Study On Preparation And Hydrogenation Performance Of Nano-Gold Catalysts

In recent years, nano-gold catalysts have attracted intensive research interest because of their unique catalytic properties. It is now generally accepted that the catalytic properties of Au can be associated with the preparation method as well as the particle size and the nature of the support. This thesis introduces a novel methodology for the synthesis of Au nanoparticles, and investigated their catalytic hydrogenating properties. The primary results have been summarized as follows:(1) Dodecylamine (DDA)-protected Au nanoparticles have been successfully prepared in water-oil two-phase method. The size of DDA-protected Au nanoparticles can be tuned through changing the reductant, controlling the reducing temperature and changing the molar ratio of DDA to Au precursor. The TEM analysis combined with UV-vis spectra indicated that increasing reducing temperature and decreasing the molar ratio of DDA to Au precursor favored the formation of small Au nanoparticles. Otherwise, the reduction of Au precursor by the intermediate species generated through benzaldehyde reacting with hydrazine hydrate yielded smaller Au nanoparticles compared with those from the reduction of gold presursor by the species generated through DDA reacting with HCHO. The as-prepared DDA-protected Au nanoparticles can be transfered from cyclohexane to water by PVP, however accompanied with the growth of Au particle size. The hydrogenation of p-nitrophenol was selected as the probe reaction for the assessment of the catalytic performance of the as-prepared DDA-protected Au nanoparticles. The primary results demonstrated a good reactivity of DDA-protected Au nanoparticles and that the biphase reaction system enabled an easy recovery of the catalysts.(2)Trishydroxymethyl aminomethan (THAM) was introduced to the surface of hydroxyapatite (HAP), TiO2, and γ-Al2O3through a hydrothermal process. The reductive species generated in situ grafted AuCl4-from aqueous solution and anchored the generating gold nanoparticles on the different supports surface. The as-prepared Au/HAP catalyst showed good performance in the catalytic reduction of nitroaromatic compounds. The XRD, XPS and TEM results indicated that gold nanoparticles were mainly present in metallic state and highly dispersed on HAP with average particle size of3.1nm. The aforementioned surface grafting method was extended to the preparation of Pd/TiO2. The XPS results indicated strong metal-support interaction in Pd/TiO2catalyst. The as-prepared Pd/TiO2 catalyst exhibited good catalytic activity and stabitity in the hydrogenation of aromatic nitro-compounds.(3) A series of Au/HAP catalysts with different molar ratio of Ca to P have been synthetized by the homogenous deposition precipitation method. The XRD, XPS, and TEM results indicated that Au particles were mainly in metallic state and highly dispersed on HAP. The surface basicity of HAP and the size of Au particles can be tuned through changing the Ca/P molar ratio. When the Ca/P molar ratios were1.70,1.67and1.63, the average size of Au nanoparticles were2.9,3.4and3.9nm, respectively. The as-prepared Au/HAP catalyst exhibited good catalytic activity in the hydrogenation of p-chloronitrobenzene.