Insights into Sustainable Nitrogen Fixation by Gas-phase Spectroscopic Measurements and Global Modeling of Reaction Intermediates in Humid Nitrogen Plasma

Ananthanarasimhan Jayanarasimhan, Robert Pierrard, Sean M. Peyres, Shurik Yatom, Davide Curreli, R. Mohan Sankaran

Research output: Contribution to journalArticlepeer-review

Abstract

There is growing interest in reacting molecular nitrogen and water to sustainably synthesize fixed forms of nitrogen such as ammonia. In particular, low-temperature plasmas can activate these relatively inert feedstocks at or near room temperature without a catalyst. However, because of the enhanced reactivity and nonequilibrium chemistry, a diverse range of products is formed, and the underlying reaction mechanisms are exceedingly complex. In this work, we studied a simplified reactor consisting of a gaseous plasma containing controlled mixtures of nitrogen gas and water vapor. Densities of key chemical species such as N, H, OH, NH, and NO were measured by emission and laser-based spectroscopy as a function of the relative humidity. A global model was constructed and the reaction network was validated by comparing calculated species densities with experiments. We discover that N, a key initial intermediate for ammonia, strongly decreases in the presence of water vapor, and as a result, ammonia formation becomes limited at high relative humidity. This decrease is surprisingly not because N itself reacts, but because one of its main sources, an excited molecular nitrogen state, is reacted away. In addition, oxidation pathways for nitrogen, which lead to NO and related products, are found to be favored over reduction pathways because the corresponding reverse reactions are less significant. Together, this understanding helps explain previously reported observations of selectivity toward nitrogen oxides over ammonia, particularly at higher relative humidities.

Original languageEnglish (US)
Pages (from-to)140-150
Number of pages11
JournalACS Sustainable Chemistry and Engineering
Volume13
Issue number1
DOIs
StatePublished - Jan 13 2025
Externally publishedYes

Keywords

  • ammonia
  • atmospheric-pressure plasma
  • laser-induced fluorescence
  • nitrogen fixation
  • plasma-liquid

ASJC Scopus subject areas

  • General Chemistry
  • Environmental Chemistry
  • General Chemical Engineering
  • Renewable Energy, Sustainability and the Environment

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