Co Nanoparticle Catalysts Encapsulated by BaO-La 2 O 3 Nanofractions for Efficient Ammonia Synthesis Under Mild Reaction Conditions.

Ruthenium catalysts may allow for realization of renewable energy-based ammonia synthesis processes using mild reaction conditions (<400 °C, <10 MPa). However, ruthenium is relatively rare and therefore expensive. Here, we report a Co nanoparticle catalyst loaded on a basic Ba/La 2 O 3 support and prereduced at 700 °C (Co/Ba/La 2 O 3 _700red) that showed higher ammonia synthesis activity at 350 °C and 1.0-3.0 MPa than two benchmark Ru catalysts, Cs + /Ru/MgO and Ru/CeO 2 . The synthesis rate of the catalyst at 350 °C and 1.0 MPa (19.3 mmol h -1 g -1 ) was 8.0 times that of Co/Ba/La 2 O 3 _500red and 6.9 times that of Co/La 2 O 3 _700red. The catalyst showed ammonia synthesis activity at temperatures down to 200 °C. Reduction at the high temperature induced the formation of BaO-La 2 O 3 nanofractions around the Co nanoparticles by decomposition of BaCO 3 , which increased turnover frequency, inhibited the sintering of Co nanoparticles, and suppressed ammonia poisoning. These strategies may also be applicable to other non-noble metal catalysts, such as nickel.