Browsing by Subject "Alumina"
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Item The design and experimental investigation of an alumina reticulate porous ceramic heat exchanger for high temperatures(2014-06) Banerjee, AayanThe present study focuses on the design, modeling and testing of an alumina heat exchanger filled with reticulate porous ceramic (RPC). The heat exchanger has been designed to operate reliably at temperatures up to 1773 K, integrate seamlessly with the reactor designed for isothermal CO2 and H2O splitting using ceria and obtain an effectiveness of >0.85 for the range of flow rates anticipated during operation of the isothermal reactor. The RPC morphology, namely porosity and pore density and the geometry of the heat exchanger are selected based on the results of a fluid flow and heat transfer model of the heat exchanger. A prototype was also tested at temperatures up to 1240 K. The permeability, inertial coefficient, overall heat transfer coefficient, effectiveness and pressure drop were measured.Item Kinetics, mechanisms, and site requirements(2016-08) DeWilde, JosephWe report the kinetics, mechanisms, and site densities of parallel ethanol dehydration and dehydrogenation over gamma-alumina (γ-Al2O3), a high surface area and thermally-stable metal oxide used both as a catalyst support and as a Lewis acid catalyst in industrial practice. We further extend our investigations to diethyl ether conversion over γ-Al2O3 to describe the reaction network for ethanol dehydration and dehydrogenation at conversions exceeding 10%. Steady state measurements demonstrate that unimolecular and bimolecular ethanol dehydration rates are inhibited by water-ethanol co-adsorbed complexes at 488 K. Reactive surface intermediates, rather than co-adsorbed complexes, inhibit the rates of ethanol dehydration and dehydrogenation at industrially-relevant temperatures (>623 K). Co-processing pyridine with ethanol/water feed mixtures results in a reversible inhibition of both unimolecular and bimolecular ethanol conversion pathways; the synthesis rates of ethylene and acetaldehyde are inhibited to a greater extent than diethyl ether synthesis rates, establishing that unimolecular reactions occur on a pool of catalytic sites separate from the pool for bimolecular dehydration reactions. An observed 1:1 ratio of acetaldehyde and ethane in the eluent verifies that ethanol dehydrogenation proceeds via a hydrogen transfer mechanism. We employ asymmetric ethers as probes to establish ether conversion on γ-Al2O3 occurs through a disproportionation pathway to form an olefin and an alcohol, rather than through a hydration pathway. Diethyl ether disproportionation rates were verified to (i) possess an intrinsic rate constant that is within a factor of two of that of unimolecular ethanol dehydration and (ii) be inhibited by pyridine to the same extent as ethylene synthesis rates from ethanol dehydration. These observations are consistent with a proposed mechanism in which ether disproportionation and unimolecular alcohol dehydration occur through a common alkoxide reaction intermediate and on a common pool of catalytic sites. Our combined investigations of alcohol and ether conversion establish the existence of two distinct pools of catalytic centers, verify all unimolecular pathways of alcohol dehydration, dehydrogenation, and ether disproportionation occur on a common set of active sites, and provide a rigorous kinetic description of these pathways.Item Nonthermal Plasma Synthesis Of Nanoparticles And Double Probe Diagnostic(2023-04) Xiong, ZichangNanoparticles are tiny particles that range in size from 1 to 100 nanometers. Their large surface area-to-volume ratio allows them to interact with their surroundings in unique ways. Nonthermal plasmas are particularly attractive sources for nanoparticle synthesis. In these plasmas, energetic plasma electrons decompose molecular gaseous precursors, producing radicals, which lead to the nucleation and growth of nanoparticles. This thesis investigates the feasibility of double probe measured in nonthermal dusty plasma and the mechanism of particle trapping and heating in nonthermal plasma synthesis of nanoparticles. This thesis also studies ICP synthesized size-tunable y-Al2O3 nanocrystals and reducing iron oxide particles by a MW hydrogen plasma. Double probes are utilized to diagnose the plasma properties of an argon:silane plasma containing nanoparticles. We demonstrate good stability of current-voltage characteristics over several minutes of operation. In addition, we developed a zero-dimensional global model to investigate the effect of the presence of nanoparticles on the plasma properties. Critical processes were investigated in nonthermal plasma synthesis of nanoparticles. We present experimental and computational evidence that, during their growth in the plasma, sub-10 nm silicon particles become temporarily confined in an electrostatic trap in radio-frequency excited plasmas until they grow to a size at which the increasing drag force imparted by the flowing gas entrains the particles, carrying them out of the trap. Furthermore, a nanoparticle heating model was used to study the temperature increase of a particle exposed to a plasma by exothermic surface reactions. y-Al2O3 is widely used as a catalyst and catalytic support due to its high specific surface area and porosity. We report a single-step synthesis of size-controlled and monodisperse, facetted y-Al2O3 nanocrystals in an inductively coupled nonthermal plasma reactor using trimethylaluminum and oxygen as precursors. Nanocrystal size tuning was achieved by varying the total reactor pressure yielding particles as small 3.5 nm, below the predicted thermodynamic stability limit for y-Al2O3. CO2 emissions from the steel production account for 8% of the global anthropogenic CO2 emissions and are a key challenge towards achieving a carbon-neutral future. We report an electrified process for reducing iron ore particles using atmospheric pressure hydrogen plasma powered by microwave energy. Iron ore particles were reduced steadily on a mesh exposed to the plasma. Moreover, in-flight iron ore reduction was achieved using the atmospheric pressure hydrogen microwave plasma, which is more than 100 times faster than the previously reported flash in-flight iron ore reduction by a thermal hydrogen technique.