(335f) Decoupling Plasma-Catalytic Interactions through Plasma-Temperature Programmed N2 Reduction and Oxidation Reactions

The potential for non-thermal plasma to activate strong chemical bonds has provided alternative routes for chemical transformations at milder reaction conditions. Plasma-activated catalysis combines plasma and catalytic contributions to enhance chemical reactions. The choice of catalytic material is pivotal in harnessing the synergistic relationship observed when stimulated by plasma. However, material design that can effectively harness the plasma-catalyst synergy depends on the fundamental understanding of relevant plasma-activated surface reaction pathways. Moreover, in these plasma-catalytic systems, plasma phase reactions can dominate, which often complicates the analysis and contribution of the catalyst surface reactivity to the overall product yields.

This presentation will focus on our recent investigation in elucidating the reactivity of plasma-activated nitrogen species on a metal surface. To do this, we employ sequential exposure of the catalyst surface to the different reactant gases in which the plasma-activated nitrogen is subjected to temperature-programmed reactions with another reactant (hydrogen or oxygen). By so doing, we can evaluate the reactivity of plasma-activated nitrogen under reductive and oxidative conditions. Under hydrogenation conditions, we observe the formation of NH₃ over different silica-supported metal catalysts (Fe, Co, Ni, and Pt). Hence, this shows that after plasma activates nitrogen, metal surfaces can perform hydrogenation chemistry to produce NH₃. Further, microkinetic modeling calculations show that the temperature of NH₃ formation scales with the activation barrier for surface hydrogenation. Under oxidative conditions over Pt and Au catalysts, we observed the formation of NO and N₂O. Interestingly, we observed that the metal affinity towards oxygen activation is critical in directing product selectivity, with Pt being more selective to NO while Au is more selective to N₂O. This further elaborates on the effect of metal surface reactivity under plasma stimulation. Taken together, our study highlights the significance of catalytic contribution and surface reactivity, which is highly relevant for guiding material selection and design principles for plasma-activated processes.