Synthesis, Characterization, and Catalytic Properties of Interlayer

Article pubs.acs.org/JPCC

Synthesis, Characterization, and Catalytic Properties of Interlayer Expanded Aluminosilicate IEZ-PLS‑3 Boting Yang, Haihong Wu,* and Peng Wu* Shanghai Key Laboratory of Green Chemistry and Chemical Processes, Department of Chemistry, East China Normal University, North Zhongshan Road 3663, Shanghai 200062, China S Supporting Information *

ABSTRACT: An interlayer expanded zeolite IEZ-PLS-3 was postsynthesized from the lamellar precursor of PLS-3 aluminosilicate by interlayer silylation with diethoxydimethylsilane (DEDMS) in HCl−EtOH solution at 443 K for 20 h. The resulting material was characterized by various techniques such as XRD, SEM, adsorption of N2, water, and benzene, and IR and NMR spectroscopies, and its catalytic properties were investigated by comparison to those of other zeolites with similar Si/Al ratios in m-xylene isomerization/disproportionation, Friedel−Crafts alkylation of anisole with benzyl alcohol, and acylation of anisole with acetic anhydride. The interlayer expansion created new 12 × 10-membered ring (MR) pores in IEZ-PLS-3. IEZ-PLS-3 showed a larger adsorption capacity of benzene than conventional PLS-3 with 10 × 8-MR channels. In the m-xylene isomerization/disproportionation reaction, IEZPLS-3 showed a higher conversion than PLS-3 and gave an isomerization to disproportionation ratio close to that of Beta zeolite, characteristic of shape-selective properties of 12-MR zeolites. IEZ-PLS-3 was more active than Beta in Friedel−Crafts alkylation and acylation reactions, implying that it is a promising solid acid catalyst for processing bulky molecules.

1. INTRODUCTION

improved properties such as enlarged pore size or higher external surface areas. With respect to interlayer expansion by silylation with monomeric silane, a serious of interlayer expanded zeolites (IEZ) have been developed by silylating the layered precursors of MWW, FER, CDO, and MCM-47 zeolites.22,23 The neighboring layers of the resulting interlayer expanded materials were bonded and pillared by SiO2(CH3)2 groups from DEDMS. To date, a variety of interlayer expanded metallosilicates, such as Ti-YNU-1,24 APZ serious,25 COE-2,26 Ti-COE-4,27 IEZ-CDO,28 and IEZ-NSI,29 have been postsynthesized by silylation or simply acid treatment without silane. These materials all have one silicon atom standing on the pillaring site between the layers. Other kinds of silanes with larger molecular dimension were also applied to the silylation of lamellar precursors, generating hierarchical hybrid organic− inorganic materials with micro/mesoporosity, including MWWBTEB30 and UTL-H1-UTL-H4.31 Furthermore, the resulting metallosilicates of Ti/Al-IEZ-WWW,22,32 Ti/Al-YNU-1,24,33 and Ti-COE-427 all showed high activities in the corresponding bulky substrate reactions. The PLS-3 aluminosilicate is a lamellar precursor of FER zeolite.34 With a layered structure similar to that of PREFER but a smaller crystal size of nanometer scale (50−150 nm), PLS-3 was readily synthesized with tetraethylammonium

Crystalline microporous aluminosilicate zeolites are promising for selective catalysis because of their strong solid acidity and uniform micropores of molecular dimension.1 With the purpose of extending catalytic applications of zeolites, it is desirable to develop new microporous structures with unique porosity and special architectural features. In particular, new zeolite structures with 12-membered ring (MR) channels or pores larger than 12-MR are highly demanded as they would minimize the diffusion restriction within micropore channels when bulky molecules are processed.2,3 Postsynthesis is an alternative for designing new zeolite structures. There are already many reports of successful conversion of known zeolites to three-dimensional (3D) crystalline materials with new structures. Actually, this kind of structural conversion mainly occurs on the lamellar precursors that are composed of the crystalline sheets of unit cell dimension.4−14 These layered precursors possess a unique layered structure consisting of rigid zeolitic laminas that are interlinked to each other via hydrogen bonding and pillared by organic species such as structure-directing agent (SDA). The interlayer linkage is relatively weak and easily broken, endowing layered zeolites with structural flexibility and diversity as well as changeable dimension with regard to interlayer distance and spatial arrangements of the layers.15,16 Thus, the layered precursors can be post modified by many approaches, such as pillaring,17 delamination,18−20 intercalation,21 and interlayer silylation,22 which generate a number of new materials with © 2014 American Chemical Society

Received: August 28, 2014 Revised: September 20, 2014 Published: September 29, 2014 24662

dx.doi.org/10.1021/jp507719y | J. Phys. Chem. C 2014, 118, 24662−24669

The Journal of Physical Chemistry C

Article

H2O:0.67 B2O3 was reacted at a temperature of 443 K for 5 days. ZSM-5, Beta, and MCM-22 samples converted into proton form using the same procedures mentioned above for PLS-3. 2.2. Characterization Methods. The X-ray powder diffraction (XRD) patterns were measured on a Rigaku Ultima IV X-ray diffractometer using Cu Kα radiation (λ = 1.5405 Å). Scanning electron microscopy (SEM) was performed on a Hitachi S-4800 microscope. Al content was determined by inductively coupled plasma emission spectrometry (ICP) on a Thermo IRIS Intrepid II XSP atomic emission spectrometer. The IR spectra were collected on a Nicolet Nexus 670 FT-IR spectrometer in absorbance mode at a spectral resolution of 4 cm−1. The sample was pressed into a self-supported wafer with 4.8 mg cm−2 thickness, which was set in a quartz cell sealed with CaF2 windows and connected to a vacuum system. After evacuation at 723 K for 2 h, pyridine adsorption was carried out by exposing the pretreated wafer to a pyridine vapor at 298 K for 0.5 h. The adsorbed pyridine was evacuated successively at different temperatures (423−723 K) for 1 h. The spectra were collected at room temperature. 27Al, 29Si, and 13C solid-state MAS NMR spectra were recorded on a Varian VNMRS400WB spectrometer under one pulse condition. 29Si NMR spectra were acquired with a 7.5 mm T3HX probe at 79.43 MHz and a spinning rate of 3 kHz. The chemical shift was referred to 2,2-dimethyl-2-silapentane-5-sulfonic acid sodium salt ((CH3)3Si(CH2)3SO3Na). 13C NMR spectra were recorded with a 7.5 mm T3HX probe at 100.54 MHz and a spinning rate of 5 kHz. The 27Al spectra were recorded at a frequency of 104.18 MHz, a spinning rate of 10.0 kHz, and a recycling delay of 4 s. KAl(SO4)2·12H2O was used as the reference for chemical shift. Nitrogen gas adsorption measurements were carried out at 77 K on a BEL-MAX gas/vapor adsorption instrument. The samples were evacuated at 573 K for at least 6 h before adsorption. Water and benzene vapor adsorption measurements were carried out at 298 K on a BEL-MAX gas/ vapor adsorption instrument. The samples were activated at 573 K under vacuum for at least 6 h before adsorption. 2.3. Catalytic Tests. The m-xylene isomerization/disproportionation reaction was carried out in a fixed-bed continuous glass down-flow reactor under atmosphere pressure. In a typical run, 0.1 g of proton-type zeolite was put into a quartz tube with an inner diameter of 11 mm, where it was activated at 673 K for 1 h in nitrogen flow. Then, a mixture of m-xylene and N2 with a molar ratio of 0.25 was fed into the reactor to start the reaction at 573−673 K. The weight hourly space velocity (WHSV) with respect to m-xylene was varied in the range of 0.85−8.44 h−1 by changing the feed rate of m-xylene. The products of the reaction were analyzed subsequently in a gas chromatograph (HP5890II) equipped with a Supelco-WAX10 capillary column (60 m length, inner diameter = 0.2 mm) and a flame ionization detector (FID). The Friedel−Crafts alkylation or acylation reactions were carried out in liquid phase with a round-bottom flask equipped with a condenser under stirring. The temperature was controlled with an oil bath. The detailed reaction conditions are shown under Results and Discussion. The reaction mixture was subjected to GC analysis (Shimadzu GC-14B) to determine the conversion and product selectivity.

hydroxide as SDA would be more useful for catalysis. The PLS3 precursor is composed of layered stacking of the FER sheets intercalated by the TEA+ species. Direct calcination of PLS-3 leads to 3D FER structure with an intersecting micropore system of 10 × 8-MR. We once investigated the detailed synthesis conditions for the PLS-3 aluminosilicates and demonstrated that they are more stable catalysts for the skeleton isomerization of 1-butene than the conventional 3D FER zeolites prepared by direct hydrothermal synthesis.34 To prepare materials with pore size >10-MR, in this study, we carried out the silylation of PLS-3 lamellar precursor, giving rise to a large-pore zeolite with an interlayer expanded structure, IEZ-PLS-3. Because severe interlayer silylation conditions such as high temperature and acid media may cause a deep dealumination and remove the active sites, we employed ethanol as a solvent to weaken the dealumination as reported previously.29 The resulting material, IEZ-PLS-3, exhibited the porosity and catalytic characteristics of 12-MR zeolites and served as active catalysts for Friedel−Crafts alkylation and acylation.

2. EXPERIMENTAL SECTION 2.1. Material Preparation. 2.1.1. Synthesis of Al-PLS-3 Precursor. The lamellar precursor PLS-3 was synthesized through a solid-state conversion of protonated kanemite using TEAOH as SDA according to literature procedures.34 Hkanemite, Al(NO3)3·9H2O, NaOH, and distilled water were dissolved in tetraethylammonium hydroxide (TEAOH; 25 wt % aqueous solution) under magnetic stirring, giving rise to a gel composition of 1.0 SiO2:1/120 Al2O3:0.2 TEA+:0.04 NaOH:6.5 H2O. This synthetic gel was charged into a stainless autoclave equipped with a Teflon liner and heated at 443 K for 6 h under static conditions. The solid product was collected by filtration, washed with distilled water, and dried overnight in an oven at 353 K, resulting in PLS-3 lamellar precursor. The resulting material was calcined in air at 823 K for 10 h to remove the organic species occluded, giving rise to PLS-3 with the 3D FER structure. The calcined sample was then converted into ammonium form by ion exchange in 1 M NH4Cl solution three times at a solid-to-liquid ratio of 1:50 for 2 h. The product was converted into proton form by calcination at 773 K for 5 h. 2.1.2. Postsynthesis of IEZ-PLS-3. Interlayer-expanded zeolite IEZ-PLS-3 was prepared by silylating PLS-3 precursor with monomeric silane DEDMS. Typically, 1.0 g of PLS-3 precursor was added to a mixture of 0.21 g of DEDMS and 30 mL of 1 or 2 M HCl/EtOH solution. The resulting mixture was then heated statically at a desirable temperature (393−443 K) for 20 h. After silylation, the solid was recovered by filtration, rinsing with distilled water, drying at 353 K, and further calcination at 823 K for 6 h to obtain IEZ-PLS-3. 2.1.3. Synthesis of Beta, ZMS-5, and MCM-22 Zeolites. For control experiments, alminosilicates with the BEA*, MFI, and MWW were hydrothermally synthesized at a Si/Al ratio of 60. Beta zeolite was synthesized from fumed silica, NaAlO2, and TEAOH at a gel composition of 1.0 SiO2:0.0083 Al2O3:0.06 Na2O:0.2 TEAOH:7H2O at 423 K for 3 days. ZSM-5 was synthesized using colloidal silica (Ludox, 30 wt %), NaAlO2 (53.0% Al2O3, 43.9% Na2O), and TPAOH (25 wt % aqueous solution) as raw materials. The gel with a composition of 1.0 SiO2:1/120 Al2O3:0.075 Na2O:0.2 TPAOH:25 H2O at 443 K was reacted for 2 days. MCM-22 was synthesized from fumed silica, piperidine (PI), NaAlO2, and H3BO3. The gel with a molar composition of 1.0 SiO2:0.0083 Al2O3:0.4 Na+:1.0 PI:15

3. RESULTS AND DISCUSSION 3.1. Synthesis of Interlayer-Expanded Zeolite IEZ-PLS3. Figure 1 shows the XRD patterns of PLS-3 precursor and the 24663



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Figure 1. XRD patterns of PLS-3 precursor (a) and the products obtained after interlayer silylation with DEDMS in 2 M HCl−EtOH at 443 K (b), in 1 M HCl−EtOH at 443 K (c), and in 2 M HCl−EtOH at 393 K (d). Other silylation conditions: precursor, 1 g; DEDMS, 0.21 g; solid-to-liquid ratio, 1:30; time, 20 h.

Figure 2. XRD patterns of as-synthesized IEZ-PLS-3 (a) and of IEZPLS-3 after calcination at 723 K (b), 773 K (c), 823 K (d), and 873 K (e).

PREFER reported previously.5,22 The XRD patterns of both PLS-3 and IEZ-PLS-3 after calcination are compared in Figure S1 in the Supporting Information. Their layer-related [200] diffractions appeared at different angles, indicating the creation of disparate pore sizes. 3.2. Characterization of Interlayer-Expanded Zeolite IEZ-PLS-3. Figure 4 shows the representative SEM images of PLS-3 and IEZ-PLS-3 crystals. The morphologies of these samples were very similar to each other. The images indicated that there was no amorphous phase, confirming that they were highly crystallized materials with high phase purity. The crystals were of rod-like morphology with a length of 50−150 nm, which was similar to the literature report.34 The interlayer silylation changed the structure at the unit cell level but did not alter the crystal morphology of microscale. The solid-state 29Si MAS NMR spectra of PLS-3 and IEZPLS-3 together with calcined IEZ-PLS-3 are shown in Figure 5. The main resonances around −110 to −120 ppm were from the silicon atoms coordinated with four silicon atoms (Q4), whereas the resonances at −101 to −110 ppm were attributable to the silicon-bearing OH groups (OH)Si(OSi)3 (Q3) and/or framework Si(OAl)(SiO)3 (Si(1Al)).15,22,25 PLS-3 precursor showed only Q3, Si(1Al), and Q4 signals (Figure 5a), whereas the spectrum of IEZ-PLS-3 showed one extra peak at −13.77 ppm (Figure 5b) at the expense of Q3, implying the presence of the SiMe2(OSi)2 moiety assigned to D2 between the FER layers.35 Because a fully pillared IEZ-FER zeolite has 4 pillaring Si atoms and 36 Si atoms in the framework per unit cell,15 the fraction of D2 resonance for ideal IEZ-FER corresponds to 10%. The relative peak area of D2 was 8.68% for IEZ-PLS-3 (Supporting Information, Table S1, no. 2), implying that about 86.8% of the bridging sites were occupied by the silylating reagents. The calcination of IEZ-PLS-3 caused the increase of Q3 signal from 13.37 to 19.71% at the expense of the D2 peak (Figure 5c and Supporting Information, Table S1, no. 2 and 3), suggesting the combustion of the methyl groups converted them into hydroxyl groups (Q2) and the adjacent Q2 then bonded with each other to form Q3; this phenomenon was similar to the literature report.15 The appearance of a weak Q2 peak (2.54%) for calcined IEZ-PLS-3 at around −90.60 ppm also indicated the uneven silylation, because the nearest hydroxyl groups of neighboring Q2 pillars will bond each other to form Q3 via calcination. These results also suggested that the expanded micropore structure of IEZ-PLS-3 was formed due to the construction of monomeric silica puncheons between the FER layers.

related products prepared under different silylation conditions. The as-synthesized PLS-3 aluminosilicate, the precursor of FER structure, was a highly crystalline material free of other phases (Figure 1a). Because the synthesis system of PLS-3 was unstable and inclined to form Beta as impurity at high Al contents,34 with the purpose of obtaining highly crystalline FER phase free of Beta impurity, the Si/Al ratio of the starting mixture was fixed at 60. With regard to the layered structure, the stacking of FER sheets along the a direction gave the characteristic [200] reflection at 2θ = 7.5° (d200 = 11.8 Å). Figure 1b shows the XRD pattern of IEZ-PLS-3, which was synthesized by direct silylation of PLS-3 precursor with DEDMS in 2 M HCl−EtOH solution at 443 K. The layerrelated diffraction [200] remained at 7.5° but did not shift to higher angle after extraction of intercalated SDA species in acid solution under high-temperature conditions, which could be taken as evidence for the successful interlayer expansion by DEDMS. The silylation conditions such as acid concentration and treatment temperature were optimized to investigate the effects of interlayer expansion on the structure order. For the sake of avoiding deep dealumination of the framework Al, we chose a mild treatment in 1 M HCl−EtOH solution at 443 K, under which IEZ-PLS-3 was obtained with a well-ordered interlayer-expanded structure (Figure 1c). When we lowered the temperature or the acid concentration, the layer-related diffraction [200] moved to higher angles (Figure 1d), implying nonuniform pillaring of silylating reagents between the layers. The thermal stability of IEZ-PLS-3 was investigated by XRD after thermal treatment at different temperatures. Figure 2 shows the powder XRD patterns of as-synthesized IEZ-PLS-3 before and after calcination up to 873 K. No structural change of IEZ-PLS-3 was observed up to 823 K, but the crystalline structure partially collapsed and became less ordered at a higher temperature of 873 K (Figure 2e). Figure 3 gives the schematic illustration for topotactic transformation of PLS-3 lamellar precursor to zeolites with different pore sizes. A three-dimensional zeolite structure of 10 × 8-MR micropores was prepared by direct calcination of PLS3 lamellar precursor. This was simply a result of removal of occluded organic species accompanied by condensation of hydroxyl groups between the layers, inducing a topotactic transformation from precursor to 3D FER topology. By interlayer silylation using DEDMS as pillar, zeolites with 12 × 10-MR channels were formed, very similar to the silylation of 24664



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Figure 3. Schematic illustration for topotactic transformation of PLS-3 lamellar precursor to 3D FER and IEZ-PLS-3.

Figure 4. SEM images of calcined PLS-3 (a) and IEZ-PLS-3 (b).

Figure 6. 13C MAS NMR spectrum of as-synthesized IEZ- PLS-3.

Figure 5. 29Si MAS NMR spectra of as-synthesized PLS-3 (a), IEZPLS-3 (b), and calcined IEZ-PLS-3 (c).

the resonances assigned to TEA+, implying that the organic SDA species were deeply extracted by silyaltion in acid solution. To confirm whether the pore size was enlarged by silylation, we have carried out the adsorption with water and benzene vapor on PLS-3 and IEZ-PLS-3. From the adsorption isotherms shown in Figure 7, IEZ-PLS-3 exhibited a higher adsorption capacity for both water and benzene than PLS-3. This phenomenon indicated IEZ-PLS-3 was more hydrophilic as it contained additional hydroxyl groups related to the Si species incorporated. This characteristic may favor the catalyzing of

The incorporation of silylating reagent groups into lamellar precursor was further investigated by 13C NMR spectroscopy. Figure 6 reveals a typical 13C NMR spectrum of as-synthesized IEZ-PLS-3. A strong resonance at −2.5 ppm was developed by silylation with DEDMS, which was attributed to the presence of (CH3)2Si groups.35 Two weak resonances at 6.80 and 52.68 ppm were due to the −CH3 and −CH2 groups of residual EtOH solvent, respectively. The spectrum was almost absent of 24665



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Figure 8. IR spectra in the hydroxyl stretching vibration region of calcined PLS-3 (a) and IEZ- PLS-3 (b).

cm−1 that was attributed to terminal isolated silanols.36 PLS-3 exhibited a very intense band at 3600 cm−1 (Figure 8a), which was characteristic of bridging Si(OH)Al groups and was taken as evidence for the incorporation of Al into the framework. The silylation decreased greatly the band intensity at 3600 cm−1 (Figure 8b). This implied a dealumination of the framework Al took place during silylation in acid at high temperature in acid solution. However, it is worth mentioning that there was still a part of tetrahedrally coordinated Al retained in the framework. ICP analysis indicated that PLS-3 had a bulk Si/Al ratio of 55, close to the gel composition (Si/Al ratio of 60) (Table 1, no. 1). The Si/Al ratio increased to 65 for IEZ-PLS-3 (Table 1, no. 2), implying the dealumination occurred by 15.4% during silylation. 27 Al NMR spectra given in Figure 9 verified qualitatively that both samples possessed the tetrahedral framework Al as they

Figure 7. Water (A) and benzene vapor (B) adsorption isotherms of calcined PLS-3 (a) and IEZ- PLS-3 (b).

hydrophilic substrates as the adsorption capacity of these molecules could be enhanced. Moreover, in comparison to PLS-3, IEZ-PLS-3 was characteristic of a much larger porosity as it adsorbed readily bulky molecules of benzene. Thus, IEZPLS-3 was potentially useful for processing bulk substrate reactions requiring open spaces. The physicochemical properties of PLS-3, IEZ-PLS-3, and other zeolites are given in Table 1. The specific surface area was Table 1. Physicochemical Properties of Different Zeolite Materials no.

sample

Si/Al ratioa

SBETb

Sextc

Vtotald

1 2 3 4

Al-PLS-3 IEZ-PLS-3 ZSM-5 Beta

55 65 55 53

411 423 406 537

138 141 83 104

0.28 0.27 0.22 0.29

a Determined by ICP. bSpecific surface area given by N2 adsorption at 77 K and calculated by the Brunauer−Emmett−Teller (BET) method. c Given by t plot. dPore volume calculated from the adsorption capacity at P/P0 = 0.9.

Figure 9. 27Al MAS NMR spectra of calcined PLS-3 (a) and IEZ-PLS3 (b).

showed a single resonance at 54 ppm.37 Nevertheless, the 54 ppm resonance was relatively broad and less intensive for IEZPLS-3 (Figure 9b), implying its Al species were less symmetrical. There was no resonance appearing at 0 ppm, which was indicative of the absence of octahedral extraframework Al. Because the catalytic properties of aluminosilicates were closely related to their Brønsted and Lewis acidity, pyridine was employed as a probe molecule to provide detailed information about the amount and strength of Brønsted and Lewis acid sites of PLS-3 and IEZ-PLS-3. The IR spectra of adsorbed pyridine in the range of pyridine ring stretching modes were measured

measured by the BET method, whereas the total volume was obtained from the isotherms at P/P0 = 0.9 because a remarkable increase in adsorption capacity due to an interparticle condensation of nitrogen occurred easily at P/P0 > 0.9 for small crystal materials. The SBET and Vtotal of IEZ-PLS-3 were larger than those of PLS-3, which was in coincidence with the aforementioned vapor adsorption data. IR and 27Al NMR spectroscopies were applied to study the coordination states of Al in zeolites. Figure 8 shows the IR spectra in the hydroxyl stretching vibration region for PLS-3 and IEZ-PLS-3. Both materials showed a sharp band at 3745 24666



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diffusion rate of these two isomers inside micropore channels.40 In addition, the disproportionation of m-xylene takes place through a bimolecular intermediate, which involves a much bulkier reaction transition state than the monomolecular isomerization process.40 Therefore, the ratio of isomerization to disproportionation (i/d) can give proof of the presence of ample space favorable for bimolecular reaction. Figure 11 shows the dependence of conversion and i/d ratio on WHSV in the m-xylene isomerization/disproportionation

after desorption at 423−723 K (Figure 10). The bands at 1599 and 1440 cm−1 associated with hydrogen-bonded and physi-

Figure 11. m-Xylene conversion and i/d ratio as a function of WHSV on calcined PLS-3 (a) and IEZ-PLS-3 (b). Reaction conditions: catalyst, 0.1 g; temperature, 623 K; time, 1 h; WHSV, 0.85−8.44 h−1.

over PLS-3 and IEZ-PLS-3. IEZ-PLS-3 gave an obviously higher conversion than PLS-3 independent of WHSV. The above pyridine adsorption IR spectra and ICP analysis verified that PLS-3 contained more Brønsted and Lewis acid sites than IEZ-PLS-3. Thus, the higher conversion achieved with IEZPLS-3 should be attributed to the interlayer expansion by silylation. The formation of expanded pores would benefit the adsorption, diffusion, and desorption of bulky aromatic molecules. The i/d selectivity data were in coincidence to this deduction. The i/d selectivity for PLS-3 was around 40, indicating isomerization occurred more easily than disproportionation for PLS-3 with smaller pores. After silylation, this index significantly reduced to 2.6−3.7 for IEZ-PLS-3. This phenomenon indicated the bimolecular reaction needing open reaction spaces took place more easily on IEZ-PLS-3, and this can be taken as proof for the expansion of pore size. Table S2 in the Supporting Information gives the p/o ratio, i/d ratio, and conversion for various zeolites with comparable Si/Al ratios. IEZ-PLS-3 showed an i/d ratio similar to that of Beta (Supporting Information , Table S2, no. 2 and 3), indicating it was featured with a shape selectivity characteristic of 12-MR large-pore zeolites. On the other hand, PLS-3 and ZSM-5 both having 10-MR channels exhibited much higher i/d ratios than IEZ-PLS-3 and Beta (Supporting Information, Table S2, no. 1 and 4). 3.3.2. Friedel−Crafts Alkylation of Anisole with Benzyl Alcohol. Having an expanded pore opening, rigid structure within FER layers, and tetrahedral Al in the framework, IEZPLS-3 would be much more effective than PLS-3 for catalyzing bulky molecules. Table S3 in the Supporting Information summarizes the results obtained on various zeolites in the alkylation of anisole with benzyl alcohol. This reaction gave two main products of 2-benzylanisole and 4-benzylanisole together with a byproduct of benzyl ether. The catalysts investigated all exhibited a higher selectivity of 4-benzylanisole than that of 2benzylanisole because of steric effect. The highest conversion

Figure 10. IR spectra of calcined PLS-3 (A) and IEZ-PLS-3 (B) after pyridine adsorption and desorption at 423 K (a), 523 K (b), 623 K (c), and 723 K (d).

cally adsorbed pyridine decreased in intensity with a rising desorption temperature. On the other hand, the bands at 1540 cm−1 corresponding to Brønsted acid sites and at 1455 cm−1 corresponding to Lewis acid sites together with the bands at 1490 cm−1 characteristic of both Brønsted and Lewis acid sites38 were more evacuation temperature resistant and remained even after desorption at 723 K. These bands were apparently correlated to the different vibration modes of the pyridine rings adsorbed on the Al species and can be taken as evidence for the presence of Brønsted and Lewis acid sites in these materials. The bands at 1540, 1490, and 1455 cm−1 decreased in intensity for silylated material IEZ-PLS-3 (Figure 10B), indicating a partial loss of acid sites by silylation as a result of dealumination. 3.3. Catalytic Performance of IEZ-PLS-3 Zeolite. Three types of reactions, that is, m-xylene isomerization/disproportionation, Friedel−Crafts alkylation of anisole with benzyl alcohol, and acylation of anisole with acetic anhydride, have been carried out to investigate the catalytic properties of IEZ-PLS-3 in comparison to other zeolites. 3.3.1. m-Xylene Isomerization/Disproportionation. The mxylene isomerization/disproportionation reaction has been used by numerous groups to characterize the pore properties of zeolites.39−41 m-Xylene can isomerize into the para and ortho isomers and disproportionate into trimethylbenzenes (TMBs) and toluene. For the isomerization of m-xylene to p-xylene and o-xylene, 10-MR pore zeolites give higher para/ortho (p/o) ratios than large-pore zeolites, owing to the differences in the 24667



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tional FER topology. Characteristic of 12-MR zeolites in porosity and catalytic performances, IEZ-PLS-3 is more active to Friedel−Crafts alkylation of anisole with benzyl alcohol and acylation of anisole with acetic anhydride than Beta, MCM-22, and ZSM-5 zeolites at comparable Si/Al ratios. IEZ-PLS-3 is expected to be a useful solid acid catalyst for processing large molecules.

and specific activity (TON) were obtained on IEZ-PLS-3. It even showed a better performance than 3D 12-MR Beta, which should be ascribed to the large porosity created by silyaltion and intrinsic active sites in FER layers suitable for this reaction. Because PLS-3 and IEZ-PLS-3 had identical crystal morphology and similar external surface area (Table 1, no. 1 and 2), their catalytic performances mainly depended on their pore sizes. Because the 12-MR pores of Beta had almost no steric hindrance for the accessibility of reactants to acid sites and for the diffusion of products out of channels, the relatively low catalytic activity on Beta might be attributed to its improper intrinsic active sites and perhaps unsuitable acid strength. For ZSM-5 of 10-MR pores, the worse catalytic performance was mainly due to geometric constraint of medium pore size and limited external surface. 3.3.3. Friedel−Crafts Acylation of Anisole with Acetic Anhydride. Figure 12 shows the catalytic results of Friedel−

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ASSOCIATED CONTENT

S Supporting Information *

Tables S1−S3 and Figure S1. This material is available free of charge via the Internet at http://pubs.acs.org.

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AUTHOR INFORMATION

Corresponding Authors

*(P.W.) Phone/fax: +86-21 62232292. E-mail: pwu@chem. ecnu.edu.cn. *(H.W.) Phone/fax: +86-21 62232292. E-mail: hhwu@chem. ecnu.edu.cn. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS We gratefully acknowledge the National Natural Science Foundation of China (21373089, U1162102), the Ph.D. Prog ram s Foundat io n of Minist ry of Ed ucation (2012007613000), the National Key Technology R&D Program (2012BAE05B02), and the Shanghai Leading Academic Discipline Project (B409).

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REFERENCES

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Figure 12. p-MAP yield in the acylation of anisole with acetic anhydride over calcined PLS-3 (a), IEZ-PLS-3 (b), Beta (c), ZSM-5 (d), and MCM-22 (e). Reaction conditions: catalyst, 0.1 g; anisole, 5.23 g; acetic anhydride, 5 mmol; temperature, 353 K.

Crafts acylation of anisole with acetic anhydride over various zeolites. The catalysts all gave selectivity >99% for the product of p-methoxyacetophenone (p-MAP). Thus, p-MAP yield based on the initial amount of acetic anhydride was used to compare the catalytic performance. IEZ-PLS-3 showed a much higher pMAP yield than PLS-3. The enhanced catalytic activity on IEZPLS-3 was probably due to easy formation of p-MAP in the 12MR micropores formed as a result of interlayer expansion. The lower activity of PLS-3 was attributed to its relatively narrow 10-MR micropore, limiting the formation of large MAP molecules. These outcomes were in coincidence with the catalytic results discussed above. In addition, the activity of IEZPLS-3 was higher than that of 3D 12-MR Beta, which is currently used industrially in acylation processes,42 indicating IEZ-PLS-3 may serve as a promising solid acid catalyst for this reaction.

4. CONCLUSIONS An interlayer expanded zeolite IEZ-PLS-3 with 12 × 10-MR micropores has been synthesized by a silylation of the lamellar precursor of PLS-3 aluminosilicate with a Si/Al ratio of 60. The silylation enlarges the interlayer pore entrance and specific surface area effectively in comparison to PLS-3 with conven24668



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Synthesis, Characterization, and Catalytic Properties of Interlayer

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