Synthesis of metal/metal-oxide hybrid nanostructures and physical and catalytic properties

Abstract

The development of novel synthetic methods and morphology control for nanoscale metal and metal-oxide particles has attracted a great deal of attention owing to their unique properties and wide catalytic applications. However, the catalytic activity of the heterogeneous nanoparticles often drops as a result of particle aggregation and decreased metal surface area during the catalytic processes. Hybrid nanostructures integrating two or more discrete nanomaterials, especially with functional metal-oxide supports, can provide superior catalytic performance such as higher catalytic activity, structural stability and further recyclability. The resulting hybrid nanocatalysts show unique physico-chemical properties and tailored properties directly influence on their catalytic activity and reusability. In chapter I, we offer a comprehensive introduction into the synthesis of metal/metal-oxide hybrid nanostructures with characteristic functionalities and a study of their physical and catalytic properties. In chapter II, we present the fabrication of three different bifunctional palladium nanocomposites with silica($SiO_2$)-based supports for catalytic reactions. The $Pd/SiO_2$ nanobeads that tiny Pd clusters are deposited inside porous silica ($SiO_2$) network, and the porosity-controlled Pd@Niphy ($Ni_3Si_2O_5(OH)_4$, nickel phyllosilicate) yolk-shell nanoparticles exhibit enhanced catalytic activities in Suzuki cross-coupling reactions due to easy transport of reaction molecules inward and outward active sites. In addition, surface-activated $Pd@SiO_2$ yolk-shell nanoparticles by an oxidant, $PhICl_2$, catalyze the homogeneous hydroalkoxylation reaction showing the homogeneity of heterogeneous catalyst. In chapter III, we introduce a hybrid system comprising metal (Pd or Au) and iron oxide ($Fe_3O_4$) components. The structural anisotropy and crystallinity of $metal-Fe_3O_4$ structures are precisely controlled producing as yolk-shell, irregular core-shell, and dumbb...