Exploring Ru/CeO2 catalysts supported by ceria MOF-derived materials for improved ammonia synthesis and decomposition efficiency at mild conditions

Ammonia (NH3) plays a crucial role in global agriculture and the development of emerging hydrogen energy systems. However, developing highly efficient catalysts for NH3 synthesis under mild conditions remains a significant challenge due to kinetic and thermodynamic limitations. In this study, we report a Ru/CeO2 catalyst synthesized using a metal-organic framework (MOF)-derived strategy, which allows for simultaneous control over the morphology of CeO2 (nanorod shaped), the concentration of oxygen vacancies, and the dispersion of Ru. The optimized catalyst containing 0.5 wt.% Ru delivered an impressive NH3 synthesis rate of 4,665 μmol gcat-1 h-1 at 400 °C and 50 bar, while maintaining excellent stability for 45 h of continuous operation. In addition, it achieved a high NH3 conversion of 93% at 550 °C and 1 bar. Notably, its performance surpasses that of conventional Ru-based catalysts by nearly twofold when normalized to the Ru loading. Comprehensive characterizations, including in situ X-ray photoelectron spectroscopy, Raman spectroscopy, and scanning transmission electron microscopy, reveal the formation of abundant oxygen vacancies, sub-nanometer Ru clusters, and strong metal support interaction. These factors collectively enhance the activation of N2 and its hydrogenation. This study highlights the effectiveness of MOF-templated defect engineering in developing robust Ru/CeO2 catalysts and provides valuable insights into structure-performance relationships. The dual functionality in both NH3 synthesis and decomposition highlights the potential of this approach for energy-efficient NH3-based energy systems.