Spherical mesoporous silica particles with entrapped metal nanoparticles are synthesized from a onestep aerosol-assisted self-assembly process using sols of an alkoxysilane, ethanol, surfactant, water, HCl, and metal precursors (e.g., salts or complexes). Utilizing nitrogen as a carrier gas, the sol is sent through an atomizer, producing aerosol droplets, which are passed through a tubular furnace heated to 400 °C. Solvent evaporation from the droplets enriches the nonvolatile components and results in the coassembly of silicate and surfactant into 3-dimensional mesostructures with incorporated metal precursors. Lamellar, cubic, and hexagonal mesostructures are achieved by using different surfactants. Subsequent calcination of the surfactant and reduction of the metal result in spherical mesostructured porous silica particles with supported metal nanoparticles. Nitrogen sorption techniques, transmission electron microscopy, scanning electron microscopy, and X-ray diffraction are used to characterize the particles. Mesoporous silica particles with 0.5% Pd are tested as a catalyst in the hydrodechlorination reaction of 1,2-dichloroethane and exhibit ∼100% conversion above 350 °C and ∼100% ethylene selectivity, demonstrating the potential of such nanocomposites as catalysts.
Lightweight, compact hydrogen storage has been one of the major bottlenecks in developing fuel cell systems applicable to powering ground vehicles. In this study, preliminary experimental examinations have been performed to evaluate vibratory densification of nanometer-scale powder particles, which directly affects the volume and weight of storage systems based on complex hydrides such as NaAlH4. Since NaAlH4 is is reactive with moisture and oxygen, and thus not possible to test in air, γ-alumina (gamma-aluminum oxide) with a similar average particle size (~50 nm) is applied as a surrogate material in this preliminary investigation. An apparatus including a tube test section to quantify the densification of a column of powder was developed for this study. Comprehensive testing has been carried out to identify the optimal vibration conditions achieving the highest densities. The study investigates the effectiveness of 1-dimensional and 2-dimensional vibration, as well as the impact of frequency patterns (constant frequency and frequency sweeping). Offering fundamental understanding of nano-powder densification using shakers, this experimental investigation provides guidelines for further study of vibration-based hydride powder densification.
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