Environmental Engineering Reference
In-Depth Information
1200
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0
150
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Calcination temperature /
0
C
Figure 8.24
Inl uence of the calcination temperature on the catalytic activity of gold
catalysts prepared by DP NaOH (
- 0.60 wt% Au;
- 0.33 wt% Au). Reproduced with
permission from [111].
Comotti
et al.
[97] reported that during the catalytic oxidation of glu-
cose (Figure 8.25), gold coagulated into larger particles owing to the for-
mation of sodium gluconate. h is is very common with other electrolytes;
promoted sol coagulation leaves a colorless, inactive solution at er about
400 s. h e growth of gold crystallites during the reaction has been fol-
lowed by X-ray dif raction (XRD) analysis at various time intervals at er
sol immobilization on carbon.
In the time over stream observation of glucose oxidation, the growth of
gold nanoparticles would decrease the catalytic performance, as particle
size > 6-7 nm is not very ef ective for glucose oxidation reaction.
h e catalytic conversion of glucose, or more generally, the rate of reac-
tion not only depends on the nature of support and nanoparticle mor-
phology but also on the reaction parameters, e.g., catalyst amount, oxygen
partial pressure, dissolved oxygen concentration, etc. A recent investiga-
tion by Prüße
et al.
[113] shows the inl uence of the apparent reaction rate
on the applied catalyst amount at reaction conditions of 20 wt% initial glu-
cose concentration and 9 bar oxygen partial pressure. Figure 8.26 indicates
that oxygen mass transfer does not limit the apparent reaction rate up to a
catalyst amount of at least 1200 mg under these conditions.
h e curves in Figure 8.27 clearly show the positive ef ect of a higher oxy-
gen partial pressure on the catalytic activity. Up to a i ve-fold increase in
activity can be achieved by raising the oxygen partial pressure from 1.5 to 9
bar. For each partial pressure a maximum curve is obtained in dependence
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