Boosted Activity of Cobalt Catalysts for Ammonia Synthesis with BaAl 2 O 4- 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, BaAl 2 O 4- x H y , that can significantly promote ammonia synthesis over Co (500 mmol g Co -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. BaAl 2 O 4- x H y with a stuffed tridymite structure has interstitial cage sites where anionic electrons are accommodated. The surface of BaAl 2 O 4- x H y with very low work functions (1.7-2.6 eV) can donate electrons strongly to Co, which largely facilitates N 2 reduction into ammonia with the aid of the lattice H - ions. The stuffed tridymite structure of BaAl 2 O 4- x H y with a three-dimensional AlO 4 -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.