Alumina-supported bimetallic catalysts with ruthenium and CoNi for enhanced ammonia decomposition

Ammonia, which comprises 17.6 wt% hydrogen, has potential as a hydrogen storage medium. Catalysts made from cost-effective transition metals such as cobalt (Co) and nickel (Ni), supported on Al2O3, are favored as substitutes for ruthenium in the process of ammonia decomposition for hydrogen generation at the point of use. A series of catalysts with the composition x%CoNi/Al2O3 (where x = 5, 10, 20, 30, and 50 wt%; and Co : Ni = 1 : 1) were synthesized using the dry mixing technique, and their activity was evaluated against analogous catalysts containing a trace amount of Ru (0.5%Ru/x%CoNi/Al2O3). The catalysts were analyzed through SEM, EDS, mapping, TEM, BET, and TPR techniques. However, they show highly agglomerated spherical particles, a trend seen from Ni/Al2O3 to CoNi/Al2O3, potentially affecting catalyst performance. The 5%CoNi bimetallic catalyst supported on Al2O3 (5%CoNi/Al2O3) demonstrated superior reactivity for ammonia decomposition (95%) at 674 degrees C, in contrast to its monometallic counterparts, Co/Al2O3 (691 degrees C) and Ni/Al2O3 (677 degrees C), at a gas hourly space velocity (GHSV) of 20 400 mL g(cat)(-1) h(-1) based on total feed. Increasing the bimetallic content to 50% on Al2O3 sustained 95% ammonia decomposition at 500 degrees C, with a minor enhancement (498 degrees C) noted for 0.5%Ru-50%CoNi/Al2O3. The improved low-temperature ammonia cracking efficiency of the CoNi bimetallic system results from the synergistic interaction between Co and Ni, which promotes effective engagement with NH2- species and establishes a balanced basic character of the bimetal on the Al2O3 support. The established reactivity trend is Co < Ni < CoNi approximate to 0.5%Ru/CoNi on Al2O3 under identical reaction conditions. Both 50%CoNi/Al2O3 and 0.5%Ru/50%CoNi/Al2O3 maintained their decomposition activity for 65 hours without any deterioration.