Rh/Cu2O nanoparticles: Synthesis, characterization and catalytic application as a heterogeneous catalyst in hydroformylation reaction

Article abstract of DOI:10.1016/j.poly.2016.08.026

In this work, we report a rapid protocol for the synthesis of Rh/Cu₂O nanoparticles (Rh/Cu₂O NPs) in aqueous medium using microwave route. The microwave energy acts as driving force in synthesis which makes the process economical. The obtained nanoparticles were characterized with the help of FEG-SEM, TEM, HRTEM, EDS, XRD, FT-IR and ICP-AES techniques. The prepared Rh/Cu₂O nanoparticles gave 100% yield of uniform spherical morphology. This is a simple, inexpensive and time saving protocol for synthesis of Rh/Cu₂O nanoparticles than conventional methods. Furthermore, we showed the catalytic application of Rh/Cu₂O nanoparticles in hydroformylation reaction for the conversion of 1-hexene to 1-hexanal at mild reaction conditions such as Rh/Cu₂O NPs (10 mg), 35 bar pressure of H₂/CO at 360 K. The reaction provides 99% conversion and high selectivity (>90%) toward aldehydes with branched aldehyde is a major product. Notably the reaction does not require the any phosphine ligand source, low catalyst loading, low temperature with major advantage of catalyst recyclability.

Full text of DOI:10.1016/j.poly.2016.08.026

Accepted Manuscript
Rh/Cu2O nanoparticles: Synthesis, characterization and catalytic application as
a heterogeneous catalyst in hydroformylation reaction
Samadhan A. Jagtap, Manohar A. Bhosale, Takehiko Sasaki, Bhalchandra M.
Bhanage
PII:
S0277-5387(16)30385-0
DOI:
http://dx.doi.org/10.1016/j.poly.2016.08.026
POLY 12163
Reference:
Polyhedron
To appear in:
Received Date:
Revised Date:
Accepted Date:
1 May 2016
20 August 2016
22 August 2016
Please cite this article as: S.A. Jagtap, M.A. Bhosale, T. Sasaki, B.M. Bhanage, Rh/Cu2O nanoparticles: Synthesis,
characterization and catalytic application as a heterogeneous catalyst in hydroformylation reaction, Polyhedron
(2016), doi: http://dx.doi.org/10.1016/j.poly.2016.08.026
This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers
we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and
review of the resulting proof before it is published in its final form. Please note that during the production process
errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

Rh/Cu2O nanoparticles: Synthesis, characterization and catalytic application as a
heterogeneous catalyst in hydroformylation reaction
Samadhan A. Jagtapa,1, Manohar A. Bhosalea,1, Takehiko Sasakib and Bhalchandra M.
Bhanagea*
a Department of Chemistry, Institute of Chemical Technology, Matunga, Mumbai 400019,
India.
b Department of Complexity Science and Engineering, Graduate School of Frontier Sciences,
The University of Tokyo, 5-1-5, Kashiwanoha, Kashiwa, Chiba 277-8561, Japan.
*Corresponding author: Tel.: +91 22 33612603; Fax: +91 22 33611020.
Email: bm.bhanage@ictmumbai.edu.in, bm.bhanage@gmail.com
1Samadhan A. Jagtap and Manohar A. Bhosale equally contribute to the work.
Abstract
In this work, we report a rapid protocol for the synthesis of Rh/Cu2O nanoparticles
(Rh/Cu2O NPs) in aqueous medium using microwave route. The microwave energy acts as
driving force in synthesis which makes the process economical. The obtained nanoparticles
were characterized with the help of FEG-SEM, TEM, HRTEM, EDS, XRD, FT-IR and ICP-
AES techniques. The prepared Rh/Cu2O nanoparticles gave 100% yield of uniform spherical
morphology. This is a simple, inexpensive and time saving protocol for synthesis of Rh/Cu2O
nanoparticles than conventional methods. Furthermore, we showed the catalytic application
of Rh/Cu2O nanoparticles in hydroformylation reaction for the conversion of 1-hexene to 1-
1

hexanal at mild reaction conditions such as Rh/Cu2O NPs (10 mg), 35 bar pressure of H2/CO
at 360 K. The reaction provides 99% conversion and high selectivity (>90%) towards
aldehydes with branched aldehyde is a major product. Notably the reaction does not require
the any phosphine ligand source, low catalyst loading, low temperature with major advantage
of catalyst recyclability.
Keywords - Rh/Cu2O; nanoparticles; microwave; heterogeneous; hydroformylation reaction.
1. Introduction
Now a days, the synthesis of shape selective nano and microstructures has received
significant attention due to their unique structures and its different properties such as, optical,
catalytic, electrical, magnetic and thermal which have widespread applications [1,2]. Many
industrial solid catalysts embrace of highly dispersed metal nanoparticles supported on metal
oxides [3], and this type of heterogeneous catalysts continue to attract a huge amount of
academic interest [4–8] in particular for fine chemicals synthesis and selective hydrogenation
and oxidation reactions [9,10]. However, most of the industrial catalysts currently used
comprise of metal particles in a large size range and in a range of morphologies, which
difficult the control of the active sites over the catalyst surfaces and rationalization of
catalytic results. Therefore, method to set up well-defined supported metal nanoparticle
catalysts are highly desired to boost our understanding of the morphological and
compositional characteristics that influence catalytic activities, the real active sites and the
role of metal–support interactions.
In this protocol the microwave energy was used for the synthesis of Rh/Cu2O NPs.
The microwave assisted synthesis of nanoparticles are gaining a lot of interest because of its
2

several advantages like rapidity, efficient and volumetric heating, selectivity, homogeneity,
fast kinetics, less energy requirements, ease of operation, compactness of equipments and
environmentally benign protocols as there are no by-products formed [11]. The efficiency of
the microwave heating is given by following equation:
P = cE2ƒε″
Wherein, P is microwave power dissipation per unit volume in solvent, c is radiation velocity,
E is electric field in the material, ƒ is radiation frequency and ε″ is the dielectric loss constant.
ε″ is the most significant parameter that resolves the ability of the a material to heat in the
microwave field. We have showed the importance of microwave assisted method for
synthesis of various metal and metal oxide nanoparticles [12‒14].
As synthesized Rh/Cu2O NPs used for the hydroformylation reaction of olefins. The
aqueous biphasic hydroformylation of propene, using Ruhrchemie/Rhone Poulenc (RCH/RP)
process has been widely used to produce n-butanal. A thermo regulated phase transfer
(TRPT) Rh(I) complex catalyst has been used to improve this catalytic system [15].
Moreover, Bonnemann et al. [16] have proved the in situ formation of Rh colloids when such
a catalyst was applied to the aqueous biphasic hydroformylation of 1-octene. Dupont et al.
[17] have reported the hydroformylation of olefins in neat conditions using unmodified or
Xantphos modified Rh(0) nanoparticles, prepared by simple hydrogenation reduction of the
chloride salts in imidazolium ionic liquids. They have shown that the particle size has a
strong influence on the selectivity of the hydroformylation. Researchers demonstrated the
hydroformylation of 1-hexene and studied Rh/ZnO and Rh/SiO2 catalysts [18,19], but these
protocols having some drawbacks such as use of moisture sensitive phospine ligand and high
catalyst loading. To overcome these drawbacks there is need to develop simple and economic
protocol for the Hydroformylation reaction.
3

Hydroformylation is one of the most important homogeneous catalytic industrial
process by use of transition metal for the production of aldehydes from alkenes using syngas
(CO/H2) [20]. The reaction was first discovered by Otto Roelen in 1938 throughout
investigations on the formation of oxygenated products in cobalt-catalyzed Fisher–Tropsch
reactions [21,22]. The great challenges in hydroformylation reaction are difficulties in
controlling the selectivity of products, the separation and recycling of the catalysts from the
reaction system. All current commercial hydroformylation reactions are based on
homogeneous catalysts, typically using rhodium complexes, which have replaced with cobalt
derivatives due to their superior activity [23,24]. These processes as well use phosphine or
phosphite ligands to boost the regioselectivity towards the expected linear or branched
aldehydes [25-28]. While homogeneous rhodium catalysts provides high conversion and
selectivity for desired product in less reaction times, they suffer from the troubles of
separating the catalyst from the reaction mixture and catalyst recycling [29].
Thus the development of a heterogeneous catalyst is highly desirable which will avoid
the loss due to high cost of rhodium metal. Rhodium based catalyst can be classified into two
main categories i.e. supported heterogeneous catalysts and dispersed homogeneous rhodium
catalysts. The intermediate class exist in between homogeneous and heterogeneous, is called
pseudohomogeneous or semi-heterogeneous nanocatalysts [30]. Our catalyst is supported
heterogeneous catalyst advantageous are recyclable, simple filtration of reaction mixture and
catalyst.
In this work, we report the heterogeneous rhodium nanoparticles supported on copper
oxide as catalyst for regioselective hydroformylation of olefins. There are so many reports on
the hydroformylation of olefins selectively to the linear aldehydes. Very few articles are
reports on the selectively branched aldehydes which is very challenging task. Thus, we
focused on the synthesis of selectively branched aldehydes.
4

2. Experimental Section
Materials: The rhodium trichloride monohydrate (RhCl3.H2O, 99.9% pure) was procured
from Parekh Industries Pvt. Ltd., India. The copper acetate (98.0% pure) procured from S. D.
Fine Chemicals Ltd., benzyl alcohol (99.0% pure) and A. R. grade citric acid monohydrate
were purchased from Spectrochem Pvt. Ltd., India. All the other L. R. grade solvents
(toluene, xylene, THF, DMF, dioxane) were purchased from commercially available
suppliers Mumbai, India and used without further purification. The Cu2O nanoparticles were
synthesized from previous report.
Synthesis of Rh/Cu2O NPs: Synthesis of uniform spherical Rh/Cu2O NPs was carried out by
two step process by microwave irradiation in domestic microwave oven (LG intellowave)
operating at 100% power of 800 watt (W) and frequency of 2.45 GHz. In first step of
experimental procedure, the Cu2O NPs was synthesized from reported procedure [31]. A
mixture of copper acetate (0.2 g) and benzyl alcohol (10 mL) was transferred to 100 mL glass
beaker and kept inside a microwave oven for 3 min at 600 W for microwave irradiation with
on–off mode having time interval of 30 s. After completion of reaction, the color of the
reaction mixture changes blue to dark red indicating formation of cuprous oxide
nanoparticles. The product was separated by centrifugation and dried in oven. In second step,
a mixture of Cu2O NPs (20 mg) and citric acid (24 mg) with 2 mL water mixed, then 2 mL of
RhCl3 (0.02 M) was added in a 50 mL glass beaker and placed in microwave oven for 2 min
at 600 watt (W) electrical powers with on/off mode. During microwave heating, the
formation of black coloured precipitate at the bottom of reaction flask was observed
indicating formation of Rh/Cu2O materials. The obtained precipitate was then washed with
distilled water and absolute ethanol several times and dried under vacuum at 60 °C for 1 h.
Characterization of Rh/Cu2O NPs: The surface morphology of as synthesized Rh/Cu2O
NPs was characterized by field emission gun-scanning electron microscopy (FEG-SEM)
5

analysis was done by Tescan MIRA 3 model with secondary electron (SE) detector between
10.0 kV to 20.0 kV and transmission electron microscopy (TEM) using Philips CM-200,
operating voltage at 120 kV. The energy dispersive X-ray spectrum (EDS) was recorded by
using Oxford instrument (model 51-ADD0007). Fourier transform infrared spectroscopy (FT-
IR) was measured on Brucker Perkin Elmer-100 spectrometer.
3. Results and Discussion
The surface morphology and elemental composition of synthesized Cu2O and
Rh/Cu2O NPs was characterized with the various analytical techniques. The as synthesized
Cu2O NPs was characterized by TEM, HRTEM, XRD and EDS analysis. The TEM and
HRTEM images show the formation of spherical morphology of Cu2O NPs (Fig. 1a and 1b).
The XRD shows the diffraction peaks at 2θ values of 29.4o, 36.3o, 61.3o, 73.5o, 77.3o
corresponds to the (110), (111), (200), (220), (311), (222) phases for Cu2O NPs (Fig. 1c).
EDS spectrum shows the copper and oxygen elements only and no other impurities are
present (Fig. 1d).
Fig. 1 (a) TEM (b) HRTEM (c) XRD and (d) EDS analysis of Cu2O NPs.
6

The surface morphology of Rh/Cu2O NPs was carried out using TEM analysis by
dispersing as synthesized Rh/Cu2O powder in ethanol, which was then subjected to a
sonication bath for 5 min. A drop from the resulting slurry was deposited on a copper grid. A
TEM micrograph of the Rh/Cu2O nanocatalyst show the formation of spherical and well
dispersed particles having size range is from 1 µm to 2 µm (Fig. 2). The morphology of
Rh/Cu2O NPs was also checked by FEG-SEM analysis (Fig. 3). The low magnification FEG-
SEM images (Fig. 3a,b,c) and high magnification FEG-SEM image (Fig. 3d) of show the
formation of uniform size and shape of spherical particles with good dispersion. Some
particles show the rough surface with extra growth of particles which is due to the high
microwave energy. The microwave energy is act as a driving force and responsible to build
the morphology of Rh/Cu2O NPs. The morphology observed in TEM analysis is good
agreement with the morphology obtained in FEG-SEM results.
Fig. 2 TEM images of Rh/Cu2O NPs.
7

Fig. 3 FEG-SEM images of Rh/Cu2O NPs.
The EDS analysis of Rh/Cu2O NPs was carried out to determine the elemental
composition of the material. EDS spectrum (Fig. 4) show the presence of rhodium, copper
and oxygen elements only and no other peak of impurities are observed. It confirms the purity
of Rh/Cu2O nanocatalyst. To check the percentage of different metals and distribution of Rh
on the surface of the Cu2O, the energy dispersive X-ray elemental composition mapping
analysis was carried out (Fig. 5). It displays oxygen (Fig. 5b, red), copper (Fig. 5c, blue) and
rhodium (Fig. 5d, green) species coexist in the material. It confirms the uniform distribution
of Rh on the Cu2O surface. The wt% of Rh present in the material was calculated from
average value of EDS analysis. The 8.5 wt% of Rh was observed in the synthesized Rh/Cu2O
material.
8

Fig. 4 EDS spectrum of Rh/Cu2O NPs.
Fig. 5 EDS elemental composition mapping analysis (a) SEM image (b) oxygen (red)
(c) copper (blue) and (d) rhodium (green) of Rh/Cu2O NPs.
In FT-IR spectrum of Rh/Cu2O NPs, the sharp peak at 514 cm-1 indicates the presence
of Cu–O stretching band of Cu2O NPs. The peak observed at 3443 cm-1 due to the moisture
absorbed by the material (Fig. 6). The elemental composition and chemical state of the
Rh/Cu2O material was analyzed by XPS (Fig. 7). The survey XPS spectra (Fig. 7a) of the
Rh/Cu2O material show the peaks of Rh, Cu and O confirming the Rh is uniformly anchored
9

on the Cu2O surface and also supporting the results similar to those of EDS (Fig. 4) and EDS
elemental composition mapping (Fig. 5). No other hetero-element including chlorine was
detected, implying no by-products or un-reacted precursors are present in the nanomaterials.
The states of each element can be more clearly identified through high-resolution XPS
analysis. Fig. 7b displays the high-resolution Rh 3d core level XPS spectrum. The spectrum
shows a low energy Rh 3d5/2 band at 307.4 eV, and a high energy Rh 3d3/2 band centred at
312.3 eV. As the Rh 3d5/2 and Rh 3d3/2 peaks for rhodium metal lie at 307.2 and 312.0 eV,
respectively, this indicates that Rh is also in the zero-valent state [32]. The high resolution
XPS spectrum for Cu2p region shows the peaks at 932.2 eV and 952.7 eV correspond to the
Cu 2p3/2 and Cu 2p1/2 respectively along with a series of shakeup satellites peaks at higher
binding energies (Fig. 7c) [33].These photoelectonic signals confirms the Cu+1 state. The
high resolution XPS spectrum for O 1s arises at 531.5 eV, attributed to presence of Cu2O
(Fig. 7d).
Fig. 6 FT-IR spectrum of Rh/Cu2O NPs.
10

Fig. 7 XPS analysis (a) survey spectrum (b) Rh 3d region (c) Cu 2p region and (d) O
1s region of Rh/ Cu2O NPs.
4. Evaluation of catalytic activity of Rh/Cu2O NPs
An optimization study of reaction conditions was carried out using hydroformylation
of 1-hexene as a model reaction as shown in Scheme 1. The various reaction parameters such
as catalyst loading, the effect of syngas (CO/H2) pressure, time, temperature and solvents
were studied for the regioselective hydroformylation of 1-hexene and the results are
summarized in Table 1 and 2. Initially we studied the effect of catalyst loading for the model
reaction (Table 1, entries 1-7). The 2 mg of catalyst provides 75% conversion with selectivity
of linear and branched aldehydes is 40% and 60% respectively along with 10% of reduction
product (Table 1, entry1). With an increase in the catalyst loading upto 5 mg, the conversion
increases to 85% and selectivity ratio of linear(n)/branched(b) was 38/62 with 9% reduction
(Table 1, entry 2). The conversion (90%) and selectivity of desired aldehydes n/b (30%/70%)
was high at the 10 mg of catalyst loading (Table 1, entry 3). The conversion was very high up
Table 1 Effect of catalyst loading of hydroformylation of 1-hexenea
11

Entry Catalyst Conversion Aldehyde (%)b
Reduction
(%)b
(mg)
2
(%)b
Linear (n)
Branched (b)
1
75
40
60
10
2
5
89
97
98
100
-
38
30
32
40
-
62
70
68
60
-
9
3
10
15
20
15
17.8
11
14
19
-
4
5
6c
7d
62
60
40
21
a Reaction conditions: olefin (1 mmol), toluene (10 mL), CO:H2 = 1:1 (50 bar), Rh/Cu2O NPs
(8.5 wt% Rh), 24 h, 100 ºC.
b Conversion and selectivity (linear/branched) were determined by GC analysis.
c The reaction using only Cu2O i.e. without rhodium metal.
d The reaction using only RhCl3.H2O.
to 98-100% but the selectivity decreases with increasing catalyst loading of 15-20 mg (Table
1, entries 4-5). The formation of products (aldehydes) was not observed with only Cu2O NPs
in absence of the rhodium metal (Table 1, entry 6). It indicates that the rhodium catalyst is
solely responsible for the hydroformylation reaction. The reaction also done only with the
rhodium trichloride monohydrate in absence of Cu2O NPs, the less conversion (62%) with
selectivity of aldehydes linear (60%) and branched (40%) was observed as compared to
Rh/Cu2O NPs. It concludes that Rh/Cu2O nanocatalyst provides the high surface area for the
12

reaction and also assists for the high conversion and excellent selectivity in hydroformylation
reaction.
Moreover, in order to increase the conversion of 1-hexene and selectivity of desired
aldehyde, we investigated the effect of syngas pressure on the model reaction at 100 ◦C for 24
h in toluene as solvent. As we increase the pressure of syngas (CO/H2) the conversion
increase up to 99% but selectivity of desired aldehydes decreases (Table 2, entries 1-5). The
15 bar of syngas pressure reaction provides less conversion (10%) and selectivity (80%) of
total aldehydes with ratio of linear to branched aldehydes is 0.68 (Table 2, entry 1). Increase
in the syngas pressure of 25 bar, the slightly increase in conversion (24%) and selectivity
(81%) of total aldehydes (Table 2 entry 2). It was noted that, the better conversion (98%) of
1-hexene and selectivity (90%) of aldehydes was better at 35 bar pressure of syngas (Table 2,
entry 4). These results clearly indicate that, 35 bar of syngas (CO/H2) pressure was optimum
for this organic transformation. At 40 bar of syngas (CO/H2) pressure, 99% conversion of 1-
hexene takes place but selectivity of branched aldehydes was decreased (Table 2, entry 5).
Next, we investigated that the effect of time, temperature and solvent for the effective
evolution of the reaction. As we decrease the reaction time from 20 h to 8 h the the reduction
product decreases from 12% to 6% but conversion decreases at 8 h of reaction time (Table 2,
entries 6-9). The most favourable reaction time could be reduced to 10 h which provides 96%
conversion (Table 2, entry 8). Decrease in the reaction time within 10 h lead to a considerable
decrease in the conversion and selectivity of product (Table 2, entry 9). Further, we checked
Table 2 Optimization study for hydroformylation of 1-hexenea.
Entry
CO:H2 (1:1) Time Temp.
(oC)
Solvent
Conv. n/b
(%)b
Reduction
(bar)
Effect of pressure
(h)
ratio
1
2
3
15
25
30
24
24
24
100
100
100
Toluene
Toluene
Toluene
10
24
70
0.68
0.66
0.47
20
19
12
13

4
35
24
100
Toluene 98
0.38
10
5
40
24
100
Toluene
99
0.42
10
Effect of time
6
7
8
9
35
35
35
35
20
15
10
8
100
100
100
100
Toluene
Toluene
99
98
0.45
0.42
0.40
0.51
12
10
9
Toluene 96
Toluene
80
6
Effect of temperature
10
11
12
13
14
35
35
35
35
35
10
10
10
10
10
120
110
90
Toluene
Toluene
100
100
0.40
0.40
0.39
0.42
0.51
12
10
8
Toluene 99
80
Toluene
Toluene
97
95
8
70
7
Effect of solvent
15
16
17
18
35
35
35
35
10
10
10
10
90
90
90
90
Xylene
THF
98
92
90
91
0.45
0.51
0.62
0.55
12
18
15
11
DMF
Dioxane
a Reaction conditions: 1-hexene (1 mmol), Rh/Cu2O NPs (10 mg), Solvent (10 mL), n- linear
aldehydes, b- branched aldehydes.
b Conversion and selectivity (linear/branched) were determined by GC analysis.
the effect of temperature on the reaction and it was observed that the conversion decreased
with reducing the reaction temperature from 120 ºC to 70 ºC (Table 2, entries 10-14). But a
gradual increase in the selectivity of aldehydes was observed. The temperature of 90 ºC was
optimum for this reaction which affords the better conversion (99%) and high selectivity
(92%) of aldehydes (Table 2, entry 12). Moreover, the effects of different solvents were
investigated for the reaction. Various non polar and polar organic solvents such as toluene,
xylene, THF, DMF, 1,4-dioxane were screened (Table 2, entries 12, 15–18). Among them,
toluene was found to be a best solvent which provided high conversion (99%) and an
excellent selectivity (92%) of aldehydes (Table 2, entry 12).
Table 3 the substrate study for hydroformylation of olefinsa.
14

Entry
Olefins
Conv.
(%)b
Aldehyde Reduction n:b ratio
(%)c
(%)b
(%)b
1
2
3
4
5
6
7
1-hexene
99
90
92
93
89
98
96
4
28:72
1-octene
92
93
91
92
91
92
8
7
9
8
9
8
35:65
Styrene
33:67
2-chlorostyrene
4-methyl styrene
Allyl benzene
68:32
35:65
4:32:64
5:29:65
4-methoxyallylbenzene 96
a Reaction conditions: olefin (1 mmol), Rh/Cu2O NPs (10 mg), toluene (10 mL), CO:H2 = 1:1
(35 bar), 90 °C, 10 h, 600 rpm.
b Conversion and selectivity (linear/branched) were determined by GC analysis.
c Chemo-selectivity for aldehyde product to total reaction product.
The conversion of the olefins to the aldehydes during the hydroformylation reaction is
presented in Table 3. Aldehydes are the major product was observed in all reactions with
trace quantity of hydrogenation products. The model reaction of 1-hexene under optimized
reaction conditions provided an excellent conversion and very good selectivity (96%) toward
branched aldehyde (Table 3, entry 1). Moreover, linear aliphatic alkenes such as 1-octene
gave a remarkable yield of the desired product as well (Table 3, entry 2). It was observed that
branched aldehyde as major product as compared to linear aldehyde in case of styrene (Table
3 , entry 3). But it is reverse in case of 2-chlorostyrene, it provides linear aldehyde as a major
product due to electron cloud present on chlorine atom (Table 3, entry 4). Substituted styrene
15

like p-Me-styrene was found to react easily, deliver good yields and selectivity of the
corresponding product (Table 3, entry 5). Allylbenzene and 4-methoxy allylbenzene offered
good selectivity for aldehyde formation with almost 100% conversion. As these olefins
having an isolated olefinic C-C bond form a phenyl ring they gave three structural aldehydes
due to isomerization reaction (Table 3, entries 6 and 7).
5. Recyclability Study
The reusability of Rh/Cu2O NPs catalyst is a great advantage in decreasing
environmental pollution and cost reduction in process chemistry. The recyclability study of
Rh/Cu2O catalyst was examined for the synthesis of aldehydes through hydroformylation of
1-hexene under the optimized reaction conditions. After completion of reaction, the reactor
was cooled to room temperature and remaining syngas (CO/H2) vented out carefully. The
catalyst was recovered by simple filtration and then washed three times with Toluene and
finally by methanol to remove traces of organic contents. The resulting catalyst was dried
under vacuum for 5 h and could be recycled up to four consecutive cycles (Table 4). With the
Rh/Cu2O, some leaching was also observed during the first run, and it is feasible that to some
extent, homogeneous catalysis can take place at this stage. However, practically no leaching
was observed during the fourth recycle run, but still, the activity remained a reasonably high
92 % conversion (Table 4 entry 4). At this point, catalysis is dominated by heterogeneous
reactions. ICP-AES analysis showed that the loss of Rh decreases with increasing recycling
number. The average leaching of Rh was 1.1%. Rh nanoparticles are an active, stable, and
recyclable catalyst for olefin hydroformylation in heterogeneous catalytic systems. The
catalyst can be recovered readily by simple filtration and reused, without evident loss of
activity after four catalytic cycles. The recycled Rh/Cu2O nanocatalyst was characterized by
TEM, FEG-SEM and EDS analysis (ESI Fig. S1 and S2). The TEM and FEG-SEM analysis
of Rh/Cu2O nanocatalyst after 4th recycle shows the agglomeration and disturbance in the
16

surface morphology of nanoparticles (ESI Fig. S1a and b). The EDS analysis of Rh/Cu2O
nanocatalyst after the 4th recycle, indicate the presence of rhodium, copper and oxygen as a
elemental composition in the material (ESI Fig. S2).
Table 4 Reusability study of Rh/Cu2O NPs catalysta
Entry
Run
1
Conversion (%)b
1
2
3
4
99
96
94
92
2
3
4
a Reaction conditions: olefin (1 mmol), Rh/Cu2O NPs (10 mg), toluene (10 mL), CO:H2 = 1:1
(35 bar), 90 °C, 10 h, 600 rpm.
b Conversion were determined by GC analysis.
4. Conclusions
In conclusion, a simple and efficient synthesis of uniform spherical Rh/Cu2O NPs via
microwave route in aqueous medium has been developed. The synthesized Rh/Cu2O NPs
showed excellent catalytic applicability for C-C bond formation in hydroformylation
reaction. Under the optimized reaction conditions various olefins furnished good to excellent
yield of the respective aldehyde products. Simple starting materials, less reaction time,
phosphine-free and mild conditions add an additional credit to the present study. The
presented reaction demonstrates the easy recovery of Rh/Cu2O nanocatalyst and the
successful reuse of the catalyst until the fourth run without loss in activity and selectivity.
The protocol would be practical for use as an economical synthetic method and offers an
alternative synthetic strategy for the practical construction of aldehyde derivatives.
Acknowledgements
17

The Authors SAJ and MAB thankful to the Council of Scientific and Industrial
Research (CSIR) India, for providing Senior Research Fellowship (SRF) and also the
financial assistance for this work by Department of Science and Technology (DST), India
under Nano Mission Project No. SR/NM/NS-1097/2011 is gratefully acknowledged. We are
thankful to Prof. Takehiko Sasaki from The University of Tokyo, Kashiwa campus, Japan for
providing XPS analysis.
References
[1] C.H. Kuo, M.H. Huang, Nano Today 5 (2010) 106.
[2] R.G. Chaudhari, S. Paria, Chem. Rev. 112 (2012) 2373.
[3] G. Ertl, H. Knozinger, F. Schuth, J. Weitkamp, Handbook of Heterogeneous Catalysis,
second ed. Wiley–VCH, Weinheim, 2008.
[4] A.T. Bell, Science 299 (2003) 1688.
[5] R.M. Rioux, H. Song, M. Grass, S. Habas, K. Niesz, J.D. Hoefelmeyer, P. Yang, G.A.
Somorjai, Top Catal. 39 (2006) 167.
[6] A. Roucoux, J. Schulz, H. Patin, Chem. Rev. 102 (2002) 3757.
[7] G.A. Somorjai, R.M. Rioux, Catal. Today 100 (2005) 201.
[8] N. Tian, Z.Y. Zhou, S.G. Sun, Y. Ding, Z.L. Wang, Science 316 (2007) 732.
[9] J.A. Anderson, M.G. Fernandez, A.A. Martinez, Supported Metals in Catalysis; Imperial
College Press: London, 2005.
[10] N. Dimitratos, J.A. Lopez-Sanchez, G.J. Hutchings, Chem. Sci. 3 (2012) 20.
[11] M.A. Bhosale, B.M. Bhanage, RSC Adv. 4 (2014) 15122.
[12] M.A. Bhosale, T. Sasaki, B.M. Bhanage, Catal. Sci. Technol. 4 (2014) 4274.
[13] M.A. Bhosale, B.M. Bhanage, Adv. Powder technol. 26 (2015) 422.
[14] M.A. Bhosale, D.R. Chenna, J.P. Ahire, B.M. Bhanage, RSC Adv., 2015, 5, 52817.
[15] Z.L. Jin, X.L. Zheng, B. Fell, J. Mol. Catal. A: Chem.116 (1997) 55.
18

[16] F. Wen, H. Bonnemann, J. Jiang, D. Lu, Y. Wang, Z. Jin, Appl. Organomet. Chem. 19
(2005) 81.
[17] A.J. Bruss, M.A. Gelesky, G. Machado, J. Dupont, J. Mol. Catal. A: Chem. 252 (2006)
212.
[18] M.L. Kontkanen, M. Tuikka, N.M. Kinnunen, S. Suvanto, M. Haukka, Catalysts 3
(2013) 324.
[19] H. Zhu, Y. Ding, L. Yan, Y. Lu, C. Li, X. Bao, L. Lin, Chem. Lett. 33 (2004) 630.
[20] R. Franke, D. Selent, A. Borner, Chem. Rev. 112 (2012) 5675.
[21] M. Vilches-Herrera, L. Domke, A. Borner, ACS Catal., 4 (2014) 1706.
[22] P.W.N.M. van Leeuwen, C. Claver, Appl. Organometal. Chem. 15 (2001) 315.
[23] M. Beller, B. Cornils, C.D. Frohning, C.W.Kohlpaintner, J. Mol. Catal. A: Chem. 104
(1995) 17.
[24] S.H. Chikkali, J.I. Vlugt, J.N.H. Reek, Coord. Chem. Rev. 262 (2014) 1.
[25] P.H. Fernandez, B.J. Benet, F.A. Vidal, Org. Lett. 15 (2013) 3634.
[26] F. Doro, J.N.H. Reek, P.W.N.M. van Leeuwen, Organometallics 29 (2010) 4440.
[27] C. Chen, Y. Qiao, H. Geng, X. Zhang, Org. Lett. 15 (2013) 1048.
[28] A.A. Dabbawala, H.C. Bajaj, R.V. Jasra. J. Mol. Catal. A: Chem. 302 (2009) 97.
[29] C. Hou, G. Zhao, Y. Ji, Z. Niu, D. Wang, Y. Li, Nano. Res. 7 (2014) 1364.
[30] M. Guerrero, N.T. Than Chau, S. Noel, A. Denicourt-Nowicki, F. Hapiot, A. Roucoux,
E. Monflier, K. Philippot. Curr. Org. Chem. 17 (2013) 364.
[31] M.A. Bhosale, K.D. Bhatte, B.M. Bhanage, Powder Technol. 235 (2013) 516.
[32] J.F. Moulder, W.F. Stickle, P.E. Sobol, K.D. Bomben, Handbook of X-ray Photoelectron
Spectroscopy (Ed.: J. Chastain), Perkin-Elmer Corp: Eden Prairie, 1, 1992, pp. 341.
[33] M.A. Bhosale, B.M. Bhanage, Adv. Powder Technol. 27 (2016) 238.
19

Graphical abstract
Rh/Cu2O nanoparticles: Synthesis, characterization and catalytic
application as a heterogeneous catalyst in hydroformylation reaction
Samadhan A. Jagtapa, Manohar A. Bhosale a, Takehiko Sasakib and Bhalchandra M.
Bhanagea,*
a Department of Chemistry, Institute of Chemical Technology, Matunga, Mumbai - 400019,
India.
b Department of Complexity Science and Engineering, Graduate School of Frontier Sciences,
The University of Tokyo, 5-1-5, Kashiwanoha, Kashiwa, Chiba 277-8561, Japan.
*Corresponding author: Tel.: 022 33612603; Fax: +91 22 33611020.
E-mail: bm.bhanage@gmail.com, bm.bhanage@ictmumbai.edu.in
This work reports a regio-selective hydroformylation of olefins to aldehydes using
Rh/Cu2O nanoparticles. Various alkenes were converted in to the aldehydes in high yield has
been reported with catalyst recyclability. The catalyst was well characterized by XPS, FEG-
SEM, TEM, FT-IR, EDS, EDS mapping and ICP-AES analysis
.
20