A controlled atmosphere in situ X-ray diffraction study of the activation and performance of ammonia synthesis catalysts derived from CeRu2, CeCo2, and CeFe2

Abstract Highly active ammonia synthesis catalysts derived from cerium intermetallic alloy precursors CeRu 2 , CeCo 2 , and CeFe 2 have been studied by in situ powder X-ray diffraction (XRD) with concurrent analysis of catalytic activity. The reaction was investigated at pressures of up to 50 bar and at temperatures up to 550 °C. Precursor activation was carried out in pure hydrogen, N 2 /H 2 , and CO/H 2 under various regimes of temperature and pressure. It is found that the formation of active catalysts depends upon the presence of cerium hydride and transition metal crystallites in the ultimate material, although there is no correlation between XRD-derived metal areas and chemical rates. The corresponding transition metal/cerium dioxide catalysts have a much lower activity for ammonia synthesis. The special activity of the hydride-based catalysts may arise from an intimate interaction between the support phase and the ultradispersed transition metal particles.