Reduction of alkenes catalyzed by copper nanoparticles supported on diamond nanoparticles

Article abstract of DOI:10.1039/c3cc39011j

Copper nanoparticles (Cu NPs) supported on diamond nanoparticles (D NPs) previously purified by Fenton treatment (Cu/D) followed by annealing with hydrogen (Cu/DH) are highly efficient and reusable heterogeneous catalysts for hydrogenation of styrene to ethylbenzene with the minimum productivity value of 30617 cycles. The Royal Society of Chemistry.

Full text of DOI:10.1039/c3cc39011j

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Reduction of alkenes catalyzed by copper
nanoparticles supported on diamond nanoparticles†‡
Cite this: Chem. Commun., 2013,
4
9, 2359
Amarajothi Dhakshinamoorthy,* Sergio Navalon, David Sempere, Mercedes Alvaro
and Hermenegildo Garcia*
Received 8th November 2012,
Accepted 6th January 2013
DOI: 10.1039/c3cc39011j
www.rsc.org/chemcomm
Copper nanoparticles (Cu NPs) supported on diamond nanoparticles images) for the deposition of metal NPs, we have reported that
(
D NPs) previously purified by Fenton treatment (Cu/D) followed by Cu NPs supported on D NPs are selective catalysts for aerobic
1
2
annealing with hydrogen (Cu/DH) are highly efficient and reusable oxidation of thiophenol to diphenyldisulfide.
heterogeneous catalysts for hydrogenation of styrene to ethyl-
benzene with the minimum productivity value of 30617 cycles.
In the present study, we report the preparation of Cu NPs
supported on D NPs (Cu/DH) and their catalytic activity in the
reduction of olefins using hydrazine hydrate as a reducing
Reduction of olefins to saturated hydrocarbons is one of the agent. The advantages of this method are low catalyst loading,
fundamental transformations in organic chemistry which is short reaction time, cost effectiveness of the catalyst and high
usually performed using transition metal catalysts such as Pt, product selectivity.
1
Pd, Rh and Ni and hydrogen as a reducing agent. Although
The characterization data of Cu/DH prepared under identical
many catalysts are highly selective and active in hydrogenation conditions as reported here by powder XRD, diffuse reflectance
reaction, the cost of these precious metals makes it convenient spectroscopy, X-ray photoelectron spectroscopy, FT-IR and high
12
to look for other alternatives. Further, as an alternative to resolution transmission microscopy have been already reported.
hydrogenation with H gas, the use of hydrazine for reduction The textural properties of various supports are given in Table S1
of olefins has attracted attention from both academia and (ESI‡). Further, activated carbon (AC), graphite (G) and multi-
2
2
–4
industry.
This reagent has the advantage of avoiding the walled carbon nanotubes (MWCNT) were also subjected to
use of flammable gas and simplifies the reactor. It is generally the same treatment as D NPs followed by deposition of Cu NPs
accepted that double bonds are reduced by diimide, which is (Table S2, Fig. S2–S12, ESI‡). It has been found that pretreatment
3
generated from hydrazine via oxidation.
of commercial D NPs with Fenton reagents is necessary in order
11
Reduction of olefins with hydrazine to the corresponding to remove amorphous carbon soot from commercial D NPs.
reduced products in high selectivity is performed using cata- The average particle size of Cu in DH, ACH, GH and MWCNTH
5
6
lysts such as guanidine, flavin derived catalysts and metal– was 3.7, 7.9, 7.8 and 7.3 nm, respectively, according to TEM. The
7
organic frameworks. It has also been reported that metal structural integrity of D, G and MWCNT was maintained
nanoparticles (NPs) supported on suitable supports can also during the above treatments as evidenced from powder XRD
8
act as a selective catalyst in hydrogenation reaction. For (Fig. S17–S19, ESI‡). The interest in D NPs as a support is because
9
10
example, Fe O4 and Ni NPs supported on K10 clay have of the inertness of their surface compared to other carbon forms
3
been reported as catalysts for the hydrogenation of styrene to or metal oxides. This inertness is particularly interesting when
ꢀ
ethylbenzene using aqueous hydrazine as a reducing agent. highly reactive intermediates (such as OH radicals generated
11
Recently, we have reported that Au NPs supported on D NPs from H
2 2
O already reported in the literature ) or reagents (such
(
Au/D) could be used as a catalyst for the degradation of phenol as hydrazine studied here) that tend to decompose spuriously
1
1
in the presence of hydrogen peroxide. In continuation of our without forming the desirable active species are involved.
quest for using D NPs as a support (see Fig. S1, ESI‡ for TEM
In preliminary experiments, styrene was selected as a model
substrate to optimize the reaction conditions. In the absence of a
catalyst 7% conversion of styrene was observed using hydrazine
hydrate as a reducing agent. Using Cu/D as a catalyst, the styrene
conversion reached to 64% with 99% selectivity in 3 h (entry 2,
Table 1). Under the same reaction conditions, Cu/DH resulted in
Instituto Univ. de Tecnolog ´ı a Qu ´ı mica CSIC - UPV and Departamento de Qu ´ı mica,
Univ. Polit ´e cnica de Valencia, Av. De los Naranjos s/n, 46022 Valencia, Spain.
E-mail: hgarcia@qim.upv.es, admguru@gmail.com; Fax: +34 9638 7807
†
Dedicated to Prof. Miguel A. Miranda with admiration and gratitude on the
occasion of his 60th anniversary.
Electronic supplementary information (ESI) available: Preparation of catalysts,
100% conversion and selectivity in 3 h (entry 3, Table 1). Fig. 1
‡
experimental procedures, and productivity data. See DOI: 10.1039/c3cc39011j
shows the temporal profile for this reaction. On the other hand,
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Table 1 Hydrogenation of styrene to ethylbenzene using hydrazine as a
a
reducing agent promoted by various catalysts
b
b
Run Catalyst
Time (h) Conversion (%) Selectivity (%)
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
—
Cu/D
Cu/DH
Cu/DH 2nd use
Cu/DH 3rd use
Cu/DH 4th use
Cu/DH
Cu/DH
Cu/DH
Cu/DH
Cu/ACH
Cu/GH
Cu/MWCNTH
Au/DH
Au/DH
Au/DH
Pd/DH
3
3
3
3
3
3
1
16
50
130
3
3
3
3
23
36
36
7
64
100
97
95
94
5
35
100
100
35
32
47
18
78
100
94
>99
>99
>99
>99
>99
>99
100
100
100
100
99
99
99
99
99
99
99
c
c
c
Fig. 2 Time conversion plot for the reduction of styrene to ethylbenzene using
Cu/DH (a), Au/DH (b), and Pd/DH as catalysts. In all cases, the selectivity of
ethylbenzene was more than 99%.
d
0
1
2
3
4
5
6
7
showed comparable activity to that of Au/DH and the two
samples were significantly less active than Cu/DH (Fig. 2).
The heterogeneity of the reaction was studied by performing
reduction of styrene to ethylbenzene using Cu/DH as a catalyst
under the present reaction conditions. After 36% conversion,
the catalyst was removed from the reaction mixture by hot
filtration, allowing the reaction to continue in the absence of
the catalyst. After 3 h, styrene conversion was increased to 42%
suggesting that Cu NPs are not leached from the support
during the course of reaction and ICP-AES showed the presence
of 1 ppm of Cu in the filtrate. Also, the chemical analysis of
Cu/DH revealed that the Cu content was maintained. It can be
seen that the catalyst could be used for three additional runs
without much activity decrease. The kinetic data (Fig. S14, ESI‡)
revealed that the catalyst exhibits similar activity having the
a
Reaction conditions: styrene (1 mmol), catalyst (20 mg), N
2
H
4
ÁH
(0.025 mL), ethanol (4 mL), 60 1C. Determined by
GC. Styrene (20 mmol), Cu/DH (20 mg), N O (2 mL), aq. NH
ÁH
0.5 mL), ethanol (20 mL), 60 1C. Styrene (50 mmol), Cu/DH (20 mg),
ÁH O (4 mL), aq. NH (0.75 mL), ethanol (40 mL), 60 1C.
2
O
b
(0.1 mL), aq. NH
3
c
2
H
4
2
3
d
(
N
2
H
4
2
3
same turnover frequency for the four runs with the value being
À1
3
68 h suggesting catalyst stability. The average Cu NPs size in
Cu/DH after the third use was found to be 3.8 nm (Fig. S2, ESI‡),
which is almost similar to that of the fresh catalyst.
Fig. 1 Temporal profile for the reduction of styrene to ethylbenzene using no
catalyst (a), and using Cu/GH (b), Cu/ACH (c), Cu/MWCNTH (d) and Cu/DH (e) as
catalysts.
It has been reported earlier that the formation of diimide
(the presumed hydrogenating species) required either H
2
O
2
or
1
6,17
air in the presence of a transition metal catalyst.
Under the
present experimental conditions with Cu/DH as a catalyst in air,
it can be assumed based on the literature that hydrazine under-
Cu/ACH, Cu/GH and Cu/MWCNTH showed lower activity
(Table 1, entries 11–13) than Cu/DH suggesting the beneficial
1
6,17
goes oxidation to diimide
which transfers hydrogen to
effect of DH as a support for Cu NPs. These results indicate that
large Cu NPs present in other supports different from DH (see
Table S2, ESI‡) are detrimental for the catalytic activity and that
Fenton treatment did not improve the catalytic activity for these
catalysts in contrast to the case of D (Table S3, ESI‡). In fact, Cu
NPs deposited on AC, G, MWCNT without any treatment exhib-
ited even slightly higher activity than with Fenton purification
and hydrogen annealing treatment.
styrene resulting in the formation of ethylbenzene. To ascertain
this hypothesis, a control experiment using Cu/DH as a catalyst
under a nitrogen atmosphere showed 2% styrene conversion in
3
h. At this point, nitrogen was removed and the reaction
continued in the presence of air showing 90% styrene conversion
in 3 h (Fig. S15, ESI†). This indirectly supports that diimide is
acting as a reagent in the reduction of styrene (Scheme 1).
The productivity and catalyst stability under our experi-
mental conditions were tested by performing the reduction in
a large excess of styrene (50 mmol). The reaction was monitored
at different time intervals and the time conversion plot is shown
We were also interested in comparing the catalytic activity of
Cu/DH with Au/DH and Pd/DH at the same metal loading for
the reduction of styrene to ethylbenzene (Fig. 2). Interestingly,
Cu/DH outperforms Au/DH in terms of initial reaction rate and
final conversion. The former catalyst gave complete conversion
of styrene in 3 h while the latter catalyst required 36 h to
complete the reaction. Hence, the higher activity of the Cu/DH
catalyst over Au/DH in the hydrogenation of styrene could be
attributed to the ability of the Cu/DH catalyst to favour the
1
3–15
formation of diimide
which is supposed to be the inter-
Scheme 1 Proposed mechanism for the reduction of styrene to ethylbenzene
mediate during the reaction. Further, Pd/DH (Fig. S13, ESI‡) using Cu/DH as a catalyst.
2
360 Chem. Commun., 2013, 49, 2359--2361
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also reduced to cyclooctane with 99% conversion and selectivity
in 8 h. Vinyl substituted heterocyclic compounds were reduced
to their corresponding products with very high conversion and
selectivity (entries 9, 12 and 13, Table 2). For example, vinyl-
cyclooctane was reduced to ethylcyclooctane with 99% conver-
sion and selectivity in 5 h. 2-Cyclohexen-1-ol was reduced to
cyclohexanol, an important intermediate for the synthesis of
nylon-66, with 95% conversion and 99% selectivity in 23 h. An
attempt to reduce phenylacetylene showed a mixture of 61%
styrene and 39% ethylbenzene at 39% conversion in 24 h. On
Fig. 3 Productivity test for the reduction of styrene to ethylbenzene at the the other hand, allylphenyl sulfide was reduced to phenylpropyl
5
0 mmol scale. The reaction conditions are given in Table 1. For the 20 mmol sulfide with 99% conversion and 96% selectivity in 8 h. Simi-
scale, see Fig. S16 (ESI‡).
larly, phenyl vinyl sulfide showed high conversion (99%) and
selectivity towards ethyl phenyl sulfide in 9 h. Allyl phenyl ether
was also reduced to phenyl propyl ether in 5 h with 99%
conversion and selectivity.
a
Table 2 Reduction of various olefins catalyzed by Cu/DH
b
b
In conclusion, Cu/DH exhibited higher catalytic activity than
its analogous catalyst Au/DH and Pd/DH for the reduction of
styrene to ethylbenzene. Further, Cu NPs supported on ACH,
GH and MWCNTH showed lower activity than Cu/DH suggest-
ing the beneficial role of DH as a support. Hydrogen annealing
improves the performance of D as support probably by decreas-
ing the population of carboxylic groups, thus leading to smaller
Cu NPs. The catalyst could also be reused without much loss in
its activity and exhibited higher productivity by giving a high
turnover number, Cu being a cheaper transition metal than Pd
and Au.
Run Substrate
Time (h) Conversion (%) Selectivity (%)
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
Styrene
3
8
8
30
8
100
100
99
60
99
89
99
94
95
99
88
99
96
99
99
95
39
99
99
99
>99
99
99
4-Fluorostyrene
4-Chlorostyrene
4-Methoxystyrene
3-Nitrostyrene
Ethyl 4-nitrocinnamate 10
a-Methylstyrene
4-Vinylstyrene
99
c
98
99
98
98
99
99
98
99
99
99
99
99
10
6
8
4-Vinylpyridine
Cyclooctene
0
1
2
3
4
5
6
7
8
9
0
8
9-Vinylanthracene
9-Vinylcarbazole
N-Vinylcaprolactam
Vinylcyclooctane
2-Vinylnapthalene
2-Cyclohexen-1-ol
Phenylacetylene
Allylphenyl sulfide
Phenyl vinyl sulfide
Allylphenyl ether
24
14
33
5
Financial support from the Spanish Ministry of Science and
Education (Consolider MULTICAT, CTQ-2012-32316) is grate-
fully acknowledged.
4
23
24
8
9
5
d
61
96
e
Notes and references
98
99
1 J. G. de Vries and C. J. Elsevier, Handbook of homogeneous hydro-
genations, Wiley-VCH, New York, 2007.
a
Reaction conditions: substrate (1 mmol), catalyst (20 mg), N
(0.025 mL), ethanol (4 mL), 60 1C. Determined by
GC. 2% of 3-aminoethylbenzene was also formed. Selectivity corre-
2
H
4
ÁH
2
O
2
W. M. N. Ratnayake, J. S. Grossert and R. Ackman, J. Am. Oil Chem.
Soc., 1990, 67, 940.
b
(
0.1 mL), aq. NH
3
c
d
3
D. J. Pasto and R. T. Taylor, Reductions with Diimide, in Organic
Reactions, ed. V. L. A. Paquette, Wiley & Sons, New York, 1991,
vol. 40, p. 91.
e
sponds to styrene and 39% of ethylbenzene was observed. 3% of
diphenyldisulfide was observed.
4
5
6
E. W. Schmidt, Hydrazine and Its Derivatives: Preparation, Properties,
and Applications, Wiley & Sons, New York, 2nd edn, 2001, vol. 1, p. 475.
M. Lamani, R. Siddappa, S. Guralamata and K. R. Prabhu, Chem.
Commun., 2012, 48, 6583.
in Fig. 3. It is interesting to note that the reduction of styrene to
ethylbenzene was completed in 130 h. The turnover number for
this reaction under these conditions was 30 617 cycles.
These results with styrene prompted us to check the scope of
Cu/DH as a catalyst with other substrates. 4-Fluoro, 4-chloro
and 3-nitrostyrenes with electron withdrawing substrates were
reduced to their corresponding substituted ethylbenzenes with
high conversion and selectivity in 8 h while 4-methoxystyrene
with a strong electron donating substituent required 30 h to
reach 60% conversion with very high selectivity.
The present catalytic system showed very high chemoselec-
tive reduction in the case of 3-nitrostyrene. A similar behavior
was observed with ethyl 4-nitrocinnamate resulting in 89%
conversion in 10 h with high selectivity towards the reduction
of CQC double bonds. On the other hand, a-methylstyrene
resulted in 99% conversion with 98% selectivity in 10 h.
Further, 4-vinylstyrene was reduced to 1,4-diethylbenzene with
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1
1
1
1
1
1
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98% selectivity in 6 h. A cyclic olefin namely cyclooctene was
This journal is c The Royal Society of Chemistry 2013
Chem. Commun., 2013, 49, 2359--2361 2361