Chemistry Reference
In-Depth Information
d
n
9
r
4
n
g
|
3
Figure 5.8
(a) Catalytic activity of different oxide-supported Au
25
(SR)
18
/MO
x
catalysts
for CO oxidation (catalyst pretreatment condition: N
2
at room temperature
(r.t.) for 0.5 h; reaction conditions: GHSV
B
7500 mL g
1
h
1
, catalyst:
0.1 g). (b) Catalytic activity of Au
25
(SR)
18
/CeO
2
after different pretreat-
ments. (c) and (d) Effect of water vapor on CO conversion over various
pretreated Au
25
(SR)
18
/CeO
2
catalysts under different pretreatment
temperatures: (c) feed gases with water vapor and (d) without vapor.
Adapted with permission from ref. 32.
.
Au
25
(SR)
18
/CeO
2
catalyst in O
2
for 1.5-2 h at 150 1C(T
pre
) led to a drastic
increase in catalytic activity (CO conversion onset temperature shifted to
r.t.), and 100% CO conversion was obtained when the reaction temperature
was as low as 100 1C (Figure 5.8b). Prolonged O
2
pretreatment at 150 1C(e.g.,
42 h) did not lead to further enhancement in catalytic activity (Figure 5.8b),
and neither did it occur when the T
pre
was increased to 250 1C (above the
thiolate desorption temperature).
It is worth noting that the drastic effect of thermal O
2
pretreatment was
not observed in the Au
25
(SR)
18
/TiO
2
system, and the Au
25
(SR)
18
/oxide cata-
lysts pretreated in N
2
(as opposed to O
2
) did not show any enhancement in
activity. A variety of characterization of the Au
25
(SR)
18
/CeO
2
catalyst showed
that the ligands remained on the cluster after the 150 1C pretreatment in O
2
.
The presence of water vapor in the feed gases exhibited a promotional
effect on the catalyst performance (Figure 5.8c and d). For example, in the
case of
feed-gas containing vapor, O
2
pretreatment at even lower
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