Journal of Colloid and Interface Science 362 (2011) 157–163

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Periodic mesoporous organosilicas with bis(8-quinolinolato)dioxomolybdenum(VI) inside the channel walls

Ying Yang a, Ying Zhang b, Shijie Hao b, Qiubin Kan a,⇑a Key Laboratory of Surface and Interface Chemistry of Jilin Province, College of Chemistry, Jilin University, Changchun 130023, PR Chinab Department of Materials Science and Engineering, China University of Petroleum, Changping District, Beijing 102249, PR China

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

Article history:Received 26 March 2011Accepted 2 June 2011Available online 7 June 2011

Keywords:Molybdenum8-QuinolinolPeriodic mesoporous organosilicas (PMOs)Cyclooctene epoxidation

0021-9797/$ - see front matter � 2011 Elsevier Inc. Adoi:10.1016/j.jcis.2011.06.008

⇑ Corresponding author. Address: Jiefang Road 25China. Fax: +86 431 88499140.

E-mail address: catalyticscience@yahoo.com.cn (Q

Novel periodic mesostructured organometallic silicas of MCM-41 type bearing homogeneously distrib-uted bis(8-quinolinolato)dioxomolybdenum(VI) inside the channel walls (denoted as MoO2Q2@PMO-x)are synthesized via a convenient one-pot method and examined as catalysts in the epoxidation of cyclo-octene. The ordered mesoporous structures as well as the organometallic groups incorporated into theframework are fully determined by comprehensive characterization techniques such as XRD, TEM, N2

adsorption/desorption, SEM, FT-IR, UV–vis spectroscopy, solid-state NMR, ICP-AES, XPS and TG/DSC.MoO2Q2@PMO-6% catalyst exhibits higher activity for the epoxidation of cyclooctene with tert-butylhydroperoxide than other MoO2Q2@PMO materials and its homogeneous or randomly grafted analogue.

� 2011 Elsevier Inc. All rights reserved.

1. Introduction

Recently, a new class of mesostructured organic–inorganichybrid materials was prepared through the surfactant–templatedpolycondensation of bridged organoalkoxysilanes ((R0O)3SiARASi(OR0)3) under acidic or basic conditions. These materials, referredto as periodic mesoporous organosilicas (PMOs), are unique astheir channel walls contain both inorganic and organic fragments.Organic fragments, such as presently reported methane (ACH2A),ethane (ACH2ACH2A), ethylene (ACH@CHA), benzene (APh), thio-phene and ferrocene, homogeneously occupy framework positionsin the walls rather than in the empty voids of the hexagonal chan-nels [1–5]. The combined advantages of ordered mesoporous struc-ture, unique pore-wall functionality, and the marriage of organicchemistry and inorganic materials chemistry offer PMOs fascinat-ing new possibilities and potential applications [6,7]. One of themain aspects in this area is, therefore, to synthesize desired orga-nometallic functionalized PMOs for extension of their applicationsin heterogeneous catalysis [8], especially in olefin epoxidations.

Molybdenum(VI) complexes of Schiff bases, bipyridyl, pyra-zolylpyidine etc., are extensively studied and proved to be efficientfor olefin epoxidations. Many strategies have been adopted to het-erogenize these homogeneous catalysts to increase catalyst stabil-ity and allow for catalyst recycling and product separation.Conventionally, their heterogenization is achieved through randomgrafting of terminally functionalized ligands first and then

ll rights reserved.

19, Changchun 130023, PR

. Kan).

introduction of metal ions. These grafted species located in thevoids of pore channels lead to pore blockage and catalyst leaching,while their inhomogeneous distributions near the pore entranceand on the external surface finally erode the catalyst selectivity[9–12]. Alternatively, sol–gel copolymerization of organometallicalkoxysilanes under template-free conditions makes the organo-metallic species distribute homogeneously in the pore channels.However, the resulting random networks with poorly orderedstructure and stability, as well as broad pore size distributions, se-verely limit their applications [13]. Synthesizing organomolybde-num(VI) functionalized PMOs could be a useful way to solve theproblems mentioned since the organometallic groups incorporatedinside the walls of ordered PMOs are uniformly distributed, holdthe merits of their homogeneous counterparts, and possess highthermal stability.

In this field, benzene or amine functionalized PMOs have beensynthesized and followed by the introduction of metal ions to formorganometallic functionalized PMOs via a two-step procedure[14,15]. Baleizão and coworkers pioneered a more elegant one-pot method to construct catalytically active vanadyl salen complexinside the framework of PMOs, which ensures the economy of syn-thetic steps and the purity of vanadyl salen complex immobilized.Unfortunately, severe leaching of vanadyl salen was observed dur-ing the acidified ethanol extraction procedure [16]. Still intriguedby the attracting features of one-pot synthesized organometallicfunctionalized PMOs, pioneering efforts have continued andrecently made great progress towards the design, synthesis andevaluation of this kind of materials. Dufaud and coworkers realizedthe formation of rhodium organophosphate bridged PMO materialwith the SBA-3 structure and found that it was highly active in

158 Y. Yang et al. / Journal of Colloid and Interface Science 362 (2011) 157–163

hydrogenation of alkenes [17]. This work was successfullyextended by Huang et al. to incorporate other organophosphanyltransition metal complexes into the framework of SBA-15 typePMOs, notably those of Pd, Au, Ru and Rh [18]. Corma et al. alsosynthesized periodic mesoporous materials with carbapalladacyclecomplexes in the framework, and these materials exhibited prom-ising activity towards the suzuki coupling [19]. Bahuleyan andcoworkers [20] found that the one-pot synthesized spherical peri-odic mesoporous organosilica bearing Ni(II) a-diimine complexesin the framework was active for ethylene polymerization. A peri-odic mesoporous material with a built-in Pd-guanidine complexwas also synthesized and was found to be active in alcohol oxida-tions [21]. As far as we know, one-pot synthesized organomolybde-num(VI) functionalized PMOs have not been reported.

Herein we first report design and characterization of a series ofnovel bis(8-quinolinolato)dioxomolybdenum(VI) bridged PMOmaterials synthesized via a convenient one-pot method, and theircatalytic properties in the epoxidation of cyclooctene with tert-butyl hydroperoxide (TBHP) as the oxidant.

2. Experimental

2.1. Catalyst preparation

2.1.1. Synthesis of MoO2Q2@PMO seriesThe synthetic strategy lies in the polycondensation of synthe-

sized bis-silylated bis(8-quinolinolato)dioxomolybdenum(VI)complexes with each other or with inorganic precursor under the

N

OHN+

OH

CH2Cl

HCHO, HCl, ZnCl2

r.t. 12 h

H Cl-

MoO2C

CH

N

O

N

O

Mo

O O

CH2

3-MPTMS

THF, N2, 15 h

S

SiOMe

OMeOMe

H2C

TEOS

+

+

CTAB

90 oC, 4 d

MoO2(1C)2-P

as-synthesized MoO2Q2@PMO-x

1C.HCl

a

b

-Si(OMe)3(OMe)3Si-

-Si(OMe)3(OMe)3Si-

Scheme 1. Schematic outline of synthesis of (

templating of surfactant micelles (see Scheme 1). Bis(5-chloro-methyl-8-quinolinolato)dioxomolybdenum(VI) (MoO2(1C)2) canbe facilely synthesized from 5-chloromethyl-8-quinolinol hydro-chloride (1C�HCl), involving only a two-step chemical transforma-tion from 8-quinolinol. Nucleophilic substitution of MoO2(1C)2 (1equiv.) with 3-mercaptopropyltrimethoxysilane (2 equiv.) leadsto bis-silylated bis(8-quinolinolato)dioxomolybdenum(VI) precur-sor, MoO2(1C)2-P (see Supporting Information and Scheme 1a).The purity and composition of 1C�HCl, MoO2(1C)2 and MoO2(1C)2-P are fully examined by liquid 1H NMR, 13C NMR, FT-IR, UV–visspectroscopy and elemental analysis (experimental details forcharacterization are reported as Supplementary Information andsee Figs. S1–S8). The MoO2(1C)2-P was used as source of silica incombination with TEOS in the synthesis of MoO2Q2@PMO materi-als, using cetyltrimethylaminoium bromide (CTAB) as the tem-plate. The molar ratios of the precursor gels used in the preferredpreparations were: (1–x) TEOS: (1/2)x MoO2(1C)2-P: 0.12 CTAB:8.0 NH3 (25%): 114 H2O: 10 EtOH, where x represents the Si molarpercentage of MoO2(1C)2-P in all silicas, and was tuned from 0% to2%, 6%, 10%, 15% and 20%. After we mixed the reactants and stirredthe mixture at room temperature for 2 h, the resulting gel wastransferred to a polyethylene container and heated at 90 �C for4 days. The solid obtained was washed with water and dried inair at 50 �C. The structure-directing agent was removed by extrac-tion of the solid with dilute ethanolic HCl acid solution at 40 �C for5 h (20 mL of 0.5 M ethanolic HCl for 0.5 g of solid). According tothe Si molar fraction of MoO2(1C)2-P in the total silicon precursors,six materials, denoted as MoO2Q2@PMO-0%, MoO2Q2@PMO-2%,

l2(dmf)2

Cl3

N

O

N

O

Mo

O O

CH2ClCH2Cl

S

Si OMeOMeOMe

EtOH-HCl

40 oC, 5 h

MoO2Q2@PMO-x

MoO2(1C)2

SiSiO

O O

Si Si O

Si Si OOO

O O

Si Si

OO

OO

O

O

SiSiO

O O

Si Si O

Si Si OOO

O O

Si Si

OO

OO

O

O

a) MoO2(1C)2-P and (b) MoO2Q2@PMO-x.

Y. Yang et al. / Journal of Colloid and Interface Science 362 (2011) 157–163 159

MoO2Q2@PMO-6%, MoO2Q2@PMO-10%, MoO2Q2@PMO-15% andMoO2Q2@PMO-20%, were obtained.

2.1.2. Synthesis of randomLy grafted MoO2Q2-MCM-41-6%RandomLy grafted MoO2Q2-MCM-41-6% was also prepared for

comparison, since the periodic structure of MoO2Q2-MCM-41-6%must be very similar to that of MoO2Q2@PMO-6%, with an arrayof parallel hexagonal channels containing bis(8-quinolinola-to)dioxomolybdenum(VI) covalently linked by two thioethers. Ina typical synthesis, 0.42 g (0.5 mmol) of MoO2(1C)2-P was mixedwith 10 mL of dried toluene, then 1.0 g of MCM-41 (MoO2Q2@PMO-0%) was added and the mixture was refluxed under N2

atmosphere for 24 h. The resulting sample was filtered off,Soxhlet-extracted with CH2Cl2 to remove any untethered speciesand dried in vacuum.

2.2. Olefin epoxidation with TBHP

Five millimole of cyclooctene and 5 mL of CHCl3 along with cer-tain amount of catalyst were added to a 100 mL two-neck flaskequipped with a stirrer and a reflux condenser. The mixture washeated to 70 �C and then 5 mmol (0.77 mL) of TBHP was injectedinto the solution to start the reaction. The liquid organic productswere quantified by using a gas chromatograph (Shimadzu, GC-8A)equipped with a flame detector and an HP-5 capillary column, andidentified by comparison with authentic samples and GC–MScoupling.

3. Results and discussion

3.1. Microstructure and surface morphology characterization

The XRD pattern of all samples shows three well defined peaksat 2h values between 2� and 5� that can be indexed as (1 0 0),(1 1 0) and (2 0 0) diffractions (Fig. 1), which is typical for a well or-dered 2D hexagonal (P6 mm) mesostructure [22]. The (1 0 0) peakintensity decreases and the higher order (1 1 0) and (2 0 0) diffrac-tions become less resolved when the Si molar ratios of MoO2(1C)2-P

Fig. 1. XRD patterns of: (a) MoO2Q2@PMO-2%, (b) MoO2Q2@PMO-6%, (c) MoO2Q2@PMoO2Q2@PMO-6% (left, inset).

in the synthesis gel increase to 15–20%, showing that the mesoporeordering decreases with the increase of Mo contents. Correspond-ingly, the (1 0 0) diffractions slightly shift to lower 2h values, whichis related to the spacing increase and wall thickness variations dueto the increased contents of organometallic moieties in the frame-work. However, the (1 0 0) peak neither shifts nor becomes weakafter template removal, exemplified by comparison of surfactant-extracted MoO2Q2@PMO-6% with the as-synthesized one (Fig. 1,inset), due to the enhanced contrast in the electron density aftertemplate removal [23]. No peaks assigned to metal species presentin the 2h range of 10–40�Can be ascribed to the uniform distribu-tion of Mo complexes in the amorphous walls [8,24]. TEM imagesof the PMO materials recorded using a parallel view to the poresexhibit honeycomb structures while the images recorded using aperpendicular view show parallel fringe structures (Fig. 2a–h).The well ordered hexagonal arrays of 2D mesoporous pores arewith uniform size estimated to be 2.5 ± 0.5 nm further confirmthe highly ordered 2D hexagonal uniform periodic mesostructures.

The Mo content gradient is reflected in the diverse but well de-fined external morphologies of MoO2Q2@PMO series. The SEM im-age (Fig. 2i) of MoO2Q2@PMO-2% shows predominated rod-likeparticles with a hexagonal cross-section. Only uniform sphericalparticles with average size of ca. 0.6 lm in diameter are observedfor MoO2Q2@PMO-6% (Fig. 2j). The transformation of hexagonalto spherical morphology occurred in MoO2Q2@PMO series in spiteof high reflection peaks in the XRD and ordered 2D structure inTEM, which is consistent with the morphology transformation ofMCM-41 with different amount of Co incorporated into its frame-work [25]. The spherical morphology is less uniform when increas-ing x value from 10% to 15% (Fig. 2k–l), indicating that moreMoO2(1C)2-P introduced could perturb the self-assembly of surfac-tant micelles and the silica precursor.

N2 adsorption analysis shows that all samples exhibit a IV typeisotherm with a sharp inflection step at P/P0 ranging from 0.25 to0.35 (Fig. 3), characteristic of mesoporous materials with orderedarrangement of cylindrical pores [26,27], which suggests that theMCM-41 type materials were successfully synthesized. The iso-therm of MoO2Q2@PMO-2% is unique as it shows two well defined

MO-10%, (d) MoO2Q2@PMO-15%, (e) MoO2Q2@PMO-20%, and (f) as-synthesized

Fig. 2. TEM and SEM images of (a, b, and i) MoO2Q2@PMO-2%, (c, d, and j) MoO2Q2@PMO-6%, (e, f, and k) MoO2Q2@PMO-10% and (g, h, and l) MoO2Q2@PMO-15%.

Fig. 3. N2 adsorption/desorption isotherms and pore size distribution profiles of (a) MoO2Q2@PMO-2%, (b) MoO2Q2@PMO-6%, (c) MoO2Q2@PMO-10%, (d) MoO2Q2@PMO-15%and (e) MoO2Q2@PMO-20%.

160 Y. Yang et al. / Journal of Colloid and Interface Science 362 (2011) 157–163

Y. Yang et al. / Journal of Colloid and Interface Science 362 (2011) 157–163 161

hysteresis loops. The one at P/P0 = 0.2–0.4 exhibits H1 type in theIUPAC classification, characteristic of the mesoporous materialswith cylindrical geometry. The other with parallel and almost hor-izontal branches at P/P0 close to the saturated vapor pressureexhibits the H4 type and presents in all samples, suggesting thepresence of mesopores embedded in a matrix with pores of muchsmaller size [27,28]. However, the segregation between adsorptionand desorption branches becomes less prominent when increasingx from 6% to 20%, originated from less mesopores created in theframework. The surface areas and pore volumes of the MoO2Q2@P-MO series also systematically decrease while the content of Mo isincreased, which suggests that the functionalization with bis(8-quinolinolato)dioxomolybdenum occurred. Table 1 indicates thatthe surface areas and pore volumes of the MoO2Q2@PMO series de-crease from 874 to 532 m2 g�1, and from 0.72 to 0.38 cm3 g�1,respectively, whereas pore sizes remain relatively unchanged. Asillustrated in Fig. 3, all samples with different Mo contents possessmonomodal and quite narrow pore size distributions centered atca. 24–25 Å, which is different from the significant pore size de-crease occurring by terminal bonding of Mo complexes to the poresurface, indicating that Mo complexes distributed homogeneouslyin the framework and thus overcame the pore blockage [29],though the content of Mo species introduced increases.

3.2. Spectroscopic characterization

Spectroscopic characterization of MoO2Q2@PMO series can getuseful information about organic and organometallic moieties,and it further confirms that the organic–inorganic componentshave been embedded into the pore walls of the synthesized PMOmaterials. FT-IR spectrum of as-synthesized MoO2Q2@PMO-6%

Table 1Textual and catalytic properties of various catalysts.

Materials C (M)a (mmol g�1) SBET (m2 g�1) VBJH (cm3 g�1) DBJHb

MoO2Q2@PMO-2% Trace 874 0.72 2.42MoO2Q2@PMO-6% 0.035 694 0.55 2.55MoO2Q2@PMO-10% 0.052 675 0.51 2.30MoO2Q2@PMO-15% 0.079 587 0.46 2.51MoO2Q2@PMO-20% 0.092 532 0.38 2.38MoO2Q2-MCM-41-6% 0.042 560 0.49 1.74MoO2(1C)2 1.949 – – –

a Estimated by ICP-AES.b Calculated from the adsorption branch.c W = Ao � DBJH (Ao = 2D100/

ffiffiffi

3p

).d Reaction conditions: catalyst 50 mg (5 mg for neat catalyst), substrate 5 mmol, solve TOF, h�1: (turnover frequency) moles of substrate converted per mole metal ion per

Fig. 4. 29Si CP/MAS NMR spect

shows peaks at 2927 and 2855 cm�1 due to the CAH stretchingof the CH3 and CH2 groups of the CTMA+ groups [30] (Fig. S9). Thesepeaks become weak in the spectrum of surfactant-extracted one,indicating that most surfactants have been removed. In the lowerfrequency region, the absorbance between 1600 and 1300 cm�1

can be ascribed to ACH2 bending modes, CAN and aromatic ringvibrations of ligands for all MoO2Q2@PMO samples [31](Fig. S10). Both as-synthesized and surfactant-extractedMoO2Q2@PMO-6% materials show 13C CP/MAS NMR spectra similarto that of MoO2(1C)2-P (Fig. S11). The resonances at 15.0, 24.0, 30.0and 52.0 ppm are observed for both samples, assigned to the car-bons of the linear chain. The peaks of the aromatic carbons ob-served at 120–160 ppm remain after CTAB removal, indicatingthe preservation of the chelate ligand structure during the hydro-thermal synthesis and the acid extraction process. In the 29Si CP/MAS NMR spectrum (Fig. 4), the presence of T2 and T3 sites, as indi-cated by signals at d = �62 and �65 ppm, suggests that the precur-sor is not simply incorporated but rather integrated into the silicanetwork [19]. Other signals were also observed in the d = �85 to�110 ppm spectral region (silica Q sites). The combined analysisof the 13C and 29Si NMR with FT-IR results clearly shows that 8-quinolinol ligands were successfully incorporated into the frame-work of the mesoporous silica.

Except for MoO2Q2@PMO-0%, other MoO2Q2@PMO samplesshow p–p⁄, n–p⁄ and metal-to-ligand charge transfer (MLCT) inthe range of 240–295, 300–350 and 500–590 nm [31], similar tothose of MoO2(1C)2, indicating that Mo complexes were incorpo-rated into the hybrid materials (Fig. S12). However, the redshift(from 507 to ca. 580 nm) and broadening of MLCT bands are ob-served upon immobilization, which can be ascribed to the interac-tion of Mo complexes with the silica framework.

(nm) D100 (nm) Wc (nm) Conversion% (epoxide yield%)d TOF (h�1) e

3.43 1.54 Trace Trace3.46 1.44 48.8 (48.8) 172.83.47 1.71 27.1 (27.1) 27.23.49 1.52 17.4 (17.4) 27.53.52 1.68 6.5 (6.5) 8.83.23 1.99 9.9 (9.9) 29.5– – 7.8 (7.8) 5.0

ent 5 ml, TBHP 5 mmol, duration 8 h and temperature 70 �C.hour.

rum of MoO2Q2@PMO-6%.

162 Y. Yang et al. / Journal of Colloid and Interface Science 362 (2011) 157–163

3.3. Surface analysis and quantification

XPS element survey scans of the surface elements ofMoO2Q2@PMO-6% reveal that Si, O, C, N and Mo elements are pres-ent on the material as expected. The compound MoO2Cl2(dmf)2

exhibits peaks at 399.1 and 531.3 eV, assigned to N 1s and O 1s,respectively [32]. The two peaks for MoO2Q2@PMO-6% signifi-cantly shift to 399.6 and 533.0 eV, respectively (Fig. S13), indicat-ing that 8-quinolinol ligands coordinated to MoO2 fragmentsinstead of Cl and dmf, and predominated OASi groups were pres-ent in the silica framework instead of Mo = O groups inMoO2Cl2(dmf)2. Correspondingly, two peaks at 233.3 and 236.4 eV for MoO2Cl2(dmf)2, assigned to Mo 3d5/2 and Mo 3d3/2, slightlyshift to 233.4 and 236.5 eV for MoO2Q2@PMO-6% (Fig. S13), indi-cating that the coordination sphere around Mo changed upon itscoordination with 8-quinolinol.

TG profiles of three representative samples, MoO2Q2@PMO-6%,MoO2Q2@PMO-10% and MoO2Q2-MCM-41-6%, show three regionsof weight loss (Fig. S14). At temperature up to about 100 �C, ca.4% weight loss observed for MoO2Q2@PMO-6% is accompanied byan endothermic differential scanning calorimetry (DSC) peak, dueto the physically adsorbed water and solvent inside the pores.The minor weight loss occurred in the range from 150 to 400 �Cis due to the loss of residual surfactant. The third region at temper-atures between 400 and 700 �C exhibits a peak centered at 630 �Cand a shoulder at ca. 506 �C, arising from the decomposition of or-ganic matrix and the partial condensation of SiAOH [33]. By com-parison of the exothermic peaks in this region, we can concludethat the embedded Mo complexes are more thermally stable (upto 690 �C) than their analogues grafted onto the surface of conven-tional mesoporous MCM-41 (450 �C). The weight loss taken be-tween 400 and 700 �C increases with the increase of MoO2(1C)2-Pcontent in the synthesis gels. Moreover, the N and Mo contentsare 0.0642 mmol g�1 (estimated by N elemental analysis) and0.0353 mmol g�1 (estimated by ICP-AES) respectively forMoO2Q2@PMO-6%, and the N/Mo molar ratio is 1.82: 1, consistentwith the N/Mo stoichiometry of the MoO2(1C)2-P molecular precur-sor, indicating that the Mo complexes remain intact in the frame-work after surviving the hydrolysis, condensation and solventextraction conditions. The surface molar ratio of N/Mo (Table S1)is comparative to that estimated by microanalysis, confirmingthe uniform distribution of active species onto the mesoporousmaterials.

3.4. Catalytic properties

The bis(8-quinolinolato)dioxomolybdenum(VI) bridged PMOframeworks may, therefore, act as potential scaffolds for heteroge-neous catalysis. As illustrated in Table 1, all catalysts are active forthe epoxidation of cyclooctene with nearly 100% of selectivity toepoxycyclooctane as expected. But to our surprise, all MoO2Q2@P-MO materials are more active than free MoO2(1C)2 catalyst. Thecyclooctene conversion first increases to 48.8% and then decreasesto 6.5% for MoO2Q2@PMO series, and MoO2Q2@PMO-6% shows thehighest conversion of 48.8% (TOF 172.8 h�1) after 8 h. These datasuggest that textual and morphological properties of MoO2Q2@P-MO materials are predominated to affect the catalytic performancewhen the metal loading is larger than 0.035 mmol g�1, since thespherical morphology is less uniform and less mesopores are cre-ated in the matrix when x is increased from 6% to 20%. The excel-lent performance of MoO2Q2@PMO-6% may be ascribed to itsuniform spherical morphology, well defined order and massivemesopores embedded in the framework facilitating the masstransfer. The absence of activity of hot filtrate solution for

MoO2Q2@PMO-6% indicates that the supported catalyst is stableand that any leaching of active species into solution is insignificant.On the other hand, MoO2Q2@PMO-6% exhibits much higheractivity than MoO2Q2-MCM-41-6% (9.9%), obviously owing to thehigher SBET, larger Vp and Dp which facilitate the diffusion andadsorption of reaction molecules.

4. Conclusions

We have successfully synthesized a series of bis(8-quinolinola-to)dioxomolybdenum(VI) functionalized PMOs via a convenientone-pot method. Organomolybdenum(VI) species are anchoredand are homogeneously distributed inside the channel walls ofhighly ordered mesoporous materials, verified by XRD, TEM, N2

adsorption/desorption, SEM, FT-IR, UV–vis spectroscopy, solid-state NMR, ICP-AES, XPS and TG/DSC techniques. All organomolyb-denum(VI) functionalized PMOs are catalytically active for theepoxidation of cyclooctene with TBHP as the oxidant, andMoO2Q2@PMO-6% shows the best catalytic performances.

Acknowledgments

This work was supported by the National Basic Research Pro-gram of China (2004CB217804) and the National Natural ScienceFoundation of China (20673046).

Appendix A. Supplementary material

Supplementary material associated with this article can befound, in the online version, at doi:10.1016/j.jcis.2011.06.008.

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