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Catalysis Communications 8 (2007) 997–1002

Influence of synthesis method on the properties andcatalytic performance of MCM-49 zeolites

Piaoping Yang a, Jianfeng Yu b,*, Ning Xu c, Jun Wang a, Tonghao Wu c,*

a School of Chemical Engineering, Harbin Engineering University, Harbin 150001, PR Chinab Department of Chemistry, Ohio-State University, Columbus, OH 43210, USA

c College of Chemistry, Jilin University, Changchun 130023, PR China

Received 6 June 2006; received in revised form 21 September 2006; accepted 5 October 2006Available online 19 October 2006

Abstract

Highly crystalline and pure MCM-49 was hydrothermally synthesized by dynamic and static methods, respectively. The properties ofthe samples were studied by N2 adsorption, XRD, TEM and FT-IR techniques. The results indicated that MCM-49 synthesized bydynamic method showed much smaller crystal and lower concentration of acid sites. The Pd-supported catalyst on MCM-49 synthesizedby static method showed higher acetone conversion in one-step synthesis of methyl isobutyl ketone from acetone, which was attributed tohigher concentration of acid sites. While the higher selectivity to methyl isobutyl ketone for Pd-supported on MCM-49 synthesized bydynamic method might be related with the lower acidity and higher BET surface area.� 2006 Elsevier B.V. All rights reserved.

Keywords: MCM-49; Static method; Dynamic methods; One-step synthesis of methyl isobutyl ketone

1. Introduction

Zeolite MCM-49 was first synthesized by Bennet et al. in1993 [1], which was composed of two independent pore sys-tems. One is defined by two-dimensional sinusoidal 10-membered-ring channels (4.0 · 5.0 A). The other pore sys-tem consists of supercages with 12-membered ring of 7.1 Ainner diameter and 18.2 A inner height. These huge intra-crystalline voids are accessible through 10-membered ringsapertures. The unique porous network of MCM-49, whosecharacteristics are between those of large and medium-porezeolites, suggests its widely use in many catalytic reactionsas supports or catalysts [2–4].

Methyl isobutyl ketone (MIBK) has been commerciallyproduced by a conventional three-step process: (i) aldol

1566-7367/$ - see front matter � 2006 Elsevier B.V. All rights reserved.

doi:10.1016/j.catcom.2006.10.016

* Corresponding authors.E-mail address: piaoping@ciac.jl.cn (T. Wu).

condensation of acetone to diacetone alcohol (DAA) overacid catalysts; (ii) acid-catalyzed DAA dehydration tomesityl oxide (MO); and (iii) selective hydrogenation ofMO to MIBK over metal supported catalysts. Because ofthe high cost, low yield and corrosive problems, three-stepsynthesis has been replaced by one-step synthesis in recentyears. Several studies were reported on one-step synthesisof MIBK, including Pd/resin [5], Pd/C with ion-exchangeresin [6,7], Pd/Zr3(PO4)2 [8], Pd/niobic acid [9], Pd/oxides[10,11], Pd/MgO [12], Pd/ZSM-5 [13], Pd/SAPO [14], Ni/Alumina [15], Pd/hydrotalcite [16], and Pd/MCM zeolites[17].

In this paper, we presented the synthesis and character-ization of MCM-49 prepared by different methods. N2

adsorption, XRD, TEM, FT-IR techniques were used tostudy the influence of synthesis methods on the propertiesof MCM-49. One-step synthesis of MIBK was used toprobe the influence of synthesis methods on the catalyticperformance for Pd-supported catalysts on MCM-49zeolites.

0.0 0.2 0.4 0.6 0.8 1.050

100

150

200

250

300

Vol

ume

Ads

orbe

d (c

m3 /g

)

Relative Pressure (P/P0)

ab

Fig. 1. N2 adsorption/desorption isotherm of MCM-49(d) (a) and MCM-49(s) (b).

998 P. Yang et al. / Catalysis Communications 8 (2007) 997–1002

2. Experimental

2.1. Synthesis of MCM-49 by dynamic method

MCM-49 was synthesized according to the literature[1] by using hexamethyleneimine (HMI) as organic tem-plates. The ratio of SiO2:Al2O3:NaOH:HMI:H2O is1:0.04:0.12:0.35:18.7 in the mother liquid. In a typical syn-thesis process, 4.564 g of NaAlO2 and 20 mL HMI werefirst dissolved in 80 mL of H2O, then 120 g of silica wasslowly added to the solution under vigorously stirringand was maintained for 30 min. After this, the slurrywas introduced into a 40 mL stainless steel autoclave,rotated at 60 rpm, and heated at 443 K for 3 days.NaMCM-49 obtained after synthesis was washed withdistilled water, dried at 393 K for 12 h and calcined at823 K for 6 h. HMCM-49 was prepared by ion-exchangeof NaMCM-49 with 1 M NH4NO3 solution at room tem-perature for 30 h. NH4MCM-49 obtained after ion-exchange was dried at 393 K for 5 h and calcined at823 K for 3 h. The obtained HMCM-49 is referred to asMCM-49(d).

2.2. Synthesis of MCM-49 by static method

The sample was prepared by a modification of the pro-cedure described above. The ratio in the mother liquid is:n(SiO2):n(Al2O3):(NaOH):n(HMI):n(H2O) = 1:0.033:0.18:0.5:40. The general process is listed below: 2.4 g of NaAlO2,1.01 g of NaOH and 12.5 mL HMI were first dissolved in160 mL of H2O, and the solution was heated to 323 K inabout 30 min, then 13.4 g of silica was slowly added tothe warm solution under stirring and kept at 323 K foranother 60 min. The slurry was then transferred to a stain-less steel autoclave and placed at 423 K for 20 days withoutrotation and stirring. HMCM-49 was obtained from thesynthesized NaMCM-49 as the same principle above. Theresulting material is referred to as MCM-49(s).

Pd/MCM-49 catalysts were prepared by ion-exchange ofHMCM-49 with aqueous solution of palladium nitrate.Ion-exchange was carried out in a rotator-evaporator for48 h at 353 K. The as-synthesized Pd/MCM-49 catalystswere dried at 393 K for 5 h and calcined at 823 K for5 h.

2.3. Characterization

The textural properties of the samples were measured ina Micromeritics ASAP 2020M apparatus by nitrogenadsorption at 77 K [18]. X-ray diffraction (XRD) patternswere recorded by a Shimadzu XRD-6000 diffractometeroperated 40 kV and 30 mA using Cu Ka radiation(k = 0.1542 nm). Transmission electron microscopy(TEM) of the samples was performed on Hitachi H-8100apparatus operating at 200 kV. Pd loading in the catalystswas determined by ICP-PLASMA 1000 after the digestionof the sample with HF solution.

The concentration of Brønsted and Lewis acid sites ofthe samples was determined after the adsorption of d3-ace-tonitrile followed by FT-IR spectroscopy, using NicoletImpact 410 spectrometer. The samples were pressed inthe form of self-supported wafers (thickness equivalent to4–6 mg/cm2), fixed in a quartz holder and then introducedinto an infrared cell with NaCl windows. d3-Acetonitrilewas pretreated by freeze–pump–thaw cycles. Beforeadsorption of d3-acetonitrile, the samples were treatedin situ by evacuation at 623 K in 10�3 Pa. Adsorptionwas carried out at 298 K for 20 min, followed by an evac-uation at the same temperature. For a quantitative charac-terization of the Brønsted acid sites (B), the C„N–Bvibration at 2296 cm�1 was used with an extinction coeffi-cient of e(B) = 2.05 ± 0.1 cm lmol�1. And for a quantita-tive evaluation of the Lewis acid sites (L), the C„N–Lvibration at 2323 cm�1 was used with the extinction coeffi-cient of e(L) = 3.6 ± 0.2 cm lmol�1 [19].

2.4. Catalytic tests

The reactions were carried out in a fixed bed tubularreactor using 0.5 g catalyst at 40 atm. Before reaction, thecatalysts were reduced ‘‘in situ’’ in flowing hydrogen at673 K for 3 h and then cooled down to the reaction temper-ature. The stream of gas mixture of hydrogen and acetonewith the molar ratio of 0.2 was introduced at a constantrate into the upper zone of the reactor, which was packedwith SiO2 pellets maintaining the reaction temperaturefor preheating and vaporization. The products were ana-lyzed by on-line gas chromatography (Shimadzu GC-14B).

3. Results and discussion

3.1. Characterization

Fig. 1 shows typical N2 adsorption/desorption iso-therms of MCM-49 synthesized by different methods.A H4-type hysteresis loop showed in all the isotherms is

Table 1Textural parameters and concentration of acid sites of the samples

Samples SBET (m2/g) Vp (cm3/g) d (A) Concentration ofBrønsted acid sites(mmol/g)

Concentration of Lewisacid sites (mmol/g)

MCM-49(s) 420 0.238 25.12 0.3510 0.2498MCM-49(d) 466 0.269 24.68 0.2620 0.24520.2%Pd/MCM-49(s) 398 0.221 25.07 0.3459 0.24660.2%Pd/MCM-49(d) 437 0.252 24.41 0.2467 0.2423

P. Yang et al. / Catalysis Communications 8 (2007) 997–1002 999

usually related to slit-shaped pores or to platelet particles.However, this figure also shows some difference betweenMCM-49(s) and MCM-49(d). At a relative pressure(p/p0) of 0.07, about 80% of the sorption capacity forMCM-49(s) is already used. While for MCM-49(d), themarked increase of the adsorption capacity up top/p0 = 0.14 exhibits the capillary condensation in mesop-ores, indicating the presence of larger mesopore volume.The results are in agreement with the literature [18].

Table 1 summarizes the textural parameters and concen-tration of acid sites of the samples. Compared with BETsurface area of 420 m2/g for MCM-49(s), a higher specificsurface area of 466 m2/g was obtained for MCM-49(d).The pore volume (Vp) of MCM-49(d) is higher than thatof MCM-49(s), while pore diameter (d) of MCM-49(d) islower than that of MCM-49(s). It can also be found thatthe BET surface area, pore volume and pore diameter of0.2%Pd/MCM-49 catalysts all decrease compared withMCM-49 zeolites, this may be caused by the covering ofsurface and partial pore blocking by Pd particles [20].

The XRD spectra of the as-synthesized and calcinedMCM-49 synthesized by different methods are shown inFigs. 2 and 3, respectively. Seen from Figs. 2a and 3a, sev-eral peaks in the XRD spectra are broad and overlap,which could be attributed to the presence of stacking faultsor to the platelets being made up of microcrystallites [21].Upon calcinations, these peaks become sharper and somenews peaks appear (Figs. 2b and 3b). From a comparisonwith the literature [1], it can be concluded that all the sam-

5 10 15 20 25 30 35 40

2θ (degree)

Inte

nsity

(a.

u.) b

a

Fig. 2. XRD spectra of as-synthesized MCM-49 (a) and calcined MCM-49 (b) synthesized by dynamic method.

ples are of high crystalline and pure phase. The spectra ofcalcined MCM-49(s) (Fig. 3b) show some sharper peaksthan those of MCM-49(d) (Fig. 2b), which may be causedby the larger particle size.

Fig. 4 shows the morphology of the samples synthesizedby different methods. All TEM images of the samples exhi-bit the absence of amorphous materials. Furthermore,TEM images show that the features of MCM-49(d) are dif-fered from MCM-49(s), showing much smaller crystals.The morphology of MCM-49(d) is very thin regular hexag-onal sheets of about 300–550 nm in diameter and 20–50 nmin thickness, while the sizes of the MCM-49(s) are approx-imately 2–3 lm in diameter and 0.3 lm in thickness. This isconsistent with the XRD results.

Fig. 5 presents the IR spectra of the C„N vibrations ofd3-acetonitrile adsorption, and the corresponding acidityvalues are listed in Table 1. Seen from the figure, the IRspectra are deconvoluted into four typical bands: two typ-ical bands with high intensity centered at 2323 cm�1 and2296 cm�1 correspond to the d3-acetonitrile adsorptionon strong Lewis acid sites (Al-Lewis sites) and Brønstedacid sites (Si–OH–Al groups), respectively [19–23]. Andthe other two bands with low intensity at about2280 cm�1 and 2251 cm�1 reflect the weak coordinationof the C„N groups to terminal Si–OH groups and C–2Hvibrations [19,22]. As shown in Fig. 5 and Table 1,MCM-49(s) shows higher amount of Brønsted acid thanthat of MCM-49(d), while the amount of Lewis acidchanges slightly. It can also be found from Fig. 5 and Table

Inte

nsity

(a.

u.)

2θ (degree)5 10 15 20 25 30 35 40

b

a

Fig. 3. XRD spectra of as-synthesized MCM-49 (a) and calcined MCM-49 (b) synthesized by static method.

Fig. 4. TEM micrograph of MCM-49(d) (a) and MCM-49(s) (b).

1000 P. Yang et al. / Catalysis Communications 8 (2007) 997–1002

1 that the concentration of acid sites of 0.2%Pd/MCM-49catalysts decrease slightly compared with MCM-49 zeo-lites. This can be explained that the large Pd particles can-not enter the channels and exchange with –OH on the innersurface which mainly contribute to the total acidity.The calculated concentration of Brønsted and Lewis acidsites of 0.2%Pd/MCM-49(s) were 0.3459 mmol/g and

2340 2320 2300 2280 2260 2240 2220 2200

Abs

orba

nce

wavenumber (cm-1)

d

c

b

a

Fig. 5. FT-IR spectra of MCM-49(s) (a); MCM-49(d) (b); 0.2%Pd/MCM-49(s) (c) and 0.2%Pd/MCM-49(d) (d) after d3-acetonitrile adsorption.

0.2466 mmol/g, respectively, while the correspondingvalues of 0.2%Pd/MCM-49(d) were 0.2467 mmol/g and0.2423 mmol/g.

3.2. Reaction results

Formation of the products has been explained by meansof Scheme 1 [12,14]. Diacetone alcohol (DAA) formed by

OH

O

(IPA)

-H2O

+H2

(Ac)

(Propene) (Propane)

acidsites

O

OH

-H2O

O

(MO)

+H2

O+H2

OH

(MIBC)

(MIBK)

acidsites

ac

O

+H2

O

(DIBK)

Scheme 1. Main reactions during acetone transformation.

Table 2Catalytic activity in one-step synthesis of MIBK over Pd-supported MCM-49 synthesized by different methods

Samples Conv. (%) Select. (%)

MIBK Pc IPA DIBK MIBC Unknown

0.2%Pd/MCM-49(s) 37.1 81.8 1.2 0.9 9.8 2.6 3.70.2%Pd/MCM-49(d) 28.9 89.1 0.6 0.7 5.5 1.3 2.8

Reaction conditions: T = 433 K, P = 40 atm and H2/acetone = 0.2.

P. Yang et al. / Catalysis Communications 8 (2007) 997–1002 1001

the aldol condensation of acetone on acid sites is dehy-drated to mesityl oxide (MO), which are hydrogenated tomethyl isobutyl ketone (MIBK) on metallic sites. MIBKmay go through additional condensation and hydrogena-tion steps to form di-isobutyl ketone (DIBK), or it maybe hydrogenated to form methyl isobutyl carbinol (MIBC).Along a parallel reaction, acetone can also be directlyhydrogenated to isopropanol (IPA), which is dehydratedand hydrogenated to propane (Pc).

Effect of synthesis method on the catalytic performancefor Pd/MCM-49 catalysts in one-step synthesis of MIBK islisted in Table 2. The conversion of acetone for 0.2%Pd/MCM-49(s) are higher than 0.2%Pd/MCM-49(d), whichcan be attributed to the higher concentration of acid sitesfor Pd/MCM-49(s) on condition that the Pd loading ofthe two catalysts are same. However, the selectivity toMIBK for Pd/MCM-49(s) increases from 81.8% to 89.1%for Pd/MCM-49(d). This may be also related with thehigher concentration of acid sites and lower surface areasfor Pd/MCM-49(s). This can be explained that the selectiv-ity to DIBK formed by condensation and hydrogenation ofMIBK is higher for Pd/MCM-49(s), which results in thedecrease of the selectivity to MIBK. And the distributionof other products is affected slightly.

The stability test for 0.2%Pd/MCM-49(d) catalyst wascarried out at 433 K, 40 atm and hydrogen/acetone = 0.2(Fig. 6). The acetone conversion only declines from28.9% to 25.3% and the selectivity is maintained aroundfor 72 h of time on stream. The results indicates that

0 20 40 60 80 100

20

40

60

80

100

20

40

60

80

100

Reaction time (hr)

Sel

ectiv

ity (

%)

Con

vers

ion

(%)

Fig. 6. The catalytic activity of Pd/MCM-49(d) as a function of reactiontime in one-step synthesis of MIBK from acetone.

0.2%Pd/MCM-49 was effective and relatively stable forthe one-step synthesis of MIBK from acetone in gasphase.

4. Conclusions

Synthesis methods markedly affect the structure and thecatalytic activity of MCM-49 zeolites. MCM-49 synthe-sized by static method showed higher concentration of acidsites than that of synthesized by dynamic method, whichcorresponding to the higher acetone conversion and DIBKselectivity. The lower concentration of acid sites and largerBET surface area may result in the higher selectivity toMIBK for Pd-supported on MCM-49 synthesized bydynamic method.

Acknowledgements

Financial supports from the National Natural ScienceFoundation of China (Grant No. 20273025) and the foun-dation of Harbin Engineering University (Grant No.002100260719) are greatly acknowledged.

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