1-s2.0-s1387181112002910-main

7/27/2019 1-s2.0-S1387181112002910-main

1/8

Post-synthesis of TiO2/MCM-41 from aqueous TiCl4 solution: Structure

characteristics and epoxy catalytic activity

Lina Ma, Jianbing Ji , Fengwen Yu, Ning Ai, Hongtao Jiang

Zhejiang Province Key Laboratory of Biofuel, Zhejiang University of Technology, Hangzhou 310014, China

a r t i c l e i n f o

Article history:

Received 27 October 2011Received in revised form 17 April 2012Accepted 7 May 2012Available online 3 August 2012

Keywords:

TiO2/MCM-41Mesoporous molecular sievesPost-synthesisCharacterizationCatalytic testing

a b s t r a c t

Titanium-containing mesoporous silica TiO2/MCM-41 (C) was prepared by impregnating MCM-41, pre-treated by refrigeration at 278 K, with aqueous TiCl4 solution as titanium precursor. In addition, TiO2/MCM-41 (H) was produced by same method but the support MCM-41 without refrigeration in order toinvestigate the influence of unrefrigerated pretreatment on the structure of TiO2/MCM-41. The dispersionand nature of titanium species were characterized by inductively coupled plasma mass spectrometry(ICP-MS), powder X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), UVvisiblediffuse reflectance spectra (UV-vis DRS), standard BrunauerEmmnettTeller (BET), X-ray photoelectronspectra (XPS), scanning electron micrographs (SEM), transmission electron microscopy (TEM). The resultsindicate that TiO2/MCM-41 (C) showed better mesoscopic order, higher dispersion of titanium oxide spe-cies, stronger interaction with the MCM-41 support. But the pore size decreases from 3.4 to 2.4 nm whenthe titanium content increases to 76.6 mg/g. TiO2/MCM-41 (C2) exhibits more excellent catalytic perfor-mance than others, and the 97.6% conversion of methyl oleate (MO) and 93.1% selectivity to epoxidationmethyl oleate (EMO) can be obtained at 353 K for 10 h.

2012 Elsevier Inc. All rights reserved.

1. Introduction

Recently much attention has been paid on the olefin epoxida-tion by various catalysis with various oxidants since epoxides areused in flexible intermediates of many industrially significantchemicals [14] such as drugs, agrochemicals, lubricants, bio-based polymers, fuel additives, polymer stabilizer, and perfumematerials. Several studies have been done to develop active cata-lytic systems for the epoxidation of different olefins using a widerange of catalysts. Catalysts based on molybdenum [5], alumina[6], titanium [7] and tungsten [8,9] have been described for thisreaction. Among them, Ti-containing catalysts enable many pro-cesses to be selectively, efficiently, and environment-friendly con-

ducted under mild condition.Usually Ti-containing catalyst is prepared by hydrothermal syn-thesis or post-synthesis. Post-synthesis has better industrializationprospect because its process is more easily to obtain than that ofhydrothermal synthesis. Inumaru [10] prepared Ti/SiO2 catalystsby the chemical vapor deposition (CVD) method using TiCl4 as tita-nium source. And Lu and co-workers [11] optimized the CVD con-ditions and got the TiSBA-15 of Ti load of 4.62 wt.% with highepoxy selectivity and activity; Marchetti and co-workers [12] pre-pared Ti/MCM-41 samples by impregnation methods using Ti-tert-

butoxide in isopropyl alcohol solution as titanium source andfound that their catalytic activities were similar as that of thehydrothermal TiMCM-41. Yang and co-worker [13] investigatedthe synthesis of TiO2/SBA-15 materials via Ti-alkoxide hydrolysisin the support-isopropanol suspension; Stein and co-workers[14] and Sun and co-workers [15] used TiCl4 in hexane as titaniumprecursor to graft titania clusters into the pores of MCM-41. How-ever, this process must be under nitrogen environment or TiCl4hydrolyzes to TiO2 in an open atmosphere.

In this work, we have investigated the post-synthesis of TiO2/MCM-41 by grafting of titanium oxide onto the MCM-41 in airusing an aqueous TiCl4 solution as precursor. And the comparisonof the influence of support with and without refrigerated pretreat-

ment on the structure of TiO2/MCM-41 was investigated. The syn-thesized materials were characterized by various physicaltechniques. At the same time, their epoxy catalytic activities ofMO were tested.

2. Experimental

2.1. Catalyst preparation

2.1.1. Preparation of MCM-41

The pure mesoporous silica MCM-41 was synthesized accordingto the reported procedure [16] by using of cetyltrimethylammo-nium bromide (CTAB, 99%) as the cationic surfactant under alkaline

1387-1811/$ - see front matter 2012 Elsevier Inc. All rights reserved.http://dx.doi.org/10.1016/j.micromeso.2012.05.005

Corresponding author. Tel./fax: +86 571 88320053.

E-mail address: [email protected] (J. Ji).

Microporous and Mesoporous Materials 165 (2013) 613

Contents lists available at SciVerse ScienceDirect

Microporous and Mesoporous Materials

j o u r n a l h o m e p a g e : w w w . e l s e v i e r . c o m / l o c a t e / m i c r o m e s o
http://dx.doi.org/10.1016/j.micromeso.2012.05.005mailto:[email protected]://dx.doi.org/10.1016/j.micromeso.2012.05.005http://www.sciencedirect.com/science/journal/13871811http://www.elsevier.com/locate/micromesohttp://www.elsevier.com/locate/micromesohttp://www.sciencedirect.com/science/journal/13871811http://dx.doi.org/10.1016/j.micromeso.2012.05.005mailto:[email protected]://dx.doi.org/10.1016/j.micromeso.2012.05.005

7/27/2019 1-s2.0-S1387181112002910-main

2/8

conditions. Briefly, a solution of CTAB/NaOH/H2O/TEOS = 1/2.7/9820/8.7 (mole ratio) was prepared and stirred for 10 h at 353 K.The solid product was filtered off, and then dried overnight at373 K. Mostly occluded surfactant was removed by calcinationsat 853 K for 0.5 h in air, yielding the mesoporous molecularMCM-41 material. The MCM-41 (BET surface area: 1437 m2/g,average pore diameter: 3.41 nm, total pore volume: 1.35 cm3/g)was used in preparation of TiO

2/MCM-41 samples support.

2.1.2. Preparation of TiO2/MCM-41

2.1.2.1. Aqueous TiCl4 solution. TiCl4 (above 99%) was used withoutany further purification. The aqueous TiCl4 solutions, the titaniumprecursor, were prepared by slowly adding, drop-wise, a givenamount of water into a certain amount of TiCl4. When water con-tacts with TiCl4 excess heat explosively generating from the exo-thermic reaction was removed by constantly shaking in ice-waterbath. And the white smoke was collected and absorbed by 2 N al-kali liquor. The color of aqueous TiCl4 solution changed from paleyellow to lemon and then to colorless. The concentration of color-less aqueous TiCl4 solutions was 0.3 and 0.4 mol/L. And the aque-ous TiCl4 solutions were kept in ice-water bath.

2.1.2.2. TiO2/MCM-41 (C). MCM-41 was dried at 373 K and thenrefrigerated in refrigerator at 278 K for overnight before impregna-tion. Following the simple impregnation to incipient wetness of0.5 g MCM-41 with 2 ml above solutions at 278 K for two days inair the samples were dried at 373 K, separately. And then the sam-ples were calcined in air at 823 K for 2 h at a heating rate of 2 K/min to obtain TiO2/MCM-41 (C1), and TiO2/MCM-41 (C2) samples.

2.1.2.3. TiO2/MCM-41 (H). MCM-41 was dried at 373 K and cooledat room temperature for 2 h. With the same impregnation to incip-ient wetness and same finishing procedure as described aboveTiO2/MCM-41 (H1) and TiO2/MCM-41 (H2) samples were obtained.

2.2. Characterizations

The titanium contents in TiO2/MCM-41 samples were deter-mined by ICP-MS (PerkinElmer Elan DRC-e). For ICP-MS studied,0.025 g of the samples was digested with 3 mL HNO3 and 1 mL ofHF in digestion high-pressure tank at 333 K for 5 h, 25 ml boricacid neutralized after cooled down and then diluted to 250 mL,respectively. The titanium concentrations of samples were deter-mined from a calibration plot made previously. XRD measure-ments were performed at room temperature using a PNAlyticalXPert PRO powder diffractometer with Cu Ka (k = 1.5404 ) radia-tion. The diffractometer was operated at 40 kV and 40 mA andscanned between 1.5 and 8 (2h) with a step size of 0.0083 andbetween 10 and 70 (2h) using steps of 0.033. FT-IR spectra wererecorded on a Nicolet 6700 FT-IR spectrometer using 0.5 mm KBr

pellets containing 2.5 wt.% samples. The UVvis DRS in the UVvis range with BaSO4 as reference were recorded using a ShimadzuUV-2550 spectrometer equipped with an integration sphereattachment. XPS were acquired recorded on Kratos AXIS UltraDLD spectrometer equipped with a dual X-ray source, of whichthe AlKa (1486.6 eV) anode and a hemispherical energy analyzerwere used. The background pressure during data acquisition waskept below 7.4 107 Pa. Measurements were performed at passenergy of 160.0 eV to ensure sufficient sensitivity for the acquisi-tion scan, while pass energy of 40.0 eV was used for the scanningof the narrow spectra of Ti 2p and C 1s to ensure sufficient resolu-tion. All the binding energies were calibrated by referencing to thecontaminant carbon (C 1s) 284.8 eV. The surface morphological de-tails of catalysts were studied by SEM (Hitachi S-4700 II). The cat-

alyst samples were mounted directly on the holders and coveredwith sputtered gold and then observed in SEM. TEM images were

obtained on a Tecnai G2 F30 S-Twin microscope operated at300 kV. The samples were dispersed in ethanol in an ultrasonicbath for several minutes, and then deposited on a Cu grid and driedby infrared heat lamp for the experiment. The specific surface areawas calculated using the standard BET method. Nitrogen adsorp-tion/desorption isotherms were measured at 77 K using micromer-itics ASAP 2010 of samples. The total pores volume was estimatedfrom the amount of nitrogen adsorbed at a relative pressure p/p

0of

0.99, assuming complete surface saturation with nitrogen, where pand p0 denote the adsorption size distribution curves were calcu-lated from the adsorption branches of the isotherms usingBarettJoynerHalenda (BJH) method.

2.3. Activity test

2.3.1. Materials

Methyl oleate (MO), the substrate for catalytic tests, was a col-orless liquid obtained from vegetable tallow by esterification,transesterification with methanol and following rectification.FAME mixture was qualitative analyzed by Agilent 9790A/5875Cgas chromatographymass spectrometry (GCMS). And the com-

positionis (wt.%) MO (84.5), methyl linoleate (2.5), methyl stearate(1.6), methyl palmitate (9.5), others (1.9) quantitative analyzed byFuli GC 9790 with a HP-INNOWAX column (30 m 0.25 mm 0.25lm) with a flame ionization detector (FID).

2.3.2. Catalytic tests

The activity test was performed at 353 K for 10 h with magneticstirring in a round bottomed flask with MO, aqueous tert-butylhy-droperoxide (TBHP, 75%) as oxygen donor and ethyl acetate as sol-vent. The analysis method was same as above.

3. Results and discussion

3.1. Characterization of TiO2/MCM-41

The amount of titanium present on the support is determinedby using ICP-MS. Table 1 shows the amounts of titanium, ex-pressed in mg/g of product.

Small-angle powder X-ray diffraction patterns of TiO2/MCM-41(H1, H2), TiO2/MCM-41 (C1, C2) samples and pure MCM-41 areshown in Fig. 1. TiO2/MCM-41 (C1, C2) samples and pure MCM-41 exhibit three well-resolved peaks indexed to d100, d110, andd200 Bragg reflection, indicating that good microscopic order andthe characteristic hexagonal features of MCM-41 are maintained(Fig. 1a, d, and e). However, the d110 and d200 reflection peaks ofTiO2/MCM-41 (H1, H2) samples become very weak and even disap-pear when the content of titanium reached 73.8 mg/g. Obviously,the incorporation process of using refrigerated pretreatment sup-

port does not lead to disorder the hexagonal structure. The inten-sity of the d100 reflection diffraction peaks at 23 decreasemoderately withthe titanium content increasing as compared withthe corresponding pure MCM-41. In addition, the reflection posi-tions of peaks shift in different level to larger diffraction angleand become slightly broader, especially for TiO2/MCM-41 (C1,

Table 1

Titanium content of TiO2/MCM-41 samples analyzed

by ICP-MS.

Samples Ti (mg/g)

TiO2/MCM-41 (H1) 62.2TiO2/MCM-41 (H2) 73.8TiO2/MCM-41 (C1) 63.3

TiO2/MCM-41 (C2) 76.6

L. Ma et al. / Microporous and Mesoporous Materials 165 (2013) 613 7

7/27/2019 1-s2.0-S1387181112002910-main

3/8

C2) samples, indicating narrowed unit cell. Wide-angle powder X-ray diffraction patterns of various samples are shown in Fig. 2.None of the typical diffraction peaks form crystalline titaniumoxide species are observed, only a broad peak resulting from amor-phous silica centered at 2 = 23 for TiO2/MCM-41 (C1, C2) samples(Fig. 2c and d). While for TiO2/MCM-41 (H1, H2) samples whichsupport without refrigerated pretreatment with very week charac-teristic peaks of crystalline anatase appear (Fig. 2a and b). Besides,the intensity of reflection peaks strengthens and the number ofpeaks increases along with the increase of titanium content.

This above result may be explained by the following two con-siderations: (i) titanium oxide species is totally incorporated intothe lattice of the MCM-41 for TiO2/MCM-41 (C) samples and (ii)

for TiO2/MCM-41 (H1, H2) samples, the formation of partial ana-tase species causes destruction and partial blocking of the poresystem. And this finding could be confirmed by SEM and TEMimages and showed in context.

In order to evaluate the formation of titanium oxide in the cat-alyst framework, FTIR, XPS and UVvis DRS were carried out. TheFT-IR spectra of pure MCM-41 and TiO2/MCM-41 samples areshown in Fig. 3. Four characteristic absorption bands are observed.All the samples exhibit the symmetric stretching vibration band of

SiOSi bridges at around 810 cm1

, the anti-symmetric vibrationband at around 1100 cm1 with a shoulder at 1220 cm1 for thetetrahedral SiO4 structure units. Finally, for Ti-containing molecu-lar sieve the important band at 960 cm1 isto beregarded asa con-sequence of stretching vibrations of SiOTi bonds. And itsincrease in intensity along with the content is generally consideredas a evidence of the incorporating of titanium into the framework[17,18] as the stretching SiO vibration mode perturbed by theneighboring metal ions. Pure MCM-41 shows very mild band(Fig. 3a). For TiO2/MCM-41 (C1, C2) samples, characteristic inten-sity band strengthens with the increase of titanium loading. Whileno typical intensity increase of IR band located at around 960 cm1

can be observed for TiO2/MCM-41 (H1, H2) samples.UVvis DRS is a very sensitive probe for the presence of extra-

frame Ti in molecular sieves. The UVvis DRS spectra of TiO2/MCM-41 (C1, C2, H1, H2) samples and anatase are given in Fig. 4.There is no peak for pure MCM-41 (not show in figure). TiO2/MCM-41 (C1, C2) (Fig. 4d and e) samples have an absorption max-imum band at about 210240 nm, which is assigned to the ligand-to-metal charge transfer involving isolated titanium atoms in tet-rahedral coordination, in which two water molecules form partof the metal coordination sphere. Although there is not obviouspeak at about 280 nm, the broad peak mean that there is probablya very weak shoulder at about 280 nm for TiO2/MCM-41 (C1, C2)samples. The shoulder at 280 nm probably corresponds to partiallypolymerized Ti species (five- and six-coordinate) in small titaniananodomains [19]. While TiO2/MCM-41 (H1, H2) samples (Fig. 4band c) show an intense band centered at 230260 nm, probablycontaining peaks at 210230 and 260270, together with a shoul-der at 310 nm. The shoulder at 310 nm, being obvious for anatase

Fig. 1. Small-angle powder XRD patterns of samples: (a) Pure MCM-41, (b) TiO2/MCM-41 (H1),(c) TiO2/MCM-41(H2), (d) TiO2/MCM-41 (C1), (e) TiO2/MCM-41(C2).

Fig. 2. Wide-angle powder XRD patterns of samples: (a) TiO2/MCM-41 (H2), (b)TiO2/MCM-41 (H1), (c) TiO2/MCM-41 (C2), (d) TiO2/MCM-41 (C1).

Fig. 3. FT-IR spectra of samples: (a) Pure MCM-41, (b) TiO2/MCM-41 (H1), (c) TiO2/MCM-41 (H2), (d) TiO2/MCM-41 (C1), (e) TiO2/MCM-41 (C2).

8 L. Ma et al. / Microporous and Mesoporous Materials 165 (2013) 613

7/27/2019 1-s2.0-S1387181112002910-main

4/8

(shown in the Fig. 4a), indicates that bulk titania is formed [20].Fig. 5 outlines the reaction scheme of potential structures resultingfrom the grafting procedure. Solution can reach internal pore(Fig. 5a) derived mainly by capillary force and titania is anchoredto the silica framework via reaction with terminal SiOH groupson the pore surface (Fig. 5b) under the slow volatilization of HClfor TiO2/MCM-41 (C) samples. And the titanium species forming

a smooth layer which coats the pore surface leads to narrow pore.Besides, with the increasing of content of titanium, polymerized Ti

species form (Fig. 4c). While for TiO2/MCM-41 (H) samples, muchof TiCl4 has formed (TiO2)n nanoclusters (Fig. 5d) or isolated TiO2unites (Fig. 5e) when TiCl4 penetrates the pore in carrier and graftsonto pore surface because of the quick volatition of HCl.

After obtaining information about the chemical nature andcoordination states of the titanium species in the samples, weinvestigated the oxidation state of the species presents on theirsurface using XPS analysis. Fig. 6 shows the Ti 2p spectra of TiO2/MCM-41 (C2, H2) samples. The deconvoluted XPS spectra of the

two samples show the presence of three different Ti species withtheir Ti2p3/2 binding energies which can be fitted with three sym-metric cures which distinguish titanium oxide species in differentchemical states according to published binding energy (BE) shiftsfor TiO2, SiO2, TiO2/SiO2mixed oxide systems, TS-1 and TiMCM-41 [14,2124]. The first species with the lowest binding energiesarising at 457.8 0.2 eV is characteristic of octahedral titaniumspecies. The proportion of peak at 457.8 0.2 eV of TiO2/MCM-41(C2) sample is far less than that of TiO2/MCM-41 (H2) sample.The largest peak at 460.0 0.2 eV for TiO2/MCM-41 (C2) sample,as same as that observed on TS-1, is attributable to tetrahedralcoordinated Ti species which is referred to titanium accommo-dated into the silica framework. TiO2/MCM-41 (H2) sample show-ing a maximum peak at 459 0.2 eV is consistent with titanium in

the octahedral environment of anatase and probably originatesfrom the anatase particles that are present on the external surface.The SEM and TEM micrographs of TiO2/MCM-41 (C) are shown

in Figs. 7 and 8, respectively. The ball-rod-like structure of TiO2/MCM-41 (C2) sample (Fig. 7a) is about 300 nm in diameter andabout 650 nm in length. And each particle consists of well-orderedhexagonal nano-channels (Fig. 8a and b) of one-dimensional mes-opores. Anatase crystallites are not present at external MCM-41surfaces in sample, demonstrating titanium oxide species are welldispersed in MCM-41 channels. However, for the TiO2/MCM-41(H2) sample, the scaly-like structure is shown in Fig. 7b. TEMimages of TiO2/MCM-41 (H2) sample (Fig. 8c and d) show the deg-radation and rupture of the MCM-41 mesostructure, which areconsistent with the small-angle XRD results. The amorphous zones

and even anatase agglomerate species were blocked in the chan-nels and formed on the external surface.

Fig. 4. UVvis DRS patterns of samples: (a) Anatase, (b) TiO2/MCM-41 (H2), (c)TiO2/MCM-41 (H1), (d) TiO2/MCM-41 (C2), (e) TiO2/MCM-41 (C1).

Fig. 5. Schematic of the grafting procedure and potential results. Only a single poreis shown. The color darkens with the increase of concentration of titanium. (a) Asingle pore of pure MCM-41. (b) A smooth layer of titanium oxide species coats thepore surface. (c) Small polymerized titanium oxide species partially form. (d)

(TiO2)n nanoclusters partially form. (e) Bulk (TiO2)n nanoclusters and isolated TiO2unites form.

Fig. 6. Ti 2p photoelectron spectra of samples: (a) TiO2/MCM-41 (C2), (b) TiO2/MCM-41 (H2).


7/27/2019 1-s2.0-S1387181112002910-main

5/8

The nitrogen adsorptiondesorption isotherms and typical poresize distributions for TiO2/MCM-41 (C2, H2) samples and ungraftedMCM-41 are shown in Fig. 9. And the average pore volume, diam-eter and BET surface area are listed in Table 2. Compared withMCM-41, TiO2/MCM-41 (C2, H2) samples have lower surface areasobviously caused by deposition of titanium oxide species. There isa noticeable difference in the shape of the isotherms and a signif-icant decrease of pore size with Ti loading for the TiO2/MCM-41(C2) sample compared to MCM-41, attributed to filling of poreswith titanium oxide species. The nitrogen sorption isotherm for

TiO2/MCM-41 (H2) sample exhibits the shape of type IV cures, typ-ical of mesoporous material, but combined with above results it

can be seen that no significant decrease of the pore size with Tiloading which suggest that mostly titanium oxide species locatedon external surface instead of incorporating with MCM-41.

3.2. Catalytic results

The catalytic performance of TiO2/MCM-41 catalysts is shownin Fig. 10. For the purpose of comparison, the catalysts were usedin these experiments containing the same amount of MO/Ti moralratio. Furthermore, pure MCM-41 or TiO2 show no transformation

toward the reaction (not shown here), while those grafted titaniumspecies on the MCM-41 support show substantial activity and yield

Fig. 7. SEM images of samples: (a) TiO2/MCM-41 (C2), (b) TiO2/MCM-41 (H2).

Fig. 8. TEM images of samples: (a) and (b) TiO2/MCM-41 (C2); (c) and (d) TiO2/MCM-41 (H2).


7/27/2019 1-s2.0-S1387181112002910-main

6/8

in the epoxidation reaction, which indicates that the titanium spe-cies loaded on the mesoporous MCM-41 act as active centers forthe selective epoxidation of MO. Their catalytic selectivity ofEMO is above 90%. This result suggests that the titanium speciesloaded on the mesoporous MCM-41 material act as active centersfor the epoxidation of MO. As shown in Fig. 10, the TiO2/MCM-41

(C) catalysts show excellent catalytic activity as compared withthe TiO2/MCM-41 (H) for this reaction. Furthermore, catalysts of

TiO2/MCM-41 (C2, H2) display better catalytic performance thanthat of TiO2/MCM-41 (C1, H1), which means that the catalytic per-formance is decided by the content and nature of titanium oxidespecies.

To get more information on the activity of these two kinds cat-alysts, the effect of TBHP/MO and Ti/MO molar ratio have been car-ried out and results are shown in Figs. 11 and 12. The effect ofTBHP/MO molar ratio (from 1.1/1 to 2.2/1) (Fig. 11) was investi-gated under 358 K, reaction time 10 h, MO/ Ti [TiO2/MCM-41(H2)] = 8.8, mass ratio of ethyl acetate/MO = 20. We observe thatthe conversion of MO increases with the increasing of TBHP/MOmolar ratio. And a maximum is obtained by using TBHP/MO molarratio of 1.55 giving a conversion 78%. Then the effect of MO/Ti mo-lar ratio was investigated under 358 K, reaction time 10 h, TBHP/

MO = 1.55, mass ratio of ethyl acetate/MO = 20 in Fig. 12. In aggre-gate TiO2/MCM-41 (C2) shows remarkable higher catalytic activity

Fig. 9. Nitrogen adsorption/desorption isotherms at 77 K and BJH pore size distribution of samples:h Calcined, pure MCM-41, 4 TiO2/MCM-41 (H2), O TiO2/MCM-41 (C2).

Table 2Textural properties of TiO2/MCM-41 (C2, H2) samples.

Sample BET surfacearea (m2/g)

Pore volume(cm3/g)

Average porediameter (nm)

TiO2/MCM-41 (C2) 882 0.44 2.44TiO2/MCM-41 (H2) 840 0.78 3.31


7/27/2019 1-s2.0-S1387181112002910-main

7/8

than TiO2/MCM-41 (H2). The range of conversion increases forTiO2/MCM-41 (H2) is bigger than that of TiO2/MCM-41 (C2) whenthe MO/Ti molar ratio changes from15 to 7, but the maximumcon-version of TiO2/MCM-41 (H2) still lower than that of TiO2/MCM-41(C2).

Besides, the solvent-free selective epoxidation of MO over TiO2/MCM-41 (C2) was investigated. In Fig. 13, the conversion of MO forthe high active catalyst TiO2/MCM-41 (C2) is below 70% even theMO/Ti reaching 8.

As we could see, the activity of the catalyst at 358 K is strongly

dependent upon the surface properties of the catalyst, MO/Ti molarratio, as well as the solvent existing.

4. Conclusion

TiO2/MCM-41 (C) and TiO2/MCM-41 (H) had been prepared bypost-synthesis step via aqueous TiCl4 solution in the support withand without refrigeration pretreatment, respectively, and charac-terized by several physical techniques. The results show that usingMCM-41 pretreated by refrigeration as the support is favor ofreducing surface temperature, resulting in no anatase formationon the MCM-41 surface. TiO2/MCM-41 (C) show better mesoscopic

order, higher dispersion of titanium oxide species, stronger inter-action with the MCM-41 support. It is revealed that the refrigera-

Fig. 10. Epoxidation performance of the selective epoxidation of MO over catalysts:I. TiO2/MCM-41 (C2); II. TiO2/MCM-41 (C1); III. TiO2/MCM-41 (H2); IV. TiO2/MCM-41 (H1). Reaction time 10h, reaction temperature 358K, mole ratio of MO/TBHP/TiO2 = 100:160:6, mass ratio of ethyl acetate/MO= 20.

Fig. 11. Effect of TBHP/MO molar ratio on the reaction conversion using catalystTiO2/MCM-41 (H2). Reaction time 10 h, reaction temperature 358 K, mole ratio ofMO/ Ti = 8.8, mass ratio of ethyl acetate/MO = 20.

Fig. 12. Effect of MO/Ti molar ratio on the epoxidation conversion of MO and yieldof EMO. Reaction time 10 h, reaction temperature 358 K, mole ratio of TBHP/MO = 1.5, mass ratio of ethyl acetate/MO = 20.

Fig. 13. Effect of MO/Timolar ratio on theepoxidation conversion of MO with TiO2/MCM-41 (C2) under solvent-free condition. Reaction time 10 h, reaction temper-ature 358 K, mole ratio of TBHP/MO = 1.6.


7/27/2019 1-s2.0-S1387181112002910-main

8/8

tion pretreatment is of crucial importance for the nature of cata-lyst. MO with highest loaded Ti retaining the ordered mesostruc-ture showed 98% conversion with 92% selectivity for EMO, andeven got 67% conversion of MO under solvent-free condition.

References

[1] H.J. Nieschlag, J.A. Rothfus, V.E. Sohns, R. Beltron Perkins, Ind. Eng. Chem. Prod.

Res. Dev. 16 (1977) 101107.[2] S. Warwel, F. Brse,C. Demes, M. Kunz, R.G. Klaas, Chemosphere 43 (2003) 39

48.[3] P. Czub, Macromol. Symp. 242 (2006) 6064.[4] F. Scholnick, H.A. MonROE Jr., E.J. Saggese, A.N. Wrigley, Urethane foams from

animal fats. II. Reaction of propylene oxide with fatty acids, J. Am. Oil Chem.Soc. 44 (1967) 4042.

[5] L. Barrio, J.M. Campos-Martn, M.P. de Frutos, J.L.G. Fierro, Ind. Eng. Chem. Res.47 (2008) 80168024.

[6] P.A.Z. Suarez, M.S.C. Pereira, K.M. Doll, B.K. Sharma, S.Z. Erhan, Ind. Eng. Chem.Res. 48 (2009) 32683270.

[7] M. Guidotti, R. Psaro, N. Ravasio, M. Sgobba, E. Giamotti, S. Grinberg, Catal.Lett.122 (2008) 5356.

[8] E. Poli, J.M. Clacens, J. Barrault, Y. Pouilloux, Catal. Today. 140 (2009) 1922.[9] K. Sato, M. Aoki, M. Ogawa, T. Hashimoto, D. Panyella, R. Noyori, Bull. Chem.

Soc. Jpn. 70 (1997) 905.

[10] K. Inumaru, T. Okuhara, M. Misono, J. Phys. Chem. 95 (12) (1991) 48264832.[11] J.M. Yao, W.C. Zhan, X.H. Liu, Y.L. Guo, Y.Q. Wang, Y. Guo, G.Z. Lu, Microporous

Mesoporous Mater. 15 (2012) 131136.[12] D. Marino, N.G. Gallrgos, J.F. Bengoa, A.M. Alvarez, M.V. Cagnoli, S.G. Casuscelli,

E.R. Herrero, S.G. Marchetti, Catal. Today 133135 (2008) 632638.[13] J. Yang, J. Zhang, L.W. Zhu, S.Y. Chem, Y.M. Zhang, Y. Tang, T.T. Zhu, Y.W. Li, J.

Hazard. Mater. B 137 (2006) 952958.[14] B.J. Aronson, C.F. Blanford, A. Stein, Chem. Mater. 9 (1997) 28422851.[15] X.C. Dong, Li Wang, J.F. Zhou, H.J. Yu, T.X. Sun, Catal. Commun. 7 (2006) 15.[16] Q. Cai, Z.S. Luo, W.Q. Pang, Y.W. Fan, X.H. Chen, F.Z. Cui, Chem. Mater. 13

(2001) 258263.[17] S. Che, S. Lim, M. Kaneda, H. Yoshitake, O. Terasaki, T. Tatsumi, J. Am. Chem.

Soc. 124 (47) (2002) 1396213963.[18] M.S. Morey, S. OBrien, S. Schwarz, G.D. Stucky, Chem. Mater. 12 (4) (2000)

898911.[19] Y. Luo, G.Z. Lu, Y.L. Guo, Y.S. Wang, Catal. Commun. 3 (2002) 129134.[20] M. Rigutto. Vanadium and titanium-containing molecular sieves, Ph.D. thesis,

Technische Universiteit Delft, 1996, 28.[21] A.O.T. Patrocnio, E.B. Paniago, R.M. Paniago, N.Y.M. Iha, Appl. Surf. Sci. 254

(2008) 18741879.[22] Y. Hasegawa, A. Ayame, Catal. Today 71 (2001) 177187.[23] A.Y. Stakheev, E.S. Shpiro, J. Apijok, J. Phys. Chem. 97 (21) (1993) 56685672.[24] O.D. Trong, M.P. Kapoor, E. Thibault, J.E. Gallot, G. Lemay, S. Kaliaguine,

Microporous Mesoporous Mater. 20 (1998) 107118.


1-s2.0-s1387181112002910-main

Documents