Rhodium complexes supported on nanoporous activated carbon for selective hydroformylation of olefins

Article abstract of DOI:10.1016/j.catcom.2016.05.021

Activated carbon with nanoporous structure, high surface area (2500 m²/g) and total pore volume (2.35 cm³/g) was prepared from Mango seed shell (Mangifera indica L.) via chemical activation method and used as support to impregnate active hydroformylation rhodium complexes HRhCO(PPh₃)₃ and Rh(acac)(CO)₂. The prepared catalysts were characterized by XRD, SEM, TEM, NMR, IR, TGA, and N₂ adsorption/desorption techniques. The supported catalysts have shown excellent selectivity for aldehydes (~ 99%) in the hydroformylation of olefins with good stability and recyclability up to 4 cycles.

Full text of DOI:10.1016/j.catcom.2016.05.021

Rhodium complexes supported on nanoporous activated carbon for selective
hydroformylation of olefins
Venkata Subba Rao Ganga, Aasif A. Dabbawala, K. Munusamy, Sayed
H.R. Abdi, Rukhsana I. Kureshy, Noor-ul H. Khan, Hari C. Bajaj
PII:
DOI:
Reference:
S1566-7367(16)30179-0
doi: 10.1016/j.catcom.2016.05.021
CATCOM 4668
To appear in:
Catalysis Communications
Received date:
Revised date:
Accepted date:
9 February 2016
22 May 2016
25 May 2016
Please cite this article as: Venkata Subba Rao Ganga, Aasif A. Dabbawala, K.
Munusamy, Sayed H.R. Abdi, Rukhsana I. Kureshy, Noor-ul H. Khan, Hari C. Bajaj,
Rhodium complexes supported on nanoporous activated carbon for selective hydroformy-
lation of olefins, Catalysis Communications (2016), doi: 10.1016/j.catcom.2016.05.021
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ACCEPTED MANUSCRIPT
Rhodium complexes supported on nanoporous activated carbon for
selective hydroformylation of olefins
Venkata Subba Rao Gangaa,b , Aasif A. Dabbawalab , Munusamy Ka,b , Sayed H. R. Abdia,b*
, Rukhsana I. Kureshya,b , Noor-ul H. Khana,b and Hari C. Bajaj a,b
aInorganic Materials and Catalysis Division, CSIR-Central Salt and Marine Chemicals
Research Institute (CSIR-CSMCRI), Bhavnagar- 364 002, Gujarat, India.
bAcademy of Scientific and Innovative Research, CSIR-Central Salt and Marine Chemicals
Research Institute (CSIR-CSMCRI), G. B. Marg, Bhavnagar- 364 002, Gujarat, India.
Abstract
Activated carbon with nanoporous structure, high surface area (2500 m2/g) and total pore
volume (2.35 cm3/g ) was prepared from Mango seed shell (Mangifera indica L.) via
chemical activation method and used as support to impregnate active hydroformylation
rhodium complexes HRhCO(PPh3)3 and Rh(acac)(CO)2. The prepared catalysts were
characterized by XRD, SEM, TEM, NMR, IR, TGA, and N2 adsorption/desorption
techniques. The supported catalysts have shown excellent selectivity for aldehydes (~99%) in
the hydroformylation of olefins with good stability and recyclability up to 4 cycles.
Keywords: Bio-wastes; Microporous-mesoporous carbon; High surface area;
Hydroformylation; olefins; Rhodium.
*Corresponding author: Tel.: +91 278 2567760, Fax: +91 278 2567562 / 2566970. Email
address: shrabdi@csmcri.org (S. H. R Abdi).
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1. Introduction
Porous carbon materials have long been commercially available as supports for precious
metals like Rh, Pt, Pd and Ru for a variety of catalytic applications [1-5]. Traditional porous
carbons, such as activated charcoal and carbon molecular sieves, are produced with random
microporosity (pore diameter <2 nm) thereby limits the diffusion of larger reactant molecules
in the pores bearing catalytically active metal particles [4]. Therefore, mesoporous carbons
(MCs) with pore size of > 2 nm would be better as supports for catalytic applications. Our
group has recently developed micro and mesoporous carbons from bio-waste through
chemical activation method, which is amenable to large scale production of microporous-
mesoporous carbons from bio-waste (MMCb) [6].
The MMCb thus developed was modified suitably to use it as support for
hydroformylation catalyst for hydroformylation (HF) of olefins, which is essentially an
addition reaction (100% atom efficient) of formyl group across carbon-carbon double bond
to produce commercially valuable aldehydes useful in manufacturing of solvents, soaps,
detergents, plasticizers and various intermediates for fine and perfumery chemicals [7]. In
particular HF of 1-hexene (Scheme S1) using homogenous or heterogeneous catalyst is
important in perfumery industry [8,9]. In heterogeneous catalytic systems, catalytic activity
and selectivity are directly influenced by choice of support materials because of their textural
properties (porosity and surface area) and uniqe interaction with active components. Much
attention has been given to inorganic metal oxides [10-13] e.g., SiO2, TiO2, Al2O3 etc., but
very few researchers have focused their efforts on carbon materials especially MCs as
support for rhodium and cobalt complexes to catalyze HF reactions, [14-20] but none
reported the use of MMCb as support.
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In the present work, we have impregnated HRh(CO)(PPh3)3 and Rh(acac)(CO)2 –well
established hydroformylation catalysts under homogeneous condition, in MMCb for their
heterogenization. The HRh(CO)(PPh3)3–MMCb (Rh-P-MMCb) and Rh(acac)(CO)2-MMCb
(Rh-Ac-MMCb) catalysts were found to be easily recyclable (4 times) and gave results
(conversion, 100%; aldehyde selectivity, 99% in the case of HF of 1-hexene), which is at par
with its homogeneous counterpart a la extended reaction time (12 h). These catalysts were
found to be equally effective for the HF of styrene and long chain olefin 1-octene.
2.
Experimental
2.1 General Remarks
HRh(CO)(PPh3)3
impregnation
Chemical activation
H3PO4
Biowaste-Mango seed shell
Activated Carbon (MMCb)
Rh-P-MMCb
Scheme 1: Synthesis of HRh(CO)(PPh3)3 –MMCb (Rh-P-MMCb)
Mango seeds (outer shell) were washed with distilled water and dried in an oven at
110 °C for 3 days. The dried mango seed shells (MSS, 10 g) were cut into small pieces and
soaked in orthophosphoric acid (20 mL) in an alumina boat initially at 110 °C for 24 h then at
400 °C for 2 h to produce activated carbon. The black hard solid mass was removed from the
reactor and washed with distilled water to remove traces of orthophosphoric acid. The wet-
mass thus obtained was dried at 110 °C for 8 h in oven and named as MMCb. For the
synthesis of HRh(CO)(PPh3)3–MMCb (Rh-P-MMCb), 1.0 g of MMCb was added to a
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solution of HRh(CO)(PPh3)3 (100 mg) in toluene (20 mL) under nitrogen atmosphere and the
resulting slurry was stirred for 18 h at room temperature. Subsequently, the solvent was
removed under reduced pressure and the resulting mass was dried at 120 °C overnight in an
oven under nitrogen. (Scheme 1)The same procedure was followed for the preparation of
catalyst Rh-Ac-MMCb.
3.
Results and discussions
The XRD (Fig.1) patterns of MMCb, Rh-P-MMCb and Rh-Ac-MMCb have shown
a very broad peak suggesting amorphous nature of these materials.
1200
MMCb
Rh-P-MMCb
Rh-Ac-MMCb
1000
800
600
400
200
0
10
20
30
40
50
60
2 (deg)
Fig. 1 PXRD patterns of MMCb, Rh-P-MMCb and Rh-Ac-MMCb.
The TGA of MMCb, Rh-P-MMCb & Rh-Ac-MMCb under nitrogen atmosphere are
shown in Fig. S1 (see supporting information). All the samples were dried under vacuum at
110 °C for 4-6 h before the TGA measurements. In the case of MMCb there was a gradual
weight loss of nearly 18.62% was observed possibly due the slow decomposition carbon as
carbon dioxide. Whereas, in the case of catalysts Rh-P-MMCb & Rh-Ac-MMCb a loss of
27.13 and 27.37% respectively were observed due to the decomposition of respective
complexes impregnated in the carbon matrix.
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The N2 adsorption-desorption isotherms (at 77 K) of MMCb, Rh-P-MMCb and Rh-Ac-
MMCb and their corresponding Density Functional Theory (DFT) pore size distribution
(PSD) curves are shown in Fig. 2 (a) and 2 (b). All the isotherms can be classified as
composition of type-I and type-IV isotherms according to IUPAC indicating the presence of
micro- and mesopores. The higher uptake of N2 at low relative pressure (p/p0<0.2) is mainly
due to the presence of micropores. The samples show H3 type of hysteresis, which is
associated with aggregated or plate like particles thereby forming slit shaped mesopores. The
nature of isotherms and hysteresis loop remained unchanged even after Rh-complex loadings,
except that there was some reduction in N2 adsorption capacity. As prepared activated carbon
(MMCb) is having high surface area (2500 m2/g) and total pore volume (2.35 cc/g) (Table
S1), which reduces on impregnation of Rh-complexes (Rh-P-MMCb & Rh-Ac-MMCb)
thereby, confirming their effective loading on porous carbon.
1800
(a)
1500
MMCb
Rh-P-MMCb
1200
Rh-Ac-MMCb
900
600
300
0
0.0
0.2
0.4
0.6
0.8
1.0
Relative Pressure (p/p )
0
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3.0
2.5
2.0
1.5
1.0
0.5
0.0
(b)
MMCb
Rh-P-MMCb
Rh-Ac-MMCb
1
10
100
Pore Width (nm)
Fig. 2 (a) Nitrogen adsorption-desorption isotherms at 77 K and (b) DFT-pore size
distribution curves of MMCb, Rh-P-MMCb, Rh-Ac-MMCb.
The 31P CP-MAS (Fig. 3) spectrum of the HRh(CO)(PPh3)3 showed well defined
characteristic doublet at 57.6 and 46.5 ppm [21] and expected these peaks in Rh-P-MMCb
get broadened and appear at 58.7 and 43.8 ppm respectively indicating successful
impregnation of active complex on the carbon support. A similar behaviour has been reported
earlier in the case of herterogenization of HRh(CO)(PPh3)3 on silica support [22].
(C)
(B)
(A)
200
150
100
50
0
-50
ppm (t1)
Fig. 3 31PNMR Spectra of H(Rh)(CO)(PPh3)3., Rh-P-MMCb and (C) Re used Rh-P-
MMCb
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The SEM images of MMCb (Fig. S2a) and Rh-P-MMCb (Fig. S2b) non-uniform
aggregates of very small, distinct particles. The textural property of MMCb was not changed
on supporting HRh(CO)(PPh3)3 to get Rh-P-MMCb indicating that the texture of carbon
support is robust.
The TEM image (Fig. 4) and elemental mapping (Fig. S2c) of the Rh-P-MMCb
showing microporous-mesoporous structure with fairly uniform distribution of metal
complex. ICP together with elemental analysis showed that the Rh-P-MMCb contains 0.6
wt% of Rhodium.
Rh-P-MMCb
10 nm
Fig. 4 TEM image of Rh-P-MMCb.
FT-IR spectrum Fig. S3 of MMCb is typical of amorphous carbon rich in C=C bonds
(broad band at 1618 cm-1), however on impregnation of HRh(CO)(PPh3)3, bands typical to
virgin complexes centered around 3431 cm-1, 1618 cm-1, 1147 cm-1, 504 cm-1 and additional
bands at 1919cm-1 and 693 cm-1 corresponding to υRh-CO and υRh-P respectively. In both
cases there were no changes observed in the IR spectra of reused catalysts clearly show that
these complexes are firmly secured on MMCB.
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3.1. Catalytic performance of the Rh catalysts
It has been reported that Rh-complexes supported on activated carbon are active
catalysts for the HF of olefins to give corresponding aldehydes in excellent yields
[2,19,20,23]. Therefore, Rh-P-MMCb was evaluated as catalyst for its activity and
selectivity for the hydroformylation of 1-hexene as model substrate with syngas (CO+H2) at
3-7 MPa pressure and 60-120 °C temperature and the results are listed in Table 1. At first we
varied pressure over 1-7 MPa (Table 1, entries1-4) keeping the reaction temperature
constant at 60 °C and found that 7 MPa pressure has given 100% 1-hexene conversion with
corresponding product aldehyde having n/iso ratio of 1.4. Hence, for subsequent variation in
reaction conditions we took 7 MPa pressure as constant and varied temperature. Increasing
temperature from 60 to 80 °C (Table 1, entries 4-5) caused slight decrease in n/iso ratio of
the product with no change in conversion, however a further increase in temperature not only
affect product selectivity but also cause isomerization of 1-hexene and in turn produce iso-
aldehydes (Table S2). The selectivity of aldehyde in hydroformylation is mainly affected by
isomerization of alkene, which is temperature dependent. At lower temperatures (60-80 °C),
the isomerization of alkene is lower and consequently the higher aldehydes selectivity can be
realized. The isomerization of alkene produces the internal alkenes which are difficult to
hydroformylated at low syngas pressure. Therefore, in the case of low syngas pressure
unreacted internal olefins remained in the system causing overall lower aldehyde selectivity.
At comparative higher syngas pressure, internal alkenes are converted into aldehydes and
therefore isomerization products of alkenes are found to decrease with an increase of syngas
pressure [9,13]. It is to be noted that at the optimized reaction condition, virgin MMCb
neither produce any product nor causes isomerization of olefin (Table1, entry 8), indicating
that the support is benign and do not by itself contribute to the product formation. Under the
optimized condition the hydroformylation of 1-hexene using Rh-Ac-MMCb as catalyst
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affected 100% products formation with n/iso ratio of 1.3 (Table 1, entry 9, which is slightly
inferior as compared to its Rh-P-MMCb. The catalytic performance of Rh-P-MMCb is also
compared with homogeneous Rh-complex at similar metal loading and reaction condition.
The Rh-P-MMCb showed comparable aldehyde selectivity to its homogenous counterpart
although require higher reaction time to get complete conversion of 1-hexene (Table 1, entry
10).
Table 1 Activity and selectivity of Rh-P-MMCb catalyst for the hydroformylation of Olefins
Entry
Pressure Temp.
Conversion
(%)
Selectivity (%)
iso-ald. n/i
MPa
(°C)
n-ald.
Isomerization
1
1.0
3.0
5.0
7.0
7.0
7.0
7.0
7.0
7.0
7.0
7.0
7.0
60
60
60
60
80
100
120
60
60
60
60
60
40
42
51
53
58
56
49
51.4
-
36
37
39
42
44
50.3
48
-
1.1
22
12
08
-
2
55
1.3
1.3
1.4
1.3
1.0
1.0
-
3
85
4
100
100
100
100
-
5
-
6
0.7
0.6
-
7
8a
9b
10c
11d
12e
100
100
100
100
53
61
48
23
47
37
52
77
1.3
1.9
0.9
3.3
-
2
-
-
Reaction conditions: catalyst-Rh-P-MMCb = 25 mg, 1-hexene = 1.0 g, pressure of CO/H2 =
a
b
7MPa (1:1), toluene = 50 mL, time = 12 h. MMCb (25 mg) as catalyst, catalyst-Rh-Ac-
MMCb., c HRh(CO)(PPh3)3 as catalyst with reaction time = 5 h, d substrate: 1-octene,
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e substrate: styrene.
The activity and selectivity of Rh-P-MMCb was further checked for the hydroformylation
reaction of 1-octene and styrene (Table1, entries 11 and 12). In the case of 1-octene iso
product formation was more (Table1, entry 11 n/iso ratio 0.9) than what was obtained with 1-
hexene and this ratio was even greater in the case of styrene (Table1, entry 12, n/iso ratio
3.3). In order to compare the performance of Rh-P-MMCb and Rh-Ac-MMCb catalysts, the
results of the closely related known catalytic systems are listed in Table S3. It is evident from
the comparison that the catalysts Rh-P-MMCb and Rh-Ac-MMCb have matching
performance notwithstanding the advantage of using easily synthesized support from bio-
waste. In conclusion both Rh-P-MMCb and Rh-Ac-MMCb were found to be effective
olefin hydroformylation catalyst to give corresponding aldehydes exclusively but with
moderate n/iso ratios.
It is know that the catalyst activity of impregnated catalyst is also depend on type of
support used and its porous structure. Therefore, we compared the efficacy of the MMCb
support, H(Rh)(CO)(PPh3)3 impregnated on various other supports viz., commercially
available activated carbon, silica, acidic alumina, zirconia, and ZnO in the hydroformylation
of 1-hexene under similar reaction conditions. The data depicted in (Fig. S4) show that Rh-P-
MMCb catalyst had fared better than others notwithstanding the utilization of bio-waste in
the preparation of support used in the present study. Rh-P-MMCB catalyst has high specific
surface area and porous structure with wide range of nanopores. Due to these properties of
support, the higher dispersion of catalyst was observed and the substrate molecules can easily
approach to active metal center without diffusion limitation. In turn, the remarkable catalyst
activity can be realized with Rh-P-MMCB in comparison to other supports.
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Reusability (4 times at 60 °C) of the catalyst Rh-P-MMCb studied in the
hydroformylation of 1-hexene under the optimized reaction conditions (Fig. S5) showed no
considerable change in conversion and selectivity over the studied cycles. Noticeably, the
ICP analysis of the organic phase obtained after first cycle showed ~3% of the rhodium
leaching, but this Rh-loss has not significantly affected the performance of the recycled
catalyst. In subsequent cycles however, the ICP analysis of the solution phase showed no
trace (if at all below detection level) of Rh metal.
4. Conclusions
MMCb having high surface area of 2500 m2/g and pore volume (2.35 cm3/g)
synthesized from waste biomass was used to support complexes HRh(CO)(PPh3)3 and
Rh(acac)(CO)2. The as-synthesized heterogeneous catalysts are recyclable and showed
excellent activity and aldehyde selectivity with moderate n/iso ratio in the hydroformylation
olefins.
Acknowledgments
CSIR-CSMCRI registration no is 094/2015. The authors acknowledge CSIR and DST
(SR/S1/OC-56/2009), New Delhi for the financial support through the Network Project on
Catalysis. G. V. S. Rao acknowledges CSIR, New Delhi, for the award of Senior Research
Fellowship and Analytical Division and Centralized Instruments Facility of CSMCRI.
References:
[1] P.G.J. Koopman, A.P.G. Kieboom, H. van Bekkum, J.W.E. Coenen, Carbon 17 (1979)
399-402.
[2] S. Dharmidhikari, M.A. Abraham, J. Supercrit. Fluids 18 (2000) 1-10.
[3] Z. Ji, S. Liang, Y. Jiang, H. Li, Z. Liu, T. Zhao, Carbon 47 (2009) 2194-2199.
11

ACCEPTED MANUSCRIPT
[4] K. Köhler, R.G. Heidenreich, J.G.E. Krauter, J. Pietsch, Chem. Eur. J. 8 (2002) 622-
631.
[5] M. Tan, G. Yang, T. Wang, T. Vitidsant, J. Li, Q. Wei, P. Ai, M. Wu, J. Zheng, N.
Tsubaki Catal. Sci. Technol. 6 (2016) 1162-1172.
[6] M. Kuppusamy, R. S. Somani and H. C. Bajaj, J. Environ. Chem. Eng., 3 (2015)
2750.
[7] E.F. Lutz, J. Chem.Educ. 63 (1986) 202.
[8] R. Franke, D. Selent, A. Börner, Chem. Rev. 112 (2012) 5675-5732.
[9] A. Dabbawala, R.V. Jasra, H.C. Bajaj, Catal. Commun. 12 (2011) 403–407.
[10]A.J. Sandee, J.N.H. Reek, P.C.J. Kamer, P.W.N.M. van Leeuwen, J. Am. Chem. Soc.
123 (2001) 8468-8476.
[11]S.J. Tauster, S.C. Fung, R.T.K. Baker, J.A. Horsley, Science 211 (1981) 1121-1125.
[12]A.J. Bruss, M.A. Gelesky, G. Machado, J. Dupont, J. Mol. Catal. A: Chem. 252
(2006) 212-218.
[13]A. Luchetti, D.M. Hercules, J. Mol. Catal. 16 (1982) 95-110.
[14]T.A. Kainulainen, M.K. Niemelä, A.O.I. Krause, J. Mol. Catal. A: Chem. 140 (1999)
173-184.
[15]B. Li, X. Li, K. Asami, K. Fujimoto, Chemistry Letters 32 (2003) 378-379.
[16]B. El Ali, J. Tijani, M. Fettouhi, M. El-Faer, A. Al-Arfaj, Applied Catalysis A:
General 283 (2005) 185-196.
[17]Y. He, G. Chen, S. Kawi, S. Wong, J.Porous. Mater. 16 (2009) 721-729.
[18]I. Pochorovski, H. Wang, J.I. Feldblyum, X. Zhang, A.L. Antaris, Z. Bao, J. Am.
Chem. Soc. 137 (2015) 4328-4331.
[19]B. Li, X. Li, K. Asami, K. Fujimoto, Energy & Fuels 17 (2003) 810-816.
12

ACCEPTED MANUSCRIPT
[20]T.A. Kainulainen, M.K. Niemelä, A.O.I. Krause, J. Mol. Catal. A: Chem. 122 (1997)
39-49.
[21]G. Wu, R.E. Wasylishen, R.D. Curtis, Can. J. Chem. 70 (1992) 863-869.
[22]K. Mukhopadhyay, A.B. Mandale, R.V. Chaudhari, Chem. Mater. 15 (2003) 1766-
1777.
[23]Y. Zhang, H.-B. Zhang, G.-D. Lin, P. Chen, Y.-Z. Yuan, K.R. Tsai, Appl. Catal. A:
Gen.187 (1999) 213-224.
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Graphical abstract
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Highlights:
 Nanoporous activated carbon derived from Mango seed shell used as support
 Rhodium complexes were heterogenized on nanoporous activated carbon
 Selective hydroformylation of olefins was investigated using supported Rh catalyst
 Supported Rh catalyst showed high selectivity towards aldehyde up to 99%
 Supported Rh catalyst was found to be stable over several recycle run
15