(7.1.1)--19.GerhardErtl---Reactionsatsoli.pdf

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1、Gerhard Ertl-Reactions at Solid Surfaces 格格哈德哈德 埃特尔埃特尔-固体固体表面化学表面化学过程过程 In our daily life,we may have become used to some of the phenomena we see and think they deserve to be so,but have we ever thought why?For example,after the rain,we can see that the small droplets on the leaves are nearly spheri

2、cal.After accidentally breaking the thermometer,the mercury droplets dropped to the ground,and the mercury droplets were spherical.Gas or liquid molecules can be adsorbed on solid surfaces All these phenomena are related to the surface.In todays class,I will introduce a a scientist Gerhard Ertl who

3、has studied the surface of matter for decades.Gerhard Ertl is a German Scientist.He won the Nobel Prize in Chemistry in 2007,for his studies of chemical processes on solid surfaces.Part One Biographical Often,chemical reactions are speeded up by surfaces,as in the case when gaseous molecules come in

4、 contact with a metal surface.Gerhard Ertl developed a number of methods for studying surface chemical reactions.He made use of techniques for producing a very pure vacuum,which had been developed within the semiconductor industry.He was able to map out details of a process of great importance in th

5、e production of artificial fertilizer:the Haber-Bosch process in which nitrogen in the air is converted to ammonia via an iron catalyst,which I have also introduced to you in our another class about the nobel prize winner-Fritz Haber.(1)Advantages for research and industry Beginning in the 1960s,Ger

6、hard Ertl wanted to gain a complete picture of a surface reaction.He developed groundbreaking methods for researching surface chemistry.Part Two Achievement His methods are still applied today,not only in academic research but also in the development of processes for the chemical industry.He also la

7、id the foundation for an understanding of car catalytic converters and fuel cells.He interpreted the mechanism of the Haber-Bosch process,which enables the production of artificial fertilizers from atmospheric nitrogen.The process was developed by two other German Chemistry Nobel Prize winners:Fritz

8、 Haber and Carl Bosch.However,it was Gerhard who first enabled a complete understanding of the process and,as a result,its optimization.(2)Influential pioneer In 1986 Gerhard Ertl became director of the Department of Physical Chemistry at the Fritz Haber Institute of the Max Planck Society in Berlin

9、.He helped focus the work of the famous institute on chemical reactions that are influenced by the structure of solid surfaces.Reactions at solid surfaces:From atoms to complexity A chemical reaction involves breaking of bonds between atoms and the formation of new ones.This process is associated wi

10、th transformation of energy and the energy diagram illustrating the progress of a reaction A+BC is illustrated in fig.1.An increase of the reaction probability(=rate)can be achieved by either increasing the temperature or by lowering the activation energy E*of the reaction.In living systems macromol

11、ecules(=enzymes)play the role of catalysts.In technical reactions mostly the interaction of molecules with the surface of a solid is decisive.The principle of this heterogenous catalysis is shown in fig.2.The atoms in the surface layer of a solid have fewer neighbours than those in the bulk and are

12、hence chemically unsaturated and may form new bonds with suitable molecules collided from the adjacent gas or liquid phase.By this step existing bonds will be modified or may even be broken.The formedsurface species may jump from one site to the near ones,then may react with others,and the formed pr

13、oduct molecules that eventually left the surface.How can the two-dimensional chemistry taking place in the chemisorbed overlayer be investigated down to the atomic scale?A possible strategy to overcome this problem had been suggested by I.Langmuir(Nobel Prize 1932)already many years ago:“Most finely

14、 divided catalysts must have structures of great complexity.In order to simplify our theoretical consideration of reactions at surfaces,let us confine our attention to reactions on plane surfaces If the principles in this case are well understood,it should then be possible to extend the theory to th

15、e case of porous bodies.In general,we should look upon the surface as consisting of a checkerboard”Fig.9 shows different surface concentrations of N atoms chemisorbed on various Fe single crystal surfaces with exposure to N2 gas.There is a pronounced influence of the surface structure:The most dense

16、ly packed(110)surface is least active,while the open(111)plane exhibits the highest sticking coefficient,and is indeed responsible for the overall activity of the industrial catalyst.All further steps involved in the ammonia synthesis reaction could be identified and analyzed similarly,so that the o

17、verall mechanism and energy diagram reproduced in fig.10 could be derived.This diagram exhibits the general features:Instead of overcoming the prohibitive high energy barrier for dissociation of the reacting molecules the catalyst offers an alternate reaction path through formation of intermediate c

18、hemisorption complexes whose energy differences can be readily surmounted by the available thermal energy.What did Ertl say in the Noble lecture?“This is no review article but a brief account for a broader audience of some of the work which had been considered to be the basis for the award.Numerous

19、coworkers were involved in our continuing attempt to understand how chemical reactions on solid surfaces take place.Without their efforts the results presented could not have been achieved,and therefore I am heartily grateful to all of them.”Thats the Nobel Prize Winner for todays class.Thank you fo

20、r listening.思思 考考 2007年10月10日，是德国科学家格哈德 埃特尔71岁的生日，当他正和妻子共进午餐庆祝生日时，一个电话打破了原本平静的氛围，他被告知获得了诺贝尔化学奖，这个消息让埃特尔喜悦之情无以言表，他称“这是一辈子只有一次的生日。”埃特尔与中国交往比较密切，自1997年起，埃特尔教授就应聘为中国科学院大连化学物理研究所催化基础国家重点实验室国际顾问委员会委员，并同时应邀开始担任大连化物所催化学报的顾问。谈到埃特尔时，几位科学家的评论如下：瑞典皇家科学院评审委员会说：“格哈德 埃特尔成功地提供了详尽描述，涉及化学反应如何在(固体)表面上发生，以此方式为现代表面化学奠定了

21、基础。”中科院大连化学物理研究所研究员李微雪说：“格哈德 埃特尔对人非常谦和，他兴致好的时候，还会邀请几位擅长小提琴和单簧管的朋友组成小乐队，一道为大家演奏几支曲子。”北京大学化学与分子工程学院院长、长江学者特聘教授吴凯说：“格哈德 埃特尔是一位了不起的科学家。”(2)THE SURFACE SCIENCE APPROACH TO HETEROGENEOUS CATALYSIS:AMMONIA SYNTHESIS The problem involved in the study of the surface chemistry of real catalysts becomes eviden

22、t if we look on an electron micrograph of the Mittasch catalyst as reproduced in fig.4:A catalyst with high activity has to exhibit a rather high specific surface area which in this case is about 20 m2/g as reflected by nanometer sized active particles.The active component itself will expose different crystal planes apart from various defects,and all these various structural parameters are expected to exhibit varying reactivity.