A facile method for synthesis of amine-functionalized mesoporous zirconia and its catalytic evaluation in Knoevenagel condensation

Article abstract of DOI:10.1016/j.apcata.2010.04.008

Amine-functionalized mesoporous zirconia was prepared by a co-condensation method using silane (aminopropyltrimethoxysilane, APTES) and zirconium butoxide. The materials were characterized by X-ray diffraction, BET surface area analysis, ¹³C magic angle spinning-nuclear magnetic resonance (NMR), Fourier-transfer infrared spectroscopy (FTIR), transmittance electron micrography (TEM), and CHN analysis. FTIR and NMR results revealed the successful grafting of organic amines onto the surface of zirconia. The catalytic activities were investigated for liquid phase Knoevenagel condensation of various aromatic aldehydes with diethyl malonate. The catalysts showed excellent yield of products at room temperature in solvent-free condition.

Full text of DOI:10.1016/j.apcata.2010.04.008

Applied Catalysis A: General 381 (2010) 226–232
Contents lists available at ScienceDirect
Applied Catalysis A: General
journal homepage: www.elsevier.com/locate/apcata
A facile method for synthesis of amine-functionalized mesoporous zirconia and
its catalytic evaluation in Knoevenagel condensation
K.M. Parida∗, Sujata Mallick, P.C. Sahoo, S.K. Rana
Colloids and Materials Chemistry Department, Institute of Minerals & Materials Technology, Bhubaneswar 751013, Orissa, India
a r t i c l e i n f o
a b s t r a c t
Article history:
Amine-functionalized mesoporous zirconia was prepared by a co-condensation method using silane
(aminopropyltrimethoxysilane, APTES) and zirconium butoxide. The materials were characterized by X-
ray diffraction, BET surface area analysis, 13C magic angle spinning-nuclear magnetic resonance (NMR),
Fourier-transfer infrared spectroscopy (FTIR), transmittance electron micrography (TEM), and CHN anal-
ysis. FTIR and NMR results revealed the successful grafting of organic amines onto the surface of zirconia.
The catalytic activities were investigated for liquid phase Knoevenagel condensation of various aromatic
aldehydes with diethyl malonate. The catalysts showed excellent yield of products at room temperature
in solvent-free condition.
Received 4 January 2010
Received in revised form 2 April 2010
Accepted 7 April 2010
Available online 14 April 2010
Keywords:
Mesoporous zirconia
Amine-functionalized
Knoevenagel condensation
© 2010 Elsevier B.V. All rights reserved.
1. Introduction
rials with high loadings and homogeneous surface coverages of
the specific functionality. This one-step method involves the co-
The past decade has seen significant advances in the synthesis
of new periodical mesoporous materials using surfactant micelle-
templated method [1]. Many research efforts have focused on the
design and preparation of organic functionalized hybrid materials
[2]. The success of such investigations will prompt the utilization
of these materials in catalysis [3,4], adsorptions [5–10], enzyme
immobilizations [11,12], sensor design [13] and drug delivery
[14]. Mesoporous materials are interesting supports for organic
functional groups due to their high surface areas, uniform and con-
trollable pore sizes, and the periodic orders of their pore packing.
Various literature reports describe methods for functionalizing
the interior pore surfaces of mesoporous solids such as MCM-
41, SBA-15, and zirconia [15–18]. Two approaches, namely direct
synthesis (co-condensation reaction) and post-synthesis (graft-
ing) have been widely investigated for incorporation of functional
groups into mesoporous materials. In the post-synthesis grafting
process, the organochlorosilanes or organoalkoxysilanes are cova-
lently attached to the surfaces of the mesoporous materials utilizing
the surface hydroxyl groups of the supported material [10,19–22].
However, this procedure normally yields low loadings and the
distribution of the anchored functionalities cannot be adequately
controlled. In the direct synthesis of mesoporous materials, organic
silica is an attractive alternative that produces functionalized mate-
condensation of siloxane and organosiloxane precursors in the
presence of the chosen templating agent [23–26].
Several aminopropyl-functionalized mesostructures have been
prepared through direct assembly as well as through grafting
reactions of pre-assembled frameworks using aminopropy-
ltrimethoxysilane as the functionalizing agent for some base-
catalyzed reactions [27,28]. Up to now, most of the work was
on the modification of the small mesopores of MCM-type silica,
on HMS-type silica, or SBA-15 mesoporous material. However,
Scholz et al. reported methacrylate-functionalized silane on sur-
faces of zirconia. Zhou et al. reported vinyl group containing
ligand functionalized zirconia [29]. Tarafdar and Pramanik reported
amine-functionalized on zirconia-silica mixed oxide [30]. How-
ever, there are few reports on amine-functionalized zirconia
[18]. Luo et al. reported amine-functionalized zirconia obtained
by post-synthesis method [18]. However preparation of amine-
functionalized zirconia using a direct method has never been
reported before. Herein, we report the surface modification of
mesoporous zirconia using aminopropyl triethoxy silane (APTES)
by a co-condensation method. The catalyst is found robust enough
to achieve high catalytic activity towards Knoevenagel condensa-
tion reactions.
2. Experimental
2.1. Synthesis of mesoporous zirconia
∗
Corresponding author at: Colloids and Materials Chemistry Department, Insti-
tute of Minerals & Materials Technology, Acharya Vihar, IMMT (CSIR), Bhubaneswar
751013, Orissa, India. Tel.: +91 674 2581635x425; fax: +91 674 2581637.
E-mail address: paridakulamani@yahoo.com (K.M. Parida).
Mesoporous zirconium (m-ZrO2) was synthesized by a sol–gel
route using zirconium butoxide as the zirconia source and
0926-860X/$ – see front matter © 2010 Elsevier B.V. All rights reserved.
doi:10.1016/j.apcata.2010.04.008

K.M. Parida et al. / Applied Catalysis A: General 381 (2010) 226–232
227
Scheme 1. Schematic presentation of synthesis of amine-functionalized zirconia.
Scheme 2. Schematic presentation of Knoevenagel condensation reaction.
cetyltrimethylammonium bromide (CTMABr) at a pH of 11.5, which
was maintained by ammonium hydroxide solution. Acetyl acetone
(acac) and ethanol controlled the rate of hydrolysis of zirconium
butoxide in water. In a mixture of water (4 mol) and NH3 (0.03 mol),
CTMABr (0.025 mol) was dissolved and stirred for 1 h. Then a mix-
ture of zirconium butoxide (0.1 mol), acetyl acetone (0.05 mol) and
ethanol (0.5 mol) was added to the template solution slowly and
this mixture was stirred for 3 h. The mixture was then refluxed
under stirring for 48 h at 90 ◦C. The resulting solid was filtered,
washed with acetone and dried for 10 h at 100 ◦C. To remove the
surfactant species, finally the samples were heated in air at a ramp
rate of 1 ◦C min−1 to 400 ◦C for 5 h.
ious wt% of amine modified m-ZrO2. Hereinafter, the samples are
named: xm-ZrO2 (co) (where x = wt% of amine which varies from
4.2 to 14.8) (Scheme 1).
2.3. Physico-chemical characterization
The BET surface area and pore size distribution were deter-
mined by multipoint N2 adsorption–desorption method at liquid
2.2. Synthesis of amine-functionalized mesoporous zirconia
The mixture containing cetyltrimethyl ammonium bromide,
2 M of NaOH (aq) and H2O was heated at 80 ◦C for 30 min at a pH
of 12. To this clear solution, zirconium butoxide and APTES were
added sequentially and rapidly. Following the addition, a white
precipitation was observed after 3 min of stirring. The reaction
temperature was maintained at 80 ◦C for 2 h. The products were iso-
lated by a hot filtration, washed with a sufficient amount of water
followed by methanol and dried under vacuum. For acid extrac-
tion, the as-obtained materials (1 g) were treated with a mixture of
ethanol (100 ml) and concentrated HCl (1 ml, 38% in weight) at 80 ◦C
for 6 h. The resulting (surfactant removed) solid products were fil-
tered and washed with ethanol, and then dried at 60 ◦C. By varying
the amount of amine from 0.586 to 2.1 ml, one could obtain var-
Table 1
Surface properties of amine modified m-ZrO2 samples.
Catalyst
Surface area (m2 g−1
)
Pore volume (cm3/g)
Pore diameter
(Å)
m-ZrO2
4.2 m-ZrO2
10.2 m-ZrO2 125
12.8 m-ZrO2 107
14.6 m-ZrO2
156
150
0.25
0.22
0.20
0.19
0.19
32
30
29
27
21
Fig. 1. N2 adsorption–desorption isotherms of m-ZrO2 (a) and 12.8% amine-
functionalized m-ZrO2 (b).
97

228
K.M. Parida et al. / Applied Catalysis A: General 381 (2010) 226–232
Fig. 4. FTIR spectra of m-ZrO2 (a) and 12.8% amine-functionalized m-ZrO2 (b).
tron microscopic figures of functionalized zirconia samples were
recorded using a Hitachi S3400N. CHN analysis was carried out in
a CHNS (O) analyzer (model: FLASH EA 1112 series). 13C MAS NMR
spectra were recorded on an AV300 NMR spectrometer. TG–DTA
was carried out in static air using a Shimadzu DT-40 thermal ana-
lyzer in the temperature range 30–1000 ◦C at a heating rate of
10 ◦C min−1
.
2.4. Catalytic reaction
The Knoevenagel condensation reaction of benzaldehyde with
diethyl malonate to form cinnamic acid was carried out in a glass
batch reactor fitted with a condenser. About 10 mmol of benzalde-
hyde (1.01 ml), 10 mmol of malonic ester (1.51 ml) and 0.025 g
catalyst taken in the reactor were stirred at room temperature in
a silicon oil bath. After 24 h of reaction, 50 ml of methanol was
added in order to soluble all the organic compounds (again stirred
for 10 min) (Scheme 2). The catalyst was recovered by centrifuga-
tion for reuse and the reaction mixture was analyzed off-line on a
Shimadzu gas chromatograph (GC-2010).
Fig. 2. BJH pore size distribution curves of m-ZrO2 (a) and 12.8% amine-
functionalized m-ZrO2 (b).
N2 temperature (−196 ◦C) by a Sorptomatic 1990 (ThermoQuest,
Italy). Prior to analyses, all the samples were degassed at 200 ◦C and
10−4 Torr pressure for 2 h to evacuate the physisorbed moisture.
The low-angle X-ray diffractograms were recorded on a Philips PW
1710 powder diffractometer using Ni filtered CuK␣ in the 2Â range
of 0–10 ◦C. The FTIR spectra were recorded using JASCO FTIR-5300
in KBr matrix in the range of 4000–400 cm−1. The scanning elec-
3. Results and discussion
3.1. Characterization
The results of nitrogen adsorption–desorption analyses are
shown in Table 1. The pure mesoporous zirconia dried at 400 ◦C
Fig. 5. 13C MAS NMR of 12. 8% amine-functionalized m-ZrO2.
Fig. 3. XRD patterns of m-ZrO2 (a) and 12.8% amine-functionalized m-ZrO2 (b).

K.M. Parida et al. / Applied Catalysis A: General 381 (2010) 226–232
229
Table 2
CHN elemental analyses and C/N ratio observed.
Catalyst
Anime content (wt%)a
Anime content (wt%)b
Ratio of amine contents (catalyst/gel)
C (wt%)
H (wt%)
N (wt%)
C/N ratio
4.2 m-ZrO2
10.2 m-ZrO2
12.8 m-ZrO2
14.6 m-ZrO2
4.2
10.2
12.8
14.6
2.9
8.4
11.4
11.8
0.69
0.82
0.89
0.80
3.66
3.94
4.54
5.41
1.36
1.49
1.62
1.25
1.31
1.38
1.45
1.15
2.79
2.86
3.13
4.71
a
Amine content in the gel.
Amine content in the catalyst found from TGA analysis.
b
showed a surface area of 156 m2 g−1. But the surface area, pore
volume and pore diameter of the amine-functionalized materi-
als decrease compared to those of the parent zirconia due to the
anchoring of amine groups.
N2 adsorption–desorption isotherms of the parent zirconia and
12.8% amine-functionalized zirconia samples are shown in Fig. 1a
and b. According the IUPAC classification, the N2 isotherms are of
type IV with a typical hysteresis loop of a mesoporous material.
The relative pressure (P/P0) of the inflection points is related to a
pore diameter in the mesopores range and the sharpness of the step
indicates the uniformity of pore size distribution.
Fig. 2 shows the BJH pore size distribution of zirconia and
12.8% amine-functionalized zirconia. From the figure, one can see
that there is a slight decrease in pore diameter of the amine-
functionalized sample in comparison to that of parent zirconia and
both the samples possess good mesoporous structural ordering and
a narrow pore size distribution.
Small angle X-ray diffraction patterns of the mesoporous zirco-
nia and 12.8% amine modified zirconia sample are shown in Fig. 3.
The low-angle XRD patterns of zirconia samples demonstrated the
mesostructure because there was only one broad peak at around
1◦ which translates to a spacing of 6.94 nm, calculated from the
Bragg Equation, 2d sin  = nꢀ. The intense and narrow XRD peak
of zirconia sample suggested a relatively organized and oriented
mesostructure [31]. The XRD pattern of amine-functionalized m-
ZrO2 is similar to that of m-ZrO2.
The FTIR spectra of mesoporous zirconia and 12.8% amine-
functionalized zirconia are presented in Fig. 4a and b. The FTIR
spectrum of zirconia shows a broad band in the region of 3410 cm−1
due to asymmetric stretching of OH group and two bands at 1621
and 1386 cm−1 which are due to bending vibrations of – (H–O–H) –
and – (O–H–O) – bonds. The band at 503 cm−1 resulted from the
existence of both tetragonal and monoclinic zirconia. The spec-
tra at 730 cm−1 are attributed to the presence of the Zr–O bond
(Fig. 4a). The presences of N–H bending vibration at 690 cm−1
and of NH2 symmetric bending vibration at 1532 cm−1 of amine-
functionalized ZrO2 nanoparticles, absent in neat zirconia, indicate
the successful grafting of organic amine onto the surface. Two new
absorption bands, namely, 800–1200 and 2800–3000 cm−1, are
observed on the spectrum of amine-functionalized ZrO2 nanopar-
ticles, suggesting that APTES has been successfully attached to the
ZrO2 nanoparticles.
Fig. 6. TEM figures of 12.8% amine-functionalized zirconia.
carbon atom bonded to silicon. The signal at 25.4 ppm corresponds
to methylene group carbon and the peak around at 45 ppm can be
attributed to methylene group carbon atoms attached to the anime
group.
Table 2 illustrates the percentage of C, H and N content which
was calculated from the CHN analysis. The C:H:N ratio does not
remain constant in all the cases, as it depends on several factors
such as the degree of functionalization on zirconia surface and the
hydrolysis of ethoxy group of APTES. The N content increases with
increase in amine content up to 12.8% and thereafter it decreases on
further increase of APTES content. This may be due to the introduc-
tion ofalarge amountofAPTESin the gel. This results in competition
between the APTES units to attach on the zirconia surface. Probably
partial hydrolysis of ethoxy group takes place for maximum attach-
ment of APTES. Upon washing, a part of the amine moiety may be
The13CMASNMRspectra of12.8% aminemodified zirconiasam-
ple are shown in Fig. 5. The sharp peak at 11.4 ppm is ascribed to the
Table 3
Conversion and selectivity of various catalysts towards Knoevenagel condensation reaction.
Catalyst
Conversion %
Selectivity (%)
Cinammic acid
Other
m-ZrO2
4.2 m-ZrO2
10.2 m-ZrO2
12.8 m-ZrO2
14.6 m-ZrO2
m-ZrO2 (with surfactant)
5
67
75
89
84
54
51
77
91
98
99
56
49
23
7
2
1
44

230
K.M. Parida et al. / Applied Catalysis A: General 381 (2010) 226–232
Table 4a
Knoevengel condensation of various aldehydes with diethyl malonate under solvent-free condition.
Reactant I (aldehyde) Product (major)
Conversion (%)
Selectivity (%)
Major
Others
89
98
98
2
95
80
2
85
15
82
93
97
85
86
94
99
90
14
6
1
10
98
83
99
90
1
10

K.M. Parida et al. / Applied Catalysis A: General 381 (2010) 226–232
231
Table 4a (Continued)
Reactant I (aldehyde)
Product (major)
Conversion (%)
Selectivity (%)
Major
Others
83
88
12
87
90
10
leached out due to lack of strong binding. Theoretically, the C/N
ratio for complete hydrolysis of ethoxy groups is 3. The C/N ratio
increases with increase in amine content of the sample. It is 4.7 for
samples containing more than 14.6% amine which may be due to
the presence of some unhydrolyzed ethoxy groups in the sample
[32]. The ratio of amine in each catalyst to the corresponding ratio
in the gel is incorporated in Table 2.
connected and is open to the surface, which is advantageous for
catalysis applications. Additionally, the pore size is very uniform
and the average pore diameters are 3–5 nm, which in line with the
N2-adsorption analysis results.
3.2. Catalytic activity towards Knoevenagel condensation
The extent of amine functionalization on the surface of zirconia
samples is calculated from TGA and the results are presented in
Table 2. The amine content is found to be 2.9%, 8.4%, 11.4% and 11.8%
for the samples with x values of 4.2, 10.2, 12.8 and 14.6, respectively.
The TEM image (Fig. 6) also proved that the zirconia possessed
a worm-like framework, which was very similar to that of the MSU
silica [33]. As can be seen from the figure, the pore system is well
Liquid phase Knoevenagel condensation of benzaldehyde and
diethyl malonate was carried out over zirconia and amine-
functionalized zirconia. The yields of cinnamic acid over various
catalysts are presented in Table 3.
In the case of unpromoted zirconia, the conversion was only 5%,
whereas the amine-functionalized zirconia sample shows signifi-
cant conversion, which clearly signifies the involvement of amine
Table 4b
Effect of various active methylene groups towards Knoevengel condensation.
Reactant II (activated methylene group)
Product (major)
Conversion (%)
Selectivity (%)
Major
Others
89
98
99
2
95
1
80
92
89
95
11
5

232
K.M. Parida et al. / Applied Catalysis A: General 381 (2010) 226–232
Table 5
Knoevenagel condensation over 12.8% amine-functionalized zirconia and comparison of the data with other reported methods.
Catalyst used
Conversion (%)
Temperature (◦C)
Reference
12.8% amine-functionalized zirconia
Amine-functionalized SBA-1
Amine-functionalized MCM-41
Functionalized ␥-Fe2O3
89
98
81
50
RT
105
RT
[This method]
[34]
[35]
[36]
50
group in the reaction. With increase in amine content the selectiv-
ity of cinammic acid increases up to 12.8%, then it decreases with
further increase in amine content.
d. The reusability test exhibits the good recycling capacity of the
functionalized material.
The Knoevenagel condensation reaction mechanisms on amine-
functionalized zirconia catalysts are described by the reaction,
where the catalyst activity is mainly due to the structural basicity
of the amine group. The reaction is initiated when a benzaldehyde
molecule reacts with a surface amine to form an amine compound.
The addition of diethyl malonate and the subsequent molecu-
lar rearrangement produces the final reaction product and water
molecules. In the reaction, the grafted organic amine acts as a Bron-
sted base.
Several organic substituents on aldehydes including 3-phenyl,
prop-2-enal were subjected to the Knoevenagel condensation using
12.8% amine-functionalized zirconia as catalyst and the results are
summarized in Table 4a. The presence of electron withdrawing
substituents (nitro group, −CN and halo group) on the aromatic
ring substantially increases the conversion while in case of elec-
tron donating group (–CH3, –OCH3, –NH2, etc.) the conversion
decreased. In the cases of electron withdrawing groups the possibil-
ity of attack of the carbanion (generated from the active methylene
group) at the carbonyl carbon is enhanced compared to that of
electron donating groups.
Acknowledgments
The authors are thankful to Prof. B.K. Mishra, Director, IMMT,
Bhubaneswar for his keen interest, encouragement and kind per-
mission to publish this work. One of the authors, Mrs. Sujata Mallick
is obliged to CSIR for a senior research fellowship.
References
[1] M.E. Davis, Nature 417 (2002) 813–821.
[2] A.P. Wight, M.E. Davis, Chem. Rev. 102 (2002) 3589–3614.
[3] I.C. Chisem, J. Rafelt, J. Chisem, J.H. Clark, D. Macquarrie, M.T. Shieh, R. Jachuck,
C. Ramshaw, K. Scott, Chem. Commun. (1998) 1949.
[4] S. Xiang, Y. Zhang, Q. Xin, C. Li, Angew. Chem., Int. Ed. 41 (2002) 821.
[5] K.Y. Ho, G. McKay, K.L. Yeung, Langmuir 19 (2002) 3019–3024.
[6] T. Yamamoto, T. Tanaka, T. Funabiki, S. Yoshida, J. Phys. Chem. B 102 (1998)
5830–8539.
[7] X. Feng, G.E. Fryxell, L.Q. Wang, A.Y. Kim, J. Liu, K.M. Kemner, Science 276 (1997)
923–926.
[8] L. Mercier, T.J. Pinnavaia, Environ. Sci. Technol. 32 (1998) 2749–2754.
[9] R.I. Nooney, M. Kalyanaraman, G. Kennedy, E.J. Maginn, Langmuir 17 (2001)
528–533.
[10] J.F. Diaz, K.J. Balkus Jr., F. Bedioui, V. Kurshev, L. Kevan, Chem. Mater. 9 (1997)
61–67.
Several active methylene compounds were subjected to Kno-
evenagel condensation using 12.8% amine-functionalized zirconia
as catalyst; the results are summarized in Table 4b. Those sub-
stituents having more electron withdrawing nature stabilize the
carbanion (due to resonance) compared to those having electron
donating nature. So malononitrile shows the highest conversion
among all the substrates. Table 5 presents a comparative feature
between the performances of 12.8% amine-functionalized zirco-
nia with other reported catalysts for Knoevenagel condensation
reaction.
[11] H.H.P. Yiu, N.P. Botting, P.A. Wright, Phys. Chem. Chem. Phys.
2983–2985.
[12] C. Lei, Y. Shin, J. Liu, E.J. Ackerman, J. Am. Chem. Soc. 124 (2002) 11242–
11243.
[13] V.S.Y. Lin, C.Y. Lai, J. Huang, S.A. Song, S. Xu, J. Am. Chem. Soc. 123 (2001)
11510–11511.
[14] C.Y. Lai, B.G. Trewyn, D.M. Jeftinija, K. Jeftinija, S. Xu, S. Jeftinija, V.S.Y. Lin, J. Am.
Chem. Soc. 125 (2003) 4451–4459.
[15] S.R. Hall, C.E. Fowler, B. Lebeau, S. Mann, Chem. Commun. 201 (1999).
[16] L. Mercier, T.J. Pinnavaia, Chem. Mater. 12 (2000) 188–196.
[17] J. Brown, R. Richer, L. Mercier, Micropor. Mesopor. Mater. 37 (2000) 41–48.
[18] K. Luo, S. Zhou, L. Wu, G. Gu, Langmuir 24 (2008) 11497–11505.
[19] S. Dai, M.C. Burleigh, Y. Shin, C.C. Morrow, C.E. Barnes, Z. Xue, Angew. Chem.
Int. Ed. 38 (1999) 1235–1239.
3 (2001)
[20] G.E. Fryxell, J. Liu, T.A. Hauser, Z. Nie, K.F. Ferris, S. Mattigod, M. Gong, R.T.
Hallen, Chem. Mater. 11 (1999) 2148–2154.
3.3. Reusability of the catalyst
[21] A. Walcarius, N. Luthi, J.L. Blin, B.-L. Su, L. Lamberts, Electrochim. Acta 44 (1999)
4601–4610.
Reusability of the catalyst was investigated by carrying
out repeated runs on the same batch of the used 12.8%
amine-functionalized zirconia as catalyst towards Knoevenagel
condensation of benzaldehyde and diethyl malonate. The catalyst
was separated by centrifugation after the reaction, washed several
times with distilled water, dried and used in the reaction with a
freshreactionmixture. Theyielddecreasedby3%inthe regenerated
sample after three cycles.
[22] V. Antochshuuk, M. Jaroniec, Chem. Mater. 12 (2000) 2496.
[23] M.H. Lin, A. Stein, Chem. Mater. 11 (1999) 3285–3295.
[24] M.H. Lim, C.F. Blanford, A. Stein, Chem. Mater. 10 (1998) 467–470.
[25] C.M. Bambrough, R.C.T. Slade, R.T. Williams, J. Mater. Chem. 8 (1998) 569–
575.
[26] C.E. Fowler, S.L. Burkett, S. Mann, Chem. Commun. (1997) 1769–1770.
[27] K.A. Utting, D.J. Macquarrie, New J. Chem. 24 (2000) 591–596.
[28] D. Brunel, F. Fajula, J.B. Nagy, B. Deroide, M.J. Verhoef, L. Veum, J.A. Peters, H.
Van Bekkum, Appl. Catal. A: Gen. 213 (2001) 73–82.
[29] S. Zhou, G. Garnweitner, M. Niederberger, M. Antonietti, Langmuir 23 (2007)
9178–9187.
[30] A. Tarafdar, P. Pramanik, Micropor. Mesopor. Mater. 91 (2006) 221–224.
[31] Y.-Q. Yao, Y.-F. Ying, M.-F. Luo, Y.-J. Wang, J.-M. Ma, Mater. Lett. 61 (2007)
192–195.
[32] S.K. Sharma, H.A. Patel, R.V. Jasra, J. Mol. Catal. A: Chem. 280 (2008) 61–67.
[33] S.A. Bagshaw, E. Prouzet, T.J. Pinnavaia, Science 269 (1995) 1242–1244.
[34] M.D. Gracia, M.J. Jurado, R. Luque, J.M. Campelo, D. Luna, J.M. Marinas, A.A.
Romero, Micropor. Mesopor. Mater. 118 (2009) 87–92.
[35] Y. Kubota, Y. Nishizaki, H. Ikeya, M. Saeki, T. Hida, S. Kawazu, M. Yoshida, H.
Fujii, Y. Sugi, Micropor. Mesopor. Mater. 70 (2004) 135–149.
[36] Y. Zhang, C. Xia, Appl. Catal. A: Gen. 366 (2009) 141–147.
4. Conclusions
a. The amine-functionalized zirconia exhibits excellent catalytic
activity for Knoevenagel condensation of aldehydes with diethyl
malonate under solvent-free conditions.
b. FTIR and NMR results revealed the successful grafting of organic
amines onto the surface of zirconia.
c. Among all the catalyst, the 12.8 wt% amine-functionalized zirco-
nia showed the highest yield (89%) of cinnamic acid.