Angewandte
Chemie
and the catalyst pellet size (40–120 mesh). The reactor effluent was
analyzed in situ by gas chromatography. Experimental details and
representative TEM images of the Au/ZrO2 catalysts can be found in
the Supporting Information.
Received: June 17, 2005
Published online: October 7, 2005
Keywords: gold · heterogeneous catalysis · hydrogenation ·
.
supported catalysts
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Figure 5. Product selectivity S of 1,3-butadiene hydrogenation over Au/
ZrO2 catalysts of different Auloadings.
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Au3+ ions remains to be elucidated. Hydrogen chemisorption
on supported gold was occasionally detected, but sometimes it
has not been detectable at all.[3,27] The remarkable activity
difference discovered between surface-type Au3+ ions and
metallic Au0 atoms could mean a different mechanism for
hydrogen activation. Comprehensive in situ spectroscopic
studies will be needed to understand the mechanistic aspect of
the surface-type Au3+ cations in the hydrogen activation.
In conclusion, we have shown that isolated Au3+ ions on a
zirconia support are obtained by loading very small amount
(< 0.1%) of gold with simple methods. These heterogenized
Au3+ ions are highly active for the selective hydrogenation of
1,3-butadiene to butenes. Further exploration of the potential
of the surface-type Au3+ ions in heterogeneous catalysis may
be the key to using the noble metal gold in areas usually
reserved for conventional precious metal catalysts such as Pt
and Pd.
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We found that the TOF data in Table 1 of this paper were
erroneous by one order of magnitude. We communicated with
the authors (Drs. Okumura and Haruta) who confirmed that
TOF (ꢀ 10À3 sÀ1) in the table was a mistyping of TOF (ꢀ 10À2 sÀ1
and kindly allowed us to make the correction herein.
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Experimental Section
A conventionally prepared ZrO(OH)2 hydrogel was calcined at
4008C to produce a ZrO2 support with BET surface area of
120 m2 gÀ1 [24]
Samples of Au/ZrO2 were prepared by loading the
.
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support with appropriate amounts of Au by the deposition–precip-
itation method with HAuCl4 precursor,[8] the concentration of which
was adjusted to yield catalysts containing 0.76, 0.23, 0.05, and
0.01 wt% Au (ICP-AES analysis). The 0.76% Au/ZrO2 sample was
treated with an aqueous solution of KCN in a process similar to that
reported by Fu et al.[11] to give 0.08% Au/ZrO2 catalyst. The Au/ZrO2
catalysts were dried and calcined at 2008C in flowing air. We also
prepared 0.76% Au/ZrO2 catalysts at different calcination temper-
atures, that is, 200, 300, and 5008C. TPR was used in combination with
XPS measurements to quantitatively characterize the oxidation state
of gold. TEM/HRTEM images were recorded on a JEM-2010F
(200 kV) transmission electron microscope.
Hydrogenation of 1,3-butadiene was conducted at 1208C in a
fixed-bed stainless steel reactor (i.d. 4 mm) at atmospheric pressure.
The reaction feed (2.15 vol% 1,3-butadiene in H2) was introduced to
the catalyst at a flow rate of 13.5 mLminÀ1 (gas hourly space velocity
(GHSV) = 8100 mLhÀ1 (gcat.)À1. Before reaction all samples (ca. 80–
120 mesh, 0.1 g diluted with 0.45 g quartz powder) were pretreated in
situ in 30 mLminÀ1 Ar at 2008C for 2 h. The selected reaction
conditions precluded any significant mass-transfer limitation in a
series of pre-experiments at fixed space velocity (GHSV=
8100 mLhÀ1 (gcat.)À1) so that the conversion of butadiene (ca.
75%) over the 0.76% Au/ZrO2 catalyst (calcined at 2008C) was not
significantly affected by changing the flow rate of the reaction feed
Angew. Chem. Int. Ed. 2005, 44, 7132 –7135
ꢀ 2005 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
7135