Study On New Technology For The Preparation Of Nano-gold Catalyst And The Performance In The Oxidation Of Cyclohexane

Nano-gold catalysts had been developing rapidly since 1990's condition and showed splendid activities in many chemical reactions at lower-temperature or a mild condition. Because of the attracting performance in fields of contaminant elimination, fine chemicals synthesis and new energy, Au was entitled green catalyst by researchers. The cyclohexanone production process by cyclohexane oxidation is the most widely used technology in the world. Cyclohexane has stable chemical properties, while the deep oxidation of cyclohexanone occurs easily. Taking this as the background,this dissertation study new preparation process of nano-gold catalyst by new technology and take further research in the oxidation of cyclohexanone.The author outlined the recent progresses in the research on the oxidation of cyclohexane and the main achievement about nano-gold catalyst, such as the preparation methods and the catalytic mechanism. Based on the generalization of research that had been done, the dissertation'research orientation and experiment strategies were proposed.In this dissertation, adsorption phase reaction technology(APRT) was employed to prepare nano-gold catalyst. Firstly, we used different modifying components to adjust surface characteristic of SiO2, After the reduction of chloroauric acid by NaBH4, nano-gold particles were produced. Several analytical methods and equipments were used to characterize the catalysts:transmission electron microscope (TEM) used to analyze particles'size and pattern; X-Ray Diffraction (XRD) used to check crystal form and gain grain size of Au; SEM-EDAX used to study the load factor of Au or Ag elements; Ultraviolet-visible diffuse-reflectance spectra (UV-Vis DRS) used to confirm interaction of Au and Ag.With these methods the author designed experiments by changing Au loading amount, batch addition of Au, ageing treatment of the catalyst, changing the modifying components and add Ag on Au catalysts.The results showed:(1)With the restrictions of absorb layer, nano-gold particles were of size less than 5nm and in good dispersity (2)Nano-gold particles could only load on modifying components with high isoelectric point, but the particles turned to be lager if the alkalinity was too strong;(3) Increasing of Au amount lead to more Au particles and lager particle diameter;(4)Batch addition of Au would form larger Au particles and result to wide particle size distribution. (5)Au and Ag had good interaction in Au-Ag bimetallic catalyst and it was easy and exact to control the ratio and amount of Au or Ag. Increasing Ag amount resulted to lager particle size while Au amount had less affection on the particle size. (6) The load factor of Au and Ag elements were as high as the calculated results.Catalytic activities were evaluated via the oxidation of cyclohexane by using both tert-butyl hydroperoxide (TBHP) and O2 as oxidant. We took the reactions in a solvent-free system. We got conclusion as follow:(1)When TBHP as the oxidant, the catalyst showed splendid activity that the reaction temperature was only 70℃under ordinary pressure. (2) Au particle size had great effect on catalytic activities. Only Au particles with size lower than several nanometer could show high activities. Smaller Au showed high activities but bad selectivity,catalytic activities dropped sharply when the Au particle size grew to some extent.(3) Nano-gold had high activities in the oxidation of cyclohexane, but less active in absorbing active oxygen; (4)Inactive modifying components such as Ni(OH)2, Mg(OH)2,Zn(OH)2 affected catalytic activity by affected the Au particle size. while active modifying components, Co(OH)2, could dissociate oxidant and transfer active oxygen to Au. This would accelerate the reaction. (5) It was the first time the Au-Ag bimetallic catalyst used in the oxidation of cyclohexane and showed high activity. Ag played the similar role as Co(OH)2 did in the transmission of active oxygen to Au. It was also showed that Ag could only utilize TBHP, while Co(OH)2 could dissociate both TBHP and O2. (6)Au nanoparticles were the catalytic active center in the Au-Ag bimetallic catalyst. Catalytic activities dropped sharply as the Au particles size grew.At last, the work in the dissertation was generalized, and problems that still need to be discussed were represented.