Knoevenagel condensation reaction on a new highly-efficient La2O2CO3-TiO2 mixed oxide catalyst: Composition-effects on C[dbnd]C bond formation

Article abstract of DOI:10.1016/j.chemphys.2020.110942

The highly efficient catalytic abilities of some mixed oxides are due to cooperative interactions between acid and base functional groups present in their active sites. New La₂O₂CO₃-TiO₂ mixed oxide catalysts wi

Full text of DOI:10.1016/j.chemphys.2020.110942

Chemical Physics 539 (2020) 110942
Contents lists available at ScienceDirect
Chemical Physics
journal homepage: www.elsevier.com/locate/chemphys
Knoevenagel condensation reaction on a new highly-efficient La O CO -
2
2
3
TiO mixed oxide catalyst: Composition-effects on C]C bond formation
2
a,⁎
a
a
b
a,⁎
Fei Wang , Kai Hu , Yanshuai Bi , Xuejiao Wei , Bing Xue
a
Advanced Catalysis and Green Manufacturing Collaborative Innovation Center, School of Petrochemical and Engineering, Changzhou University, Changzhou 213164, PR
China
b
School of Chemical Engineering and Materials, Changzhou Institute of Technology, Changzhou 213022, PR China
A R T I C L E I N F O
A B S T R A C T
Keywords:
The highly efficient catalytic abilities of some mixed oxides are due to cooperative interactions between acid and
base functional groups present in their active sites. New La O CO -TiO mixed oxide catalysts with different La/
2 2 3 2
La O CO -TiO
2
2
3
2
Mixed oxide
Ti molar ratios successfully synthesized through a facile solvothermal method were investigated for the
Knoevenagel condensation
Acid-base property
Synergetic effect
Knoevenagel condensation reaction of various carbonyl compounds derivatives with malononitrile. The analy-
tical determinations, including XRD, Raman, HRTEM, N
2
adsorption/desorption and TPD of CO
2
O
and NH
CO -TiO
) exhibited
3
2
,
witnessed the structural characteristics of the as-prepared La
2
O
2
CO
3
-TiO
2
mixed oxide catalysts. La
2
2
3
mixed oxide catalyst having molar ratio La/La + Ti = 0.09 composition (La
2
O
2
CO (0.09)-TiO
3
2
highest conversion of benzaldehyde for Knoevenagel reaction of benzaldehyde with malononitrile. More im-
portantly, this catalyst could be successfully applicable to the Knoevenagel condensation of various carbonyl
compounds derivatives with high yields above 85%. This acid-base bifunctional synergetic effect between
La
2
O
2
CO
3
and TiO
2
contributes to improve the catalytic property of the catalyst.
1
. Introduction
Knoevenagel condensation is one of the most fundamental and
a monodisperse rhodium/platinum nanoparticles (RhPt/TC@GO NPs)
by the help of thiocarbamide-functionalized graphene oxide (TC@GO),
which obtained high yield of Benzylidenemalononitrile in a short
period of time for Knoevenagel condensation. Nevertheless, those cat-
alysts still faced some practical problems, such as blockage and collapse
of the pores in MOF, loss of basic sites during the reaction, very com-
plicated preparation process and so on [24–26].
versatile reactions for the C]C bond formation and preparing α, β-
unsaturated compounds, such as fine chemical intermediates, ther-
apeutic and pharmacological products [1–3]. In normal conditions, this
reaction contains condensation of aldehydes/ketones with active me-
thylene hydrogen compounds under weak base catalysts [4–6]. Many
homogeneous catalysts such as ammonia, ammonium salts, ethylene-
diamine, primary and secondary amines or urea have been used for this
reaction and exhibited excellent activity [7–9]. However, industrial
utilization of those catalysts have been limited due to separation diffi-
culties and environmental effect unfriendly [10,11]. Therefore, more
and more solid base catalysts have attracted extensive attention be-
cause they are reusable, low-cost and least possibly contaminated by
the reaction medium [12–15], which include zeolites [16], amine-
functionalized materials [17], metal-organic frameworks (MOF) [18],
metal oxide [19], and so on [20,21]. Recently, Elhamifar et al. [22]
reported a new amine-containing ionic liquid-based ordered meso-
La
2
O
2
CO is a promising solid base oxide, which has been widely
3
used as the catalyst itself or the support for solid catalysts and effec-
tively catalyze many heterogeneous reaction. Shen et al. [27] demon-
strated a copper nanoparticles dispersed rod-shaped La
2
O
2
CO which
3
efficiently catalyzed transfer dehydrogenation of primary aliphatic al-
cohols with an aldehyde yield of up to 97%. Wan et al. [28] observed
that one of the rod-shaped La
2
O
2
CO samples exhibited the best cata-
3
lytic properties among the investigated samples in the oxidative cou-
pling of methane (OCM) at low temperatures (420–500 °C). In addition,
its specific activity was 20 times greater than that of any of the other
rod-shaped samples. Yu et al. [29] reported that the shape effect sig-
nificantly improves the performance of Ir/La
2
O
2
CO catalyst in the
3
porous organosilica (PMO-IL-NH
2
) nanocatalyst, which exhibited high
steam reforming of glycerol at high temperatures up to 650 °C toward a
yields, selectivities and excellent recycling stability for the Knoevenagel
reaction of aldehydes with ethyl cyanoacetate. Sen et al. [23] developed
sustainable hydrogen production. These results indicated that the en-
hanced activities were ascribed to surface basicity of La
2
O
2
CO .
3
⁎
Corresponding authors.
E-mail addresses: wangfei@cczu.edu.cn (F. Wang), xuebing@cczu.edu.cn (B. Xue).
https://doi.org/10.1016/j.chemphys.2020.110942
Received 30 April 2020; Received in revised form 15 July 2020; Accepted 30 July 2020
Available online 02 August 2020
0301-0104/ © 2020 Elsevier B.V. All rights reserved.

F. Wang, et al.
Chemical Physics 539 (2020) 110942
Recently, it has been reported that the addition of other metal oxide to
heated to 473 K in He flow (40 mL min−1) and held for 1 h. When the
La
2
O
2
CO
3
can lead to improvements in catalytic activity. Suiba et al.
temperature was cooled down to room temperature, NH
3
was in-
[
30] report a high biodiesel yield (> 95%) in less than 5 min under
troduced into the quartz tube reactor for 0.5 h. Subsequently, the
sample was purged in He flow for 2 h. Finally, the temperature was
mild reaction conditions (< 100 °C) on a ZnO/La
2
O
2
CO heterogeneous
3
−1
catalyst.
increased to 1073 K at a rate of 5 K min . The amount of NH
orbed was monitored by an on-line mass spectrometer.
3
des-
Therefore, the aim of this work is to develop new bi-functional acid-
base heterogeneous catalyst through synthesis of 2-benzylidenemalo-
nonitrile by the Knoevenagel condensation reaction. In this work, we
2.3. Performance tests
attempted to prepare the new La
2
O
2
CO
3
-TiO mixed oxide catalysts
2
with different La/Ti molar ratios via a facile solvothermal method. The
catalytic activities of these catalysts were tested for Knoevenagel con-
densation reaction of benzaldehyde with malononitrile. In order to
explore the substrate scope and generality of aldehydes, various sub-
stituted carbonyl compounds derivatives were examined using
In a 10 mL round-bottomed flask, carbonyl compounds (5 mmol),
malononitrile (5 mmol) and 5 mL of acetonitrile (ACN) was taken. Then
a amount of the La
2
O
2
CO
3
(x)-TiO mixed oxide catalyst was added to
2
above solution and the mixture was heated to 323 K. At the end of the
reaction, the reaction mixture was cooled to room temperature and the
catalyst was recovered by filtration method. Quantitative analysis of
various substituted carbonyl compounds derivatives was conducted
with an Agilent 6820 GC equipped with a FID. The conversion of car-
bonyl compounds and selectivity of products were quantified using n-
propanol as an internal standard. The conversion of benzaldehyde is
La
2
O
2
CO
3
(0.09)-TiO
2
mixed oxide as a catalyst under optimal condi-
CO -
tions. In addition, the possible reaction mechanism over the La
2
O
2
3
TiO mixed oxide catalysts was also investigated.
2
2
. Experimental
.1. Catalyst preparation
In this study, La CO
determined by the equation of Conv(benzaldehyde) = (C
0
− C
is the initial concentration of benzaldehyde and
is the real time concentration of benzaldehyde. The selectivity of 2-
i
)/
2
C
0
C
i
× 100%, where C
0
2
O
2
3
-TiO mixed oxide with various molar ratios
2
benzylidenemalononitrile is determined by the equation of Selec(2-
of La/Ti were prepared via a facile solvothermal method using La
benzylidenemalononitrile) = P
i
/(C
0
− C
i
) × 100%, where P is the real
i
(
NO
NO
3
3
)
)
3
·6H
3
·6H
2
O and Ti(OC
2
O and C OH were mixed under vigorously stirring to form
and CH COOH was
4
H
9
)
4
as precursors. An aqueous solution of La
time concentration of 2-benzylidenemalononitrile.
(
H
2 5
solution A. Solution B, consisted of Ti(OC
4
H
9
)
4
3
3
. Results and discussion
added dropwise into solution A. After stirred at room temperature for
1
h, the above mixed solution was transferred into an autoclave
The XRD patterns for La
2
O
2
CO
3
(x)-TiO mixed oxides after calci-
2
(
100 mL), heated to 433 K and maintained at that temperature for 12 h.
nation at 500 °C for 4 h with different La/Ti molar ratios were shown in
Fig. 1. The diffraction lines of the samples at 13°, 22.8°, 29.5°, 30.7°,
The precipitation product was washed, dried at 343 K for 24 h and then
calcined at 773 K for 4 h in air. The obtained samples were named as
3
1.3° and 44.4° appeared, which were consistent with (020), (110),
La
La
2
2
O
2
2
CO
3
3
(x)-TiO
2
, where × represented La/La + Ti molar ratio in
(
130), (−101), (101) and (200) crystal planes of monoclinic lan-
thanum oxide carbonate phase (m-La CO , JCPDS#48–1113)[31].
For La CO (0.09)-TiO sample, the main peaks between 20° and 65°
were found and no significant difference were observed compared with
O
CO
-TiO
2
mixed oxide. For comparison, pure TiO
2
catalysts were
catalysts were
2
O
2
3
also prepared by the same method. Pure La
2
O
2
CO
3
2
O
2
3
2
prepared by simple precipitation method.
La
These results suggested that TiO
lattice to form mixed oxide for maintaining the monoclinic La
2
O
2
CO
3
sample although intensities of peaks slightly decreased.
2.2. Catalyst characterization
2
was incorporated into the La
2
O
2
O
2
CO
2
CO
3
3
X-ray powder diffraction (XRD) patterns were recorded on a D/MAX
500/PC powder diffractometer (Rigaku) using a CuKα radiation
structure. When the La and Ti content were equal, characteristic peaks
2
of La
and 48.0° appeared, which can be attribute to (101), (004) and (200)
crystal planes of anatase titanium dioxide phase (α-TiO
JCPDS#21–1272) [32].These results indicated that La CO (0.5)-
2
O
2
CO decreased continually and some small peaks at 25.3°, 37.8°
3
source operated at 40 kV and 200 mA from 5° to 70° (in 2 θ) with the
−
1
scanning rate of 20° min
.
2
,
Transmission electron microscope (TEM, JEOL JEM-2100) was ap-
plied for the detailed microstructure and composition information.
Raman spectra were recorded on a micro-Raman system (Renishaw
ViaReflex) equipped with an Ar-Kr laser, by exciting at 514.5 nm.
The textural properties, i.e. specific surface area (SBET), total pore
volume (Vpore) and pore diameter (Dpore) were measured on an
Autosorb-iQ2-MP (Quantachrome Instruments) in standard analysis
mode. The specific surface area of the samples was calculated using the
BET method, whereas the pore diameter was evaluated by applying the
Barrett-Joyner-Halenda (BJH) algorithm to the isotherm desorption
branch.
2
O
2
3
Temperature-programmed desorption of CO
2
(CO -TPD) experi-
2
ments were tested on Micromeritics ASAP2020 with a TCD. First, The
as-prepared La
2
O
2
CO
3
-TiO mixed oxide sample (100 mg) was heated
−1
2
to 473 K in He flow (40 mL min ) and held for 1 h. When the tem-
perature was cooled down to room temperature, the sample was ex-
−
1
posed to a mixture of 30 vol% CO /He (30 mL min ) for 0.5 h at
2
−1
4
23 K. After being purged with He (30 mL min ) for 2 h, the sample
−1
was heated to 1073 K at a rate of 5 K min . The amount of CO
desorbed was monitored by an on-line mass spectrometer.
2
Temperature-programmed desorption of ammonia (NH -TPD) ex-
3
Fig. 1. XRD patterns of the La
2
O
2
CO
3
(x)-TiO mixed oxide catalysts with dif-
2
periments were tested on Micromeritics ASAP2020 with a TCD. First,
The as-prepared La CO -TiO mixed oxide sample (100 mg) was
ferent La/Ti molar ratios.
2
O
2
3
2
2

F. Wang, et al.
Chemical Physics 539 (2020) 110942
Fig. 2. TEM and HRTEM images of pure La
2
O
2
CO
3
(a, b) and TiO
2
(c, d) samples.
TiO
TiO
TiO
2
2
2
sample contain two phases: monoclinic La
2
O
2
CO and anatase
3
phase of La
2
O
2
CO the monoclinic phase of La
3
2
O
2
CO
3
, respectively. An
−1
2−
. For La
increased obviously while peaks of La
CO -TiO
2
O
2
CO
3
(0.91)-TiO
2
sample, characteristic peaks of anatase
intense band at 1086 cm
can be assigned to the vibration of CO
3
2
2
O
2
CO
mixed oxide.
CO
3
largely vanished,
group of lanthanum oxycarbonate[34]. When molar ratio of La and Ti
which indicated formation of a La
2
O
2
3
was 10:1, all diffraction peaks were attributed to the vibration of La-O
2
−
For comparing morphology structue of pure La
2
O
2
3
and TiO
2
and CO
TiO
three new peaks at 399, 520, and 643 cm
attributed to the anatase phase of TiO and no obviously change was
found for characteristic peaks of La CO . On increase of Ti content,
no characteristic bands of La CO can be observed and peaks in-
tensity of the anatase phase of TiO increased significantly. There was
clear evidence for the formation of La CO (0.09)-TiO mixed oxide,
which were consistent with XRD patterns.
Nitrogen adsorption/desorption studies were carried out on the
CO (x)-TiO mixed oxide catalysts with different La/Ti molar
ratios in order to investigate the effect of composition on surface area
and porosity (Fig. and Table 1). These results revealed all
La CO (x)-TiO mixed oxide catalysts to be porous and The
3
group, which confirmed the formation of La
2
2
O
2
CO
sample, only
appeared, which can be
3
(0.91)-
samples were firstly presented in Fig. 2. Fig. 2a presented irregular
2
mixed oxide successfully. For La
2
O
2
CO
3
(0.5)-TiO
−
1
particle morphology with size of 30–40 nm, and good crystallinity of
pure La
2
O
2
CO
3
sample. As shown in a high-resolution TEM (HRTEM) in
2
2
Fig. 2b, one set of lattice fringes with a spacing of 0.672 nm was at-
tributed to the (020) plane of La CO . Fig. 2c and 2d showed that
pure TiO samples exhibit regular morphological structures with
homogeneous particles. Particles size of TiO samples was about
CO sample. The in-
2
O
3
2
O
2
3
2
O
2
3
2
2
2
2
O
2
3
2
1
0–15 nm, which was much smaller than La
2
O
2
3
terlayer distance was identified to be 0.354 nm. This value agrees with
the spacing of the (101) planes of a anatase titanium dioxide structure,
which was also observed in the XRD results.
La
2
O
2
3
2
Fig. 3 showed the morphology structure of the La
2
O
2
CO
3
(x)-TiO
2
5
mixed oxides catalysts with different La/Ti molar ratios. As displayed in
Fig. 3a, sphere-like nanoparticles morphology was observed for
2
O
2
3
2
2
N isotherms of all as-prepared catalysts were type IV, according to the
La
2
O
2
CO
3
(0.91)-TiO
2
sample. From HRTEM image (Fig. 3b), the spa-
IUPAC classification characteristics of mesoporous materials (Fig. 5)
cing of (110) plane of La
which was attributed to the insertion of Ti
La CO . For La CO (0.5)-TiO sample, no obvious change was
found for particles size and morphology compared to La CO (0.91)-
TiO sample (Fig. 3c). With Ti content equal to La content, lattice
spacing of 0.347 nm was ascribed to the the (101) plane of TiO na-
species was gradually introduced to
lattice (Fig. 3d). However, morphology of La CO (0.09)-TiO
sample was different from La CO (0.91)-TiO and La CO (0.5)-
2
O
2
CO
3
decreased from 0.39 nm to 0.363 nm,
[35] and the obtained values were summarized in Table 1. It was found
4+
ions into lattice of
that the BET surface areas of all La
2
O
2
CO
3
2
(x)-TiO
CO
content increasing, while their pore volume are lower than that of pure
2
mixed oxide cata-
2
O
2
3
2
O
2
3
2
lysts were higher than that of pure La
2
O
3
and increased with Ti
2
O
2
3
2
La
2
O
2
CO and decreased with Ti content increasing. This might be due
4+
3
2
to the substitution of Ti ion which has a smaller cationic radius in the
3
+
3+
noparticles, indicating that La
TiO
La lattice location. The change of pore diameter had the same se-
2
2
O
2
3
2
quence as the BET surface areas. Among them, La
2
O
2
CO
3
(0.09)-TiO
2
2
−1
2
O
2
3
2
2
O
2
3
mixed oxide exhibited the largest specific surface area (118.5 m g ),
3
TiO
2
samples. Self-assembly of particles with interparticle voids with
average pore diameter (6.2 nm) and the smallest pore volume (0.28 cm
−
1
size of 15 nm were found (Fig. 3e). The particles were highly crystalline
and displayed an interplanar spacing of 0.365 nm, corresponding to the
g
).
Basicity and acidity of the La
with different La/Ti molar ratios were measured by TPD of CO
NH , respectively. These profiles were revealed in Fig. 6. Fig. 6a
showed CO -TPD profile of La CO (0.91)-TiO , La CO (0.5)-TiO
and La CO (0.09)-TiO
2
O
2
CO
3
(x)-TiO
2
mixed oxide catalysts
(
101) lattice planes of TiO
2
nanoparticles (Fig. 3f). These results in-
2
and
3
+
dicated that La species were well dispersed and incorporated into the
TiO structure, which formed the La CO -TiO mixed oxide.
Fig. 4 presented Raman spectra for the 200–1200 cm
CO (x)-TiO mixed oxide samples calcined at 500 °C for 4 h with
different La/Ti molar ratios. As previous literature, peaks at 399, 520,
3
2
2
O
2
3
2
2
2
O
2
3
2
2
O
2
3
2
−
1
region for
2
O
2
3
2
catalysts. The amount and strength of basic
La
2
O
2
3
2
sites of the catalyst can be seen in two different temperature regions.
The temperature peaks at 50–150 °C and 150–450 °C were attributed to
weak and medium-strong basic sites [36], respectively. The total basic
−
1
and 643 cm
[33] and at 226, 294, 315, 340, 356, 437(sh) and
50 cm [34] confirmed the anatase phase of TiO and the monoclinic
−1
4
2
concentration were summarized in Table 2. Both La
2
O
2
CO
3
(0.91)-TiO
2
3

F. Wang, et al.
Chemical Physics 539 (2020) 110942
Fig. 3. TEM and HRTEM images of the La
2
O
2
CO
3
(x)-TiO
2
mixed oxide catalysts with different La/Ti molar ratios: (a, b) La
2
O
2
CO
3
(0.91)-TiO
2
; (c, d) La
2
O
2
3
CO (0.5)-
TiO
2
; (e, f) La
2
O
2
CO
3
(0.09)-TiO samples.
2
Fig. 4. Raman spectra for the La
2
O
2
CO
3
(x)-TiO
2
mixed oxide catalysts with
Fig. 5. Nitrogen adsorption isotherm for the La O CO (x)-TiO mixed oxide
2
2
3
2
different La/Ti molar ratios.
catalysts with different La/Ti molar ratios.
and La
basic sites (about 0.38 mmol CO
La CO (0.09)-TiO catalyst (0.18 mmol CO
of all mixed oxides were revealed by NH -TPD analysis (Fig. 6b and
Table 2). The La CO (0.09)-TiO catalyst possessed obviously the
maximum amount of acidic sites (0.58 mmol NH /g), which was about
2
O
2
CO
3
(0.5)-TiO
2
showed a similar to total concentration of
/g), which higher than
/g). The acid properties
10 times larger than La O CO (0.91)-TiO (0.07 mmol NH /g) and
2
2
3
2
3
2
La O CO (0.5)-TiO catalysts (0.05 mmol NH /g). Comparative results
2
2
3
2
3
2
O
2
3
2
2
of the NH -TPD and CO -TPD data, all La O CO (x)-TiO mixed oxide
3
2
2
2
3
2
3
catalysts possess both acidic and basic sites. Interestingly, the
2
O
2
3
2
La O CO (0.91)-TiO catalyst had the most acid-base sites and highest
2
2
3
2
3
acid-base concentrations than other mixed oxides.
4

F. Wang, et al.
Chemical Physics 539 (2020) 110942
Table 1
Table 2
BET surface areas, total pore volume and average pore diameter of
Surface acidity-basicity for La
ferent La/Ti molar ratios.
2
O
2
CO
3
(x)-TiO
2
mixed oxide catalysts with dif-
La
2
O
2
CO
3
(x)-TiO
2
mixed oxide catalysts with different La/Ti molar ratios.
[
a]
2
−1
[b]
[c]
(cm g−1
3
[a]
[b]
Samples
S
BET
(m
g
)
D
pore
(nm)
V
pore
)
Samples
Total basicity (mmol
Total acidity (mmol NH
3
/
CO /g)
2
g)
La
La
La
La
2
2
2
2
O
O
O
O
2
2
2
2
CO
CO
CO
CO
3
27.5
32.5
65.8
21.4
18.1
7.9
0.21
0.23
0.23
0.28
0.22
3
(0.91)-TiO
3
(0.5)-TiO
3
(0.09)-TiO
2
2
La
2
La
2
La
2
O
2
O
2
O
2
CO
CO
CO
3
3
3
(0.91)-TiO
(0.5)-TiO
(0.09)-TiO
2
0.18
0.39
0.38
0.07
2
2
0.050.050.04
0.58
118.5
56.6
6.2
2
TiO
2
10.2
[
a]
Density of total basic sites determined by CO
2
-TPD based on unit mass of
[
[
[
a]
b]
c]
S
BET: BET surface area.
the sample (mmol CO /g)
2
[b]
D
pore: pore diameter calculated according to the BJH method.
Density of total acid sites determined by NH -TPD based on unit mass of
3
V
pore: total pore volume.
the sample (mmol NH /g)
3
The catalytic activity of the La
2
O
2
CO
3
(x)-TiO
2
mixed oxide catalysts
Table 3
with different La/Ti molar ratios was tested in Knoevenagel con-
densation reactions. In the beginning, benzaldehyde and malononitrile
were used as model reactants for the Knoevenagel condensation.
Initially the reaction was carried out in acetonitrile solvent. Influence of
Influence of composition effect of La O CO (x)-TiO mixed oxide on the
2
2
3
2
[
a]
Knoevenagel reaction of benzaldehyde with malononitrile.
composition effect of La
2
O
2
CO
3
(x)-TiO
2
mixed oxide on the
Knoevenagel reaction was carried out (Table 3). Almost no reaction was
observed in absence of catalysts. A maximum 2-benzylidenemalononi-
.
trile yield of 90.1% was obtained for La
2
O
2
CO
3
(0.09)-TiO
CO
mixed oxide catalysts increased with the increase of Ti content of the
2
catalyst at
[
b]
[c]
[d]
Entry
Catalyts
Blank
Conversion
%)
Selectivity
(%)
Yield
(%)
5
0 °C for 4 h. We also found that catalytic activity of La
2
O
2
3
(x)-TiO
2
(
1
2
3
4
5
6
3
> 99
> 99
> 99
> 99
> 99
> 99
2.9
mixed oxides. For pure La
2
O
2
CO
3
and TiO as catalysts, 2-benzylide-
2
La
La
La
2
2
2
O
2
O
2
O
2
CO
CO
CO
3
3
3
13
12.9
4.0
nemalononitrile yield was only 12.9% and 57.3%, respectively. These
results suggested that the La/Ti mole ratio played an important role on
the catalytic activity.
(0.91)-TiO
2
2
4.1
68.8
90.2
57.4
(0.5)-TiO
2
68.1
90.1
57.3
La O CO (0.09)-TiO
2
2
3
In order to explore the substrate scope and generality of aldehydes,
various substituted carbonyl compounds derivatives were examined
TiO
2
[
a]
Reaction condition: benzaldehyde (5 mmol), malononitrile (5 mmol),
using La
2
O
2
CO
3
(0.09)-TiO mixed oxide as a catalyst under optimal
2
acetonitrile (5 mL), temperature (50 °C), time (4 h), catalyst (50 mg).
conditions, and the corresponding results are shown in Table 4. For the
Knoevenagel condensation between malononitrile with aromatic alde-
hydes, aliphatic aldehydes, furfural, orcyclohexanone (entries 1–7), the
[
[c]
[d]
b]
GC conversion based on benzaldehyde.
Selectivity based on GC results.
GC yield.
La
2
O
2
CO
3
(0.09)-TiO mixed oxide catalyst exhibited far better catalytic
2
performance. Among them, 4-hydroxybenzaldehyde, methoxy- and
ethoxy- substituted hydroxybenzaldehyde afforded 100% yield. Based
occurs smoothly. Subsequent elimination of water results in formation
of the products. It could be found that enough amount acidic and basic
on the above results, La
2
O
2
CO
3
(0.09)-TiO mixed oxide catalyst can
2
sites of La
2
O
2
CO
3
(0.09)-TiO mixed oxide were the driving force for
2
highly efficiently catalyze reactions with different kinds of carbonyl
high conversion of benzaldehyde.
compounds.
According to above results,
a tentative mechanism of the
Knoevenagel condensation catalyzed by La
2
O
2
CO
3
(0.09)-TiO mixed
2
4
. Conclusions
oxide catalyst on the basis of reported works was proposed and shown
in Scheme 1. Firstly, through abstracting a proton the methylene carbon
In conclusion, highly uniform and nanosized La
2
O
2
2
CO
3
-TiO
2
mixed
of malononitrile was activated by basic sites of La
2
O
2
CO
3
on
oxide catalysts with different La/Ti molar ratios (La
O
2
CO (x)-TiO )
3
2
La
2
O
2
CO
3
(0.09)-TiO mixed oxide and then carbanion was formed. In
2
were successfully prepared using a facile solvothermal method. Given
the meantime, acidic sites of TiO
2
activated carbonyl oxygen of the
4+
the smaller Ti
La CO -TiO
oxide. Among different La/Ti molar ratios, the La
incorporated into the La
mixed oxide presented smaller crystallite size than pure
CO (0.09)-TiO
2
O
2
CO
3
structure, the
benzaldehyde and generated a carbocation. Finally, when the formed
carbocation was attacked by the carbanion, a dehydration reaction
2
O
2
3
2
2
O
2
3
2
Fig. 6. (a) CO
2
-TPD, (b) NH
3
-TPD patterns for the La
2
O
2
CO
3
(x)-TiO mixed oxide catalysts with different La/Ti molar ratios.
2
5

F. Wang, et al.
Chemical Physics 539 (2020) 110942
Table 4
Knoevenagel condensation reactions with various substituted carbonyl compounds catalyzed by La
2
O
2
CO
3
(0.09)-TiO
2
mixed oxide catalysts.[a]
Conversion[ (%)
b]
Selectivity[c] (%)
Yield[d] (%)
94.9
Entry
Carbonyl compounds
1
O
96.2
100
H C
H
3
2
3
87.2
93.1
100
98
87.2
89.7
H
O
O
4
5
O
70.3
100
100
100
70.3
100
H
O
H
OH
6
7
100
100
100
100
100
100
O
OH
O
CHO
O
OH
[
[
[
[
a]
b]
c]
d]
Reaction condition: substituted carbonyl compounds (5 mmol), malononitrile (5 mmol), acetonitrile (5 mL), temperature (50 °C), time (4 h), catalyst (50 mg).
GC conversion based on substituted carbonyl compounds.
Selectivity based on GC results.
GC yield.
mixed oxide catalyst exhibited best catalytic performance for
Knoevenagel reaction of benzaldehyde with malononitrile than other
mixed oxide and pure catalysts. The highest activity with the conver-
sion 90.2% and selectivity above 99% for 2-benzylidenemalononitrile
can be observed using La
2
O
2
CO
3
(0.09)-TiO mixed oxide as catalyst,
2
which present the maximum amount of acidic and basic sites. In ad-
dition, using other different carbonyl compounds substrates, most
condensations proceeded smoothly to give the corresponding products
with excellent yields, which proved the generality of the
La
2
O
2
CO
3
(0.09)-TiO mixed oxide catalyst. Furthermore, a correlation
2
between catalytic activity and acid-base property of the mixed oxide
was observed. Both higher acidity and basicity of La
2
O
2
CO
3
(0.09)-TiO
2
mixed oxide catalyst were remarkably favorable for Knoevenagel re-
action, which also play an important role on activating benzaldehyde
and malononitrile, respectively, and thus enhance the formation of 2-
benzylidenemalononitrile.
CRediT authorship contribution statement
Scheme 1. a tentative mechanism of the Knoevenagel condensation catalyzed
by La CO (0.09)-TiO mixed oxide catalyst.
2
O
2
3
2
Fei Wang: Conceptualization, Data curation, Writing - review &
editing, Project administration, Supervision. Kai Hu: Visualization,
6

F. Wang, et al.
Chemical Physics 539 (2020) 110942
Investigation. Yanshuai Bi: Visualization, Investigation, Writing - ori-
ginal draft. Xuejiao Wei: Writing - review & editing. Bing Xue: Writing
[15] B. Sakthivel, A. Dhakshinamoorthy, Chitosan as a reusable solid base catalyst for
Knoevenagel condensation reaction, J. Colloid Interface Sci. 485 (2017) 75–80.
[
[
[
16] J.N. Appaturi, M. Selvaraj, S.B.A. Hamid, Synthesis of 3-(2-furylmethylene)-2, 4-
pentanedione using DL-Alanine functionalized MCM-41 catalyst via Knoevenagel
condensation reaction, Microporous Mesoporous Mater. 260 (2018) 260–269.
17] Y.M. Zhang, J. Zhang, M.M. Tian, G. Chu, C.S. Quan, Fabrication of amino-func-
-
review & editing, Funding acquisition.
Declaration of Competing Interest
tionalized Fe
3 4 3 2
O @Cu (BTC) for heterogeneous Knoevenagel condensation, Chin. J.
Catal. 37 (2016) 420–427.
18] A. Dhakshinamoorthy, N. Heidenreich, D. Lenzen, N. Stock, Knoevenagel con-
densation reaction catalysed by Al-MOFs with CAU-1 and CAU-10-type structures,
CrystEngComm 19 (2017) 4187–4193.
The authors declare that they have no known competing financial
interests or personal relationships that could have appeared to influ-
ence the work reported in this paper.
[19] J.B.M. de Resende Filho, G.P. Pires, J.M.G. de Oliveira Ferreira, E.E. Teotonio,
J.A. Vale, Knoevenagel condensation of aldehydes and ketones with malononitrile
3 4 2
catalyzed by amine compounds-tethered Fe O @SiO nanoparticles, Catal. Lett.
Acknowledgements
1
47 (2017) 167–180.
[
[
[
[
20] N. Anbu, R. Maheswari, V. Elamathi, P. Varalakshmi, A. Dhakshinamoorthy,
Chitosan as a biodegradable heterogeneous catalyst for Knoevenagel condensation
between benzaldehydes and cyanoacetamide, Catal. Commun. 138 (2020) 105954.
21] N. Anbu, S. Hariharan, A. Dhakshinamoorthy, Knoevenagel-Doebner condensation
promoted by chitosan as a reusable solid base catalyst, Mol. Catal. 484 (2020)
110744.
This work was financially supported by the National Natural Science
Foundation of China (No. 21878027, 21802008, 21503023) and
Advanced Catalysis and Green Manufacturing Collaborative Innovation
Center, Changzhou University.
22] D. Elhamifar, S. Kazempoor, B. Karimi, Amine-functionalized ionic liquid-based
mesoporous organosilica as a highly efficient nanocatalyst for the Knoevenagel
condensation, Catal. Sci. Technol. 6 (2016) 4318–4326.
References
23] B. Şen, E.H. Akdere, A. Şavk, E. Gültekin, Ö. Paralı, H. Göksu, F. Şen, A novel
thiocarbamide functionalized graphene oxide supported bimetallic monodisperse
Rh-Pt nanoparticles (RhPt/TC@GONPs) for Knoevenagel condensation of aryl al-
dehydes together with malononitrile, Appl. Catal. B 225 (2018) 148–153.
24] M. Almáši, V. Zeleňák, M. Opanasenko, J. Čejka, A novel nickel metal-organic
framework with fluorite-like structure: gas adsorption properties and catalytic ac-
tivity in Knoevenagel condensation, Dalton Trans. 43 (2014) 3730–3738.
25] M. Srasra, S. Delsarte, E.M. Gaigneaux, Effects of the nitridation of Y and USY
zeolites on their catalytic activity for the base catalyzed knoevenagel condensation,
Top. Catal. 52 (2009) 1541–1548.
[
1] X.Y. Li, B.N. Lin, H.B. Li, Q. Yu, Y. Ge, X. Jin, X.H. Liu, Y.H. Zhou, J.P. Xiao, Carbon
doped hexagonal BN as a highly efficient metal-free base catalyst for Knoevenagel
condensation reaction, Appl. Catal. B 239 (2018) 254–259.
[
[
[
[
2] M.R. Shakil, A.G. Meguerdichian, H. Tasnim, A. Shirazi-Amin, M.S. Seraji, S.L. Suib,
Syntheses of ZnO with different morphologies: catalytic activity toward coumarin
synthesis via the knoevenagel condensation reaction, Inorg. Chem. 58 (2019)
5
703–5714.
[
[
[
[
3] M.L. Gao, M.H. Qi, L. Liu, Z.B. Han, An exceptionally stable core–shell MOF/COF
bifunctional catalyst for a highly efficient cascade deacetalization–Knoevenagel
condensation reaction, Chem. Commun. 55 (2019) 6377–6380.
26] H.F. Wang, Y.S. Wang, A.Z. Jia, C.Y. Wang, L.M. Wu, Y.F. Yang, Y.J. Wang, A novel
bifunctional Pd-ZIF-8/rGO catalyst with spatially separated active sites for the
tandem Knoevenagel condensation-reduction reaction, Catal. Sci. Technol. 7 (2017)
4] R. Otomo, R. Osuga, J.N. Kondo, Y. Kamiya, T. Yokoi, Cs-Beta with an Al-rich
composition as a highly active base catalyst for Knoevenagel condensation, Appl.
Catal. A 575 (2019) 20–24.
5
572–5584.
[
27] F. Wang, R.J. Shi, Z.Q. Liu, P.J. Shang, X.Y. Pang, S. Shen, Z.C. Feng, C. Li,
W.J. Shen, Highly efficient dehydrogenation of primary aliphatic alcohols catalyzed
5] G. Varga, Á. Kukovecz, Z. Kónya, P. Sipos, I. Pálinkó, Green and selective toluene
oxidation–Knoevenagel-condensation domino reaction over Ce-and Bi-based CeBi
mixed oxide mixtures, J. Catal. 381 (2020) 308–315.
by Cu nanoparticles dispersed on rod-shaped La
2
O
2
CO
3
, ACS Catal. 3 (2013)
3
CO catalysts
8
90–894.
6] H.F. Wang, Y.S. Wang, Y. Guo, X.K. Ren, L.M. Wu, L. Liu, Z.T. Shi, Y.J. Wang, Pd
nanoparticles confined within triazine-based carbon nitride NTs: An efficient cat-
alyst for Knoevenagel condensation-reduction cascade reactions, Catal. Today 330
[
[
28] Y.H. Hou, W.C. Han, W.S. Xia, H.L. Wan, Structure sensitivity of La
2
O
2
in the oxidative coupling of methane, ACS Catal. 5 (2015) 1663–1674.
29] X.Y. Huang, C.X. Dang, H. Yu, H.J. Wang, F. Peng, Morphology effect of Ir/
La2O2CO3 nanorods with selectively exposed 110 facets in catalytic steam re-
forming of glycerol, ACS Catal. 5 (2015) 1155–1163.
(
2019) 124–134.
[
[
[
7] H. Xu, L.Y. Pan, X.M. Fang, B.Y. Liu, W.K. Zhang, M.H. Lu, Y.Q. Xu, T. Ding,
H.B. Chang, Knoevenagel condensation catalyzed by novel Nmm-based ionic liquids
in water, Tetrahedron Lett. 58 (2017) 2360–2365.
[
[
30] L. Jin, Y.S. Zhang, J.P. Dombrowski, C.H. Chen, A. Pravatas, L.P. Xu, C. Perkins,
2 2 3
S.L. Suib, ZnO/La O CO layered composite: A new heterogeneous catalyst for the
8] L.S. Huang, Y.H. Lai, C. Yang, D.Z. Xu, Iron-catalyzed one-pot oxidation/
Knoevenagel condensation reaction using air as an oxidant, Appl. Organomet.
Chem. 33 (2019) e4910.
efficient ultra-fast microwave biofuel production, Appl. Catal. B 103 (2011)
00–205.
31] C. Wang, Y.Q. Yang, Z.C. Zhang, F.H. Liao, J. Ju, Z.J. Shi, J.H. Lin, Y.T. Li,
F.Q. Huang, Synthesis of nanostructured La /La CO : Eu phosphors from arc-
2
9] H.M. He, Q.Q. Zhu, F.X. Sun, G.S. Zhu, Two 3D metal–organic frameworks based on
CoII and ZnII clusters for Knoevenagel condensation reaction and highly selective
luminescence sensing, Cryst. Growth Des. 18 (2018) 5573–5581.
2
O
3
2
O
2
3
discharged graphene-contained composites, Mater. Lett. 134 (2014) 176–179.
[
[
32] Y. Wang, H. Yang, W. Zou, Preparation of amorphous sphere-like TiO
2
with ex-
[
10] Z.C. Miao, Y. Luan, C. Qi, D. Ramella, The synthesis of a bifunctional copper metal
organic framework and its application in the aerobic oxidation/Knoevenagel con-
densation sequential reaction, Dalton Trans. 45 (2016) 13917–13924.
11] A.M. Caminade, R. Laurent, Homogeneous catalysis with phosphorus dendrimer
complexes, Coord. Chem. Rev. 389 (2019) 59–72.
cellent photocatalytic performance, Mater. Lett. 254 (2019) 54–57.
33] P. Rayo, J. Ancheyta, J. Ramírez, A. Gutiérrez-Alejandre, Hydrotreating of diluted
Maya crude with NiMo/Al
2 3 2
O -TiO catalysts: effect of diluent composition, Catal.
[
[
Today 98 (2004) 171–179.
[
[
3 2 2 3
34] F. Wang, N. Ta, Y. Li, W.J. Shen, La(OH) and La O CO nanorod catalysts for
12] K. Tarade, S. Shinde, S. Sakate, C. Rode, Pyridine immobilised on magnetic silica as
an efficient solid base catalyst for Knoevenagel condensation of furfural with acetyl
acetone, Catal. Commun. 124 (2019) 81–85.
Claisen-Schmidt condensation, Chin. J. Catal. 35 (2014) 437–443.
35] L. Zhao, J.G. Yu, B. Cheng, Preparation and characterization of SiO
2
/TiO
2
com-
posite microspheres with microporous SiO
State Chem. 178 (2005) 1818–1824.
core/mesoporous TiO shell, J. Solid
2 2
[
[
13] W.P. Kong, F.J. Liu, Y. Liu, Design of nitrogen-doped graphitized 2D hierarchical
porous carbons as efficient solid base catalysts for transesterification to biodiesel,
Green Chem. (2020), https://doi.org/10.1039/c9gc03960k.
[
36] K. Chen, X.P. Duan, H.H. Fang, X.L. Liang, Y.Z. Yuan, Selective hydrogenation of
CO
2 2 2 3
to methanol catalyzed by Cu supported on rod-like La O CO , Catal. Sci.
14] Y.Y. Li, T.Y. He, R.R. Dai, Y.L. Huang, X.P. Zhou, T.F. Chen, D. Li, Bifunctional
Gyroidal MOFs: highly efficient lewis base and lewis acid catalysts, Chem.-An Asian
J. 14 (2019) 3682–3687.
Technol. 8 (2018) 1062–1069.
7