Theory meets experiment in ammonia decomposition on Li14Cr2N8O: From order to disorder under reaction conditions

Abstract

Heterogeneous catalysts have long been considered rigid structures hosting localized active sites, but growing evidence from both experiments and simulations is revealing a more dynamic picture in which the entire catalyst evolves under reaction conditions. In this study, we explore such behavior in Li14Cr2N8O, a lithium chromium nitride oxide recently proposed as a candidate for ammonia decomposition. Using machine learning-accelerated molecular dynamics, combined with in situ x-ray diffraction and catalytic activity measurements, we show that the pristine material undergoes significant structural transformation upon exposure to ammonia at elevated temperature. Surface disorder, lithium mobility, and the progressive formation of amides and imides give rise to a reactive interface, where chromium centers mediate key redox processes. These interfacial fluctuations create the conditions necessary for key steps in ammonia decomposition, including N–N coupling, hydride formation, and hydrogen release. Our findings highlight the importance of a global, dynamic view of heterogeneous catalysts under operando conditions, where activity arises not from predefined sites but from the evolving nature of the catalyst.