Boosted Activity of Cobalt Catalysts for Ammonia Synthesis with BaAlOH 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, BaAlOH, that can significantly promote ammonia synthesis over Co (500 mmol g h at 340 °C and 0.90 MPa) with a very low activation energy (49.6 kJ mol; 260-360 °C), which outperforms the state-of-the-art Co-based catalysts, being comparable to the latest Ru catalyst at 300 °C. BaAlOH with a stuffed tridymite structure has interstitial cage sites where anionic electrons are accommodated. The surface of BaAlOH with very low work functions (1.7-2.6 eV) can donate electrons strongly to Co, which largely facilitates N reduction into ammonia with the aid of the lattice H ions. The stuffed tridymite structure of BaAlOH with a three-dimensional AlO-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.