Environmental Engineering Reference
In-Depth Information
50
Al
2
O
3
ZrO
2
TiO
2
CeO
2
NPC
AC
40
30
20
10
0
0
123
Diameter of Au particles/nm
4
5678
Figure 8.23
Turnover frequencies for glucose oxidation (glucose reacted (mol) per
number of surface Au atoms (mol) per second) versus the diameter of the Au particles.
Filled and open symbols indicate samples prepared by SG and DP, respectively. Reaction
conditions: 5 wt% glucose solution (175 mL), Au catalyst (30 mg), O
2
(120 mLmin
-1
),
50
°
C, pH 9.0. Reproduced with permission from [111].
maintained a higher catalytic activity than that of Au/ZrO
2
(DP) at lower
temperature. h e apparent activation energies were calculated to be 27, 53,
72 and 96 kJmol
-1
for Au supported on Al
2
O
3
(SG), ZrO
2
(DP), NPC (SG)
and AC (SG), respectively. h e activation energies for glucose oxidation
dif ered according to the nature of the support and tended to be lower for
Au on metal oxides, as the activation energy over unsupported Au colloids
was reported to be 47 kJ mol
-1
.
Further investigation was carried out by Baatz
et al.
[112] on the inl u-
ence of the calcinations temperature on the catalytic activity of glucose
oxidation over gold nanoparticles supported on Al
2
O
3
. h erefore, they
investigated with two dif erent catalysts (0.36 wt% Au/Al
2
O
3
and 0.60 wt%
Au/Al
2
O
3
) which were calcined at temperatures between 150 and 220
°
C
and between 150 and 300
C, respectively. Figure 8.24 shows the maximum
activity depending on the calcination temperature at about 200
°
C in the
case of the catalyst with 0.36 wt% Au content, and a broader maximum
between 200 and 250
°
C for the catalyst with 0.60 wt% gold content. For
both catalysts, a signii cantly lower activity was observed when they were
prepared at calcination temperatures below 200
°
C. h is is caused by an
incomplete reduction of the catalysts. h e decrease in activity at tempera-
tures higher than the optimum temperature could be caused by a sintering
of small gold particles to larger agglomerates. Due to these results, 200
°
°
C
was chosen as the optimum calcination temperature.
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