Ni/Pd@MIL-101: Synergistic catalysis with cavity-conform Ni/Pd Nanoparticles

Article abstract of DOI:10.1002/anie.201205078

A perfect fit: Cavity-conform bimetallic Ni/Pd nanoparticles of different composition were generated in the metal-organic framework MIL-101. Experimental evidence and molecular dynamic simulations indicate the existence of mixed bimetallic particles. Pronounced synergistic effects have been observed in liquid-phase catalysis. Copyright

Full text of DOI:10.1002/anie.201205078

Angewandte
Chemie
DOI: 10.1002/anie.201205078
Bimetallic Catalysis
Ni/Pd@MIL-101: Synergistic Catalysis with Cavity-Conform Ni/Pd
Nanoparticles**
Justus Hermannsdçrfer, Martin Friedrich, Nobuyoshi Miyajima, Rodrigo Q. Albuquerque,
Stephan Kꢀmmel, and Rhett Kempe*
Porous coordination polymers (PCP)[1] or metal–organic
frameworks (MOF)[2] are currently being intensively inves-
tigated, for example regarding gas storage,[3] separation,[4]
sensing,[5] and as catalysts.[6] In view of catalytic applications,
PCP/MOFs are well-suited to stabilize very small metal
nanoparticles (MNP) without blocking their surface by
strongly binding ligands. The cavities and windows of the
PCP/MOFs can regulate particle size and simultaneously
Figure 1. Size-selective cavity loading of MIL-101 (left: cavity-conform;
center: undersized cavity loading; right: introduction of a second
metal).
guarantee access to the catalytically active sites of the MNP.
In comparison to loading by solution infiltration,[7] solid
grinding,[8] microwave irradiation,[9] and surface grafting,[10]
the MOCVD method (metal–organic chemical vapor depo-
sition) developed by Fischer and co-workers is of advantage
especially in terms of control and high metal loadings
(> 5 wt%).[11] The host structures MOF-5,[2] MOF-177,[26]
and MIL-101[27] have mainly been used for loading with
different MNPs (Fe,[12–15] Co,[15,16] Cu,[12,13,17] Zn,[12,13,17,18] Sn,[12]
Pt,[12,14] Au,[12,19] Pd,[12–14,20–23] Ru,[14,24] and Ni).[25] The signifi-
cantly higher stability of MIL-101 to hydrolysis in comparison
to MOF-5 and MOF-177 makes it attractive for the synthesis
of robust catalyst systems.[22,23] Debatable (independent from
the loading method used) is the question as to whether the
generated MNPs are localized inside the PCP/MOF cavities
or not. Frequently, MNPs larger than the cavities and particles
localized on the outer surface of the PCP/MOF crystallite
were observed. Recently, we could show that one can
synthesize MIL-101 cavity-conform PdNPs by applying the
MOCVD method using the precursor [(C5H5)Pd(C3H5)]
followed by reduction with H2 at room temperature
(Figure 1, left).[23] If the reduction is carried out at 708C,
significantly smaller PdNPs were generated. Their diameter
seems to be determined by the window sizes and not so much
by the cavity sizes (Figure 1, center).[23] This observation
allows to conclude that the remaining space can be used to
load a second metal. Thus, bimetallic NPs in the sub-
nanometer range (< 10 nm) are accessible (Figure 1, right).
This is interesting for catalytic applications for a number of
reasons. Very small NPs have a very large surface-to-volume
ratio. The dilution of costly noble metals by inexpensive
metals such as Ni is economical. Bimetallic NP catalysts can
show synergistic effects regarding activity and/or selectivity as
(for instance) observed for Au/Pt NPs supported on spherical
polyelectrolyte brushes.[28]
We report herein on the generation of cavity-conform Ni/
Pd NPs of different composition and their synergism in the
catalytic hydrogenation of dialkyl ketones. The synthesis of
bimetallic NPs in PCP/MOF by MOCVD has not been
significantly investigated.[14] Catalytic synergy effects of
cavity-conform bimetallic MNPs stored in PCP/MOF cavities
are not known. PCP/MOFs were used as support (localization
of the MNP also at the outer surface of the PCP/MOF
crystallites and/or regarding the size, not cavity-conformity)
for bimetallic Au/Pd and Ag/Au NPs and catalytic synergism
could be observed.[29,30] The optimal synthesis of the Ni/
Pd@MIL-101 catalysts was firstly investigated with respect to
two loading versions, namely successively and simultaneously.
The successive loading seems attractive, as the undersized
PdNPs offer enough room to form cavity-conform bimetallic
particles. Admittedly, the PdNPs could function as agglom-
eration sites and initiate excessive particle growth. The
simultaneous loading becomes difficult owing to the different
reduction behavior of the two precursors. A 1:1 loading with
Pd and Ni precursors, [(C5H5)Pd(C3H5)] and [(C5H5)2Ni],
leads to (after reduction) NPs that are mainly in the size range
of the MIL-101 cavities for both variants (Supporting
Information, Figure S1). For successive loading, comparably
more oversized particles were generated. PXRD (powder X-
ray diffraction) shows two separated Ni and Pd 111 peaks for
[*] J. Hermannsdçrfer, M. Friedrich, Prof. Dr. R. Kempe
Lehrstuhl Anorganische Chemie II, Universitꢀt Bayreuth,
95440 Bayreuth (Germany)
E-mail: kempe@uni-bayreuth.de
Dr. N. Miyajima
Bayerisches Geoinstitut, Universitꢀt Bayreuth,
95440 Bayreuth (Germany)
Prof. Dr. R. Q. Albuquerque, Prof. Dr. S. Kꢁmmel
Theoretische Physik IV, Universitꢀt Bayreuth,
95440 Bayreuth (Germany)
Prof. Dr. R. Q. Albuquerque
Institute of Chemistry of S¼o Carlos, University of S¼o Paulo,
13560-970 S¼o Carlos (Brazil)
[**] This project was financially supported by the Deutsche For-
schungsgemeinschaft, SFB 840.
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/anie.201205078.
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the successive loading (Supporting Information, Figure S2),
with the Ni peak being considerable weaker. In contrast, the
simultaneous loading shows a single broad 111 peak, indicat-
ing bimetallic NPs. The synthesis of the PdxNiy@MIL-101
catalyst systems with an exact adjustment of the Pd to Ni ratio
by substitution of Pd by Ni in 20 weight percent steps
(Supporting Information, Figure S3) was therefore carried
out by applying the simultaneous loading. First, the reduction
was carried out at 708C and 50 bar H2 pressure for 20 h (1.
generation).[23] TEM (transmission electron microscopy)
confirm NPs from 2 to 3 nm (Supporting Information, Fig-
ure S4–S6) for the systems with high Pd content (Pd > Ni).
Additionally, the formation of large particles at the outer
surface of the MIL-101 crystals (Supporting Information,
Figure S7) is observed at high Ni content. Pure Ni@MIL-101
follows this tendency and leads to NPs that are clearly over
the size of the MIL-101 cavities. Owing to an increasing
particle size with increasing Ni content, the reduction
conditions were optimized. Cavity-conform bimetallic NPs
could be generated by increasing the temperature and
reducing the pressure (second generation; Figure 2).
PXRD and IR spectroscopy investigations confirm the
stability of the support under the relatively harsh reduction
conditions (Supporting Information, Figure S11, S12, S14).
Elemental analysis shows an average metal loading of
18 wt%, which matches with the calculated metal content
(Supporting Information, Figure S15). Even a small amount
of Pd changes the reduction behavior of [(C5H5)2Ni] and
prevents the formation of larger Ni particles. HR TEM EDS
measurements of Pd4Ni1@MIL-101 und Pd3Ni2@MIL-101
indicate bimetallic particles. EDS investigations of the
whole sample and a few of the single particles show identical
Ni:Pd ratios (Figure 3). In combination with the catalytic
activity and the calculations carried out (see below), the
formation of bimetallic Ni/Pd NPs can be concluded. In
comparison to pure MIL-101, N2 physisorption shows a low-
ered surface for the loaded systems, which results from
a higher sample weight and the occupation of pores by MNP
(Supporting Information, Table S2). Interestingly, pure
Pd@MIL-101 und pure Ni@MIL-101 show a larger specific
surface than the mixed systems. This might be explained by
the localization of some MNPs on the outer surface for
Ni@MIL-101 and the formation of undersized MNPs in case
of Pd@MIL-101.
The PdxNiy@MIL-101 catalyst systems were investigated
in different hydrogenation reactions. For the reduction of
phenol and cyclic ketones (Figure 4) and dialkyl ketones
(Table 1), a clearly pronounced synergistic effect is observed.
The mixed Ni/Pd catalysts are definitely more active than the
pure Pd or Ni catalysts. Generally, the hydrogenation of
dialkyl ketones is difficult to accomplish by heterogeneous
catalysts.[31] Aryl alkyl ketones are hydrogenated without
problems by these catalysts.[23] Neither 3-heptanone nor
cyclohexanone are reduced by the Ni@MIL-101 catalyst
under the conditions used. Pd@MIL-101 also has clearly
lower conversions, which are comparable to that of Pd on
activated carbon (Pd/C). In contrast, the combination of both
metals in the bimetallic PdxNiy@MIL-101 catalyst systems
shows high conversions also at 258C (Table 1, entry 1).
Figure 2. TEM investigations of the PdxNiy@MIL-101 catalyst systems
using the optimized reduction conditions (second generation). With
increasing Ni content, the reduction temperature is increased and the
pressure is reduced (Pd5, Pd4Ni1, Pd3Ni2 =708C/50 bar;
Pd2Ni3 =708C/5 bar; Pd1Ni4, Ni5 =908C/5 bar). The reduction time
was 20 h. The averaged metal loading is 18 wt%. The substitution of
Pd by Ni was carried out in 20 wt% steps.
Table 1 shows the results of the reduction of 3-heptanone
under different conditions. The use of a mixture of pure
Pd@MIL-101 and pure Ni@MIL-101 in a 3:2 ratio (entries 4,
5, and 11) shows a clearly lower catalytic activity than the
corresponding catalyst Pd3Ni2@MIL-101 and as Pd4Ni1@MIL-
101 (entries 7 and 8). The conversions of a corresponding
mixture of Pd/C and Ni powder (Merck) (entries 6 and 12) are
lower. The lower conversions (under analogous conditions) of
the mixture of pure Pd@MIL-101 and Ni@MIL-101 catalyst in
comparison to the bimetallic cavity-conform PdxNiy@MIL-
101 catalyst systems indicate a synergistic catalysis effect that
is based on bimetallic particles. A comparison between
successive and simultaneous loading (entries 8 and 9) shows
that the successive loading leads to catalytically less active Ni/
Pd NP structures. Experiments with first-generation
PdxNiy@MIL-101 (15–17) also yielded lower conversions
than that of the second generation. The adjustment of the
reduction conditions towards cavity-conform NPs has a pos-
itive influence on the activity as well.
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tures. Two examples are shown in Figure 5. The left
structure (a) is the energetically most favorable struc-
ture that we found by tempering. It is characterized by
a strong mixing of the Ni and Pd atoms and a corre-
spondingly corrugated surface. The right structure (b)
was formed by tempering of a Ni-core/Pd-shell particle.
Ni atoms have migrated towards the surface during
tempering and the particle no longer has a core–shell
structure. Its surface is still rich in Pd and has an energy
that is about 120 eV (2%) higher than that of particle
(a). If the Pd/Ni ratio is changed to 3:5, a truncated
octahedron with a perfect Ni core of 805 atoms and
a closed Pd shell with 484 atoms can be constructed.
These “magic” numbers of atoms should make core–
shell NP energetically more favorable. The energy
differences between a core–shell particle and randomly
mixed NPs become smaller, but tempering again leads
to mixed bimetallic NPs as energetically preferred
structures. Thus, the MD simulations support the
existence of bimetallic Ni/Pd NPs. Ni/Pd NPs are
different in comparison to (for instance) Au/Pt or Au/
Pd NPs, which were also used in catalysis. For these,
NPs having an Au shell were predicted to be the
energetically more stable on the basis of empirical
potentials and DFT calculations.[32]
Figure 3. HR TEM EDS analysis of Pd4Ni1@MIL-101. The Ni/Pd ratio is
identical if the bulk sample is considered and if single particles are analyzed.
The d-spacing (fringes) of the Ni/Pd NP observed by TEM (for example, for
Pd3Ni2@MIL-101 [111] 2.19(5) ꢂ) matches with the expected value and the
PXRD data (Supporting Information, Figure S14).
The differences in size of the Ni and the Pd atoms
could be a reason for the mixing of the atoms in the Ni/
Pd NPs.[32b] Thus, well-fitted surface boundaries are
difficult to create. The resulting corrugated structure
could enable the observed synergistic catalysis effects.
According to the phase diagram, Ni and Pd are miscible in the
relevant temperature range.[33]
Table 1: Catalytic results of the reduction of 3-heptanone with
PdxNiy@MIL-101.[a]
Entry
System
T
[8C]
t
[h]
Conversion
[%]
Pd/ketone
[mol%ꢃ10À3
]
1
2
3
4
5
6
7
8
Pd3Ni2
Pd3Ni2
Pd3Ni2
Pd5 +Ni5
Pd5 +Ni5
Pd/C+Ni pwd
Pd3Ni2
Pd4Ni1
Pd3Ni2 (sB)
Pd5
25
35
60
35
35
35
35
35
35
35
60
60
60
60
60
60
60
27
20
20
20
40
20
20
20
20
20
20
20
20
20
20
20
20
50
80
75
14
25
12
80
72
22
1
10
8
60
52
12
5
2.88
2.88
1.44
2.88
2.88
2.88
2.88
2.88
2.88
4.75
1.85
1.85
1.13
1.13
1.13
1.13
1.13
Figure 4. Reduction of cyclohexanone (0.18 mg Pd (0.52ꢃ10À3 mol%),
350 mL, 608C, 24 h) and cycloheptanone (0.36 mg Pd
(0.8ꢃ10À3 mol-%), 500 mL, 608C, 48 h) at 20 bar H2; w/o=without
catalyst.
The hypothesis of the formation of bimetallic Ni/Pd NPs is
also supported by molecular dynamics (MD) calculations.
NPs with 1289 atoms (which means a number of atoms that
allows a closed octahedron to be formed in the experimentally
relevant size range of 3.5 nm) were constructed in three
different ways: as Ni-core/Pd-shell NPs, as Ni-shell/Pd-core
NPs, and as NPs with a random distribution of the atoms. 3:2
was chosen as the Pd to Ni ratio in accordance with the ratio
at which experimentally high conversions were observed. All
of the structures were first heated to 1400 K and afterwards
slowly tempered to generate energetically favorable struc-
9
10
11
12
13
14
15
16
17
Pd5 +Ni5
Pd/C+Ni pwd
Pd3Ni2
Pd4Ni1
Pd3Ni2 (G1)
Pd4Ni1 (G1)
Ni5 (G1)
0
[a] T=temperature; sL=successive loading; Pd5 +Ni5 =Pd5@MIL-
101+Ni5@MIL-101; Pd/C=Pd on activated carbon (5 wt% Pd); Ni
pwd=nickel powder (Merck); G1=first generation.
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[1] a) B. F. Abrahams, B. F. Hoskins, D. M. Michail, R. Robson,
Nature 1994, 369, 727 – 729; b) B. F. Hoskins, R. Robson, J. Am.
Chem. Soc. 1989, 111, 5962 – 5964.
[2] H. Li, M. Eddaoudi, M. OꢀKeeffe, O. M. Yaghi, Nature 1999, 402,
276 – 279.
[3] M. P. Suh, H. J. Park, T. K. Prasad, D.-W. Lim, Chem. Rev. 2012,
112, 782 – 835.
[4] J.-R. Li, J. Sculley, H.-C. Zhou, Chem. Rev. 2012, 112, 869 – 932.
[5] L. E. Kreno, K. Leong, O. K. Farha, M. Allendorf, R. P.
Van Duyne, J. T. Hupp, Chem. Rev. 2012, 112, 1105 – 1125.
[6] a) M. Yoon, R. Srirambalaji, K. Kim, Chem. Rev. 2012, 112,
1196 – 1231; b) A. Dhakshinamoorthy, H. Garcia, Chem. Soc.
Rev. 2012, 41, 5262 – 5284.
[7] a) M. Sabo, A. Henschel, H. Froede, E. Klemm, S. Kaskel, J.
Mater. Chem. 2007, 17, 3827 – 3832; b) N. V. Maksimchuk, M. N.
Timofeeva, M. S. Melgunov, A. N. Shmakov, Y. A. Chesalov,
D. N. Dybtsev, V. P. Fedin, O. A. Kholdeeva, J. Catal. 2008, 257,
315 – 323; c) H. Liu, Y. Liu, Y. Li, Z. Tang, H. Jiang, J. Phys.
Chem. C 2010, 114, 13362 – 13369; d) Y. Pana, B. Yuana, Y. Li, D.
He, Chem. Commun. 2010, 46, 2280 – 2282; e) A. Henschel, K.
Gedrich, R. Kraehnert, S. Kaskel, Chem. Commun. 2008, 4192 –
4194.
[8] T. Ishida, M. Nagaoka, T. Akita, M. Haruta, Chem. Eur. J. 2008,
14, 8456 – 8460.
[9] M. S. El-Shall, V. Abdelsayed, A. El Rahman, S. Khder,
H. M. A. Hassan, H. M. El-Kaderi, T. E. Reich, J. Mater.
Chem. 2009, 19, 7625 – 7631.
[10] Y. K. Hwang, D. Y. Hong, J. S. Chang, S. H. Jhung, Y. K. Seo, J.
Kim, A. Vimont, M. Daturi, C. Serre, G. Fꢁrey, Angew. Chem.
2008, 120, 4212 – 4216; Angew. Chem. Int. Ed. 2008, 47, 4144 –
4148.
[11] a) S. Hermes, M.-K. Schrçter, R. Schmid, L. Khodeir, M.
Muhler, A. Tissler, R. W. Fischer, R. A. Fischer, Angew. Chem.
2005, 117, 6394 – 6397; Angew. Chem. Int. Ed. 2005, 44, 6237 –
6241; b) M. Meilikhov, K. Yusenko, D. Esken, S. Turner, G. V.
Tendeloo, R. A. Fischer, Eur. J. Inorg. Chem. 2010, 3701 – 3714.
[12] S. Hermes, F. Schrçder, S. Amirjalayer, R. Schmid, R. A. Fischer,
J. Mater. Chem. 2006, 16, 2464 – 2472.
[13] M. Mꢂller, O. Lebedev, R. A. Fischer, J. Mater. Chem. 2008, 18,
5274 – 5281.
[14] F. Schrçder, S. Henke, X. Zhang, R. A. Fischer, Eur. J. Inorg.
Chem. 2009, 3131 – 3140.
[15] M. Meilikhov, K. Yusenko, R. A. Fischer, Dalton Trans. 2010, 39,
10990 – 10999.
[16] M. Meilikhov, K. Yusenko, A. Torrisi, B. Jee, C. Mellot-
Draznieks, A. Pçppl, R. A. Fischer, Angew. Chem. 2010, 122,
6348 – 6351; Angew. Chem. Int. Ed. 2010, 49, 6212 – 6215.
[17] M. Mꢂller, S. Hermes, K. Kꢃhler, M. W. E. van den Berg, M.
Muhler, R. A. Fischer, Chem. Mater. 2008, 20, 4576 – 4587.
[18] D. Esken, H. Noei, Y. Wang, C. Wiktor, S. Turner, G. V.
Tendeloo, R. A. Fischer, J. Mater. Chem. 2011, 21, 5907 – 5915.
[19] a) D. Esken, S. Turner, O. I. Lebedev, G. Van Tendeloo, R. A.
Fischer, Chem. Mater. 2010, 22, 6393 – 6401; b) M. Mueller, S.
Turner, O. I. Lebedev, Y. Wang, G. van Tendeloo, R. A. Fischer,
Eur. J. Inorg. Chem. 2011, 1876 – 1887.
Figure 5. Structures of bimetallic Ni/Pd NPs based on MD simula-
tions. a) A bimetallic mixed structure of low energy for Pd775Ni514. b) A
structure of higher energy that was simulated starting from a Ni-core/
Pd-shell particle and that already shows Ni atoms (gray) on the
surface.
Reusability tests were carried out for the synergistically
interesting Pd3Ni2@MIL-101 system (hydrogenation of 3-
heptanone). After each catalytic experiment, the catalyst was
centrifuged, the reaction mixture was decanted off, and the
catalyst was washed with THF. The catalyst was again
separated from THF by decanting and dried at 10À3 bar and
308C for 2 h. Reusability studies at 608C and 358C show no
significant decrease in the conversion in 7 or 10 catalytic
cycles, respectively (Supporting Information, Figures S24,
S25). PXRD investigations confirm the stability of the MIL-
101 support (Supporting Information, Figure S26). TEM
investigations show no increase in the particle size after
multiple use in catalysis (Supporting Information, Fig-
ure S27). Similarly, ICP-OES analyses show stable Ni/Pd,
Pd/Cr and Ni/Cr ratios (Supporting Information, Table S4).
The specific surface does not change even after multiple
cycles (Supporting Information, Table S2).
In summary, we introduce a bimetallic synergistically
acting catalyst system. By MOCVD, the sublimable metal–
organic precursors [(C5H5)Pd(C3H5)] and [(C5H5)2Ni] can be
loaded quantitatively and in different mixtures into the
porous host structure of MIL-101. Cavity-conform Ni/Pd
NPs of different composition were generated by an optimized
reduction of the loaded precursors by H2. The so-formed
catalysts are active in the hydrogenation of dialkyl ketones.
High catalytic efficiency is only observed if both metals
operate synergistically and are nearly atomically dispersed.
The bimetallic Ni/Pd NP catalysts are reusable. The MIL-101
support combines ideally stability and good access of the
educts to the catalytically active sites. The synthesis of such
bare (bi)metallic NPs, which are tunable regarding their size,
is generally of great interest.[34]
Received: June 28, 2012
Revised: August 24, 2012
Published online: October 12, 2012
[20] a) S. Hermes, D. Zacher, A. Baunemann, C. Wçll, R. A. Fischer,
Chem. Mater. 2007, 19, 2168 – 2173; b) D. Esken, X. Zhang, O. I.
Lebedev, F. Schrçder, R. A. Fischer, J. Mater. Chem. 2009, 19,
1314 – 1319.
[21] S. Turner, O. I. Lebedev, F. Schrçder, D. Esken, R. A. Fischer, G.
Van Tendeloo, Chem. Mater. 2008, 20, 5622 – 5627.
[22] S. Proch, J. Herrmannsdçrfer, R. Kempe, C. Kern, A. Jess, L.
Seyfarth, J. Senker, Chem. Eur. J. 2008, 14, 8204 – 8212.
[23] J. Hermannsdçrfer, R. Kempe, Chem. Eur. J. 2011, 17, 8071 –
8077.
Keywords: bimetallic catalysis · metal–organic frameworks ·
nickel · palladium · porous coordination polymers
.
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ꢀ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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Angewandte
Chemie
[24] F. Schroeder, D. Esken, M. Cokoja, M. W. E. van den Berg, O. I.
Lebedev, G. van Tendeloo, B. Walaszek, G. Buntkowsky, H. H.
Limbach, B. Chaudret, R. A. Fischer, J. Am. Chem. Soc. 2008,
130, 6119 – 6130.
[25] a) Y. K. Park, S. B. Choi, H. J. Nam, D. Y. Jung, H. C. Ahn, K.
Choi, H. Furukawa, J. Kim, Chem. Commun. 2010, 46, 3086 –
3088; b) P.-Z. Li, K. Aranishi, Q. Xu, Chem. Commun. 2012, 48,
3173 – 3175.
[26] H. K. Chae, D. Y. Siberio-Pꢁrez, J. Kim, Y. B. Go, M. Eddaoudi,
A. J. Matzger, M. OꢀKeeffe, O. M. Yaghi, Nature 2004, 427, 523 –
527.
[27] G. Fꢁrey, C. Mellot-Draznieks, C. Serre, F. Millange, J. Dutour, S.
Surblꢁ, I. Margiolaki, Science 2005, 306, 2040 – 2042.
[28] M. Schrinner, S. Proch, Y. Mei, R. Kempe, N. Miyajima, M.
Ballauff, Adv. Mater. 2008, 20, 1928 – 1933.
[30] H.-L. Jiang, T. Akita, T. Ishida, M. Haruta, Q. Xu, J. Am. Chem.
Soc. 2011, 133, 1304 – 1306.
[31] M. J. Jacinto, R. Landers, L. M. Rossi, Catal. Commun. 2009, 10,
1971 – 1974.
[32] a) D. T. Tran, R. L. Johnston, Proc. R. Soc. London Ser. A 2011,
467, 2004 – 2019; b) R. Ferrando, J. Jellinek, R. L. Johnston,
Chem. Rev. 2008, 108, 845 – 910; c) H. B. Liu, U. Pal, J. A.
Ascencio, J. Phys. Chem. C 2008, 112, 19173 – 19177; d) L.
Leppert, S. Kꢂmmel, Phys. Chem. C 2011, 115, 6694 – 6702; e) J.
Kaiser, L. Leppert, H. Welz, F. Polzer, S. Wunder, N. Wanderka,
M. Albrecht, T. Lunkenbein, J. Breu, S. Kꢂmmel, Y. Lu, M.
Ballauff, Phys. Chem. Chem. Phys. 2012, 14, 6487 – 6495.
[33] M. Hansen, K. Anderko, Constitution of Binary Alloys,
McGraw-Hill, New York, 1958.
[34] a) C. Vollmer, C. Janiak, Coord. Chem. Rev. 2011, 255, 2039 –
2057; b) S. F. L. Mertens, C. Vollmer, A. Held, M. H. Aguirre, M.
Walter, C. Janiak, T. Wandlowski, Angew. Chem. 2011, 123,
9909 – 9912; Angew. Chem. Int. Ed. 2011, 50, 9735 – 9738.
[29] X. Gu, Z.-H. Lu, H.-L. Jiang, T. Akita, Q. Xu, J. Am. Chem. Soc.
2011, 133, 11822 – 11825.
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