorporated in the as-prepared catalyst was optimized, and the results showed that among the series of catalysts, the HPW/ED-grafted MIL-101 catalyst with 40 wt% HPW had the highest activity and good stability for olefin esterification. This investigation sheds light on the conversion of 1-butene into high-value SBAC via the amine-functionalized MIL-101-supported HPW catalysts. © 2019 Taiwan Institute of Chemical Engineers. Published by Elsevier B.V. All rights reserved.
1. Introduction Increasing C4 hydrocarbon production and stringent environmental regulations have impelled refineries to seek a substitute for methyl tert-butyl ether (MTBE), which is classified as a possible carcinogen by the US Environmental Protection Agency (EPA) [1,2]. Since sec–butyl acetate (SBAC) can be used as a clean gasoline additive and has a high octane number, SBAC is highly desired as a replacement for MTBE [3,4]. In addition, the use of 1-butene can be effectively expanded via converting 1-butene directly into SBAC [5]. The traditional SBAC synthesis process is catalyzed primarily by sulfuric acid; this process produces a great quantity of wastewater and spent acid with a high regeneration cost [6]. The replacement of strong mineral acids by solid acids has attracted wide attention in view of environmental friendliness. The solid acid catalysts were used for the olefin esterification. Patwardhan and Sharma [5] prepared the catalysts of cation exchange resins for the olefin esterification, but the esterification performances of these catalysts need to be improved. The catalytic effect of unsupported heteropoly compounds on the esterification of acrylic acid and ethylene has been studied [7]. Silica-supported sulfuric
∗
Corresponding author. E-mail address: [email protected] (Y. Fan).
acid was also applied to the olefin esterification by the gas-phase reaction, but its active components are easily lost [8]. In recent years, Keggin-type heteropoly acids, especially H3 PW12 O40 (HPW), have been applied in various catalytic reactions with bright prospects [9–12]. Owing to the poor specific surface area (1–5 m2 /g) of this material and the difficult separation from products when used as a homogeneous catalyst, HPW is loaded onto different carriers, such as silica [13,14], activated carbon [15], ion-exchange resins [16] or mesoporous molecular sieves [17], to obtain heterogeneous catalysts and overcome these problems. However, these heterogeneous catalysts still exhibit some deficiencies, such as easy inactivation, easy aggregation and low loading of HPW [18–20]. Therefore, it is important for HPW to be loaded on suitable carriers, which can improve the dispersion of HPW and the interaction between HPW and carriers. More than 10,0 0 0 metal–organic framework (MOF) structures are known [21]. Some of these structures have been viewed as promising materials in the fields of catalysis, gas storage and release, chromatographic separation, drug release and so on [22-24]. With two types of quasi-spherical mesoporous cages (2.9 and 3.4 nm) accessible through pentagonal and hexagonal windows (1.2 and 1.6 nm), MIL-101(Cr) is a good alternative due to its numerous unsaturated metal sites, high adsorption capacity, and good chemical, thermal and hydrothermal stability [25,26]. Amine groups have been introduced into MIL-101 via grafting ethylenediamine (ED) onto the unsaturated chromium (III) sites
https://doi.org/10.1016/j.jtice.2019.03.022 1876-1070/© 2019 Taiwan Institute of Chemical Engineers. Published by Elsevier B.V. All rights reserved.
202
L. Yan, J. Xu and T. Duan et al. / Journal of the Taiwan Institute of Chemical Engineers 99 (2019) 201–206
Fig. 1. X-ray diffraction patterns of the different samples: MIL-101(a), 30 wt% HPW/EDG-MIL-101 (b), and 30 wt% HPW@MIL-101 (c).
[27]. Apart from exhibiting the excellent capture of gases (such as CO2 ) [28,29], the as-obtained ED grafted MIL-101 can also be further functionalized via postsynthetic modification in which a variety of functional groups and transition metals are incorporated into MIL-101 via interactions with amine groups [30–32]. However, no study has reported the support of phosphotungstic acid on amino-functionalized MIL-101 for the preparation of SBAC via the esterification of 1-butene with acetic acid. Herein, we propose a novel strategy for preparing dispersed and stabilized HPW via the charge interaction between HPW and ED grafted MIL-101 (EDG-MIL-101). In this method, the HPW anions are bonded to the positively charged surface of EDG-MIL-101, which effectively disperses and stabilizes HPW on EDG-MIL-101. The as-prepared catalyst exhibits a higher SBAC yield for the direct esterification of olefins than does the catalyst prepared by the encapsulation of HPW in the mesoporous cages of MIL-101. Furthermore, the HPW content incorporated in the as-prepared catalyst was adjusted, and an optimal HPW/EDG-MIL-101 catalyst with superior activity and stability for olefin esterification was obtained. 2. Experimental section The synthesis of MIL-101(Cr) was performed according to the literature [33]. All experimental details are found in Supplementary Material. 3. Results and discussion 3.1. Effects of HPW-introduced pathways on the performance of the corresponding catalysts 3.1.1. XRD characterization The XRD patterns of MIL-101, 30 wt% HPW/EDG-MIL-101 and 30 wt% HPW@MIL-101 are shown in Fig. 1. The XRD peak intensity of MIL-101 decreases after loading HPW due to interference from the diffraction of HPW. The three samples present typical diffraction peaks at 2θ = 2.83°, 3.31°, 8.45° and 9.07°, which are assigned to MIL-101 [34,35], indicating that the crystal structures of MIL-101 are well maintained after loading HPW. 3.1.2. SEM characterization MIL-101, EDG-MIL-101, 30 wt% HPW@MIL-101 and 30 wt% HPW/EDG-MIL-101 have octahedral crystal morphology with sizes
Fig. 2. FT-IR spectra of the different samples: HPW (a), 30 wt% HPW@MIL-101 (b), 30 wt% HPW/EDG-MIL-101 (c), EDG-MIL-101 (d), and MIL-101 (e).
in the range from 200 to 600 nm (Fig. S1), which demonstrates that after being modified by ED and loaded with HPW, the crystal morphology of MIL-101 remains unchanged. There are some larger crystalline aggregations on 30 wt% HPW@MIL-101 than on 30 wt% HPW/EDG-MIL-101 (Fig. S1), implying better pore structure on the latter.
3.1.3. FT-IR characterization In Fig. 2, the FT-IR spectra of the five samples are depicted. The bands at 1620 and 1400 cm−1 are assigned to the stretching vibration of COOH, and the bands appearing at 1550 and 1506 cm−1 are attributed to the stretching vibration of C=C in benzene rings [36]. In addition, the spectrum of EDG-MIL-101 contains bands at 1583 cm−1 (the in-plane bending vibration of –N–H) and 1051 cm−1 (the stretching vibration of –C–N), indicating that ED was successfully grafted on MIL-101 [37,38]. The N content determined by the XRF analysis is 2.33 mmol/g catalyst, which is equivalent to 0.386 of ethylenediamine molecules per Cr site, close to one ethylenediamine molecules per trimer of chromium octahedra for EDG-MIL-101. This result indicates that open metal sites in MIL-101 are successfully grafted with ethylenediamine [27]. In 30 wt% HPW/EDG-MIL-101, the band at 1583 cm−1 corresponding to –N–H shifts to 1594 cm−1 , and the intensity of the band at 1051 cm−1 corresponding to –C–N decreases, suggesting a strong interaction between the grafted amino groups and HPW. As for 30 wt% HPW/EDG-MIL-101 and 30 wt% HPW@MIL-101, several differences are found in the 80 0–120 0 cm−1 region from the spectra in Fig. 2. The bands centered at 1081, 984, 889 and 803 cm−1 appearing in pure HPW are assigned to P-O in the central PO4 tetrahedron, W=O in the exterior WO6 octahedron, W– Ob –W bridges and W–Oc –W bridges, respectively [39]. In 30 wt% HPW/EDG-MIL-101, the band at 803 cm−1 assigned to W–Oc –W redshifts to 824 cm−1 , and the band at 889 cm−1 assigned to W– Ob –W shifts to 900 cm−1 ; these obvious redshifts further demonstrate the strong interaction between the grafted amino groups and HPW. In 30 wt% HPW@MIL-101, the band at 803 cm−1 assigned to W–Oc –W shifts to 814 cm−1 , and the band at 889 cm−1 assigned to W–Ob –W shifts to 894 cm−1 ; these redshifts originate from the confining effect of cages in MIL-101 on HPW [40]. By comparison, 30 wt% HPW/EDG-MIL-101 has higher redshifts than does 30 wt% HPW@MIL-101, indicating a stronger interaction between HPW and the carrier for the former than for the latter.
L. Yan, J. Xu and T. Duan et al. / Journal of the Taiwan Institute of Chemical Engineers 99 (2019) 201–206
Fig. 3. N2 adsorption–desorption isotherms of the different samples: 30 wt% HPW@MIL-101 (a), 30 wt% HPW/EDG-MIL-101 (b), and MIL-101 (c). Table 1 Specific surface area and pore volume of the samples. Sample
BET surface area (m2 /g)
Pore volume (cm3 /g)
MIL-101 30 wt% HPW@MIL-101 30 wt% HPW/EDG-MIL-101
2799 1468 2199
1.51 0.70 1.21
3.1.4. Nitrogen adsorption–desorption The nitrogen adsorption–desorption isotherms of MIL-101, 30 wt% HPW@MIL-101 and 30 wt% HPW/EDG-MIL-101 are shown in Fig. 3. All the samples exhibit type-I isotherms. When P/P0 is in the range of 0–0.1, the N2 adsorptive volumes of the samples increase rapidly, reflecting the existence of abundant micropores [41]. As there are two secondary uptakes at approximately P/P0 = 0.1 and 0.2, two types of nanoporous windows exist in the framework of the samples, which is consistent with the pore structure of MIL-101 [28]. After loading the same amount of HPW on MIL-101, the N2 adsorptive volume decreased more in 30 wt% HPW@MIL-101 than in 30 wt% HPW/EDG-MIL-101, in agreement with the results in Table 1. As listed in Table 1, 30 wt% HPW/EDG-MIL-101 has a larger specific surface area and pore volume than does 30 wt% HPW@MIL-101. This result is explained as follows: in 30 wt% HPW@MIL-101, partial mesoporous cages of MIL-101 are occupied by HPW [40], leading to the blocking of cages and thereby a low pore structure. By contrast, HPW in 30 wt% HPW/EDG-MIL-101 is evenly distributed on the outer surface and pore channels of EDGMIL-101 through the anchoring action of grafted amino groups, greatly reducing the blocking of cages and thus improving the pore structure. 3.1.5. Catalytic performance The catalytic performances of 30 wt% HPW@MIL-101 and 30 wt% HPW/EDG-MIL-101 with the increasing reaction time in C4 olefin esterification are shown in Fig. 4. The obtained SBAC yield is an average of three repeated experiments and the relative standard deviation of the SBAC yield is also displayed as the error bar in Fig. 4. The SBAC yield over 30 wt% HPW@MIL-101 rapidly decreases when the reaction time increases from 8 to 24 h. Meanwhile, the yield of SBAC over 30 wt% HPW/EDG-MIL-101 is kept at about 30.67 wt%, indicating the good stability of this catalyst. The higher SBAC yield of 30 wt% HPW/EDG-MIL-101 than that of 30 wt% HPW@MIL-101 is clarified as follows. On the one hand,
203
Fig. 4. Yield of SBAC over 30 wt% HPW@MIL-101 (black) and 30 wt% HPW/EDG-MIL101 (red). (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)
for 30 wt% HPW@MIL-101, HPW is encapsulated in partial mesoporous cages of MIL-101 [39], leading to less diffusion space and fewer active sites for the reactants, intermediates and products. In contrast, in 30 wt% HPW/EDG-MIL-101, one amine group of ED is grafted on unsaturated metal sites of MIL-101, and the other interacts with HPW; consequently, HPW is highly dispersed on the outer surface and pore channels of EDG-MIL-101 and not confined to mesoporous cages. Thus, 30 wt% HPW/EDG-MIL-101 has enough diffusion space and active sites for the reactants, intermediates and products. On the other hand, the diameter of the HPW anion (1.3–1.4 nm) is smaller than the large pore window diameter (1.6 nm) of MIL-101 [42], and HPW is easily removed from the carrier under a polar environment such as acidic solution [43,44]. During the esterification process, the fact that HPW has solubility in acetic acid [45,46] makes HPW leach out from the mesoporous cages of MIL-101 (Table S2), and thereby, the SBAC yield of 30 wt% HPW@MIL-101 is inferior to that of 30 wt% HPW/EDG-MIL-101. The stronger interaction between HPW and the carrier in 30 wt% HPW/EDG-MIL-101 than in 30 wt% HPW@MIL-101 (Fig. 2) restrains the loss of HPW, which improves the SBAC yield. 3.2. HPW/EDG-MIL-101 catalysts with different HPW loadings 3.2.1. XRD characterization Fig. 5 shows the XRD patterns of EDG-MIL-101 and the corresponding catalysts. The XRD peak intensity of EDG-MIL-101 decreases gradually with increasing HPW content due to the gradually declining proportion of EDG-MIL-101 in the catalyst. When the HPW content is 20–40 wt%, the diffraction peaks from MIL-101 remain strong, demonstrating that a suitable HPW loading has little influence on the MIL-101 structure. For 50 wt% HPW/EDG-MIL-101, some diffraction peaks at 2θ = 5°∼7° for MIL-101 disappear, and the relative intensity of the main peaks at 2θ = 2.83°, 3.31° and 8.45° is drastically reduced. These peak changes occur because excessive HPW reacts with the oxygencontaining functional groups in MIL-101 [47], causing local damage to the MIL-101 skeletal structure. 3.2.2. TEM characterization The TEM images of the four catalysts are displayed in Fig. 6. With the HPW loadings of 20–40 wt%, the catalysts present regular octahedral crystal morphology in accordance with MIL-101.
204
L. Yan, J. Xu and T. Duan et al. / Journal of the Taiwan Institute of Chemical Engineers 99 (2019) 201–206
As listed in Table 2, with an increase in HPW loading, the specific surface area and pore volume of these catalysts gradually decrease due to the occupation of the surfaces and pore channels by HPW. When the HPW loading is 50 wt%, the crystal structure of MIL-101 is partially destroyed (Fig. 5), resulting in a sharp decrease in the specific surface area and pore volume. The acidity results of the HPW/EDG-MIL-101 catalysts with different HPW loadings are shown in Table 2 and Fig. S4. With the increase of HPW loading, the number of B acid sites over the catalysts increases. The 50 wt% HPW/ED-MIL-101 catalyst has the most B acid sites (129.4 μmol/g) among these catalysts. It is known that the B acid sites are crucial for the olefin esterification, while excessive B acid sites aggravate olefin polymerization [48]. As a result, a suitable number of B acid sites corresponding to a moderate HPW loading is pursued for superior olefin esterification.
Fig. 5. X-ray diffraction patterns of the different samples: EDG-MIL-101 (a), 20 wt% HPW/EDG-MIL-101 (b), 30 wt% HPW/EDG-MIL-101 (c), 40 wt% HPW/EDG-MIL-101 (d), and 50 wt% HPW/EDG-MIL-101 (e).
With an HPW loading of 50 wt%, the catalyst presents aggravated crystalline agglomeration. 3.2.3. FT-IR characterization The FT-IR spectra of the different HPW/EDG-MIL-101 catalysts not only present the characteristic peaks assigned to EDG-MIL-101 but also exhibit the characteristic peaks belonging to HPW (Fig. S2). In these catalysts, the intensity of –C–N band decreases, and the redshifts in the –N–H, W–Ob –W and W–Oc –W bands for HPW are observed (Fig. S2). These results indicate that there is a strong interaction between HPW and the EDG-MIL-101 carrier over these catalysts. 3.2.4. Nitrogen adsorption–desorption and acidity characterizations For the different HPW/EDG-MIL-101 catalysts, the N2 adsorption capacity decreases with an increase in HPW loading (Fig. S3).
3.2.5. Catalytic performance All reactions were carried out under the optimum conditions (Figs. S5 and S6). The effects of HPW loading on the yield and selectivity of SBAC over the HPW/EDG-MIL-101 catalysts for the direct esterification of olefins are shown in Fig. 7. The SBAC yield increases from 19.68 to 36.72 wt% when the HPW loading increases from 20 to 40 wt% (Fig. 7(A)). However, in the case of HPW loading > 40 wt%, the SBAC yield decreases with increasing HPW loading. Among the EDG-MIL-101 supported catalysts with different HPW loadings, 40 wt% HPW/EDG-MIL-101 has the highest k and TOF values (Table S3), indicating its advantages in the olefin esterification. As shown in Fig. 7(B), a change in the HPW loading minimally influences the SBAC selectivity, which is consistently above 97 wt%, indicating high SBAC selectivity over this series of catalysts. According to the reaction mechanism for B acid-catalyzed olefin esterification [12–14], HPW with B acidity plays an important role. Generally, more HPW loading produces more active sites, which are favorable for olefin esterification. When the HPW loading is 20–40 wt%, HPW is well dispersed on EDG-MIL-101 (Fig. 5) with regular octahedrons of crystals (Fig. 6); the specific surface areas of these catalysts are between 1491 and 2799 m2 /g, and the pore volumes are from 0.87 to 1.51 cm3 /g (Table 2), further indicating the good dispersion of HPW and the well-retained MIL-101 crystal
Fig. 6. TEM images of the catalysts: 20 wt% HPW/EDG-MIL-101 (a), 30 wt%. HPW/EDG-MIL-101 (b), 40 wt% HPW/EDG-MIL-101 (c), and 50 wt% HPW/EDG-MIL-101 (d).
L. Yan, J. Xu and T. Duan et al. / Journal of the Taiwan Institute of Chemical Engineers 99 (2019) 201–206
205
Table 2 Specific surface area, pore volume and B acidity of the four catalysts. Catalyst
BET surface (m2 /g)
Pore volume (cm3 /g)
B acidity (μmol/g)
20 wt% 30 wt% 40 wt% 50 wt%
2253 2199 1491 763
1.32 1.21 0.87 0.44
70.4 99.1 110.7 129.4
HPW/EDG-MIL-101 HPW/EDG-MIL-101 HPW/EDG-MIL-101 HPW/EDG-MIL-101
Fig. 8. Effect of reaction time on SBAC yield over 40 wt% HPW/EDG-MIL-101.
recycling runs, indicating the good stability of this catalyst (Fig. S7 and Table S4). 4. Conclusions
Fig. 7. Yield of SBAC (A) and selectivity of SBAC (B) over the HPW/EDG-MIL-101 catalysts with different HPW loadings.
HPW was stabilized on amine-functionalized MIL-101 by the charge interaction between the HPW anions and the positively charged surface of EDG-MIL-101. The as-prepared catalyst shows higher activity for the direct esterification of olefins than does the catalyst prepared by the encapsulation of HPW in the mesoporous cages of MIL-101 due to the good dispersion and anchoring of HPW on EDG-MIL-101. Furthermore, the HPW content incorporated in the as-prepared catalyst was adjusted, and the results showed that among the series of catalysts, the HPW/EDG-MIL-101 catalyst with 40 wt% HPW had the highest SBAC yield and good stability for olefin esterification. The results presented herein provide a facile route for preparing supported HPW with high dispersion and stability to produce high-value SBAC. Acknowledgments
structure. The above factors enhance the olefin esterification performance of these catalysts with the 20–40 wt% HPW loadings. However, when the HPW loading is more than 40 wt%, crystalline agglomeration is aggravated (Fig. 6), and the MIL-101 framework is partially damaged (Fig. 5). As a result, the specific surface area and pore volume decrease dramatically (Table 2), and thereby, the 50 wt% HPW/EDG-MIL-101 catalyst presents unsatisfactory activity for olefin esterification. The reaction stability of optimal 40 wt% HPW/EDG-MIL-101 is investigated in Fig. 8. During the test, the SBAC yield is maintained at 36.70 wt%, indicating the superior activity and stability of this catalyst in the direct esterification of olefins. The yield of SBAC over 40 wt% HPW/EDG-MIL-101 is kept at about 36.65 wt% in three
The authors gratefully acknowledge the financial support of the National Natural Science Foundation of China (Grant Nos. U1162116 and 21076228). Supplementary materials Supplementary material associated with this article can be found, in the online version, at doi:10.1016/j.jtice.2019.03.022. References [1] Hartley WR, Englande AJ, Harrington DJ. Health risk assessment of groundwater contaminated with methyl tertiary butyl ether (MTBE). Water Sci Technol 1999;39:305–10.
206
L. Yan, J. Xu and T. Duan et al. / Journal of the Taiwan Institute of Chemical Engineers 99 (2019) 201–206
[2] Squillace PJ, Zogorski JS, Wilber WG, Price CV. Preliminary assessment of the occurrence and possible sources of MTBE in groundwater in the United States, 1993–1994. Environ Sci Technol 1996;30:1721–30. [3] Nadim F, Zack P, Hoag GE, Liu S. United States experience with gasoline additives. Energy Policy 2001;29:1–5. [4] Hu XN, Li H, Liu LS. Gasoline composition containing sec-butyl acetate with high octane number and preparation method thereof. Chn. Pat, CN102234549A, 2011. [5] Patwardhan AA, Sharma MM. Esterification of carboxylic acids with olefins using cation exchange resins as catalysts. React Polym 1990;13:161–76. [6] Bhattacharyya SK, Lahiri GR. Catalytic esterification of saturated carboxylic acids with ethylene under high pressure. J Appl Chem 1963;13:544–7. [7] Kenichi S, Masaaki N, Toshiro S, Shoichiro W, Kuniaki M. USP 1993(5189201). [8] Dijs IJ, van Ochten HL, van Walree CA, Geus JW, Jenneskens LW. Alkyl sulphonic acid surface-functionalised silica as heterogeneous acid catalyst in the solvent-free liquid-phase addition of acetic acid to camphene. J Mol Catal A Chem 2002;188:209–24. [9] Keggin JF. The structure and formula of 12-phosphotungstic acid. Proc R Soc Lond Ser A 1934;144:75–100. [10] Li H, He L, Lu J, Zhu W, Xue J, Yan W, et al. Deep oxidative desulfurization of fuels catalyzed by phosphotungstic acid in ionic liquids at room temperature. Energy Fuels 2015;23:1354–7. [11] Kukovecz Á, Balogi Z, Kónya Z, Toba M, Lentz P, Niwa SI, et al. Synthesis, characterisation and catalytic applications of sol–gel derived silica–phosphotungstic acid composites. Appl Catal A Gen 2002;228: 83–94. [12] Yan XM, Lei JH, Liu D, Wu YC, Liu W. Synthesis and catalytic properties of mesoporous phosphotungstic acid/SiO2 in a self-generated acidic environment by evaporation-induced self-assembly. Mater Res Bull 2007;42:1905–13. [13] Bigi F, Corradini A, Quarantelli C, Sartori G. Silica-bound decatungstates as heterogeneous catalysts for H2 O2 activation in selective sulfide oxidation. J Catal 2007;250:222–30. [14] Khder AERS. Preparation, characterization and catalytic activity of tin oxide– supported 12-tungstophosphoric acid as a solid catalyst. Appl Catal A Gen 2008;343:109–16. [15] Schwegler MA, Vinke P, Eijk MVD, Bekkum HV. Activated carbon as a support for heteropolyanion catalysts. Appl Catal A Gen 1992;80:41–57. [16] Frusteri F, Arena F, Bonura G, Cannilla C, Spadaro L, Di Blasi O. Catalytic etherification of glycerol by tert-butyl alcohol to produce oxygenated additives for diesel fuel. Appl Catal A Gen 2009;367:77–83. [17] Kozhevnikov IV, Kloetstra KR, Sinnema A, Zandbergen HW, Bekkum HV. Study of catalysts comprising heteropoly acid H3 PW12 O40 supported on MCM-41 molecular sieve and amorphous silica. J Mol Catal A Chem 1996;114:287–98. [18] Sheng X, Zhou Y, Zhang Y, Xue M, Duan Y. Immobilization of 12-tungstophosphoric acid on LaSBA-15 and its catalytic activity for alkylation of o-xylene with styrene. Chem Eng J 2012;179:295–301. [19] Singh S, Patel A. 12-tungstophosphoric acid supported on mesoporous molecular material: synthesis, characterization and performance in biodiesel production. J Clean Prod 2014;72:46–56. [20] Park Y, Shin WS, Choi SJ. Ammonium salt of heteropoly acid immobilized on mesoporous silica (SBA-15): an efficient ion exchanger for cesium ion. Chem Eng J 2013;220:204–13. [21] Long JR, Yaghi OM. The pervasive chemistry of metal-organic frameworks. Chem Soc Rev 2009;38:1213. [22] Andrew Lin KY, Hsieh YT. Copper-based metal organic framework (MOF), HKUST-1, as an efficient adsorbent to remove p-nitrophenol from water. J Taiwan Inst Chem E 2015;50:223–8. [23] Lin KY, Chang HA. Zeolitic Imidazole Framework-67 (ZIF-67) as a heterogeneous catalyst to activate peroxymonosulfate for degradation of Rhodamine B in water. J Taiwan Inst Chem E 2015;53:40–5. [24] Umesh NM, Rani KK, Devasenathipathy R, Sriram B, Liu YX, Wang SF. Preparation of Co-MOF derived Co(OH)2 /multiwalled carbon nanotubes as an efficient bifunctional electro catalyst for hydrazine and hydrogen peroxide detections. J Taiwan Inst Chem E 2018;211:73–81. [25] Granadeiro CM, Barbosa ADS, Silva P, Paz FAA, Saini VK, Pires J, et al. Monovacant polyoxometalates incorporated into MIL-101(Cr): novel heterogeneous catalysts for liquid phase oxidation. App Catal A Gen 2013;453:316–26.
[26] Férey G, Mellotdraznieks C, Serre C, Millange F, Dutour J, Surblé S, et al. A chromium terephthalate-based solid with unusually large pore volumes and surface area. Science 2005;309:2040–2. [27] Hwang YK, Hong DY, Chang JS, Jhung SH, Seo YK, Kim J, et al. Amine grafting on coordinatively unsaturated metal centers of MOFs: consequences for catalysis and metal encapsulation. Angew Chem Int Ed 2008;47:4144–8. [28] Lin Y, Kong C, Chen L. Direct synthesis of amine-functionalized MIL-101(Cr) nanoparticles and application for CO2 capture. Rsc Adv 2012;2:6417–19. [29] Abid HR, Rada ZH, Duan X, Sun H, Wang S. Enhanced CO2 adsorption and selectivity of CO2 /N2 on amino-MIL-53(Al) synthesized by polar co-solvents. Energy Fuels 2018;32:4502–10. [30] Wang T, Song X, Luo Q, Yang X, Chong S, Zhang J, et al. Acid-base bifunctional catalyst: carboxyl ionic liquid immobilized on MIL-101-NH2 for rapid synthesis of propylene carbonate from CO2 and propylene oxide under facile solvent-free conditions. Micropor Mesopor Mat 2018;267:84–92. [31] Yin HQ, Yang J, Yin XB. Ratiometric fluorescence sensing and real– time detection of water in organic solvents with one-pot synthesis of Ru@MIL-101(Al)-NH2 . Anal Chem 2017;89:13434–40. [32] Carson F, Pascanu V, Bermejo GA, Zhang Y, Plateroprats AE, Zou X, et al. Influence of the Base on Pd@MIL-101-NH2 (Cr) as Catalyst for the Suzuki-Miyaura Cross-Coupling Reaction. Chemistry 2015;21:10896–902. [33] Yang J, Zhao Q, Li J, Dong J. Synthesis of metal–organic framework MIL-101 in TMAOH-Cr(NO3 )3 -H2 BDC-H2 O and its hydrogen-storage behavior. Micropor Mesopor Mat 2010;130:174–9. [34] Bauer S, Serre C, Devic T, Horcajada P, Marrot J, Férey G, et al. High-throughput assisted rationalization of the formation of metal organic frameworks in the iron(iii) aminoterephthalate solvothermal system. Inorg Chem 2008;47:7568. [35] Juan-Alcañiz J, Ramos-Fernandez EV, Lafont U, Gascon J, Kapteijn F. Building MOF bottles around phosphotungstic acid ships: one-pot synthesis of bi-functional polyoxometalate-MIL-101 catalysts. J Catal 2010;269:229–41. [36] Fazaeli R, Aliyan H, Moghadam M, Masoudinia M. Nano-rod catalysts: building MOF bottles (MIL-101 family as heterogeneous single-site catalysts) around vanadium oxide ships. J Mol Catal A Chem 2013;374–375:46–52. [37] Luo X, Ding L, Luo J. Adsorptive removal of Pb(II) ions from aqueous samples with amino-functionalization of metal-organic frameworks MIL-101(Cr). J Chem Eng Data 2015;60:1732–43. [38] Ramanathan T, Fisher FT, And RSR, Brinson LC. Amino-functionalized carbon nanotubes for binding to polymers and biological systems. Chem Mater 2011:17. [39] Hu X, Lu Y, Dai F, Liu C, Liu Y. Host–guest synthesis and encapsulation of phosphotungstic acid in MIL-101 via “ bottle around ship ”: an effective catalyst for oxidative desulfurization. Micropor Mesopor Mat 2013;170:36–44. [40] Zang Y, Shi J, Zhao X, Kong L, Zhang F, Zhong Y. Highly stable chromium(III) terephthalate metal organic framework (MIL-101) encapsulated 12-tungstophosphoric heteropolyacid as a water-tolerant solid catalyst for hydrolysis and esterification. React Kinet Mech Cat 2013;109:77–89. [41] Liu Z, Chen Y, Sun J, Lang H, Gao W, Chi Y. Amine grafting on coordinatively unsaturated metal centers of MIL-101 Cr for improved water absorption characteristics. Inorg Chim Acta 2018;473:29–36. [42] Cowan JJ, Bailey AJ, Heintz RA, Bao TD, Hardcastle KI, Hill CL, et al. Formation, isomerization, and derivatization of Keggin tungstoaluminates. Inorg Chem 2001;40:6666–75. [43] Tsukuda E, Sato S, Takahashi R, Sodesawa T. Production of acrolein from glycerol over silica-supported heteropoly acids. Catal Commun 2007;8:1349–53. [44] Hoo PY, Abdullah AZ. Direct synthesis of mesoporous 12-tungstophosphoric acid SBA-15 catalyst for selective esterification of glycerol and lauric acid to monolaurate. Chem Eng J 2014;250:274–87. [45] Xie W, Yang X, Hu P. Cs2.5 H0.5 PW12 O40 encapsulated in metal-organic framework UiO-66 as heterogeneous catalysts for acidolysis of soybean oil. Catal Lett 2017;147:1–11. [46] Dias JA, Osegovic JP, Drago RS. The solid acidity of 12-tungstophosphoric acid. J Catal 1999;183:83–90. [47] Schwegler MA, Vinke P, van der Eijk M, van Bekkum H. Activated carbon as a support for heteropolyanion catalysts. Appl Catal A Gen 1992;80:41–57. [48] Gee JC, Fisher S. Direct esterification of olefins: the challenge of mechanism determination in heterogeneous catalysis. J Catal 2015;331:13–24.
Contents lists available at ScienceDirect
Journal of the Taiwan Institute of Chemical Engineers journal homepage: www.elsevier.com/locate/jtice
Phosphotungstic acid anchored on amine-functionalized MIL-101: An effective catalyst for the direct esterification of 1-butene to sec-butyl acetate Lulu Yan, Jundong Xu, Tingting Duan, Bingbing Zhao, Yu Fan∗ State Key Laboratory of Heavy Oil Processing, China University of Petroleum, Beijing 102249, PR China
a r t i c l e
i n f o
Article history: Received 6 October 2018 Revised 19 March 2019 Accepted 30 March 2019 Available online 9 April 2019 Keywords: Phosphotungstic acid Ethylenediamine grafted MIL-101 Charge interaction Dispersion Olefin esterification
a b s t r a c t This article proposes a novel strategy for enhancing the dispersion and stability of supported H3 PW12 O40 (HPW) via the charge interaction between HPW anions and amino groups originating from ethylenediamine (ED) grafted on the unsaturated metal sites of MIL-101. Due to its larger specific surface area and pore volume as well as stronger interactions between HPW and the carrier, the as-prepared catalyst exhibited a higher sec–butyl acetate (SBAC) yield for the direct esterification of olefins than did the catalyst prepared by the encapsulation of HPW in the mesoporous cages of MIL-101. In addition, the HPW content incorporated in the as-prepared catalyst was optimized, and the results showed that among the series of catalysts, the HPW/ED-grafted MIL-101 catalyst with 40 wt% HPW had the highest activity and good stability for olefin esterification. This investigation sheds light on the conversion of 1-butene into high-value SBAC via the amine-functionalized MIL-101-supported HPW catalysts. © 2019 Taiwan Institute of Chemical Engineers. Published by Elsevier B.V. All rights reserved.
1. Introduction Increasing C4 hydrocarbon production and stringent environmental regulations have impelled refineries to seek a substitute for methyl tert-butyl ether (MTBE), which is classified as a possible carcinogen by the US Environmental Protection Agency (EPA) [1,2]. Since sec–butyl acetate (SBAC) can be used as a clean gasoline additive and has a high octane number, SBAC is highly desired as a replacement for MTBE [3,4]. In addition, the use of 1-butene can be effectively expanded via converting 1-butene directly into SBAC [5]. The traditional SBAC synthesis process is catalyzed primarily by sulfuric acid; this process produces a great quantity of wastewater and spent acid with a high regeneration cost [6]. The replacement of strong mineral acids by solid acids has attracted wide attention in view of environmental friendliness. The solid acid catalysts were used for the olefin esterification. Patwardhan and Sharma [5] prepared the catalysts of cation exchange resins for the olefin esterification, but the esterification performances of these catalysts need to be improved. The catalytic effect of unsupported heteropoly compounds on the esterification of acrylic acid and ethylene has been studied [7]. Silica-supported sulfuric
∗
Corresponding author. E-mail address: [email protected] (Y. Fan).
acid was also applied to the olefin esterification by the gas-phase reaction, but its active components are easily lost [8]. In recent years, Keggin-type heteropoly acids, especially H3 PW12 O40 (HPW), have been applied in various catalytic reactions with bright prospects [9–12]. Owing to the poor specific surface area (1–5 m2 /g) of this material and the difficult separation from products when used as a homogeneous catalyst, HPW is loaded onto different carriers, such as silica [13,14], activated carbon [15], ion-exchange resins [16] or mesoporous molecular sieves [17], to obtain heterogeneous catalysts and overcome these problems. However, these heterogeneous catalysts still exhibit some deficiencies, such as easy inactivation, easy aggregation and low loading of HPW [18–20]. Therefore, it is important for HPW to be loaded on suitable carriers, which can improve the dispersion of HPW and the interaction between HPW and carriers. More than 10,0 0 0 metal–organic framework (MOF) structures are known [21]. Some of these structures have been viewed as promising materials in the fields of catalysis, gas storage and release, chromatographic separation, drug release and so on [22-24]. With two types of quasi-spherical mesoporous cages (2.9 and 3.4 nm) accessible through pentagonal and hexagonal windows (1.2 and 1.6 nm), MIL-101(Cr) is a good alternative due to its numerous unsaturated metal sites, high adsorption capacity, and good chemical, thermal and hydrothermal stability [25,26]. Amine groups have been introduced into MIL-101 via grafting ethylenediamine (ED) onto the unsaturated chromium (III) sites
https://doi.org/10.1016/j.jtice.2019.03.022 1876-1070/© 2019 Taiwan Institute of Chemical Engineers. Published by Elsevier B.V. All rights reserved.
202
L. Yan, J. Xu and T. Duan et al. / Journal of the Taiwan Institute of Chemical Engineers 99 (2019) 201–206
Fig. 1. X-ray diffraction patterns of the different samples: MIL-101(a), 30 wt% HPW/EDG-MIL-101 (b), and 30 wt% HPW@MIL-101 (c).
[27]. Apart from exhibiting the excellent capture of gases (such as CO2 ) [28,29], the as-obtained ED grafted MIL-101 can also be further functionalized via postsynthetic modification in which a variety of functional groups and transition metals are incorporated into MIL-101 via interactions with amine groups [30–32]. However, no study has reported the support of phosphotungstic acid on amino-functionalized MIL-101 for the preparation of SBAC via the esterification of 1-butene with acetic acid. Herein, we propose a novel strategy for preparing dispersed and stabilized HPW via the charge interaction between HPW and ED grafted MIL-101 (EDG-MIL-101). In this method, the HPW anions are bonded to the positively charged surface of EDG-MIL-101, which effectively disperses and stabilizes HPW on EDG-MIL-101. The as-prepared catalyst exhibits a higher SBAC yield for the direct esterification of olefins than does the catalyst prepared by the encapsulation of HPW in the mesoporous cages of MIL-101. Furthermore, the HPW content incorporated in the as-prepared catalyst was adjusted, and an optimal HPW/EDG-MIL-101 catalyst with superior activity and stability for olefin esterification was obtained. 2. Experimental section The synthesis of MIL-101(Cr) was performed according to the literature [33]. All experimental details are found in Supplementary Material. 3. Results and discussion 3.1. Effects of HPW-introduced pathways on the performance of the corresponding catalysts 3.1.1. XRD characterization The XRD patterns of MIL-101, 30 wt% HPW/EDG-MIL-101 and 30 wt% HPW@MIL-101 are shown in Fig. 1. The XRD peak intensity of MIL-101 decreases after loading HPW due to interference from the diffraction of HPW. The three samples present typical diffraction peaks at 2θ = 2.83°, 3.31°, 8.45° and 9.07°, which are assigned to MIL-101 [34,35], indicating that the crystal structures of MIL-101 are well maintained after loading HPW. 3.1.2. SEM characterization MIL-101, EDG-MIL-101, 30 wt% HPW@MIL-101 and 30 wt% HPW/EDG-MIL-101 have octahedral crystal morphology with sizes
Fig. 2. FT-IR spectra of the different samples: HPW (a), 30 wt% HPW@MIL-101 (b), 30 wt% HPW/EDG-MIL-101 (c), EDG-MIL-101 (d), and MIL-101 (e).
in the range from 200 to 600 nm (Fig. S1), which demonstrates that after being modified by ED and loaded with HPW, the crystal morphology of MIL-101 remains unchanged. There are some larger crystalline aggregations on 30 wt% HPW@MIL-101 than on 30 wt% HPW/EDG-MIL-101 (Fig. S1), implying better pore structure on the latter.
3.1.3. FT-IR characterization In Fig. 2, the FT-IR spectra of the five samples are depicted. The bands at 1620 and 1400 cm−1 are assigned to the stretching vibration of COOH, and the bands appearing at 1550 and 1506 cm−1 are attributed to the stretching vibration of C=C in benzene rings [36]. In addition, the spectrum of EDG-MIL-101 contains bands at 1583 cm−1 (the in-plane bending vibration of –N–H) and 1051 cm−1 (the stretching vibration of –C–N), indicating that ED was successfully grafted on MIL-101 [37,38]. The N content determined by the XRF analysis is 2.33 mmol/g catalyst, which is equivalent to 0.386 of ethylenediamine molecules per Cr site, close to one ethylenediamine molecules per trimer of chromium octahedra for EDG-MIL-101. This result indicates that open metal sites in MIL-101 are successfully grafted with ethylenediamine [27]. In 30 wt% HPW/EDG-MIL-101, the band at 1583 cm−1 corresponding to –N–H shifts to 1594 cm−1 , and the intensity of the band at 1051 cm−1 corresponding to –C–N decreases, suggesting a strong interaction between the grafted amino groups and HPW. As for 30 wt% HPW/EDG-MIL-101 and 30 wt% HPW@MIL-101, several differences are found in the 80 0–120 0 cm−1 region from the spectra in Fig. 2. The bands centered at 1081, 984, 889 and 803 cm−1 appearing in pure HPW are assigned to P-O in the central PO4 tetrahedron, W=O in the exterior WO6 octahedron, W– Ob –W bridges and W–Oc –W bridges, respectively [39]. In 30 wt% HPW/EDG-MIL-101, the band at 803 cm−1 assigned to W–Oc –W redshifts to 824 cm−1 , and the band at 889 cm−1 assigned to W– Ob –W shifts to 900 cm−1 ; these obvious redshifts further demonstrate the strong interaction between the grafted amino groups and HPW. In 30 wt% HPW@MIL-101, the band at 803 cm−1 assigned to W–Oc –W shifts to 814 cm−1 , and the band at 889 cm−1 assigned to W–Ob –W shifts to 894 cm−1 ; these redshifts originate from the confining effect of cages in MIL-101 on HPW [40]. By comparison, 30 wt% HPW/EDG-MIL-101 has higher redshifts than does 30 wt% HPW@MIL-101, indicating a stronger interaction between HPW and the carrier for the former than for the latter.
L. Yan, J. Xu and T. Duan et al. / Journal of the Taiwan Institute of Chemical Engineers 99 (2019) 201–206
Fig. 3. N2 adsorption–desorption isotherms of the different samples: 30 wt% HPW@MIL-101 (a), 30 wt% HPW/EDG-MIL-101 (b), and MIL-101 (c). Table 1 Specific surface area and pore volume of the samples. Sample
BET surface area (m2 /g)
Pore volume (cm3 /g)
MIL-101 30 wt% HPW@MIL-101 30 wt% HPW/EDG-MIL-101
2799 1468 2199
1.51 0.70 1.21
3.1.4. Nitrogen adsorption–desorption The nitrogen adsorption–desorption isotherms of MIL-101, 30 wt% HPW@MIL-101 and 30 wt% HPW/EDG-MIL-101 are shown in Fig. 3. All the samples exhibit type-I isotherms. When P/P0 is in the range of 0–0.1, the N2 adsorptive volumes of the samples increase rapidly, reflecting the existence of abundant micropores [41]. As there are two secondary uptakes at approximately P/P0 = 0.1 and 0.2, two types of nanoporous windows exist in the framework of the samples, which is consistent with the pore structure of MIL-101 [28]. After loading the same amount of HPW on MIL-101, the N2 adsorptive volume decreased more in 30 wt% HPW@MIL-101 than in 30 wt% HPW/EDG-MIL-101, in agreement with the results in Table 1. As listed in Table 1, 30 wt% HPW/EDG-MIL-101 has a larger specific surface area and pore volume than does 30 wt% HPW@MIL-101. This result is explained as follows: in 30 wt% HPW@MIL-101, partial mesoporous cages of MIL-101 are occupied by HPW [40], leading to the blocking of cages and thereby a low pore structure. By contrast, HPW in 30 wt% HPW/EDG-MIL-101 is evenly distributed on the outer surface and pore channels of EDGMIL-101 through the anchoring action of grafted amino groups, greatly reducing the blocking of cages and thus improving the pore structure. 3.1.5. Catalytic performance The catalytic performances of 30 wt% HPW@MIL-101 and 30 wt% HPW/EDG-MIL-101 with the increasing reaction time in C4 olefin esterification are shown in Fig. 4. The obtained SBAC yield is an average of three repeated experiments and the relative standard deviation of the SBAC yield is also displayed as the error bar in Fig. 4. The SBAC yield over 30 wt% HPW@MIL-101 rapidly decreases when the reaction time increases from 8 to 24 h. Meanwhile, the yield of SBAC over 30 wt% HPW/EDG-MIL-101 is kept at about 30.67 wt%, indicating the good stability of this catalyst. The higher SBAC yield of 30 wt% HPW/EDG-MIL-101 than that of 30 wt% HPW@MIL-101 is clarified as follows. On the one hand,
203
Fig. 4. Yield of SBAC over 30 wt% HPW@MIL-101 (black) and 30 wt% HPW/EDG-MIL101 (red). (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)
for 30 wt% HPW@MIL-101, HPW is encapsulated in partial mesoporous cages of MIL-101 [39], leading to less diffusion space and fewer active sites for the reactants, intermediates and products. In contrast, in 30 wt% HPW/EDG-MIL-101, one amine group of ED is grafted on unsaturated metal sites of MIL-101, and the other interacts with HPW; consequently, HPW is highly dispersed on the outer surface and pore channels of EDG-MIL-101 and not confined to mesoporous cages. Thus, 30 wt% HPW/EDG-MIL-101 has enough diffusion space and active sites for the reactants, intermediates and products. On the other hand, the diameter of the HPW anion (1.3–1.4 nm) is smaller than the large pore window diameter (1.6 nm) of MIL-101 [42], and HPW is easily removed from the carrier under a polar environment such as acidic solution [43,44]. During the esterification process, the fact that HPW has solubility in acetic acid [45,46] makes HPW leach out from the mesoporous cages of MIL-101 (Table S2), and thereby, the SBAC yield of 30 wt% HPW@MIL-101 is inferior to that of 30 wt% HPW/EDG-MIL-101. The stronger interaction between HPW and the carrier in 30 wt% HPW/EDG-MIL-101 than in 30 wt% HPW@MIL-101 (Fig. 2) restrains the loss of HPW, which improves the SBAC yield. 3.2. HPW/EDG-MIL-101 catalysts with different HPW loadings 3.2.1. XRD characterization Fig. 5 shows the XRD patterns of EDG-MIL-101 and the corresponding catalysts. The XRD peak intensity of EDG-MIL-101 decreases gradually with increasing HPW content due to the gradually declining proportion of EDG-MIL-101 in the catalyst. When the HPW content is 20–40 wt%, the diffraction peaks from MIL-101 remain strong, demonstrating that a suitable HPW loading has little influence on the MIL-101 structure. For 50 wt% HPW/EDG-MIL-101, some diffraction peaks at 2θ = 5°∼7° for MIL-101 disappear, and the relative intensity of the main peaks at 2θ = 2.83°, 3.31° and 8.45° is drastically reduced. These peak changes occur because excessive HPW reacts with the oxygencontaining functional groups in MIL-101 [47], causing local damage to the MIL-101 skeletal structure. 3.2.2. TEM characterization The TEM images of the four catalysts are displayed in Fig. 6. With the HPW loadings of 20–40 wt%, the catalysts present regular octahedral crystal morphology in accordance with MIL-101.
204
L. Yan, J. Xu and T. Duan et al. / Journal of the Taiwan Institute of Chemical Engineers 99 (2019) 201–206
As listed in Table 2, with an increase in HPW loading, the specific surface area and pore volume of these catalysts gradually decrease due to the occupation of the surfaces and pore channels by HPW. When the HPW loading is 50 wt%, the crystal structure of MIL-101 is partially destroyed (Fig. 5), resulting in a sharp decrease in the specific surface area and pore volume. The acidity results of the HPW/EDG-MIL-101 catalysts with different HPW loadings are shown in Table 2 and Fig. S4. With the increase of HPW loading, the number of B acid sites over the catalysts increases. The 50 wt% HPW/ED-MIL-101 catalyst has the most B acid sites (129.4 μmol/g) among these catalysts. It is known that the B acid sites are crucial for the olefin esterification, while excessive B acid sites aggravate olefin polymerization [48]. As a result, a suitable number of B acid sites corresponding to a moderate HPW loading is pursued for superior olefin esterification.
Fig. 5. X-ray diffraction patterns of the different samples: EDG-MIL-101 (a), 20 wt% HPW/EDG-MIL-101 (b), 30 wt% HPW/EDG-MIL-101 (c), 40 wt% HPW/EDG-MIL-101 (d), and 50 wt% HPW/EDG-MIL-101 (e).
With an HPW loading of 50 wt%, the catalyst presents aggravated crystalline agglomeration. 3.2.3. FT-IR characterization The FT-IR spectra of the different HPW/EDG-MIL-101 catalysts not only present the characteristic peaks assigned to EDG-MIL-101 but also exhibit the characteristic peaks belonging to HPW (Fig. S2). In these catalysts, the intensity of –C–N band decreases, and the redshifts in the –N–H, W–Ob –W and W–Oc –W bands for HPW are observed (Fig. S2). These results indicate that there is a strong interaction between HPW and the EDG-MIL-101 carrier over these catalysts. 3.2.4. Nitrogen adsorption–desorption and acidity characterizations For the different HPW/EDG-MIL-101 catalysts, the N2 adsorption capacity decreases with an increase in HPW loading (Fig. S3).
3.2.5. Catalytic performance All reactions were carried out under the optimum conditions (Figs. S5 and S6). The effects of HPW loading on the yield and selectivity of SBAC over the HPW/EDG-MIL-101 catalysts for the direct esterification of olefins are shown in Fig. 7. The SBAC yield increases from 19.68 to 36.72 wt% when the HPW loading increases from 20 to 40 wt% (Fig. 7(A)). However, in the case of HPW loading > 40 wt%, the SBAC yield decreases with increasing HPW loading. Among the EDG-MIL-101 supported catalysts with different HPW loadings, 40 wt% HPW/EDG-MIL-101 has the highest k and TOF values (Table S3), indicating its advantages in the olefin esterification. As shown in Fig. 7(B), a change in the HPW loading minimally influences the SBAC selectivity, which is consistently above 97 wt%, indicating high SBAC selectivity over this series of catalysts. According to the reaction mechanism for B acid-catalyzed olefin esterification [12–14], HPW with B acidity plays an important role. Generally, more HPW loading produces more active sites, which are favorable for olefin esterification. When the HPW loading is 20–40 wt%, HPW is well dispersed on EDG-MIL-101 (Fig. 5) with regular octahedrons of crystals (Fig. 6); the specific surface areas of these catalysts are between 1491 and 2799 m2 /g, and the pore volumes are from 0.87 to 1.51 cm3 /g (Table 2), further indicating the good dispersion of HPW and the well-retained MIL-101 crystal
Fig. 6. TEM images of the catalysts: 20 wt% HPW/EDG-MIL-101 (a), 30 wt%. HPW/EDG-MIL-101 (b), 40 wt% HPW/EDG-MIL-101 (c), and 50 wt% HPW/EDG-MIL-101 (d).
L. Yan, J. Xu and T. Duan et al. / Journal of the Taiwan Institute of Chemical Engineers 99 (2019) 201–206
205
Table 2 Specific surface area, pore volume and B acidity of the four catalysts. Catalyst
BET surface (m2 /g)
Pore volume (cm3 /g)
B acidity (μmol/g)
20 wt% 30 wt% 40 wt% 50 wt%
2253 2199 1491 763
1.32 1.21 0.87 0.44
70.4 99.1 110.7 129.4
HPW/EDG-MIL-101 HPW/EDG-MIL-101 HPW/EDG-MIL-101 HPW/EDG-MIL-101
Fig. 8. Effect of reaction time on SBAC yield over 40 wt% HPW/EDG-MIL-101.
recycling runs, indicating the good stability of this catalyst (Fig. S7 and Table S4). 4. Conclusions
Fig. 7. Yield of SBAC (A) and selectivity of SBAC (B) over the HPW/EDG-MIL-101 catalysts with different HPW loadings.
HPW was stabilized on amine-functionalized MIL-101 by the charge interaction between the HPW anions and the positively charged surface of EDG-MIL-101. The as-prepared catalyst shows higher activity for the direct esterification of olefins than does the catalyst prepared by the encapsulation of HPW in the mesoporous cages of MIL-101 due to the good dispersion and anchoring of HPW on EDG-MIL-101. Furthermore, the HPW content incorporated in the as-prepared catalyst was adjusted, and the results showed that among the series of catalysts, the HPW/EDG-MIL-101 catalyst with 40 wt% HPW had the highest SBAC yield and good stability for olefin esterification. The results presented herein provide a facile route for preparing supported HPW with high dispersion and stability to produce high-value SBAC. Acknowledgments
structure. The above factors enhance the olefin esterification performance of these catalysts with the 20–40 wt% HPW loadings. However, when the HPW loading is more than 40 wt%, crystalline agglomeration is aggravated (Fig. 6), and the MIL-101 framework is partially damaged (Fig. 5). As a result, the specific surface area and pore volume decrease dramatically (Table 2), and thereby, the 50 wt% HPW/EDG-MIL-101 catalyst presents unsatisfactory activity for olefin esterification. The reaction stability of optimal 40 wt% HPW/EDG-MIL-101 is investigated in Fig. 8. During the test, the SBAC yield is maintained at 36.70 wt%, indicating the superior activity and stability of this catalyst in the direct esterification of olefins. The yield of SBAC over 40 wt% HPW/EDG-MIL-101 is kept at about 36.65 wt% in three
The authors gratefully acknowledge the financial support of the National Natural Science Foundation of China (Grant Nos. U1162116 and 21076228). Supplementary materials Supplementary material associated with this article can be found, in the online version, at doi:10.1016/j.jtice.2019.03.022. References [1] Hartley WR, Englande AJ, Harrington DJ. Health risk assessment of groundwater contaminated with methyl tertiary butyl ether (MTBE). Water Sci Technol 1999;39:305–10.
206
L. Yan, J. Xu and T. Duan et al. / Journal of the Taiwan Institute of Chemical Engineers 99 (2019) 201–206
[2] Squillace PJ, Zogorski JS, Wilber WG, Price CV. Preliminary assessment of the occurrence and possible sources of MTBE in groundwater in the United States, 1993–1994. Environ Sci Technol 1996;30:1721–30. [3] Nadim F, Zack P, Hoag GE, Liu S. United States experience with gasoline additives. Energy Policy 2001;29:1–5. [4] Hu XN, Li H, Liu LS. Gasoline composition containing sec-butyl acetate with high octane number and preparation method thereof. Chn. Pat, CN102234549A, 2011. [5] Patwardhan AA, Sharma MM. Esterification of carboxylic acids with olefins using cation exchange resins as catalysts. React Polym 1990;13:161–76. [6] Bhattacharyya SK, Lahiri GR. Catalytic esterification of saturated carboxylic acids with ethylene under high pressure. J Appl Chem 1963;13:544–7. [7] Kenichi S, Masaaki N, Toshiro S, Shoichiro W, Kuniaki M. USP 1993(5189201). [8] Dijs IJ, van Ochten HL, van Walree CA, Geus JW, Jenneskens LW. Alkyl sulphonic acid surface-functionalised silica as heterogeneous acid catalyst in the solvent-free liquid-phase addition of acetic acid to camphene. J Mol Catal A Chem 2002;188:209–24. [9] Keggin JF. The structure and formula of 12-phosphotungstic acid. Proc R Soc Lond Ser A 1934;144:75–100. [10] Li H, He L, Lu J, Zhu W, Xue J, Yan W, et al. Deep oxidative desulfurization of fuels catalyzed by phosphotungstic acid in ionic liquids at room temperature. Energy Fuels 2015;23:1354–7. [11] Kukovecz Á, Balogi Z, Kónya Z, Toba M, Lentz P, Niwa SI, et al. Synthesis, characterisation and catalytic applications of sol–gel derived silica–phosphotungstic acid composites. Appl Catal A Gen 2002;228: 83–94. [12] Yan XM, Lei JH, Liu D, Wu YC, Liu W. Synthesis and catalytic properties of mesoporous phosphotungstic acid/SiO2 in a self-generated acidic environment by evaporation-induced self-assembly. Mater Res Bull 2007;42:1905–13. [13] Bigi F, Corradini A, Quarantelli C, Sartori G. Silica-bound decatungstates as heterogeneous catalysts for H2 O2 activation in selective sulfide oxidation. J Catal 2007;250:222–30. [14] Khder AERS. Preparation, characterization and catalytic activity of tin oxide– supported 12-tungstophosphoric acid as a solid catalyst. Appl Catal A Gen 2008;343:109–16. [15] Schwegler MA, Vinke P, Eijk MVD, Bekkum HV. Activated carbon as a support for heteropolyanion catalysts. Appl Catal A Gen 1992;80:41–57. [16] Frusteri F, Arena F, Bonura G, Cannilla C, Spadaro L, Di Blasi O. Catalytic etherification of glycerol by tert-butyl alcohol to produce oxygenated additives for diesel fuel. Appl Catal A Gen 2009;367:77–83. [17] Kozhevnikov IV, Kloetstra KR, Sinnema A, Zandbergen HW, Bekkum HV. Study of catalysts comprising heteropoly acid H3 PW12 O40 supported on MCM-41 molecular sieve and amorphous silica. J Mol Catal A Chem 1996;114:287–98. [18] Sheng X, Zhou Y, Zhang Y, Xue M, Duan Y. Immobilization of 12-tungstophosphoric acid on LaSBA-15 and its catalytic activity for alkylation of o-xylene with styrene. Chem Eng J 2012;179:295–301. [19] Singh S, Patel A. 12-tungstophosphoric acid supported on mesoporous molecular material: synthesis, characterization and performance in biodiesel production. J Clean Prod 2014;72:46–56. [20] Park Y, Shin WS, Choi SJ. Ammonium salt of heteropoly acid immobilized on mesoporous silica (SBA-15): an efficient ion exchanger for cesium ion. Chem Eng J 2013;220:204–13. [21] Long JR, Yaghi OM. The pervasive chemistry of metal-organic frameworks. Chem Soc Rev 2009;38:1213. [22] Andrew Lin KY, Hsieh YT. Copper-based metal organic framework (MOF), HKUST-1, as an efficient adsorbent to remove p-nitrophenol from water. J Taiwan Inst Chem E 2015;50:223–8. [23] Lin KY, Chang HA. Zeolitic Imidazole Framework-67 (ZIF-67) as a heterogeneous catalyst to activate peroxymonosulfate for degradation of Rhodamine B in water. J Taiwan Inst Chem E 2015;53:40–5. [24] Umesh NM, Rani KK, Devasenathipathy R, Sriram B, Liu YX, Wang SF. Preparation of Co-MOF derived Co(OH)2 /multiwalled carbon nanotubes as an efficient bifunctional electro catalyst for hydrazine and hydrogen peroxide detections. J Taiwan Inst Chem E 2018;211:73–81. [25] Granadeiro CM, Barbosa ADS, Silva P, Paz FAA, Saini VK, Pires J, et al. Monovacant polyoxometalates incorporated into MIL-101(Cr): novel heterogeneous catalysts for liquid phase oxidation. App Catal A Gen 2013;453:316–26.
[26] Férey G, Mellotdraznieks C, Serre C, Millange F, Dutour J, Surblé S, et al. A chromium terephthalate-based solid with unusually large pore volumes and surface area. Science 2005;309:2040–2. [27] Hwang YK, Hong DY, Chang JS, Jhung SH, Seo YK, Kim J, et al. Amine grafting on coordinatively unsaturated metal centers of MOFs: consequences for catalysis and metal encapsulation. Angew Chem Int Ed 2008;47:4144–8. [28] Lin Y, Kong C, Chen L. Direct synthesis of amine-functionalized MIL-101(Cr) nanoparticles and application for CO2 capture. Rsc Adv 2012;2:6417–19. [29] Abid HR, Rada ZH, Duan X, Sun H, Wang S. Enhanced CO2 adsorption and selectivity of CO2 /N2 on amino-MIL-53(Al) synthesized by polar co-solvents. Energy Fuels 2018;32:4502–10. [30] Wang T, Song X, Luo Q, Yang X, Chong S, Zhang J, et al. Acid-base bifunctional catalyst: carboxyl ionic liquid immobilized on MIL-101-NH2 for rapid synthesis of propylene carbonate from CO2 and propylene oxide under facile solvent-free conditions. Micropor Mesopor Mat 2018;267:84–92. [31] Yin HQ, Yang J, Yin XB. Ratiometric fluorescence sensing and real– time detection of water in organic solvents with one-pot synthesis of Ru@MIL-101(Al)-NH2 . Anal Chem 2017;89:13434–40. [32] Carson F, Pascanu V, Bermejo GA, Zhang Y, Plateroprats AE, Zou X, et al. Influence of the Base on Pd@MIL-101-NH2 (Cr) as Catalyst for the Suzuki-Miyaura Cross-Coupling Reaction. Chemistry 2015;21:10896–902. [33] Yang J, Zhao Q, Li J, Dong J. Synthesis of metal–organic framework MIL-101 in TMAOH-Cr(NO3 )3 -H2 BDC-H2 O and its hydrogen-storage behavior. Micropor Mesopor Mat 2010;130:174–9. [34] Bauer S, Serre C, Devic T, Horcajada P, Marrot J, Férey G, et al. High-throughput assisted rationalization of the formation of metal organic frameworks in the iron(iii) aminoterephthalate solvothermal system. Inorg Chem 2008;47:7568. [35] Juan-Alcañiz J, Ramos-Fernandez EV, Lafont U, Gascon J, Kapteijn F. Building MOF bottles around phosphotungstic acid ships: one-pot synthesis of bi-functional polyoxometalate-MIL-101 catalysts. J Catal 2010;269:229–41. [36] Fazaeli R, Aliyan H, Moghadam M, Masoudinia M. Nano-rod catalysts: building MOF bottles (MIL-101 family as heterogeneous single-site catalysts) around vanadium oxide ships. J Mol Catal A Chem 2013;374–375:46–52. [37] Luo X, Ding L, Luo J. Adsorptive removal of Pb(II) ions from aqueous samples with amino-functionalization of metal-organic frameworks MIL-101(Cr). J Chem Eng Data 2015;60:1732–43. [38] Ramanathan T, Fisher FT, And RSR, Brinson LC. Amino-functionalized carbon nanotubes for binding to polymers and biological systems. Chem Mater 2011:17. [39] Hu X, Lu Y, Dai F, Liu C, Liu Y. Host–guest synthesis and encapsulation of phosphotungstic acid in MIL-101 via “ bottle around ship ”: an effective catalyst for oxidative desulfurization. Micropor Mesopor Mat 2013;170:36–44. [40] Zang Y, Shi J, Zhao X, Kong L, Zhang F, Zhong Y. Highly stable chromium(III) terephthalate metal organic framework (MIL-101) encapsulated 12-tungstophosphoric heteropolyacid as a water-tolerant solid catalyst for hydrolysis and esterification. React Kinet Mech Cat 2013;109:77–89. [41] Liu Z, Chen Y, Sun J, Lang H, Gao W, Chi Y. Amine grafting on coordinatively unsaturated metal centers of MIL-101 Cr for improved water absorption characteristics. Inorg Chim Acta 2018;473:29–36. [42] Cowan JJ, Bailey AJ, Heintz RA, Bao TD, Hardcastle KI, Hill CL, et al. Formation, isomerization, and derivatization of Keggin tungstoaluminates. Inorg Chem 2001;40:6666–75. [43] Tsukuda E, Sato S, Takahashi R, Sodesawa T. Production of acrolein from glycerol over silica-supported heteropoly acids. Catal Commun 2007;8:1349–53. [44] Hoo PY, Abdullah AZ. Direct synthesis of mesoporous 12-tungstophosphoric acid SBA-15 catalyst for selective esterification of glycerol and lauric acid to monolaurate. Chem Eng J 2014;250:274–87. [45] Xie W, Yang X, Hu P. Cs2.5 H0.5 PW12 O40 encapsulated in metal-organic framework UiO-66 as heterogeneous catalysts for acidolysis of soybean oil. Catal Lett 2017;147:1–11. [46] Dias JA, Osegovic JP, Drago RS. The solid acidity of 12-tungstophosphoric acid. J Catal 1999;183:83–90. [47] Schwegler MA, Vinke P, van der Eijk M, van Bekkum H. Activated carbon as a support for heteropolyanion catalysts. Appl Catal A Gen 1992;80:41–57. [48] Gee JC, Fisher S. Direct esterification of olefins: the challenge of mechanism determination in heterogeneous catalysis. J Catal 2015;331:13–24.