MOR zeolite supported Bronsted acidic ionic liquid: An efficient and recyclable heterogeneous catalyst for ketalization

Article abstract of DOI:10.1039/c4ra00092g

In order to widen the application of ionic liquids as efficient and renewable heterogeneous catalysts, supported ionic liquids (SILs) have received considerable attention. A novel heterogeneous catalyst MOR zeolite supported Bronsted acidic ionic liquid (BAIL@MOR) was therefore prepared, characterized and applied in the ketalization reaction. The influences of reaction temperature, time, and catalyst loading have also been investigated in detail. Combined characterization results of XRD, FT-IR, SEM, TG-DTG and N ₂ adsorption-desorption suggested that the BAIL [CPES-BSIM][HSO ₄] was successfully immobilized on the surface of MOR zeolite by covalent bonds. Moreover, the catalytic performance tests demonstrated that the catalyst BAIL@MOR exhibited excellent catalytic activities in the ketalization of cyclohexanone with glycol, 1,2-propylene glycol and 1,3-butylene glycol under mild reaction conditions, as comparable with the homogeneous catalysis of the precursors [BSmim][HSO₄] and H₂SO₄. In addition, the catalyst BAIL@MOR was also found to be reusable five times without a significant loss of its catalytic activity. Thus, the heterogeneous catalyst BAIL@MOR can act as a promising candidate for the ketalization reaction.

Full text of DOI:10.1039/c4ra00092g

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MOR zeolite supported Brønsted acidic ionic liquid:
an efficient and recyclable heterogeneous catalyst
for ketalization
Cite this: RSC Adv., 2014, 4, 12160
*
*
Zhang-Min Li, Yan Zhou, Duan-Jian Tao, Wei Huang, Xiang-Shu Chen
and Zhen Yang
In order to widen the application of ionic liquids as efficient and renewable heterogeneous catalysts,
supported ionic liquids (SILs) have received considerable attention. A novel heterogeneous catalyst MOR
zeolite supported Brønsted acidic ionic liquid (BAIL@MOR) was therefore prepared, characterized and
applied in the ketalization reaction. The influences of reaction temperature, time, and catalyst loading
have also been investigated in detail. Combined characterization results of XRD, FT-IR, SEM, TG-DTG
and N2 adsorption–desorption suggested that the BAIL [CPES-BSIM][HSO4] was successfully immobilized
on the surface of MOR zeolite by covalent bonds. Moreover, the catalytic performance tests
demonstrated that the catalyst BAIL@MOR exhibited excellent catalytic activities in the ketalization of
cyclohexanone with glycol, 1,2-propylene glycol and 1,3-butylene glycol under mild reaction conditions,
as comparable with the homogeneous catalysis of the precursors [BSmim][HSO4] and H2SO4. In addition,
the catalyst BAIL@MOR was also found to be reusable five times without a significant loss of its catalytic
activity. Thus, the heterogeneous catalyst BAIL@MOR can act as a promising candidate for the
ketalization reaction.
Received 6th January 2014
Accepted 19th February 2014
DOI: 10.1039/c4ra00092g
www.rsc.org/advances
of functional BAILs and the homogeneous ILs catalysts tend to
cause difficulties in product purication and catalyst recovery.
Introduction
To overcome the above-mentioned problems, there has been a
surge of interest in immobilization of ILs, the so-called sup-
ported ILs (SILs), using various polymeric and inorganic
support materials in order to improve their applicability in
industrial catalytic processes.8
Generally, SILs are prepared by coating a thin layer of IL lm
onto and/or into the surface of desired solid support materials.
Such SILs-based heterogeneous catalyst (SILC) systems not only
retain the important physical and chemical features of ILs, such
as nonvolatility, designability, and good thermal stability, but
also possess several attractive advantages in terms of catalyst
recovery, regeneration, and reuse. In 2002, Mehnert's group9
had rstly developed a novel SILC, which was prepared by dis-
In recent years, ionic liquids (ILs) have received widespread
attention as a new type of eco-friendly reaction medium and
green solvent, owing to their particular properties such as
negligible vapor pressure, wide liquid range, excellent
solubility, high catalytic activity and good selectivity. ILs
present broad application prospects in the eld of catalysis
and have been successfully used in many organic reactions
such as alkylation,1 esterication,2 nitration,3 acetalization,4
ketalization5 and so on, for which ILs obviously exhibit high
catalytic activity and selectivity. The synthesis and applica-
tion of ILs therefore have been concerned and reported
extensively so far.
In 2002, Cole et al.6 had rstly synthesized functionalized
Brønsted acidic ionic liquids (BAILs) beared with an alkyl
sulfonic acid and used these BAILs for the esterication of
acetic acid with ethanol. On the basis of Cole's work, Gui et al.7
had further illustrated the merits of using SO3H-functionalized
BAILs for esterication. Despite the excellent conversions and
selectivities, several drawbacks of SO3H-functional ILs are still
restricted their further applications. For example, the high cost
solving
a
homogeneous
transition
metal
catalyst,
[Rh(NBD)(PPh3)2][PF6], within a multi-layer of [BMIM][PF6] on
silica gel. Aer that, a variety of SILCs, including mesoporous
material,10,11 carbon nanotubes,12 magnetic nanoparticles13,14 or
polymer-immobilized15,16 quaternary ammonium salts, phos-
phonium salts, and imidazolium alkyl salts, have been exten-
sively developed for many reactions. For example, Luo et al.14
had successfully synthesized novel Fe3O4 nanoparticle sup-
ported ILs catalyst for the one-pot synthesis of benzoxanthenes.
Doherty et al.16 reported peroxometalate-based polymer immo-
bilized ionic liquids as efficient and recyclable catalyst for
hydrogen peroxide-mediated oxidation.
Jiangxi Inorganic Membrane Materials Engineering Research Centre, College of
Chemistry and Chemical Engineering, Jiangxi Normal University, Nanchang 330022,
People's Republic of China. E-mail: djtao@jxnu.edu.cn; cxs66cn@jxnu.edu.cn; Fax:
+86-791-88120843; Tel: +86-791-88121974
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However, despite the excellent catalytic performance and
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good recyclability, most of these SILCs always showed signi-
cantly lower catalytic activity than the homologous homo-
geneous IL catalysts because of the lower degree of exposure of
the catalytic sites.17 In addition, the SILC systems oen contain
mesoporous silica, carbon nanotube and polystyrene as the
supporting materials. A few examples of supported ILs can be
found in the literatures where zeolite is employed as the sup-
porting material.18–20 Therefore, our efforts have been focused
on the appropriate zeolite as support material that can effec-
tively promote the catalytic reactivity of SILCs in comparison
with the corresponding homogeneous IL catalysts.
As well known, mordenite (MOR) with a crystalline zeolite
framework exhibits a higher hydrothermal stability and it is
widely used as Brønsted acid catalyst for cracking, isomer-
isation, and alkylation reactions in the petrochemical industry,
which makes MOR zeolites suitable for a potentially new sup-
porting material.21–23 Therefore, the introduction of SO3H-
functionalized BAILs is expected to add strong Brønsted acidity
of MOR zeolite. Herein, we report a novel heterogeneous cata-
lyst MOR zeolite supported SO3H-functionalized BAIL (BAIL@
MOR) and its application as a highly efficient and reusable
catalyst in the ketalization reaction for the rst time. X-ray
diffraction (XRD), Fourier transform infrared (FT-IR), scanning
electron microscope (SEM), thermogravimetry analysis (TG) and
N2 adsorption–desorption isotherms were then employed to
characterize the catalyst BAIL@MOR in detail. Moreover, the
effects of catalytic reaction parameters including temperature,
catalyst loading and reaction time on the ketal yield and
selectivity were explored to obtain the optimum conditions, and
the reusability of the catalyst BAIL@MOR was also studied.
Scheme 1 General route for the synthesis of catalyst 3 BAIL@MOR.
solvent ethanol was removed by rotatory evaporation. Thus the
product 1 N-(3-propyltriethoxysilane)imidazole was obtained as
a viscous liquid of light-yellow. In the second step, the synthe-
sized precursor 1 (27.2 g), 1,4-butane sultone (13.6 g), and
ethanol (100 mL) were mixed and stirred at 50 ꢀC for 8 h. Aer
that, sulfuric acid (9.8 g) solution in water was added slowly,
ꢀ
and the mixture was stirred at 60 C for 12 h to complete the
reaction. The resulting solution was thenꢀwashed with ether for
three times and dried in vacuum at 95 C to remove ethanol,
water, and unreacted components until the weight of the
residue remained constant. Therefore, the BAIL 2 [CPES-BSIM]-
[HSO4] was obtained as a viscous liquid of yellow and its yield
was near to 81%.
Preparation of BAIL@MOR
Experimental
Materials
MOR zeolite was rstly pretreated in the hydrochloric acid
solution (4 wt%) at 50 ꢀC for 1 h to dissolve Al-rich amorphous
3-Chloropropyltriethoxysilane (CPES, purity $98%), cyclo- materials on the surface of zeolite. At the end of hydrothermal
pentanone (purity $98%), 1,3-butylene glycol (purity $98%) treatment, the samples were washed repeatedly with deionized
and ion-exchange resin Amberlyst 15 were purchased from water and then dehydrated for 8 h at 80 ꢀC under vacuum to
Aladdin (Shanghai, China). Imidazole (purity $99%) and 1,4- remove physisorbed water that would be harmful to the
coupling reaction.25 For immobilization, 2.0 g of pretreated
butane sultone (purity $99%) were purchased from Shanghai
Bangcheng Chemical Company (Shanghai, China). Commer- MOR zeolite was added into the previously well-mixed solution
cially available mordenite zeolite powder (Si/Al ratio ¼ 18) was containing 1.0 g of BAIL 2 [CPES-BSIM][HSO4] and 100 mL of
ꢀ
purchased from Wako Pure Chemical (Code HS-642, Osaka, anhydrous toluene, and the mixture was reuxed at 110 C for
Japan). Other reagents such as cyclohexanone, glycol, and 1,2- 24 h under nitrogen. Aerwards, the sample was ltrated and
propylene glycol were of analytical grade and used without any extracted with dichloromethane by Soxhlet extraction for 24 h to
further purication.
remove excessive BAIL 2. The resultant solid was then dried at
80 ꢀC under vacuum for overnight and designated as catalyst 3
BAIL@MOR.
Preparation of BAILs
The BAIL 2 [CPES-BSIM][HSO4] was prepared by reference to the
procedure reported previously (Scheme 1).24 In a 250 mL well-
Catalyst characterization
dried ask, imidazole (6.8 g) and sodium ethoxide (6.8 g) were XRD patterns of samples were recorded on a Rigaku ULTIMA IV
˚
dissolved in ethanol (100 mL), and the mixture was being stirred diffractometer equipped with Cu Ka radiation (l ¼ 1.542 A). A
ꢀ
at 70 C for 8 h under nitrogen atmosphere. Aer that, CPES continuous scan mode was used to collect 2q from 5 to 45ꢀ, and
(24.08 g) was added slowly over a period of 0.5 h, and the scanning step size was 0.02ꢀ as counting time of 10 s. FT-IR
mixture was continuously reuxed for 12 h under nitrogen spectra in the range of 400–4000 cmꢁ1 were measured on a
atmosphere. Then, the byproduct NaCl was ltered off, and the Nicolet 6700 spectrophotometer with anhydrous KBr as
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standard. The particle size and morphology of samples were
determined by FE-SEM (HITACHI SU8020) with an acceleration
voltage of 5 kV. Nitrogen adsorption–desorption at ꢁ196 ꢀC was
measured on a BELSORP-mini II apparatus aer the samples
ꢀ
were degassed at 100 C for 15 h under vacuum. The specic
surface area was then calculated using the Brunauer–Emmett–
Teller (BET) method. The TG-DTG curves were recorded on a
Diamond TG/DTA thermal analyzer. Samples were heated froꢁm1
room temperature up to 800 ꢀC with a heating rate of 10 ꢀC min
under nitrogen airow.
Catalytic test
In a typical run, the ketalization reaction was performed in a
100 mL round bottom ask with a magnetic stirrer. Weighed
amounts of cyclohexanone, glycol, and catalyst (BAIL@MOR)
were mixed and typically allowed to proceed for 0.5–2 h with
vigorous stirring and heating at the designed temperature. Aer
the reaction, the heterogeneous catalyst was ltered off, and
then the product contained the expected ketal was detected by
gas chromatography. All the samples were analyzed using HP
6890 GC analyzer (Agilent) equipped with an FID detector. A
capillary column HP-1 (methyl polysiloxane, 30 m ꢂ 0.32 mm ꢂ
1 mm) was used to determine the composition of the samples
Fig. 1 Powder XRD patterns of MOR (a) and catalyst 3 (b).
analysis. Fig. 2 gives the FT-IR spectra of BAIL 2 and catalyst 3,
as well as MOR zeolite for comparison. It was indicated that the
FT-IR spectrum of MOR zeolite (a) had the characteristic Si–O
vibrations at around 460, 812, and 1047 cmꢁ1, respectively.10 In
the hydroxyl region, the sharp band at 1630 cmꢁ1 and the broad
band at 3440 cmꢁ1 can be attributed to a combination of the
stretching vibration of Si–OH groups and the H–O–H stretching
mode of adsorbed water.14 For BAIL 2 (c), the C–H stretching
with nitrogen as the carrier gas at a ow rate of about 3 mL minꢁ1
.
The temperatures of the column, the inlet, and the detector
ꢀ
were kept at 180, 200, and 250 C, respectively.
vibrations were clearly observed at 2871, 2987, and 3150 cmꢁ1
,
Denition of ketal yield and selectivity
respectively. The characteristic peaks were also found at 1448
and 1586 cmꢁ1, which can be attributed to the C]C stretching
vibration and the C]N stretching vibration of the imidazole
ring.27 The bands around 1039 and 1165 cmꢁ1 were associated
with the signals of C–S and S]O bonds, indicating the existence
of –SO3H group.28 Therefore, in comparison with MOR zeolite,
the catalyst 3 exhibited the same characteristic bands of MOR
zeolite network such as the Si–O–Si vibrations (812 and
1047 cmꢁ1), the stretching vibration of Si–OH groups, and the –OH
stretching vibration of adsorbed water (1630 and 3440 cmꢁ1).
The yield of ketal is dened as the ratio of the number of moles
of ketal production in the reaction to the total number of moles
of ketone initially added. The selectivity for ketal is dened as
the ratio of the number of moles of ketal to the number of moles
of ketal and other products which were detected by GC.
moles of ketal
Yield ¼
moles of ketone initially added
moles of ketal
Selectivity ¼
moles of ðketal þ other productsÞ
Results and discussion
Catalyst characterization
Fig. 1 displays the high-angle powder XRD patterns of MOR and
BAIL@MOR. Fig. 1a shows that the XRD pattern of MOR had the
typical peaks at diffraction angles of 6.51ꢀ, 9.77ꢀ, 13.45ꢀ, 22.20ꢀ,
25.63ꢀ, 26.25ꢀ and 27.67ꢀ, which was consistent well with those
reported by Lu et al.21 and Campbell et al.26 These characteristic
peaks were also present in the powder XRD patterns of catalysts
3 BAIL@MOR, suggesting that the immobilization of BAIL 2 on
the surface of MOR zeolite did not signicantly affect the skel-
eton of MOR zeolite (Fig. 1a and b).
The covalent binding of BAIL to the surface of MOR in
catalyst 3 BAIL@MOR was further conrmed by FT-IR spectrum Fig. 2 FT-IR spectra of MOR (a), catalyst 3 (b), and BAIL 2 (c).
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Moreover, it was found that the Si–OH stretching vibration of
catalyst 3 at 1630 cmꢁ1 was much weaker than that of MOR
zeolite, whereas the Si–O–Si vibration of catalyst 3 at 812 cmꢁ1
was stronger than that of MOR zeolite. This suggests that some
of Si–OH groups on the surface of MOR were connected with
BAIL obviously by the covalent binding of Si–O–Si groups. In
addition, the catalyst 3 also demonstrated newly developed C–H
stretching and/or N–H stretching vibration (2871, 2987, 3150
cmꢁ1), and imidazolium ring stretching (1448, 1586 cmꢁ1).
Thus, the above results indicate that the BAIL was successfully
graed onto the MOR zeolite.14
SEM was performed to characterize the morphology of
catalyst 3 BAIL@MOR and MOR zeolite as shown in Fig. 3. It
was seen that uniform MOR zeolite was in the size of 1–2 mm
(Fig. 3A). Aer the introduction of [CPES-BSIM][HSO4], the size
of BAIL@MOR had no obvious change (Fig. 3C), indicating that
the morphological homogeneity of these MOR particles was
maintained aer BAIL graing. However, the SEM images also
reveals MOR particles coalescence through formation of inter-
particle necks that are possibly due to the presence of the BAIL
covering the MOR surfaces (Fig. 3D). In addition, at high
magnications, it was observed that the surface of MOR was
rough, whereas the surface of BAIL@MOR was much plain
(Fig. 3B and D). This nding demonstrated that the surface of
MOR had been coated with BAIL [CPES-BSIM][HSO4] success-
fully, forming a compact and thin surface layer.
Fig. 4 Thermogravimetric (A) and differential thermogravimetric (B)
results of MOR (a), catalyst 3 (b), and BAIL 2 (c).
showed three distinct steps of weight losses in the combined
TG-DTG curves upon heating from room temperature to 700 ꢀC
under airow (Fig. 4b). The rst weight loss at 90 ꢀC was due to
the removal of surface-adsorbed water.29 The second weight loss
at 210 ꢀC was probably due to the loss of surface silanol groups
and structural water within MOR zeolite. The third weight loss
at 250–380 ꢀC was assigned to the successive decomposition of
the imidazolium-functionalized trialkoxysilane moiety and
alkyl sulfonic acid group.24 Thus, it was demonstrated that the
Furthermore, thermal analysis was performed to monitor the
decomposition proles of MOR, BAIL 2, and catalyst 3 (Fig. 4).
The TG curve of the bare MOR support presents a minor weight
loss in the range of 50–120 ꢀC, which is attributed to the release
of physisorbed water (Fig. 4a). As for BAIL 2, a signicant weight
loss, contributing nearly 80 wꢀt% of the sample, was seen in the
ꢀ
catalyst 3 exhibited good thermal stability onward 160 C and
the residual weight was about 75% around 700 ꢀC. On the basis
of these results, it can be concluded that most BAIL 2 [CPES-
BSIM][HSO4] have been well loaded on the MOR zeolite support.
This is also indirect evidence of the success of immobilization
of BAIL on MOR zeolite.
ꢀ
temperature range from 100 C to 700 C (Fig. 4c). In compar-
ison with MOR support and BAIL 2, the catalyst 3 BAIL@MOR
Fig. 5 shows the N2 adsorption–desorption isotherms of
MOR zeolite and catalyst 3 BAIL@MOR. It was clearly that all
the samples exhibit type-I curves at p/p0 ¼ 0.0–1.0, which is
characteristic of a microporous structure.21 From the BET
Fig. 3 The whole and magnified SEM images of MOR (A and B), and Fig. 5 N2 adsorption–desorption isotherms of MOR zeolite (a) and
catalyst 3 (C and D).
catalyst 3 (b).
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surface area analysis, the catalyst 3 was found to have relatively catalyst (entry 4). In addition, it was also showed that the
lower BET surface areas compared with MOR zeolite. For conversion of cyclohexanone in the presence of the resin
example, MOR zeolite showed the BET surface area of Amberlyst 15 and H2SO4 was 60.6% and 70.6% at 2 h,
339 m2 gꢁ1, whereas the BET surface area of catalyst 3 was only respectively (entries 5 and 6). This nding demonstrated that
71 m2 gꢁ1. The decreases in the BET surface areas of catalyst 3 the heterogeneous catalysis of catalyst 3 plays the equal
were attributed to the immobilization of BAIL onto the catalytic performance in comparison with the homogeneous
framework of MOR zeolite, resulting in the block of micropores catalysis of H2SO4, showing BAIL@MOR could be used as
and the decrease of surface areas. This nding further revealed efficient heterogeneous SILs catalysts in the ketalization
that the BAIL had been successfully graed onto the framework reaction.
of MOR zeolite. Similar results had also been reported
previously by Liu et al.30
Effects of reaction parameters
Since the catalyst 3 BAIL@MOR showed good catalytic activity,
the effects of reaction parameters such as temperature, reac-
Catalytic performance of BAIL@MOR
tion time and catalyst loading were examined in detail. First,
the ketalization reaction of cyclohexanone was performedꢀin
[BSmim][HSO4] and MOR zeolite support were employed as
catalysts for the ketalization reaction of cyclohexanone with
glycol to assess their catalytic activities, and then the results
were listed in Table 1. It was obvious that MOR zeolite cata-
lyzed the reaction to have conversion of 27.9% at 2 h, showing
that the support material MOR zeolite has relatively poor
catalytic activity (entry 1). In sharp contrast, with the successful
immobilization of BAIL 2 onto the MOR support, the catalyst 3
gives a drastic increase in the catalytic activity and the
conversion of cyclohexanone at 2 h was nearly 70%, as
comparable with the corresponding homogeneous catalysis of
[BSmim][HSO4] under the identical reaction conditions
(entries 2 and 3). It is mainly due to the cooperation of
Brønsted acid site from BAILs and MOR zeolite.20 Besides, the
BAILs was supported on the out surface of MOR zeolite which
was microporous structure. This nding illustrated that MOR
support plays a catalytic role on the ketalization reaction, and
the heterogeneous catalysis of catalyst 3 can remain high
catalytic performance, even though the nominal weight of the
immobilized BAIL over BAIL@MOR was signicantly less than
the pure BAIL.
ꢀ
ꢀ
the presence of catalyst 3 BAIL@MOR at 30 C, 40 C, 50 C,
and 60 ꢀC, with cyclohexanone to glycol molar ratio of 1 : 1,
and catalyst loading of 0.5 wt% (based on the mass of cyclo-
hexanone). Fig. 6 shows the effect of reaction temperature on
the conversion of cyclohexanone. It was indicated that the
conversion of cyclohexanone increased rapidly with
the increase in the reaction temperature. For example, the
conversion of cyclohexanone at 2 h increased obviously from
ꢀ
ꢀ
58% to 70% with the rise of temperature from 30 C to 50 C.
However, a slight increase in the conversion of cyclohexanone
at 2 h was observed while the temperature was increased from
ꢀ
ꢀ
50 C to 60 C. This result suggests that an optimized reaction
ꢀ
temperature should choose at 50 C to reach the considerable
catalytic activity.
The effect of different catalyst loadings on the conversion of
cyclohexanone was studied by varying the catalyst loading from
0.1 wt% to 1 wt% at a temperature of 50 ꢀC and with cyclo-
hexanone to glycol molar ratio of 1 : 1. The results as shown in
Fig. 7 indicated that, with an increase in the relative amount of
catalyst, the rate of ketalization reaction was enhanced, result-
ing in a higher reaction rate for the conversion of cyclohexa-
none. For example, the conversion of cyclohexanone increased
from 60% to 70% with the increase in the amount of catalyst 3
For comparison, the ketalization of cyclohexanone was also
studied without catalyst or in the presence of two conventional
catalysts. As it has been found, in the absence of a catalyst,
the cyclohexene conversion was very low, showing that the
ketalization reaction was very difficult to occur without
Table 1 Ketalization of cyclohexanone with glycol under various
reaction systemsa
The conversion of
cyclohexanoneb (%)
Entry
Catalyst
0.5 h
2 h
TOFc (hꢁ1
)
1
2
3
4
5
6
MOR
19.5
62.9
67.7
0.9
50.6
67.0
27.9
69.5
71.3
3.8
60.6
70.6
—
BAIL@MOR
[BSmim][HSO4]
Blank
Amberlyst 15
H2SO4
1835
230
—
—
71
a
Cyclohexanone (50 mmol), glycol (50 mmol), catalyst (0.5 wt%, based
b
on the mass of cyclohexanone), reaction temperature (50 ꢀC). The
conversion of cyclohexanone was achieved by GC analysis, and no
byproducts were found by GC. TOF dened as mol(ketalization) per
mol(SO3H) per h (full reaction time).
c
Fig. 6 Effect of temperature on the conversion of cyclohexanone with
time using catalyst 3.
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methyl group is benecial to the nucleophilic ability of 1,2-
propylene glycol and thus the yield of ketal. Future, it was also
found that the yields were too low in the ketalization of cyclo-
pentanone with the three diols (entries 4–6). The similar results
were also obtained by Qi et al.31 This fact was attributed to the
relative reactivity and stability of cyclohexanone with six-
membered ring in comparison to cyclopentanone with ve-
membered ring. Furthermore, we compared the catalytic
performance of catalyst 3 with the results of other heteroge-
neous catalysts which published in the literatures (entries 7–
10).32–35 It was found that a large excess of diol was oen taken to
improve the performance of those heterogeneous catalysts, and
a dehydrative agent for removing the water generated in the
ketalization reaction must be also required to achieve consid-
erable yield. By contrast, without the aid of dehydrative agent
and much more diol, the catalyst 3 also displays the comparable
catalytic performance in comparison with H2SO4 and those
heterogeneous catalysts under mild conditions, indicating that
BAIL@MOR can act as an efficient heterogeneous catalyst for
the ketalization reaction.
Fig. 7 Effect of catalyst loading on the conversion of cyclohexanone
with time using catalyst 3.
from 0.1 wt% to 0.5 wt%. However, only a fair change was
obtained in the conversion of cyclohexanone when the amount
of catalyst was increased 2 fold from 0.5 wt% to 1.0 wt%. Beyond
a certain catalyst loading, the conversion of cyclohexanone was
improved slightly with increasing of catalyst loading. This
implies that the further increase in the amount of catalyst is not
very necessary for the conversion of reactants. Considering the
reaction rate and the cost of catalyst, 0.5 wt% is taken as the
optimum catalyst loading and used in most of the ketalization
experiments.
In order to investigate the scope on catalyst 3 BAIL@MOR in
the synthesis of other ketals, the ketalization reactions of
ketones with different diols were also tested under the optimal
condition. The results were summarized in Table 2. It was
demonstrated that the catalyst 3 performed high catalytic
performances in the ketalization reaction of cyclohexanone
with glycol, 1,2-propylene glycol and 1,3-butylene glycol,
affording the corresponding ketals in excellent yields (entries 1–
3). Compared with the other two diols, 1,2-propylene glycol
possessing an electron-donating methyl group resulted in the
highest yield of corresponding ketal (80%), showing that the
Recycling of catalyst
The recycling capability is of importance for the evaluation of a
heterogeneous catalyst. Thus, a series of repetitive experiments
had been conducted to test the reusability of catalyst 3
BAIL@MOR and reproducibility of catalytic performance
ꢀ
(temperatures of 50 C, cyclohexanone to glycol molar ratio of
1 : 1, catalyst loading of 0.5 wt%, and reaction time of 0.5 h and
2 h). In each cycle, the catalyst 3 was separated from the reac-
tion mixture by ltration and then washed with dichloro-
methane, followed by drying before the next run. The
conversions of cyclohexanone from ve consecutive runs thus
were as shown in Fig. 8. The results demonstrated that catalyst 3
can be recycled for up to ve times with no appreciable decrease
in the conversion of cyclohexanone, which demonstrates that
the prepared catalyst 3 possesses excellent stability and reus-
ability. The slight decrease in conversions should be probably
because the slight loss of partial catalyst 3 along the continuous
separation process.
Table 2 Ketalization of different ketones with diols
Molar Catalyst
ratio dosage
Yield/ Sel./
Entry Catalyst
Ketones
Diols
Reaction conditions
50 ꢀC, 2 h
%
%
Ref.
1
2
3
4
5
6
7
BAIL@MOR
Cyclohexanone Glycol
1,2-Propylene glycol
1,3-Butylene glycol
Cyclopentanone Glycol
1 : 1
0.245 g
69.5
80.1
68.1
28.3
39.4
40.0
80.7
100 This
100 study
100
100
100
1,2-Propylene glycol
1,3-Butylene glycol
100
99.7 32
HY zeolite
Cyclohexanone Catechol
1 : 1
0.25 g
Reux temperature,
cyclohexane 10 mL, 4 h
8
Amorphous tin(IV)
phosphate
Bismuth subnitrate Cyclohexanone Glycol
HMCM-22 Cyclohexanone Glycol
Cyclohexanone Glycol
1 : 1.3 1/65 mole of Dean–Stark conditions, 3 h
91
—
33
34
ketone
9
10
1 : 1.5 0.25 g
1 : 1.2 0.2 g
82 ꢀC, cyclohexane 15 mL, 0.5 h 94.5
Dean–Stark conditions, 2 h 98.5
—
100 35
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Fig. 8 The recycle test of catalyst 3 in the ketalization reaction of
cyclohexanone with glycol.
Conclusions
In this study, a novel heterogeneous catalyst BAIL@MOR was
successfully prepared, characterized and applied in the ketali-
zation reaction. On the basis of characterization results, the
BAIL [CPES-BSIM][HSO4] was proved to be immobilized
successfully onto MOR zeolite. Moreover, the catalytic perfor-
mance tests demonstrated that BAIL@MOR played excellently
catalytic performances in the ketalization of cyclohexanone
with glycol, 1,2-propylene glycol and 1,3-butylene glycol, as
comparable with the homogeneous catalysis of the precursors
[BSmim][HSO4] and H2SO4. The conversion of cyclohexanone
was also found to improve effectively by increasing the reaction
temperature and catalyst loading in the presence of BAIL@MOR
as catalyst. In addition, the recycling tests showed that
BAIL@MOR could be reused for ve times without a signicant
loss of its catalytic activity. The heterogeneous catalyst
BAIL@MOR therefore can act as an efficient and promising
candidate for the ketalization reaction.
Acknowledgements
The authors are grateful for the nancial support of this study
from the National Natural Science Foundations of China (no.
21206063), and the Science & Technology Supporting Programs
and the International Technological Cooperation Programs of
Jiangxi Provincial Department of Science and Technology (no.
20123BBE50081 and 20132BDH80003).
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RSC Adv., 2014, 4, 12160–12167 | 12167