Sol-Gel Synthesis and subsequent Flame-based metal decoration of Mesoporous silica nanomaterials
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Mesoporous Silica Nanomaterials (MSNs) have been in the spotlight since their inception, owing to their unique properties. They have high accessible surface areas and easily tunable porosity. They are also thermally stable and are hence perfect candidates for a variety of applications. They are used in a diverse range of fields such as drug delivery, CO2 mitigation, and catalysis, amongst many others. In this thesis, we first synthesize MSNs with different morphologies via the sol-gel route and then demonstrate their decoration with nickel metal nanoparticles using a flame-driven High Temperature Reducing Jet (HTRJ) reactor. In a typical procedure, an aqueous precursor suspension containing nickel nitrate hexahydrate) and MSNs is injected into the throat of a converging-diverging nozzle. Hot combustion products of a fuel-rich hydrogen flame are accelerated through the nozzle, atomizing the precursor. The resultant droplets evaporate and the precursor molecules decompose, initiating nucleation of solid particles. The reducing environment in the reaction chamber converts nickel oxide to nickel, as it is reducible by hydrogen in the presence of water. To stop further growth of these particles, the post-reaction zone is quenched with nitrogen and the particles are collected on a filter membrane.Various analyses such as Transmission Electron Microscopy (TEM), specific surface area measurements (SBET) and X-Ray Diffraction (XRD) were carried out to determine the size, porosity and final structures. N2 adsorption/desorption measurements helped to ascertain the pore sizes and volumes. MSNs with varying morphologies and pore diameters varying from 2.0-2.9 nm were synthesized, and a maximum specific surface area of 1800m2/g was achieved. MSNs were successfully decorated with nickel, as shown by TEM imaging and Energy Dispersive X-ray Spectroscopy (EDS) analysis. By coupling wet chemistry and vapor phase techniques, as demonstrated in this thesis, a variety of MS-supported metal catalysts could be designed and produced, including multicomponent mixtures and metal alloys. Such metal-decorated MSNs can potentially be employed as catalysts in the dry reforming of methane.