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leeying

至尊木虫 (职业作家)

[交流] 问关于活性炭的一个问题

大家都知道很多催化剂载体都有等电点,这也是我们制备负载型催化剂所要考虑的,那么活性炭有没有等电点那,有是多少?没有,有是为什么那?

[ Last edited by daiqiguang on 2007-5-11 at 09:30 ]
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penfee

荣誉版主 (文学泰斗)

文献杰出贡献文献杰出贡献文献杰出贡献文献杰出贡献文献杰出贡献文献杰出贡献文献杰出贡献

1


paracyclophane(金币+1):谢谢penfee!呵呵,什么时候到大连来参观参观,你们那里有我的好几个朋友啊
根据等电点理论, 催化剂载体和前驱体之间存
在的相互作用取决于载体表面电荷及离子电荷, 存
在一个等电点p H 值(用p HIEP 表示, 在此p H 值
下载体表面电荷为零. 当浸渍液p H > p HIEP时, 载
体就从浸渍液中吸附阳离子, p H < p HIEP时就吸附
阴离子) .

活性炭载体的等电点p H 值
为8 左右.
6楼2006-08-10 19:10:07
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grapeberry

铁虫 (知名作家)

0.25

我做催化剂的时候,没有使用等电点这个概念。
2楼2006-08-09 16:37:28
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leeying

至尊木虫 (职业作家)

关于等电点


paracyclophane(金币+1):3x!
关于等电点

Uniform filling of the pores can be achieved using the incipient wetness technique, using concentrated solutions at pH
values that minimize adsorption. The pH is adjusted to take account of the isoelectric point of the support (Table 7). To
overcome the problem of aggregation during the drying step and nonuniformity of the adsorption using the incipient
wetness technique, greater quantities of liquid can be used and, in the extreme, this involves the use of a large excess of
dilute solution, which has been used by Wang and Hall (21) to prepare monolayer molybdenum/alumina catalysts.
Table 7. Isoelectric Points of Various Oxides
Oxide IEPS Adsorption
Sb2O5 <0.4 Cations
WO3 hydrous <0.5
SiO2 1.0–2.0
MnO2 3.9–4.5 Cations or anions
SnO2 ~5.5
TiO2 (anatase, rutile) ~6
-Fe2O3 6.5–6.9
ZrO2 hydrous ~6.7
CeO2 hydrous ~6.75
Cr2O3 hydrous 6.5–7.5
, -Al2O3 7.0–9.0
-Fe2O3 ~8.9 Anions
ZnO 8.4–9.0
La2O3 hydrous 8.7–9.7
MgO ~10.4
12.1–12.7
Controlled adsorption from solution uses highly diluted solutions of the additive and the pH is adjusted to control the
rate of adsorption. The method has been optimized for MoO3/ -Al2O3 and WO3/ -Al2O3 catalysts (20-22). The pH is
used to control two factors: (1) the surface charge of the support and (2) the size of oxyanions of molybdenum and
tungsten. It must be recognized that the surface of the oxide support changes its polarization according to the value of
the pH of the solution and the isoelectronic point, which is also known as the zero charge point (Table 7) (23). At a pH
below the isoelectronic point, the surface is positively charged and, therefore, attracts anions while, at a pH above the
isoelectronic point, the surface becomes negatively charged and, hence, attracts cations. An example of the control of
surface charge affecting adsorption is shown in Fig. 4 for the adsorption of cobalt and tungsten species onto -Al2O3.
The isoelectric point of alumina is ca pH 8–9 and the lack of adsorption of cobalt at pH <6 is due to the inability of the
positively charged cobalt cations to adsorb in the positively charged alumina surfaces. Additionally, at pH >8, cobalt
precipitates from the solution as hydroxides or basic carbonates. Hence, for alumina, there is a very narrow pH window
that can be used for the controlled adsorption of positively charged cations (22, 24). The reverse situation is observed
for the tungsten, and also molybdenum, species because of the negative charge of the tungstate and polytungstate
anions, which are readily adsorbed onto the positively charged alumina surface below pH 8.

[ Last edited by leeying on 2006-8-9 at 16:51 ]
3楼2006-08-09 16:50:25
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leeying

至尊木虫 (职业作家)

怎么没有人跟贴亚
4楼2006-08-10 08:26:16
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