Chemistry Reference
In-Depth Information
d
n
4
r
4
n
g
|
0
Figure 3.12 Discriminative catalytic performance of the prepared catalysts in the
aerobic oxidation of benzyl alcohol to benzaldehyde.
catalytic performance.
99
In addition, since the promoter ion, Co
II
or Pb
II
,
occupies the 'hidden' sites inside the narrow channels where the substrates
are dicult to access, the total amount of ruthenium was decreased by the
pretreatment and the ruthenium species that can be involved in the reaction
was predominantly located on the surface. Compared with Ru-HAP, a high
TOF was observed for RuCo-HAP (1.7 mol%) catalyst.
100
The experimentally proposed reaction mechanism for the aerobic alcohol
oxidation by supported ruthenium hydroxide catalysts [Ru(OH)
x
/support,
support
ΒΌ
TiO
2
or Al
2
O
3
] was investigated theoretically by means of ab initio
quantum chemistry calculations with model catalysts 'Ru(OH)
3
(OH
2
)
3
' and
'RuCl
3
(OH
2
)
3
' for Ru(OH)
x
/support and RuCl
x
/support, respectively.
101
The
experimentally proposed alcoholate formation and b-hydride elimination
steps could be verified. In addition, the structure of ruthenium in Ru/HAP
was investigated using infrared spectroscopy in the attenuated total
reflection mode (ATR-IR) (Figure 3.13).
102
The spectroscopic data support
the existence of a hydrated RuO
x
-like phase, which was identified by over-
tone signals of Ru-O bonds at
.
1850 cm
1
and is likely organized as a two-
dimensional phase on the apatite.
Ruthenium supported on alumina [Ru(OH)
x
/Al
2
O
3
] was developed by
Yamaguchi and Mizuno as a powerful and recyclable catalyst for the selective
aerobic oxidation of both activated and non-activated alcohols.
103-105
Benzyl
alcohol was converted into benzaldehyde in over 99% yield and the sub-
sequent six runs with the recovered catalyst gave benzaldehyde quantita-
tively. The reaction hardly proceeded in the presence of Ru(OH)
3
and
B
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