Surface Structure Characterization Of Solid Catalysts

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.