Competitive hydrogenation/dehalogenation of halogenoarenes with surfactant-stabilized aqueous suspensions of rhodium and palladium colloids: A major effect of the metal nature

Article abstract of DOI:10.1016/j.molcata.2006.11.004

The original palladium colloidal suspensions with an average size of 2.7 nm have been synthesised by reducing Na₂PdCl₄ with sodium borohydride and were stabilized by water soluble N,N-dimethyl-N-cetyl-N-(2-hydroxyethyl)ammonium chloride salt. The catalytic hydrogenation and dehalogenation of various halogenoarenes have been investigated with this aqueous suspension of palladium nanoparticles and compared with the well-known rhodium suspension. The influences of the halogen fragment and the experimental conditions have also been studied. It was observed that the kinetics and selectivity of the competitive dehalogenation/hydrogenation depend on the nature of metal colloids and the hydrogen pressure.

Full text of DOI:10.1016/j.molcata.2006.11.004

Journal of Molecular Catalysis A: Chemical 266 (2007) 221–225
Competitive hydrogenation/dehalogenation of halogenoarenes with
surfactant-stabilized aqueous suspensions of rhodium and palladium
colloids: A major effect of the metal nature
a
a
a,∗
b
Bastien L e´ ger , Audrey Nowicki , Alain Roucoux , Jean-Paul Rolland
a
Equipe Synth e` se Organique et Syst e` mes Organis e´ s, UMR CNRS 6226, “Sciences Chimiques de Rennes”,
Ecole Nationale Sup e´ rieure de Chimie de Rennes, Avenue du Gal Leclerc, 35700 Rennes, France
UMR CNRS 6026, “Interactions Cellulaires et Mol e´ culaires” Equipe Structure et Dynamique des Macromol e´ cules,
Universit e´ de Rennes I, 35042 Rennes, France
b
Received 20 September 2006; received in revised form 27 October 2006; accepted 1 November 2006
Available online 10 November 2006
Abstract
The original palladium colloidal suspensions with an average size of 2.7 nm have been synthesised by reducing Na
2
4
PdCl with sodium boro-
hydride and were stabilized by water soluble N,N-dimethyl-N-cetyl-N-(2-hydroxyethyl)ammonium chloride salt. The catalytic hydrogenation and
dehalogenation of various halogenoarenes have been investigated with this aqueous suspension of palladium nanoparticles and compared with the
well-known rhodium suspension. The influences of the halogen fragment and the experimental conditions have also been studied. It was observed
that the kinetics and selectivity of the competitive dehalogenation/hydrogenation depend on the nature of metal colloids and the hydrogen pressure.
©
2006 Elsevier B.V. All rights reserved.
Keywords: Hydrogenation; Dehalogenation; Colloids; Rhodium; Palladium
1
. Introduction
rhodium and iridium particles for the hydrogenation of aromatic
9,10], heteroaromatic [11] compounds under mild conditions,
[
The last decade has evidenced an ever-increasing interest in
the nanometric size chemical species namely metal nanopar-
ticles and their applications in various areas such as catalysis
and also for platinum colloids for the asymmetric hydrogenation
of ethyl pyruvate [12]. In this paper, we report the synthesis and
the characterization of the analogous palladium aqueous suspen-
sion and the efficient nanoparticles stabilization which depends
on the surfactant/Pd ratio. We describe the use of this nanoparti-
cles suspension for the dehalogenation of arylhalides, and more
particularly of chlorobenzene. The catalytic hydrodehalogena-
tion of halogenated aromatic wastes has been recognized as
an important chemical transformation in organic synthesis as
well as in industrial applications [13], as it is considered as an
environmentally friendly and cost saving alternative to tradi-
tional incineration disposal. In that context, the development
of new dechlorination methods to remove toxic aryl halides
under aqueous conditions remains a topic of interest. Due to
the harmful nature of arylchlorides, a great number of hydrode-
halogenation reactions with homogeneous or heterogeneous
catalysts have been reported with ruthenium or rhodium and
especially with palladium [13,14]. Few reports have described
the use of rhodium nanoparticles in a sol–gel matrix [15] or pal-
ladium immobilized on MontK10 [16,17]. Recently, Uozomi
[
1,2]. The development of soluble nanoparticles or colloids as
highly active nanocatalysts has been the focus of considerable
effort in terms of preparation to prevent agglomeration and to
control particle size [3–7]. In this context, various stabilizers
have been investigated according to the “organic” or “aqueous”
nature of media which generally depends on the nature of the
precursor, namely metals salts or organometallic compounds.
Our approach is to use ionic surfactants to prepare and stabilize
aqueous colloidal suspensions of metallic particles. Previously,
we have described the easy synthesis of N,N-dimethyl-N-cetyl-
N-(2-hydroxyethyl)ammonium salts HEA16X with X = Br, Cl,
I, CH3SO3, BF4 [8]. Among these compounds, the chloride salt
HEA16Cl has particularly been studied as a protective agent for
∗
Corresponding author. Tel.: +33 2 23 23 80 37; fax: +33 2 23 23 81 99.
E-mail address: alain.Roucoux@ensc-rennes.fr (A. Roucoux).
1
381-1169/$ – see front matter © 2006 Elsevier B.V. All rights reserved.
doi:10.1016/j.molcata.2006.11.004

2
22
B. L e´ ger et al. / Journal of Molecular Catalysis A: Chemical 266 (2007) 221–225
described the hydrodechlorination of chloroarenes with an
amphiphilic polystyrene-poly(ethyleneglycol) resin dispersion
of palladium nanoparticles under aqueous conditions [18]. Here,
we demonstrate the efficient activity of our aqueous palladium
suspension in dehalogenation of various arene derivatives and
show the influence of the halogen group. Finally we com-
pare rhodium and palladium nanoparticles in the competitive
dehalogenation–hydrogenation of the aromatic ring.
(50 mL). The reduction occurs instantaneously and is charac-
terized by a color change from yellow to black. The obtained
suspensions are stable for several weeks.
2.3.1.1. General procedure for hydrogenation under atmo-
spheric hydrogen pressure. A 25 mL round bottom flask,
charged with 10 mL of aqueous suspension of the appropriated
Rh(0) or Pd(0) catalyst and a magnetic stirrer, was connected
with a gas burette (500 mL) and a flask to balance the pres-
sure. The flask was closed by a septum, and the system was
filled with hydrogen. The halogenoarene compounds ([sub-
strate]/[metal] = 100) was injected through the septum and the
2
. Experimental
2
.1. Starting materials
−
1
mixture was stirred at 1500 min . The reaction was monitored
by the volume of gas consumed and by gas chromatography.
Turnover frequency (TOF) was determined for 100% conver-
sion.
Rhodium chloride hydrate and sodium tetrachloropalladate
II were obtained from Strem Chemicals and Alfa Products,
respectively. Sodium borohydride and all halogenoarenes were
purchased from Aldrich or Acros and used without further purifi-
cation. Water was distilled twice before use by conventional
method. The surfactant HEA16Cl was prepared as previously
reported and was fully characterized [8].
2.3.1.2. General procedure for hydrogenation under hydrogen
pressure. The stainless steel autoclave was charged with the
previously prepared aqueous suspension of Pd(0) (10 mL) and
−3
a magnetic stirrer. The appropriate substrate (3.8 × 10 mol,
100 equiv.) was added into the autoclave and dihydrogen was
admitted to the system at constant pressure (up to 40 bar). The
mixture was stirred until the reaction was finished. Samples for
gas chromatographic analysis were removed from time to time.
The TOF was determined for 100% conversion.
2
2
.2. Analytical procedures
.2.1. TEM-analysis
The transmission electronic microscopic studies were con-
ductedusingaFEITechna ¨ı G2Spheraat200 kV(cathodeLaB6).
Samples were prepared by a dropwise addition of the stabi-
lized palladium nanoparticles in water onto a copper sample
mesh covered with carbon. The colloidal dispersion was par-
tially removed after 1 min using cellulose before transferring to
the microscope. The picture is obtained at X 80.000 with a video
GATAN USC1000 (CCD detector 2048X2048) and associated
software DIGITAL Micrograph. Measurement of about 970 par-
ticles was made with program SCION Image (NIH) and was
analyzed with KaleidaGraph program providing the histograms
of the nanoparticles size distribution.
3. Results and discussion
The aim of the present work was the synthesis of stable
palladium nanoparticles and their use in the dehalogenation
of various benzene derivatives. Our approach is to use col-
loidal metallic particles finely dispersed in water and protected
by surfactants. In preliminary studies, we have shown the
efficiency of the water soluble N,N-dimethyl-N-cetyl-N-(2-
hydroxyethyl)ammonium chloride salt to stabilize various metal
colloids. In a first step, we have optimized the preparation of
the aqueous suspension in catalytic reaction conditions. We
have compared the stability of the suspension before and after
catalysis in the dechlorination of chlorobenzene as standard
reaction. Then, the characterization of the best system was real-
ized by microscopy experiments (TEM). Finally, the colloidal
suspension was investigated in the catalytic dehalogenation of
various aromatic substrates and compared with rhodium sus-
pension which gives complete hydrogenation of the aromatic
ring.
2
.2.2. Gas chromatography
All analyses were performed using a Carlo Erba GC 6000
with a FID detector equipped with an Alltech AT1 column (30 m,
0
4
8
.25 mm i.d.). Parameters were as follows: initial temperature,
◦
◦
0 C; initial time, 10 min; ramp, 10 C/min; final temperature,
◦
◦
0 C; final time, 30 min; injector temperature, 220 C; detector
◦
temperature, 250 C.
2
2
.3. Catalytic tests
.3.1. Synthesis of the aqueous palladium(0) suspension
3.1. Preparation and characterization of palladium colloids
The aqueous suspensions of palladium nanoparticles were
prepared following our previously described rhodium suspen-
sion synthesis [9].
The catalytically active aqueous suspension was made
of palladium(0) colloids prepared by reducing sodium
tetrachloropalladate II with sodium borohydride in dilute
aqueous solution of chloride surfactant, N,N-dimethyl-N-cetyl-
N-(2-hydroxyethyl)ammonium chloride salt HEA16Cl. The
molecular ratio R = HEA16Cl/Pd was optimized to prevent
aggregation and to provide a good stability after catalysis to
investigate the potential recycling of the aqueous phase. Specif-
An aqueous solution of surfactant HEA16Cl (544 mg,
−
3
−1
1
.7 × 10 mol L in 40 mL H2O) was added in a flask con-
−
4
taining 16 mg of sodium borohydride (4.2 × 10 mol). Then
this solution was quickly added under vigorous stirring to an
aqueous solution (10 mL) of the precursor Na2PdCl4 (50 mg,
−4
1
.7 × 10 mol) to obtain an aqueous Pd(0) colloidal suspension

B. L e´ ger et al. / Journal of Molecular Catalysis A: Chemical 266 (2007) 221–225
223
Fig. 1. Transmission electron micrograph (scale bar = 20 nm) and size distribution histogram of Pd/HEA16Cl suspension.
ically, the hydrogenation of chlorobenzene into benzene in
standard conditions (20 C, 1 bar H2, [substrate]/[Pd] = 100) was
3.2. Catalytic performances
◦
studied with different ratios of HEA16Cl/Pd = 2, 3, 5 and 10.
The visual stability of the suspension was observed after 3 h
of reaction. A molar ratio ≥2 was sufficient to maintain sta-
ble Pd colloids. Nevertheless, a molar ratio R < 10 leads to
the precipitation of the suspension after catalysis. To conclude,
we have imposed a ratio HEA16Cl/Pd = 10 for the stable and
reproducible synthesis of Pd nanoparticles and their use in the
dehalogenation of benzene derivatives under aqueous condi-
tions.
This optimized active aqueous suspension was character-
ized. The histogram of the particle sizes distribution of the
Pd/HEA16Cl systems has been determined by transmission
electron microscopic observations (Fig. 1). The mean diame-
ter of the Pd nanoparticles, calculated from about 970 particles
found in an arbitrary chosen area, corresponds to an average
diameter of 2.7 nm with 85% of colloids between 1.50 and
First, we have studied the hydrodechlorination of different
organic chlorides using Pd/HEA16Cl and hydrogen (1 or 10 bar)
in water (Table 1). Hydrodechlorination of chlorobenzene to
benzene was complete in about 3 h at atmospheric hydro-
gen pressure. In the same conditions, functionalized chloride
compounds (2-chlorophenol, 4-chloroanisole, 4-chlorotoluene)
were slowly transformed into benzene derivatives in less than
24 h. This study was extended to the dechlorination of two poly-
chlorinated species (1,2- and 1,3-dichlorobenzene) and shows
complete benzene formation without intermediates. The reac-
tion was also investigated under 10 bar H2. Surprisingly, we
observed that hydrogen pressure was not a crucial parameter
to increase the kinetics. This behaviour could be explained by a
more favourable partial oxidation of palladium particles by HCl
under hydrogen pressure [19]. In all cases, the hydrogenolysis
is the major reaction under 1 or 10 bar H2. Nevertheless, the
hydrodechlorination of chlorobenzene performed under 40 bar
3
.50 nm.
Table 1
Hydrogenolysis of a series of aryl chlorides with Pd colloidal suspensiona
b
Substrate
PH2 (bar)
Product
Conversion (%)
Reaction time (h)
Chlorobenzene
Chlorobenzene
Chlorobenzene
1
10
40
1
10
1
10
1
10
1
Benzene
Benzene
Benzene/cyclohexane
Phenol
Phenol
Anisole
Anisole
Toluene
Toluene
Benzene
Benzene
Benzene
Benzene
100
100
80/20
>98
100
100
100
100
88
>97
91
>97
100
3.2
1.5
22
2
2
4
4
4
4
1
1
1
1
-Chlorophenol
-Chlorophenol
-Chloroanisole
-Chloroanisole
-Chlorotoluene
-Chlorotoluene
,2-Dichlorobenzene
,2-Dichlorobenzene
,3-Dichlorobenzene
,3-Dichlorobenzene
24
22
c
24
22
6.5
5.5
20.5
22.8
23
10
1
10
18.4
a
Conditions: palladium 3.4 × 10 mol, substrate 3.4 × 10−3 mol, HEA16Cl 3.4 × 10−4 mol, substrate/Pd = 100 (molar ratio), water (10 mL), temperature (293 K).
−5
b
c
Determined by GC analysis.
Not optimised.

2
24
B. L e´ ger et al. / Journal of Molecular Catalysis A: Chemical 266 (2007) 221–225
Table 2
Hydrodehalogenation of halobenzene compounds with colloidal suspension of Pd
a
b
Substrate
PH2 (bar)
Product
Conversion (%)
Reaction time (h)
Chlorobenzene
Iodobenzene
1
1
Benzene
Benzene
100
0
3.2
7
Bromobenzene
Bromobenzene
1
10
1
1
10
Benzene
Benzene
Toluene
Chlorobenzene
Chlorobenzene
100
100
100
100
100
10.3
7.3
24
24
6.3
3
3
3
-Bromotoluene
-Bromochlorobenzene
-Bromochlorobenzene
a
Conditions: palladium 3.4 × 10 mol, substrate 3.4 × 10−3 mol, HEA16Cl 3.4 × 10−4 mol, substrate/Pd = 100 (molar ratio), water (10 mL), temperature (293 K).
−5
b
Determined by GC analysis.
of H2 shows the simultaneous formation of benzene and cyclo-
hexanewithafinalratioof80/20. Thepotentialrecyclingprocess
of the suspension was also studied. Successive hydrogenations
of chlorobenzene were carried out after simple decantation of
the aqueous phase containing palladium nanoparticles in a sep-
arating funnel. No loss of activity was observed after two runs.
After a third run, the activity significantly decreased with a con-
version of 32% due to a surface deactivation with produced HCl
but no sedimentation of nanoparticles was observed.
This preliminary investigation shows that the activity was
influenced by the nature of the functional groups. Particularly,
the kinetics decreases with OH and OMe groups on the aromatic
ring and a light destabilization of the catalytic system with the
formation of aggregates is observed. This phenomenon could
be explained by a presumed interaction between oxygen and
palladium. We have already reported similar observation with
NH2 functional group as fragment on aromatic ring in recycling
studies of aniline hydrogenation with rhodium nanoparticles
system and stopped the cleavage of the C–Cl bond. Conse-
quently, we could presume that iodobenzene is a poison of
palladium nanoparticles in our conditions and justify the absence
of reactivity when iodobenzene was alone used as a substrate.
Under hydrogen pressure, dehydrobromation was still slower
than standard dehydrochlorination (1 bar H2, 20 C). Finally, in
catalytic conditions, chloride compounds were better tolerated
than other halides.
The hydrogenolysis of 3-bromotoluene was complete in 24 h
but we observed a small amount of black precipitate at the end
of the reaction. The hydrogenation of 3-chlorobromobenzene
shows the formation of chlorobenzene as final product with
the exclusive hydrogenolysis of the C–Br bond. The same phe-
nomenon is obtained under 10 bar of H2. The C–Cl bond has
never been hydrogenolysed, suggesting the negative effect of
the bromide atom on the hydrogenolysis process. We have
also observed that the turnover frequency calculated for the
hydrogenolysis of the C–Br bond in 3-bromochlorobenzene
◦
−
1
[
9]. This behaviour was not observed with pure heterogeneous
(TOF = 4 h ) is 2.5 times higher than the one of bromoben-
−
1
catalysts [20].
zene (TOF = 10 h ). This decreased reaction rate for the C–Br
bond in the 3-chlorobromobenzene could be explained by
electric (negative inductive and positive mesomeric effects)
and steric effects induced by the presence of the chlo-
ride substituent. Moreover, the cleavage of the C–Br bond
In a second step, we have investigated the influence of halide
(Table 2). The dehalogenation of chlorobenzene, iodobenzene,
bromobenzene was essentially performed at 1 bar of H2. The
reactivity observed in the individual hydrogenolysis processes
varied in the following sequence ClBz > BrBz ꢀ IBz. Chloro
and bromo derivatives proceeded in quantitative yields to the
corresponding aromatic products. In the same conditions, no
reaction was curiously observed with iodobenzene. To explain
this absence of reactivity, we have tested the dehalogenation of
chlorobenzene in the presence of iodobenzene. Two reactions
have been investigated according to the addition of iodobenzene
at the beginning and after 30% of conversion. In both cases, after
stirring for 1 h, no hydrogen consumption was detected indi-
cating that iodobenzene had completely inhibited the catalytic
−
1
(281 kJ mol ) is less energetically demanding than the C–Cl
−
1
bond (340.2 kJ mol ). Similar observations have been reported
by Urbano for the liquid-phase hydrodehalogenation of the 4-
chlorobromobenzene with supported palladium catalysts [21].
We have previously described the efficient hydrogenation
of various benzene compounds in biphasic systems by the
analogous Rh/HEA16Cl [8,9]. To complete this study, the
hydrodechlorination of chlorobenzene and chlorotoluene has
been carried out with the similar aqueous suspension of rhodium
nanoparticles under 10 bar of H2 (Table 3). Interestingly, the
Table 3
Effect of the metal nanoparticle nature on the hydrodechlorination of chlorobenzene derivativesa
b
Substrate
Metal
PH2 (bar)
Product
Conversion (%)
Reaction time (h)
Chlorobenzene
Chlorobenzene
Pd
Rh
Pd
Rh
10
10
10
10
Benzene
Cyclohexane
Toluene
100
100
>90
100
1.5
1.7
6
4-Chlorotoluene
-Chlorotoluene
4
Methylcyclohexane
7.3
a
Conditions: palladium or rhodium 3.4 × 10 mol, substrate 3.4 × 10−3 mol, Pd/HEA16Cl = 10, Rh/HEA16Cl = 2, substrate/metal = 100 (molar ratio), water
−5
(
10 mL), temperature (293 K).
b
Determined by GC analysis.

B. L e´ ger et al. / Journal of Molecular Catalysis A: Chemical 266 (2007) 221–225
225
aqueous rhodium suspension leads to the cleavage of the
C–Cl bond and also to the total hydrogenation of the aro-
matic ring, whereas the palladium system is only limited to
the hydrogenolysis of the C–Cl bond. The partial hydrogena-
tion of the aromatic ring with palladium colloids has just been
observed under 40 bar of H2. Nevertheless, the activity of the
reaction decreases with rhodium nanoparticles in comparison
with palladium nanoparticles. The kinetic analysis of the dehy-
drochlorination of chlorobenzene with rhodium system suggests
that the dehalogenation and the hydrogenation were carried out
in a consecutive process. Finally, according to the preliminary
choice of the metal, the reaction will lead to the formation of
benzene or cyclohexane derivatives as the final product.
[2] A. Roucoux, K. Philippot, in: J.G. de Vries, C.J. Elsevier (Eds.), The
Handbook of Homogeneous Hydrogenation, Wiley–VCH, 2006.
[
3] D.L. Feldheim, C.A. Foss Jr., Marcel Dekker, Metal nanoparticles: synthe-
sis, characterization and applications, New York, 2002.
4] A. Roucoux, J. Schulz, H. Patin, Chem. Rev. 102 (2002) 27.
5] D. Astruc, F. Lu, J. Ruiz Aranzaes, Angew. Chem., Int. Ed. 44 (2005)
7852.
[
[
[
[
[
[
6] M.A. El-Sayed, Acc. Chem. Res. 34 (2001) 257.
7] M. Moreno-Manas, R. Pleixats, Acc. Chem. Res. 36 (2003) 638.
8] A. Roucoux, J. Schulz, H. Patin, Adv. Synth. Catal. 345 (2003) 222.
9] J. Schulz, A. Roucoux, H. Patin, Chem. Eur. J. 6 (2000) 618.
[
10] V. M e´ vellec, A. Roucoux, E. Ramirez, K. Philippot, B. Chaudret, Adv.
Synth. Catal. 346 (2004) 72.
11] V. M e´ vellec, A. Roucoux, Inorg. Chim. Acta 357 (2004) 3099.
12] V. M e´ vellec, C. Mattioda, J. Schulz, J.P. Rolland, A. Roucoux, J. Catal.
[
[
2
25 (2004) 1.
13] (a) F. Alonzo, I.P. Beletskaya, M. Yus, Chem. Rev. 102 (2002) 4009;
b) Y. Monguchi, A. Kume, H. Sajiki, Tetrahedron 62 (2006) 8384.
14] For some examples dechlorination of chloroarenes with palladium, see;
[
[
4
. Conclusion
(
(
(
(
(
(
a) R. Kang, X. Ouyang, J. Han, X. Zhen, J. Mol. Catal. A: Chem 175
2001) 153;
b) R.E. Maleczka Jr., R.J. Rahaim Jr., R.R. Teixeira, Tetrahedron Lett. 43
2002) 7087;
The present work reports catalytic activities of an aque-
ous suspension of nanoparticles in dehydrohalogenation of aryl
halides. The colloidal palladium(0) suspension based on the
classical approach developed in our laboratory has been opti-
mized for this application. The chloride salt HEA16Cl has been
used to efficiently stabilize palladium colloids. In the dehy-
drohalogenation process, rhodium and palladium nanoparticles
have been compared. We have shown that the aqueous palladium
suspension was efficient for the cleavage of the C–Cl bond and
reusable in two successive runs. Nevertheless, poorly results
have been obtained with bromo compounds; in that case, the
hydrogenolysis is efficient but the formation of aggregates is
observed at the end of the catalysis.
c) H. Sajiki, A. Kume, K. Hattori, K. Hirota, Tetrahedron Lett. 43 (2002)
7247;
d) P.P. Cellier, J.-F. Spindler, M. Taillefer, H.-J. Cristau, Tetrahedron Lett.
4 (2003) 7191;
e) O. Navarro, H. Kaur, P. Mahjoor, S.P. Nolan, J. Org. Chem. 69 (2004)
173;
f) P. Selvam, S.U. Sonavane, S.K. Mohapatra, R.V. Jayaram, Tetrahedron
Lett. 45 (2004) 3071;
g) C. Xia, J. Xu, W. Wu, X. Liang, Catal. Commun. 5 (2004) 383–
86;
h) H.M. Roy, C.M. Wai, T. Yuan, J.-K. Kim, W.D. Marshall, Appl. Catal.
(
4
(
3
(
(
3
(
A 271 (2004) 137–143.
The rhodium nanoparticles were active for the hydrodechlo-
rination. Under hydrogen pressure, the slow hydrogenation of
the aromatic ring was also obtained and cyclohexane derivatives
were produced as the final products. The hydrogenation of the
aromatic ring with palladium system could only be performed
under significant hydrogen pressure (>40 bar of H2).
[
[
[
15] J. Blum, A. Rosenfeld, F. Gelman, H. Schumann, D. Avnir, J. Mol. Catal.
146 (1999) 117.
16] X.L. Zhen, J.R. Han, R.H. Kang, X.M. Ouyang, Chin. Chem. Lett. 12
(
2001) 287.
17] Y.H. Dong, Q.Z. Meng, R.H. Kang, Chin. Chem. Lett. 14 (2003)
68.
3
[
[
[
18] R. Nakao, H. Rhee, Y. Uozumi, Org. Lett. 7 (2005) 163.
19] G. Del Angel, J.L. Benitez, J. Mol. Catal. A: Chem. 165 (2001) 9.
20] T. Vincent, S. Spinelli, E. Guibal, Ind. Eng. Chem. Res. 42 (2003)
References
5968.
[
21] M.A. Aramendia, V. Borau, I.M. Garcia, C. Jim e´ nez, A. Marinas,
J.M. Marinas, J.M. Marinas, F.J. Urbano, Appl. Catal. B 43 (2003)
[
1] (a) G. Schmid (Ed.), Nanoparticles. From Theory to Application,
Wiley–VCH, Weinheim, 2004;
71.
(
b) G. Schmid, in: K.J. Blabunde (Ed.), Nanoscale Materials in Chemistry,
Wiley-Interscience, New York, 2001.