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小木虫论坛-学术科研互动平台 » 化学化工区 » 催化 » 催化反应 » 讨论一下“机械催化”产氢吧
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shijinwen

金虫 (小有名气)
★ ★
berlin(金币+2):可喜可贺，就您的理解，谈谈您的看法
引用回帖:
berlin(金币+0):兔子很少给交流贴加分的，估计也是被题目所吸引，拜托楼主给出一个具体的定义，或者说明一下什么是“机械产氢”，我等洗耳恭听

文献叙述如下
“Some characteristic features to be
noted of mechano-catalytic overall water splitting are as follows:
(1) The reaction proceeds by the mechanical energy provided
by rubbing the oxide powder at the interface between a rotating
stirring rod and the bottom of a reaction vessel. Any vigorous
stirring without rubbing the bottom of the reaction vessel cannot
cause the reaction, suggesting that the collision between the
oxide particles or with the stirring rod is ineffective. The rate
of H2 and O2 evolution monotonically increases with the rate
of rotation of a stirring rod.
(2) The reaction is highly dependent on the type of oxide
material. Effective materials are NiO, Co3O4, Cu2O, Fe3O4,
RuO2, and IrO2 among binary oxides. Interestingly, CuO and
Fe2O3 are inert. Some ternary oxides containing Cu(I), Ni(II),
or Co(II) such as CuAlO2 and CuFeO2 also show the activity.
Typical photocatalysts such as TiO2 and ZnO are completely
inactive.
(3) The reaction is also dependent on the material of the
bottom of the reaction vessel. Quartz and Pyrex glasses gave
the best results among the materials examined so far. Alumina
and CaF2 also showed low but definite activity. Some organic
materials such as PTFE and acrylate were also examined, and
a small amount of H2 but no O2 was obtained.
(4) The conversion efficiency from mechanical to chemical
energy is a few percent. Mechanical energy is that consumed
at the interface between the rotating stirring rod and the bottom
of the reaction vessel, which was estimated by the torque andthe rate of reVolution in water with and without rubbing the
bottom of the Vessel. The chemical energy estimated by the rate
of water decomposition was then diVided by the mechanical
energy (see ref 3 for details). A typical value for NiO in a Pyrex
reaction vessel is 4.3%.
(5) The reaction rate depends on the ambient pressure. The
reaction is typically carried out under reduced pressure where
only water vapor remains in a closed gas circulation system.
With increasing pressure of H2 and O2 in the system, the reaction
rate decreases. Typically, when 30-100 Torr (1 Torr ) 133.3
Pa) of H2 and O2 mixture is accumulated, the system is
evacuated to continue the reaction.
(6) Distilled water seems to be the best media for the reaction.
Whenever any electrolytes are added, the rate of H2 and O2
evolution is retarded. When the reaction was carried out in a
mixture of methanol and water, both H2 and O2 evolutions were
observed, although the amount of O2 was slightly less than
stoichiometric. In water vapor atmosphere without liquid water,
no reaction takes place.
(7) From the isotope experiment using a H2
18O/H2
16O
mixture, the isotope composition of evolved O2 coincided with
that of water within the experimental error.
(8) No photoirradiation effect is observed for all mechanocatalysts
except Cu2O.1,2,4,5 However, even for Cu2Oit is not
attributed to the photon energy conversion but to some effect
that maintains the higher activity of the mechano-catalytic
reaction by some unknown mechanism.”

这样看了大家可能还是不是很明白。还是请见附件的原文吧

顺便恭喜自己有权限上传附件为大家服务了，

[ Last edited by shijinwen on 2006-12-6 at 09:37 ]
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11楼2006-12-06 09:27:22
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daiqiguang

荣誉版主 (知名作家)

优秀版主
★ ★ ★ ★ ★
berlin(金币+5):那能见笑，鼓励还来不及呢...
再提供三篇文献：
1. Reply to "Comment on 'A Study of Mechano-Catalysts for Overall Water Splitting'"
Hara, M.; Domen, K.
J. Phys. Chem. B.; (Comment); 2004; 108(49); 19078-19078.  DOI:
2. A Study of Mechano-Catalysts for Overall Water Splitting
Hara, M.; Komoda, M.; Hasei, H.; Yashima, M.; Ikeda, S.; Takata, T.; Kondo, J. N.; Domen, K.
J. Phys. Chem. B.; (Article); 2000; 104(4); 780-785.  DOI: 10.1021/jp993441h

3. Comment on "A Study of Mechano-Catalysis for Overall Water Splitting"
Ross, D. S.
J. Phys. Chem. B.; (Comment); 2004; 108(49); 19076-19077.  DOI:

从昨天开始知道机械催化这个概念后，就开始看文献，初步形成了自己的概念：文章大概讲的是：Cu2O, NiO, Co3O4,CuAlO2，and Fe3O4等少数材料（催化剂）在搅拌的情况下能将水直接分解为H2和O2！！
Hara等人在最初的光催化水制H2 研究中发现：当撤掉光源时水继续分解，但当停止搅拌时则不能产生H2、O2。另外，产生H2的速度与搅拌子有关，也就是搅拌的越快产H2速度越快！由此，他们提出了机械催化概念——机械能通过催化剂直接转变为化学能！实验还发现如果产生的H2、O2不及时移走，反应会逐渐停止！！
Hara等人在J. Phys. Chem. B.上文章出来后，Ross给与了反驳，说：Hara等人的机械催化分解水制氢其实就是热分解水产生氢，因为搅拌过程中摩擦力可以产生高达1500度的高温，在如此高的温度下并存在适当催化剂条件下，水当然可以分解！随后，Hara也给与反驳并从能量上的理论计算以及各种比较一再证明他的机械催化没问题，而且他还透漏目前他们正在通过microplasma（微等离子体）概念来解释这个显现——our attention has turned to microplasma to explain this phenomenon. Microplasma is the emission of electrons, ions, and photons due to tribocharging and is observed at sliding contacts of insulators and semiconductors in various gases and liquids, even at low sliding velocities.9 Such triboplasma would lead to various chemical decompositions, such as the  confirmed decomposition of n-butane.10 Tribocharging is expected to be highly dependent on the material used, suggesting that  microplasma may be a promising candidate as the mechanism of our mechanical water splitting. More detailed study is therefore necessary to determine how tribocharging of these active oxides differs from that of nonactive oxides.


说实话我对这个所谓的“机械催化”也不太认可，尤其是日本人（哈哈）！！感觉就是普通的催化，只不过他所采用的几种催化剂正好具备催化分解水的性能！！我的想法有点类似Ross，机械搅拌只不过是提供能量的一种方式而已，如果他们做在加热或微波条件下是否同样可以分解水，我想结果更能令人信服！！另外，搅拌还有一种加快传输的作用（不搅拌停止反应），反应的控制步骤也许在传质方面！！



自己的一点小看法，大家见笑了！！

[ Last edited by daiqiguang on 2006-12-6 at 10:17 ]
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有事请到www.chemj.cn上找chemj，谢谢
12楼2006-12-06 10:16:00
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hasee

银虫 (小有名气)
有意思！！！和楼上一样，我也觉得所有相关文献中关于这个概念的描述有些不能令人信服，是不是还有其它的因素在里面呢？等把这些文献都看看再谈一下体会吧。希望大家继续讨论！嘿嘿，很“悬”的一个概念！
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13楼2006-12-06 12:10:21
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jbz1124

金虫 (著名写手)
知道的楼主可以详细的说说
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14楼2006-12-06 12:58:17
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shijinwen

金虫 (小有名气)
★ ★ ★
berlin(金币+3):Go on, Can U give U reason?
引用回帖:
Originally posted by daiqiguang at 2006-12-6 10:16:
再提供三篇文献：
1. Reply to "Comment on 'A Study of Mechano-Catalysts for Overall Water Splitting'"
Hara, M.; Domen, K.
J. Phys. Chem. B.; (Comment); 2004; 108(49); 19078-19078.  DOI: ...

你对新问题的反应速度和处理方式让在下非常佩服，真诚的向你学习。
相信以后自己再遇到问题，不会放n天再去理会。

另外，
引用回帖:
搅拌还有一种加快传输的作用（不搅拌停止反应），反应的控制步骤也许在传质方面！！

我认为传质作为控制步骤地可能性比较小

[ Last edited by shijinwen on 2006-12-6 at 13:38 ]
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15楼2006-12-06 13:11:55
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shijinwen

金虫 (小有名气)
引用回帖:
berlin(金币+3):Go on, Can U give U reason?

我认为传质作为控制步骤地可能性比较小。因为据文献中报道，CuO无活性，而Cu2O有活性，价态的变化会导致活性迥然的差异。如果说传质是控制步骤，那么我没法理解价态的变化和传质的联系。

[ Last edited by shijinwen on 2006-12-6 at 16:04 ]
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16楼2006-12-06 16:00:59
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ju317

金虫 (小有名气)
呵呵，终于碰到同行了。有关机械催化：可能换句话说是摩擦催化更加的合适一些。是摩擦反应在催化领域的应用吧。其中的机理问题还需要再深入的讨论。
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17楼2006-12-06 22:14:38
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shijinwen

金虫 (小有名气)
引用回帖:
Originally posted by ju317 at 2006-12-6 22:14:
呵呵，终于碰到同行了。有关机械催化：可能换句话说是摩擦催化更加的合适一些。是摩擦反应在催化领域的应用吧。其中的机理问题还需要再深入的讨论。

呵呵，文章中本身也提到了一些不能解释的问题
“As a whole, the experimental results in this work indicate
the possibility of the redox mechanism for mechano-catalytic
overall water splitting, but there exist several facts to be
answered before the model is accepted.”

个人以为，文章中的实验现象有讨论价值。姑且先抛开“机械催化”的概念的正确性，至少有一点需要我们解决：实验中遇到的反应的本质到底是什么？
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18楼2006-12-06 22:33:48
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可可西里

木虫之王 (文学泰斗)

甾体者说
引用回帖:
Originally posted by shijinwen at 2006-12-6 10:33 PM:



呵呵，文章中本身也提到了一些不能解释的问题
“As a whole, the experimental results in this work indicate
the possibility of the redox mechanism for mechano-catalytic
overall water splitting ...

找到文章的不足之处

接着写一篇
赞一下 回复此楼
求助文献下载后，及时评分和EPI。
19楼2006-12-06 23:43:28
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ju317

金虫 (小有名气)
呵呵，ls的头像，挺有诱惑的。

其实，有关机械催化的研究，在摩擦方面，已经进行进行了较长的时间了。不过，目前仍就属于新型的。
日本人，过多的强调了电子－空穴理论；
我觉得，这个反应有多相催化的影子，但是，不完全属于多相催化。本质上是摩擦催化。为什末会反应？首先：在催化剂的界面上，一定会存在吸附现象；而在摩擦条件下，化学物质的特殊的化学键，会受到挤压，变形：应该是摩擦起到了活化键能的作用。
催化剂本身是一定要发生化学反应的，否则就起不到催化的作用了。
但是，催化后如何回到原来的状态呢？
（这些物质是半导体氧化物，大家流行电子－空穴假说。这里我就不是很清楚了）
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20楼2006-12-07 00:21:54
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