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d
n
4
r
4
n
g
|
2
.
Figure 4.11
(Top) HRTEM images of titania-supported Au shell-Pd core nanoparti-
cles; and (bottom) impact of annealing and Au/Pd surface alloying
upon catalytic activity and selectivity towards cinnamyl alcohol aerobic
selox.
Adapted from Ref. 129 with permission from Elsevier.
Scott and co-workers prepared Au core-Pd shell nanoparticles and ex-
plored the catalytic cycle for alcohol selox in order to assess their associated
stability.
131-135
In situ Pd K and Pd L
III
edge XAS of a Au nanoparticle-Pd(
II
)
salt solution was undertaken in order to discriminate two possible reaction
mechanisms (Figure 4.12). No evidence was found that crotyl alcohol oxi-
dation was accompanied by Pd
21
reduction on to Au nanoparticles, resulting
in the formation of a metallic Pd shell (with oxygen subsequently regener-
ating electron-deficient palladium), therefore b-H elimination was proposed
as the favoured pathway. Scott and co-workers proposed that the Au core
prevents the re-oxidation of surface Pd
0
atoms; no Pd-O and Pd-Cl contri-
butions were observed by EXAFS.
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