Room-temperature hydrogenation of citral catalyzed by palladium-silver nanocrystals supported on SnO2

Article abstract of DOI:10.1002/ejic.201500057

We have developed two strategies to optimize Pd catalysts. On one hand, Ag was introduced into Pd and then they were applied to the selective hydrogenation of citral under mild conditions. The addition of metallic Ag could tune the selectivity of Pd and made it suitable for the selective hydrogenation of the conjugated double bond. The selectivity of citronellal increased from 0 (for Pd/C and Pd_0.7Ag_0.3/C) to 96% (for Pd_0.4Ag_0.6/C) as the Ag content increased. On the other hand, the addition of SnO₂ made the Pd catalysts more inclined to activate the C=O bond and gave better performance for the hydrogenation of the conjugated double bond compared with the corresponding Pd-Ag catalysts. The selectivity of citronellal increased from 0 (for Pd_0.7Ag_0.3/C) to 76% (for Pd_0.7Ag_0.3-SnO₂/C was used) after the addition of SnO₂. On the basis of these results, we developed a catalyst (Pd_0.6Ag_0.4-SnO₂/C) with the best catalytic performance for the selective hydrogenation of citral (the conversion of citral reached 99%, and the selectivity was up to 96%). We have developed two strategies to optimize Pd catalysts for the selective hydrogenation of citral and exploited a catalyst (Pd_0.6Ag_0.4-SnO₂/C) with the best catalytic performance (the conversion of citral reached 99%, and the selectivity was up to 96%).

Full text of DOI:10.1002/ejic.201500057

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DOI:10.1002/ejic.201500057
Room-Temperature Hydrogenation of Citral Catalyzed by
Palladium–Silver Nanocrystals Supported on SnO2
Shuo Wang,[a,b] Rongan Shen,[b] Zheng Chen,[b] Jiaxi Wang,*[a]
Dingsheng Wang,*[b] and Yadong Li[b]
Keywords: Heterogeneous catalysis / Nanocrystals / Hydrogenation / Palladium / Silver / Tin
We have developed two strategies to optimize Pd catalysts.
On one hand, Ag was introduced into Pd and then they were
applied to the selective hydrogenation of citral under mild
clined to activate the C=O bond and gave better performance
for the hydrogenation of the conjugated double bond com-
pared with the corresponding Pd–Ag catalysts. The selecti-
conditions. The addition of metallic Ag could tune the selec- vity of citronellal increased from 0 (for Pd0.7Ag0.3/C) to 76%
tivity of Pd and made it suitable for the selective hydrogen-
ation of the conjugated double bond. The selectivity of citro-
nellal increased from 0 (for Pd/C and Pd0.7Ag0.3/C) to 96%
(for Pd0.4Ag0.6/C) as the Ag content increased. On the other
hand, the addition of SnO2 made the Pd catalysts more in-
(for Pd0.7Ag0.3–SnO2/C was used) after the addition of SnO2.
On the basis of these results, we developed a catalyst
(Pd0.6Ag0.4–SnO2/C) with the best catalytic performance for
the selective hydrogenation of citral (the conversion of citral
reached 99%, and the selectivity was up to 96%).
Introduction
The selective hydrogenation of α,β-unsaturated aldehydes
and ketones, such as acrolein, methacrolein, croton-
aldehyde, E-cinnamaldehyde, citral, and benzalacetone, is
an important step in the preparation of different kinds of
materials and intermediates in fine chemistry.[1,2] Citral is
one of the major components of the essential oils from
various plants, including lemon myrtle, litsea citrate, litsea
cubeba, and lemon.[3–5] Citral has a conjugated double
bond (C=C), an isolated double bond (C=C), and a carb-
onyl group (C=O).[6,7] The reaction pathways for the hyd- Scheme 1. Pathways for the hydrogenation of citral.
rogenation of citral are complicated and give various prod-
ucts such as citronellal (CAL), citronellol, geraniol, nerol,
to citronellal over Pd catalysts through the tuning of the
menthol, and others through the hydrogenation of the C=C
reaction conditions[12–14] and the selection of different sup-
and C=O bonds (Scheme 1). Therefore, it is challenging to
ports, including Al2O3, zeolite, CaCO3, TiO2, and sepio-
control the selectivity of the hydrogenation of citral.
lite.[15–18] However, the selectivities to the desired products
Catalysts based on palladium are commonly used for the
over these catalysts are not promising, likely because of the
hydrogenation of carbon–carbon multiple bonds in various
poor selectivity of Pd for the hydrogenation of C=C and
kinds of substrate.[8–11] Palladium catalysts have a higher
C=O.
ability to activate carbon–carbon multiple bonds than other
In recent decades, bimetallic nanoparticles (BNPs) have
noble metals such as Pt, Ru, and Rh. There have been sev-
attracted passionate attention.[19–24] They have received
eral previous reports of the selective hydrogenation of citral
steadily growing interest and have been widely applied to
catalysis. They exhibit better catalytic performance (espe-
[a] School of Chemical Engineering, Hebei University of
cially for activity and selectivity) than that of monometallic
Technology,
nanoparticles (NPs).[25,26] The catalytic performance of
Tianjin 300130, P. R. China
E-mail: wangjiaxi@hebut.edu.cn
BNPs is associated with their composition because each
metal in the BNPs can tune the electronic state of the cata-
lytically active component.[27]
Herein, we introduced another metal (Ag) to tune the
electronic structure of Pd and make it suitable for the
formation of citronellal by the selective hydrogenation of
http://www.hebut.edu.cn/
[b] Department of Chemistry, Tsinghua University,
Beijing 100084, P. R. China
E-mail: wangdingsheng@mail.tsinghua.edu.cn
http://www.tsinghua.edu.cn/
Supporting information for this article is available on the
WWW under http://dx.doi.org/10.1002/ejic.201500057.
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citral. Furthermore, the addition of SnO2 could improve
the reactivity of the conjugated double bond. The morph-
ologies, phase structures, and chemical composition were
studied by transmission electron microscopy (TEM), energy
dispersive X-ray (EDX) spectroscopy, powder X-ray diffrac-
tion (XRD), X-ray photoelectron spectroscopy (XPS), and
FTIR spectroscopy. The hydrogenation of citral was per-
formed under a H2 balloon at room temperature (25 °C).
The possible mechanism was also studied.
Results and Discussion
In the synthesis of PdxAg1–x BNPs, Pd(acac)2 (acac =
acetylacetonate) and AgOOCCF3 (silver trifluoroacetate)
were used as the precursors. Oleylamine (OAm) was used
as the solvent and surfactant. Both of the precursors were
dissolved in OAm and oleic acid at 60 °C and reduced by
borane–tert-butylamine. The transmission electron micro-
scopy (TEM) images of the as-prepared PdxAg1–x (x = 0–
1) BNPs (Figure 1) showed that all of the BNPs were mono-
disperse particles and had an average size of ca. 3 nm.
When Pd(acac)2 was used as the only precursor, Pd NPs
with a particles size of ca. 3 nm (Figure S1a in the Support-
ing Information) were obtained; when AgOOCCF3 was
used as the only precursor, Ag NPs with a particles size of
ca. 8 nm (Figure S1b) were produced.
Figure 2. XRD patterns of PdxAg1–x/C (x = 0–1).
X-ray photoelectron spectroscopy (XPS) showed the
binding energy peaks of Pd and Ag in the products (Fig-
ure 3, a and b). The strong Ag 3d5/2 signals were located at
367.8–367.9 eV, which are lower than that of the pure metal
(368.3 eV); the dominant peaks at 335.4–335.6 eV were
attributed to Pd 3d5/2. The Pd peaks only shifted when there
were enough Ag atoms to sufficiently disturb the Pd–Pd
bonding.[28] In addition, energy dispersive X-ray (EDX)
spectroscopy (Figure S2) and inductively coupled plasma
atomic emission spectrometry (ICP-AES) showed that the
exact Pd/Ag molar ratios of the synthesized PdxAg1–x BNPs
were similar to the proportions of their precursors. The Ag-
rich surface of the Pd–Ag alloy could be also detected by
XPS and ICP-AES (Table S1).
Figure 1. TEM images of PdxAg1–x (x = 0–1) NPs: (a) Pd0.7Ag0.3
(b) Pd0.6Ag0.4, (c) Pd0.5Ag0.5, and (d) Pd0.4Ag0.6
,
.
The powder X-ray diffraction (XRD) patterns of the as-
prepared PdxAg1–x (x = 0–1) BNPs are shown in Figure 2.
The shift of the (111) diffraction peak corresponding to Pd
(JCPDS 65-6174) towards that of Ag (JCPDS 65-2871) as
Figure 3. XPS spectra of PdxAg1–x
.
The pathways for the hydrogenation of citral are shown
the Ag content increases demonstrates the formation of the in Scheme 1. Citronellal (3) and 3,7-dimethyl-1-octanal (5)
bimetallic structure of the obtained NPs.
were the two principal products in our system. The BNPs
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were loaded on active carbon before use (details are pro-
The presence of SnO2 species could provide positive elec-
vided in the Experimental Section). The catalytic perform- tron-donating effects from the precious metal atoms to the
ance of the as-synthesized PdxAg1–x/C was evaluated in the promoters, and this effect could lead to the C=C bond acti-
selective hydrogenation of citral. The reaction was per- vation decreasing and C=O bond activation increas-
formed with 2-propanol as the solvent at room temperature ing.[31,32] Therefore, compared with the corresponding Pd–
and under normal pressure (Table 1). Two benchmark cata- Ag catalysts, it is easier for PdxAg1–x supported on SnO2 to
lysts, commercial Pd/C and home-made Pd/C were initially activate the C=O bond of citral, and the conjugated C=C
tested. They had high activity but low selectivity for 3 in bond adjacent to the C=O bond was more readily activated
the present system (Table 1, Entries 1 and 2). In addition, than the isolated C=C bond far from the C=O bond. On
as the ratio of Ag increased, the selectivity for 3 increased account of the constraints of the Pd–Ag catalysts, there was
from 0 to 96% (Table 1, Entries 3–6). The activity of the a small amount of saturated and unsaturated alcohol. Con-
PdxAg1–x catalysts began to decline when the Pd/Ag molar sequently, compound 3 could be obtained with a conversion
ratio reached 2:3, and Ag particles were inactive in this re- of 99% and selectivity of 96% with Pd0.6Ag0.4–SnO2/C as
action system.
the catalyst (Table 1, Entry 10).
Next, we investigated the possible reaction paths for the
reduction of citral to citronellal and other products. The
influence of the catalyst loading and the initial concentra-
tion of citral on the conversion and selectivity were studied
with PdxAg1–x/C and PdxAg1–x–SnO2/C as the catalysts. A
series of conversion and selectivity versus time curves were
plotted (Figure S4). The conversion and selectivity versus
time for the Pd0.6Ag0.4/C catalyst are shown in Figure 4 (a),
and the conversion of citral reach almost 99% within
Table 1. Hydrogenation of citral catalyzed by PdxAg1–x–SnO2/C.[a]
Entry Catalyst
Time [h] Conv. [%]
Selectivity [%][b]
3
5
Others[c]
1
2
3
4
5
6
7
8
commercial Pd/C
home-made Pd/C
Pd0.7Ag0.3/C
Pd0.6Ag0.4/C
Pd0.5Ag0.5/C
Pd0.4Ag0.6/C
Ag/C
Pd–SnO2/C
Pd0.7Ag0.3–SnO2/C
Pd0.6Ag0.4–SnO2/C
Pd0.5Ag0.5–SnO2/C
Pd0.4Ag0.6–SnO2/C
SnO2/C
12
12
12
12
12
12
12
12
12
12
12
12
12
99
99
99
99
99
56
–
99
99
99
64
12
–
96
94
85
77
13
–
4
6
15
15
6
4
–
4
5
2
2
2
–
–
8
81
96
–
40 min, whereas it took nearly 12 h with the Pd0.6Ag0.4
SnO2/C catalyst (Figure 4, b). However, when Pd0.6Ag0.4
–
–
–
4
92
19
2
–
–
SnO2/C was used, the selectivity of citronellal remained
9
76
96
98
98
–
10
11
12
13
–
[a] Reaction conditions: substrate 1 (1 mmol), catalyst (0.8 mol-%
based on Pd) in 2-propanol (3 mL) at room temperature, H2 bal-
loon. [b] The conversion and selectivity were analyzed by GC, and
n-dodecane was used as the internal standard. [c] Others including
but not limited to 2, 4, 6, and 7 produced by the hydrogenation of
citral.
Various ratios of Pd and Ag catalysts gave different selec-
tivity for citronellal, and this was ascribed to the following
two factors: Firstly, the conjugated C=C bond is easier to
activate than the isolated C=C bond because of the delocal-
ization of electrons in the conjugated C=C–C=O bonds.[29]
Secondly, as the Ag atoms practically did not adsorb
hydrogen, the addition of Ag to Pd may change the struc-
ture of the Pd particles and lead to a decreased quantity of
absorbed hydrogen on the Pd–Ag catalysts.[30] Therefore,
the Pd–Ag catalysts exhibited decreased selectivity for the
isolated C=C bond and enhanced selectivity to citronellal.
Under these conditions, the activity and selectivity could
not increase at the same time. Thus, we introduced SnO2
colloid as a promoter of the PdxAg1–x BNPs, (the details
are provided in the Experimental Section). The TEM image
of Pd0.6Ag0.4–SnO2 (Figure S1) showed that the Pd0.6Ag0.4
BNPs were well supported on SnO2. The XRD patterns
also revealed that the intensity of PdxAg1–x–SnO2
supported on active carbon (Figure S3 in the Supporting
Information) was quite strong compared with that of
PdxAg1–x BNPs. The amount of Pd–Ag BNPs loaded on
the surface of SnO2 was detected by ICP-AES (Table S1).
Figure 4. Conversion and selectivity versus time for the hydrogen-
ation of citral with Pd1–xAgx–SnO2 (x = 0–1) catalysts: (a)
Pd0.6Ag0.4/C and (b) Pd0.6Ag0.4–SnO2/C; ᭿ conversion of citral (1),
᭹ selectivity of CAL (3), ᭡ selectivity of DCAL (5). Reaction con-
ditions: citral (1 mmol), catalyst (0.8 mol-% based on Pd) in 2-
propanol (3 mL) at room temperature under a H2 balloon.
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above 95% as the reaction proceed to 99% conversion. On
the contrary, when Pd0.6Ag0.4/C was used as the catalyst,
the selectivity of citronellal began to decrease after 20 min
and declined to less than 10% after 12 h. The turnover
frequencies (TOFs, Table S3) decreased as the Ag content
increased or as SnO2 was added. Furthermore, we could
obtain citronellal with high selectivity under mild condi-
tions compared with those reported previously (Table S4).
Finally, to study the stability of the Pd0.6Ag0.4–SnO2/C
catalyst, it was recycled in the hydrogenation of citral under
the previous conditions after centrifugation and filtration
(Figure 5). The results showed that the catalyst is still highly
active (97% conversion of citral) and selective (96%
citronellal) after four cycles. TEM (Figure S5) showed that
the Pd0.6Ag0.4–SnO2/C catalyst had no clear changes after
use. In the FTIR spectra (Figure S6 in the Supporting In-
Experimental Section
Chemicals: Commercial Pd/C, Pd(acac)2 and tin(IV) oxide (15% in
H2O colloidal dispersion) were obtained from Alfa Aesar, silver
trifluoroacetate and oleylamine (OAm) were purchased from J&K
Chemical, and activated carbon was obtained from TCI. Analyti-
cal-grade ethanol, cyclohexane, and oleic acid were purchased from
Beijing Chemical Reagents. All of the chemicals were used without
further purification.
Synthesis: In a typical preparation of Pd0.5Ag0.5 nanocrystals, silver
trifluoroacetate (14.5 mg) and Pd(acac)2 (20 mg) were dissolved in
OAm (1 mL) and injected into OAm (5 mL) and oleic acid (200 μL)
at 60 °C with vigorous stirring for 10 min. Then, a solution of
borane–tert-butylamine (100 mg, 1.15 mmol) in OAm (1 mL) was
added quickly into the previous solution, and the reaction mixture
immediately turned black. After 5 min, the flask was heated to
90 °C for a further 1 h. After cooling to room temperature, the
solution was washed with ethanol (40mLϫ3) and then dispersed
in cyclohexane for future use.
formation), the peaks at ν = 2920 and 2877 cm–1 were
˜
assigned to the symmetric methylene stretches and the anti-
symmetric methyl group; therefore, we concluded that the
hydrophobic long chain ligand had capped the catalyst. The
The procedure for the typical preparation of Pd0.5Ag0.5–SnO2 was
the same as that for the synthesis of Pd–Ag BNPs, and oleic acid
was used as the stabilizer for SnO2. After 1 h, tin(IV) oxide
COOH modes at ν = 3431 and 1601 cm–1 indicated the an-
˜
choring of oleic acid. The weakening of the peaks showed (250 μL, 37.5 mg, 15% in H2O colloidal dispersion) was added
dropwise into the reaction mixture with vigorous stirring for a fur-
ther 1 h at 120 °C. After cooling to room temperature, the solution
was washed with ethanol (40mLϫ3) and then dispersed in cyclo-
hexane for future use.
that the excess ligand on the surface of the Pd–Ag catalyst
had decreased after four cycles, and this may enhance the
reactivity of the catalyst.
For the preparation of PdxAg1–x/C (0ϽxϽ1) and PdxAg1–x–SnO2/
C (0ϽxϽ1) catalysts, the activated carbon was added into the
dispersions of PdxAg1–x (0ϽxϽ1) and PdxAg1–x–SnO2 (0Ͻx1) at
a loading of 3 wt.-% (based on Pd and Ag, the actual content is
shown in Table S2), and the mixtures were stirred overnight. The
catalysts were obtained through centrifugation and drying under
vacuum.
Characterization: The powder XRD patterns were recorded with a
Bruker D8 ADVANCE X-ray powder diffractometer with Cu-Kα
radiation (λ = 1.5406 Å). The sample compositions were deter-
mined by ICP-AES, and the particle size and dispersion were inves-
tigated with a Hitachi H-800 transmission electron microscope
(TEM). The X-ray photoelectron spectroscopy (XPS) was con-
ducted with a Thermo Fisher ESCALAB 250Xi spectrometer
equipped with a monochromatic Al X-ray source.
Figure 5. Recycling experiment of Pd0.6Ag0.4–SnO2/C catalyst in
the hydrogenation of citral for 12 h.
Catalytic Properties: For a typical run, citral (1 mmol) and
PdxAg1–x/C or PdxAg1–x–SnO2/C catalyst (0.8 mol-% of citral
based on Pd and Ag) were placed in a 10 mL flask with 2-propanol
(3 mL) as the solvent. A H2 balloon was introduced after the flask
was purged three times with H2. The reaction was performed at
room temperature (25 °C) for the specified time. Liquid samples
were analyzed by gas chromatography with a Thermo Finnigan
chromatograph equipped with a flame ionization detector and a
DB-WAX capillary column (J&W, 30 m, 0.25 mm i.d.) with nitro-
gen as the carrier gas.
Conclusions
We successfully prepared
a
selective bimetallic
Pd0.6Ag0.4–SnO2/C catalyst for the hydrogenation of citral
to citronellal. The conversion reached 99%, and the selec-
tivity for citronellal reached 96%. For the Pd catalyst, either
alloying with Ag or support on SnO2 improved its selecti-
vity to citronellal. This result implies that the performance
of an active metal catalyst can be tuned by the introduction
of another metal. Transition metal oxide (TMO) supports
also effectively improved the performance of noble metal
catalysts. We anticipate that such methods could be ex-
tended to the development of specific heterogeneous cata-
lysts for other important reactions.
Supporting Information: (see footnote on the first page of this arti-
cle): Compositions of the as-prepared catalysts by ICP-AES and
XPS (Tables S1 and S2); TEM images of Pd, Ag, and
Pd0.6Ag0.4–SnO2 (Figure S1); XRD patterns of as-prepared
PdxAg1–x–SnO2/C (x = 0–1; Figure S2); EDX spectra of as-pre-
pared PdxAg1–x (x = 0–1; Figure S3); and conversion and selectivity
versus time in the hydrogenation of citral PdxAg1–x/C (x = 0–1)
and PdxAg1–x–SnO2/C (x = 0–1) catalysts (Figure S4).
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[13] C. Schmöger, A. Stolle, W. Bonrath, B. Ondruschka, T. Keller,
K. D. Jandt, ChemSusChem 2009, 2, 77–82.
[14] J. Zhu, M. Li, M. Lu, J. Zhu, Catal. Sci. Technol. 2013, 3, 737–
744.
[15] M. Steffan, M. Lucas, A. Brandner, M. Wollny, N. Oldenburg,
P. Claus, Chem. Ing. Tech. 2006, 78, 923–929.
[16] C. Schmöger, T. Gallert, A. Stolle, B. Ondruschka, W. Bonrath,
Chem. Eng. Technol. 2011, 34, 445–451.
[17] S. Yilmaz, S. Ucar, L. Artok, H. Gulec, Appl. Catal. A 2005,
287, 261–266.
[18] V. Satagopan, S. B. Chandalia, J. Chem. Technol. Biotechnol.
1994, 59, 257–263.
Acknowledgments
Financial support of this work by the State Key Project of Funda-
mental Research for Nanoscience and Nanotechnology (grant
numbers 2011CB932401, 2011CBA00500, 2012CB224802), the
Foundation for the Author of National Excellent Doctoral Disser-
tation of P. R. China (201321), the Specialized Research Fund for
the Doctoral Program of Higher Education (20130002120013), and
the National Natural Science Foundation of China (NSFC)
(21231005, 21471089, 21322107) is gratefully acknowledged.
[19] V. R. Stamenkovic, B. Fowler, B. S. Mun, G. Wang, P. N. Ross,
C. A. Lucas, N. M. Markovic, Science 2007, 315, 493–497.
[20] S. Guo, S. Sun, J. Am. Chem. Soc. 2012, 134, 2492–2495.
[21] B. Yoon, C. M. Wai, J. Am. Chem. Soc. 2005, 127, 17174–
17175.
[1]
[2]
[3]
[4]
[5]
[6]
L. N. Protasova, E. V. Rebrov, H. E. Skelton, A. E. H. Wheat-
ley, J. C. Schouten, Appl. Catal. A 2011, 399, 12–21.
N. M. Bertero, A. F. Trasarti, B. Moraweck, A. Borgna, A. J.
Marchi, Appl. Catal. A 2009, 358, 32–41.
E. Salminen, P. Virtanen, K. Kordás, J. Mikkola, Catal. Today
2012, 196, 126–131.
J. K. Kim, C. S. Kang, J. K. Lee, Y. R. Kim, H. Y. Han, H. K.
Yun, Entomol. Res. 2005, 35, 117–120.
A. Stolle, T. Gallert, C. Schmöger, B. Ondruschka, RSC Adv.
2013, 3, 2112–2153.
[22] N. A. Dehm, X. Zhang, J. M. Buriak, Inorg. Chem. 2010, 49,
2706–2714.
[23] Z. Niu, D. Wang, R. Yu, Q. Peng, Y. Li, Chem. Sci. 2012, 3,
1925–1929.
[24] Q. Zhang, X. Guo, Z. Liang, J. Zeng, J. Yang, S. Liao, Nano
Res. 2013, 6, 571–580.
[25] L. Li, Z. Niu, S. Cai, Y. Zhi, H. Li, H. Rong, L. Liu, L. Liu,
W. He, Y. Li, Chem. Commun. 2013, 49, 6843–6845.
[26] S. Cai, H. Duan, H. Rong, D. Wang, L. Li, W. He, Y. Li, Acs
Catal. 2013, 3, 608–612.
[27] H. Rong, S. Cai, Z. Niu, Y. Li, Acs Catal. 2013, 3, 1560–1563.
[28] D. A. Slanac, W. G. Hardin, K. P. Johnston, K. J. J. Stevenson,
J. Am. Chem. Soc. 2012, 134, 9812–9819.
H. Surburg, J. Panten, Common Fragrance and Flavor Materi-
als, Wiley-VCH, Weinheim, Germany, 2006.
[7] U. K. Singh, M. A. Vannice, J. Catal. 2001, 199, 73–84.
[8] M. Armbrüster, G. Wowsnick, M. Friedrich, M. Heggen, R.
Cardoso-Gil, J. Am. Chem. Soc. 2011, 133, 9112–9118.
[9] K. Han, H. Zuo, Z. Zhu, G. Cao, C. Lu, Y. Wang, Ind. Eng.
Chem. Res. 2013, 52, 17750–17759.
[29] R. Liu, Y. Yu, K. Yoshida, G. Li, H. Jiang, M. Zhang, F. Zhao,
S. Fujita, M. Arai, J. Catal. 2010, 269, 191–200.
[30] Q. Zhang, J. Li, X. Liu, Q. Zhu, Appl. Catal. A 2000, 197, 221–
228.
[10] A. Jung, A. Jess, T. Schubert, W. Schütz, Appl. Catal. A 2009,
362, 95–105.
[31] K. Liberková, R. Touroude, J. Mol. Catal. A 2002, 180, 221–
[11] P. A. Robles-Dutenhefner, M. G. Speziali, E. M. B. Sousa,
E. N. dos Santos, E. V. Gusevskaya, Appl. Catal. A 2005, 295,
52–58.
[12] M. A. Aramendía, V. Borau, C. Jimenez, J. M. Marinas, A.
Porras, F. J. Urbano, J. Catal. 1997, 172, 46–54.
230.
[32] A. Vicente, G. Lafaye, C. Especel, P. Marécot, C. Williams, J.
Catal. 2011, 283, 133–142.
Received: January 21, 2015
Published Online: ᭿
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Supported Bimetallic Catalysts
S. Wang, R. Shen, Z. Chen, J. Wang,*
D. Wang,* Y. Li ................................ 1–6
We have developed two strategies to optim-
ize Pd catalysts for the selective hydrogen-
ation of citral and exploited a catalyst
(Pd0.6Ag0.4–SnO2/C) with the best catalytic
performance (the conversion of citral re-
ached 99%, and the selectivity was up to
96%).
Room-Temperature Hydrogenation of
Citral Catalyzed by Palladium–Silver
Nanocrystals Supported on SnO2
Keywords: Heterogeneous catalysis / Nano-
crystals / Hydrogenation / Palladium / Sil-
ver / Tin
Eur. J. Inorg. Chem. 0000, 0–0
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