Unraveling Nonequilibrium Generation of Atomic Nitrogen and Hydrogen in Plasma-Aided Ammonia Synthesis

Nonequilibrium generation of atomic nitrogen and hydrogen
governing
ammonia production both in the gas phase and on the catalyst surface
is critical to plasma-aided ammonia synthesis. Here, this work studies
the nonequilibrium generation of atomic nitrogen and hydrogen with
a focus on the kinetic role of vibrational energy transfer of hydrogen
molecules in plasma-aided ammonia synthesis. By combining two-photon
absorption laser-induced fluorescence measurements and plasma kinetic
modeling, we found that plasma not only generates ammonia but also
produces critical H, N, and NH radicals via both electron impact and
vibrational energy transfer excitations. The vibrational energy transfer
from the excited hydrogen H2(v = 1) to
higher vibrational levels H2(v = 2–3)
via the V–V exchange (H2(v)–H2(v)) and V–V′ exchange (N2(v)–H2(v)) significantly enhances the H and NH production and then promotes
the coupling between N and NH for ammonia synthesis both in the gas
phase and on the catalyst surface.