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.
Highlights
As one of the most important inorganic chemicals, ammonia is responsible for supporting approximately 27 % of global population [1, 2]
New single phase Sm-doped cerium oxynitrides have been synthesized for the first time
The apparent activity energy of our Fe-Ce1zSmzO2-xNy catalysts with z ≥ 0.3 is in the range of 45 kJ/mol, among the lowest Ea for all reported ammonia synthesis catalysts [5,7,27]
Summary
As one of the most important inorganic chemicals, ammonia is responsible for supporting approximately 27 % of global population [1, 2]. The Haber-Bosch process for ammonia synthesis is regarded as one of the greatest inventions of the last century [1]. A great deal of effort has been made to develop new ammonia synthesis catalysts to allow the operation of the Haber-Bosch process at reduced temperature and pressure. Intensive investigations have been carried on Ru-based catalysts promoted through a variety of different support materials Ru/HT-C12A7:e− [3], Ru/ Ba-Ca(NH2)2 [4], Ru/BaTiO3-xHx [5], Ru/TiH2, Ru/BaTiO2.5H0.5 [6] and Ru/BaCeO3-xNyHz [7]. The promotional effects of applied electric fields to ammonia synthesis have been re ported [12]. The use of single atom catalysts for electrochemical syn thesis of ammonia has been investigated through density functional theory calculations [13]. Due to the high cost of Ru, large scale appli cation is limited with around ten ammonia synthesis plants using
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