催化反应 第4章：催化剂的结构（上）.ppt

1、第四章 催化剂的结构(上),催化剂: 结构与活性关系 催化剂的选择性分四个层次: 化学选择性(chemo-selectivity), 立体选择性(stereo-selectivity), 对映体选择性(enantio-selectivity), 和局域选择性(regio-selectivity)。催化剂选择功能的实现依赖于催化剂的结构电子的或几何的结构。 当代催化化学的中心论题是提高催化剂的专一性(specificity), 因而催化剂的结构设计至关重要。,一. 分子筛催化剂 (chemo 2. 骨架由多元环组成; 3. 有笼(cage)和孔道(channel); 4. 酸性随硅铝比变化而变化

2、.,固体酸/碱催化剂的种类,分子筛的人工合成始于40年代，主要是合成低/中硅铝比的沸石。60年代Mobil合成了高硅沸石ZSM-5并迅速在炼油工业中获得大规模应用，由此开始了分子筛合成与应用的新时代。,ZSM-5有分子级的孔道，亲油疏水，水热稳定性高。,分子筛的人工合成,沸石(zeolite)在真空下脱水得到分子筛(molecular sieves)，因为其规整的孔道结构可以“筛分”分子。现在倾向于把所有这一类有规整孔道的骨架化合物统称为分子筛。,典型人工合成分子筛示意,Supercage (1.3 nm) 左：八面沸石 右：丝光沸石(mordenite) Si/Al 3 Y型分子筛,分子筛的

3、人工合成,分子筛的人工合成,择形选择性,择形选择性,分子筛的结构-活性关系: 1. 分子筛的酸性不是晶体性质而是表面的从而是非晶特性. 2. 硅铝混合显然是改变了O-H键的键强, 原理同担载催化剂. 3. 分子筛的立体选择性(择形)是晶体的结构所致.,Metal oxides, particularly those of the transition metals, are widely used as catalysts. For this purpose, they are often supported on other oxides such as aluminas (m.p. 200

4、0 oC) and silicas (m.p. 1700 oC) of different types. The oxide supports have high melting points and surface areas and are somewhat amorphous in nature.,2.氧化物的表面化学,小结：吸附与络合之化学原理比较,2.1 简评表面化学,In comparison with studies on other materials, studies of catalysts pay much more attention to the behavior o

5、n the surface or at the atomic level. Due to this point, although catalysis studies and others investigate the same materials in the same framework (from macro to meso to micro), the strategies and the methods are greatly different from each other.,Surface chemistry/physics has opened up a new world

6、 in the last 40 years. Initially, scientists believed that studies on ideal surfaces would finally give us a key to open the black box of catalysis. Great progress has also been made in the studies on ideal oxide surfaces in the last ten years. How much the research of surface science based on ideal

7、 surfaces influence the science of catalysis is still an open question, however.,2.1 简评表面化学,Phenomenon: Ideal surface is not perfect,Phenomenon: Reconstruction,Figure 8. The hydrogen induced paired new reconstruction of Ni110.78 Part a shows the direction of the pairing displacements of the top laye

8、r atoms; b shows a plan view of the reconstructed surface, while c shows a cross sectional view. Hydrogen atoms have been omitted for clarity.,a),b),c),Phenomenon: Reconstruction,Figure 9. The Cu110-(23)-N structure.105 The small dark circles represent the N atoms, the white circles represent the ps

9、eudo-100layer,and the shaded circles represent the underlying 110 substrate.Part a shows a plan view of the surface, while b displays a cross sectional view through the surface.The outermost, 100-like, layer is buckled by 0.52 by the registry mismatch with the second layer.,a),b),Phenomenon: Reconst

10、ruction and Relaxation,Concept: Site,Concept: Ensemble (domain),岩盐（100）：MgO/CaO/MnO/NiO/CoO,(Henrich/Cox, Cambridge, 1994),2.2 氧化物的表面化学,钙钛矿(100)：SrTiO3/BaTiO3/WO3/NaXWO3,(Henrich/Cox, Cambridge, 1994),2.2 氧化物的表面化学,钙钛矿(111)：SrTiO3/BaTiO3/WO3/NaXWO3,(Henrich/Cox, Cambridge, 1994),2.2 氧化物的表面化学,金红石(110)

11、：TiO2/SnO2/RuO2,(Henrich/Cox, Cambridge, 1994),2.2 氧化物的表面化学,金红石(100)：TiO2/SnO2/RuO2,(Henrich/Cox, Cambridge, 1994),2.2 氧化物的表面化学,刚玉：Al2O3/Ti2O3/V2O3/-Fe2O3,(Henrich/Cox, Cambridge, 1994),2.2 氧化物的表面化学,纤维锌矿：ZnO,(Henrich/Cox, Cambridge, 1994),2.2 氧化物的表面化学,尖晶石：MoO3/Cu2O/V2O5/PbO/-Al2O3/(M3O4),(Henrich/Cox, Cambridge, 1994),2.2 氧化物的表面化学,Steps on oxide surfaces,(Henrich/Cox, Cambridge, 1994),2.2 氧化物的表面化学,2.3 Concept: Two-dimensional order,An example of two -dimension long distance ordered (Gallowy,Benitez and Salmeron),2.3 Concept: Two-dimensional order,2.3 Concept: Two-dimensio