Chemistry Reference
In-Depth Information
Scheme 6 Fe
+
-catalysed
oxidation of CO [
321
]. Step
1 is oxygen atom
abstraction; step 2 is oxygen
atom transfer
(Scheme
6
). In the first step, Fe
+
reacted with N
2
O by oxygen atom transfer to yield
FeO
+
, which transferred an oxygen atom to CO in the second step to yield neutral
CO
2
and regenerate the atomic Fe
+
catalyst. The exploration of gas-phase transi-
tion-metal catalytic cycles has continued in the intervening 4 decades and been
reviewed on several occasions [
28
,
29
,
287
,
322
,
323
]. Here we focus on complete
gas-phase catalytic cycles that are catalysed by gold nanoclusters. Readers are also
directed to Sect.
4
for data relevant for potential catalytic cycles whose final step
(s) has not yet been realised.
CO
þ
N
2
O
!
CO
2
þ
N
2
ð
71
Þ
Bernhardt's group has used a variable-temperature ion trap to examine related
oxidation of CO by N
2
O occurring on the coinage metal cluster cations Au
3
+
(at 300 K) and Ag
3
+
(at 230 and 250 K) [
287
]. They studied the reactions of Au
3
+
and Ag
3
+
with N
2
O only, CO only and with both N
2
O and CO in the ion trap. Both
Au
3
+
and Ag
3
+
react with N
2
O via a series of oxygen atom abstraction reactions
(Eq. (
72
), with
n
1-3). Additional products formulated as M
3
O
n
(N
2
O
2
)
m
+
were
¼
observed (where
n
¼
1-3 for
m
¼
¼
Ag and Au;
n
¼
2and3for
m
¼
1forM
2for
Au).When only COwas in the ion trap, Au
3
+
reacted
to exclusively give Au
3
(CO)
3
+
(Eq. (
73
), with
n
¼
Ag;
n
¼
2for
m
¼
¼
M
2forM
3) while Ag
3
+
gave a combination
¼
of Ag
3
(CO)
+
and Ag
3
(CO)
2
+
(Eq. (
73
), with
n
¼ 1and2).WhenbothN
2
OandCO
were in the ion trap two main products were observed for Au
3
+
:Au
3
(CO)
3
+
and
Au
3
(CO
2
)
3
+
. The observation of the latter product suggests that oxidation of all each
oxygen atom in the oxide Au
3
O
3
+
reacted with one CO molecule to produce CO
2
that
remained bound to the cluster (Eq. (
74
)). While the authors did not examine the CID
reactions of the product Au
3
(CO
2
)
3
+
, if this were to undergo losses of three molecules
of CO
2
(Eq. (
75
)), then this would formally close a catalytic cycle for the oxidation of
CO (Eq. (
71
)). Finally, oxidation of CO when N
2
O was present in the trap proceeded
via a different process for Ag
3
+
, which is shown in Eq. (
76
):
M
3
þ
M
3
O
3
þ
n
N
2
O
!
n
N
2
ð
72
Þ
ð
n
M
3
þ
n
CO
!
M
3
CO
ð
73
Þ
Þ
3
Au
3
O
3
þ
3CO
!
Au
3
CO
2
ð
ð
74
Þ
