Supporting Information
Pd–Pb Alloy Nanocrystals with Tailored Composition for
Semihydrogenation: Taking Advantage of Catalyst Poisoning**
Wenxin Niu, Yongjun Gao, Weiqing Zhang, Ning Yan,* and Xianmao Lu*
anie_201503148_sm_miscellaneous_information.pdf
Experimental Section
Chemicals and Materials. Palladium(II) chloride (PdCl2), L-ascorbic acid, lead(II)
nitrate
(Pb(NO3)2),
cetyltrimethylammonium
lead(II)
chloride
acetate
trihydrate
solution
(CTAC,
(Pb(CH3CO2)2•3H2O),
25
wt.
%
in
H2O),
polyvinylpyrrolidone (PVP, average Mw≈55,000), and Lindlar catalyst (~ 5%
palladium on calcium carbonate; poisoned with lead) were obtained from
Sigma-Aldrich. Cetyltrimethylammonium bromide (CTAB) was obtained from Acros
Organics. A 10 mM H2PdCl4 solution was prepared by dissolving 1 mmol of PdCl2 in
10 mL of 0.2 M HCl solution and further diluting to 100 mL with water. All aqueous
solutions were prepared using ultrapure de-ionized water (Barnstead, 18.2 MΩ cm-1).
Synthesis of Cubic Pd Seeds. Cubic Pd seeds were synthesized according to a
previously reported method.1,2 In a typical synthesis, 10 mL of 12.5 mM CTAB
solution in a 20 mL vial was heated at 95 ºC. After 5 min, 0.5 mL of 10 mM H2PdCl4
solution was added. After another 5 min, 80 μL of 100 mM ascorbic acid solution was
quickly added. The reaction was stopped after 10 min and stored at 40 °C for future
use.
Lead(II)-Assisted Growth of Pd/Pb Alloy Nanocrystals. In a typical synthesis,
certain amount of 1 mM Pb(NO3)2 solution was added to 5 mL of 0.1 M CTAB
solution kept in a 60 ºC water bath. Then 125 μL of 10 mM H2PdCl4 solution and 40
μL of the Pd cubic seed solution were added. After gentle mixing, 50 μL of 0.1 M
ascorbic acid solution was added and the solution was gently mixed. The resulting
solution was placed in a water bath at 60 ºC without disturbance. After 2 h, the
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products were collected by centrifugation (10000 rpm, 3 min). The precipitates were
redispersed in water. The centrifugation/redispersion procedures were repeated once
more and the final product was redispersed in 0.5 mL of water.
Synthesis of Pd Octahedral Nanocrystals. The Pd octahedral nanocrystals were
synthesized in a similar procedure as the Pd/Pb nanocrystals, except that 125 μL of 1
M HCl solution was added and CTAC was used instead of CTAB.
Scale-up syntheses of Pd-Pb nanocrystals for hydrogenation reactions. The
syntheses of various Pd and Pd-Pb nanocrystals can be easily scaled up 100 times
with similar conditions. After the reaction, the products were collected by
centrifugation (10000 rpm, 3 min) and redispersed in 10 mL of 10 mM PVP aqueous
solution. After 2 hours, the products were centrifuged and redispersed in 10 mL of 10
mM PVP ethanol solution. Finally, the products were centrifuged and redispersed in
10 mL of ethanol. The PVP-stabilized nanocrystals are highly dispersible in ethanol.
Hydrogenation reactions of various Pd-Pb nanocrystals. For a typical
hydrogenation reaction, 0.32 mL of the Pd-Pb alloy solution (0.5 mol% Pd) was
added into a 10 mL flask. Then a balloon containing hydrogen was connected to the
flask. The air in the system was evacuated and backfilled with hydrogen for at least
five times. Then 2 ml of 0.2 mM alkyne was added into the system by a syringe. The
reaction was conducted at room temperature (25 ºC). Then the solution was analyzed
by Agilent 7890 GC-FID and GC-MS equipped with HP-5 column respectively so
that the conversion and selectivity for different products can be achieved according to
the results from GC and GC-MS.
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Instrumentation. Scanning electron microscopy (SEM) images and energy
dispersive X-ray (EDX) analysis were acquired using a JEOL JSM-6700F scanning
electron
microscope.
Transmission
electron
microscopy
(TEM)
images,
high-resolution TEM (HRTEM) images, selected-area electron diffraction (SAED),
and EDX mapping analysis were acquired using a JEOL JEM-2100F transmission
electron microscope operating at 200 kV. X-ray photoelectron spectroscopy (XPS)
was performed on a Kratos AXIS UltraDLD spectrometer using monochromatic Al Kα
X-ray source (1486.71 eV). C 1s at 285 eV was used as the charge reference to
determine core level binding energies. X-ray diffraction (XRD) patterns were
obtained on a Bruker D8 Discover with GADDS and Cu Kα radiation. FTIR spectra
were measured on a Bio-Rad FTS-3500ARX FT-IR spectrometer. Generally, 0.15 g
KBr was pressed into a thin tablet and concentrated solution containing catalyst
nanocrystals was coated on the KBr disk and dried at room temperature in fume. This
KBr disk covered with catalysts was used to collect FTIR background spectrum. Then
equivalent styrene was dropped on the catalyst-covered KBr disk. After styrene was
dried at room temperature in fume hood, FTIR spectra were collected.
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Figure S1. SEM images of Pd-Pb nanocrystals synthesized in the presence of
different amounts of 10 mM Pb(NO3)2 with different overall atomic concentration and
surface atomic concentration of Pb, respectively: (a): 0 µL, 0%, 0%; (b) 5 µL, 2.7%,
0%; (c) 7 µL, 3.2%, 0.1%; (d)7.5 µL, 3.4%, 0.2%; (e) 10 µL, 5.1%, 0.6%; (f)12.5 µL,
6.7%, 1.3%; (g) 15 µL, 8.4%, 2.1%; (h) 20 µL, 10.7%, 13.8%; (i) 30 µL, 12%, 22%;
(j)40 µL, 14.2%, 27%; (k) 80 µL, 15.7%, 24.1%; (l) 120 µL,14.6%, 22.6%. Scale bar:
100 nm.
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Figure S2. SEM images of Pd-Pb nanocrystals synthesized in the presence of
different amounts of 10 mM lead(II) acetate: (a-c): 0, 7.5, 40 µL. Scale bar: 100 nm.
Figure S3. (a, d) TEM images, (b, c) Pd and Pb EDX elemental mapping,
respectively, and (e, f) Pd and Pb EDX linear scan of cuboctahedra Pd-Pb alloy
nanocrystals, respectively. Scale bars: 20 nm.
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Figure S4. (a, b)TEM images of Pd nanocubes before and after treating with Pb(II)
ions. In a typical treating process, Pd nanocubes, 125 μL of 10 mM Pb(NO3)2 solution,
and 50 μL of 0.1 M ascorbic acid solution were added to 5 mL of 0.1 M CTAB
solution and gently mixed. The mixture was reacted at 60 ºC for two hours. Scale bars:
50 nm. (c) XPS spectra of Pd nanocubes after treating with Pb(II) ions.
Figure S5. SEM images of octahedral Pd nanocrystals for control experiments. Scale
bars: (a) 500 nm, (b) 200 nm.
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Figure S6. Hydrogenation of phenylacetylene on commercial (a) Lindlar catalysts
and (b) Pd/C catalysts. (c) Comparison of the selectivity towards styrene of
commercial Lindlar catalyst and Pd-Pb octahedral NCs with 27.02% surface Pb
(Sample E).
Figure S7. FTIR spectra of styrene adsorbed on Pd-Pb nanocrystals of different
shapes and composition.
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Figure S8. XPS spectrum of Pd 3d region of Pd-Pb alloy NCs.
Figure S9. Large-scale SEM images of cuboctahedral Pd-Pb alloy NCs demonstrating
their monodispersity. Scale bars: (a) 500 nm, (b) 200 nm.
Figure S10. XPS spectrum of Pb 4f after treating Pd nanocubes with Pb(II) ions in the
absence of ascorbic acid. The binding energies of Pb 4f7/2 and 4f5/2 core levels are
located at 139.1 and 143.9 eV, both corresponding to Pb(II) species. This result
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demonstrate that no deposition of metallic Pb was formed in the absence of ascorbic
acid and ascorbic acid is essential for the reduction of Pb(II).
Reference
(1) Niu, W.; Li, Z.-Y.; Shi, L.; Liu, X.; Li, H.; Han, S.; Chen, J.; Xu, G. Cryst.
Growth Des. 2008, 8, 4440.
(2) Niu, W.; Zhang, L.; Xu, G. Acs Nano 2010, 4, 1987.
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