Bimetallic catalysts provide new routes toward sustainable ammonia synthesis, but the structural dynamics controlling their performance under real-world conditions remain poorly understood. Here, we combine in situ gas-cell and multimodal electron microscopy to disentangle the temperature-, pressure-, and chemistry-dependent restructuring of AuRu catalysts, revealing pathways accessible only at atmospheric pressure. As synthesized, AuRu nanocatalysts are polycrystalline face-centered-cubic alloys with Au/Ru intermixing that phase-segregate into Au- and Ru-rich domains with elevated temperature (>450 {\deg}C). Increased pressure (~1 atm in 3:1, hydrogen:nitrogen) unlocks pronounced faceting and internal nanovoid formation, which systematic gas-chemistry variation identifies as hydrogen-driven. Density functional theory-based interatomic potentials show that hydrogen can amplify Au/Ru diffusion asymmetry, promoting nanovoid formation via a gas-mediated Kirkendall mechanism. Together, these results bridge the pressure gap between traditional in situ electron microscopy and benchtop ammonia reactors, enabling resolution of distinct restructuring stimuli in multicomponent systems.
@article{arxiv.2602.00433,
title = {Ammonia Catalyst Evolution Under Reactor Conditions Revealed by Environmental and Multimodal Electron Microscopy},
author = {Amy S. McKeown-Green and Parivash Moradifar and Zisheng Zhang and Cedric Lim and Andrew Barnum and Lin Yuan and Robert Sinclair and Frank Abild-Pedersen and Colin Ophus and Jennifer A. Dionne},
journal= {arXiv preprint arXiv:2602.00433},
year = {2026}
}
Comments
{\dag} These authors contributed equally to this work. This work was conducted at Stanford University