AUTHOR=Wang Gaoxue , Batista Enrique R. , Yang Ping 

TITLE=N2-to-NH3 conversion by excess electrons trapped in point vacancies on 5f-element dioxide surfaces

JOURNAL=Frontiers in Chemistry

VOLUME=10

YEAR=2023

URL=https://www.frontiersin.org/journals/chemistry/articles/10.3389/fchem.2022.1051496

DOI=10.3389/fchem.2022.1051496

ISSN=2296-2646

ABSTRACT=<p>Ammonia (NH<sub>3</sub>) is one of the basic chemicals in artificial fertilizers and a promising carbon-free energy storage carrier. Its industrial synthesis is typically realized <italic>via</italic> the Haber−Bosch process using traditional iron-based catalysts. Developing advanced catalysts that can reduce the N<sub>2</sub> activation barrier and make NH<sub>3</sub> synthesis more efficient is a long-term goal in the field. Most heterogeneous catalysts for N<sub>2</sub>-to-NH<sub>3</sub> conversion are multicomponent systems with singly dispersed metal clusters on supporting materials to activate N<sub>2</sub> and H<sub>2</sub> molecules. Herein, we report single-component heterogeneous catalysts based on 5<italic>f</italic> actinide dioxide surfaces (ThO<sub>2</sub> and UO<sub>2</sub>) with oxygen vacancies for N<sub>2</sub>-to-NH<sub>3</sub> conversion. The reaction cycle we propose is enabled by a dual-site mechanism, where N<sub>2</sub> and H<sub>2</sub> can be activated at different vacancy sites on the same surface; NH<sub>3</sub> is subsequently formed by H<sup>−</sup> migration on the surface <italic>via</italic> associative pathways. Oxygen vacancies recover to their initial states after the release of two molecules of NH<sub>3</sub>, making it possible for the catalytic cycle to continue. Our work demonstrates the catalytic activities of oxygen vacancies on 5<italic>f</italic> actinide dioxide surfaces for N<sub>2</sub> activation, which may inspire the search for highly efficient, single-component catalysts that are easy to synthesize and control for NH<sub>3</sub> conversion.</p>