Amorphous metal-aluminophosphate catalysts for aldol condensation of n-heptanal and benzaldehyde to jasminaldehyde

Article abstract of DOI:10.1016/S1872-2067(14)60206-0

Amorphous aluminophosphate (AlP) and metal-aluminophosphates (MAlPs, where M = 2.5 mol% Cu, Zn, Cr, Fe, Ce, or Zr) were prepared by coprecipitation method. Their surface properties and catalytic activity for the synthesis of jasminaldehyde through the aldol condensation of n-heptanal and benzaldehyde were investigated. The nitrogen adsorption-desorption isotherms showed that the microporosity exhibited by the aluminophosphate was changed to a mesoporous and macroporous structure which depended on the metal incorporated, with a concomitant change in the surface area. Temperature-programmed desorption of NH₃ and CO₂ revealed that the materials possessed both acidic and basic sites. The acidic strength of the material was either increased or decreased depending on the nature of the metal. The basicity was increased compared to AlP. All the materials were X-ray amorphous and powder X-ray diffraction studies indicated the absence of metal oxide phases. The Fourier transform infrared analysis confirmed the presence of phosphate groups and also the absence of any M-O moieties in the materials. The selected organic reaction occurred only in the presence of the AlP and MAlPs. The selectivity for the jasminaldehyde product was up to 75% with a yield of 65%. The best conversion of n-heptanal with a high selectivity to jasminaldehyde was obtained with FeAlP as the catalyst, and this material was characterized to have less weak acid sites and more basic sites.

Full text of DOI:10.1016/S1872-2067(14)60206-0

Chinese Journal of Catalysis 36 (2015) 209–215
a v a i l a b l e a t w w w . s c i e n c e d i r e c t . c o m
j o u r n a l h o m e p a g e : w w w . e l s e v i e r . c o m / l o c a t e / c h n j c
Article
Amorphous metal‐aluminophosphate catalysts for aldol
condensation of n‐heptanal and benzaldehyde to jasminaldehyde
A. Hamza, N. Nagaraju*
Catalysis Research Laboratory, St. Joseph’s College P.G. and Research Centre, Bangalore 560027, India
A R T I C L E I N F O
A B S T R A C T
Article history:
Amorphous aluminophosphate (AlP) and metal‐aluminophosphates (MAlPs, where M = 2.5 mol%
Cu, Zn, Cr, Fe, Ce, or Zr) were prepared by coprecipitation method. Their surface properties and
catalytic activity for the synthesis of jasminaldehyde through the aldol condensation of n‐heptanal
and benzaldehyde were investigated. The nitrogen adsorption‐desorption isotherms showed that
the microporosity exhibited by the aluminophosphate was changed to a mesoporous and
macroporous structure which depended on the metal incorporated, with a concomitant change in
the surface area. Temperature‐programmed desorption of NH3 and CO2 revealed that the materials
possessed both acidic and basic sites. The acidic strength of the material was either increased or
decreased depending on the nature of the metal. The basicity was increased compared to AlP. All the
materials were X‐ray amorphous and powder X‐ray diffraction studies indicated the absence of
metal oxide phases. The Fourier transform infrared analysis confirmed the presence of phosphate
groups and also the absence of any M‐O moieties in the materials. The selected organic reaction
occurred only in the presence of the AlP and MAlPs. The selectivity for the jasminaldehyde product
was up to 75% with a yield of 65%. The best conversion of n‐heptanal with a high selectivity to
jasminaldehyde was obtained with FeAlP as the catalyst, and this material was characterized to
have less weak acid sites and more basic sites.
Received 17 June 2014
Accepted 1 August 2014
Published 20 February 2015
Keywords:
Amorphous aluminophosphate
Metal‐aluminoposphate
Surface property
Acid‐base bi‐functional catalyst
Aldol condensation
Jasminaldehyde
© 2015, Dalian Institute of Chemical Physics, Chinese Academy of Sciences.
Published by Elsevier B.V. All rights reserved.
1. Introduction
to design unique bifunctional catalysts. In recent years, many
reports have been published on the catalytic application of
Amorphous aluminophosphate (AlP) and metal‐alumino‐
phosphates (MAlPs) have gained significant importance in ca‐
talysis owing to their flexible textural properties, surface acidi‐
ty, and thermal stability [1–3]. The structural and acidic prop‐
erties of amorphous AlP can be fine‐tuned by controlling the
preparation conditions and also by adding selected transition
metals during the synthesis. The addition of a transition metal
during synthesis can lead to the formation of Lewis and
Brönsted acid sites along with basic sites [4]. These acidic and
basic sites along with redox properties suggest the possibility
amorphous AlP and MAlPs in a wide range of organic trans‐
formations including dehydrogenation [5], cracking [6], trans‐
esterification [7], and alkylation [8], and as supports for other
catalytic systems such as oxides [9].
Jasminaldehyde (α‐pentylcinnamaldehyde) is a well‐known
flavor and fragrance and also an important pharmaceutical
intermediate. It is synthesized by the aldol reaction of
n‐heptanal and benzaldehyde catalyzed by sodium or potassi‐
um hydroxide in stoichiometric amounts [10]. The reaction is
catalyzed by both acids and bases (Scheme 1). The use of a
* Corresponding author. Tel: +91‐9886765750; Fax: +91‐8022245831; E‐mail: nagarajun@yahoo.com
DOI: 10.1016/S1872‐2067(14)60206‐0 | http://www.sciencedirect.com/science/journal/18722067 | Chin. J. Catal., Vol. 36, No. 2, February 2015

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A. Hamza et al. / Chinese Journal of Catalysis 36 (2015) 209–215
O
O
O
MAlP
O
2-n-pentyl-2-n-nonenal
Benzaldehyde
n-Heptanal
Jasminaldehyde
Scheme 1. Condensation reaction of n‐heptanal and benzaldehyde to form jasminaldehyde.
caustic liquid as the catalyst is not eco‐friendly due to envi‐
ronmental pollution and also has many other drawbacks such
as separation difficulties, corrosion of reactor lining and diffi‐
cult reagent handling. These drawbacks and difficulties can be
overcome by the use of fine‐tuned solid catalysts with good
efficiency. There have been reports on the use of solid catalysts
such as Mg‐Al mixed oxide [11], magnesium organo‐silicates
[12] and silica‐alumina [13] for this reaction. Climent et al. [14]
reported the superior activity of solid acid molecular sieves in
aldol and Knoevenagel condensation reactions, and found that
MCM‐41 was a better catalyst than microporous aluminosili‐
cates. Sudheesh et al. [15] investigated the application of a bi‐
opolymer chitosan as a solid catalyst for the condensation of
heptanal and benzaldehyde at 140 °C. Corma’s group [16]
studied the catalytic activity of various basic solids and com‐
pared their activity with that of amorphous AlP and ammo‐
nia‐treated AlP for the aldol condensation of n‐heptanal and
benzaldehyde. They reported the high activity of amorphous
AlP characterized by the presence of weak acidic sites along
with very weak basic sites. In their investigation, the catalyst
was prepared by the Lindblad method [17] in which ammoni‐
um phosphate was used as the phosphorous source instead of
phosphoric acid. In this method, the authors generated basic
sites on AlP by using ammonia. However, some of the catalyti‐
cally active acid sites may also be lost. As aldol condensation is
catalyzed by both acidic and basic materials, it would be inter‐
esting to evaluate the catalytic influence of these sites on aldol
condensation, and this was selected for the present study.
In the present work, we prepared AlP and MAlPs using
phosphoric acid as a phosphorous source and ammonium hy‐
droxide as precipitating agent. Precipitation was carried at ice
temperature to obtain particles with a smaller size and high
surface area, by Von Weimarn precipitation under relatively
super saturated conditions [18]. These materials were tested
for their catalytic activity in the synthesis of jasminaldehyde by
the condensation of n‐heptanal and benzaldehyde under reflux
conditions. An attempt was made to evaluate the struc‐
ture‐activity relationship of these catalysts.
dropwise addition of the ammonia solution for 20 min in order
to obtain particles with high surface areas. For example, pure
AlP was prepared by mixing Al(NO3)3·9H2O and 85% of H3PO4
in the desired molar ratio in 500 mL of de‐ionized water at ice
temperature to get a homogeneous solution. To the above clear
solution, 28% liquid ammonia was added dropwise from a bu‐
rette until the pH reached 7.5. The AlP gel thus obtained was
filtered, washed thoroughly with distilled water and dried at
120 °C in an air oven for 10 h. The dried samples were pow‐
dered and further calcined at 350 °C for 5 h.
The MAlPs were prepared by mixing Al(NO3)3·9H2O and the
metal salt in 500 mL of de‐ionized water followed by 85% of
H3PO4 in the desired molar ratio at ice temperature to get a
homogeneous solution. To the above clear solution, 28% liquid
ammonia was added dropwise from a burette until the pH
reached 7.5. The resulting precipitate was processed in a simi‐
lar procedure to that used for the AlP preparation. In the prep‐
aration of the MAlPs, the metal precursors used were the ni‐
trates of Cu, Zn, Cr, and Fe, and ceric ammonium nitrate and
zirconyl oxychloride for Ce and Zr. The phosphorous to total
metal molar ratio was kept 1:1 in all the catalysts with 2.5
mol% of the metal.
2.2. Material characterization
N2 adsorption‐desorption isotherms were determined using
a Micromeritics Tristar 3000 instrument. In a typical meas‐
urement, 0.2 g of the material (40–60 mesh) was degassed at
250 °C for 2 h in N2 flow. After cooling to room temperature,
the catalyst was loaded in the instrument for adsorption study
using N2 as adsorbate. The X‐ray diffraction (XRD) patterns of
the materials were analyzed using a Rigaku instrument (Japan)
with Cu Kα radiation. Fourier transform infrared (FT‐IR) spec‐
tra were recorded using a Thermo‐Scientific Nicolet IR‐380
instrument and the KBr pellet technique. Temperature‐pro‐
grammed desorption of ammonia (NH3‐TPD) experiments
were performed on a pulse Chemisorb instrument (Mi‐
cromeritics). In a typical experiment, 0.15 g of sieved particles
(40–60 mesh) was pretreated at 250 °C for 1 h in He flow,
cooled to room temperature and then 5% NH3/N2 gas was
passed through the bed for 30 min. After purging with He for
10 min to remove excess ammonia present on the surface,
NH3‐TPD was performed in the temperature range of 35–800
°C at a heating rate of 10 °C/min. The TCD signals were meas‐
ured after reaching 100 °C and a waiting time of 15 min to re‐
move physisorbed ammonia. The CO2‐TPD experiments were
carried out on the same instrument with a similar procedure as
described above using CO2 as the adsorbate.
2. Experimental
2.1. Material preparation
The pure and metal‐loaded AlPs were prepared by an earli‐
er reported co‐precipitation method [3] from the correspond‐
ing metal salts using 85% of H3PO4 as the phosphorous source
and 28% ammonia solution as the precipitating agent. All the
materials were prepared at ice temperature and with the

A. Hamza et al. / Chinese Journal of Catalysis 36 (2015) 209–215
211
2.3. Catalytic activity test
1.4
The catalytic condensation of n‐heptanal and benzaldehyde
was performed in a three necked round bottom (RB) flask. A
reflux condenser was fitted to one of the necks and the other
two were used for purging with inert gas and sampling. Calcu‐
lated amounts of n‐heptanal, benzaldehyde and the catalyst
were placed in the RB flask, purged with N2 and heated in an oil
bath at a predetermined temperature. The reaction mixture
was agitated using a magnetic stirrer. After a fixed time, the
reaction mixture was cooled, ethanol added and the catalyst
was separated by filtration. The reaction mixture was analyzed
using a Thermo‐Scientific GC (Chemito 8610) with a 5% SE‐30
packed column of length 8 ft (240 cm) and diameter of 1–8 inch
(2.5–20 cm). The reaction products were also analyzed using
GC‐MS.
1.2
1.0
0.8
0.6
0.4
0.2
0.0
AlP
CuAlP
CrAlP
CeAlP
ZnAlP
FeAlP
ZrAlP
0
20
40
60
80
100
Pore diameter (nm)
Fig. 1. Pore size distributions of AlP and MAlPs.
3. Results and discussion
AlP, CuAlP, and ZnAlP exhibited Type V isotherms and H4
hysteresis loops with limiting adsorption. The CrAlP, FeAlP,
CeAlP, and ZrAlP exhibited Type V isotherms with H3 type
hysteresis loop which did not exhibit any limiting adsorption at
high p/p0 values (Fig. 2). The hysteresis can be attributed to
capillary condensation taking place in a narrow range of tubu‐
3.1. Surface and bulk properties
3.1.1. Surface area and porosity
The surface areas of the samples determined by the BET
method are given in Table 1. All the materials were found to
possess a high surface area in the range from 152 to 188 m2/g.
While there was not much change in the surface area with di‐
valent Cu‐ and ZnAlPs, a substantial decrease was observed
with the trivalent and tetravalent metal‐loaded samples except
for CrAlP. A substantial decline in the surface area was ob‐
served in the case of FeAlP and ZrAlP. From Table 1, it can be
noted that the average pore diameter and total pore volume
were increased significantly with hetero‐metal incorporation in
the AlP. This indicated a change in the type of pores from mi‐
cropores to meso‐ and to macropores in some cases. An inter‐
esting observation was that due to metal loading of the pure
AlP, the total pore volume was increased from 0.5 to a maxi‐
mum of 1.05 ml/g. The maximum pore volume and pore diam‐
eter were achieved with the FeAlP and ZrAlP samples. In Fig. 1,
the pore volume versus pore diameter is plotted for pure AlP,
and all the MAlPs. In AlP, CuAlP, and ZnAlP, the pore size dis‐
tributions (PSDs) were comparatively narrow with a mesopo‐
rous structure while in the case of CrAlP, FeAlP, CeAlP, and
ZrAlP, significant amounts of macropores were also present
along with the mesopores.
300
200
AlP
100
600
400
200
CuAlP
ZnAlP
CrAlP
0
400
200
0
600
300
0
600
300
0
FeAlP
Table 1
MAlPs and their surface and acidic‐basic properties.
600
300
Metal Surface Pore
Sample content * area volume diameter acidity
(wt%) (m2/g) (ml/g)
Pore
Total
Total
basicity
ZrAlP
CeAlP
(nm) (mmol/g) (10–6 mmol/g)
0
600
AlP
—
181
188
177
181
153
172
152
0.50
0.74
0.68
0.90
1.03
0.85
1.05
10.9
15.5
14.8
19.6
26.4
19.5
27.1
0.101
0.117
0.107
0.124
0.043
0.055
0.053
2.6
9.6
9
CuAlP
ZnAlP
CrAlP
FeAlP
CeAlP
ZrAlP
1.93
2.32
2.18
2.15
1.96
2.25
300
0
30
13
29
55
0.2
0.4
0.6
0.8
1.0
Relative pressure (p/p0)
* Analyzed by ICP‐AES.
Fig. 2. N2 adsorption‐desorption isotherms of AlP and MAlPs.

212
A. Hamza et al. / Chinese Journal of Catalysis 36 (2015) 209–215
lar pores, confirming the large number of pores [19]. The H4
type hysteresis isotherm of AlP, CuAlP, and ZnAlP revealed the
presence of more microporous structure with very narrow
slit‐like pores, which is complimentary to the surface area re‐
sults. The H4 type hysteresis in the high valent MAlPs revealed
widened pores with aggregates of plate‐like particles. The
comparatively low pressure hysteresis loops in the former case
also pointed to a dominant amount of micropores. In the met‐
al‐loaded samples, the relative pressure at which hysteresis
was observed was shifted to higher p/p0 when compared to
AlP.
AlP
CeAlP
FeAlP
ZnAlP
ZrAlP
CuAlP
CrAlP
3.1.2. Powder XRD results
XRD patterns of AlP and MAlPs catalysts are shown in Fig. 3.
Amorphous AlP is characterized by a broad peak at 2θ =
20°–40°, which indicates the tetrahedral structure [20]. All the
calcined materials were found to be amorphous and showed a
similar pattern with a broad peak at 2θ = 25°. The intensity of
this peak was reduced with metal loading and further broad‐
ening of the peak was observed, indicating a decrease in parti‐
cle size. The amorphous nature persisted even after high tem‐
perature drying which was shown by the XRD figures of high
temperature‐dried (850 °C) samples that showed no metal
oxide peaks.
800 1200 1600 2000 2400 2800 3200 3600 4000
Wavenumber (cm1)
Fig. 4. FT‐IR spectra of AlP and MAlPs.
3.1.4. NH3‐TPD results
The acidic properties of the materials were evaluated by
NH3‐TPD studies. It was found that the acidity depended on the
type of metals incorporated in the AlP (Fig. 5 and Table 1).
While the acidity of CuAlP, ZnAlP, and CrAlP were higher than
that of the pure AlP, the acidity of FeAlP, CeAlP, and ZrAlP were
lower. The number of acidic sites in the divalent MAlPs was
higher than in the trivalent and tetravalent MAlPs. The higher
acidity of CuAlP and ZnAlP may be due to the formation of
more Brönsted acidic sites. The anion vacancies formed by the
substitution of trivalent Al or P by the divalent metals may lead
to the abstraction of proton during the sol‐gel transition, which
in turn may result in the Brönsted acid sites. The CuAlP materi‐
al was slightly more acidic than ZnAlP, and CuAlP was the most
acidic catalyst of all the MAlPs in this work. The lower acidity of
trivalent CrAlP and FeAlP may be due to maintaining elec‐
tro‐neutrality by the substitution of Al3+ or by the formation of
fewer Brönsted acidic sites due to the substitution of the P5+.
FeAlP was less acidic than CrAlP, which may be due to the suc‐
3.1.3. FT‐IR results
The FT‐IR spectra of AlP and MAlPs are shown in Fig. 4. All
the phosphates showed a nearly similar spectrum in the OH
stretching vibration region (3600–3000 cm−1) with a broad
band centered at 3500 cm−1, which was attributed to surface
hydroxyl groups associated with the metal, aluminum, and
phosphorous atoms [21]. The weak absorption bands around
1640 cm–1 indicated the presence of adsorbed water molecules.
All the samples exhibited the characteristic absorption peaks of
the asymmetric vibrations of phosphate in the range of
1100–1140 cm–1. The IR spectra also exhibited shoulder peaks
at 725 and 507 cm–1 which were respectively assigned to the
symmetric stretching mode of P–O–P and bending mode of
O–P–O bonds [22].
CuAlP
CrAlP
ZnAlP
AlP
FeAlP
CeAlP
ZrAlP
ZrAlP
CeAlP
FeAlP
CrAlP
ZnAlP
CuAlP
AlP
10
20
30
40
50
60
70
100
200
300
400
500
600
700
2/(o )
Temperature (oC)
Fig. 3. XRD patterns of AlP amd MAlPs.
Fig. 5. NH3‐TPD profiles of AlP and MAlPs.

A. Hamza et al. / Chinese Journal of Catalysis 36 (2015) 209–215
213
cessful incorporation of Fe into the AlP while the increased
Table 2
acidity of the latter was due to the existence of unsubstituted
Cr3+ and formation of Cr6+ by oxidation during calcination of the
precipitate. This can also be explained in terms of the difficulty
of Cr to occupy the tetrahedral structure. The number of weak
acidic sites further decreased in the tetravalent MAlPs, CeAlP
and ZrAlP, which may be due to fewer Brönsted sites created
due to decreased anion vacancies. On the substitution of Al by
the tetravalent metals Ce and Zr, the excess positive charge
may lead to the formation of weak Lewis acidic sites rather
than strong Brönsted acid sites. The order of acidity of the
MAlPs was CrAlP > CuAlP > ZnAlP > AlP > FeAlP = CeAlP =
ZrAlP.
Catalytic performance in the condensation of heptanal with benzalde‐
hyde to jasminaldehyde (JA).
2‐h reaction
4‐h reaction
Selectivity
(%)
PNAa JA
Selectivity
(%)
PNAa
n‐Heptanal
conversion
(%)
n‐Heptanal
conversion
(%)
Catalyst
JA
55
41
36
53
71
63
65
AlP
41
31
35
31
59
47
51
40
54
61
50
66
54
60
60
46
39
50
34
46
40
46
50
52
39
75
65
67
45
59
64
47
29
37
35
CuAlP
ZnAlP
CrAlP
FeAlP
CeAlP
ZrAlP
Reaction conditions: heptanal to benzaldehyde molar ratio = 1:5, 140 °C,
catalyst 10 wt%, atmospheric pressure.
3.1.5. CO2‐TPD results
The CO2‐TPD studies revealed the formation of weak and
medium strength basic sites, and that the basicity of all the
MAlPs was stronger than pure AlP irrespective of the valence of
the metal (Fig. 6 and Table 1). In CrAlP, some strong basic sites
were also formed. The total basicity of AlP, CuAlP, and ZnAlP
were lower than that of CrAlP, FeAlP, CeAlP, and ZrAlP. The
order of basicity was ZrAlP > CeAlP > FeAlP > CrAlP > ZnAlP =
CuAlP > AlP.
a 2‐n‐pentyl 2‐n‐nonenaldehyde.
porosity. The trend in catalytic activity was explained based on
the change in the strength and concentration of acid/base sites
as result of the incorporating metals into AlP.
With the incorporation of the divalent metals Cu and Zn, the
activity was increased slightly but the selectivity towards jas‐
minaldehyde decreased. The higher conversion may be due to
the created basic sites and the lower selectivity due to the in‐
creased acidity. Of the trivalent MAlPs, CrAlP which was a
higher acidity than AlP gave the lowest heptanal conversion
and selectivity to jasminaldehyde. Interestingly, a very high
conversion of heptanal and selectivity to jasminaldehyde were
obtained with FeAlP, CeAlP, and ZrAlP, in which acidity was
significantly decreased and they possessed a higher basicity
than pure AlP. Thus FeAlP in which the acidity was decreased
significantly and with more basic sites was the highest heptanal
conversion at 4 h reaction time with the highest selectivity to
jasminaldehyde. In general, the MAlPs with more weak acidic
sites than AlP gave an inferior catalytic performance in aldol
condensation and those with less acidity than AlP gave a supe‐
rior performance.
The performance with respect to both the activity and selec‐
tivity was improved by the loading of Fe, Ce, and Zr metals in
the AlP. The basic sites are believed to help to abstract the pro‐
ton from n‐heptanal to form the corresponding enolate ion and
the acidic sites to activate the benzaldehyde which does not
have a α‐hydrogen atom. The carbonyl group of activated ben‐
zaldehyde is then attacked by the enolate ions to form the con‐
densation products [11]. Corma’s group [16] also reported the
importance of the tuned acidic‐basic sites of amorphous AlP.
The authors have tried to boost the basic strength of AlP by the
modification of the surface by ammonia treatment, and found
that increased basic sites did not favor the aldol condensation,
but rather that an optimized acidity was required for a high
conversion of heptanal and benzaldehyde and higher selectivity
to jasminaldehyde. From the above observations, it was clear
that the superior activity and selectivity with FeAlP as catalyst
was due to the optimum level of weak acidic and basic sites,
which supports the combined acid‐base mechanism. Further
optimization of the reaction conditions were carried out using
this catalyst.
3.2. Catalytic activity studies
The catalytic activity of the AlP and MAlPs was investigated
for the synthesis of jasminaldehyde through the condensation
of n‐heptanal with benzaldehyde (Table 2). All the catalysts
exhibited activity with more than 30% jasminaldehyde selec‐
tivity and 20% n‐heptanal conversion. The byproduct formed
was 2‐n‐pentyl‐2‐n‐nonenal, which was formed by the self
condensation of n‐heptanal. The selectivity towards jas‐
minaldehyde as well as the n‐heptanal conversion gradually
increased with reaction time and doubled from 2 to 4 h. A
higher (75%) n‐heptanal conversion was achieved using 2.5%
FeAlP. The surface area and porosity of the MAlPs did not have
any direct correlation with the catalytic performance since all
the materials prepared in this work have high surface area and
FeAlP
ZnAlP
CeAlP
ZrAlP
CrAlP
AlP
CuAlP
100
200
300
400
500
600
Temperature (oC)
Fig. 6. CO2‐TPD profiles of AlP and MAlPs.

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A. Hamza et al. / Chinese Journal of Catalysis 36 (2015) 209–215
Table 3
Table 5
Effect of FeAlP catalyst amount on the performance.
Effect of heptanal to benzaldehyde molar ratio on the condensation of
heptanal with benzaldehyde to jasminaldehyde over FeAlP.
m(catalyst)/m(heptanal)
Heptanal conversion
JA selectivity
(%)
0
5
10
15
20
(%)
4
36
75
80
88
(%)
23
45
71
60
49
Heptanal to benzaldehyde molar ratio
1:1
1:2
1:3
JA selectivity (%)
22
30
47
56
71
69
74
1:4
1:5
1:7
1:10
FeAlP as catalyst, heptanal to benzaldehyde molar ratio 1:5, 140 °C, 4 h.
140 °C, catalyst 10 wt%, 4 h.
3.2.1. Effect of the catalyst amount
The effect of catalyst amount on the conversion of
n‐heptanal and selectivity to jasminaldehyde was studied by
varying the amount of FeAlP catalyst from 5% to 20% with
respect to the amount of n‐heptanal (Table 3). The maximum
selectivity of 71% with a conversion of 75% was observed us‐
ing 10% catalyst. Further increase in catalyst amount to 20%
improved the conversion to 88% but the selectivity to jas‐
minaldehyde decreased to 49%, which is not desirable. The
decrease in the selectivity to jasminaldehyde with more cata‐
lyst was due to the self condensation of 1‐heptanal to
2‐pentyl‐non‐2‐enal due to the increase in the number of weak
acid sites, which lead to the activation of the carbonyl group of
heptanal rather than proton abstraction. The reaction carried
out without any catalyst resulted in negligible conversion. Fur‐
ther optimization studies were carried out with 10% FeAlP
catalyst as it exhibited high activity.
hyde increased with an increase in the molar ratio of the
heptanal‐benzaldehyde. As the concentration of 1‐heptanal was
decreased on increasing the benzaldehyde to 1‐heptanal mole
ratio, the self‐condensation of 1‐heptanal seems to be sup‐
pressed significantly. A ratio of 1:5 was the best for satisfactory
catalyst performance. There was not much increase in the jas‐
minaldehyde selectivity with further increase in the molar ratio
after 1:5.
3.2.4. Reusability of the catalyst
The reusability of the FeAlP catalyst was tested by five recy‐
cles. It was found that the conversion and selectivity of the cat‐
alysts remained almost the same in all experiments. The slight
change in activity may be due to physical loss of the catalyst
during separation. The catalyst in the reaction mixture after
each experiment was separated by filtration and stirred in ace‐
tone for 15 min, washed thoroughly to remove the organics and
the sample was dried slowly to 250 °C. The observations are
given in Fig. 7.
3.2.2. Effect of reaction temperature
The effect of reaction temperature on the condensation of
heptanal and benzaldehyde over FeAlP was investigated by
varying the temperature from 80 to 150 °C using the FeAlP
catalyst. The heptanal conversion increased from 9.3% to 81%
accompanied by an increase in selectivity to jasminaldehyde on
increasing the reaction temperature (Table 4). The selectivity
towards jasminaldehyde decreased with the increase of tem‐
perature beyond 140 °C. However, the tendency to undergo self
condensation of heptanol decreased with an increase of reac‐
tion temperature up to 140 °C. It was concluded that 140 °C is
the optimum temperature with the FeAlP catalyst.
4. Conclusions
Amorphous AlP, and MAlPs of Cu, Zn, Cr, Fe, Ce, and Zr were
synthesized by the coprecipitation method without using a
surfactant. The samples were characterized for their surface,
bulk, and acid‐base properties. By incorporating a suitable
metal in AlP, the surface area, porosity and acidic‐basic proper‐
Conversion of n-heptanal
Selectivity for jasminaldehyde
3.2.3. Effect of molar ratio of n‐heptanal to benzaldehyde
The molar ratio of heptanal to benzaldehyde played an im‐
portant role in the selectivity of the desired product, jas‐
minaldehyde. The molar ratio did not play a significant role in
heptanal conversion (Table 5). The selectivity to jasminalde‐
80
70
60
50
40
30
20
10
0
Table 4
Effect of reaction temperature on the condensation of heptanal with
benzaldehyde to jasminaldehyde over FeAlP.
Temperature (°C)
Heptanal conversion (%)
JA selectivity (%)
80
9.3
22
47
75
81
36
47
54
71
52
100
120
140
150
R
R1
R2
R3
R4
R5
Fig. 7. Reusability of the FeAlP in the aldol condensation of n‐heptanal
Heptanal to benzaldehyde molar ratio 1:5, catalyst 10 wt%, 4 h.
with benzaldehyde.

A. Hamza et al. / Chinese Journal of Catalysis 36 (2015) 209–215
215
Graphical Abstract
Chin. J. Catal., 2015, 36: 209–215 doi: 10.1016/S1872‐2067(14)60206‐0
O
Amorphous metal‐aluminophosphate catalysts for aldol
condensation of n‐heptanal and benzaldehyde to
jasminaldehyde
O
ALDOL CONDENSATION
O
A. Hamza, N. Nagaraju*
O
St. Joseph’s College P.G. and Research Centre, India
ACIDIC & BASIC SITES
Amorphous aluminophosphate and metal‐aluminophosphates
(metal = Cu, Zn, Cr, Fe, Ce, and Zr) were investigated for their
surface and bulk properties, and as catalyst for the synthesis of
jasminaldehyde through aldol condensation of n‐heptanal and
benzaldehyde without a solvent.
MAlPs
Chem, 1994, 4: 331
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[6] Campelo J M, Garcia A, Luna D, Marinas J M, Romero A A, Navio J A,
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[8] Nagaraju N, Kuriakose G. Green Chem, 2002, 4: 269
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ties were significantly altered. The porosity and acid‐base be‐
haviour depended on the type of metals used. These materials
were used as catalyst for the synthesis of the industrially im‐
portant fine chemical jasminaldehyde through the condensa‐
tion of n‐heptanal and benzaldehyde. The high catalytic activity
of FeAlP was attributed to the cooperative role of optimum
amounts of acidic and basic sites of weaker strength. A higher
molar ratio of benzaldehyde suppressed the self‐condensation
of n‐heptanal, which improved the selectivity to jasminalde‐
hyde. The optimum temperature for high selectivity and con‐
version was 140 °C. An increase in catalyst amount played an
important role in selectivity but not in the conversion of
n‐heptanal.
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The authors acknowledge Sud‐Chemie India Ltd. Cochin for
support to carry out some of the instrumental analysis work.
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