Catalysis Science & Technology
Paper
by controlling the catalytic chemistry of Pd based on catalyst
design principles. The Pd catalysts currently used in the
anthraquinone process are mainly prepared by an impregna-
tion method, which is poor in controlling sizes and shapes.
The obtained Pd particles did not present a uniform, well-
defined atomic structure on the surface. A potential method
to improve their catalytic performance is to replace these par-
ticles with single-crystal nanoparticles enclosed by specific
All Pd nanocrystals were collected by centrifugation with
acetone and washed with deionized water. After that, 30 mg
of Pd cubes (using KBr as capping agent), cuboctahedra and
octahedra were dispersed in 20 mL of deionized water. Then
10 g of γ-Al O was added into the Pd slurry with magnetic
2
3
stirring. The material was vigorously mixed for 2 h and was
left to stand at 45 °C for 12 h. The obtained samples were
filtered, washed with deionized water and dried at 120 °C
under vacuum. The obtained catalysts were named as Pd-
Cube/Al O , Pd-Cuboct/Al O and Pd-Octa/Al O , respectively.
18
highly active facets. A wide variety of nanocrystals enclosed
by different facets have been prepared by carefully control-
ling reaction conditions, which provide an opportunity to
understand the relationship between crystal facets and
2
3
2
3
2 3
2.3 One-step synthesis of Pd/Al
In order to enhance the stability of Pd nanocrystals on the
γ-Al support, we developed a one-step synthesis method to
prepare the Pd/Al O catalyst. The detailed procedures were
2 3
O
1
9–23
reactivity.
Herein, we prepared Pd cubes, cuboctahedra and octahe-
dra with exposed (100) and (111) facets. They were supported
on γ-Al O as catalysts and used for EAQ hydrogenation
2 3
O
2
3
2
3
as follows: 10 g of γ-Al
solution containing 3.7 mmol of KBr, 0.14 mmol of PVP and
.5 mmol of L-ascorbic acid. The slurry was heated to 80 °C.
Then 4 mL of aqueous Na PdCl solution (70.5 mM) was
2 3
O was dispersed in 36 mL of aqueous
reaction in order to compare the catalytic performance of
different facets. Meanwhile, density functional theory (DFT)
calculations were applied in an attempt to establish a rela-
tionship between the reaction mechanism and different
facets. On the basis of these results, we prepared a high-
performance supported Pd nanocrystal catalyst with high
stability of Pd components by using a one-step synthesis
method.
0
2
4
introduced and stirred for 3 h. The obtained sample was
filtered, washed with deionized water, and dried at 120 °C
under vacuum. The obtained catalyst was denoted as Pd-
2 3
Situ/Al O .
For comparison, a supported Pd catalyst was prepared by
the traditional impregnation method and named as Pd-
2
. Experimental
Im/Al
2 3 2 3
O . 10 g of γ-Al O was dispersed in 20 mL of aqueous
2
.1 Chemicals
Na PdCl (AR; Energy Chemical, China); polyIJvinylpyrrolidone)
PVP; molecular weight 58 000 g mol ; AR; J&K Chemical,
China); KBr, KCl, L-ascorbic acid and formaldehyde solution
40%) (AR, Guangfu Chemical, China); γ-Al (AR, CNOOC
Na PdCl solution (28.2 mmol). Then, the material was vigor-
2
4
ously mixed for 2 h and was left to stand at 45 °C for 12 h.
The obtained sample was filtered, washed with deionized
water, dried at 120 °C and calcined in static air at 500 °C.
2
4
−1
(
(
2 3
O
2.4. Catalyst characterization
Tianjin Chemical Research Institute, China); EAQ, trioctyl
phosphate and trimethylbenzene (AR, TCI, Japan). All chemicals
were used as received.
N
2
adsorption–desorption isotherms were determined at
−196 °C using an ASAP 2000 analyzer (Micromeritics, USA).
Inductively coupled plasma-atomic emission spectroscopy
(ICP-AES) was carried out using an Iris advantage device
(Thermo Jarrel Ash, USA). Transmission electron microscopy
2
.2 Synthesis of Pd nanocrystals and then loading on
γ-Al support
The detailed procedures of the synthesis of Pd nanocrystals
2 3
O
(
TEM) and scanning transmission electron microscopy
2
4
(STEM) analysis were carried out using a JEOL JEM2010
microscope under an accelerating voltage of 200 kV (JEOL,
Japan). An AMI-200ip was used to perform pulse chemisorp-
tion to determine the CO uptake (Thermo Jarrel Ash, USA).
The catalysts were reduced at 300 °C respectively for 1 h and
then cooled to room temperature in He. Pulse CO chemisorp-
tion was performed using a 500 μL pulse of CO in a He car-
rier gas. A 1 : 1 CO/Pd ratio was assumed to determine the Pd
surface content of the catalysts.
were described as follows: a) synthesis of Pd cubes: 12 mL
of aqueous Na PdCl solution (63.8 mM) was introduced into
2
4
3
1
2 mL of an aqueous solution containing 0.378 mmol of PVP,
.36 mmol of L-ascorbic acid and 10 mmol of KBr or a mix-
ture of 0.2 mmol of KBr and 9.8 mmol of KCl at 80 °C. The
solution was stirred for 3 h. b) Synthesis of Pd cuboctahedra
1
8
and octahedra: they were prepared using the prepared Pd
nanocubes (using a mixture of KBr and KCl as a capping
agent) as seeds. 0.7 mL or 1.0 mL of the prepared Pd cube
slurry was mixed with acetone and then centrifuged. The col-
lected cubes were washed several times with deionized water
and then re-dispersed in 1 mL of deionized water. 32 mL of
aqueous solution containing 0.378 mmol of PVP and 400 μL
of formaldehyde solution was added. The obtained solution
was stirred for 0.5 h and heated to 60 °C. Then 12 mL of
aqueous Na PdCl solution (39.6 mM) was introduced with
2.5 Catalytic performance test
The hydrogenation experiment was carried out in an auto-
clave at 0.2 MPa and 50 °C. The working solution was pre-
pared by dissolving 120 g of solid EAQ in 1 L of a mixed sol-
vent composed of trioctyl phosphate and trimethylbenzene
with a volume ratio of 1 : 1. Pd-Cube/Al O , Pd-Cuboct/Al O ,
2
4
2
3
2 3
stirring and allowed to react for 3 h at 60 °C.
Pd-Octa/Al O and Pd-Situ/Al O were pretreated at 300 °C in
2 3 2 3
This journal is © The Royal Society of Chemistry 2015
Catal. Sci. Technol., 2015, 5, 2630–2639 | 2631