16 research outputs found
Thermal Stability and Crystallinity in Sputtered Scandia Stabilized Zirconia Thing Films
No full textThis senior thesis project studies the synthesis of solid oxide fuel cell electrolytes using magnetron sputtering. Materials used in bilayer electrolytes were studied individually for phase stability
Plasma-Assisted Catalysis for the Activation of N<sub>2</sub>
No full textPlasma-assisted catalysis is a process combining non-thermal plasma and solid catalysts to drive difficult chemical transformations at low temperatures and atmospheric pressure, and to achieve production rates and/or selectivities beyond what either system could do individually. This thesis examines the interactions between nitrogen activated by a dielectric barrier discharge plasma and supported metal catalysts primarily for driving low temperature atmospheric pressure ammonia synthesis, but also for the coupling of nitrogen with oxygen and hydrocarbons. Initial studies focused on evaluating the ammonia production rates over various supported metal catalysts (Ni, Ru, Co, Fe and Pt) in a N2/H2 plasma discharge. Here we distinguished between plasma phase production rates and ammonia production from plasma-catalyst interactions through careful kinetic studies and measurement of background plasma reactivity. By isolating plasma-catalyst interactions, we observed how plasma parameters like discharge power control catalytic activity and demonstrate the importance of N2 activation by the plasma. We further show through comparison with microkinetic models, that plasma-phase N2 activation shifts the well-known thermal catalyst activity trends for ammonia synthesis. This non-thermal N2 activation also dramatically alters thermodynamic control of this system allowing for conversion beyond the thermal equilibrium limit. Direct observation of plasma-catalyst interactions through inelastic neutron scattering makes it clear that plasma activation of N2 facilitates the adsorption of N on a catalyst surface at atmospheric pressure and low temperature. In the final part of this dissertation, we show that this plasma activated N is not only able to be hydrogenated to NH3, but can also be coupled to oxygen over a wide range of different metals.</p
Inelastic Neutron Scattering Observation of Plasma-Promoted Nitrogen Reduction Intermediates on Ni/-Al2O3
No full text
Plasma-Catalytic Ammonia Synthesis Beyond the Equilibrium Limit
No full textWe explore the consequences of non-thermal plasma activation on product yields in catalytic ammonia synthesis, a reaction that is equilibrium-limited at elevated temperatures. We employ a minimal microkinetic model that incorporates the influence of plasma activation on N2 dissociation rates to predict NH3 yields into and across the equilibrium-limited regime. NH3 yields are predicted to exceed bulk thermodynamic equilibrium limits on materials that are thermal-rate-limited by N2 dissociation. In all cases, yields revert to bulk equilibrium at temperatures at which thermal reaction rates exceed plasma-activated ones. Beyond-equilibrium NH3 yields are observed in a packed bed dielectric-barrier-discharge reactor and exhibit sensitivity to catalytic material choice in a way consistent with model predictions. The approach and results highlight the opportunity to exploit synergies between non-thermal plasmas and catalysts to affect transformations at conditions inaccessible through thermal routes
wfschneidergroup/SI-mehta-plasma-N2-vibrations: Supporting Data
No full text<p>Supporting dataset for our publication "Overcoming Ammonia Synthesis Scaling Relations with Plasma-enabled Catalysis", Nature Catalysis, 2018, <a href="https://www.nature.com/articles/s41929-018-0045-1">https://www.nature.com/articles/s41929-018-0045-1</a></p>
Plasma-catalytic ammonia synthesis beyond the equilibrium limit
No full textAbstract: We explore the consequences of nonthermal plasma-activation on product yields in catalytic ammonia synthesis, a reaction that is equilibrium-limited at elevated temperatures. We employ a minimal microkinetic model that incorporates the influence of plasma-activation on N-2 dissociation rates to predict NH3 yields into and across the equilibrium-limited regime. NH3 yields are predicted to exceed bulk thermodynamic equilibrium limits on materials that are thermal-rate-limited by N-2 dissociation. In all cases, yields revert to bulk equilibrium at temperatures at which thermal reaction rates exceed plasma-activated ones. Beyond-equilibrium NH3 yields are observed in a packed bed dielectric barrier discharge reactor and exhibit sensitivity to catalytic material choice in a way consistent with model predictions. The approach and results highlight the opportunity to exploit synergies between nonthermal plasmas and catalysts to affect transformations at conditions inaccessible through thermal routes
Distinguishing Plasma Contributions to Catalyst Performance in Plasma-Assisted Ammonia Synthesis
No full textPlasma-assisted catalysis is the process of electrically activating gases in the plasma-phase at low temperatures and ambient pressure to drive reactions on catalyst surfaces. Plasma-assisted catalytic processes combine conventional heterogeneous surface reactions, homogeneous plasma phase reactions, and coupling between plasma-generated species and the catalyst surface. Herein, we perform kinetically controlled ammonia synthesis measurements in a dielectric barrier discharge (DBD) plasma-assisted catalytic reactor. We decouple contributions due to plasma phase reactions from the overall plasma-assisted catalytic kinetics by performing plasma-only experiments. By varying the gas composition, temper- ature, and discharge power, we probe how macroscopic reaction conditions affect plasma-assisted ammonia synthesis on three different γ-alumina-supported transition metal catalysts (Ru, Co, and Ni). Our experiments indicate that the overall reaction and plasma-phase reaction are first-order in both N2 and H2. In contrast, the rate contributions due to plasma-catalyst interactions are first-order in N2 but zeroth order in H2. Furthermore, we find that the tuning of the plasma discharge power is more effective in controlling catalytic performance than the increasing of bulk gas temperature in plasma-assisted ammonia synthesis. Finally, we show that adding a catalyst to the DBD reaction alters the way that productivity scales with the specific energy input (SEI). KEYWORDS
wfschneidergroup/SI-mehta-beyond-eq: Version 1
No full textSupplementary Dataset: Plasma-Catalytic Ammonia Synthesis Yields Beyond the Equilibrium Limi
