Exsolution of Fe, Co, and Ni supported catalysts from LaBO3 (B = Fe, Co, Ni) perovskites for ammonia synthesis†

Abstract

The traditional impregnation method for preparing supported catalysts often faces challenges such as particle agglomeration and weak support–metal interactions. This study focuses on utilizing the exsolution method to prepare Fe, Co, and Ni supported catalysts from ABO₃-type perovskites, aiming to overcome these challenges. Experimental results show that LaBO₃ perovskites with different B site metals (B = Fe, Co, Ni) exhibit different metal exsolution kinetics in the ammonia synthesis reaction. LaNiO₃ demonstrates an initial activity of 782.2 μmol g⁻¹ h⁻¹ within the first 2 hours of the reaction, maintaining stability beyond 80 hours. In contrast, LaFeO₃ and LaCoO₃ exhibit prolonged initiation periods for the metal exsolution process, reaching activities of 7873.8 μmol g⁻¹ h⁻¹ and 8046.7 μmol g⁻¹ h⁻¹, respectively, after approximately 80 hours. The degree of B-site metal exsolution was investigated using X-ray absorption fine structure (XAFS) and Rietveld refinement of XRD data, revealing exsolution rates of 72.03%, 69.3%, and 86.3% for Fe, Co, and Ni, respectively, after 80 hours of reaction. This study not only introduces the exsolution method for ammonia synthesis but also empirically validates several computational predictions, thereby supporting both theoretical and practical research.