Synthesis Of Metal@Silica Core-shell Nanostructures For Hydrogen Production From Ammonia Borane

Recently, hydrogen has attracted considerable attention and recognition as a globally accepted clean energy carrier. The search for safe and efficient hydrogen storage materials still remains one of the most challenging barriers in the “hydrogen economy” society. Due to the high hydrogen capacity and environmentally friendly nature, ammonia borane（NH3BH3, AB） complex is recognized as one of the most promising candidates for chemical hydrogen storages. So far, not only monometallic and bimetallic but also trimetallic catalysts have been studied for hydrolytic dehydrogenation of AB. However, most of them in nano-size are easily aggregated, leading to the loss of the catalytic activity and reusability performance. Therefore, the high-stability and high-performance catalysts are currently receiving considerable attention. This thesis focused on the preparation, characterization and catalytic hydrogen generation of core-shell metal@SiO2, the main contents are as follows:Ultrafine platinum nanoparticles（NPs） with size of ⁴ nm embedded in Si O2（Pt@SiO2） had been synthesized in a NP-5/cyclohexane reversed-micelle system followed by NaBH4 reduction. As compared to free Pt NPs and Si O2 supported Pt NPs, Pt@SiO2 presents higher catalytic activity to release a stoichiometric amount of hydrogen from aqueous AB（H2/AB = 3.0） with a turnover frequency（TOF） value of 158.6 mol H2（mol Pt min）-1, relative high values for Pt-based nanocatalysts. After recycle test and heat treatment with high temperature（C₄00）, the morphology and catalytic performance of the sample remain almost unchanged.Co@SiO2 supported dispersed Ag NPs（Ag/Co@SiO2） have been successfully synthesized by using AB as a reductant via a impregnation-reduction route, in which Co@SiO2 were synthesized using Co（NH3）6Cl3 as precursor in the NP-5/cyclohexane reverse micelles microemulsion. In contrast to free Ag nanoparticles, SiO2 supported Ag nanoparticles, core-shell Co@SiO2 nanoparticles, and the physical mixtures of Ag and Co@SiO2 nanoparticles, bimetallic Ag/Co@SiO2 nanoparticles shows a superior activity in hydrogen generation from AB solution. The activation energy（Ea = 24.9 k J/mol） for this catalyst was obtained by carrying out the hydrolysis reaction at different temperatures, which is lower than most of the bimetallic catalysts. After five recycle test, there is no obvious decreaces in catalytic activity, indicating the good recycle stability of catalysts.