Accessing and Stabilizing Metastable States by Coupling Plasma and Surface Chemistry

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With support from the Chemical Catalysis program in the Division of Chemistry, Casey O’Brien and William Schneider of the University of Notre Dame are working collaboratively (1) to clarify the mechanisms by which atmospheric pressure plasmas couple with solid surfaces to access and stabilize metastable nitrogen species, and (2) to explore the potential to exploit these metastable states to drive novel reactions. The integration of atmospheric pressure plasmas with heterogeneous catalysts (plasma catalysis) has recently gained considerable attention because of its potential to carry out transformations that are difficult or impossible using conventional thermal catalysis, and in modular units powered by renewable electricity. Realization of this potential would lead to more energy-efficient and environmentally sustainable chemical processes. Nitrogen activation in particular has attracted substantial interest in the plasma catalysis community because of the ability of plasma to activate the strong dinitrogen triple bond. Preliminary work in the O’Brien lab suggests that the types of adsorbed nitrogen species relevant to plasma catalysis may be richer than previously thought. This project focuses on clarifying the nature and reactivity of plasma-generated nitrogen species using spectroscopic techniques developed in the O’Brien lab and computational approaches in the Schneider lab. The theory-informed spectroscopic approach and proof-of-concept catalytic examples will broadly impact both catalysis science and technology. This research will also enhance advanced scientific education through training of graduate students in experimental and computational research, communication, scientific rigor, and the ethical conduct of research.This proposal explores a strategy to access, stabilize, and concentrate metastable intermediates that are thermally inaccessible by coupling plasma and surface chemistry, and to exploit these metastable species for novel surface reactions. Casey O’Brien and William Schneider will collaboratively explore these concepts in the context of nitrogen activation. Recent unpublished work in the O’Brien lab suggests that metastable azides, or N3, are stabilized by metal surfaces during exposure to N2 plasmas. While preliminary experiments indicate that LTP(low temperature plasma)-exposed metal surfaces can accommodate metastable N3 species, there are many fundamental science questions that remain unanswered: (i) What is the identity (N2, N3, or other) and nature of this species? (ii) Is this species formed in the plasma first and subsequently trapped by the metal surface, or does the surface facilitate its formation? (iii) How reactive are these surface-adsorbed species towards other reactants? This project will address these fundamental science questions to develop strategies to exploit metastable species generally, and azides specifically, to drive chemical transformations that cannot be achieved by conventional thermal catalysis or plasma alone. To this end, this project integrates experimental and computational approaches to clarify the mechanisms by which atmospheric pressure plasmas couple with solid surfaces to access and stabilize metastable N3 species and explore the potential to exploit these metastable states to drive novel reactions. The work leverages state-of-the-art in-situ spectroscopy techniques developed in the O’Brien, and density functional theory calculations that predict the relationship between surface composition, structure, products, and reactivity, providing a theoretical framework for understanding and guiding experiments.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.