【作者】 赵曦；

【导师】 魏刚；

【作者基本信息】 北京化工大学 ， 材料学， 2009， 博士

【摘要】 表面科学是一门新兴的边缘学科,涉及广阔的领域。材料的表面所呈现出的和体相不同的结构特点对材料的性能有显著的影响。本工作选取了在表面科学研究中具有典型意义的三个体系——两种催化体系和一种负催化体系,建立了针对不同体系的表征方法,用这些方法对材料表面结构进行了表征,获得了一系列表面结构参数,进而构筑了结构与其性能之间的关系。首先研究的是Ziegler-Natta催化体系。Ziegler-Natta催化体系发展至今已经五十多年,但是表征和机理方面的研究进展缓慢,其原因是该催化体系复杂,活性中心在催化剂中所占的比例小,对水氧高度敏感,致使催化剂的表征非常困难,尤其是表面结构的表征更加困难。本工作针对Ziegler-Natta催化体系建立了由红外光谱、热分析、X射线光电子能谱、X射线衍射、扫描电镜等组成的系统表征方法.找到了避免空气中的水和氧影响表征结果的措施,制备了由一系列成份简单的配合物和模型催化剂组成的简化研究体系。通过表征并以DFT计算和分子几何构型理论为基础,研究了催化剂各组分在载体表面的相互作用,给电子体能够和MgCl2形成稳定配合物,并且能够配位在表面不饱和Mg上,造成表面Cl的缺失,促进了MgCl2晶格畸变;还发现在催化剂中给电子体和TiCl4分别配位在MgCl2的表面,但同时给电子体和TiCl4之间也存在着间接作用——给电子体会减弱MgCl2和TiCl4之间的配合,TiCl4则增强MgCl2和给电子体之间的配合；三种内给电子体EB、DBW和BMF在MgCl2表面配位形式不同,从分子几何构型的角度解释了这种差异的原因。本工作还探索了Ziegler-Natta催化体系的表征结果、表面结构和催化剂性能之间的关系,为进一步提高催化体系的性能提供了依据。在前人提出的活性中心模型的基础上,建立了新的活性中心模型,该模型能够很好地解释本文中的试验结果。VOx-Ti02是一种负载型的金属氧化物催化剂,能够用于多个体系的氧化还原催化反应中。本工作建立了XPS、XRD、TPD等表征方法,对VOx-TiO2催化表面结构进行了研究,重点探讨了VOx的单层分散、VOx和TiO2之间的相互作用以及VOx在TiO2表面的存在形式。通过XPS测定,得出了VOx在TiO2颗粒表面覆盖层的厚度。XRD测定发现,VOx表面的单层阈值为1.7%。SIMS谱图显示,VOx在TiO2表面的存在形式为(VO2) nO2,并且表面存在VOx和TiO2的羟基化。对失活过程的研究表明,VOx-TiO2催化剂的高温失活原因是V进入了金红石TiO2的表面晶格中,而不再以VOx的形式存在。催化作用的反面是负催化作用。虽然负催化作用的研究成果已经形成了相对独立的缓蚀科学,但两者的研究在理论上往往起到互补作用。因此,本工作还研究了负催化作用,建立了由XPS、AFM、SEM和电化学手段组成的系统表征方法,对磷系负催化剂在碳钢表面形成的膜的结构进行了表征,测定了膜的组成、厚度、形貌,并用AFM观察了膜的形成过程,发现成膜过程中有机膦酸和Zn2-Ca2+、Fe2+发挥协同效应,形成难溶的螯合物,螯合物颗粒在碳钢表面不断沉淀,晶粒逐渐长大,最终形成对铁的腐蚀反应具有负催化作用的致密保护膜。该保护膜同时抑制腐蚀反应的阴极过程和阳极过程。XPS测定显示,碳钢表面保护膜的致密层厚度约为40nm。本工作证明,表面表征技术在各种材料表面结构的研究中既有相似之处,又各有特色,但对认识材料的结构及其与性能之间的关系都能发挥重要作用。表面结构的深入研究为今后新材料的制备以及材料性能的改善奠定了基础,最终将推动材料科学的进步。更多还原

【Abstract】 Surface science is a new developing and crossed-knowledge science, involving wide fields. The surface structure influences the material performance greatly, so the characterization of material surface is very important. Three typical systems were chosen to be researched with surface analysis technique——two catalyst systems and one negative catalyst system, and special characterization methods were established for different systems. With these characterization methods, a series surface structure parameter is required, and the relationship between structure and performance was built.The first system we studied is Ziegler-Natta catalyst. More than fifty years have been passed since Ziegler-Natta catalyst was discovered, but the development of catalytic mechanism and characterization methods is rather slow, because it’s high sensitivity to moisture and oxygen, the complexity of it’s components, and the low concentration of it’s active center. The special methods of IR, XPS, and XRD were established in this paper, which help us to analyze the catalysts without the influence of moisture and oxygen. The preparation of complexes and model catalysts provide us a relative simple system to analyze. Based on characterization of XPS, XRD, FT-IR, TA and SEM, DFT calculation and molecule geometry, the interaction among different components was investigated. The results show that donors coordinate on unsatured Mg atom on MgCl2 surface, and promote the distortion of MgCl2 crystal lattice. In catalyst, donors and TiCl4 coordinated on MgCl2 surface separately, but not independently——the existence of TiCl4 strengthen the interaction between MgCl2 and donors, and donors weaken the interaction between TiCl4 and MgCl2. Three internal donors (EB, DBW, BMF) coordinate on MgCl2 surface with different forms, and the reason is elucidated with molecule geometry. The relationship of analysis spectrum, surface structure and catalyst performance was also discussed in this paper. Based on the previous active site models, a new active site model was suggested, and all of the experiment results in this paper can be explained well with this model.The second system is VOx-TiO2 catalyst. VOx-TiO2 catalyst is a redox catalyst, widely used in some organic reaction systems. In these years, the research of VOx-TiO2 catalysis mechanism focused on VOx monolayer dispersing, the interaction between VOx and TiO2, and the existence form of VOx on TiO2 surface. In this paper, all of the three aspects were discussed. With the characterization of SIMS, XPS, XRD, TPD and TEM, the thickness of VOX surface layer, the monolayer thresholds of VOx and vanadium species on TiO2 surface were all investigated, (VO2) nO2 molecule structure model was proposed to explain the catalyst surface structure. The change of surface structure during catalyst deactivation at high temperature was also discussed, and it helps us to understand catalyst deactivation reason and prolong catalyst life.Negative catalysis is another side of catalysis process. Although negative catalysis has already developed into a relatively independent anti-corrosion science, the studies of these two areas can be complementary. So the negative catalysis was also investigated in this paper. A systemic characterization methods, including XPS、AFM、SEM and electrochemical methods, were built to research the negative catalysis film formed with organic phosphonic acid and zinc salt on carbon steel. With the characterization methods we established in this paper, the composition and thickness of protective film were investigated with XPS depth profile, the film formation process was observed with AFM. During the film formation, with the synergism of phosphonic acid, Zn2+ in agents, Ca2+ in water, Fe2+ come from intitial corrosion products, the insoluble chelates deposited on carbon steel surface. With the growth and increasement of chelate particle, the carbon steel surface is covered with the chelate particles entirely. The protective film prevents both of cathode and anode process at the same time. The thickness of compact protective film measured with XPS is about 40nm.This study prove that surface analysis methods have similarities and characteristics in research of various material surface structure, but its important role in investigation of material structure and performance should to be stressed. With the studies of functional material surface structure, a bridge connected mechanism and performace is built, and it will promote the progress of material science enventurely.更多还原