X. Wang et al.
and then washed with deionized water three times. The final solid was
dried at 608C and ground with a mortar and pestle.
Conclusion
Typical procedure for selective hydrogenation of CAL: The liquid-phase
hydrogenation of CAL was carried out in a glass batch reactor (2.0 mL,
SUPELCO) closed with a Teflon septum and equipped with a pressure
gauge and a side arm with an on–off lock. A microsyringe was able to
inject and withdraw liquid or gas through the lock. Typically, the reactor
with CNT-immobilized Pd nanocrystals (10 mg) or Pd colloids (0.1 g; de-
ionized water as the solvent, containing 0.051 mg cluster wires, 1.0 mg
icosahedra, and 0.096 mg nanocubes) and CAL (50.0 mg, 0.5 mmol) in
isopropanol (1.0 mL) was purged with hydrogen for three times and then
hydrogen was introduced (5 bar). The reaction was assumed to start
when the reactor was introduced into the oil bath at 508C and vigorously
stirred (ca. 1000 rpm). At a desired reaction time, the reaction mixtures
(20 mL) were taken through the microsyringe and analyzed with a HP gas
chromatography equipped with a flame ionization detector (FID) and a
FFAP column. n-Nonane was used as an internal standard to calibrate
the reaction products.
We have demonstrated the highly selective synthesis of Pd
nanocrystals with three different shapes (cluster nanowires,
icosahedra, and nanocubes) in an environmentally benign
solvent using one-pot method. In particular, the cluster
nanowire was synthesized for the first time. By immobiliza-
tion of Pd nanocrystals on CNTs and g-Al2O3, the catalytic
activity and stability of Pd nanocrystals was greatly en-
hanced in the liquid-phase hydrogenation of CAL and gas-
phase hydrogenation of 1,3-butadiene. The TOFs and reac-
tion rates of the immobilized Pd cluster nanowires were
about two orders of magnitude higher than those of the Pd
nanocubes and one order of magnitude higher than those of
commercial Pd/C and/or Pd/g-Al2O3 catalysts in both reac-
tions.
Typical procedure for selective hydrogenation of 1,3-butadiene: 1,3-Buta-
diene hydrogenation was performed in a continuous-flow quartz tube mi-
croreactor (i.d.=6 mm) at room temperature (238C) and atmospheric
pressure. CNT-immobilized Pd nanocrystals (10 mg; 15 mg for g-Al2O3,
5 mg for commercial Pd/C) were used in a powder form as-prepared and
diluted with quartz sand (440 mg, >100 mesh). The immobilized Pd and
commercial Pd/C catalysts were ground and screened in sizes of 100–
120 mesh. The reactant gas, containing a mixture of 1,3-butadiene, H2,
and N2 with a volume ratio of 1:49:97, was passed through the CNT-im-
mobilized icosahedra, nanocubes, and g-Al2O3-immobilized nanocubes at
the rate of 18.8 mLminÀ1. In a series of pre-experiments at a fixed reac-
tant flow rate of 18.8 mLminÀ1, we found that the CNT- and g-Al2O3-im-
mobilized Pd icosahedra and nanocubes exhibited 1,3-butadiene conver-
sions ranging from 1 to 57%. Specifically the reaction rate of CNT-im-
mobilized Pd icosahedra (2.50 molhÀ1 per g of Pd) was not affected by
changing the flow rate of the reaction feed and by using various catalyst
pellet sizes (140–160 mesh). However, 100% conversion was found on
CNT- and g-Al2O3-immobilized Pd cluster nanowires and commercial
carbon-supported Pd catalyst at room temperature (238C) and atmos-
pheric pressure. Therefore, the flow rate of the reaction feed was in-
creased from 18.8 to 76.9 mLminÀ1 for the CNT- and g-Al2O3-immobi-
lized Pd cluster nanowires, and commercial carbon-supported Pd catalyst.
In this case, we found that the reaction rate of CNT-immobilized Pd clus-
ter nanowires (22.0 molhÀ1 per g of Pd) was not significantly affected
Experimental Section
Chemicals: PdCl2, PVP (MW=30000), CAL, isopropanol, and ethanol
were analysis reagent (A.R.) grade and purchased from the Beijing
Chemical Reagent Company. NaF, NaI, ethylenediaminetetraacetic acid
disodium salt (EDTA·2Na), and sodium dodecyl sulfate (SDS) were
A.R. grade and purchased from the Beijing Research Institute for Non-
ferrous Metals. The reactant gases 1,3-butadiene, N2, and H2 were pur-
chased from the Beijing AP Beifen Gases Industry Company. CNTs
(inner diameter 5–8 nm and outer diameter 8–15 nm; BET surface area
185 m2gÀ1) supplied by Tsinghua University were heated at reflux in a
concentrated sulfuric acid (98%)/nitric acid (68%) mixture (3:1 v/v)
under vigorous stirring for 3 h at 808C. Pd/C with 3.0 wt% Pd was pur-
chased from Aldrich. g-Al2O3 (BET surface area 170 m2gÀ1) was pur-
chased from Merck. All reagents were used as received without further
purification. Deionized water was used for the synthesis of nanocrystals.
Synthesis of Pd cluster nanowires: PdCl2 solution (1 mL, 90 mm), NaF
(21 mg), SDS (289 mg), and PVP (300 mg) were added to deionized
water (7.0 mL) and stirred for 10 min at room temperature. The resulting
homogeneous brown solution was transferred to a 12 mL Teflon-lined
stainless-steel autoclave. The sealed vessel was then heated at 2208C for
6 h before it was cooled to room temperature. The products were sepa-
rated by centrifugation at 11000 rpm for 20 min and further purified
twice with deionized water.
AHCTUNGERTG(NNUN <20%) by further changing the flow rate of the reaction feed and by
using various catalyst pellet sizes (140–160 mesh). The reactor effluent
was analyzed online by using a SP-6890 (FID, GDX-501 as an adsorbent)
gas chromatograph.
Synthesis of Pd icosahedra: A solution of PdCl2 in water (1 mL, 90 mm),
EDTA·2Na (372 mg), and PVP (60 mg) were added to deionized water
(7.0 mL) and stirred for 10 min at room temperature. The resulting ho-
mogeneous brown solution was transferred to a 12 mL Teflon-lined stain-
less-steel autoclave. The sealed vessel was then heated at 1608C for 6 h
before it was cooled to room temperature. The products were separated
by centrifugation at 11000 rpm for 20 min and further purified twice with
deionized water.
Acknowledgements
This work made use of the resources of the Beijing National Center for
Electron Microscopy. This work was supported by the NSFC (20725102,
20921001, and 20903119), the State Key Project of Fundamental Re-
search for Nanoscience and Nanotechnology (2011CB932402), and the
Program for New Century Excellent Talents in University (NCET).
Synthesis of Pd nanocubes: A solution of PdCl2 in water (1 mL, 90 mm),
EDTA·2Na (372 mg), PVP (60 mg), and NaI (75 mg) were added to de-
ionized water (7.0 mL) and stirred for 10 min at room temperature. The
resulting homogeneous brown solution was transferred to
a 12 mL
Teflon-lined stainless-steel autoclave. The sealed vessel was then heated
at 1608C for 6 h before it was cooled to room temperature. The products
were separated by centrifugation at 11000 rpm for 20 min and further pu-
rified twice with deionized water.
Preparation of supported Pd catalysts: CNT- and g-Al2O3-immobilized
Pd nanocrystals were prepared by combining a solution containing a cer-
tain amount of Pd colloids dispersed in water with a suspension of CNTs
or g-Al2O3 in ethanol. The mixture was sonicated for 40 min and stirred
for 6 h. After being left overnight, the precipitate was suction filtered
[2] a) K. M. Bratlie, H. Lee, K. Komvopoulos, P. D. Yang, G. A. Somor-
2644
ꢀ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2012, 18, 2639 – 2645