Plasma-Assisted Catalysis for the Activation of N₂

Plasma-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.