Platinum/3,3?-thiodipropionic acid nanoparticles as recyclable catalysts for the selective hydrogenation of trans-cinnamaldehyde

Article abstract of DOI:10.1016/j.catcom.2013.09.008

Platinum nanoparticles as spherical aggregates were prepared by the reduction of a Pt(II) salt with hydrazine using 3,3?-thiodipropionic acid as a protective agent, and characterized by IR, XRF, XRD, and SEM where agglomerates have been visualized. The average crystallite size was 6 nm. For the first time such nanoparticles were evaluated as catalysts in the hydrogenation of unsaturated aldehydes. Hydrogenation of trans-cinnamaldehyde yielded cinnamyl alcohol with a selectivity of up to 83% at complete substrate conversion. At 30 C, the catalyst could be recycled and reused for three runs with only slight losses in activity and selectivity.

Full text of DOI:10.1016/j.catcom.2013.09.008

Catalysis Communications 43 (2014) 57–60
Contents lists available at ScienceDirect
Catalysis Communications
journal homepage: www.elsevier.com/locate/catcom
Short Communication
Platinum/3,3´-thiodipropionic acid nanoparticles as recyclable catalysts
for the selective hydrogenation of trans-cinnamaldehyde
Anastasia Pournara a,c, Dimitra Kovala-Demertzi ⁎, Nikolaos Kourkoumelis ,
a,
b
c
c,
Spyros Georgakopoulos , Ioannis D. Kostas ⁎⁎
a
University of Ioannina, Department of Chemistry, Sector of Inorganic and Analytical Chemistry, 45110 Ioannina, Greece
University of Ioannina, Medical School, Medical Physics Laboratory, 45110 Ioannina, Greece
National Hellenic Research Foundation, Institute of Biology, Medicinal Chemistry and Biotechnology, Vas. Constantinou 48, 11635 Athens, Greece
b
c
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 26 July 2013
Received in revised form 5 September 2013
Accepted 7 September 2013
Available online 13 September 2013
Platinum nanoparticles as spherical aggregates were prepared by the reduction of a Pt(II) salt with hydrazine
using 3,3´-thiodipropionic acid as a protective agent, and characterized by IR, XRF, XRD, and SEM where agglom-
erates have been visualized. The average crystallite size was 6 nm. For the first time such nanoparticles were
evaluated as catalysts in the hydrogenation of unsaturated aldehydes. Hydrogenation of trans-cinnamaldehyde
yielded cinnamyl alcohol with a selectivity of up to 83% at complete substrate conversion. At 30 °C, the catalyst
could be recycled and reused for three runs with only slight losses in activity and selectivity.
Keywords:
Platinum nanoparticles
©
2013 Elsevier B.V. All rights reserved.
3,3´-Thiodipropionic acid
Heterogeneous catalysis
Selective hydrogenation
Cinnamaldehyde
Cinnamyl alcohol
1
. Introduction
of the C O bond, and it is affected by several factors including the size
of the NPs as the selectivity for CALH formation is increased by increas-
ing their size [6–8]. Since the selectivity can be strongly dependent on
the substrate conversion, high selectivity to CALH at high conversion
level is a very important issue from a synthetic point of view. Amongst
a large number of metal NPs for the hydrogenation of CALD, high selec-
tivity towards CALH (N80%) at a high substrate conversion (N80%) has
Catalysis by metal nanoparticles (NPs) has received a remarkable
research effort as it stands at the frontier between homogeneous and
heterogeneous catalysis, and attention has been focused on the recov-
ery and reuse of these nanocatalysts. [1,2]. NPs have a large surface
area-to-volume ratio compared to bulk materials, making them highly
attractive for catalysis. For the preparation of stable metal NPs, various
stabilizers have been used such as polymers, dendrimers, ligands, and
surfactants.
3
been reported by monometallic NPs such as Pt/PVP/FeCl (conversion
84%; selectivity 99%) [9,10], Pt/CTA/montmorillonite (89%; 80%) [11],
Pt/Na–Y (100%; 92%) [12], Pt/K-10 (96%; 96%) [13], Pt/SBA-15 (95%;
80%) [14], bimetallic NPs such as Pt–Fe/C (99%; 85%) [15], Co doped Pt
nanocrystals (80%, N99%) [16], and also by bimetallic NPs on carbon
nanotubes such as Pt–Co/CNTs (86%; 93%) [17] and Pt–Ru/CNTs (80%;
93–95%) [18–20]. These catalysts should be considered as the best
metal NPs for the hydrogenation of CALD with respect to both high ac-
tivity and selectivity towards CALH, but however, catalyst recycling and
reusability were not investigated.
Herein, we report the preparation of platinum NPs by reduction
of Pt(II) with hydrazine, using 3,3´-thiodipropionic acid (TDPC) as a
protective agent (TDPC/Pt molar ratio = 0.1), and some preliminary re-
sults on the hydrogenation of CALD. TDPC has a strong affinity to the
surfaces of metal NPs due to sulfur atoms, and gold, platinum and palla-
dium small sized (b3.2 nm) as well as larger sized (37.2 nm) silver NPs
with a very good stability for more than a half year, using TDPC as a pro-
tective agent, have previously been prepared by another process; Pt NPs
for instance, were prepared by reduction of Pt(IV) with potassium
Hydrogenation of α,β-unsaturated aldehydes such as cinnamaldehyde
(CALD), is a challenge of high importance as hydrogenation of the C C
bond leads to hydrocinnamaldehyde (HCALD) used in the flavouring
industry [3] and in the synthesis of pharmaceuticals [4], while hy-
drogenation of the C O bond produces cinnamyl alcohol (CALH)
used in the manufacture of perfumes [5]. A considerable attention
has been focused on heterogeneous hydrogenation by metal NPs with
the aim to remain both activity and selectivity [6–8]. The hydrogenation
of the C C bond is thermodynamically and kinetically favoured over the
C O bond, and thus the reaction leads mainly to HCALD, but however,
several noble metal NPs have been developed for the hydrogenation
⁎
⁎
Corresponding author. Tel.: +30 26510 98425; fax: +30 26510 44831.
Corresponding author. Tel.: +30 210 7273878; fax: +30 210 7273831.
E-mail addresses: dkovala@cc.uoi.gr (D. Kovala-Demertzi), ikostas@eie.gr (I.D. Kostas).
⁎
1566-7367/$ – see front matter © 2013 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.catcom.2013.09.008

58
A. Pournara et al. / Catalysis Communications 43 (2014) 57–60
respectively. The average crystallite size was therefore 6.0 nm. The
similar values found across all Bragg angles indicate minimal strain
broadening effects. It has previously been reported that the diameter
of Pt NPs stabilized with TDPC is decreased by increasing the TDPC/Pt
molar ratio with the largest size being 2.7 nm at TDPC/Pt molar ratio of
0.5 [21]. The NPs formed by a TDPC/Pt molar ratio of 0.1 as presented in
this communication, have 6.0 nm crystallite size, which is in agreement
with the above-mentioned observation, where it has been also sug-
gested that the stabilizer inhibits the growth of NPs producing uniform
particle size patterns [21].
Scheme 1. Preparation of Pt nanoparticles.
bitartrate, and the ratio of TDPC/Pt was 0.5–4.0 [21]. However, metal/
TDPC NPs as catalysts for the hydrogenation of unsaturated aldehydes
have not been reported up to date.
2
. Results and discussion
Scanning electron microscopy (SEM) images of the Pt NPs (Fig. 2)
reveal that they form spherical aggregates, which are approximately
of uniform size. Minimum sizes resolved were in the range of 20–45 nm.
The values obtained by powder diffraction patterns were smaller than the
diameters observed in the SEM images where agglomerates have been
visualized.
2
.1. Synthesis and characterization of platinum nanoparticles
The platinum NPs were prepared from sodium tetrachloroplatinate
using tetraethylammonium chloride to extract PtCl2
−
into the or-
4
ganic phase (Scheme 1). Reduction of Pt(II) was achieved with aque-
ous hydrazine in the presence of TDPC, using a molar ratio TDPC/
Pt = 0.1. On addition of the reducing agent, the organic phase
changed colour from yellow–orange to black–brown, indicating re-
duction of the platinum(II) ions. XRF analysis indicated 78% of Pt.
2.2. Hydrogenation of trans-cinnamaldehyde
Preliminary results on the evaluation of Pt/TDPC NPs as catalysts
in the hydrogenation of CALD are given below (Scheme 2, Table 1).
Hydrogenations were carried out in ethanol with 1.9% NPs/CALD
per weight (Pt/CALD molar ratio = 1:100) at 30 or 60 °C under 30 bar
of hydrogen. In all experiments at a high or quantitative substrate
conversion, the hydrogenation was highly selective towards the
C O bond and the formation of CALH as the major product; HCALD
(in some experiments) and HCALH were also formed. The forma-
tion of acetals, ethers or other side products was less than 1% or
−
1
In the IR spectrum of TDPC, the broad strong band at 2950 cm
is
…
assigned to the ν(OH H) modes due to intermolecular H-bonding
22,23], and the strong band at 1695 cm− corresponding to the vi-
1
[
bration frequency ν(C O) supports the intermolecular hydrogen
…
bonds of the type C O H–O in the uncoordinated TDPC. These
bands are replaced by strong bands at 1626 and 1398 cm− for the
1
ν
asym(COO) and νsym(COO), respectively, in the Pt NPs after depro-
−
1
tonation. The difference Δ[νasym(COO) − νsym(COO)] = 228 cm
1
is close to that found for the monodentate carboxylato group
nonexistence as detected by H NMR and GC–MS. As the tempera-
230–240 cm ). The ν(CS) bands at 661 and 642 cm−1 in the free
−1
ture is increased from 30 to 60 °C, the conversion of CALD is in-
creased at a reaction time of 6 h, while the selectivity for CALH is
slightly decreased as part of CALH is further hydrogenated to
HCALH (entries 3, 2). After 12 h at 30 °C, the conversion was quan-
titative with 83% selectivity for CALH (entry 4).
(
TDPC are replaced by bands with a lower intensity in the Pt NPs,
−
1
which are shifted to a lower frequency at 521 and 478 cm , respec-
tively, suggesting interaction of platinum through sulfur [23,24].
The X-ray powder diffraction pattern of the Pt NPs is shown in
Fig. 1. The three Bragg peaks are assigned to the Pt face-centered
cubic (Fm-3m) phase. Crystallite size evaluation was carried out
using the Scherrer equation where the mean nanocrystal size is de-
rived from the peak width at half-maximum (FWHM). Line profile
analysis was performed using the pseudo-Voigt fitting approxima-
tion. Crystallite sizes according to the measured FWHM values of
each peak (111), (200), (220), were found 6.3, 5.9, and 5.8 nm,
The feasibility of recycling the catalyst at 30 °C was also examined
for three cycles (Fig. 3). After each cycle, the autoclave including
the reaction mixture was cooled with an ice-water cooling bath,
the supernatant solution was decanted and analyzed by GC, GC–MS
1
and H NMR, and the remaining nanocatalyst was dried under vacu-
um and used for the next cycle with only slight losses in activity and
selectivity (entry 4).
Fig. 1. X-ray diffraction patterns of Pt(0) nanoparticles.

A. Pournara et al. / Catalysis Communications 43 (2014) 57–60
59
Fig. 2. SEM images of the of the Pt(0) nanoparticles at (a) low and (b) high magnification.
Scheme 2. Hydrogenation of trans-cinnamaldehyde and some characteristic 1H NMR chemical shifts.
Since catalysis was performed by a Pt/CALD ratio of 1:100 under
0 bar of hydrogen affording TOFs of up to 16 h , the activity should
constraints for C C bond approach to the surface in contrast to C O bond,
and thus could contribute to the selective C O hydrogenation.
–1
3
not be considered as high as some other highly active Pt NPs for
the hydrogenation of α- and β-unsaturated aldehydes [6–8]. For in-
–
1
stance, unsupported Pt/PVP/FeCl
3
NPs afforded TOF of 188 h for
3. Conclusions
CALD hydrogenation under 40 bar of hydrogen; however, both the
activity and the selectivity for CALH dramatically drop down without
the metal cation as a promoter [9,10]. A higher activity compared to our
catalyst is also achieved by several supported NPs, such as Pt/CTA/
In conclusion, platinum nanoparticles as approximately uniform sized
spherical aggregates have been prepared using 3,3´-thiodipropionic acid
(TDPC) as a protective agent. The process displays differences from the
previously reported method for the synthesis of Pt/TDPC nanoparticles,
concerning the starting platinum salt (Pt(II) instead of Pt(IV)), the
reductant (hydrazine instead of potassium bitartrate), and the
TDPC/Pt molar ratio (0.1 instead of 4.0–0.5) offering the possibility
of increasing their crystallite size to 6 nm instead of 1.0–2.7 nm in
the previous report. For the first time such nanoparticles were used
–1
montmorillonite with TOF of 130 h under 5 bar of hydrogen [11],
and Pt–Ru bimetallic NPs on carbon nanotubes with TOFs of up to
–1
3
56 h under 20 bar of hydrogen [20]. However, it is noteworthy to
mention that although the majority of unsupported monometallic NPs
without any promoter exhibit higher selectivity on C C hydrogenation
providing the saturated aldehyde, at a complete substrate conversion
the presented Pt/TDPC NPs display comparable or somewhat lower se-
lectivity for the formation of the unsaturated alcohol as other highly se-
lective systems [9–20]. The good stability of the Pt/TDPC NPs as uniform
sized spherical aggregates with a relatively large size could lead to steric
Table 1
a
Hydrogenation of trans-cinnamaldehyde catalyzed by Pt/TDPC nanoparticles.
Entry
T (°C)
Time (h)
Conversion (%)b
TON/
Selectivity (%)b
CALH/HCALD/HCALH
TOF(h 1)c
–
1
2
3
4
60
60
30
30
12
6
6
N99
96
87
99/8.3
96/16.0
87/14.5
99/8.3
98/8.2
95/7.9
77:–:23
79:6:15
82:7:11
83:–:17 (cycle 1)
83:4:13 (cycle 2)
78:7:15 (cycle 3)
12
N99 (cycle 1)
9
9
8 (cycle 2)
5 (cycle 3)
a
Reaction conditions: Pt/CALD molar ratio = 1:100; EtOH; P(H
Determined by H NMR spectroscopy.
TOF = Moles of CALD transformed per mole of Pt per hour.
2
) = 30 bar.
b
c
1
Fig. 3. Conversion of CALD and selectivity for CALH by the catalyst recycling.

60
A. Pournara et al. / Catalysis Communications 43 (2014) 57–60
as catalysts in the hydrogenation of trans-cinnamaldehyde, an im-
portant reaction of academic and industrial interest, and provided
promising preliminary results. Although the activity is not as high
as several other very reactive catalytic systems for this reaction, the
selectivity towards cinnamyl alcohol was found to be of up to 83%
at complete substrate conversion, comparable or somewhat lower
with the most selective platinum catalysts described in the litera-
ture. The sedimentation of these nanoparticles opened a route to
easy recycling, and thus, at 30 °C the nanocatalyst could be recycled
and reused for three runs with only slight losses in activity and selec-
tivity as an important additional benefit. This first study concerning
the use of monometallic Pt/TDPC nanoparticles on the hydrogena-
tion of cinnamaldehyde provides important information on the cata-
lytic activity of these systems.
References
[
[
1] D. Astruc, Nanoparticles and Catalysis, Wiley-VCH Verlag GmbH & Co, KGaA,
Weinheim, 2008.
2] L.D. Pachón, G. Rothenberg, Appl. Organomet. Chem. 22 (2008) 288–299.
[3] K. Bauer, D. Garbe, Ullman Encyclopedia, 3rd ed., A11, VCH, New York, 1988, p. 141.
[
[
4] A. Müller, J. Bowers, WO Patent Application WO 99/08989, First Chemical Corpora-
tion, 1999.
5] M. Lashdaf, A.O.I. Krause, M. Lindblad, M. Tiitta, T. Venäläinen, Appl. Catal. A 241
(2003) 65–75.
[6] P. Gallezot, D. Richard, Catal. Rev. Sci. Eng. 40 (1998) 81–126.
[7] P. Mäki-Arvela, J. Hájek, T. Salmi, D.Yu. Murzin, Appl. Catal. A 292 (2005) 1–49.
[8] Y. Yuan, S. Yao, M. Wang, S. Lou, N. Yan, Curr. Org. Chem. 17 (2013) 400–413.
[9] W. Yu, H. Liu, M. Liu, Q. Tao, J. Mol. Catal. A Chem. 138 (1999) 273–286.
10] W.W. Yu, H. Liu, J. Mol. Catal. A Chem. 243 (2006) 120–141.
11] D. Manikandan, D. Divakar, T. Sivakumar, Catal. Commun. 8 (2007) 1781–1786.
12] J. Hájek, P. Kačer, V. Hulínský, L. Červený, D.Yu. Murzin, Res. Chem. Intermed. 32
(2006) 795–816.
[
[
[
[13] G. Szöllösi, B. Török, L. Baranyi, M. Bartók, J. Catal. 179 (1998) 619–623.
[14] A.K. Prashar, S. Mayadevi, R.N. Devi, Catal. Commun. 28 (2012) 42–46.
[15] L. Zhao, X.-S. Xu, K.-C. Zhang, X.-H. Yan, Acta Phys. -Chim. Sin. 28 (2012) 923–927.
[16] W.O. Oduro, N. Cailuo, K.M.K. Yu, H. Yang, S.C. Tsang, Phys. Chem. Chem. Phys. 13
(2011) 2590–2602.
Acknowledgments
This work has been co-financed by the European Social Fund — ESF,
the Greek national funds of the NSRF Heraclitus II programme, and the
programme FP7-REGPOT-2009-1 under Grant agreement no. 245866
[
[
17] Y. Li, Z.-G. Li, R.-X. Zhou, J. Mol. Catal. A Chem. 279 (2008) 140–146.
18] H. Vu, F. Gonçalves, R. Philippe, E. Lamouroux, M. Corrias, Y. Kihn, D. Plee, P. Kalck, P.
Serp, J. Catal. 240 (2006) 18–22.
(
ARCADE). We also thank Dr. Christina Papachristodoulou (University
[19] E. Castillejos, P.-J. Debouttière, L. Roiban, A. Solhy, V. Martinez, Y. Kihn, O. Ersen, K.
Philippot, B. Chaudret, P. Serp, Angew. Chem. Int. Ed. 48 (2009) 2529–2533.
of Ioannina, Department of Physics) for XRD and XRF measurements.
[
20] J. Teddy, A. Falqui, A. Corrias, D. Carta, P. Lecante, I. Gerber, P. Serp, J. Catal. 278
2011) 59–70.
[21] Y. Tan, X. Dai, Y. Li, D. Zhu, J. Mater. Chem. 13 (2003) 1069–1075.
(
Appendix A. Supplementary data
[
22] K. Prout, S. Hernández-Cassou, Acta Crystallogr. B Struct. Sci. 38 (1982) 338–340.
[
23] H. Ramsis, A. Ennaciri, J.L. Delarbre, L. Maury, J. Raman Spectrosc. 29 (1998)
Supplementary data to this article can be found online at http://dx.
doi.org/10.1016/j.catcom.2013.09.008.
3
31–341.
[24] J. Wiecek, V. Dokorou, Z. Ciunik, D. Kovala-Demertzi, Polyhedron 28 (2009) 3298–3304.