LAUSR

Abstract For the first time, new Sm doped cerium oxynitrides with the formula Ce1-zSmzO2-xNy (z ≤ 0.5) are synthesized in order to maximize the concentration of anion vacancies. Single phase Sm-doped CeO2-xNy were confirmed by XRD, HRTEM and Rietveld refinement. These oxynitrides show a great promotion effect for the low-cost Fe catalyst for the ammonia synthesis. At 350 °C and 1 MPa, the activity of 80 wt% Fe- 20 wt% Ce1-zSmzO2xNy is one of the highest reported for non-Ru catalysts for the Haber-Bosch reaction. The apparent activation energy of the 80 wt% Fe- 20 wt% Ce1-zSmzO2xNy catalysts with z ≥ 0.3 is around 45 kJ/mol, which is in the lowest range among all reported ammonia synthesis catalysts. Introduction of nitrogen vacancies through doping may facilitate the mobility of nitrogen vacancies. This study demonstrates doped oxynitrides with a large concentration of anion vacancies, particularly nitrogen vacancies are excellent promoters/co-catalysts for ammonia synthesis.