Accessing and Stabilizing Metastable States by Coupling Plasma and Surface Chemistry

在化学系化学催化项目的支持下，圣母大学的Casey O‘Brien和William Schneider正在合作(1)阐明大气压等离子体与固体表面耦合以获取和稳定亚稳态氮物种的机制，(2)探索利用这些亚稳态来驱动新反应的潜力。大气压等离子体与多相催化剂(等离子体催化)的集成最近得到了相当大的关注，因为它有可能实现使用传统热催化难以或不可能实现的转化，以及在以可再生电力为动力的模块单元中。实现这一潜力将导致更节能和环境可持续的化学过程。氮的活化尤其引起了等离子体催化领域的极大兴趣，因为等离子体能够激活强的二氮三键。奥布莱恩实验室的初步工作表明，与等离子体催化相关的吸附氮物种的类型可能比之前认为的更丰富。这个项目的重点是利用奥布莱恩实验室开发的光谱技术和施耐德实验室的计算方法来澄清等离子体产生的氮物种的性质和反应性。以理论为基础的光谱方法和概念验证的催化实例将广泛影响催化科学和技术。这项研究还将通过对研究生进行实验和计算研究、交流、科学严谨性和研究的伦理行为方面的培训来加强高级科学教育。这项建议探索了一种策略，以获取、稳定和浓缩通过耦合等离子体和表面化学在热上无法获得的亚稳态中间体，并利用这些亚稳态物种进行新的表面反应。凯西·奥布莱恩和威廉·施奈德将在氮气活化的背景下合作探索这些概念。奥布莱恩实验室最近未发表的工作表明，亚稳态叠氮化合物，或N3，在暴露在氮等离子体中时，由金属表面稳定。虽然初步实验表明，LTP(低温等离子体)暴露的金属表面可以容纳亚稳态的N3物种，但仍有许多基础科学问题尚未回答：(I)这种物种的身份(N2、N3或其他)和性质是什么？(Ii)这种物质是首先在等离子体中形成，然后被金属表面捕获，还是表面促进了它的形成？(Iii)这些表面吸附物种对其他反应物的反应性如何？这个项目将解决这些基础科学问题，以开发战略，一般利用亚稳定物种，特别是叠氮化物，以推动仅靠传统的热催化或等离子体无法实现的化学转化。为此，该项目结合了实验和计算方法，以阐明大气压等离子体与固体表面耦合以获取和稳定亚稳态N3物种的机制，并探索利用这些亚稳态来驱动新反应的可能性。这项工作利用了在O‘Brien开发的最先进的原位光谱技术，以及预测表面组成、结构、产品和反应性之间关系的密度泛函理论计算，为理解和指导实验提供了一个理论框架。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

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.