(220c) Pathways for NH3 Formation from N, H, and N2(v) in Plasma Catalysis
AIChE Annual Meeting
Monday, November 14, 2022 - 4:15pm to 4:36pm
NH3 synthesis by plasma catalysis at atmospheric pressure has been previously demonstrated , but pathways for NH3 formation involving plasma-derived radical (N, H) and vibrationally excited species (N2(v)) over catalytic surfaces have not been clearly identified. We measure densities of N, H, and N2(v) produced by an atmospheric pressure plasma jet using threshold ionization molecular beam mass spectrometric techniques [2-3] and correlate consumption of these species with NH3 formation in a packed bed of nonporous metal wools of Fe, Ni, and Ag. Results show that formation of NH3 and consumption of N, H, and N2(v) is faster over the catalytic surfaces than in the gas phase. N consumption correlates with NH3 formation when the ratio between the H density and N density at the inlet is greater than 3 (stoichiometric for NH3 formation) for all three metals. For Ni and Ag, N consumption is ~100% selective to NH3 formation. For Fe, selectivity to NH3 formation is dependent on the H2 density. When the ratio between H density and N density at the inlet is less than 1, N consumption does not correlate with NH3 formation for all three metals, indicating that NH3 formation is limited by H density at these conditions. N2(v) consumption exhibits no correlation with NH3 formation for any of the examined metals, indicating that surface-mediated vibrational relaxation of N2(v) is more significant than dissociative adsorption at these conditions. These correlations between NH3 formation and consumption of plasma-derived intermediates, preliminary spectroscopic studies probing identity of catalyst-bound surface species formed in N2/H2 plasma, and design and operation of a reactor that enables these measurements will be discussed.
 M. L. Carreon, J. Phys. D: Appl. Phys. 52 (2019) 483001
 J. Jiang et al., J. Phys. D: Appl. Phys. 55 (2022) 225206
 J. Jiang et al., in preparation.