Cobalt-Promoted Ni/Al₂O₃ Catalyst for Efficient Ammonia Decomposition

We synthesize and characterize a series of γ-Al2O3-supported monometallic (9Ni/Al, 12Ni/Al, 12Co/Al) and bimetallic (12NixCo/Al, where x = 3 and 1) catalysts and evaluate their catalytic performance in the NH3 decomposition reaction. We also use the Temkin–Pyzhev rate law to determine the relevant parameters for the five catalysts. The bimetallic catalysts reveal a higher degree of reduction and smaller particle size than the monometallic catalysts, resulting in a larger effective alloy surface area. Peak shifts in the X-ray diffraction (XRD) patterns of the reduced bimetallic catalysts confirm the formation of a Ni–Co alloy, which is further corroborated by analysis of other characterization techniques. Kinetic studies reveal that NH3 decomposition follows the Temkin–Pyzhev rate law, and an increase in NH3 and/or H2 partial pressure decreases the conversion. The synergy between Ni and Co lowers the energy barrier for NH3 decomposition and reduces the inhibitory role of H2. Notably, the 12Ni3Co/Al catalyst exhibited the lowest apparent activation energy of 42.8 kJ/mol. This catalyst also shows the highest effective alloy surface area. Thus, the best catalytic performance of 12Ni3Co/Al is attributed to the improved alloy surface area and lowering of the activation energy. These findings underscore the importance of tuning the Ni/Co ratio to enhance the catalytic activity and stability through alloy formation and reduce the apparent activation energy. Furthermore, the successful application of tuning the Ni/Co ratio over a high-surface-area γ-Al2O3 support opens future improvements in this catalytic system.