Stable and recyclable MIL-101(Cr)-Ionic liquid based ...

Journal of Molecular Liquids 236 (2017) 385–394

Contents lists available at ScienceDirect

Journal of Molecular Liquids journal homepage: www.elsevier.com/locate/molliq

Stable and recyclable MIL-101(Cr)–Ionic liquid based hybrid nanomaterials as heterogeneous catalyst Hassan M.A. Hassan a,⁎, Mohamed A. Betiha b,⁎, Shaimaa K. Mohamed a, E.A. El-Sharkawy a, Emad A. Ahmed a a b

Department of Chemistry, Faculty of Science, Suez University, Suez, Egypt Egyptian Petroleum Research Institute, Cairo 11727, Nasr City, Egypt

a r t i c l e

i n f o

Article history: Received 27 January 2017 Received in revised form 9 April 2017 Accepted 11 April 2017 Available online 13 April 2017 Keywords: Solid acid catalyst MIL-101 Ionic liquid Esterification Friedel–Crafts Acylation Acidity

a b s t r a c t Brönsted acidic ionic liquid, N-methyl-2-pyrrolidonium methyl sulfonate ([NMP]+ CH3SO− 3 ) immobilized on MIL-101(Cr) was fabricated by simple impregnation method with a good combination of MIL-101(Cr) and IL species. The worthiness of IL/MIL-101(Cr), as a Brönsted acid catalyst, has been examined for the esterification of acetic acid with amyl alcohol and Friedel–Crafts acylation of anisole. Our findings demonstrated that IL/MIL101(Cr) catalyst exhibited distinct catalytic activity with respect to the other catalysts towards the esterification reaction and Friedel–Crafts acylation of anisole. The Brönsted acidic catalysts loaded on MIL-101(Cr) as a new category of porous materials are probably auspicious heterogeneous catalysts for acid-catalyzed to replace the use of traditional homogeneous catalysts. Furthermore, the catalyst can be easily removed from the reactions mixtures and reuse for posterior reactions, more than six times without any considerable decay in catalytic performance. © 2017 Elsevier B.V. All rights reserved.

1. Introduction For assorted applications, such as adsorption, membrane science, and catalysis, acid catalysts are abundantly under-exploited in the chemical industry [1]. Mineral acids as homogeneous catalysts usually have high catalytic activity, however, they have many disadvantages as side reactions, corrosion and huge amounts of harmful wastes, which can cause environmental problems [2]. Recently, the reusable rigid acidic catalysts became much significant due to their prospect to substitute harmful homogeneous acidic catalysts in industrial operations [3,4]. Acidic heterogeneous catalyzing agents can be effectively isolated from the reaction blend by filtration or centrifugation and don't require any special treatments, consequently giving an ecologically favorable process and decreasing the expense of handling [5]. Another favorability of the heterogeneous catalyst is the reusability [6,7]. The field of metal–organic frameworks (MOFs), a new category of porous materials self-assembled from metal ions or clusters and polytopic rigid organic linkers, has provided a good candidate for catalytic applications owing to (i) effective framework in comparison with other micro- and mesoporous materials. (ii) Well-defined channels with a tunable pore size that able to accommodate various species with different sizes and shape. (iii) MOF backbone can be incorporated ⁎ Corresponding authors. E-mail addresses: [email protected] (H.M.A. Hassan), [email protected] (M.A. Betiha).

http://dx.doi.org/10.1016/j.molliq.2017.04.034 0167-7322/© 2017 Elsevier B.V. All rights reserved.

with multiple metals and/or organic linkers (multivariate (MTV) functionalization), leading to possible functional sites of unique distribution within the pores while the original structure is retained [8–12]. Recently, several strategies for acid sites functionalizing MOFs have been introduced, including post-synthesis and metal encapsulation to tuned framework through coordination bonds between metal center and Lewis or base guests [13], post framework sulfonation, amination, N-substituted aminosulfonic acids and encapsulation of heteropolyacids [14–16]. In spite of these promising approaches, the development of general and facile methods to introduce more sites within MOFs remains a challenge. Today, an ionic liquids (ILs) as environmental-friendly acidic catalysts have received wide attention because of their unique characteristics likes considerable solubility, negligible volatility, non-flammable, non-corrosive and remarkable thermal stability. Ionic liquids (ILs) are defined as salt with a melting point lower than the boiling point of water. Typically, ILs are composed of organic onium cations and inorganic anions. Additionally, the solubility of ionic liquids in various reaction media can be controlled and easily fine-tuned by changing of both cations and anions [17–24]. Ionic liquids (ILs) have emerged as alternative solvents for various organic syntheses and attracted increasing attention for various catalytic applications. However, there are some drawbacks in the catalytic field such as limited solubility in organic compounds (especially polar molecules), causing not only the loss of catalytic efficiency but also resulted in the difficulty of purification due

386

H.M.A. Hassan et al. / Journal of Molecular Liquids 236 (2017) 385–394

2.2.2. Synthesis of N-methyl-2-pyrrolidonium methyl sulfate (IL) The Brønsted acidic IL (N-methyl-2-pyrrolidonium methyl sulfonate, ([NMP]+ CH3SO3]) was prepared (Scheme 1) as described elsewhere [31] with slight modification. Typically, 9.9 g of N-methyl-2-pyrrolidone (0.1 mol) was stirred with (15 ml) ethyl acetate in a 50 ml round flask. After that, 9.6 g of methane sulfonic acid (0.1 mol) in 15 ml ethyl acetate was added dropwise within 30 min in an ice bath. The reaction continued for extra 4 h at ambient temperature. Finally, ethyl acetate was taken away under diminished pressure at 80 °C till the initial volume added.

to the high viscosity of the reaction media. Among attempts have been made to overcome these problems is immobilization the ILs on solid porous materials such as crosslinked polystyrene-divinylbenzene [24], mesoporous materials [7] and Fe3O4 nanoparticles [25]. Indeed, utilization of immobilized acidic ionic liquids (ILs) on robust backings as heterogeneous catalysts displays many advantages other than the use of acidic ILs directly. Such immobilization may lead to boost the available effective sites on the catalyst surface and reduces the used amount of ILs. The ionic liquid layer on the support surface acts as a homogeneous medium for the catalyzed processes however the catalyst macroscopically seems solid, consequently it is easily separated from the medium [2]. Despite the fact that there are abundant future prospects to apply MOFs as solid supports for ILs, ILs/MOFs composites showed considerable properties owing to the nanosizing of ILs than the bulk ionic liquid that showed the usual melting or freezing characteristics [26]. Thus, it is very interesting and significant to prepare and explore for the first time the application of chemically confinement ILs-MOFs for catalysis. As a prevalent Acidic catalyzed model reaction, Esterification is a standout among the most connected reactions in organic chemistry, with the hugeness in the synthesis of fragrances, polymers, and paints [27]. As well, Friedel–Crafts acylation of aromatics is a critical process, which is typically utilized as a part of fine synthetic, pharmaceutical commercial projects polymers, and paints, etc. [28]. Herein, we demonstrate how to chemically incorporate highly Brønsted acidic IL, N-methyl-2-pyrrolidonium methyl sulfonate, into porous MIL-101(Cr) to avoiding leaching of ILs through grafting the IL into the residual terephthalic species coordinated to CUS (coordinatively unsaturated metal sites) in MIL-101(Cr) by simple impregnation method under ambient conditions as a significant heterogeneous and economically acidic catalyst for esterification and Friedel–Crafts acylation reactions.

2.2.3. Synthesis of IL/MIL-101(Cr) catalysts The impregnation reaction encapsulation technique was used to encapsulate N-methyl-2-pyrrolidonium methyl sulfonate IL onto MIL101(Cr) framework. In a typical synthesis, 2.0 g of IL was diluted with 10 times volume of ethyl acetate was added to 1 g of MIL-101(Cr) suspended in 10 ml ethyl acetate under stirring for 4 h at 45 °C. Then, the solvent was removed under vacuum at 80 °C and stirring of 150 rpm. The obtained gel was extracted in Soxhlet extractor using ethanol/toluene (1:1) as co-solvent, and the weight of the obtained solid was determined to explore the maximum capacity of MIL-101(Cr). To maximize the ratio of IL occluded in MIL-101(Cr) pores, different loading of IL behind maximum capacity are prepared and donated as X% MIL-101(Cr) where X (5, 10, 15, 20) indicates the percent ratio of the ionic liquid on MIL-101(Cr). The elemental composition based C, N, H % only for MIL-101(Cr): C, 43.00; H, 2.26%, while after grafting the IL become C, 42.73; H, 2.46; N, 0.32% (5% IL/MIL-101(Cr)), C, 42.44; H, 2.67; N, 0.65% (10% IL/MIL-101(Cr)), C, 42.17; H, 2.87; N, 0.98% (15% IL/MIL101(Cr)) and C, 41.96; H, 3.02; N, 1.23% (20% IL/MIL-101(Cr)). Consequently, the real grafting percent after Soxhlet extraction is of 4.6, 9.2, 13.7, and 17.2% for 5, 10, 15 and 20% IL/MIL-101(Cr), respectively.

2. Experimental

2.3. Characterization

2.1. Chemicals

X-ray diffraction patterns were recorded by means of X'PERT X-ray diffractometer, equipped with Cu-kα radiation (40 kV, 40 mA) (λ = 1.5406 Å). The diffractogram is in the 2θ range of 4 to 20°, with a scanning speed of 2° in 2/min. For the FT-IR spectra, a KBr disk containing the sample was prepared and scanned from 4000 to 500 cm−1 using (Shimadzu FT-IR, Japan). The nitrogen physisorption isotherms and the specific surface area were measured at − 196 °C using the Quantachrome Autosorb iQ MP gas sorption analyzer. Prior to the analysis, the samples were degassed at 150 °C for 12 h. Transmission electron microscopy (TEM) images were taken using a JEOL JEM-2010 electron microscope operating at 200 kV. The surface electronic states of the prepared catalysts were characterized by XPS (X-ray photoelectron spectroscopy) on ESCALAB 250 spectrometer. The acidity measurement of the samples was investigated using potentiometric titration [32,33].

All the used chemicals in this work were of analytical grade and used as received without further purification. Chromium (III) nitrate nonahydrate (Cr(NO3)3·9H2O, 99%), hydrofluoric acid (HF, 48%), Nmethyl-2-pyrrolidone (C5H9NO, 99.5%), 1-pentanol (CH3(CH2)4OH, 99%), acetic acid, (CH3CO2H, 99%), anisole (CH3OC6H5, 99.7%), acetic anhydride ((CH3CO)2O, 99.5%) and toluene (C6H5CH3, 99.5%) were taken up from Sigma–Aldrich Chemicals. Methane sulfonic acid (CH3SO3H, 99%), ammonium fluoride (NH4F, 98%), terephthalic acid (TPA, 98%), ethanol (CH3CH2OH, 99%), and ethyl acetate (CH3COOC2H5, 99%) were purchased from ACROS Organics. 2.2. Synthesis 2.2.1. Synthesis of MIL-101(Cr) Hydrothermal synthesis of MIL-101(Cr) from Cr(NO3)3.9H2O, TPA and deionized water was in accordance with a described procedure [29]. Typically, a Cr(NO3)3·9H2O (6.0 g), terephthalic acid (3.76 g) and HF (0.75 ml) were dissolved in 75 ml of H2O in Teflon beaker, then introduced into 150-ml Teflon-line autoclave. The mixture was then heated in an oven at 220 °C for 8 h. By the end of the reaction, the temperature lowered to the ambient temperature, and the developed green-colored powder was obtained by filtration to remove the excess recrystallized terephthalic acid. The MIL-101(Cr) was first activated by suspending into 300 ml water with stirring for 5 h at 70 °C and then separated using a fine pore fritted glass filter followed by drying at 150 °C on standing overnight to take out powdered MIL-101(Cr) [30]. The second activation for the same sample was carried out by soaking the sample in 150 ml 30 mM NH4F and stirred for 10 h at 60 °C. Finally, the solid product was separated by filtration and washed with hot water and then vacuum dried at 80 °C for 12 h.

2.4. Catalytic performance 2.4.1. Esterification reaction The esterification reaction was carried out using a certain percent of catalyst (1, 3, 5 and 10%). Typical, a mixture of acetic acid and amyl alcohol (1:1) were stirred and heated to achieve the reaction temperature (30, 60, 80 and 100 °C). The activated catalyst was then added, and the mixture was stirred for 1 h. The reaction mixture was then collected and analyzed using GC (Varian Technologies, model 3800 GC, capillary column DHA-100). 2.4.2. Friedel–Crafts acylation Friedel–Crafts acylation of anisole with acetic anhydride was carried out by mixing (20 mmol) anisole, (5 mmol) acetic anhydride followed by magnetically stirred and heated to achieve the reaction temperature (80–120 °C). Then activated catalyst (5 wt%) was added and the


387

Scheme 1. Schematic representation of synthesis of IL/MIL-101(Cr) catalyst.

3. Results and discussion 3.1. XRD analysis of IL/MIL-101(Cr) catalyst Powder X-Ray diffraction (PXRD) analysis was performed to investigate the structural benignity of the parent MIL-101(Cr) after loading with IL species. As shown in Fig. 1, the PXRD pattern of MIL-101(Cr) sample perfectly agreed with that previously cited PXRD pattern [11, 34], confirming the successful preparation of pure MIL-101(Cr). It is also worth mentioning that the PXRD patterns of IL/MIL-101(Cr) are closely similar to that of the parent MIL-101(Cr) although the intensity of the diffraction peak becomes slightly broader and weaker, indicating the crystal structure of the MIL-101(Cr) remained unchanged after the loading of the IL species. 3.2. FT-IR and XPS characterization of IL/MIL-101(Cr) catalyst FT-IR studies were performed to check whether the MIL-101(Cr) structures were unaltered after loading with IL species. FT-IR spectra of the pure MIL-101(Cr), pure IL species and 20%IL/MIL-101(Cr) samples are presented in Fig. 2a. Inspection of such FTIR spectra revealed that the main spectral features of MIL-101(Cr) could be obviously observed even the loading with 20% IL. The representative diagnostic bands correspond to the framework \\(O\\C\\O)\\ groups around 1550 and 1423 cm−1 as reported by Ferey et al. [29] are observed. Moreover, bands at 1017 and 749 cm−1 assigned to δ(C\\H) and γ(C\\H) vibrations of the aromatic rings, respectively. The weak bands in the region of 700–400 cm− 1 are assigned to both In-plane and out-ofplane bending modes of the COO-groups [34,35]. On the other hand, IL species shows five characteristic bands at 1658, 1200, 1000–750, 1056 and 780 cm−1 which are due to C_O, S_O, S\\O, C\\N, and C\\H inplane and out of plane stretching vibration, respectively, of IL species.

It is clear that the band at 1658 cm−1 is shifted to lower wavelength by 25 cm−1, indicating an interaction between C_O of IL and CUS of Cr(III) of MIL-101(Cr). These features of the IL confirm the loading and stability of the IL species within the MIL-101(Cr) framework. In addition, the MIL-101(Cr) framework was unaltered by the loading of IL, and further confirmation of this was obtained from (PXRD) measurements. Therefore it was significant to recognize which form of IL was obtained within MIL-101(Cr) by XPS technique. The XPS spectrum of Cr2p for 20%IL/MIL-101(Cr) material is shown Fig. 2b. Two peaks at 577.4 and 587.2 eV due to Cr2p1/2 and Cr2p3/2 signals, however, the value of these signal appeared in high value [35], suggesting the flow

20% IL/MIL-101

15% IL/MIL-101

Intensity (a.u.)

mixture stirred for 1 h at the required temperature. After the reaction completion, the catalyst was separated from the reaction temperature by centrifugation. Finally, the reaction mixture was analyzed using GC–MS (HP GCD system equipped with EID). The conversion was calculated depending on the gas chromatographic analysis of the remaining acetic anhydride.

10% IL/MIL-101

5% IL/MIL-101

MIL-101

4

6

8

10

12

14

16

18

20

2θ Fig. 1. XRD patterns of bare MIL-101(Cr) and IL/MIL-101(Cr) catalysts with 5–20 wt% IL species.

388

H.M.A. Hassan et al. / Journal of Molecular Liquids 236 (2017) 385–394 1000

(a)

MIL-101 5% IL/MIL-101 10% IL/MIL-101 15% IL/MIL-101 20% IL/@MIL-101

20% IL/ MIL-101(Cr)

Volume adsorbed (cc/g)

% transimitance (a.u.)

800

MIL-101(Cr)

IL

600

400

200

2000

1800

1600

1400

1200

1000

800

600

400 0

wavenumber cm-1

0.0

0.2

0.4

0.6

0.8

1.0

P/Po

Relative intensity

(b)

Fig. 3. Nitrogen adsorption-desorption isotherms at −196 °C for bare MIL-101(Cr) and IL/ MIL-101(Cr) catalysts with 5–20 wt% IL species (full ads., empty des.).

N1

3.3. Surface area and porosity of IL/MIL-101(Cr) catalyst

397

398

399

400

401

402

403

284

286

288

290

292

294

Relative intensity

C1S

Relative intensity

282

570

Cr2p1/2 Cr2p3/2

575

580

585

590

Binding energy (eV) Fig. 2. (a) FTIR spectra of bare MIL-101(Cr), IL species and 20% IL/MIL-101(Cr). (b) XPS spectra of 20% IL/MIL 101(Cr).

The consequences of the sorption measurements of the MIL-101(Cr) and IL/MIL-101(Cr) samples with different loading percentages on MIL101(Cr) are depicted in Fig. 3. Literature values of Cr-MIL-101 compounds are given for comparison [36]. The obtained SBET and pore size distribution values of the prepared Cr-MIL-101 fall within the range of values of previously reported literature. The relatively low surface area may be due to the presence of small amount of impurities. MIL101(Cr) exhibited Type I isotherm with secondary uptake at P/P0 ∼ 0.1 and P/P0 ∼ 0.2, indicating the presence of microporosity according to IUPAC classification of adsorption isotherms [37]. In all isotherms, two-characteristic curve stage is observed, resulting from the N2-filling of two different size cages [38]. The major adsorption of N2 in the adsorption isotherms occurred at low relative pressure (i.e., P/P0 ≈ 0.08). It was reported that the MIL-101(Cr) had two types of microporous cages; the smaller one possessed pentagonal windows with a diameter of 1.2 nm while the larger cage contained pentagonal– hexagonal windows with a diameter in the range of 1.45–1.60 nm. Hence, a secondary adsorption step in the range of 0.1 b P/P0 b 0.2 arose by these two types of microporous windows [29]. The IL/MIL101(Cr) also showed this secondary adsorption near P/P0 ≈ 0.12. The adsorption of nitrogen in the low-pressure regime by IL/MIL-101(Cr) was more than that of the virgin one. This suggested that the embedding of the IL species within the MIL-101(Cr) pores up to 20 wt% provided additional micropores in its framework. Moreover, the IL/MIL-101(Cr) samples with different IL contents showed the same isotherm shape further confirming that the original pores structure of MIL-101(Cr) was very well unchanged after IL loading. The summarized textural parameters of the synthesized materials including the virgin MIL-101(Cr) are cited in Table 1. The surface area and total pore volume decreased with increasing loading percentage of the IL species, which may indicate

Table 1 Texture and acidic properties of pure and IL-loaded MIL-101(Cr) catalysts.

of electron density towards the Cr3 + atom. The XPS spectrum of C1S displayed three peaks at 284.6, 286.7 and 288.4 eV, corresponding to phenyl, C\\N\\C, and C_O signals, respectively. The N1S peak of nitrogen atom showed two peaks at 399.9 and 401.7 eV corresponding to protonated amine and amine enol form (C_N+), indicating interaction of IL through oxygen atom with CUS of MIL-101(Cr), which is in good agreement with FTIR results.

Sample

Acid amount BET surface area Pore volume Ei (ccg−1) (mV) (mmol n-butylamine g−1) (m2 g−1)

MIL-101 5%IL/MIL-101 10%IL/MIL-101 15%IL/MIL-101 20%IL/MIL-101

2348 2049 1857 1696 1587

1.32 0.93 0.89 0.78 0.64

27 121 236 256 469

0.14 0.26 0.38 0.56 0.98


389

500

MIL-101(Cr) 5% IL/MIL-101(Cr) 10% IL/MIL-101(Cr) 15% IL/MIL-101(Cr) 20% IL/MIL-101(Cr)

450 400 350

E (mV)

300 250 200 150 100 50 0 0

0.2

0.4

0.6

0.8 1 1.2 V (ml) n-butylamine added

1.4

1.6

1.8

2

Fig. 5. Potentiometric titration curves of n-butyl amine in acetonitrile for bare MIL-101(Cr) and IL/MIL-101(Cr) catalysts with 5–20 wt% IL species.

crystal exhibits cubic shape. As also evident from Fig. 4, the crystal structure of the support material remained unaltered after loading of the IL species into the surface, which is consistent with PXRD patterns (Fig. 1). 3.5. Surface acidity measurements Potentiometric titration investigated the surface acidity of the bare MIL-101(Cr) as well as various loaded IL/MIL-101(Cr) samples with nbutylamine. The relative strength and the total number of acid sites present in the solids can be estimated adopting this technique. The value of meq amine/g solid, where the plateau is reached, represents the total number of acid centers. While the initial electrode potential (Ei) demonstrates the maximum acid sites strength. Accordingly, the acid strength of these sites may be ranked according to the following scale: Ei N 100 mV (very strong sites), 0 b Ei b 100 mV (strong sites), − 100 b Ei b 0 mV (weak sites) and Ei b − 100 mV (very weak sites) [39,40]. Fig. 5 depicts the titration curves of the prepared catalysts, where the total number of acid sites/g catalyst and the initial electrode potential (E i ) was summarized in Table 1. It was observed, the pure MIL-101(Cr) presented strong acid sites, Ei = 27 mV, while loading of IL species has a significant increase in both surface acidity and acid strength. With further increase of IL contents up to 20 wt% IL, an increase in surface acidity and acid strength (Ei = 469 mV) was observed. The observed increase in the acidity as due to the increase in IL species content from 5 to 20% is quite expected, simply, because IL did presumably act as the acid site constituents of the examined systems. Thus, such increase in the IL content has actually reflected the increase in the concentration of the acidic centers. 3.6. Catalytic activity of IL/MIL-101(Cr) in esterification reaction

Fig. 4. TEM images of (a) pure MIL-101(Cr) (b) 10% IL/MIL-101(Cr) (c) 20% IL/MIL-101(Cr).

the partial pore clogging of the porous structure of MIL-101(Cr) framework by the ionic liquid species. 3.4. TEM characterization of IL/MIL-101(Cr) catalyst Fig. 4 displays typical TEM images of pure MIL-101(Cr) and IL/ MIL-101. Based on the TEM observation, the pure MIL-101(Cr)

In several South American countries, biofuel ethanol is established from sugar cane fermentation [41]. There are considerable byproducts generated from this process, among them the so-called fusel oil. The fusel oil is a complex mixture consists mainly of isoamyl alcohol (N60 wt/wt%) and water and has received increasing awareness for its conversion to more valuable products [42,43]. The amyl acetate is widely used in the food, pharmaceutical, perfumery industry and as a green solvent. The catalytic performance was investigated towards the formation of amyl acetate from acetic acid and amyl alcohol using IL/MIL-101(Cr) as

390


(a)

80

(b)

Yield %

75

70

65

60

1.0

1.5

2.0

2.5

3.0

3.5

4.0

4.5

5.0

Reaction time/h 80

(d)

(c)

84

75

Yield %

82

Yield %

80 78

70 65 60

76 74

55

72

50 0

2

4 6 8 Amount of catalyst (%)

10

12

30

45

60 75 Temperature (oC)

90

105

Fig. 6. Optimum conditions of the catalytic activity of IL/MIL-101(Cr) catalysts on pentyl acetate yield: influence of IL content in IL/MIL-101(Cr) catalyst (a), influence of reaction time over 20% IL/MIL-101(Cr) (b), influence of catalyst (20% IL/MIL-101(Cr)) dose (c), influence of reaction temperature (d).

the catalyst in a batch-type process, which proceeds as described in the following equation:

comparison to the others. The reaction in amyl alcohol esterification proceeded more efficient, and this may be attributed to the more alteration of pores hydrophobicity caused by the N-methyl-2-pyrrolidonium methyl sulfonate that enhances the diffusibility of amyl alcohol within the MIL-101(Cr) pores to reach the catalytic acid centers within pores, and revealed that the catalytic conversion occurred inside the MIL101(Cr) pores.

Influence of various operating condition such as IL content, reaction time, catalyst amount and reaction temperature were studied for optimization the reaction conditions by the utilization 20% IL/MIL-101(Cr) as a model catalyst.

3.6.2. Effect of the reaction time The influence of the reaction time on the amyl acetate yield percentage was studied over 1% of 20% IL/MIL-101(Cr) at 100 °C using acetic acid to amyl alcohol 1:1. The results obtained are shown in Fig. 6b. A gradual increase in the yield percentage of amyl acetate with increase the reaction time can be observed. The yield percentage of amyl acetate was observed as (66, 71, 72, 75.05 and 75%) after (1, 2, 3, 4 and 5 h) respectively. Therefore, no clear effect on the yield percentage of amyl acetate was observed on further increase in the reaction time N 4 h. This suggests that 4 h is the optimum reaction time to be sufficient to attain the equilibrium.

3.6.1. Effect of the ionic liquid (IL) content The change in the yield percent of amyl acetate as a function of IL content was graphically represented in Fig. 6a. The reaction was carried out over 1% catalyst amount at 100 °C using acetic acid to amyl alcohol 1:1. A control experiment was performed to earn more insight about the esterification mechanism. The results of the yield percent of the esterification reaction between acetic acid and amyl alcohol in the presence of pure MIL-101(Cr) showed almost no activity in the esterification, which is likely owing to the absence of Brönsted acid sites. While MIL101(Cr) loaded with different amounts of IL species showed significantly increased in the yield percentage of amyl acetate, attain the maximum activity of 75% yield for 20% IL/MIL-101(Cr). Recently, S.K. Abd El Rahman et al., [11] investigated the esterification reaction between acetic acid and n-butanol over 0.05 g HPW/MIL-101(Cr) catalyst at 120 °C for 1 h. The results revealed that the sample 70 wt% HPW/MIL101(Cr) exhibited 92.3% conversion with 100% selectivity. Also, JuanAlcañiz et al., [41] showed that the esterification over HPW loaded MIL-101 at 110 °C exhibited 60% conversion for 5 h. Moreover, sulfonic acid functionalized MIL-101 showed an excellent yield of butyl acetate (99.5%) after 2 h [44]. These results demonstrate that our catalysts possess incentive catalytic performance under the reaction conditions in

3.6.3. Effect of the catalyst amount In order to investigate the effect of catalyst amount on the amyl acetate yield, a set of esterification experiments with various weight percent (1, 3, 5 and 10% based on the weight of both acetic acid and amyl alcohol) of 20% IL/MIL-101(Cr) catalyst were conducted at 80 °C for 4 h using acetic acid to amyl alcohol 1:1. The yield percentage of amyl acetate as a function of catalyst amount (%) are shown in Fig. 6c. On the basis of the results pertaining to the assessment of the relative contribution of catalyst amount on the catalytic performance, one is inclined to forward that, the yield percentage increased with an increase in the catalyst amount up to 5%. Such increase would indicate that the number of Brönsted acid sites was increased. An additional increase in the catalyst amount up to 10% no significant changes in the yield percent were observed. Therefore, 5% is the optimum IL/MIL-101(Cr)


391

Table 2 Comparison of catalytic performance of various catalysts in the esterification reaction. Catalyst

Reaction conditions

Conversion References %

[NMP]+ CH3SO− 3

1-Butanol (7.4 g, 0.1 mol), equivalent acetic acid (6 g, 0.1 mol) and [NMP]+ CH3SO3 (5 g, 0.025 mol) at 100 °C for 4h Esterification of acetic acid with n-butanol (molar ratio 1:1) at 110 °C with 3 g of catalyst per mol of acetic acid for 5h The reaction was carried out over 0.05 g catalyst at 120 °C for 1 h using acetic acid to n-butanol molar ratio 1:1. 0.2 g of catalyst, 0.1 mol of n-hexanol, and 0.1 mol of acetic acid at 110 °C for 6 h Esterification of n-butanol and acetic acid (1:1 M fraction) using 3 g of the catalyst (specified in the graph) per mole of reactant at 70 °C for 375 min. 0.3 g of catalyst, 0.1 mol of n-hexanol, and 0.1 mol of acetic acid at 110 °C for 5 h. 0.3 g of catalyst, 0.1 mol of n-hexanol, and 0.1 mol of acetic acid at 110 °C for 5 h. 5% catalyst with mixture of acetic acid and pentanol (1:1), the reaction temperature (80 °C), for 4 h.

97

[31]

60

[41]

92.3 58.3 40

[42] [45] [45]

44.2 65.1 82.4

[46] [46] Present work

MIL-101(Cr) with 20 wt% POM encapsulated 70 HPW/MIL-101 HPW/MIL-101 HSO3-MIL-101(Cr) HCl S/MIL-101 S-MIL-101 20%IL/MIL-101

amount for the esterification of acetic acid to amyl acetate under the current reaction conditions. 3.6.4. Effect of reaction temperature The influence of reaction temperature on the yield percent of amyl acetate was studied by varying the reaction temperature between 30 and 100 °C as shown in Fig. 6d, using 1% catalyst (20% IL/MIL-101(Cr)) conducted for 4 h using acetic acid to amyl alcohol 1:1. Inspection of Fig. 6d showed that, increase the esterification temperature from 30 to 80 °C resulted in a significant increase in the yield percentage of amyl acetate from 50 to 72%. However, the esterification reaction remains almost unaltered with further increase the temperature up to 100 °C. At higher temperature, the viscosities of the reaction mixture were decreased result in an increase in the reaction rate as more energy is being supplied for the reaction to occur. Thus, the yield of the ester product is enhanced. Additionally, the boiling point of N-amyl alcohol is 137 to 139 °C. Temperature higher than this will burn the alcohol and will result in much lower yield [43]. Consequently, we have considered 80 °C as the proper reaction temperature for amyl acetate formation. Table 2, presents a brief comparison of some catalytic activity data collected from different published papers [11,31,41,45,46] of various catalysts for esterification reaction using different catalysts taking

into consideration the reaction conditions. Summing up, the reported results within the frame of present work do reflect that porous MOFs, supported with ionic liquids as (IL/MIL-101) offers a new, exciting opportunities for the heterogeneous esterification reaction.

3.6.5. Reaction mechanism Although a detailed reaction mechanism of homogeneously catalyzed liquid phase esterification is well known [47], there still no focusing on the heterogeneously catalyzed gas phase reaction. Chu et al. [48] studied the esterification reaction of n-butanol with acetic acid by dodecatungstosilicic acid immobilized on activated carbon as acidic catalyst. Accordingly, the results showed that the esterification mechanism takes place through the protonation of the alcohol as an intermediate. However, most of the articles are focusing on the protonation of the carboxylic acid as the reaction intermediate. Therefore, based on those reports, the esterification mechanism proceed via the protonation of acetic acid by a proton donated from Brönsted acid sites, IL/MIL101(Cr) surface, forming protonated carboxylic acid intermediate, as shown in Schemes 2. This protonated intermediate then interacts with amyl alcohol generating the corresponding ester, amyl acetate, and water.

Scheme 2. Reaction mechanism for the esterification of amyl alcohol with acetic acid over Brönsted acid sites.


90 80 70 60 50 40 30 20 10 0

90

(a)

(a)

80 70 60

Conversion %

Conversion%

392

50 40 30

1st

2nd 3rd 4th 5th Number of Cycles

6th

5%IL /mil-101 10%IL /mil-101 15%IL /mil-101 20%IL /mil-101

20 10

(b)

0

20

40

60

80

100

120

140

160

180

200

Time, min 90

(b)

80

79.8

78.07 67.54

70

Conversion %

60 50 40 30

26.04

80

(c)

With catalyst After filtration

20 10

Conversion %

75

0 20

30

40

50

60

70 80 90 o Temperature, C

100

110

120

130

70

(c)

80 70

65

60 30

60

90

120

150

180

210

240

Reaction time, min Fig. 7. (a) Recycling ability of 20% IL/MIL-101(Cr) catalyst in amyl acetate yield (b) TEM image of 20% IL/MIL-101(Cr) catalyst after the 6th run (c) hot filtration test for 20% IL/ MIL-101(Cr) catalyst in amyl acetate yield.

3.6.6. Catalyst recycling and hot filtration test The most distinct features of heterogeneous catalysts over homogeneous catalysts is the ability to separating the catalyst from the reaction mixture and reuse it for subsequent reactions until the catalyst is sufficiently deactivated. The stability of the catalyst, 20% IL/MIL-101 was conducted at 80 °C utilizing 5% of catalyst amount and reactant molar ratio 1:1. After each esterification run, the reaction products were separated followed by detection of the yield % of amyl acetate by means of GC. The catalyst was dried and directly transferred to the fresh reaction mixture for the next runs. The results revealed that 20% IL/MIL-101 catalyst exhibited outstanding reusability with slight activity loss as compared with the first run (Fig. 7a). The slight decrease in the catalytic activity may due to the minor catalyst loss during the separation process along with the possibility of partial deactivation of ionic liquid species ([NMP]+ CH3SO3 −) [49]. We examined the leaching behavior of the

Conversion %

60 50 40 30 20 Anisole Benzaldehyde

10 20

40

60

80 100 o Temperature ( C)

120

Fig. 8. Friedel–Crafts acylation of anisole with acetic anhydride: influence of IL content in IL/MIL-101(Cr) catalyst (a) influence of reaction temperature over 20% IL-MIL-101(Cr) (b) effect of different substrate (c).

used catalyst after six repetitive catalytic runs by TEM as shown in Fig. 7b. As demonstrated in Fig. 7b, the IL leaching little impact on the reduction of catalyst activity during the recycling process. Other fascinating features of the original and recovered IL/MIL-101 catalysts include the stability of the catalyst since identical XRD patterns before and after catalysis (not shown). These results confirm that the crystal structure of MIL-101 did not change after the ionic liquid loading as the


393

Table 3 Comparison of catalytic performance of various catalysts in the Friedel–Crafts acylation. Catalyst

Reaction conditions

Conversion References %

Hierarchical ZSM-5 HPW/MCM-41 (60% loading) Nanocrystalline ZSM-5 of 90-nm particle sizes HPA/SiO2 HPW/SiO2 40% Beta zeolites (βS, nano-sized) H-BEA/SiC 20%IL/MIL-101

0.2 g of catalyst, 125 mmol of anisole, and 25 mmol of acetic anhydride at 70 °C, for 70 min. 0.1 g of catalyst, 20 mmol of anisole, and 5 mmol of acetic anhydride at 120 °C, for 1 h.

80 44.2

[50] [51]

0.2 g of catalyst, The mole ratio of anisole to acetic anhydride was 8:1, at 100 °C, for 5 h

66.2

[52]

170 mg of catalyst An anisole to acetic anhydride ratio of 10:1 at 90 °C for 250 min. 0.5 g of catalyst, 2.31 mmol of anisole, 97.5 mmol acetic anhydride. at 83 °C for 250 min.

65 80

[53] [54]

The reaction was carried out in a fixed bed reactor at 120C and 3.7 MPa (the initial molar ratio of anisole/acetic anhydride is 5 and the weight hourly space velocity is 10 h−1). 2 g of catalyst, 6 mmol of anisole, 3 mmol acetic anhydride at 120 °C for 5 h 5% catalyst with mixture of anisole and acetic anhydride of molar ratio 1:1, at 80 °C, for 1 h.

93

[55]

87 78.9

[56] Present work

diffraction peaks of the MIL-101 are retained for all the IL-loaded samples. Therefore, this catalyst exhibited significant performance for esterification reaction, and this gives the catalyst promising in industrial scale. In order to emphasize the heterogeneous nature of esterification reaction using IL/MIL-101(Cr) as a catalyst and that the measured overall activity was not owing to leached IL species, the hot catalyst filtration test was carried out (Fig. 7c). An experiment under the optimum condition was performed then, the reaction was stopped after 60 min of reaction, and the catalyst was removed from the reaction mixture by filtration, and the filtrate was allowed to continue the reaction under the same condition. The results revealed that no significant increase in the yield % after removal of 20% IL/MIL-101(Cr) catalyst, definitely indicating that the active sites were not leached out from MIL-101(Cr) into the solution and the observed catalysis is truly heterogeneous on the catalyst surface. 3.7. Catalytic activity of IL/MIL-101(Cr) in Friedel–Crafts acylation 3.7.1. Effect of the ionic liquid (IL) content The change in the conversion % of acetic anhydride as a function of IL content was observed in Fig. 8a. The reaction was performed over 5% catalyst amount at 100 °C using anisole: acetic anhydride 4:1 M ratio for 1 h [50]. It could be observed that pure MIL-101 did not show up any activity for the acylation of anisole with acetic anhydride. However, the loading of MIL-101 with IL results in an increase in the conversion % as a function of IL content passing a maximum at IL content of 20 wt%. The loading MIL-101(Cr) with 5% IL brought about increase in % conversion of acetic anhydride to 45%. While an increase of percentage conversion of about 79% was observed upon increasing the IL content up maximum limit 20 wt%. 3.7.2. Effect of reaction temperature The influence of reaction temperature on the conversion % of acetic anhydride was studied by varying the reaction temperature from 30 to 120 °C as shown in Fig. 8b, using 5% catalyst (20% IL/MIL-101(Cr)) conducted for 1 h using anisole: acetic anhydride 4:1 M ratio. Fig. 8b demonstrates that the reaction temperature had a significant influence on the acylation of anisole. The conversion % remarkably increased with increasing the reaction temperature within the range 30–100 °C. However, a further increase in the reaction temperature up to 120 °C led to a marginal increase in the conversion %. Consequently, we have considered 100 °C as the optimum reaction temperature for Friedel–Crafts acylation of anisole. Table 3, represents a comparison of some catalytic activity data collected from different articles [50–54] of various catalysts for Friedel–Crafts acylation with this work taking into consideration the reaction conditions. Summing up, the reported results within the frame of present work do reflect that porous MOFs, supported with ionic liquids as (IL/MIL-101(Cr)) offers a new, exciting opportunities for heterogeneous Friedel–Crafts acylation.

3.7.3. Effect of different substrate on Friedel–Crafts acylation Fig. 8c, displays the impact of the different substrate contain electron-donating group as anisole and the electron-withdrawing group as benzaldehyde on the Friedel–Crafts acylation. It was observed that anisole acylation with acetic anhydride was performed more rapidly than benzaldehyde. These could be attributed to the resonance effect of the methoxy group far outweighs its polar effect. Hence, the carbocation intermediate (and the transition state) derived from the electrophilic substitution of anisole is more stable relative to starting materials than the carbocation (and transition state) derived from the electrophilic substitution of benzaldehyde. In other words, the methoxy group activates the benzene ring towards ortho and para substitution. 4. Conclusion Economically acidic IL-supported on MIL-101(Cr) catalyst was successively synthesized by simple impregnation method. IL/MIL-101(Cr) exhibited distinct catalytic performance and reusability with respect to the other catalysts towards the esterification of acetic acid with amyl alcohol and Friedel–Crafts acylation of anisole this give the catalyst promising in industrial sectors. Additionally, from this work, it can be suggested that the metal–organic frameworks (MOFs) as new categories of porous materials supported with the ionic liquid, open a new avenue for designing and developing the next generation acidic catalyst and offers a new, exciting opportunities for heterogeneous acid-catalyzed reaction. References [1] M.A. Betiha, H.M. Hassan, A.M. Al-Sabagh, S.K. Abd El Rahman, E.A. Ahmed, Direct synthesis and the morphological control of highly ordered mesoporous AlSBA-15 using urea-tetrachloroaluminate as a novel aluminum source, J. Mater. Chem. 22 (2012) 17551–17559. [2] R. Skoda-Földes, The use of supported acidic ionic liquids in organic synthesis, Molecules 19 (2014) 8840–8884. [3] S.A. Hassan, A.M. Al-Sabagh, N.H. Shalaby, S.A. Hanafi, H.A. Hassan, Catalytic performance of organically templated nano nickel incorporated-rice husk silica in hydroconversion of cyclohexene and dehydrogenation of ethanol, Egypt. J. Pet. 22 (2013) 179–188. [4] H.M. Hassan, M.A. Betiha, S.K. Mohamed, E. El-Sharkawy, E.A. Ahmed, Salen-Zr (IV) complex grafted into amine-tagged MIL-101 (Cr) as a robust multifunctional catalyst for biodiesel production and organic transformation reactions, Appl. Surf. Sci. 412 (2017) 394–404. [5] Y.C. Sharma, B. Singh, J. Korstad, Advancements in solid acid catalysts for ecofriendly and economically viable synthesis of biodiesel, Biofuels Bioprod. Biorefin. 5 (2011) 69–92. [6] H.-C. Zhou, J.R. Long, O.M. Yaghi, Introduction to metal–organic frameworks, Chem. Rev. 112 (2012) 673–674. [7] H.M. Hassan, M.A. Betiha, S.K. Abd El Rahman, M. Mostafa, M. Gallab, Hafnium pentachloride ionic liquid for isomorphic and postsynthesis of HfKIT-6 mesoporous silica: catalytic performances of Pd/SO42−/HfKIT-6, J. Porous. Mater. 23 (2016) 1339–1351. [8] S. Kitagawa, Metal–organic frameworks (MOFs), Chem. Soc. Rev. 43 (2014) 5415–5418.

394


[9] H.M. Hassan, M.A. Betiha, R.F. Elshaarawy, M.S. El-Shall, Promotion effect of palladium on Co3O4 incorporated within mesoporous MCM-41 silica for CO oxidation, Appl. Surf. Sci. 402 (2017) 99–107. [10] S.M. Cohen, Postsynthetic methods for the functionalization of metal–organic frameworks, Chem. Rev. 112 (2011) 970–1000. [11] S.K. Abd El Rahman, H.M. Hassan, M.S. El-Shall, Metal-organic frameworks with high tungstophosphoric acid loading as heterogeneous acid catalysts, Appl. Catal. A Gen. 487 (2014) 110–118. [12] Y.-B. Zhang, H. Furukawa, N. Ko, W. Nie, H.J. Park, S. Okajima, K.E. Cordova, H. Deng, J. Kim, O.M. Yaghi, Introduction of functionality, selection of topology, and enhancement of gas adsorption in multivariate metal–organic framework-177, J. Am. Chem. Soc. 137 (2015) 2641–2650. [13] M.G. Goesten, J. Juan-Alcañiz, E.V. Ramos-Fernandez, K.S.S. Gupta, E. Stavitski, H. van Bekkum, J. Gascon, F. Kapteijn, Sulfation of metal–organic frameworks: opportunities for acid catalysis and proton conductivity, J. Catal. 281 (2011) 177–187. [14] D. Britt, C. Lee, F.J. Uribe-Romo, H. Furukawa, O.M. Yaghi, Ring-opening reactions within porous metal−organic frameworks, Inorg. Chem. 49 (2010) 6387–6389. [15] J. Juan-Alcañiz, J. Gascon, F. Kapteijn, Metal–organic frameworks as scaffolds for the encapsulation of active species: state of the art and future perspectives, J. Mater. Chem. 22 (2012) 10102–10118. [16] T. Welton, Room-temperature ionic liquids. Solvents for synthesis and catalysis, Chem. Rev. 99 (1999) 2071–2084. [17] P. Wasserscheid, W. Keim, Ionic liquids—new “solutions” for transition metal catalysis, Angew. Chem. Int. Ed. 39 (2000) 3772–3789. [18] R. Sheldon, Catalytic reactions in ionic liquids, Chem. Commun. 23 (2001) 2399–2407. [19] Q. Yao, OsO4 in ionic liquid [bmim] PF6: a recyclable and reusable catalyst system for olefin dihydroxylation. Remarkable effect of DMAP, Org. Lett. 4 (2002) 2197–2199. [20] H.M. Zerth, N.M. Leonard, R.S. Mohan, Synthesis of homoallyl ethers via allylation of acetals in ionic liquids catalyzed by trimethylsilyl trifluoromethanesulfonate, Org. Lett. 5 (2003) 55–57. [21] R. Rajagopal, D. Jarikote, R. Lahoti, T. Daniel, K. Srinivasan, Ionic liquid promoted regioselective monobromination of aromatic substrates with N-bromosuccinimide, Tetrahedron Lett. 44 (2003) 1815–1817. [22] A. Kumar, S.S. Pawar, Converting exo-selective Diels−Alder reaction to endo-selective in chloroloaluminate ionic liquids, J. Org. Chem. 69 (2004) 1419–1420. [23] X. Mi, S. Luo, J.-P. Cheng, Ionic liquid-immobilized quinuclidine-catalyzed Morita− Baylis−Hillman reactions, J. Org. Chem. 70 (2005) 2338–2341. [24] M. Betiha, H.M. Hassan, E. El-Sharkawy, A. Al-Sabagh, M. Menoufy, H.M. Abdelmoniem, A new approach to polymer-supported phosphotungstic acid: application for glycerol acetylation using robust sustainable acidic heterogeneous–homogenous catalyst, Appl. Catal. B Environ. 182 (2016) 15–25. [25] H. Wan, Z. Wu, W. Chen, G. Guan, Y. Cai, C. Chen, Z. Li, X. Liu, Heterogenization of ionic liquid based on mesoporous material as magnetically recyclable catalyst for biodiesel production, J. Mol. Catal. A Chem. 398 (2015) 127–132. [26] Z. Wu, C. Chen, L. Wang, H. Wan, G. Guan, Magnetic material grafted poly (phosphotungstate-based acidic ionic liquid) as efficient and recyclable catalyst for esterification of oleic acid, Ind. Eng. Chem. Res. 55 (2016) 1833–1842. [27] G.A. Olah, Friedel-Crafts and Related Reactions. 1 (1963). General Aspects, Interscience Publ., 1963 [28] A. Henschel, K. Gedrich, R. Kraehnert, S. Kaskel, Catalytic properties of MIL-101, Chem. Commun. 35 (2008) 4192–4194. [29] D.Y. Hong, Y.K. Hwang, C. Serre, G. Ferey, J.S. Chang, Porous chromium terephthalate MIL-101 with coordinatively unsaturated sites: surface functionalization, encapsulation, sorption and catalysis, Adv. Funct. Mater. 19 (2009) 1537–1552. [30] Z. Du, Z. Li, S. Guo, J. Zhang, L. Zhu, Y. Deng, Investigation of physicochemical properties of lactam-based brønsted acidic ionic liquids, J. Phys. Chem. B 109 (2005) 19542–19546. [31] H. Zhang, F. Xu, X. Zhou, G. Zhang, C. Wang, A Brønsted acidic ionic liquid as an efficient and reusable catalyst system for esterification, Green Chem. 9 (2007) 1208–1211. [32] K.N. Rao, K.M. Reddy, N. Lingaiah, I. Suryanarayana, P.S. Prasad, Structure and reactivity of zirconium oxide-supported ammonium salt of 12-molybdophosphoric acid catalysts, Appl. Catal. A Gen. 300 (2006) 139–146. [33] M.S. El-Shall, V. Abdelsayed, S.K. Abd El Rahman, H.M. Hassan, H.M. El-Kaderi, T.E. Reich, Metallic and bimetallic nanocatalysts incorporated into highly porous coordination polymer MIL-101, J. Mater. Chem. 19 (2009) 7625–7631.

[34] G. Férey, Hybrid porous solids: past, present, future, Chem. Soc. Rev. 37 (2008) 191–214. [35] T.A. Vu, G.H. Le, C.D. Dao, L.Q. Dang, K.T. Nguyen, P.T. Dang, H.T. Tran, Q.T. Duong, T.V. Nguyen, G.D. Lee, Isomorphous substitution of Cr by Fe in MIL-101 framework and its application as a novel heterogeneous photo-Fenton catalyst for reactive dye degradation, RSC Adv. 4 (2014) 41185–41194. [36] G. Férey, C. Mellot-Draznieks, C. Serre, F. Millange, J. Dutour, S. Surblé, I. Margiolaki, A chromium terephthalate-based solid with unusually large pore volumes and surface area, Science 309 (2005) 2040–2042. [37] M. Thommes, K. Kaneko, A.V. Neimark, J.P. Olivier, F. Rodriguez-Reinoso, J. Rouquerol, K.S. Sing, Physisorption of gases, with special reference to the evaluation of surface area and pore size distribution (IUPAC Technical Report), Pure Appl. Chem. 87 (2015) 1051–1069. [38] K. Leng, Y. Sun, X. Li, S. Sun, W. Xu, Rapid synthesis of metal–organic frameworks MIL-101 (Cr) without the addition of solvent and hydrofluoric acid, Cryst. Growth Des. 16 (2016) 1168–1171. [39] J. Otera, J. Nishikido, Reaction of alcohols with carboxylic acids and their derivatives, Esterification: Methods, Reactions, and Applications, second ed. 2010, pp. 3–157. [40] E. Rafiee, S. Eavani, H3PW12O40 supported on silica-encapsulated γ-Fe2O3 nanoparticles: a novel magnetically-recoverable catalyst for three-component Mannich-type reactions in water, Green Chem. 13 (2011) 2116–2122. [41] J. Juan-Alcañiz, E.V. Ramos-Fernandez, U. Lafont, J. Gascon, F. Kapteijn, Building MOF bottles around phosphotungstic acid ships: one-pot synthesis of bi-functional polyoxometalate-MIL-101 catalysts, J. Catal. 269 (2010) 229–241. [42] M.C. Ferreira, A.J. Meirelles, E.A. Batista, Study of the fusel oil distillation process, Ind. Eng. Chem. Res. 52 (2013) 2336–2351. [43] A. Sarin, Biodiesel: Production and Properties, Royal Society of Chemistry, 2012. [44] Y. Zang, J. Shi, F. Zhang, Y. Zhong, W. Zhu, Sulfonic acid-functionalized MIL-101 as a highly recyclable catalyst for esterification, Catal. Sci. Technol. 3 (2013) 2044–2049. [45] J. Juan-Alcañiz, R. Gielisse, A.B. Lago, E.V. Ramos-Fernandez, P. Serra-Crespo, T. Devic, N. Guillou, C. Serre, F. Kapteijn, J. Gascon, Towards acid MOFs–catalytic performance of sulfonic acid functionalized architectures, Catal. Sci. Technol. 3 (2013) 2311–2318. [46] Y. Zang, J. Shi, X. Zhao, L. Kong, F. Zhang, Y. Zhong, 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. Catal. 109 (2013) 77–89. [47] I. Roberts, H.C. Urey, A study of the esterification of benzoic acid with methyl alcohol using isotopic oxygen, J. Am. Chem. Soc. 60 (1938) 2391–2393. [48] W. Chu, X. Yang, X. Ye, Y. Wu, Vapor phase esterification catalyzed by immobilized dodecatungstosilicic acid (SiW12) on activated carbon, Appl. Catal. A Gen. 145 (1996) 125–140. [49] E. Santacesaria, D. Gelosa, P. Danise, S. Carra, Vapor-phase esterification catalyzed by decationized Y zeolites, J. Catal. 80 (1983) 427–436. [50] A. Padmanabhan, R. Selvin, H.L. Hsu, L.W. Xiao, Efficient acylation of anisole over hierarchical porous ZSM-5 structure, Chem. Eng. Technol. 33 (2010) 998–1002. [51] S.K. Abd El Rahman, H.M. Hassan, M.S. El-Shall, Acid catalyzed organic transformations by heteropoly tungstophosphoric acid supported on MCM-41, Appl. Catal. A Gen. 411 (2012) 77–86. [52] R. Selvin, H.-L. Hsu, T.-M. Her, Acylation of anisole with acetic anhydride using ZSM5 catalysts: effect of ZSM-5 particle size in the nanoscale range, Catal. Commun. 10 (2008) 169–172. [53] B. Bachiller-Baeza, J. Anderson, FTIR and reaction studies of the acylation of anisole with acetic anhydride over supported HPA catalysts, J. Catal. 228 (2004) 225–233. [54] L.A. Cardoso, W. Alves Jr., A.R. Gonzaga, L.M. Aguiar, H.M. Andrade, Friedel–Crafts acylation of anisole with acetic anhydride over silica-supported heteropolyphosphotungstic acid (HPW/SiO 2), J. Mol. Catal. A Chem. 209 (2004) 189–197. [55] X. Ji, Z. Qin, M. Dong, G. Wang, T. Dou, J. Wang, Friedel–Crafts acylation of anisole and toluene with acetic anhydride over nano-sized Beta zeolites, Catal. Lett. 117 (2007) 171. [56] G. Winé, C. Pham-Huu, M.-J. Ledoux, Acylation of anisole by acetic anhydride catalysed by BETA zeolite supported on pre-shaped silicon carbide, Catal. Commun. 7 (2006) 768–772.