The Preparation Of Noble Metal Nanoparticles And The Research Of The Catalytic Performance

Gold nanoparticles supported on metal oxides show remarkable catalytic activity in COoxidation at low temperatures. Deposition-precipitation method is usually be used to preparegold catalysts. But the size of Au nanoparticles is more controllable throughcolloid-precipitation method. Brust was the first one who used phase transfer catalyst (PTC)and thiol compound to prepare the Au colloid in organic phase. However, the PTC is hard to beremoved above the Au colloid and the use of thiol can lead to the catalyst poisoning. In thispaper, the PTC and thiol can be replaced by extractants to make the Au colloid well dispersed inorganic phase. Au ions can be extracted from aqueous phase to organic phase by extractants andthe Au nanoparticles after reduction can be protected by extractants.In this essay, HAuCl4was used as the precursor of gold. Trioctylamine,bis(2-ethylhexyl)amine and N,N,N’N’-tetraoctyl-thiodiglycolamide(TOTDGA) were used asextractants. NaBH4aqueous or DMF was used as reductant. The diluent was toluene. A seriesof gold colloid which were dispersed in organic phase were prepared by use different kinds ofextractants, control the concentration of extractants and use different reductants. Aunanoparticles were supported on nano-TiO2through colloid-precipitation method to prepare thenano-gold catalyst. The colloid and catalysts were characterized by HRTEM, UV-visspectrophotometer, TGA and FT-IR. The catalyst which was prepared by this method wascapped with extractant and the layer of organic prevented Au nanoparticles from agglomerate.The Au nanoparticles show narrower size distribution and smaller by the use of0.025Mtrioctylamine, compared with other concentrations and types of extractants. The Au/TiO2catalyst which was prepared through colloid-precipitation in above conditions showed higheractivity in CO oxidation than the other conditions and CO could be totally oxidized at200℃.Au nanopraticles can disperse in aqueous phase by protect of surfactants (eg. PVA or PVP).The Au colloid also can be supported on the surface of TiO2and γ-Al2O3throughcolloid-precipitation method. The factors affecting catalyst activity were discussed, whichincluded the kinds of surfactants, the quantity of surfactant, kinds of supports, calcination gasatmosphere and Au loadings. When appropriate PVA is used as surfactant, the catalytic activityis higher than the use of PVP. The active component of the catalyst would be largely covered and lead to the catalyst deactivation if the surfactant is added excessively. When γ-Al2O3is usedas the support, the catalytic ability is lower than TiO2. The calcination gas atmosphere couldinfluence the CO oxidation ability. The catalytic ability is higher when20vol.%O2/N2is usedas the gas atmosphere than20vol.%H2/N2. The catalytic ability is high when the loadingamount of Au is1%than0.5%, but if Au loading was above1%, the Au nanoparticles willcoagulate during the preparation of catalysts.CeO2nanoparticles were prepared through hydrothermal method and were used as thesupport of Au/CeO2catalyst. CeO2calcined in different temperature could influence thecatalytic activity. The change of Au/CeO2catalyst structure before and after catalytic reactionwas characterized by HRTEM. The decomposition temperature of the organic compounds onthe surface of the catalyst was detected by TGA and the organic materials could not be totallyremoved unless T>600℃. Thus the organic compounds on the surface were the influencefactor on the catalytic ability. When CeO2was calcined at350℃, the catalytic activity of theAu/CeO2catalyst was higher than the other conditions and CO could be oxidated totally at100℃.