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d
n
4
r
4
n
g
|
0
Figure 3.13
(a) HAADF-STEM image of the as-prepared RuHAp; (b) time-dependent
ATR-IR spectra of the as prepared RuHAp in contact with an Ar-satur-
ated benzyl alcohol solution (0.02 M) and (offset) the ATR-IR spectrum
of RuHAp after contact for 1 h with the reaction mixture under stopped-
flow conditions; ATR-IR spectrum of neat benzyl alcohol (bottom);
(c) selected phase-resolved spectra with 101 phase angle difference
obtained during an MES (Modulation Excitation Spectroscopy) experi-
ment in which the feed was periodically changed between H
2
- and
O
2
-saturated solvent. Conditions: cyclohexane solvent, benzyl alcohol
0.02 M, O
2
(H
2
), 333 K, flow rate 0.6 mL min
1
.
.
anhydrous RuO
2
. TOFs ranging from 4 h
1
(for secondary allylic alcohols) to
18
1
(for 2-octanol) were observed in trifluorotoluene, and in the solvent-free
oxidation of 2-octanol at 150 1C a TOF of 300 h
1
was observed. Since
Ru(OH)
x
has a one-dimensional chain-like core structure,
106
and dehydrative
condensation easily occurs upon heating (4100 1C),
107
dispersion of Ru(OH)
x
on metal oxide supports, such as Al
2
O
3
and TiO
2
,
108,109
is needed to control
both the structure and the size of Ru(OH)
x
. Mizuno and co-workers also
synthesized a ruthenium hydroxide species on magnetite [Ru(OH)
x
/
Fe
3
O
4
].
110
1-Phenylethanol was quantitatively oxidized to acetophenone and
the collection of the catalyst on the wall of the reaction vessel was achieved
by using an external permanent magnet (Figure 3.14). Treatment with
aqueous NaOH was needed for the second run and a recycling experiment
under the same reaction conditions gave a slightly lower yield of acet-
ophenone (93%).
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