(220d) Accessing Meta-Stable States through Plasma Catalysis

Low temperature plasmas (LTPs) are partially ionized gases in which high energy electrons collide with gas molecules to produce a highly reactive chemical environment, including free electrons, ions, radicals, and vibrationally- and electronically-excited molecules, at bulk temperatures (~300-600 K) at which such species are thermally inaccessible. The integration of atmospheric pressure LTPs into catalytic systems has recently gained considerable attention because of its potential to carry out transformations that are difficult or impossible using conventional thermal catalysis (e.g. CH₄, N₂, and CO₂ activation), and in modular units powered by renewable electricity. In this talk, I will demonstrate using a newly developed multi-modal operando polarization-modulation infrared reflection absorption spectroscopy tool that plasma-enhanced catalysis can access meta-stable surface-adsorbed species that can only be accessed through the integration of plasma with catalytic surfaces. Specifically, we will demonstrate that, in the presence of nitrogen plasma, azide (N₃) species are stabilized on metal (e.g. Ni, Ag, Au) surfaces with extraordinary stability and unique reactivity. We will demonstrate that surface-adsorbed atomic nitrogen species, which are deposited onto the metal surfaces during exposure to N₂ plasmas, are critical for the formation of azide species. However, deposition of atomic nitrogen species is not alone sufficient to access the surface-adsorbed azide species. We will show that plasma-activated N₂ interacts with surface-adsorbed atomic nitrogen to form the corresponding azide species, which is stable up to ~500 K. Finally, we will demonstrate that this surface-adsorbed azide species has unique reactivity compared to atomic nitrogen. This work demonstrates that meta-stable states can be accessed by integrating plasmas with catalysts, and that these meta-stable states have unique reactivity that is not typically considered in plasma-enhanced reactions involving N₂.