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2H
2
O
H
2
HOOH
H
2
+ O
2
C
3
H
6
1
2
C
3
H
6
O+H
2
O
H
2
O +
O
2
Figure 8.11
Routes for water formation in propene epoxidation using hydrogen and
oxygen [77].
100
2400
H
2
O
2
C
3
H
6
1800
95
1200
H
2
O
2
C
3
H
6
90
600
85
0
0
5
10
15
20
0
5
10
15
20
(
a
)
H
2
eiciency (%)
(
b
)
H
2
eiciency (%)
Figure 8.12
Selectivity towards propene oxide (a) and deactivation rate constant (b) as a
function of hydrogen ei ciency at dif erent reactant concentrations (1 wt% Au on Ti-SiO
2
,
403K, GHSV 10000 mL g
cat
-1
h
-1
; the concentration of one reactant is varied while the other
two are i xed at 10 vol%) [77].
catalyst prepared by solid-state grinding method was very much effec-
tive in dispersing gold nanoclusters on a variety of supports, irrespec-
tive of the isoelectric pH of the oxides (Figure 8.13). However, since
there is still controversy about whether deposition-precipitation or
solid-state grinding is the best method to prepare gold nanocluster,
further research is needed.
h e usage of a microreactor system for the direct epoxidation of propene
over a gold-titania-based catalyst system using a mixture of hydrogen, oxy-
gen and propene allows for the safe operation of the reaction in the explo-
sive regime [73, 75-76]. h e propene concentration does not inl uence the
propene oxide formation rate; however, higher propene concentrations
signii cantly reduce the catalyst deactivation rate. Hydrogen increases the
rate of the epoxidation reaction, while it only has a minor inl uence on
the rate of deactivation and reactivation. Oxygen has a benei cial ef ect on
the epoxidation reaction, slightly decreases the deactivation rate, and is
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