Room temperature synthesis of ZnAlPO4 nanoparticles and their catalytic applications

Article abstract of DOI:10.1039/c3ra41760c

Here, we report a simple method for the synthesis of ZnAlPO₄ nanoparticles possessing stable structures even after the removal of the structure directing agent. The material can act as an efficient bi-functional catalyst for the alkylation of acetophenone with benzyl alcohol.

Full text of DOI:10.1039/c3ra41760c

RSC Advances
View Article Online
View Journal | View Issue
COMMUNICATION
Room temperature synthesis of ZnAlPO nanoparticles
4
and their catalytic applications3
Cite this: RSC Advances, 2013, 3, 13651
a
a
b
a
Peta Sreenivasulu, Devaki Nandan, B. Sreedhar and Nagabhatla Viswanadham*
Received 12th April 2013,
Accepted 28th June 2013
DOI: 10.1039/c3ra41760c
www.rsc.org/advances
Here, we report a simple method for the synthesis of ZnAlPO
4
thermally stable MAlPO
protonated organic SDA and H
4
materials by using novel SDAs, where the
O played a charge-balancing role
nanoparticles possessing stable structures even after the removal
of the structure directing agent. The material can act as an
efficient bi-functional catalyst for the alkylation of acetophenone
with benzyl alcohol.
2
as per the host–guest charge density matching principle proposed
6
by Stucky et al. In some cases, fluoride ions were also employed
as structure directing agents along with organic amines to
facilitate the formation of some special cage structures, such as
a double 4-ring and to compensate the changes in the frame-
The synthesis of the aluminophosphate (AlPO ) class of molecular
4
7,8
sieves has been paid immense attention since its first discovery by
work.
1
Wilson in 1982. Due to its exceptional hydrophilic properties and
The control of molecular sieve synthesis on the nanoscale is
gaining importance due to their high surface area and improved
accessibility to active sites, because the small crystal size results in
the presence of a shorter path length in the nanoaggregates, when
compared to those in the corresponding microscale materials.
Furthermore, the pore channels in the nanosystem also facilitate
the facile diffusion of the reactants and products required for the
efficient conversion of reactants with improved catalyst life; the
heat transformation ability, the zeotype AlPO material has been
4
successfully used in closed solar cooling systems. However, the
3+
5+
neutral framework charge obtained by the presence of Al and P
make this material non-acidic and this limits its applications in
catalysis. This limitation has been successfully overcome by the
introduction of a divalent heteroatom, such as Mg, Co and Zn,
into the framework of the AlPO to create a negative charge in the
4
framework responsible for acidity. The quantity of the heteroatom
in the framework is directly related to the concentration of acidic
9
most important property desired by both academia and industry.
Several efforts have been made in recent years to obtain
nanoparticles of the desired size, morphology and crystallinity
through the optimization of the synthetic procedure, where a
special emphasis was given to the stabilization of the nanopar-
sites. This has resulted in the synthesis of a wide variety of metal
2
aluminophosphates (MAlPO s), that exhibit the characteristics of
4
zeolites and also show novel physicochemical properties suitable
for acid-catalyzed reactions, magnetism, photoluminescence and
10,11
ticles in suspension and to decrease the production price.
A
3–4
ion-exchange applications. However, the introduction of high
numbers of heteroatoms into the framework of AlPO leads to its
typical synthesis of nanosized materials involved the use of excess
organic additives and different solvents (water, methanol, ethanol,
etc.). The crystal size was reduced in most cases by increasing the
concentration of the organic template significantly, replacing the
water with other solvents, decreasing the synthesis temperature
and extending the crystallization process. Unfortunately, these
conditions made the synthesis of the nanocrystalline material
complicated and economically non-viable, due to the large
consumption of the expensive organic template and the increased
4
structural instability, which increases as the number of heteroa-
5
toms increases.
AlPO and MAlPO materials are commonly synthesized under
4
4
12
hydrothermal conditions using structure directing agents (SDAs)
that are specific for each type of material. Many heteroatom-
containing aluminophosphates are unstable after the removal of
SDAs which greatly limits their applications in catalysis and
adsorption. Recently, research has been undertaken to synthesize
1
3
consumption of energy.
The a-alkylation of ketones is an industrially important
reaction, where a transition metal based catalyst is used in the
a
Catalysis and Conversion Processes Division, Indian Institute of Petroleum, Council
of Scientific and Industrial Research, Dehradun, 248005, India.
E-mail: nvish@iip.res.in; Fax: 91-135-2525702; Tel: 91-135-2525856
presence of a strong base such as KOH and a hydrogen trapping
14–16
reagent such as an olefin.
Since Zn is known for its
b
CSIR-Indian Institute of Chemical Technology, Hyderabad, India.
dehydrogenation activity and MAlPO s have good catalytic
4
E-mail: sreedharb@iict.res.in
applications, attempts have been made in the present study to
3
Electronic supplementary information (ESI) available: Experimental details, wide
angle XRD, EDX, SEM images, IR spectra, etc. See DOI: 10.1039/c3ra41760c
apply a ZnAlPO
4
material for this reaction. Here, for the first time,
This journal is ß The Royal Society of Chemistry 2013
RSC Adv., 2013, 3, 13651–13654 | 13651

View Article Online
Communication
RSC Advances
we report a novel method for the room temperature synthesis of a
nanosized ZnAlPO material possessing a stable structure, using
4
tetrapropylammonium bromide (TPABr) and fluoride as template
and co-template. The material retained its structural identity even
after the removal of the template by calcination, which makes the
present material useful for high temperature applications. The
novelty of the present work lies in (1) the first synthesis of a
nanosized ZnAlPO4 material, (2) the economical and room
temperature synthesis of the nanomaterial and (3) its potential
catalytic application for an a-alkylation reaction.
A typical synthetic method involves the dispersion of
aluminum nitrate and zinc nitrate powders in a solution of
ammonium orthophosphate with vigorous stirring at room
temperature, followed by the sequential addition of tetrapropy-
lammonium bromide and hydrofluoric acid, and leaving the
resultant mixture stirring for one hour to obtain a homo-
geneous gel with an overall molar composition of
4
Fig. 2 FTIR spectra of the ZnAlPO samples.
the DTA analysis, indicating no further weight loss, suggesting the
structural stability of the ANA crystalline phase of the ZnAlPO
The structural identity of all the ZnAlPO samples was
confirmed by FTIR spectroscopy (Fig. 2 and Fig. S3, ESI ), where
the samples, before and after calcination exhibited the character-
4
.
2 3 2 5 2
0.1Al O : 0.011Zn : 0.35P O : 0.0016SDA : 0.1HF : 3H O.
The crystallization was carried out at room temperature by
adding a few drops of ammonia and the white crystals obtained
were filtered and washed with copious amount of de-ionized
water and dried at room temperature overnight, followed by
calcination for 5 h at 500 uC. The samples obtained before and
after calcination were denoted as ZAP and ZAPC, respectively.
4
3
3
2
istic vibrational bands associated with the [PO
4
]
unit (1127, 504
21
21 19
cm ) and pseudo-lattice Al (748 cm ). Furthermore, the two
21
bands obtained at 1009 and 990 cm should be caused by the
incorporation of Zn into the framework and were assigned to the
4
The X-ray diffraction patterns of the ZnAlPO samples (Fig. 1)
20,21
vibrations of Zn–O–P.
The additional bands observed in the
indicate the formation of a crystalline material with some ANA
17
samples before calcination (which disappeared after calcination)
are related to the stretching vibrations of the SDA. The EDX
zeotype structure (ZAP), which upon calcination yielded a
prominent phase of ANA along with an enhancement in the
analysis (Fig. S4, ESI
alumina and phosphorous species in the samples.
The structural morphology of the ZnAlPO samples before and
after calcination are shown in Fig. 3a and 3b; the sample
synthesized at room temperature (ZAP) exhibited a spherical
morphology, and well-defined spheres of 5 mm size were obtained
after calcination (ZAPC). The internal structure of the materials
3
) also confirmed the presence of zinc,
3
intensity of the peaks (ZAPC) (Fig.S1, ESI ). This may be due to the
presence of impurity phases and the template in the as-
synthesized sample (ZAP) which were decomposed during
calcination to give the pure crystalline structure (ZAPC). This
4
synthesis of an ANA zeotype of ZnAlPO is the first of its kind to be
4
4
reported. The structural stability of the ZnAlPO sample was
confirmed by TGA-DTA analysis (Fig. S2, ESI ), where the sample
3
showed a weight loss at 80–150 uC, related to the desorption of
physically/chemically sorbed water and a high temperature weight
loss, at up to 450 uC, related to the decomposition of the organic
18
template and HF. There was no peak observed above 450 uC in
4
Fig. 3 SEM and TEM images of the ZnAlPO samples; (a) and (b) represent the SEM
images of ZAP and ZAPC, while (c) and (d) represent the TEM images of ZAP and
ZAPC.
4
Fig. 1 Wide angle XRD patterns of the ZnAlPO samples.
1
3652 | RSC Adv., 2013, 3, 13651–13654
This journal is ß The Royal Society of Chemistry 2013

View Article Online
RSC Advances
Communication
three reaction cycles. These results indicated a better performance
of the ZAPC catalyst, when compared with previously reported
results (ESI Table 1). A reference experiment conducted in the
3
Table 1 Catalytic performance of the ZnAlPO
4
(ZAPC) sample
Selectivity (%)
Catalyst
Acetophenone conversion
P1
P2
P3
absence of the catalyst, using only acetophenone and benzyl
alcohol, ascertained that no reaction occurred and confirmed the
a
ZAPC
100
98
26
20
40
60
34
20
b
catalytic role of the ZnAlPO . At this stage, the role of the ANA
4
ZAPC
phase of the material in catalysis is not clear. However, the
nanometer particles obtained in the present study may be
a
b
Fresh catalyst. Used catalyst.
responsible for the catalytic activity of the ZnAlPO
ANA zeolites, as well as ZnAlPO materials obtained in the
and the nano level material of the ANA
4
. In general,
4
23,24
micrometer range
was measured by TEM (Fig. 3c and 3d), where, the samples ZAP
and ZAPC exhibited spherical particle aggregates of 30–40 nm size.
phase obtained in the present method, are important for material
applications.
The ANA zeotype (ZAPC) exhibited the highest acidity (Fig. S5, ESI
3
)
In summary, the present study describes a novel method for
and catalytic activity towards the alkylation of acetophenone with
benzyl alcohol, where the conversion of acetophenone was
observed to be almost 100% with the selectivity of three products,
namely benzaldehyde (P1), 1-hydroxy-1,3-diphenylpropane (P2)
and 1,3-diphenylpropane (P3) in 26%, 40% and 34%, respectively
the synthesis of ANA zeotype nanostructures of a ZnAlPO material
4
with high thermal stability. The synthesis of ZnAlPO possessing
4
an ANA zeotype obtained by just the room temperature mixing of
chemical ingredients is reported for the first time and provides an
effective synthetic method using a simple organic template,
TPABr, with a short synthesis time. Moreover, the material
retained its structure even after the removal of the organic
template through calcination, that further revealed the suitability
of these materials for high temperature applications. The ANA
zeotype material also exhibited an excellent catalytic activity in the
conversion of benzyl alcohol with considerable selectivity towards
the alkylated products of acetophenone through a bi-functional
reaction network facilitated by the presence of the dehydrogena-
tion functional Zn in combination with acidic protons. These
findings open up an opportunity to explore the potential of this
class of materials for various high temperature applications.
The authors thank the director, IIP for his encouragement. PS
and DN acknowledge the CSIR, New Delhi for awarding fellow-
ships. We are thankful to the XRD, IR, SEM and GC-MS groups at
IIP for analysis.
(Table 1). Used catalyst gave the maximum quantity of 1-hydroxy-
1,3-diphenylpropane (P2) compared to the other products P1 and
P3 (the maximum reaction was to stop at the hydrogenation
product), which may be due to the maximum number of Zn active
sites being present, compared to the acidic proton active sites (the
maximum product P2 is the alcohol compared to the dehydro-
genation product). This can be explained by a bi-functional
mechanism facilitated by the presence of Zn and the acidic proton
on the catalyst, where the formation of benzaldehyde occurred
through the dehydrogenation of benzyl alcohol on the Zn sites,
followed by the reaction of the resultant benzaldehyde with
acetophenone to form an alkylation product, in the presence of
the acidic sites (Fig. 4). Here, the hydrogen evolved from benzyl
alcohol could be utilized in the hydrogenation steps of the
alkylation intermediates, to form products P2 and P3, whose
derivatives have potential pharmaceutical and therapeutic applica-
22
tions. The effective conversion of benzyl alcohol observed in the
reaction demonstrated the effective dehydrogenation activity of
the Zn sites and the catalyst exhibited a comparable activity after
References
1
2
3
4
5
6
S. T. Wilson, B. M. Lok, C. A. Messina, T. R. Cannan and
E.M. Flanigen, J. Am. Chem. Soc., 1982, 104, 1146.
I. Saadoune, F. Cora and C. R. A. Catlow, J. Phys. Chem. B, 2003,
1
07, 3003.
A. K. Cheetham, G. F ´e rey and T. Loiseau, Angew. Chem., Int. Ed.,
999, 38, 3268.
1
E. M. Flanigen, B. H. Lok, R. L. Patton and S. T. Wilson, Pure
Appl. Chem., 1986, 58, 1351.
U. Lohse, B. Parlitz, D. M u¨ ller, E. Schreier, R. Bertram and
R. Fricke, Microporous Mater., 1997, 12, 39.
(a) X. Bu, P. Feng and G. D. Stucky, J. Am. Chem. Soc., 1998, 120,
1
1204; (b) P. Feng, X. Bu and G. D. Stucky, Nature, 1997, 388,
35.
M. R. Cavellec, D. Riou and G. F ´e rey, Inorg. Chim. Acta, 1999,
91, 317.
7
7
8
2
K. H. Lii, Y. F. Huang, V. Zima, C. Y. Huang, M. H. Lin, Y.
C. Jiang, F. L. Liao and S. L. Wang, Chem. Mater., 1998, 10,
2599.
9
(a) S. Mintova, N. Petkov, K. Karaghiosoff and T. Bein, Mater.
Sci. Eng., C, 2002, 19, 111; (b) Tosheva and V. P. Valtchev, Chem.
Mater., 2005, 17, 2494; (c) S. Mintova, N. Olson, V. Valtchev and
Fig. 4 Scheme for reaction pathways.
This journal is ß The Royal Society of Chemistry 2013
RSC Adv., 2013, 3, 13651–13654 | 13653

View Article Online
Communication
RSC Advances
T. Bein, Science, 1999, 283, 958; (d) W. Song, J. F. Woodworth, V.
H. Grassian and S. C. Larsen, Langmuir, 2005, 21, 7009.
0 (a) B. A. Holmberg, H. Wang, J. M. Norbeck and Y. Yan,
16 (a) X. Cui, Y. Zhang, F. Shi and Y. Deng, Chem.–Eur. J., 2011, 17,
1021; (b) Y. M. A. Yamada and Y. Uozumi, Tetrahedron, 2007,
63, 8492.
1
Microporous Mesoporous Mater., 2003, 59, 13; (b) O. Larlus,
S. Mintova and T. Bein, Microporous Mesoporous Mater., 2006,
17 M. M. J. Treacy and J. B. Higgins, Fourth Revised Edition,
Elsevier, New York, 2001.
96, 405.
1
8 D. E. Akporiaye, H. Fjellvag, E. N. Halvorsen, J. Hustveit,
A. Karlsson and K. P. Lillerud, J. Phys. Chem., 1996, 100, 16641.
9 D. L. Sun, J. R. Deng and Z. S. Chao, Chemistry Central Journal.,
007, 1 : 27, 1.
0 T. J. Munoz, A. Prakash, L. Kevan and K. J. Balkus, J. Phys.
Chem. B, 1998, 102, 1379.
1 O. Pawlig and R. Trettin, Chem. Mater., 2000, 12, 1279.
2 J. F. Delhomel, R. Hanf and K.C. Bertrand, U. S. Patent,
,258,182 B2, 2012.
3 M. Kohoutkov ´a , A. Klou ´z kov ´a , J. Maixner and M. Mr ´a zov ´a ,
Ceramics – Silik a´ ty, 2007, 51(1), 9.
1
1 (a) Z. J. Li, C. M. Lew, S. A. Li, D. I.Medina and Y. S. Yan, J. Phys.
Chem. B, 2005, 109, 8652; (b) Z. J. Li, S. A. Li, H. M. Luo and Y.
S. Yan, Adv. Funct. Mater., 2004, 14, 1019.
1
2
1
1
2 S. C. Larsen, J. Phys. Chem. C, 2007, 111, 18464.
3 H. V. Heyden, S. Mintova and T. Bein, J. Mater. Chem., 2006, 16,
14.
4 (a) T. D. Nixon, M. K. Whittlesey and J. M. J. Williams, Dalton
2
5
2
2
1
Trans., 2009, 753; (b) G. Guillena, D. J. Ram ´o n and M. Yus,
Angew. Chem., Int. Ed., 2007, 46, 2358; (c) F. Shibahara and M.
J. Krische, Chem. Lett., 2008, 37, 1102; (d) F. Alonso, P. Riente
and M. Yus, Eur. J. Org. Chem., 2008, 4908.
8
2
24 S. K. Saha, H. Maekawa, B. Suresh, S. A. Waghmode, R. Mulla,
1
5 (a) M. Morita, Y. Obora and Y. Ishii, Chem. Commun., 2007,
850; (b) Y. Iuchi, Y. Obora and Y. Ishii, J. Am. Chem. Soc., 2010,
32, 2536; (c) R. Mart ´ı nez, D. J. Ram o´ n and M. Yus, Tetrahedron,
006, 62, 8988.
K. Komura, Y. Kubota1, Y. Sugi and S. J. Cho, Mater. Trans.,
2
1
2
2005, 46, 2659.
1
3654 | RSC Adv., 2013, 3, 13651–13654
This journal is ß The Royal Society of Chemistry 2013