Boosted Activity of Cobalt Catalysts for Ammonia Synthesis with BaAl2O4–x H y Electrides

Electrides are promising support materials to promote transition metal catalysts for ammonia synthesis due to their strong electron-donating ability. Cobalt (Co) is an alternative non-noble metal catalyst to ruthenium in ammonia synthesis; however, it is difficult to achieve acceptable activity at low temperatures due to the weak Co–N interaction. Here, we report a novel oxyhydride electride, BaAl2O4–x H y , that can significantly promote ammonia synthesis over Co (500 mmol gCo –1 h–1 at 340 °C and 0.90 MPa) with a very low activation energy (49.6 kJ mol–1; 260–360 °C), which outperforms the state-of-the-art Co-based catalysts, being comparable to the latest Ru catalyst at 300 °C. BaAl2O4–x H y with a stuffed tridymite structure has interstitial cage sites where anionic electrons are accommodated. The surface of BaAl2O4–x H y with very low work functions (1.7–2.6 eV) can donate electrons strongly to Co, which largely facilitates N2 reduction into ammonia with the aid of the lattice H– ions. The stuffed tridymite structure of BaAl2O4–x H y with a three-dimensional AlO4-based tetrahedral framework has great chemical stability and protects the accommodated electrons and H– ions from oxidation, leading to robustness toward the ambient atmosphere and good reusability, which is a significant advantage over the reported hydride-based catalysts.