Dual Catalytic Activity of Palladium Doped with a Rhodium Complex in a One-pot, Four Step Process

Article abstract of DOI:10.1002/cctc.201500240

The extraction of the two competing reactions from the same catalyst - a composite catalytic-complex@catalytic-metal - is reported. A Wilkinson rhodium based catalyst entrapped within metallic palladium catalyst is shown to perform both hydroformylation and hydrogenation with a ratio that depends on H₂ and CO pressures. Here we demonstrate this special reactivity in a one-pot, four step sequence, which include hydroformylations of phenyl acetylenes, reduction of nitrobenzene to aniline, carbonyl-amine condensations forming imines; and imine reductions.

Full text of DOI:10.1002/cctc.201500240

DOI: 10.1002/cctc.201500240
Communications
Dual Catalytic Activity of Palladium Doped with
a Rhodium Complex in a One-pot, Four Step Process
Leora Shapiro,[a] Matthias Driess,*[b] and David Avnir*[a]
The extraction of the two competing reactions from the same
catalyst—a composite catalytic-complex@catalytic-metal—is
reported. A Wilkinson rhodium based catalyst entrapped
within metallic palladium catalyst is shown to perform both
hydroformylation and hydrogenation with a ratio that depends
on H2 and CO pressures. Here we demonstrate this special re-
activity in a one-pot, four step sequence, which include hydro-
formylations of phenyl acetylenes, reduction of nitrobenzene
to aniline, carbonyl-amine condensations forming imines; and
imine reductions.
molecular homogeneous catalysts, including organometallic,[7]
polymeric,[8] and inorganic catalysts[9] (we recall that the classi-
cal supports for dispersed metals included mainly ceramic and
polymeric supports, but never metals); the second direction is
to affect the catalytic properties of the metal by doping it;[10]
and the third direction has been the utilization of the catalytic
properties of both the metal and the dopant[11]—progress in
the latter direction is the main topic of this report. Some exam-
ples for the first direction include enantioselective electrohy-
drogenations with alkaloid@Ag,[12] the acid catalyzed pinacol–
pinacolone rearrangement by Nafion@Ag,[13] the hydrogena-
tion of styrene with [RhCl(cod){Ph2P(C6H4SO3Na)}]@Ag,[7] the
Introduction
Friedel–Crafts
adamantylation
of
aromatics
by
H3[P(Mo3O10)4]@Ag and H3[P(W3O10)4]@Ag,[9] the partial enantio-
selective hydrogenation of ketones with (À)-cinchoni-
dine@Pd,[14] and the biocatalyzed hydrolysis of p-nitrophenyl
phosphate with acid phosphatase@Au.[15] An example of the
second direction—affecting the catalytic activity of the
metal—is the efficient oxidation of methanol to formaldehyde
by silver doped with Congo red.[10a,b] These reports demon-
strated the synthesis of products that cannot be obtained by
the separate components, as well as improved stabilities and
higher conversions. All of these types of reactivity are possible
because the 3D metallic cage which forms around the dopant
consists of tight aggregates of metal crystallites, and this
porous hierarchal nature, allows on one hand diffusion of sub-
strate and product molecules in and out of the catalytic mate-
rial, yet not allowing the dopant to leach out even in the sol-
vent used for entrapment. The accumulated data with these
materials has shown that 3D entrapment and 2D adsorptions
are completely different processes, and the pattern of per-
formance in the reported applications was witnessed solely in
the entrapped 3D case.
Despite the fact that metals have been a key component in
catalysis since its birth, methods for affecting their elementary
properties and thus also their catalytic activity have been
limited, and have included co-chemisorption of molecules,
which are not substrate molecules, alloying the metal with an-
other metal,[1] downsizing to the nanoscale,[2] affecting the
metal particle through their interaction with their support.[3]
Recently we have introduced a novel approach to that chal-
lenge: Doping the metal with molecules.[4] The metals doping
methodology, which has been developed in the past decade,
gave rise to the ability of merging properties from the very
rich library of several tens of millions of organic molecules
with the rather limited library of metals, resulting in the forma-
tion of new metallic hybrids, denoted molecule@metal, with
new or improved properties, practically wherever metals have
been used.[4,5] Needless to say, metal catalysis is one of the
areas to potentially gain most from this new materials method-
ology.[6] In principle, three directions in catalysis can be identi-
fied: First, using the metal as a heterogenization support for
We return now to the third direction, where both the metal
and the dopant are catalysts. This stimulating possibility al-
ready yielded some interesting observations. For instance, ex-
ceptional synergism between dopant and metal—a rhenium
complex entrapped within a silver was recently reported for
alkene epoxidations.[16] Yet another demonstration of the hori-
zon opened by this direction has been the report on a one-pot
dual catalytic reaction from the hybrid catalytic material, Na-
fion@Pd,[11a] where the Nafion acts as an acidic catalyst and the
palladium as a hydrogenation and disproportionation catalyst
in a two catalytic step process. Here we widen the scope of
catalyst@catalyic-metal concept to two new aspects: First, we
introduce the option of entrapment of an organometallic cata-
lytic complex in a catalytic metal. Specifically we demonstrate
this concept by entrapping a rhodium complex - Wilkinson’s
catalyst [(RhCl(TPPS)3] (TPPS=triphenylphosphine-3-sulfonic
[a] L. Shapiro, Prof. D. Avnir
Institute of Chemistry and the Center for
Nanoscience and Nanotechnology
The Hebrew University of Jerusalem
Jerusalem 91904, (Israel)
E-mail: david.avnir@mail.huji.ac.il
[b] Prof. M. Driess
Institute of Chemistry: Organometallic and Inorganic Materials, Sekr. C2
Technische Universität Berlin
Strasse des 17. Juni 135, 10623 Berlin (Germany)
Fax: (+49) 3031429732
E-mail: matthias.driess@tu-berlin.de
Supporting information for this article is available on the WWW under
http://dx.doi.org/10.1002/cctc.201500240.
This publication is part of a Special Issue on Palladium Catalysis. To view
the complete issue, visit:
http://onlinelibrary.wiley.com/doi/10.1002/cctc.v7.14/issuetoc
ChemCatChem 2015, 7, 2033 – 2037
2033
ꢀ 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Communications
acid sodium salt)) within metallic Pd, [Rh]@Pd in short. Second,
we aimed at increasing the number of one-pot reactions, and
report here a four step sequence, including reduction of nitro-
benzene to aniline, hydroformylations of phenyl acetylenes,
carbonyl-amine condensations forming imines, and imine re-
ductions. The main synthetic challenge has been how to tailor
reaction conditions that will accommodate in one pot both
the oxo-reaction and the hydrogenation. Although hydrogena-
tion is usually a straightforward reaction of molecular hydro-
gen addition and is known to be catalyzed by both palladium
and rhodium, hydroformylation is a more complex reaction of
addition of CO and hydrogen to a carbon-carbon double or
triple bond resulting in linear and branched aldehydes. Hydro-
formylation of alkynes and specifically aryl alkynes and unsym-
metrical alkynes is especially difficult, as usually the selectivity
towards hydroformylation rather than hydrogenation is chal-
lenging; here is how we solved it:
Results and discussion
As the multiple activity of [Rh]@Pd is dictated by the material
characteristics of this doped metal, we begin with this aspect
of the study, and then move on to its reactivity. SEM images,
Figure 1, display the typically aggregated porosity of the
matrix, an important feature that allows substrate molecules to
penetrate and reach the entrapped Rh catalyst, and allows
product molecules to diffuse out.
Figure 2. Top–Adsorption-desorption isotherms of nitrogen is indicative of
the mesoporosity of [Rh]@Pd. Bottom–Shown is the compliance to the BET
equation: The perfect compliance is indicative of the homogeneity of the
composite material.
Figure 1. SEM images of the dual catalyst [Rh(TPPS)3Cl]@Pd, ([Rh]@Pd). Left
bar, 2 mm; right bar 200 nm.
Figure 3. XRD analysis of the composite [Rh]@Pd.
Further characterization of this porosity is provided by the
shape of the nitrogen adsorption-desorption isotherm
(Figure 2, top) which is typical of a mesoporous material;
indeed, the BJH-calculated average pore diameter is ꢀ10 nm
(see the Supporting Information) and the calculated BET sur-
face area is 13.5 m2 gÀ1 (for comparison purposes with classical
catalysts supports such as carbon and alumina, recall that the
weight of Pd is much higher than C or Al, that is, in terms of
per mol atoms, the comparative surface area is higher). An im-
portant observation is that the compliance to the BET equation
is excellent (Figure 2, bottom)—this indicates the homogeneity
of the physisorption sites, and, therefore, also the homogenei-
ty of the composite material, that is, of good dispersion of the
dopant in the metal.
X-ray diffraction (XRD) analysis indicates clearly that the FCC
crystal nature of the palladium nanocrystallites is not affected
by the entrapment (Figure 3). Notably, the XRD spectrum
shows no signs of zinc and palladium oxide, and likewise not
seen are metallic rhenium crystals. The average size of the Pd
nanocrystals, as determined by the Scherer equation is
ꢀ2.8 nm, somewhat smaller than, but in agreement with pre-
vious reports.[11a] The presence of the Rh complex was con-
firmed by EDAX analysis (Figure 4). The EDAX analysis also re-
veals the ligand’s phosphorous, as well as oxygen and zinc
(which probably originate from small amounts of PdO and
ZnO on the surface, but as these are not seen by XRD, they are
apparently residual).
ChemCatChem 2015, 7, 2033 – 2037
www.chemcatchem.org
2034
ꢀ 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Communications
ucts is obtained, and, interestingly, no styrene is observed as
potential intermediate. The most successful reactions were per-
formed when the reaction vessel was charged with hydrogen/
carbon monoxide molar ratio of 1:4 at pressures of 100 and
400 psi (total reaction pressure of 500 psi; 1 psi=68.9 mbar).
The large excess of CO ensured the successful progress of the
hydroformylation rather than hydrogenation. The optimized
temperature was 958C—at lower temperatures, hydrogenation
to ethylbenzene was the preferred reaction. Solvent selection
was also critical: In addition to the other factors mentioned, se-
lection of the right polar solvent is important for the success
of a hydroformylation reaction;[20] chlorinated solvents were
found to be more useful than methanol and hexanes.
Duration of 48 h was needed for the completion of the full
reaction set under optimal conditions. Although reduction was
the fastest process, hydroformylation was slow, and so was the
condensation reaction. The ratio of linear: branched products
(N-phenylbenzenepropanamine and b-methyl-N-phenylbenze-
neethanamine), under the optimal conditions was 1:1.9. When
a blank hydroformylation reaction was performed with no ni-
trobenzene in the reaction vessel, hydrogenation of phenylace-
tylene to ethylbenzene was observed as well (35%). Another
important aspect of the four-step sequence is that the final re-
duction of the imine to amine pulls the whole sequence to
completion. This is so because the imine formation is an equi-
librium reaction which releases water as a by-product. The
shifting of the imine formation is assisted by water removal,
and therefore several beads of molecular sieves were added to
the reaction vessel.
Figure 4. EDAX analysis of [Rh]@Pd.
As described above, our aim has been to combine in one
catalytic material the ability to hydroformylate and to hydro-
genate. As metallic palladium catalyzes hydrogenation, but
practically does not catalyze hydroformylation, it was selected
as the entrapping metal of choice. On the other hand, rhodium
complexes are widely used to catalyze hydroformylation reac-
tions,[17] but the efficiency of Willkinson-type catalysts in hydro-
genations is greatly decreased as the number of the triphenyl-
phosphine groups increases,[18] and thus this complex was se-
lected as the organometallic complex to be entrapped. Al-
though combinations of rhodium (both as metal particles and
in the form of a complex) and palladium were anchored onto
silica to explore hydrogenation and hydroformylation separate-
ly,[19] their one-pot competition over hydrogen was not ex-
plored.
Shown in Figure 5 are the details of the optimization experi-
ments (average of at least four repetitions), which led to the
optimal conditions of 100:400 psi of hydrogen to CO. To com-
pare the results of the experiments under different pressures,
the experiment was allowed to run for 6 days to reach near
completion under the different conditions. Depending on the
CO/H2 ratio, the linear branched products ratio varied in the
range 1:1.5–1:2. Additional hydrogen pressures of 400, 200,
and 50 psi, as well as the use of hydrogen at atmospheric pres-
sure (15 psi), all with CO pressure of 400 psi were tested. When
hydrogen at atmospheric pressure was used, the hydroformyla-
tion reaction did not take place at all and hydrogenation of ni-
trobenzene to aniline took place only in part. If hydrogen is
scarce, the reduction processes are slowed down, due to occu-
pation of the catalyst pores by CO molecules. This is why even
after a long reaction time of 6 days phenylacetylene was still
observed at pressures of 50 psi and lower. The fact that at low
levels of hydrogen of 50 psi reduction of phenylacetylene to
Indeed, the main problem which was solved in this study
has been to carefully find the right hydrogen pressure that will
allow hydroformylation and hydrogenation at the same time—
too much reduces all of the starting substrates and prevents
hydroformylation, and too little allows partial hydroformylation
and partial hydrogenation. Thus, we regard the extraction of
the two competing reactions from the same catalyst, as shown
below, as a non-trivial result of this study. Specifically, as men-
tioned above, we performed the hydroformylation reaction on
terminal aryl-alkynes resulting in the corresponding branched
and linear aldehydes, the reduction of nitrobenzene to aniline,
the condensation of both products to the corresponding
imines, and their reduction to the substituted amines
(Scheme 1). Under the optimal conditions described in the Ex-
perimental Details none of the potential hydroamination prod-
Scheme 1. Typical reactions sequence of the hybrid catalyst. Molecular sieves were added to assist in pulling the reaction towards the imine.
ChemCatChem 2015, 7, 2033 – 2037
www.chemcatchem.org
2035
ꢀ 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Communications
a slight reduction in yield from 80% down to 72%; interesting-
ly only the branched product was obtained. Further recycles
do not yield satisfactory values.
In conclusion, the independent reactions of hydrogenation
and hydroformylation, catalyzed by a hybrid catalyst of a rhodi-
um complex entrapped within palladium was demonstrated
and investigated. We showed that consecutive catalytic reac-
tions using one combined catalyst can lead to interesting ways
in which multiple step processes are performed; we believe
these observations are of interest in the general context of
heterogeneous catalysis.
Experimental Section
Figure 5. Dependence of products and intermediate distributions on the hy-
Preparation of the [Rh]@Pd catalyst: Synthesis of the catalyst: Rh
atoms (9”10À4 mol) in the form of [(RhClCOD)2] (COD=cycloocta-
diene) were placed in a round bottom flask along with TPPS (tri-
phenylphosphine-3-sulfonic acid sodium salt, 2.7”10À3 mol) and
dissolved with methanol (55 mL). The mixture was stirred over-
night at 558C and evaporated to dryness, resulting in [Rh(TPPS)3Cl],
denoted [Rh] for short. Entrapment of [Rh] in Pd: [Rh] was dis-
solved in triply distilled water (160 mL) and then PdCl2 (9”
10À3 mol) was added, the temperature was set to 408C and Zn
granules (0.01 mol) were added. The mixture was stirred for five
days during which the slurry blackened, and then the product,
[Rh]@Pd, was filtered, washed with water three times and then
with HCl (0.1m, 30 mL), and dried overnight in a desiccator. Before
use, the catalyst was ground using an agate mortar and pestle for
several minutes, until the metal crumbs were homogeneous to the
eye. TGA analysis average indicates a Rh/Pd weight ratio of 1:8 in
the final product, [Rh]@Pd.[21]
The one-pot, four step multiple catalytic reaction: The dried cat-
alyst (0.13 g, 1.1”10À3 mol Pd, 9.8”10À5 mol Rh) was placed in
a pressure vessel. Nitrobenzene (0.1 mL, 9.8”10À4 mol) and phenyl-
acetylene (0.1 mL, 9.1”10À4 mol), and 1,2-dichloroethane (3.0 mL)
were added along with ꢀ10 beads of molecular sieves (4 Š). A
feed of H2 (100 psi) and CO (400 psi) was inserted to the reaction
mixture, which was heated to 908C for 2 days. The reaction com-
ponents were identified by NMR spectroscopy and gas chromatog-
raphy. NMR was measured after evaporation and compared, when
possible, to known spectra, or an NMR prediction tool was used.[21]
Recyclability test: The dried catalyst (0.13 g, 1.1”10À3 mol Pd,
9.8”10À5 mol Rh) was placed in a pressure vessel. Nitrobenzene
(0.1 mL, 9.8”10À4 mol) and phenylacetylene (0.1 mL, 9.1”
10À4 mol), and 1,2-dichloroethane (3.0 mL) were added along with
ꢀ10 beads of molecular sieves (4 Š). A feed of H2 (100 psi) and CO
(400 psi) was inserted to the reaction mixture, which was heated to
908C for 2 days. Then, the supernatant was poured off, centrifuged
at 50000 rpm for 20 min and evaporated for measurement. The re-
maining catalyst was collected back into the reaction vessel for fur-
ther use.
drogen pressure at fixed CO pressure of 400 psi.
styrene does take place may indicate that the hydroformyla-
tion process passes though initial reduction to styrene in this
particular system. Here the branched product begins to form
at a 5% level. The hydroformylation of acetylene was slightly
greater at 100 psi compared to 200 psi of hydrogen. The main
by-product was ethylbenzene, and the percentage of this
product grows as the pressure of hydrogen increases. At high
levels of hydrogen, reduction to ethylbenzene occurs (as is the
reduction of nitrobenzene to aniline) that is, reduction of the
double bond takes place rather easily and other reactions,
such as hydroamination or hydroformylation are observed to
a lesser degree. When the ratio was increased to 400:400 (a
total of 800 psi), hydrogenation to ethyl benzene with little hy-
droformylation took place.
To assure that the observed reaction sequence is not due to
leached [Rh], the supernatant solution was tested for possible
catalytic effects according to the same procedure for 6 days
under heating. No hydroformylation was observed, but the
presence of some palladium nanoparticles was detected by
minor reduction to styrene, ethyl benzene and aniline, and
also some hydroamination—the first and the last do not form
with the hybrid catalyst. Finally, the ability to affect the reac-
tions sequence of Scheme 1 was additionally tested on three
substituted phenylacetylenes: 4-chlorophenlacetylene, 4-fluo-
rophenlacetylene, and 4-methodxyphenlacetylene. Indeed, it
was found to work as well, and the results are summarized in
Table 1.
Table 1. Yields of final products for various acetylenes.
Instrumentation: For SEM measurements a Sirion (FEI) microscope
was used, operating at 5 kV, fitted with an EDS free detector. Sam-
ples were prepared by placing the air-dried powder on an alumi-
num stub suitable for SEM using carbon double side tape. Ther-
mogravimetric analysis was performed by using a Mettler–Toledo
TGA/SDTA 851e from 50 to 800 8C at a heating rate of 108CminÀ1
in flowing N2. Specific surface area was calculated from nitrogen
adsorption/desorption isotherms obtained by using a Micromeritics
ASAP 2000 surface analyzer, using the BET equation. Gas chromato-
graphs were measured by using an Agilent 7890A GC, fitted with
an HP-5 column. Solution analysis was performed by introducing
Substrate
Yield [%]
Linear
Ratio
Branched
Total
phenylacetylene
54.3
48.9
25.7
25.6
28.6
17.2
6.8
82.9
66.1
32.5
45.2
1.9
2.8
3.8
1.3
4-fluorophenylacetylene
4-chlorophenylacetylene
4-methoxyphenylacetylene
19.6
Recyclability experiment was performed with a focus on the
performance of the entrapped [Rh]: the second cycle showed
ChemCatChem 2015, 7, 2033 – 2037
www.chemcatchem.org
2036
ꢀ 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Communications
[5] a) G. Palmisano, V. Augugliaro, R. Ciriminna, M. Pagliaro, Can. J. Chem.
2009, 87, 673–677; b) V. B. Kumar, Y. Koltypin, A. Gedanken, Z. e. Porat,
J. Mater. Chem. A 2014, 2, 1309–1317.
[6] A. Thomas, M. Driess, Angew. Chem. Int. Ed. 2009, 48, 1890–1892;
Angew. Chem. 2009, 121, 1922–1924.
[7] I. Yosef, R. Abu-Reziq, D. Avnir, J. Am. Chem. Soc. 2008, 130, 11880–
11882.
[8] H. Behar-Levy, D. Avnir, Chem. Mater. 2004, 16, 3197–3202.
[9] S. Krackl, A. Company, Y. Aksu, D. Avnir, M. Driess, ChemCatChem 2011,
3, 227–232.
[10] a) Y. Aouat, G. Marom, D. Avnir, V. Gelman, G. E. Shter, G. S. Grader, J.
Phys. Chem. C 2013, 117, 22325–22330; b) Y. Aouat, Y. Azan, G. Marom,
D. Avnir, Sci. Adv. Mater. 2013, 5, 598–605; c) G. E. Shter, H. Behar-Levy,
V. Gelman, G. S. Grader, D. Avnir, Adv. Funct. Mater. 2007, 17, 913–918;
d) Y. Binyamin, G. E. Shter, V. Gelman, D. Avnir, G. S. Grader, Catal. Sci.
Technol. 2011, 1, 1593–1599.
sample solutions by direct spitless injection (1 mL by volume). For
the chromatography procedure, the oven temperature was elevat-
ed from 808C to 2208C at 2.58CminÀ1
, then to 2608C at
208CminÀ1 and held at the final temperature for 10 min. Helium
carrier gas flow was 1.5 mLmin<-M>1. X-ray diffraction (XRD) mea-
surements were performed with a Philips automated powder dif-
fractometer (with a PW1830 generator, PW1710 control unit,
PW1820 vertical goniometer, 40 kV, 30 mA, CuKa1 (1.5406 Š), step-
scan mode 0.02 sÀ1). NMR spectra were recorded with Bruker DRX-
400 in CDCl3.
Acknowledgements
[11] L. Shapiro, D. Avnir, ChemCatChem 2013, 5, 2195–2198.
[12] H. Yang, D. Chi, Q. Sun, W. Sun, H. Wang, J. Lu, Chem. Commun. 2014,
50, 8868–8870.
We acknowledge the support of the Einstein Foundation, Berlin,
and the Israel Science Foundation (grant no. 703/12).
[13] H. Behar-Levy, D. Avnir, Adv. Funct. Mater. 2005, 15, 1141–1146.
[14] L. Durµn Pachón, I. Yosef, T. Z. Markus, R. Naaman, D. Avnir, G. Rothen-
berg, Nat. Chem. 2009, 1, 160–164.
[15] R. Ben-Knaz, D. Avnir, Biomaterials 2009, 30, 1263–1267.
[16] A. Indra, M. Greiner, A. K. Gericke, R. Schlçgl, D. Avnir, M. Driess, Chem-
CatChem 2014, 6, 1935–1939.
Keywords: heterogeneous catalysis · mesoporous materials ·
multiple catalysis · organic–inorganic hybrid composites ·
supported catalysts
[17] P. W. N. M. v. Leeuwen, C. Clever, Rhodium Catalyzed Hydroformylation,
Kluwer Academic Publishers, The Netherlands, 2000.
[18] C. Daniel, N. Koga, J. Han, X. Y. Fu, K. Morokuma, J. Am. Chem. Soc.
1988, 110, 3773–3787.
[19] a) R. Abu-Reziq, D. Avnir, I. Miloslavski, H. Schumann, J. Blum, J. Mol.
Catal. A 2002, 185, 179–185; b) H. Gao, R. J. Angelici, J. Mol. Catal. A
1999, 145, 83–94.
[1] a) J. L. Fernµndez, D. A. Walsh, A. J. Bard, J. Am. Chem. Soc. 2005, 127,
357–365; b) M. S. Chen, D. Kumar, C. W. Yi, D. W. Goodman, Science
2005, 310, 291–293; c) E. Antolini, Energy Environ. Sci. 2009, 2, 915–
931; d) H.-L. Jiang, Q. Xu, J. Mater. Chem. 2011, 21, 13705–13725.
[2] a) R. Narayanan, M. A. El-Sayed, J. Phys. Chem. B 2005, 109, 12663–
12676; b) D. Astruc, F. Lu, J. R. Aranzaes, Angew. Chem. Int. Ed. 2005, 44,
7852–7872; Angew. Chem. 2005, 117, 8062–8083; c) B. Lim, M. Jiang,
P. H. C. Camargo, E. C. Cho, J. Tao, X. Lu, Y. Zhu, Y. Xia, Science 2009, 324,
1302–1305; d) M. Haruta, M. Date, Appl. Catal. A 2001, 222, 427–437;
e) M. C. Daniel, D. Astruc, Chem. Rev. 2004, 104, 293–346.
[20] R. Franke, D. Selent, A. Bçrner, Chem. Rev. 2012, 112, 5675–5732.
[21] L. Patiny, J. Wist, 2015.
[3] T. Y. Chung, C. S. Tsao, H. P. Tseng, C. H. Chen, M. S. Yu, J. Colloid Interface
Sci. 2015, 441, 98–105.
Received: March 6, 2015
Revised: April 17, 2015
[4] D. Avnir, Acc. Chem. Res. 2014, 47, 579–592.
Published online on June 18, 2015
ChemCatChem 2015, 7, 2033 – 2037
www.chemcatchem.org
2037
ꢀ 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim