Journal of Non-Crystalline Solids 355 (2009) 2209–2215

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Journal of Non-Crystalline Solids

journal homepage: www.elsevier .com/ locate/ jnoncrysol

Synthesis and characterization of mesoporous, tungsten-containing molecularsieve composites

Xiaoli Zhang, Chengyuan Yuan, Minyan Li, Biao Gao, Xiangyu Wang, Xiucheng Zheng *

Department of Chemistry, Zhengzhou University, Zhengzhou 450001, China

a r t i c l e i n f o a b s t r a c t

Article history:Received 30 October 2008Received in revised form 28 July 2009Available online 9 September 2009

Keywords:Metal–matrix compositesCatalysisX-ray diffractionSEM S100Scanning electron microscopyPorosityNano-compositesFTIR measurements

0022-3093/$ - see front matter � 2009 Elsevier B.V. Adoi:10.1016/j.jnoncrysol.2009.08.007

* Corresponding author. Tel.: +86 371 67781780; faE-mail address: zhxch@zzu.edu.cn (X. Zheng).

Mesoporous, tungsten-containing molecular sieve (W-SBA-15) composites were successfully synthesizedvia one-step hydrothermal processing using tetraethyl orthosilicate (TEOS) as the silica precursor, sodiumtungstate as the tungsten precursor, and pluronic P123 triblock polymer (EO20PO70EO20, Mav = 5800) as astructure-directing reagent. The influence of various synthesis factors, such as TEOS/sodium tungstate(Si/W) molar ratios, stirring solution temperatures, TEOS pre-hydrolysis time, and crystallizationtemperatures, on the structure of the W-SBA-15 composite were investigated. The prepared materials werecharacterized by using X-ray diffraction (XRD), infrared spectroscopy (IR), diffuse reflectance ultraviolet–visible spectroscopy (DR UV–vis), scanning electron microscopy (SEM), and nitrogen adsorption–desorp-tion measurements. The results showed that all the W-SBA-15 composite materials retained the mesoporestructure of SBA-15 and the tungsten oxide species successfully substituted silica in the framework.

� 2009 Elsevier B.V. All rights reserved.

1. Introduction

SBA-15, a new type of ordered mesoporous material achievedby using a triblock copolymer as structure-directing agent understrongly acidic conditions, has attracted considerable attention inthe fields of heterogeneous catalysis and nanoscale materials [1].SBA-15 possesses a high surface area (600–1000 m2 g�1) and isformed by a hexagonal array of uniform tubular channels with tun-able pore diameters in the range of 5–30 nm which are obviouslylarger than those of MCM-41. Especially given its thicker walls(31–64 Å), SBA-15 provides a thermal stability and hydrothermalstability that exceed those for the thinner walled MCM-41 materi-als [2,3]. Furthermore, metal-containing SBA-15 materials havebeen successfully incorporated by direct synthesis process suchas Al [4], CrAl [5], Ti [3], TiAl [6] and Ru [7]. These materials havealso attracted much attention due to their potential applications.

Tungsten-containing mesoporous silica is an important catalyticmaterial for metathesis and selective oxidation reaction. To date,scholars have prepared some tungsten-containing mesoporousmaterials and investigated their catalytic properties. Yang et al. [8]prepared W-MCM-48 material under hydrothermal conditions viapH adjustment. The catalytic experiment indicated that the W-MCM-48 material was very active as a heterogeneous catalyst forthe selective oxidation of cyclopentene to glutaraldehyde. W-SBA-

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15 material was synthesized via a one-step co-condensationsol–gel method, and the tungsten-substituted mesoporous SBA-15catalysts showed excellent catalytic performance in the metathesisof 1-butene to high-value olefins [9]. Hu et al. [10] directly preparedordered SBA-15 mesoporous silica containing tungsten oxides andtungsten carbides. Moreover, they proposed a model of tungsten dis-tribution in W-SBA-15 and analyzed the mechanism of carburiza-tion. However, to the best of our knowledge, few literatures havereported the influence of synthesis factors on the specific structuraland tungsten distribution in SBA-15 in details so far.

In this work, W-SBA-15 composite were synthesized via directlyhydrothermal process. The influence of various synthesis parame-ters, such as stirring solution temperatures, TEOS pre-hydrolysistime, Si/W molar ratios and crystallization temperatures, on thestructure of W-SBA-15 composite was discussed in the light ofcharacterization results. The results will be helpful for the investi-gation of their catalytic properties in the green synthesis of adipicacid in the further study.

2. Experimental

2.1. Preparation of W-SBA-15 composite

W-SBA-15 composite were prepared using Pluronic P123 tri-block polymer (EO20PO70EO20, Mav = 5800, Aldrich) as template un-der acidic conditions. Briefly, 2.0 g of P123 was added to 55 ml ofHCl solution to yield a transparent solution. After stirring for 4 h

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at the pre-designated temperatures (30, 40, 50 and 60 �C, respec-tively), 4.2 g of tetraethylorthosilicate (TEOS) was slowly addedinto the solution, stirred for the pre-designated time (0, 0.5, 1.0,2.0 h, respectively). Then, some aqueous sodium tungstate solution(Si/W = 20, 30, 40 and 50, respectively) were added dropwise un-der vigorous stirring, and the solution stirred for another 24 h.The prepared sample was further hydrothermally treated at thepre-designated crystallization temperatures (100, 120 and 140 �C,respectively) for two days. The solid products were recovered byfiltration and calcined at 550 �C for 6 h to obtain a pale-yellowpowder of W-SBA-15.

Pure SBA-15, herein, was also prepared by hydrothermal meth-od according to Ref. [11] for the comparison purpose.

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(a) Pure SBA-15 (100 oC)

2 Theta (deg.)

Fig. 1. Low-angle XRD patterns of pure SBA-15 and W-SBA-15 composite synthe-sized with different crystallization temperatures.

2.2. Characterization of samples

N2 adsorption–desorption experiments were performed with aQuantachrome NOVA 1000e surface area and pore size analyzer.Before measurement, the samples were degassed at 150 �C undervacuum (1.33 Pa) for 1.5 h. The specific surface area of sampleswas determined using the Brunauer–Emmett–Teller (BET) method.The pore volume and pore size distribution were derived from thedesorption profiles of the isotherms using the Barrett–Joyner–Halanda (BJH) method. The related curves are just drawn as guidesto the eyes. Furthermore, the analytic systematic error was about1.0 % and the random error was about 0.3% in the case.

X-ray powder diffraction (XRD) patterns of the samples wererecorded using a PW3040/60 diffractometer with nickel filteredCu Ka radiation (k = 1.5418 ÅA

0

) at scanning rates of 0.3� min�1 inthe 2h range of 0.5–5�. Large-angle XRD patterns of the sampleswere recorded with the same diffractometer at scanning rates of4� min�1 in the 2h range of 15–80�. The related curves are justdrawn as guides to the eyes. Furthermore, the analytic systemhas not obvious systematic error and the random error was about1.0%.

Scanning electron microscopy (SEM) images were taken using aHITACHI S4800 scanning electron microscope. For the SEM obser-vations, the samples were deposited on a sample holder and coatedwith Au, using an accelerating voltage of 10.0 kV. The analytic sys-tem has not obvious systematic error and random error.

IR spectra were recorded on a Thermoscientific Nicolet 380 IRspectrometer at 2 cm�1 resolution using a KBr pellet technique. Be-fore measurement, all samples and KBr were dried in loft drier at373 K overnight. The sample diluted in KBr (2 wt%) was pressedinto a wafer (40.5 mg cm�2 thickness). The spectra were collectedin absorbance mode. The related curves are just drawn as guidesto the eyes. Furthermore, the analytic system has not obvious sys-tematic error and random error.

Diffuse reflectance UV–vis spectra were collected on a HitachiU-3010 UV–vis spectrophotometer with BaSO4 as reference. Thecurves are smoothed with Fast Fourier Transform Algorithm meth-od (FFT Filter) and the number point is 5. Furthermore, the analyticsystem has not obvious systematic error and random error.

Fig. 2. Nitrogen sorption isotherms and pore size distributions (insert) of pure SBA-15 (a) 100 �C and W-SBA-15 composite synthesized with different crystallizationtemperatures: (b) 100 �C, (c) 120 �C and (d) 140 �C.

3. Results

3.1. Influence of the crystallization temperatures

Low-angle XRD analysis is an effective probe for the meso-structure materials. Fig. 1 shows the low-angle XRD patterns ofpure SBA-15 and W-SBA-15 composite synthesized with differentcrystallization temperatures. It can be seen that all samples exhib-ited XRD patterns with one very intense diffraction peak and twoweak peaks, which are characteristic of 2-D hexagonal (P6mm)structure with excellent textural uniformity. Moreover, compared

with pure SBA-15, there was a gradual shift towards lower anglesfor the peaks (1 0 0), (1 1 0) and (2 0 0) of W-SBA-15. Meanwhile,the peaks of W-SBA-15 also shifted towards lower angles withincreasing of crystallization temperature.

Fig. 2 shows the nitrogen sorption isotherms and pore size dis-tributions of pure SBA-15 and W-SBA-15 composite as mentionedabove. All the isotherms were similar and displayed characteristicsof type IV with H1-type hysteresis loops which are typical of mes-oporous materials. Furthermore, the sharpness of the adsorptionbranches at relative pressures between 0.60 and 0.85 is indicativeof a narrow mesopore size distribution (Fig. 2 insert). The BET sur-face area, pore volume and pore diameter obtained from N2

adsorption measurements, as shown in Table 1, indicated thatthe introduction of tungsten oxide caused the decreased of surfacearea. Opposite behavior were observed for the pore volume, porediameter and the wall thickness. For the W-SBA-15 composite,the surface area decreased obviously with the increasing of thecrystallization temperatures (lower 140 �C). Meanwhile the other

Table 1Pore structure parameters of pure SBA-15 and W-SBA-15 composite crystallized at different temperatures.

Crystallization temperatures(�C)

BET area(m2 g�1)

Pore volume(cm3 g�1)

Mean pore diameter(nm)

XRD d(1 0 0) spacing(nm)

Cell parameter(nm)

Wall thickness(nm)

SBA-15 (1 0 0) 630 ± 8 0.86 ± 0.03 5.47 ± 0.07 9.03 ± 0.09 10.43 ± 0.10 4.96 ± 0.05W-SBA-15 (1 0 0) 614 ± 8 1.08 ± 0.03 6.06 ± 0.08 9.65 ± 0.10 11.14 ± 0.10 5.08 ± 0.05W-SBA-15 (1 2 0) 528 ± 7 1.07 ± 0.02 8.11 ± 0.10 13.31 ± 0.10 15.37 ± 0.11 8.48 ± 0.06W-SBA-15 (1 4 0) 394 ± 7 1.09 ± 0.02 11.04 ± 0.09 – – –

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Fig. 3. Low-angle XRD patterns of W-SBA-15 composite prepared at differentstirring solution temperatures: (a) 30 �C, (b) 40 �C, (c) 50 �C and (d) 60 �C.

Fig. 4. Nitrogen sorption isotherms and pore size distributions (insert) of W-SBA-15 composite prepared at different stirring solution temperatures: (a) 30 �C, (b)40 �C, (c) 50 �C and (d) 60 �C.

Table 2Pore structure parameters of W-SBA-15 composite prepared at different stirring solution

Temperatures(�C)

BET area(m2 g�1)

Pore volume(cm3 g�1)

Mean diameter(nm)

30 662 ± 6 0.97 ± 0.02 5.85 ± 0.0940 714 ± 7 1.08 ± 0.03 6.06 ± 0.0750 652 ± 6 1.07 ± 0.03 6.53 ± 0.0860 663 ± 6 1.12 ± 0.02 6.74 ± 0.08

X. Zhang et al. / Journal of Non-Crystalline Solids 355 (2009) 2209–2215 2211

physical parameters increased (Table 1). It also can be seen fromFig. 2 that higher crystallization temperatures may lead to widerpore size distribution.

3.2. Influence of the stirring solution temperatures

Figs. 3 and 4 illustrates the low-angle XRD patterns and nitro-gen sorption isotherms of W-SBA-15 composite prepared at differ-ent stirring solution temperatures, respectively. As shown in Fig. 3,The XRD patterns showed well-resolved peaks that can be indexedas (1 0 0), (1 1 0) and (2 0 0) diffraction peaks associated withP6mm order hexagonal structure. The isotherms also displayedcharacteristics of type IV with H1-type hysteresis loops (Fig. 4),indicating that the ordered hexagonal structure was formed inthese cases. W-SBA-15 sample synthesized at 30 �C displayed low-er value of pore volume, pore diameter and the wall thicknesscompared with the others. However, when the temperature roseup to 60 �C, the wall thickness decreased (from 5.08 to 4.65 nm)as shown in Table 2.

3.3. Influence of the different TEOS pre-hydrolysis time

The evolution of XRD patterns of W-SBA-15 composite synthe-sized with different TEOS pre-hydrolysis time is shown in Fig. 5.Comparing with W-SBA-15 composite synthesized with the

temperatures.

XRD d(1 0 0) spacing(nm)

Cell parameter(nm)

Wall thickness(nm)

9.45 ± 0.10 10.91 ± 0.11 5.06 ± 0.059.65 ± 0.10 11.14 ± 0.11 5.08 ± 0.05

10.05 ± 0.10 11.61 ± 0.11 5.08 ± 0.059.86 ± 0.10 11.39 ± 0.11 4.65 ± 0.05

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Fig. 5. Low-angle XRD patterns of W-SBA-15 composite synthesized with differentTEOS pre-hydrolysis time: (a) 0.0 h, (b) 0.5 h, (c) 1.0 h and (d) 2.0 h.

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Fig. 6. Nitrogen sorption isotherms and pore size distributions (insert) of W-SBA-15 composite synthesized with different TEOS pre-hydrolysis time: (a) 0.0 h, (b)0.5 h, (c) 1.0 h and (d) 2.0 h.

2212 X. Zhang et al. / Journal of Non-Crystalline Solids 355 (2009) 2209–2215

addition of TEOS and sodium tungstate synchronously (TEOSpre-hydrolysis 0.0 h) and TEOS pre-hydrolysis 1.0 h, the compositesynthesized with TEOS pre-hydrolysis 0.5 and 2.0 h exhibited low-er peak angles.

Fig. 6 illustrates the N2 adsorption–desorption isotherms andthe corresponding pore size distribution of the W-SBA-15 compos-ite synthesized with different TEOS pre-hydrolysis time. All sam-ples exhibited typical type IV with H1-type hysteresis loops.

Table 3Pore structure parameters of W-SBA-15 composite synthesized with different TEOS pre-h

TEOS pre-hydrolysis time(h)

BET area(m2 g�1)

Pore volume(cm3 g�1)

Mean pore dia(nm)

0 689 ± 6 1.10 ± 0.03 6.39 ± 0.090.5 690 ± 6 1.12 ± 0.03 6.47 ± 0.091.0 714 ± 7 1.08 ± 0.03 6.06 ± 0.092.0 687 ± 6 1.05 ± 0.03 6.09 ± 0.09

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Fig. 7. Low-angle (A) and large-angle (B) XRD patterns of W-SBA-15 composite synthesiSi/W = 40 and (e) Si/W = 50.

Table 3 shows the pore structure parameters of W-SBA-15 com-posite synthesized with different TEOS pre-hydrolysis time. all theW-SBA-15 composite exhibited similar surface area and the mate-rial with TEOS pre-hydrolysis 0.5 h exhibited the largest pore vol-ume (1.12 cm3 g�1) and mean pore diameter (6.47 nm).

3.4. Influence of the Si/W molar ratios

The low-angle and large-angle XRD patterns of pure SBA-15 andW-SBA-15 composite synthesized with various Si/W molar ratiosare shown in Fig. 7. Firstly, it can be seen from Fig. 7(A) that thecharacteristic peaks of the SBA-15 hexagonal structure are obviousin the patterns of W-SBA-15 prepared with different Si/W molarratios. Secondly, compared with pure SBA-15, there was a gradualshift towards lower angles for the (1 0 0) peak of W-SBA-15 dis-playing larger cell parameter. In addition, it is interesting thatthe intensity of W-SBA-15 with Si/W = 40 shows a dramatic de-crease. As shown in Fig. 7(B), the characteristic peaks of WO3

(monoclinic (P21/n), 2h = 23.08�, 23.58�, 33.28�, etc.) are not pres-ent in the patterns of W-SBA-15 composite.

Fig. 8 illustrates the N2 adsorption–desorption isotherms andthe corresponding pore size distribution of the W-SBA-15 compos-ite synthesized with various Si/W molar ratios. All samples exhib-ited typical type IV with H1-type hysteresis loops. Furthermore,the sample with Si/W = 40 exhibited the largest pore diameter.

It is known that diffuse reflectance UV–vis spectroscopy is avery sensitive probe for the presence of extra-framework transitionmetal oxides in different heteroatomic mesostructures [9,11].Here, the DR UV–vis spectra of W-SBA-15 composite synthesizedwith various Si/W molar ratios ((Si/W = 20, 30, 40 and 50) in theregion of 200–600 nm are depicted in Fig. 9. As can be seen fromFig. 9, two bands around 220 and 240 nm have been resolved.

ydrolysis time.

meter XRD d(1 0 0) spacing(nm)

Cell parameter(nm)

Wall thickness(nm)

9.61 ± 0.10 11.10 ± 0.11 4.71 ± 0.059.87 ± 0.10 11.40 ± 0.11 4.93 ± 0.059.53 ± 0.10 11.00 ± 0.11 4.94 ± 0.059.65 ± 0.10 11.14 ± 0.11 5.05 ± 0.05

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Fig. 8. Nitrogen sorption isotherms and pore size distributions (insert) of W-SBA-15 composite synthesized with various Si/W molar ratios: (a) Si/W = 20, (b) Si/W = 30, (c) Si/W = 40 and (d) Si/W = 50.

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Fig. 9. DR UV–vis spectra of W-SBA-15 composite synthesized with various Si/Wmolar ratios: (a) Si/W = 20, (b) Si/W = 30, (c) Si/W = 40 and (d) Si/W = 50.

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Fig. 10. IR spectra of W-SBA-15 composite synthesized with various Si/W molar rati

X. Zhang et al. / Journal of Non-Crystalline Solids 355 (2009) 2209–2215 2213

Furthermore, the intensity of the band around 220 nm in-creased with the decrease of Si/W molar ratios in the range of30–50. However, when the Si/W molar ratios decrease to 20, anobvious shoulder band centered at about 400 nm appeared.

The fourier transform infrared (IR) spectra of pure SBA-15 andW-SBA-15 composite synthesized with various Si/W molar ratiosin the wavenumber range 4000–2400 and 1400–400 cm�1 areshown in Fig. 10. As shown in Fig. 10(A), the bands around3745 cm�1 can be assigned to the stretching vibration mode of iso-lated terminal silanol (Si–OH) groups [12]. Meanwhile, the bandsaround 3430 cm�1 can be assigned to the hydrogen-bonded Si-OH groups because of geminal Si–OH of Q2 and adjacent Q3 [10].As shown in Fig. 10(B), the band at 1080 and 810 cm�1 correspondsto characteristic of anti-symmetric vibration nonbridging oxygenatoms (Si–Od�) of Si–O–H bonds and symmetric stretching vibra-tion (Si–O–Si)sym of tetrahedral SiO4�

4 for SBA-15 [13,14]. Further-more, as seen in Fig. 10(B), no typical band located at around960 cm�1 can be observed for the pure SBA-15. However, W-SBA-15 exhibits an infrared band at around 960 cm�1.

Fig. 11 shows the SEM images of W-SBA-15 composite synthe-sized with Si/W = 40 and 20, respectively. The images reveal thatboth the W-SBA-15 retained the well-defined wheat-like macro-structure of pure SBA-15 [10]. And the particles aggregated to-gether with rope-like domains with relatively uniform sizes of4 lm. No WO3 crystals or amorphous congeries could be foundon the surface of W-SBA-15 with Si/W = 40 as confirmed inFig. 11(a). When the Si/W molar ratio is equal to 20, although nostrong characteristic peaks of crystalline WO3 appeared in XRDpatterns as shown in Fig. 7(B) and the rope-like domains were stilllargely maintained, a significant degradation in macroscopic struc-ture can be observed.

4. Discussion

Compared with pure SBA-15, there was a gradual shift towardslower angles for the peaks of W-SBA-15 due to the fact that the W–O bond is longer than that of Si–O [15]. Furthermore, the peaks ofW-SBA-15 also shifted towards lower angles with increasing ofcrystallization temperature, but only a little change happenedwhen the temperature rose up to 140 �C. This suggests that highertemperature make against the substitution of tungsten species.

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os: (a) pure SBA-15, (b) Si/W = 20, (c) Si/W = 30, (d) Si/W = 40 and (e) Si/W = 50.

Fig. 11. SEM images of W-SBA-15 composite synthesized with (a) Si/W = 40 and (b) Si/W = 20.

2214 X. Zhang et al. / Journal of Non-Crystalline Solids 355 (2009) 2209–2215

Comparing with W-SBA-15 composite synthesized with theaddition of TEOS and sodium tungstate synchronously (TEOS pre-hydrolysis 0.0 h) and TEOS pre-hydrolysis 1.0 h, the composite syn-thesized with TEOS pre-hydrolysis 0.5 and 2.0 h exhibited lowerpeak angles, displaying that the latter had larger cell parameterand higher doping of tungsten oxides [16].

It is known that the framework of SBA-15 began to grow afterthe TEOS hydrolysis 0.5 h and the whole framework appearedwhen the TEOS hydrolysis time rose up to 2.0 h. In order to makemore tungsten species introduce into silica framework, an optimalTEOS hydrolysis time is necessary. The addition of tungsten specieswill destroy the formation of framework when the TEOS hydrolysistime lower 0.5 h. On the other hand, tungsten species can notintroduce into silica framework easily once the formation of theSBA-15 structure.

It is interesting that the intensity of W-SBA-15 with Si/W = 40shows a dramatic decrease. In our opinion, the reason may be thatmore WO3 entered the SBA-15 framework which leads to more dis-ruption of the structure in the Si/W = 40 case. As shown in Fig. 7(B),the characteristic peaks of WO3 (monoclinic (P21/n), 2h = 23.08�,23.58�, 33.28�, etc.) are not present in the patterns of W-SBA-15composite. This suggests that WO3 crystallites are not formed.

The band centered at about 220 nm in the UV–vis spectroscopyimplies the presence of a ligand-to-metal charge transfer involvingisolated transition metal sites [9,11], and is generally considereddirect proof that transition metal atoms have been incorporatedinto the framework of a molecular sieve [9]. From the above spec-troscopic studies, we inferred that tungsten species successfullyincorporated into the framework SBA-15 with the presence in tet-rahedral coordination denoted as c-W by Hu et al. [10]. The bandcentered at ca. 240 nm may be attributed to a distorted tetrahedralcoordination environment or the existence of some tungsten spe-cies in an octahedral coordination environment [9]. In other words,these tungsten species are inside SBA-15 channels or in the intra-channel surfaces of the SBA-15 denoted as a-W and b-W by Huet al. [10], respectively.

Furthermore, the intensity of the band around 220 nm in-creased with the decrease of Si/W molar ratio in the range of 30–50, suggesting that the amount of framework tungsten oxide spe-cies increased. However, when the Si/W molar ratio decrease to 20,an obvious shoulder band centered at about 400 nm appeared,implying that some extra-framework tungsten species haveformed in the sample. Hu et al. [9] suggested these tungsten spe-cies in bulk WO3 or cluster formation. In combined with thelarge-angle XRD results, we supposed, herein, that the extra-framework tungsten species (WO3 particles) were highly dispersedin the SBA-15 host. The results reflected that the molar ratio ofSi/W should be larger than 30 to obtain high quality tungstensubstituted SBA-15 materials.

The fourier transform infrared (IR) spectra of pure SBA-15 andW-SBA-15 composite synthesized with various Si/W molar ratiowere consistent with the IR results by Yang et al. [17] who deemedthe band at 3400 cm�1 to the O–H stretching vibrations mode ofthe silanols involved in hydrogen interactions with the adsorbedwater molecules.

The band at around 960 cm�1 has been widely used to charac-terize the incorporation of metal ions in the silica framework asthe stretching Si-O vibration mode perturbed by the neighboringmetal ions [18,19]. The presence of an infrared band around960 cm�1 is a piece of direct evidence for the isomorphous substi-tution of Si by W ions in W-SBA-15. This result also suggests thattungsten species are actually imbedded into the lattice of SBA-15.

In addition, the results of the low-angle XRD patterns and thenitrogen sorption isotherms of W-SBA-15 composite synthesizedunder the present conditions indicated that the addition of tung-sten species retained the ordered mesoporous structure of SBA-15. This means that the hydrothermal synthesis process appearsto be an effective method for the preparation of W-SBA-15 com-posite materials.

5. Conclusions

Tungsten species were effectively introduced into the frame-work of mesoporous molecular sieves SBA-15 by a one-step hydro-thermal process. The influence of various synthesis parameters onthe physico-chemical properties of W-SBA-15 composite materialswere discussed in detail. The W-SBA-15 composite is anticipated tobe an effective catalyst in the green synthesis of adipic acid, a topicof future study.

Acknowledgements

The authors are grateful to the financial support of the Innova-tion Experiment Fund of Zhengzhou University (No. 2007CXSY045)and the financial support of the Innovation Fund for Elitists of He-nan Province (No. 0221001200).

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