Exsolved Ru on BaCexOy Catalysts for Thermochemical Ammonia Synthesis

Abstract

Ammonia (NH3) is a carbon-free and hydrogen-rich (17.8 wt% H2) chemical that has the potential to revolutionize the energy sector. Compared with hydrogen (H2), NH3 can be easily liquefied, stored, and transported globally. However, the conventional thermocatalytic process to synthesize NH3 accounts for 2% of global energy consumption and 1.2% of CO2 emissions annually. To make the process further efficient, new catalysts must be developed to allow for NH3 synthesis in milder conditions with high thermal stability. To this end, we have developed ruthenium (Ru) supported on perovskite (BaCexOy) via a ball-milling-assisted exsolution method that allows for a more tunable morphology. Reactivity is compared with the catalyst prepared via the conventional impregnation technique. The as-synthesized catalysts are characterized by XRD, H2-TPR, TEM, XPS, and APT. The NH3 synthesis is carried out in a packed-bed tube reactor thermochemically. Using N2 instead of Ar as the carrier gas during exsolution can favour reactivity by increasing active sites and perhaps improving metal-support interaction. The impregnated sample shows higher reactivity than the exsolved catalyst; however, the long-term durability is slightly better using the exsolved catalyst. Finally, APT results interestingly show that the exsolved catalyst is more resistant to hydride formation and hydrogen poisoning, which is one of the main deactivation mechanisms for such metallic catalysts.