In summary, a novel microfibrous-structured gold catalyst was
successfully obtained by gold galvanic deposition on a paper-like
microfibrous structure of 8 mm Cu-fibers. The catalyst showed
excellent heat conductivity and demonstrated remarkable low-
temperature activity in the gas-phase selective oxidation of
several typical alcohols. The selective oxidation proceeds via
Reactivity tests
The gas-phase selective oxidation of alcohols on these catalysts
with molecular oxygen was carried out on a fixed-bed quartz
tube reactor (i.d., 16 mm) under atmospheric pressure as
10d,e
described previously.
Circular chips (16.1 mm diameter) of
the microfibrous-structured Au/Cu-fiber catalysts were punched
down from their large sheet sample and packed layer-up-layer
into the tube reactor. Note that the diameter of 0.1 mm, larger
than the i.d. of the tubular reactor, was retained deliberately to
avoid the appearance of the gap between the reactor wall and the
edges of the catalyst chips thereby preventing the gas bypassing.
Alcohols were fed continuously using a high-performance liquid
pump, in parallel with an O
feed using the calibrated mass flow controllers, into the reactor
heated to the desired reaction temperature. The effluent was
cooled using an ice-salt bath (-15 C) to liquefy the condensable
vapors for analyzing by an HP 5890 gas chromatography-flame
ionization detector (GC-FID) with a 60 m HP-5 ms capillary
column. The gas-phase products such as H , CO and C1-C3
x
hydrocarbons were analyzed by an HP-5890 GC with a thermal
conductivity detector (TCD) and a 30 m AT-plot 300 capillary
column.
alcohol dehydrogenation at the Cu
2
O sites and sequential O
2
reduction on Au/Cu-fiber catalyst. The AuCu alloy formed
during the reaction can significantly accelerate the reaction by
catalyzing the oxidation of surface hybrid species formed in the
dehydrogenation step to release free active Cu O sites.
2
We are grateful for the financial support from the
NSF of China (21076083, 20973063), the MOST of China
2
(oxidant) and N (diluted gas)
2
(
2011CB201403, 2007AA05Z101), the Fundamental Research
Funds for the Central Universities, the Shanghai Rising-Star
Program (10HQ1400800), and the Shanghai Leading Academic
Discipline Project (B409). We thank the Electron Spectroscope
Center of the East China Normal University for assistance with
◦
1
TEM measurements and J. G. Jiang for solid-state H NMR
2
measurements.
Experimental section
Catalyst preparation
Sinter-locked 3D microfibrous networks consisting of 5 vol%
Notes and references
8
mm Cu (IntraMicron Inc., USA) fibers and 95 vol% void
volume were built up by the regular papermaking/sintering
1 T. Mallat and A. Baiker, Chem. Rev., 2004, 104, 3037.
2 A. Corma and H. Garcia, Chem. Soc. Rev., 2008, 37, 2096.
10
processes. 5 g of Cu-fibers and 1.5 g of cellulose fibers were
added into water (1 L) and stirred vigorously to produce a
uniform suspension. The resulting suspension was transferred
into the head box of a 159 mm dia. circular sheet former
3
J. L. Gong and C. B. Mullins, Acc. Chem. Res., 2009, 42,
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4 (a) S. Biella and M. Rossi, Chem. Commun., 2003, 378; (b) J. Fan, Y.
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(
ZCX-159A, made in China) and a 159 mm circular preform
5
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was then formed by draining and drying in air. The as-made
3
◦
preform paper was oxidized in air at 300 C to remove the
2
cellulosic binders and subsequently sintered in hydrogen at 900
◦
C to create the three-dimensional sinter-locked networks. Au
2
001, 123, 6826; (c) R. A. Sheldon, I. W. C. E. Arends, G. J. T. Brink
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an appointed amount of HAuCl
resulting samples was dried overnight at 80 C and calcined
in air at temperature range between 100 and 300 C for 2 h to
4
at room temperature. The
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◦
◦
(
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obtain Au/Cu-fiber catalysts.
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Catalyst characterization
8
9
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a Rigaku Uitima IV diffractometer (Cu-Ka)), scanning elec-
tron microscope (SEM, Hitachi S-4800), transmission electron
microscope (TEM, JEOL-JEM-2010 instrument at 200 kV),
UV-visible diffuse reflectance spectroscopy (UV-vis DRS, Shi-
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1
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(
MAS-NMR, 400 MHz, Varian VNMR-SYS-400WB, rotation
frequency ~ 4.5 kHz). The catalysts were also studied by tem-
perature programmed desorption (TPD) on a Quantachrome
ChemBET 3000 chemisorption apparatus with a TCD. Au
loading of the Au-3/Cu-fiber-200 was determined to be 2.8 wt%
by inductively coupled plasma atomic emission spectrometry
1
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45; (c) M. Conte, H. Miyamura, S. Kobayashi and V. Chechik, J.
(
ICP-AES) on a Thermo Scientific iCAP 6300 ICP spectrometer.
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5
8 | Green Chem., 2011, 13, 55–58
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