Scalable Preparation of Micro-Meso-Macroporous Polymeric Solid

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Kinetics, Catalysis, and Reaction Engineering

Scalable Preparation of Micro-Meso-Macroporous Polymeric Solid Acids Spheres From Controllable Sulfonation of Commercial XAD-4 Resin Weiping Kong, Yong Liu, and Fujian Liu Ind. Eng. Chem. Res., Just Accepted Manuscript • DOI: 10.1021/acs.iecr.8b03834 • Publication Date (Web): 26 Sep 2018 Downloaded from http://pubs.acs.org on October 2, 2018

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Industrial & Engineering Chemistry Research

Scalable Preparation of Micro-Meso-Macroporous Polymeric Solid Acids Spheres From Controllable Sulfonation of Commercial XAD-4 Resin

Weiping Kong†, Yong Liu*‡ and Fujian Liu*†

†

College of Chemistry and Chemical Engineering, Shaoxing University, Shaoxing,

Zhejiang Province, 312000, PR China. E-mail: [email protected] ‡

Henan Key Laboratory of Polyoxometalate, College of Chemistry and Chemical

Engineering, Henan University, Kaifeng, Henan Province, 475004, PR China. E-mail: [email protected]

1

ACS Paragon Plus Environment

Industrial & Engineering Chemistry Research 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

ABSTRACT

Efficient micro-meso-macroporous solid acids spheres with controllable acid strength were successfully synthesized by simultaneously grafting of -SO3H and -SO2CF3 onto the network of commercial XAD-4 resin, the synthesized solid acids are designated as XAD-4-SO3H and XAD-4-SO3H-SO2CF3. Various characterizations show that XAD-4-SO3H and XAD-4-SO3H-SO2CF3 possess high BET surface areas, hierarchical porous structures with combined micro-meso-macropores, high concentrations of acid sites and strong acid strength. Catalytic tests show that XAD-4-SO3H and XAD-4-SO3H-SO2CF3 exhibit superior activities and good reusability in various acid-catalyzed reactions including esterification of acetic acid with cyclohexanol, acylation of anisole with acetyl chloride, and catalytic synthesis of bisphenol-A. Their activities were better than the solid acids of Amberlyst-15, SBA-15-SO3H-0.1, H3PW12O40 and acidic zeolites. This work develops a new method for scalable transformation of commercially macroporous resin into efficient porous solid acids, which promotes their wide in the industrial catalysis. KEYWORDS: Micro-meso-macropores; Solid acids; Acid-catalysis; Reusability; Sulfonation.

2


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1. INTRODUCTION

As the widely used reactions in chemical engineering, acid catalysis shows significant applications in the fields of green chemistry, biomass catalytic transformation and petrochemical engineering 1-10. The most commonly used acids are the homogeneous acid catalysts such as H2SO4, HCl, AlCl3 etc, which are very efficient in different kinds of

acid-catalyzed

reactions

such

as

alkylation,

isomerization,

polymerization, Koch carbonylation and biofuels production

11,12

esterifications,

. However, the

homogeneous acids catalysts have the drawbacks such as complicated regeneration process, high corrosion on facility and environmentally hazardous, which strongly constrain them used as green and sustainable catalysts in the industry 13. Introduction of acidic sites into suitable supports to give the solid acids, which show unique characteristics such as reductive corrosion, environmental friendly, good catalytic activities and selectivity in comparison with the homogeneous acids

14,15

. Natural clays,

zeolites, sulfated metal oxides and heteropolyacids are the widely reported solid acids, which showed good activities in a variety of reactions such as esterifications, isomerization, alkylation and biomass conversions 14,15. However, relatively low BET surface areas, limited acid density, and easily hydrolysis of the acidic sites decrease their activities and lives in various acid-catalyzed reactions 16. The solid acids with polymer networks could be easily functionalized with abundantly acidic sites in comparison with inorganic network. In addition, the polymeric 3



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networks show controllable wettability for reactants and good stability to water, which result in their enhanced compatibility with organic reactants

17-21

. The most commonly

used polymeric solid acids are commercially acidic porous resins such as Amberlyst-15 and Nafion NR50, which show high contents of acid sites and strong acidity. However, the poor porosity makes mostly acidic sites anchored on their networks inaccessible to the guest molecules

22-24

, which results in their limited catalytic activities and bad

resistant for carbon deposition. Therefore, the promotion of the BET surface areas, introduction of hierarchical porosity, rational enhancement of acid strength and surface wettability are the main problems should be concerned in the field. Although some porous polymeric solid acids such as sulfonated nanoporous polydivinlybenzene and ordered mesoporous polymers have been successfully developed, their high cost and complicated synthetic processes are not favorable for the industrial applications

25-27

. Up

to now, there were still few reports on scalable preparation of highly nanoporous polymeric solid acids from widely used, commercial feedstocks, which plays important role for their applications in industrial scale. Herein, we successfully synthesize micro-meso-macroporous polymeric solid acids spheres (XAD-4-SO3H&XAD-4-SO3H-SO2CF3) from sulfonation of commercially macroporous XRD-4 resin, both -SO3H and -SO2CF3 could be simultaneously anchored onto XRD-4 network. The synthesized solid acids have very large BET surface areas, combined micro-meso-macroporosity, superior stability, suitable wettability and adjustable

acid

strength.

Interestingly,

the

resultant

4


XAD-4-SO3H

and

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XAD-4-SO3H-SO2CF3 could be used as efficient and reusable solid acids, which are successfully used in esterification, acylation of anisole with acetyl chloride and catalytic synthesis of bisphenol-A. Their activities were much better than commercial Amberlyst-15, sulfonic groups functionalized mesoporous silica, H3PW12O40, and zeolites in these reactions. Abundant, hierarchical nanoporosity largely promotes the mass transfers, and adjustable strong acidity effectively decreases activation energy in the mentioned reactions, which result in their enhanced catalytic activities. The preparation of XAD-4-SO3H and XAD-4-SO3H-SO2CF3 develops new route for scalable transformation of commercialized feedstocks into efficient porous polymeric solid acids with good spherical morphology.

2. EXPERIMENTAL DETAILS

2.1 Chemicals and reagents All the chemicals were analytical grade, which were used as the purchased. XAD-4 macroporous resin spheres, 3-mercaptopropyltrimethoxysilane (3-MPTS), triblock copolymer of poly(ethyleneoxide)–poly(propyleneoxide)–poly(ethyleneoxide) (P 123, Mw=5800), Amberlyst-15 and trifluoromethanesulfonate were supplied by Sigma-Aldrich Co., Ltd. USA. Tetraethyl orthosilicate (TEOS), HSO3Cl, CH2Cl2, cyclohexanol, acetic acid, phenol, acetone, anisole, H3O40PW12, acetyl chloride and dodecane were obtained

5



from Aladdin Co., Ltd. China. ZSM-5 and USY zeolites were obtained from Sinopec Catalyst Company.

2.2 Catalysts preparation

XAD-4-SO3H was synthesized from sulfonation of commercially porous XAD-4 resin. Typically, 7 mL of HSO3Cl was slowly dispersed into 35 mL of CH2Cl2 at 0 °C, followed by addition of 2.0 g of XAD-4 resin into the mixture. After sulfonation for 24 h, 500 mL of water was slowly introduced into the mixture. The sulfonated sample of XAD-4-SO3H was collected by filtration, washed with large amount of ethanol and water for removing of residual CH2Cl2 and absorbed acids, which was then dried at 80 °C under vacuum condition. To get a XAD-4-SO3H with full hydrogen form, the XAD-4-SO3H was activated with 1 M H2SO4 for 24 h, washed with abundant water to remove physical absorbed H2SO4, and vacuumly dried at 80 °C. Compared with classical sulfonation method by sulfuric acid, HSO3Cl was more active, 18,28 and large amount of sulfonic group could be grafted onto the network of XAD-4. In addition, the strong acidity of HSO3Cl results in formation of abundant micropores in the synthesized samples to give hierarchically micro-meso-macroporous structure in the sample. 18,27 The acid strength of XRD-4 derived solid acids could be strongly enhanced by treating of XAD-4-SO3H with HSO3CF3, which makes -SO2CF3 group (strong electron withdrawing property) grafted onto XAD-4-SO3H. Typically, 1.5 g of XAD-4-SO3H was 6


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dispersed into 50 mL of toluene, then 10 mL of HSO3CF3 was introduced, the reaction temperature was performed at 100 °C for 24 h, which results in the formation of XAD-4-SO3H-SO2CF3. XAD-4-SO3H-SO2CF3 could be collected from filtration, washed with CH2Cl2 to remove physical absorbed HSO3CF3, and vacuumly dried at 80 °C.

2.3 Characterizations

Physical adsorption-desorption tests were carried out on a Micromeritics ASAP 3020M system. Before the experiment, the samples were degassed at 120 °C for 10 h. The pore diameter of the samples was estimated by using Barrett–Joyner–Halenda (BJH) model. Fourier transform infrared spectroscopy (FT-IR) was determined on the Bruker 66V FT-IR spectrometer. Thermogravimetric analysis (TGA) was recorded under an air flow (30 mL/min-1) with a Setsys Evolution analyzer using 5 mg of sample and a heating rate of 10 °C/min. Transmission electron microscope (TEM) images were collected by JEM-3010 electron microscope (JEOL, Japan) at an acceleration voltage of 300 kV. Surface wettability was evaluated by using contact angles method, which were collected on DSA10MK2G140, Kruss Company. X-ray photoelectron spectroscopy (XPS) measurements were performed on a Thermo Fisher Scientific EscaLab 250Xi instrument. Catalyst charging during the measurement was compensated by an electron flood gun. Scanning electron microscope (SEM) images were tested on FESEM JSM-6700F with the acceleration voltage of 5 kV. 7



The 31P solid-state NMR resonances of the synthesized solid acids were collected on Bruker Ascend-500 spectrometer with the resonance frequency of 202.34 MHz, where a 4 mm triple-resonance MAS probe with a spinning rate of 12 kHz was used. The pulse width (π/2) for 31P was 4.5 µs, and a recycle delay was 30 s, 31P MAS NMR spectra with high power proton decoupling were tested. The 31P chemical shift was corrected based on 1 M aqueous H3PO4. Before the experiment: the samples were firstly pretreated under a vacuum condition (below 10-3 Pa) at 453 K for 24 h, then trimethylphosphine oxide (TMPO) probe molecule was slowly absorbed onto the samples.

2.4 Catalytic reactions

2.4.1 Acylation 5.5 mL (50 mmol) of anisole and 0.71 mL (10 mmol) of acetyl chloride were mixed into a flask reactor, which were equipped with condensing and stirring system. Then, 0.2 g of fresh catalyst was quickly introduced. The reaction system was quickly heated up to 60 °C, which was lasted for 5 h. The activities of different catalysts were determined based on the conversion of acetyl chloride, where n-dodecane acted as the internal standard was also introduced.

2.4.2 Catalytic bisphenol-A synthesis

8


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Bisphenol-A could be synthesized via condensation of phenol with acetone catalyzed by solid acids catalysts. 70 mmol of phenol, 10 mmol of acetone and 0.07 g of solid acid catalyst were added into a flask reactor, which were equipped with condensing and stirring system. Then, the reaction system was heated up to 85 °C and lasted for 24 h, and the main products were p,p'-bisphenol-A and o,p-bisphenol-A, respectively. In this reaction, n-dodecane acted as the internal standard was also introduced. 2.4.3 Esterification Esterification of acetic acid with cyclohexanol was operated as the following procedure: 0.2 g of catalyst, 11.5 mL of cyclohexanol and 17.5 mL of acetic acid were added into a flask reactor, which were equipped with condensing and stirring system. Then, the reaction system was heated up to 100 °C and stirred for 5 h, where n-dodecane acted as the internal standard was also introduced. In these catalytic reactions, the conversion of substrates and the yields of products were tested by Agilent 7890A gas chromatography, which was equipped with a flame ionization detector and a HP-INNOWax capillary column (30 m).

3. RESULTS AND DISCUSSION

3.1 N2 adsorption-desorption isotherms

9



Figure 1 (A) Nitrogen adsorption-desorption isotherms and (B) pore diameter distribution of XAD-4, XAD-4-SO3H and XAD-4-SO3H-SO2CF3.

Figure 1 shows the N2 adsorption-desorption isotherms and pore diameter distribution of XAD-4, XAD-4-SO3H and XAD-4-SO3H-SO2CF3. Notably, the type-IV isotherms with relatively large volume adsorption were observed in these samples, which shows the steep increase at relative pressure (P/P0) ranged from 0.5 to 0.95. The above results confirm that abundant micro-meso-macroporosity was formed in both XAD-4 and their derived solid acids 27. The structural parameters of various solid acid catalysts were also illustrated in Table 1. Notably, the BET surface areas of XAD-4-SO3H and XAD-4-SO3H-SO2CF3 were 827 and 796 m2/g respectively, similar with those of XAD-4 10


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(808 m2/g) and SBA-15-SO3H-0.1 (820 m2/g), which were larger than the reported porous solid acids of SBA-15-Ar-SO3H (626 m2/g), SBA-15-SO2CF3 (579 m2/g) and USY zeolite (723 m2/g). In contrast, the BET surface of commercial Amberlyst-15 was as low as 40 m2/g. Therefore, the XRD-4 derived solid acids show higher BET surface areas in comparison with various reported hierarchically nanoporous solid acids to date

29-35

.

Correspondingly, the pore sizes of XAD-4, XAD-4-SO3H and XAD-4-SO3H-SO2CF3 are distributed at 23.7 21.6 and 4.5 nm (Figure 1B), respectively. The structural parameters of the samples were illustrated in Table S1. Compared with XAD-4 and XAD-4-SO3H, the decreased pore diameter in XAD-4-SO3H-SO2CF3 should be attributed to the treatment by HSO2CF3, which may result in formation of abundant micro-nano defects and partial collapse of meso-macropores onto its networks due to the very strong acidity and corrosivity of HSO2CF3

18,32

. Abundant defects of XAD-4-SO3H-SO2CF3 results in

its a larger BET surface area and enhanced microporosity in comparison with XAD-4 and XAD-4-SO3H. Hierarchical nanoporosity and large BET surface areas make the acid sites more accessibility to the guest molecules in the synthesized solid acids. Meanwhile, XAD-4-SO3H-SO2CF3 and XAD-4-SO3H show the acid contents up to 2.78 and 3.11 mmol/g respectively, which were much higher than the reported mesoporous solid acids with both silica and polymer networks (1.29-2.13 mmol/g). Although Amberlyst-15 has the acid concentration as high as 4.70 mmol/g, its very poor porosity may lead to limited mass transfer and low exposure degree of anchored acid sites.

11



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Table 1 The textural characteristics and acid concentrations of different solid acids. S contents a

H+ contents b

SBET c

VP c

DP c

(mmol g-1)

(mmol g-1)

(m2 g-1)

(cm3 g-1)

(nm)

XAD-4

-

-

808

1.05

23.7

XAD-4-SO3H-SO2CF3

3.61

2.78

827

0.66

4.5

XAD-4-SO3H

3.02

3.11

796

1.15

21.6

Amberlyst-15

4.30

4.70

45

0.31

40.0

SBA-15-SO2CF3 d

1.41

1.29

579

0.48

5.8

SBA-15-Ar-SO3H e

1.38

1.43

626

0.72

6.3

SBA-15-SO3H-0.1f

1.36

1.39

820

1.40

7.3

USY

-

718

0.32

-

FDU-15-SO3H g

1.80

447

0.33

2.5

Samples

a

2.13

Determined by elemental analysis. b Evaluated by acid-base titration. c Estimated from

N2 adsorption-desorption isotherms, and pore size distribution estimated from BJH model. d-g

Parameters from Ref. 33-35, 17.

3.2 TEM and element mapping

12


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Figure 2 TEM images of (A) XAD-4-SO3H and (B) XAD-4-SO3H-SO2CF3, (C-F) STEM image and elemental maps of XAD-4-SO3H-SO2CF3.

Figure 2 shows TEM images of XAD-4-SO3H and XAD-4-SO3H-SO2CF3. Notably, both

samples

have

abundant

and

hierarchical

nanoporosity

13


with

combined


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micro-meso-macroporosity, and the pore sizes cover rather wide ranges from 4 to 50 nm. XAD-4-SO3H-SO2CF3 shows a decreased pore sizes in comparison XAD-4-SO3H, similar results could also be found in N2 physical adsorption-desorption isotherms. Furthermore, the STEM images and elemental maps of XAD-4-SO3H are also illustrated in Figure 2C-F, abundant and hierarchical nanoporosity could also be confirmed in XAD-4-SO3H. In addition, the signals associated with carbon, oxygen and sulfur are homogeneously dispersed into XAD-4-SO3H, suggesting the successful introducing of sulfonic group in the XAD-4-SO3H. Similar hierarchical micro-meso-macroporosity and homogeneous dispersion of C, O and S could also be confirmed by SEM images and elemental maps (As depicted in Figure S1). The above results indicate the hierarchical nanoporosity of XAD-4 based solid acids, and the acid sites were homogeneously dispersed into the samples. 3.3 XPS spectra Figure 3 shows the XPS measurements of XAD-4-SO3H and XAD-4-SO3H-SO2CF3. Both XAD-4-SO3H-SO2CF3 and XAD-4-SO3H displayed the signals of carbon, oxygen and sulfur, suggesting successful grafting of sulfonic group in the synthesized solid acids. In addition to carbon, oxygen and sulfur, a new peak at around 690 eV assigned to F1s, could be observed in XAD-4-SO3H-SO2CF3, indicating -SO2CF3 group has been successful grafted onto the network of XAD-4-SO3H

27

. Correspondingly, the XPS

spectra of C1s show two peaks centered at around 284.7 and 291.4 eV, which suggest the presence of C-C bond, and mixed signals of C-S, C-F bonds in both samples 14


27

.

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Interestingly, the signals of S2p and O1s in XAD-4-SO3H-SO2CF3 shift to the higher bind energy as compared with XAD-4-SO3H. This phenomenon was attributed to the successful grafting of -SO2CF3 onto the network of XAD-4-SO3H-SO2CF3, which exhibits strong electron withdrawing property and plays a crucial role for the enhancement of the intrinsic acid strength in XAD-4-SO3H-SO2CF3. The successful grafting of -SO3H and -SO2CF3 could be further confirmed by FT-IR spectrum (Figure S1). The vibrational peaks at around 1017, 1045 and 1170 cm−1 could be found in XAD-4-SO3H-SO2CF3, which could be assigned to the characteristic peaks of the C–S, S=O

and

C-F

bonds

27

,

further

suggesting

XAD-4-SO3H-SO2CF3 in this work (Figure S2).

15


successful

preparation

of


Figure 3 XPS spectroscopy measurements of (A) C1s, (B) S2p, (C) O1s and (D) F1s of XAD-4-SO3H and XAD-4-SO3H-SO2CF3. 3.4 31P solid state NMR resonance

Figure 4 31P solid-state MAS NMR spectra of (a) XAD-4-SO3H-SO2CF3 and (b) XAD-4-SO3H adsorbed with TMPO.

Figure 4 depicts the solid-state 31P MAS NMR spectra of XAD-4-SO3H-SO2CF3 and XAD-4-SO3H after adsorption of TMPO, which is thought to be an advanced and reliable technique for evaluation of acidity of the acidic catalysts with different structural characteristics such as zeolites, heteropolyacids and different kinds of liquid acids 36–39. It 16


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is noteworthy that 31P chemical shift of the absorbed TMPO on various acid catalysts can accurately reveal their acid strength 39. Notably, XAD-4-SO3H shows 31P chemical shifts at around 56.7 and 77.2 ppm, which suggest the presence of both weak and relative strong sites in the sample, the weak acid site should be carboxylic acid site, which derived from the oxidation of alkyl chain in the polymer network during sulfonation process

40

; The strong acid site should be assigned to the sulfonic group, indicating

abundant acid sites were introduced into the XAD-4 via the sulfonation process 41. After treating of XAD-4-SO3H with HSO3CF3 to give XAD-4-SO3H-SO2CF3, which shows much

enhanced

acid

strength.

For

instance,

the

31

P

chemical

shifts

of

XAD-4-SO3H-SO2CF3 were increased to 72.8 and 82.3 ppm, and the acid dispersion also become sharp in comparison with XAD-4-SO3H. The mentioned phenomenon should be attributed to successful grafting of -SO2CF3 onto XAD-4-SO3H, the strong electron-withdrawing property of -SO2CF3 largely changes the electronic environment and engineers the acid sites of -SO3H and -COOH in the sample. The above results confirm that both -SO3H and -SO2CF3 have been successfully anchored onto the commercial XRD-4 macroporous resin, which can be also confirmed by XPS and FT-IR results. Moreover, the acidity of the XAD-4 derived solid acids could be adjusted via rational controlling introduction of -SO3H and -SO2CF3 onto its network. 3.5. Thermal stabilities To investigate thermal stabilities of the synthesized solid acids, thermal gravity analysis of XAD-4-SO3H and XAD-4-SO3H-SO2CF3 was carried out, and commercial 17



solid acid of Amberlyst-15 was also tested for comparison. As shown in Figure 5, XAD-4-SO3H and XAD-4-SO3H-SO2CF3 show better thermal stabilities than that of Amberlyst-15. Notably, obvious three weight loss steps associated with desorption of absorbed water, decomposition of acidic group and destruction of polymer networks could be observed in all the samples, and the corresponding temperature distribution ranges were distributed at around 30-150 °C, 250-450 °C and 500-860 °C

18

. The

destruction of sulfonic group and network in the Amberlyst-15 were centered at around 320 and 600 °C. Interestingly, the decomposition temperatures of acidic groups and polymer network in XAD-4-SO3H and XAD-4-SO3H-SO2CF3 were centered at around 400 and 700 °C, much higher than that of Amberlyst-15. The above results confirmed relatively good thermal of the synthesized XAD-4 based solid acids.

100

XAD-4-SO3H Amberlyst 15 XAD-4-SO3H-SO2CF3

80

TG (%)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 18 of 32

60

40

20

0

100

200

300

400

500

600

°

Temperature ( C) 18


700

800

900

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Figure 5 Thermal gravity analysis curves of Amberlyst-15, XAD-4-SO3H and XAD-4-SO3H-SO2CF3. 3.4 Catalytic applications

Figure 6 Relationship between reaction time and cyclohexanol conversion catalyzed by various solid acid catalysts.

Figure 6 shows relationship between catalytic performances and reaction time in the esterification of acetic acid with cyclohexanol catalyzed by various solid acid catalysts, and the product was cyclohexyl acetate with nearly 100 % selectivity. Esterification is a 19



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kind of important reaction for scalable preparation of biofuels and perfumes in the industry 42. Notably, XAD-4-SO3H and XAD-4-SO3H-SO2CF3 exhibit excellent catalytic activities in the reaction as compared with SBA-15-SO3H-0.1, H3PW12O40 and Amberlyst-15 based on the catalytically kinetic curves. For example, the conversions of cyclohexanol

into

cyclohexyl

acetate

catalyzed

by

XAD-4-SO3H

and

XAD-4-SO3H-SO2CF3 were up to 39.9 and 41.3 % for 1 h of reaction, while the widely reported solid acids such as heteropolyacid H3PW12O40, SBA-15-SO3H-0.1 and Amberlyst-15 gave very low conversions of cyclohexanol at 31.9, 11.2 and 11.5 %. Further prolongate to 5 h, the conversions of cyclohexanol could be promoted to 84.3 and 85.1 % in presence of XAD-4-SO3H and XAD-4-SO3H-SO2CF3 catalysts, and reaction equilibrium was nearly achieved. However, H3PW12O40, SBA-15-SO3H-0.1 and Amberlyst-15 still gave very low cyclohexanol conversion at 72.3, 49.3 and 50.9 %. Especially for SBA-15-SO3H-0.1 and Amberlyst-15, their kinetic curves were far from equilibrium as compared with XAD-4 derived solid acids. The above results confirm excellent activities of XAD-4 derived solid acids.

Table 2 Catalytic data of various solid acid catalysts in the acylation of anisole with acetyl chloride. Run

Catalysts

Conversion (%)

Sel. p-product

Sel. o-product

a

(%) b

(%) b

20


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a

1

XAD-4-SO3H

71.7

98.2

1.8

2

XAD-4-SO3H-SO2CF3

79.6

98.8

1.2

3

XAD-4-SO3H-SO2CF3 c

78.4

98.3

1.7

4

H3O40PW12

61.7

97.9

2.1

5

Amberlyst-15

55.2

96.3

3.7

6

SBA-15-SO3H-0.1

43.5

96.5

3.6

Determined by using gas chromatography based on internal standard method.

b

Analyzed by using gas chromatograph-mass spectrometer (GC-MS). c 5th cycling. Furthermore,

the

synthesized

solid

acids

of

XAD-4-SO3H

and

XAD-4-SO3H-SO2CF3 also show superior activities in acylation and condensation, which were important acid-catalyzed liquid reactions in the industry. Table 2 and Table 3 illustrate the catalytic data in acylation of anisole with acetyl chloride and condensation of phenol with acetone over various solid acid catalysts. Notably, XAD-4-SO3H-SO2CF3 shows much enhanced activities in comparison with XAD-4-SO3H. The activities of XAD-4 derived solid acids were much better than the widely reported solid acids of Amberlyst-15, SBA-15-SO3H-0.1 and H3PW12O40. For instance, in acylation of anisole with

acetyl

chloride,

the

conversion

of

acetyl

chloride

catalyzed

by

XAD-4-SO3H-SO2CF3 was as high as 79.6 % for 5 h (Table 2, run 2), which were much higher than those of XAD-4-SO3H (71.7 %, Table 2, run 1), H3PW12O40 (61.7 %, Table 2, run 3), SBA-15-SO3H-0.1 (43.5 %, Table 2, run 5), Amberlyst-15 (55.2 %, Table 2, run 4).

21



Page 22 of 32

Meanwhile, XAD-4-SO3H-SO2CF3 and XAD-4-SO3H show good selectivity for the p-product, the selectivity for the p-product was ranged from 96.5-98.8 % (Table 2). XAD-4-SO3H-SO2CF3 also shows good reusability in the reaction, the conversion of acetyl chloride was still up to 78.4 % after 5th cycling of XAD-4-SO3H-SO2CF3, and nearly no decreasing of activity in comparison with fresh XAD-4-SO3H-SO2CF3. The recycled XAD-4-SO3H-SO2CF3 also shows similar selectivity for the corresponding o,p-products as that of fresh XAD-4-SO3H-SO2CF3. Moreover, as presented in the Table 3, XAD-4-SO3H-SO2CF3 also shows impressive catalytic activities and satisfied selectivity in the catalytic synthesis of bisphenol-A. Notably, XAD-4-SO3H and XAD-4-SO3H-SO2CF3 shows enhanced catalytic activities in comparison

with

variously

reported

solid

acids

including

Amberlyst-15,

SBA-15-SO3H-0.1, H-ZSM-5 and H-USY. XAD-4-SO3H and XAD-4-SO3H-SO2CF3 gave the yields of bisphenol-A up to 20.1 and 24.1 % for 5 h reaction (Table 3, run 5&6), much better than those of Amberlyst-15 (13.2 %, Table 3, run 1), especially is almost 4 times higher than H-ZSM-5 (4.6 %). More interestingly, XAD-4-SO3H and XAD-4-SO3H-SO2CF3 shows very good selectivity for p,p'-bisphenol-A/o,p'-bisphenol-A (9.8 and 9.9 Table 2) in comparison with commercial Amberlyst-15 (9.4), SBA-15-SO3H-0.1 (9.5), H-ZSM-5 (8.8) and H-USY (8.4). The superior catalytic activities of XAD-4-SO3H and XAD-4-SO3H-SO2CF3 are mainly attributed to their unique

structural

characteristics

such

as

large

surface

areas,

hierarchical

micro-meso-macroporosity, strong acid strength and good distribution of acid sites. 22


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Compared with XAD-4-SO3H, the better activities of XAD-4-SO3H-SO2CF3 in the above mentioned reactions should be attributed to its enhanced acid strength.

Table 3 Catalyze condensation of phenol with acetone for the synthesis of bisphenol-A over various solid acids. OH

OH O

+

+ HO

OH

p,p'-bisphenol-A

Run

a

Samples

OH

o,p'-bisphenol-A

Yields of bisphenol-A

p,p'/o,p'

(%) a

molar ratio

1

Amberlyst-15

13.2

9.4

2

H-ZSM-5

4.6

8.8

3

H-USY

8.3

8.4

4

SBA-15-SO3H-0.1

11.3

9.5

5

XAD-4-SO3H

20.1

9.9

6

XAD-4-SO3H-SO2CF3

24.1

9.8

Calculated from gas chromatography based on standard curve method. TOF is based on

mmol of phenol per mmol of active site.

4. CONCLUSIONS

23



Efficient micro-meso-macroporous polymeric solid acids of XAD-4-SO3H and XAD-4-SO3H-SO2CF3 have been successfully prepared through controlling sulfonation of commercial XAD-4 macroporous resin. The resultant XAD-4 derived acid catalysts possess high BET surface areas, hierarchical nanoporosity, superior thermal stabilities, strong acid sites with very good distribution. Therefore, XAD-4-SO3H and XAD-4-SO3H-SO2CF3 were very active and stable for catalyzing the acylation, condensation and esterification. In the above reactions, variously conventional solid acids including commercial Amberlyst-15, sulfonic group functionalized ordered mesoporous silica and acidic zeolites were chosen as the counterpart for comparison. This work develops a new route for scalable preparation of nanoporous polymeric solid strong acids from commercial feedstocks, which will largely promote the applications of nanoporous polymeric solid acids in the field of industrial catalysis.

ASSOCIATED CONTENT Supporting Information. The Supporting Information is available free of charge via the Internet at http://pubs.acs.org.” The SEM images, elemental mapping and FT-IR spectra of the XAD-4 based solid acids (Figure S1&S2).

AUTHOR INFORMATION 24


Page 24 of 32

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Corresponding Author * E-mail: [email protected] * E-mail: [email protected]

Notes The authors declare no competing financial interest.

ACKNOWLEDGEMENTS This work was supported by support of the National Natural Science Foundation of China (Nos. 21573150 and 21203122), and the National Natural Science Foundation of Zhejiang Province (LY15B030002).

25



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Scalable Preparation of Micro-Meso-Macroporous Polymeric Solid

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