Ambient-Pressure Ammonia Thermocatalyst Prepared by Exsolution of Cu-Ru-Fe Heterostructures

Ammonia synthesis is typically done by the Haber-Bosch process and is critical for sustainable agriculture. It additionally is gaining significant interest in the energy sector as a chemical hydrogen carrier. The Haber-Bosch process is an energy-intensive method for making ammonia; therefore, there is great interest in developing catalysts for the thermochemical production of ammonia at comparatively lower pressures and temperatures. This effort has been blocked by a lack of active catalysts, which can simultaneously activate nitrogen bond scission, relieve the effects of hydrogen poisoning, and maintain nanoscale stability for extended periods of time. Here, we report the exsolution of heterogeneously structured trimetallic Ru-Cu-Fe nanoparticles from lanthanum ferrate backbones. By exploiting the immiscibility regions in the Ru-Cu-Fe phase diagram, nanoscale catalytic heterostructures from these three metals were formed and found to catalyze thermochemical ammonia synthesis at atmospheric pressure (0.1 MPa) at 7.54 mmol/g_cat/h. Copper, which is not active for ammonia synthesis, was shown to be a promoter by limiting the growth of Ru nanoparticles during exsolution to 2 nm owing to the immiscibility between Cu and Ru.