Study On Preparation And Hydrogenation Performance Of Nano-gold Catalysts

In recent years, gold nancatalysts have attracted widespread interest because of its unique catalytic properties. It is now generally accepted that the unexpected activity of supported gold catalysts is related to the preparation method, the particle size of gold, and the nature of (?)e support. Therefore, how to make nanoparticles highly dispersed and stable is the key in the preparation process. Focusing on the scientific issues, this thesis explores a kind of new method to prepare stable, highly dispersed gold nanoparticles, and investigate its catalytic properties. The main results presented in the dissertation have been summarized as follows:(1) Highly dispersed gold nanoparticles supported on organic-inorganic hybrid silica have been successfully prepared through a novel and facile approach. In the process,3-aminopropyltriethoxysilane (APTES) was hydrolyzed in HCHO aqueous solution to prepare silica with organic functional groups (-CH2CH2CH2NHCH2OH) formed through the reaction between-NH2and HCHO, then the silica reacted with HAuCl4in aqueous solution. The TEM, XRD, XPS, NMR results indicated metallic Au nanoparticles were highly dispersed on silica with an average particles size1.8±0.5nm. The reduction of metal precursors was attributed to-RNHCH2OH group during the prepartion, and the as-obtained Au/SiO2exhibited good catalytic activity and stability for hydrogenation of aromatic nitro-compounds with H2.(2) We found a reductive organic silicane (CH3O)SiCH2CH2OCH2CHCH2O (GPTMS) by seeking after. In the novel process, the reductive group is introduced onto silica by a co-condensation method, thus the modified silica can reduce gold precursors to form Au/SiO2. The TEM, XRD, and NMR results indicated noble metal nanoparticles were highly dispersed on silica with an average particles size5.2±1.0nm. The diol species derived from3-glycidoxypropyl groups of GPTMS were confirmd to serve as the true reductants for metal precursors and the as-obtained Au/SiO2exhibited good catalytic activity for hydrogenation of aromatic nitro-compounds with H2. And we expand the in situ thought to the preparation of Ag, Pt, and Pd noble metal catalysts.(3) We take advantage of the in situ thought and expand it to the preparation of gold nanocatalysts on different kinds of supports via grafting method. We take advantage of the in situ thought and expand it to the preparation of gold nanocatalysts on different kinds of supports via grafting method.In the preparation,the GPTMS was grafted onto Fe(OH)x, TiO2, Al2O3supports with-OH under NH3-H2O condition, and then the supports with reductive organic functional groups reacted with HAuCl4in aqueous solution. The Au/Fe(OH)x catalysts prepared under NH3·H2O condition show the best catalytic activity, selectivity and stability for liquid phase catalytic hydrogenation of aromatic nitro-compounds with H2. The TEM and XRD results indicated metallic Au nanoparticles were highly dispersed on supports.