Abstract
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.