Highly efficient transfer hydrogenation of carbonyl compounds over supported nickel and palladium nanoparticles
Cite this paper: Vietnam J. Chem., 2021, 59(2), 192-197
Article
DOI: 10.1002/vjch.202000142
Highly efficient transfer hydrogenation of carbonyl compounds over
supported nickel and palladium nanoparticles
Co Thanh Thien*, Nguyen Nhut Minh, Vo Ly Dinh Khang
University of Science, Vietnam National University - Ho Chi Minh City,
227 Nguyen Van Cu, District 5, Ho Chi Minh City 70000, Viet Nam
Submitted August 24, 2020; Accepted November 14, 2020
Abstract
In this work, metal nanoparticles were successfully synthesized through the reduction of metal salts using reducing
agents such as: ethylene glycol (EG) and sodium borohydride (NaBH4). These metal nanoparticles were impregnated
into the supports M-X (M = Ni, Pd; X = Bent, C, Zeolite, and Al2O3) in high yield. The physio-chemical properties of
these catalysts were characterized by various techniques such as UV-Vis spectroscopy, powder X-ray diffraction
(PXRD), Transmission electron microscopy (TEM) and the specific surface area of M-X was evaluated by N2
adsorption isotherm analysis at 77 K. All results corroborated the loading process. Literally, TEM images indicated that
the palladium and nickel nanoparticles size are 6 and 13 nm, respectively. The efficiency of these catalysts was
performed on the transfer hydrogenation of various carbonyl substrates in the presence of potassium hydroxide at
atmosphere pressure. The results showed that both nickel and palladium supported X catalysts exhibited high activities
over 99 % within 60 min in the presence of potassium hydroxide.
Keywords. Nickel, palladium nanoparticles, nanocatalysts, hydrogenation, supported catalysts.
1. INTRODUCTION
On the other hand, immobilization of the
metallic nanoparticles on solid materials has
received a great interest because of their use in
industrial application. Although nanocatalysts serve
as an excellent heterogeneous catalyst, they usually
need an additional support to obtain thermal stability
as well as improve the catalytic activity. Thus,
varieties of materials such as zeolites, aluminum
oxides, aluminosilicates, activated carbon, zinc
oxides, etc. have been used as supports for
Although hydrogenation has been mentioned since
the late 19th century,[1,2] yet it is still attracting the
attention of many scientists by its convenient and
powerful method to access a variety of industrial
applications from fine chemicals to pharmaceuticals
synthesis.[3,4] Usually, transfer hydrogenation was
performed at high temperatures, and long reaction
times, yet the low activity was observed. Recently, a
numbers of reports have shown the hydrogenation
with high efficiency, stability, and easy recovery
when palladium catalyst was used.[5–8] However,
palladium is relatively high-cost metal compared
with other noble metals. The industrial application
of palladium catalysts will be limited due to their
cost. Thus, palladium was significantly replaced by
nickel which is now familiar catalyst in the
hydrogenation of carbonyl compounds. For
examples, Sebakhy et al. was dispersed nickel-
doped aegirine nanocatalysts for the selective
hydrogenation of olefinic molecules at 140200
oC[9]. Whereas Francisco A. and coworkers carried
out the transfer hydrogenation of acetophenone with
excellent activity under nickel nanoparticles at 76 oC
within 24h except the low selectivity was
obtained.[10] Hence, nickel-based catalysts with
excellent activity and selectivity are still necessary.
nanocatalysts.[11-13]
Among
these
materials,
bentonites, zeolites, activated carbon, and aluminum
oxide are widely used as catalyst and support for
quite a lot of reactions as well.
This study focused on the preparation of nickel
and palladium nanoparticles supported on
bentonites, zeolites, activated carbon, and aluminum
oxide. The reason for including the synthesis of
palladium catalyst in this report is that we would like
to compare the activity to the nickel catalysts in the
same manner. Catalytic activity was evaluated via
the transfer hydrogenation of benzaldehyde and
ketone.
2. MATERIALS AND METHODS
2.1. Materials
192 Wiley Online Library © 2021 Vietnam Academy of Science and Technology, Hanoi & Wiley-VCH GmbH
Vietnam Journal of Chemistry
Co Thanh Thien et al.
Unless otherwise noted, all experiments were carried and 1.0 mL solution of KOH 5 % in IPA. H2 gas was
out in air. Reagent grade nickel chloride hexahydrate directly fed to the reaction through Schlenk-lines at
(NiCl2.6H2O, 98 %), palladium (II) chloride (PdCl2, atmospheric pressure within 60 min. The conversion
99 %), aluminum oxide (Al2O3, 99 %), ethylene of the substrate and selectivity of the products were
glycol (EG, 99.5 %) and sodium borohydride recorded through GC and GC/MS analysis. The
(NaBH4, 98 %) were purchased from Merck. Binh experiment was repeated several times to minimize
Thuan bentonite (Bent) and activated carbon were the error.
purchased from the local suppliers. Isopropanol
(IPA, 99 %) was purchased from CHEMSOL and 3. RESULTS AND DISCUSSION
used without further purification.
Palladium nanoparticles were simply prepared via
the reduction of PdCl2 by EG. In reality, the reaction
mixture was turned black within 3h at 140 C after
2.2. Characterization
o
The morphology of catalysts was examined by a addition of EG in the alkaline solution (sodium
scanning electron microscope (SEM, JEOL series hydroxide).[15]
JSM-7401F). Transmission electron microscopy
•Pd *Ni
(TEM) images were collected using FEI Tecnai G2
F20. The X-ray diffraction (XRD) data of all
•
(h)
•
•
•
(g)
•
•
samples were collected in a Bruker D8 powder X-
ray diffractometer with CuKα radiation running at 35
kV/30 mA in the 2θ range 5o75o with a step size of
0.2o/min. Nitrogen adsorption–desorption isotherms
were collected at 77 K using Brunauer–Emmett–
(f)
(e)
•
•
(d)
(c)
*
*
*
*
*
*
Teller
calculation
(BET,
AUTOSORB-1C
(b)
(a)
*
*
Quantachrome). GC/MS analysis was measured by
an Agilent 7890A (HP5 column 30 m0.25 mm,
FID detector). The element analysis was conducted
by atomic emission spectroscopy (AES) on an ICP-
MS 7500 series (Agilent). All the catalytic
experiments were carried out in a multireactor
(Carousel 12+).
20
30
40
50
2q/°
Figure 1: Powder XRD patterns showing (a) Ni-
Bent; (b) Ni-C; (c) Ni-Zeolite; (d) Ni-Al2O3; (e) Pd-
Bent; (f) Pd-C; (g) Pd-Zeolite; (h) Pd-Al2O3
2.3. Preparation
On the other hand, as the previous report,[14]
nickel nanoparticles were prepared by the reduction
of nickel salt (NiCl2.6H2O) using the combination of
sodium borohydride and ethylene glycol as
reduction agents.[16-18] Both paladium and nickel
nanoparticles were successfull anchored into
supports X in high loading yield.
As shown in figure 1 (a-d) the typical powder
XRD patterns of supported nickel nanoparticles, in
which the appearance of the characteristic peaks of
metallic nickel at 2θ were at 44.55o and 51.78o
which are previously reported by Li and
coworkers.[19] Likewise, figure 1 (e-h) described the
XRD patterns of supported palladium nanoparticles
which is corresponding to the 2q values of 40.01 and
46.70o.[20] However, the diffraction signals are rather
weak, it could be explained that the concentration of
metal particles in the catalytic samples was low.
Besides, the XRD patterns of the supports as
shown in the figure 1, the peaks of Zeolite and Al2O3
located at the position of 2θ = 21.90°; 24.21°;
27.43°; 30.25°; 33.21°; 34.53°; 36.17o; 45.50°; and
The nickel and palladium nanoparticles were
prepared in the same process as mentioned in the
previous report.[14] The obtained metal nanoparticles
were directly impregnated into the supports X (X =
Bent, C, Zeolite, and Al2O3 which were calcinated at
120 oC for 7 h) in suitable amount at room
temperature under vacuum. The process was
repeated several times to maximize the content of
metal on the supports. The obtained catalysts were
dried at 60 oC under vacuum for 6h.
2.4. Catalytic test
The catalytic activity of metal nanocatalysts was
simply investigated through the hydrogenation of
carbonyl compounds under liquid phase in the
alkaline solution (potassium hydroxide). The
catalytic test was performed in a 20 cc reactor-tube
o
at 60 C under reflux condensation. In this process,
2.0 mol% of catalyst was added to the hydrogenation
of benzaldehyde (0.005 mol), isopropanol (5.0 mL)
Vietnam Journal of Chemistry
Highly efficient transfer hydrogenation of...
25.90°; 35.43°; 38.04°; 43.61°; 52.92°; 57.77o; and well dispersed. On the other hand, as shown in
66.80o; 68.42o, respectively. Meanwhile, the figure 3, SEM images of both supported nickel and
activated carbon and Bent are amorphous lattice palladium nanoparticles, therein the characteristic
structure leading to the XRD patterns as noise at the surface of M-C and M-Zeolite were found to be
baseline.
smooth and rough (figure 3c, d, g, h), whereas, the
Figure 2 illustrated the TEM images of metal surface of M-Al2O3 and M-Bent displays nearly
nanoparticles as well as the average diameter of the smooth surface characteristic (figure 3a, b, e, f).
catalysts. Namely, figure 2a showed TEM images Literally, in the case of Ni-C catalyst (figure 3c), the
scaled at 50 nm of the nickel nanoparticles, in which surface was covered by big spherical cubic blocks
the average particles diameter are about 13 nm. which could make the specific surface area of the
Meanwhile, figure 2b described that the average catalyst better.
particles size of palladium nanoparticles was 6 nm
5
10
15
20
Diameter (nm)
.
(a)
2
4
6
8
10
Diameter (nm)
(b)
Figure 2: TEM images taken at 50 nm of (a) Ni nanoparticles; (b) Pd nanoparticles
In contrast, the surface of Ni-Al2O3 (Figure 3a) microporosity of X supported metal nanoparticles
contained many of slit-shapes between the pores. was collected from BET measurement, in which the
Likely, the small spherical shapes on the surface of pore size distributions as well as the specific surface
Pd-Zeolite (figure 3h) were found out. It is revealed area of the prepared catalysts are corresponding to
that the metal nanoparticles are well dispersed on the the SEM images. Furthermore, in all cases, the
surface of the supports which have a nearly spherical supported catalysts possessed the specific surface
morphology. More importantly, no metal area lower than the parent supports. That could be
aggregation formation was observed on the SEM explained that almost the metal nanoparticles were
images of catalysts.
anchored into the pores of supports leading to the
In addition, as shown in table 1, the decrement of specific surface area of the catalysts.
Vietnam Journal of Chemistry
Co Thanh Thien et al.
Indeed, in the Table 2, the concentration of the metal alkaline solution.
particles distributed on the supports is quite low
based on atomic emission spectroscopy (AES)
analysis. Especially, in the case of palladium
catalysts, only 0.91 % was obtained with bentonites.
The catalytic activity of transfer hydrogenation
of carbonyl compounds in the liquid phase was
evaluated by addition of 2.0 mol% of M-X catalysts
to the carbonyl substrates and hydrogen gas in the
Table 1: The characteristic surface of catalysts
Catalysts
SBET (m2.g-1)
Zeolite Al2O3
Bent
C
Blank
Ni
Pd
54.082 318.364 64.780 16.990
23.103 128.007 56.408 8.902
15.406 92.556 12.159 2.771
(a)
(b)
(c)
(d)
(e)
(f)
(g)
(h)
Figure 3: SEM micrographs (a) Ni-Al2O3; (b) Ni-Bent; (c) Ni-C; (d) Ni-Zeolite; (e) Pd-Al2O3; (f) Pd-Bent;
(g) Pd-C; (h) Pd-Zeolite
Table 2: Concentration of metal nanoparticles in
supports based on EDX and AES measurements
60 °C within 1 hour.[21] Hence in this study, the
transfer hydrogenation of carbonyl substrates was
performed under similar conditions. It is noted that
all the catalysts gave 100 % selectivity of benzyl
alcohol, therefore it will not mention the selectivity
in this report. Indeed, most of catalysts gave a high
hydrogenate activity within 1h. Namely, M-Bent
gave 93.0 and 95.0 % conversion in cases of Ni and
Pd catalysts, respectively.
Parent supports (X)
Catalysts
(%)
Bent
6.96
0.91
C
Zeolite Al2O3
Ni
Pd
7.78
2.88
6.55
2.10
4.68
1.30
Meanwhile, over 99 % conversion were obtained
in both cases of M-C and M-Zeolite regardless of M
is Ni or Pd. Even though, the parent supports gave
The previous report indicated that the
hydrogenation got the best activity in isopropanol at
Vietnam Journal of Chemistry
Highly efficient transfer hydrogenation of...
moderate activity of up to 52 % in case of Zeolite. could be explained in terms of the concentration of
These could be explained in terms of the palladium in the catalytic samples as well as the
morphological surface of the catalysts as well as the supported carbon which is carbon Vulcan with
concentration of the metal loaded on the supports as nanoparticles size (50 nm) leading to the better
shown in Table 2. It is clear that the catalytic activity conversion compared to our Pd-Zeolite catalyst
of hydrogenation exhibited an excellent conversion (94.7 %). In general, it could be confirmed that the
of carbonyl substrates in base solution.
activity of nickel catalysts increased significant
According to figure 4, it indicated that both M-C based on the concentration of the metal on the
and M-Zeolite catalysts gave the best activity in the supports. Simultaneously, it could replace the
transfer hydrogenation of benzaldehyde. Thus, the palladium catalyst in the furture of catalytic transfer
influence of functional group as well as their hydrogenation.
position on the benzaldehyde was performed based
on M-Zeolite catalysts. Besides, table 3 illustrated
Blank
Ni
that regardless of the position of functional group,
Pd
99.9
metha- or para-substitute, the transfer hydrogenation
exhibited the excellent efficiency. Except the
secondary carbonyl substrate, as shown in entry 5,
even the reaction was carried out at 90 oC within 3 h,
the activity was till low, namely, only 72.7 %
conversion was obtained in the case of Pd-Zeolite as
catalyst. In reality, C. Neelakandeswari and
coworkers carried out the hydrogenation of
99.6
99.6
99.4
100
80
97.3
95.4
95.0
93.0
60
52.8
52.1
51.9
o
benzophenone at 90 C within 3 hrs, 71.4 %
44.5
40
conversion was observed over nickel nanoparticles
supported on aluminosilicate.[22] However, in the
previous study published elsewhere,[21] 99 %
conversion of p-chlorobenzaldehyde was obtained in
the presence of 15 %Pd-C as catalyst (entry 2). It
Bent
C
Zeolit
Al2O3
--
Figure 4: The activity of transfer hydrogenation of
benzaldehyde over M-X catalysts
Table 3: Conversion of transfer hydrogenation of the carbonyl substrates over catalysts
Conversion (%)
Entry
Substrates
Products*
Ni-
Pd-
Zeolite
Zeolite
1
2
99.4
90.1
99.6
94.7
CHO
CHO
CH2OH
CH2OH
Cl
Cl
O2N
O2N
3
86.9
92.1
CHO
CHO
CH2OH
CH2OH
4
H3CO
H3CO
H3CO
H3CO
89.5
75.8
90.8
72.7
O
OH
5**
CH3
CH3
*The absolute selectivity of alcohol products were observed in all cases.
**Reaction was carried out at 90 oC within 3 h.
4. CONCLUSIONS
synthesized.
All
the
physio-chemical
characterization of the catalysts was defined in
In summary, the catalysts M-X (M = Ni, Pd; X = detail. In which TEM image and XRD illustrated
Bent, C, Zeolite, Al2O3) were successfully that metal particles size was around 6 and 13 nm in
Vietnam Journal of Chemistry
Co Thanh Thien et al.
nanoparticles in hydrogen-transfer reductions:
Characterisation and nature of the catalyst, Appl.
Catal. A Gen., 2010, 378(1), 42-51.
the case of Pd and Ni, respectively. These
incorporated as M0 inside X. Furthermore, the
catalytic test indicated that almost the supported
nanocatalysts exhibited high catalytic activities in
the hydrogenation of benzaldehyde, especially with
Ni-Zeolite catalyst, the productivity conversion
acquired 99.4 % within 60 min at 60 C as well as
75.8 % conversion was observed in the transfer
hydrogenation of ketone substrate.
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Acknowledgments. The authors would like to thank
Vietnam National University-Ho Chi Minh City for
financial support under grant number C2019-18-13.
14. T. T. Co, T. K. A. Tran, T. H. L. Doan, T. D. Diep.
Preparation of Nickel Nanocatalysts and Application
to the Hydrodechlorination of 3-Chlorophenol under
Liquid Phase, J. Chem., 2021, 2021(8580754), 1-9.
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Corresponding author: Co Thanh Thien
Department of Physical Chemistry
University of Science, VNU Ho Chi Minh City, 227 Nguyen Van Cu, District 5
Ho Chi Minh City 70000, Vietnam; E-mail: ctthien@hcmus.edu.vn.
6 trang
18/04/2022
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