固體表面化學反應機制 從 2007 年諾貝爾化學獎談起 ---

1. 固體表面化學反應機制 從2007年諾貝爾化學獎談起--- 國立中央大學物理系 蔡茂盛 M. S. Zei Ph.D 1971 Freie University Berlin, Germany, 在哈伯研究所 (Fritz-Haber-Institut)工作 35 年(1970 – 2004).

2. 簡介如何用表面物理科學儀器－光電子顯微鏡(PEEM)、低/高能電子繞射(LEED,RHEED)、電子能量損失光譜 (EELS)、掃瞄穿隧顯微鏡(STM)等儀器，來觀察(測)一氧化碳CO在鉑單晶表面上的氧化過程。由EELS得知分子態的氧在室溫下因在鉑表面的化學吸附(chemisorption)，導致分子鍵(Molecular bonding)的減弱，使其解離成原子態氧(Oad)，另由STM觀察原子態氧(Oad)及化學吸附態的一氧化碳在鉑(III)表面上分別形成(2×2)-O,及c(4×2)-CO構造的區域(domains)，其氧化反應機制是兩吸附態的反應物(reactants)在區域交界處(Domain boundaries)結合成二氧化碳CO2。催化反應過程中，發現反應氣體分子在固體觸媒的化學吸附，導致固體表面原子結構的變化並非如同傳統觀念認為：「催化劑只使化學反應加速，本身不會起任何變化」。 觸媒表面上的原子在反應過程中，是不斷在移動中。觸媒表面原子的遷移性(mobility)會因反應分子或離子的強吸附(Strong bonding)而導致表面原子遷移性(mobility)的提高; (mobility-enhancement by chemisorption of atoms/ions)。

3. 今天的報告內容 (固體表面化學反應) 1). Haber-Bosch NH3 Synthesis 2). Fischer-Tropsch synthesis 3). 2007年諾貝爾化學獎 CO + O2 oxidation on Pt surfaces 4). Methanol fuel cell 5). Structural change of catalyst-surface induced by chemisorption 化學反應導致觸媒的 表面原子結構的變化

4. Kaiser Wilhelm Institut fur Physikalische Chemie und Elektrochemie

6. Fritz-Haber Institut der Max-Planck-Gesellschaft

7. Ernst Ruska Abteilung Elektron-Mikroskopie 07.2006

10. Haber哈伯及Bosch分別於1918及1931年獲得諾貝爾化學獎。Haber哈伯及Bosch分別於1918及1931年獲得諾貝爾化學獎。 每年生產 NH3 10000 萬吨 100 million tons 450o C and 300 bar ?

11. Ni-catalyst, 700C 20 bar CO + H2 天然氣 O2, H2O 排除

12. 為什么在放熱(性)的反应ΔH = - 46kJ/mol, 合成溫度在 450o C? 450oC Desorption of the chemisorbed N-species on FeO

13. WGS = water gas-shift reaction 用於由煤得到的合成氣体

15. History Since the invention of the original process by the German researchers Franz Fischer and Hans Tropsch, working at the Kaiser Wilhelm Institute in the 1920s, many refinements and adjustments have been made, and the term "Fischer-Tropsch" now applies to a wide variety of similar processes (Fischer-Tropsch synthesis or Fischer-Tropsch chemistry). Fischer and Tropsch filed a number of patents, e.g. US patent no. 1,746,464, applied 1926, published 1930 [3]. The process was invented in petroleum-poor but coal-rich Germany in the 1920s, to produce liquid fuels. It was used by Germany and Japan during World War II to produce ersatz fuels. Germany's synthetic fuel production reached more than 124,000 barrels per day (19,700 m³/d) from 25 plants ~ 6.5 million tons in 1944.[4] After the war, captured German scientists recruited徵募( in Operation Paperclip continued to work on synthetic fuels in the United States in a United States Bureau of Mines program initiated by the Synthetic Liquid Fuels Act. In Britain, Alfred August Aicher obtained several patents for improvements to the process in the 1930s and 1940s, e.g. British patent no. 573,982, applied 1941, published 1945 [5]. Aicher's company was named Synthetic Oils Ltd. (There is no connection with the Canadian company of the same name.)

16. Rd CH4 Ni

17. Another important reaction is the • water gas shift reaction: • H2O + CO → H2 + CO2 • Although this reaction results in formation of unwanted CO2, it can be used to shift the H2:CO ratio of the incoming Synthesis gas. • This is especially important for synthesis gas derived from coal, which tends to have a ratio of ~0.7 compared to the ideal ratio of ~2. Fe

21. Structural transformation of the reconstructed Pt(100) surface COad → CO2 ↑ (100)-(1x1) (100)-hex Pt(100) COad + O2→ CO2 ↑

22. PCO ↓, ψ ↑ CO-氧化反應呈現震盪現象的解釋 Ads. CO Oscillation of CO oxidation on Pt-surface Phys. Rev.Lett. 49(1982) 177

23. EELS Spectrum of ads. Oxygen on Pt(111) at 300 K 只出顯在300 oK

24. (Sub-Micron) 結構成像 Oscillation of CO oxidation on Pt surface 一氧化碳及氧在鉑金薄膜表面上氧化過程所形成的光電子顯微鏡 (PEEM) 圖像，其中暗亮區域分別對應於氧分子及一氧化碳在鉑表面上的吸附區域。

25. STM images for CO + O2 oxidation on Pt(111) Science 12 (1997) 1931 STM images

26. Orientation change of the c(4x2)-damain C(4x2)-CO → (2x2)-O

27. CO oxidation 其氧化反應機制是兩吸附態的反應物(reactants)在區域交界處(Domain boundaries)結合成二氧化碳CO2 via Langmuir-Hinschelwood mechanism

28. H+ H+

29. Methanol (CH3OH) fuel cell (-) 氧分子在鉑上降低活化能成原子態氧 Cathode: 1/5 O2 + 6 H+ + 6 e- → 3 H2O H+ (-) Anode: CH3OH + H2O +Pt → CO2 + 6 H+ + 6 e- Pt-O + H+ + e- →Pt-OH Pt-OH + H+ + e- → Pt-H2O catalyst (+) Nafion Pt-(CH3OH)ads → Pt-COads + 4 H+ + 4 e-

30. Surface reactions on catalyst surface 重奌在說明觸媒表面的功能 Anode: Pt + CH3OH → Pt-CO + 4 H+ + Pt + 4 e- Pt-CO + Pt- H2O → CO2 + 2 e + 2 H+ 2Pt CH3OH Pt → CO2 + 6 H+ + 6 e- Catalyst decreasing the activation energy, facilitating chem. reaction

31. Ru-islands with regular lateral periodicity of around 20 A grown on Pt(111) surface Ru-deposited Pt(111) substrate surface Ru-deposited layers 釕在鉑 (111) 表面上所形成的超結構在電解液中因CO的氧化過程，導致釕在鉑(111)表面上所形成的超結構明顯消失 (loss of the long-range order)[6]。 After Ru/Pt(111) towards CO electro-oxidation in HClO4 , disappearing the long range-order as demonstrated by RHEED 証明 Ru-原子的移動

32. RHEED patterns for Pt(111) covered by Ru (0.64 ML) deposit, showing satellite reflections indicated by arrows Satellite reflections show that the Ru adlayer with additional lateral periodicity of around 20 A is formed

33. Structural transformation of the reconstructed Pt(100) surface COad → CO2 ↑ (100)-(1x1) (100)-hex Pt(100) COad + O2→ CO2 ↑

34. 鉑單 晶面(100) 在CO- oxidation ; 由六面单胞(hex-unit cell) 轉化成四面单胞(square unit cell, 1x1) 來囘轉(變)化, 來解釋 陪同CO-氧化反應呈現的震盪現象 証明: 觸媒表面上的原子在反應過程中，是不斷在移動中。 以及鉑/釕因CO-在氧化反應所引起的結構變化 並非如同傳統觀念認為：「催化劑只使化學反應加速，本身不會起任何變化」。

35. Conclusion 1). Strong adsorption of the reactants on the catalyst surface leads to decrease the activation energy of molecular dissociation. 2). CO-oxidation on Pt surfaces and NH3 synthesis on FeO proceed via Langmuir-Hinschelwood mechanism, i.e., reaction by the adsorbed atomic species on catalyst surface. 3). Structural change of catalyst surface is accompanied by the catalytic reactions. The mobility of the surface atoms is enhanced by the strong adsorption of the reactants. 實例說(証)明, 固體表面化學反應的重要

36. East Berlin 柏林圍牆1989 前 West Berlin

37. Berlin, 1989

39. 05.2003, Fritz-Haber Institute der Max-Planck-Gesell. Berlin, Germany