Role of the active metal (Fe, Co and Ni) on the activity of Nd2O3-supported catalysts for ammonia synthesis

Nd2O3-supported Fe, Co, and Ni monometallic catalysts were synthesised and used in the ammonia synthesis reaction. The effect of active metal on the physicochemical and catalytic properties was investigated using, e.g., TPR, TPD, XRD, and STEM. The results showed that the kind of active metal used is the factor determining the catalytic activity in ammonia synthesis. The highest ammonia formation rate was exhibited by Co/Nd2O3, whereas the highest intrinsic reaction rate (reflected as the TOF value) was shown by Fe/Nd2O3. Ni/Nd2O3 showed almost no activity in ammonia synthesis. The high ammonia formation rate observed for Co/Nd2O3 was attributable to the well-distributed Co nanoparticles (NPs) on the Nd2O3 support. The Co NPs were less prone to sintering than Fe NPs under reaction conditions. Thus, although showing lower TOF than Fe NPs, the better distribution of Co NPs resulted in an improved ammonia formation rate. These findings highlight the importance of rational catalyst design for improving ammonia synthesis efficiency.