Immobilization of a heteropolyacid catalyst on the

aminopropyl-functionalized mesostructured cellular

foam (MCF) silica

Heesoo Kim a, Ji Chul Jung a, Sung Ho Yeom b, Kwan-Young Lee c,Jongheop Yi a, In Kyu Song a,*

a School of Chemical and Biological Engineering, Institute of Chemical Processes, Seoul National University,

Shinlim-dong, Kwanak-ku, Seoul 151-744, South Koreab Department of Environmental and Applied Chemical Engineering, Kangnung National University, Kangnung 210-702, South Korea

c Department of Chemical and Biological Engineering, Korea University, Annam-dong, Sungbuk-ku, Seoul 136-701, South Korea

Received 12 October 2006; received in revised form 21 December 2006; accepted 18 January 2007

Available online 23 January 2007

Abstract

Mesostructured cellular foam (MCF) silica with high surface area (>600 m2/g) and large pore volume (�1.16 cm3/g) was

synthesized via a surfactant templating method. The MCF silica was then modified by grafting 3-aminopropyl-triethoxysilane

(APTES) to create a positive charge on the surface, and thus, to provide sites for the immobilization of H3PMo12O40. By taking

advantage of the overall negative charge of [PMo12O40]3�, the H3PMo12O40 catalyst was chemically immobilized on the

aminopropyl group of the surface modified MCF silica as a charge matching component. The mesopore structure of MCF silica

was maintained even after the surface modification step and the subsequent immobilization step of H3PMo12O40. The H3PMo12O40

species were finely and molecularly dispersed on the surface modified MCF silica via chemical immobilization.

# 2007 Elsevier Ltd. All rights reserved.

Keywords: A. Inorganic compounds; A. Surfaces; D. Surface properties

1. Introduction

Mesostructured cellular foam (MCF) silica with large pores in the range of 20–50 nm has been successfully

synthesized using a PEO-PPO-PEO triblock copolymer (Pluronic P123), tetraethyl orthosilicate, and 1,3,5-

trimethylbenzene (TMB) as an organic template, a silica source, and a swelling agent, respectively [1,2]. Due to the

unique pore characteristics such as high surface area and large pore volume, MCF silica has been utilized in many

fields of science and engineering, including adsorption, separation, and catalysis [3,4]. In order to use mesoporous

silica as a supporting material in catalysis, mesoporous silica has been modified using organic silanes such as

3-aminopropyl-triethoxysilane (APTES) with a terminal amine group (–NH2) and 3-mercaptopropyl-triethoxysilane

(MPTES) with a terminal thiol group (–SH) [5–8]. A grafting method, in which the hydroxyl group of the mesoporous

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Materials Research Bulletin 42 (2007) 2132–2142

* Corresponding author. Tel.: +82 2 880 9227; fax: +82 2 889 7415.

E-mail address: inksong@snu.ac.kr (I.K. Song).

0025-5408/$ – see front matter # 2007 Elsevier Ltd. All rights reserved.

doi:10.1016/j.materresbull.2007.01.010

silica reacts with the organic silane to form a functional group on the surface layer of mesoporous silica by covalent

bonding, is one of the promising methods for the surface functionalization of mesoporous silica [9].

Heteropolyacids (HPAs) are early transition metal oxygen anion clusters [10]. Among the various HPA structural

classes, Keggin-type [11] HPAs have been widely employed as homogeneous and heterogeneous catalysts for acid–

base and oxidation reactions [12–16]. The Keggin-type HPA has a soccer ball-shape with a molecular size of ca. 1 nm

[17]. One of the disadvantages of HPA catalysts is that their surface area is very low (<10 m2/g). To overcome the low

surface area, HPA catalysts have been supported on the inorganic porous materials such as mesoporous molecular

sieve (MCM-41, HMS) [18], mesoporous silica (SBA-15) [19], carbon gel [20], and mesoporous g-alumina [21] by an

impregnation method. Another promising approach for increasing the surface area of HPA catalysts is to take

advantage of the overall negative charge of the heteropolyanion. By this method, HPA catalysts have been

immobilized on the polymer materials such as poly-4-vinylpyridine [22], polyaniline [23], and polystyrene [24] to

obtain molecularly dispersed HPA catalysts. However, such an attempt utilizing inorganic supporting materials has

been restricted due to the difficulty in forming a positive charge on the inorganic supporting materials. A successful

example for the immobilization of HPA catalyst on an inorganic support can be found in a recent report [25]. It was

reported that H3PMo12O40 (a typical Keggin-type HPA) was chemically immobilized on a porous carbon by forming a

positive charge on the support via surface modification [25]. HPAs have also been successfully immobilized on the

mesoporous materials such as HMS [26,27], MCM-41 [28], and SBA-15 [29], by grafting APTES onto the surface of

mesoporous materials, and thus, by providing anchoring sites for heteropolyanions. However, no attempt has been

made to immobilize an HPA catalyst on the aminopropyl-functionalized mesostructured cellular foam (MCF) silica.

Furthermore, no systematic investigation on the amount of APTES used for the surface functionalization of

mesoporous materials has been conducted yet.

In this work, mesostructured cellular foam (MCF) silica was prepared via a surfactant templating method. The

MCF silica was then modified by grafting 3-aminopropyl-triethoxysilane (APTES) to create a positive charge on the

surface, and thus, to provide sites for the immobilization of H3PMo12O40. By taking advantage of the overall negative

charge of [PMo12O40]3�, the H3PMo12O40 catalyst was chemically immobilized on the surface modified MCF (SM-

MCF) silica as a charge matching component. The characteristics of the H3PMo12O40 catalyst immobilized on the SM-

MCF silica were extensively investigated.

2. Experimental

2.1. Preparation of MCF silica

MCF silica was prepared according to a reported method [1]. Four grams of a PEO-PPO-PEO triblock copolymer

(Pluronic P123, BASF), an organic template, was dissolved in 150 ml of a 1.6 M HCl solution at 35 8C. Four grams of

1,3,5-trimethylbenzene (TMB, Fluka), a swelling agent, was added to the solution containing the organic template.

The resulting solution was then slowly added to 8.5 g of tetraethyl orthosilicate (TEOS, Fluka), a silica source. The

resulting mixture was stirred at 35 8C for 24 h, and it was maintained at 80 8C for 24 h. After filtering and drying the

solid product, it was calcined at 550 8C for 5 h to yield the MCF silica.

2.2. Surface modification of MCF silica and immobilization of H3PMo12O40

Fig. 1 shows the schematic procedures for the surface modification of MCF silica and the subsequent

immobilization of H3PMo12O40 (PMo12) on the surface modified MCF (SM-MCF) silica. The surface modification of

the MCF silica was achieved by reacting hydroxyl group of the MCF silica with 3-aminopropyl-triethoxysilane

(APTES, Aldrich) under a nitrogen atmosphere. A known amount of APTES was slowly added to a dry toluene

solution containing 1 g of MCF silica with constant stirring at room temperature. After the solid product was filtered

and dried, it was calcined at 180 8C for 2 h to yield the SM-MCF silica. A series of SM-MCF silica samples (SM-

MCF-0.5, SM-MCF-1.0, SM-MCF-1.5, SM-MCF-2.0, and SM-MCF-3.0) were prepared by adjusting the amount of

APTES added to 1 g of MCF silica. For example, SM-MCF-0.5 denotes the SM-MCF silica prepared by the addition

of 0.5 mmol of APTES to 1 g of MCF silica.

The immobilization of H3PMo12O40 (PMo12) on each of the SM-MCF silica support was achieved as follows.

SM-MCF silica (1 g) was added to an acetonitrile solution containing PMo12 (0.5 g) with vigorous stirring at room

H. Kim et al. / Materials Research Bulletin 42 (2007) 2132–2142 2133

temperature, and the resulting solution was maintained at room temperature for 24 h. The solid product was filtered,

and then it was dried overnight at 80 8C to yield the PMo12/SM-MCF silica samples (PMo12/SM-MCF-0.5, PMo12/

SM-MCF-1.0, PMo12/SM-MCF-1.5, PMo12/SM-MCF-2.0, and PMo12/SM-MCF-3.0).

2.3. Characterization

N2 adsorption–desorption isotherms of MCF silica, SM-MCF silica, and PMo12/SM-MCF silica samples were

obtained using an ASAP-2010 instrument (Micromeritics). The surface areas and pore volumes of the prepared

samples were calculated using the BET equation and the BJH model, respectively. Nitrogen contents were

determined by CHN elemental analyses (EC Instrument, EA1110). PMo12 contents in the PMo12/SM-MCF silica

samples were measured by ICP-AES analyses (Shimadz, ICP-1000IV). Infrared spectra of the prepared samples were

obtained with a FT-IR spectrometer (Nicolet, Impact 410). Pore structures of the samples were examined by TEM

(Jeol, JEM-2000EXII). Small angle X-ray scattering (SAXS) patterns of the samples were recorded on a GADDS

apparatus (Bruker) using Cu Ka radiation. The acid property of PMo12/SM-MCF silica and the state of PMo12 in the

PMo12/SM-MCF silica were confirmed by NH3-TPD measurements. For the TPD measurements, each catalyst

(unsupported PMo12 or PMo12/SM-MCF silica, 10 mg on the basis of PMo12) was charged in a quartz reactor

of the conventional TPD apparatus. The sample was pretreated at 200 8C for 2 h under a flow of helium (20 ml/min) to

remove any physisorbed organic molecules. Twenty milliliters of NH3 was then pulsed into the reactor every

minute at room temperature under a flow of helium (5 ml/min), until the acid sites were saturated with NH3. The

physisorbed NH3 was removed by evacuating the catalyst sample at 50 8C for 1 h. The furnace temperature was

increased from room temperature to 500 8C at a rate of 5 8C/min under a flow of helium (10 ml/min). The desorbed

NH3 was detected using a GC-MSD (Agilent, 5975MSD-6890N GC). The chemical states of the prepared samples

were examined by 13C CP-MAS, 29Si CP-MAS, and 31P CP-MAS NMR analyses (Bruker, AVANCE 400 WB, DSX-

400). TGA analyses were conducted using a TGA-50 instrument (Shimadz) at a heating rate of 5 8C/min. The crystal

states of PMo12 in the PMo12/SM-MCF silica samples were confirmed by XRD measurements (MAC Science,

M18XHF-SRA).

H. Kim et al. / Materials Research Bulletin 42 (2007) 2132–21422134

Fig. 1. Schematic procedures for the surface modification of MCF silica and the subsequent immobilization of PMo12 on the surface modified MCF

(SM-MCF) silica.

3. Results and discussion

3.1. Physical properties of SM-MCF silica and PMo12/SM-MCF silica

Fig. 2 shows the surface area and nitrogen content of SM-MCF silica as a function of the amount of APTES used.

The amount of aminopropyl functional group in the SM-MCF silica was indirectly measured by CHN elemental

analysis. The surface area of the SM-MCF silica was decreased with increasing amount of APTES used, while the

nitrogen content in the SM-MCF silica was roughly increased with increasing amount of APTES used. As expected, no

nitrogen was detected in the bare MCF silica sample. These results strongly suggest that aminopropyl functional group

was successfully grafted on the MCF silica via the surface modification step. It was also found that the nitrogen content

was linearly increased with increasing amount of APTES used up to 2.0 mmol. However, no additional increase of

nitrogen content was observed when the amount of APTES was greater than 2.0 mmol.

Fig. 3 shows the surface area and PMo12 content of PMo12/SM-MCF silica with respect to the amount of APTES

used. The surface area of the PMo12/SM-MCF silica was decreased with increasing amount of APTES used, while the

H. Kim et al. / Materials Research Bulletin 42 (2007) 2132–2142 2135

Fig. 2. Surface area and nitrogen content of SM-MCF silica as a function of the amount of APTES used.

Fig. 3. Surface area and PMo12 content of PMo12/SM-MCF silica as a function of the amount of APTES used.

PMo12 loading in the PMo12/SM-MCF silica was roughly increased with increasing amount of APTES used. The

PMo12/SM-MCF silica showed a lower surface area than the corresponding SM-MCF silica, due to the loading of the

PMo12 species (Figs. 2 and 3). Although the nitrogen content in the SM-MCF silica was the highest when 2.0 mmol of

APTES was used (Fig. 2), no substantial difference in PMo12 loading was found in the PMo12/SM-MCF silica when

the amount of APTES exceeded 1.0 mmol (Fig. 3). The amount of PMo12 loaded in the PMo12/SM-MCF-1.0 was

found to be 10.6 wt%. The above results indicate that 1.0 mmol of APTES was sufficient to modify the surface of the

MCF silica for the maximum loading of PMo12 species. It is likely that the aminopropyl functional group in the SM-

MCF silica was formed in layers when the amount of APTES exceeded 1.0 mmol (Figs. 2 and 3). However, the surface

area of PMo12/SM-MCF silica was still decreased even after the saturation of PMo12/SM-MCF silica at 1.0 mmol of

APTES. It is believed that the decrease of surface area of PMo12/SM-MCF-1.5 and PMo12/SM-MCF-2.0 was due to

the decrease of micropore surface area, which was attributed to the blocking of micropores by excess amount of

APTES and to the partial collapse of micropores without changing the mesopore structure.

We also attempted to support PMo12 on pure MCF silica. In this case, however, the PMo12 species were completely

dissolved out during the washing step. In other words, PMo12 species could not be successfully immobilized on the

surface of unmodified MCF silica, due to the absence of anchoring sites for the PMo12 species. The above results imply

that surface modification of MCF silica to provide anchoring sites for PMo12 species is essential for the successful

immobilization of PMo12 species on the MCF silica.

Fig. 4 shows the NH3-TPD profiles of unsupported PMo12 and PMo12/SM-MCF-1.0. For the comparison purpose, a

TPD experiment of PMo12/SM-MCF-1.0 in the absence of NH3 adsorption was also conducted. As shown in Fig. 4, the

PMo12/SM-MCF-1.0 in the absence of NH3 adsorption showed a broad NH3-TPD peak due to the decomposition of

aminopropyl group at high temperature, indicating that APTES was successfully grafted in the PMo12/SM-MCF-1.0.

Furthermore, the evolution of NH3 originated from the decomposition of aminopropyl group in the PMo12/SM-MCF-

1.0 started to occur at ca. 250 8C. This is roughly in good agreement with the thermal decomposition temperature

measured by TGA analysis (Fig. 11), considering that a TPD profile can shift by experimental conditions such as

heating rate and carrier flow rate. On the other hand, the PMo12/SM-MCF-1.0 with NH3 adsorption showed a broad

NH3-TPD peak at low temperature. The area of NH3-TPD profile observed in the PMo12/SM-MCF-1.0 with NH3

adsorption corresponds to the amount of NH3 originated from the decomposition of aminopropyl group and the

chemically adsorbed NH3 on the acid sites of PMo12/SM-MCF-1.0. Therefore, the difference in NH3-TPD peak area

between PMo12/SM-MCF-1.0 with NH3 adsorption and PMo12/SM-MCF-1.0 without NH3 adsorption is equivalent to

the acid sites existed in the PMo12/SM-MCF-1.0. The area of NH3-TPD profile observed in the unsupported PMo12

corresponds to the amount of NH3 adsorbed on the acid sites of H3PMo12O40. The amount of NH3 obtained by

subtracting the peak area of PMo12/SM-MCF-1.0 in the absence of NH3 adsorption from the peak area of PMo12/SM-

MCF-1.0 with NH3 adsorption was found to be 1/10 of the amount of NH3 adsorbed on the unsupported PMo12. Simple

calculation reveals that the real state of PMo12/SM-MCF-1.0 is H0.3(�NH3)2.7PMo12O40/SM-MCF-1.0. This result

H. Kim et al. / Materials Research Bulletin 42 (2007) 2132–21422136

Fig. 4. NH3-TPD profiles of unsupported PMo12 and PMo12/SM-MCF-1.0.

indicates that the PMo12/SM-MCF-1.0 catalyst retains very small amounts of acid sites compared to the unsupported

H3PMo12O40.

Fig. 5 shows the N2 adsorption–desorption isotherms and pore size distributions of MCF silica, SM-MCF-1.0, and

PMo12/SM-MCF-1.0. All the samples exhibited typical IV type isotherms and H1 type hysteresis loops at high relative

pressures. This indicates that MCF silica with large pore size distribution was successfully prepared. Interestingly, the

SM-MCF-1.0 and PMo12/SM-MCF-1.0 showed very similar isotherm patterns and pore size distributions (inset)

compared to those of MCF silica, indicating that the mesopore structure of MCF silica was still maintained even after

the surface modification step and the subsequent immobilization step of PMo12.

Fig. 6 shows the TEM images of MCF silica, SM-MCF-1.0, and PMo12/SM-MCF-1.0. Disordered pore arrays of

MCF silica can be clearly seen in all samples. The pore diameters of all samples determined from TEM images were

ca. 20 nm with no great difference, in good agreement with the pore size distribution calculated from the BJH isotherm

model (inset of Fig. 5).

Fig. 7 shows the small angle X-ray scattering (SAXS) patterns of MCF silica, SM-MCF-1.0, and PMo12/SM-MCF-

1.0. Unlike highly ordered mesoporous silica materials such as SBA-15 and MCM-41, all the prepared samples

showed a single SAXS peak in the range of 2u = 0–18 due to the presence of mesopores. Although a certain plane or

space group of MCF silica, SM-MCF-1.0, and PMo12/SM-MCF-1.0 was not observed, the appearance of single SAXS

peak in these samples is well consistent with a previous report [30]. The above result supports that the MCF silica was

H. Kim et al. / Materials Research Bulletin 42 (2007) 2132–2142 2137

Fig. 5. N2 adsorption–desorption isotherms and pore size distributions of MCF silica, SM-MCF-1.0, and PMo12/SM-MCF-1.0.

Fig. 6. TEM images of (a) MCF silica, (b) SM-MCF-1.0, and (c) PMo12/SM-MCF-1.0.

successfully prepared in this work and that the mesopore structure of MCF silica was still maintained after the surface

modification step and the subsequent immobilization step of PMo12.

3.2. Chemical immobilization of PMo12 on SM-MCF silica

The successful immobilization of the PMo12 catalyst on the aminopropyl-functionalized MCF silica was confirmed

by FT-IR analyses as shown in Fig. 8. A band at 1630 cm�1 observed in all samples can be assigned to the –OH

vibration of physisorbed H2O. In the case of MCF silica, SM-MCF-1.0, and PMo12/SM-MCF-1.0, the Si–O–Si bands

originated from MCF silica were observed at around 1000–1250, 800, and 475 cm�1. A broad band at 2700–

3400 cm�1 and a weak band at around 1500 cm�1 observed in the SM-MCF-1.0 and PMo12/SM-MCF-1.0 are

attributed to the –NH3+ stretching vibration, indicating the presence of aminopropyl functional group in the SM-MCF-

1.0 and PMo12/SM-MCF-1.0 [5,6].

The primary structure of unsupported PMo12 can be identified by the four characteristic IR bands appearing at

1064 cm�1 (P–O band), 964 cm�1 (Mo O band), 868 and 789 cm�1 (Mo–O–Mo bands). The characteristic IR bands of

PMo12 in the PMo12/SM-MCF-1.0 were different from those of unsupported PMo12. The P–O band in the PMo12/SM-

MCF-1.0 sample was not clearly identified due to overlap by the broad Si–O–Si band. However, Mo O and Mo–O–Mo

H. Kim et al. / Materials Research Bulletin 42 (2007) 2132–21422138

Fig. 7. SAXS patterns of MCF silica, SM-MCF-1.0, and PMo12/SM-MCF-1.0.

Fig. 8. FT-IR spectra of MCF silica, SM-MCF-1.0, unsupported PMo12, and PMo12/SM-MCF-1.0.

bands of PMo12 in the PMo12/SM-MCF-1.0 appeared at slightly shifted positions compared to those of the unsupported

PMo12, indicating a strong interaction between PMo12 and SM-MCF silica [25].

The chemical states of the prepared samples were further examined by 13C CP-MAS, 29Si CP-MAS, and 31P CP-

MAS NMR analyses. Fig. 9(a) shows the solid-state 13C CP-MAS NMR spectra of MCF silica and SM-MCF-1.0. SM-

H. Kim et al. / Materials Research Bulletin 42 (2007) 2132–2142 2139

Fig. 9. (a) 13C CP-MAS NMR spectra of MCF silica and SM-MCF-1.0, (b) 29Si CP-MAS NMR spectra of MCF silica and SM-MCF-1.0, and (c) 31P

CP-MAS NMR spectra of unsupported PMo12 and PMo12/SM-MCF-1.0.

MCF-1.0 obviously showed three chemical shifts at d = 9 (C1), 24 (C2), and 43 (C3) ppm, while MCF silica exhibited

no resonance peak. The three resonance peaks observed in the SM-MCF-1.0 were attributed to different carbon atoms

(C1, C2, and C3) in the APTES. This result indicates that aminopropyl functional groups were successfully grafted on

the MCF silica.

Fig. 9(b) shows the solid-state 29Si CP-MAS NMR spectra of MCF silica and SM-MCF-1.0. MCF silica showed

three chemical shifts at d = �110 (Q4), �102 (Q3), and �92 (Q2) ppm due to the different surroundings. On the other

hand, SM-MCF-1.0 showed a distinctive chemical shift at d = �68 (T3) ppm, which was attributed to APTES grafted

on the MCF silica. The peak intensity ratio of Q3/Q4 for MCF silica was higher than that for SM-MCF-1.0, and Q2 peak

observed in the MCF silica disappeared in the SM-MCF-1.0. These results indicate that hydroxyl groups of MCF silica

reacted with APTES by covalent bonding and that highly condensed silicate network was formed.

Fig. 9(c) shows the solid-state 31P CP-MAS NMR spectra of unsupported PMo12 and PMo12/SM-MCF-1.0.

Unsupported PMo12 showed a chemical shift at d = �3.2 ppm. This resonance peak corresponds to the structural

phosphorus in PMo12, in good agreement with previous reports [14,29]. On the other hand, the chemical shift of

PMo12/SM-MCF-1.0 appeared at d = �4.7 ppm. These results indicate that PMo12 species were successfully

immobilized on SM-MCF-1.0 in the PMo12/SM-MCF-1.0 via strong chemical interaction.

Fig. 10 shows the XRD patterns of unsupported PMo12, MCF silica, SM-MCF-1.0, and PMo12/SM-MCF-1.0. The

unsupported PMo12 catalyst showed the characteristic XRD pattern of the HPA. On the other hand, MCF silica and

SM-MCF-1.0 showed no characteristic XRD peak due to the amorphous nature of MCF silica. What is interesting is

that PMo12/SM-MCF-1.0 also showed no characteristic XRD pattern, even though 10.6 wt% PMo12 was loaded on the

SM-MCF-1.0. This indicates that the PMo12 species were not in a crystal state but in an amorphous-like state,

demonstrating that the PMo12 species are finely and molecularly dispersed on the SM-MCF-1.0. It should be noted that

the aminopropyl functional group of SM-MCF silica retaining a positive charge served as an anchoring site for the

chemical immobilization of [PMo12O40]3�.

3.3. Thermal stability of SM-MCF silica and PMo12/SM-MCF silica

The thermal stability of unsupported PMo12, SM-MCF-1.0, and PMo12/SM-MCF-1.0 was examined by TGA

analyses, as shown in Fig. 11. Thermal scanning was done at temperatures ranging from 25 to 600 8C in a stream of air.

The PMo12 catalyst experienced a significant weight loss in the low temperature region below 150 8C due to the

removal of crystalline water molecules, and then it was finally decomposed at 430 8C, in good agreement with a

previous report [14]. TGA profiles of SM-MCF-1.0 obtained before and after the immobilization of PMo12 revealed

that the weight loss at temperatures below 200 8C was less than 2 wt%, which was attributed to the removal of small

amounts of physically adsorbed water and residual solvent. It appears that the weight loss observed at temperatures

above 280 8C in the SM-MCF-1.0 and PMo12/SM-MCF-1.0 samples may be due to the decomposition of aminopropyl

groups that had been grafted to the SM-MCF-1.0 silica. This indicates that the SM-MCF-1.0 and PMo12/SM-MCF-1.0

samples are thermally stable at temperatures below 280 8C.

H. Kim et al. / Materials Research Bulletin 42 (2007) 2132–21422140

Fig. 10. XRD patterns of unsupported PMo12, MCF silica, SM-MCF-1.0, and PMo12/SM-MCF-1.0.

It is believed that the PMo12/SM-MCF-1.0 can be potentially available as a finely and molecularly dispersed PMo12

catalyst in the oxidation reactions performed below 280 8C. In a preliminary catalytic reaction performing a vapor-

phase ethanol conversion at 230 8C, it was revealed that the PMo12/SM-MCF-1.0 catalyst showed a higher ethanol

conversion than the unsupported PMo12 catalyst. Furthermore, the PMo12/SM-MCF-1.0 catalyst exhibited an

enhanced oxidation catalytic activity (formation of acetaldehyde) and a suppressed acid catalytic activity (formation

of ethylene and diethylether).

4. Conclusions

MCF silica was prepared via a surfactant templating method. The MCF silica was then modified by grafting APTES

to create a positive charge on the surface, and thus, to provide sites for the immobilization of PMo12. By taking

advantage of the overall negative charge of [PMo12O40]3�, the PMo12 catalyst was immobilized on the SM-MCF silica

as a charge matching component. It was found that the aminopropyl functional group of the SM-MCF silica served as

an efficient anchoring site for the immobilization of PMo12. It was also revealed that the mesopore structure of MCF

silica was maintained even after the surface modification step and the subsequent immobilization step of PMo12. In the

PMo12/SM-MCF silica, the PMo12 species were finely and molecularly dispersed on the SM-MCF silica via chemical

immobilization.

Acknowledgement

The authors wish to acknowledge support from the Korea Science and Engineering Foundation (KOSEF R01-2004-

000-10502-0).

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