Turning properties of Ni/Al2O3 catalyst to improve catalytic ammonia decomposition for green hydrogen production: pH does matter!
Quoc Cuong, Youngmin Kim, Geo Jong Kim, Younghwan Im, Thien An Le, Gye Hong Kim, Kyoung Chul Ko, Ho‐Jeong Chae
Abstract
• Physicochemical properties of Ni/Al 2 O 3 catalysts are engineered with the CADH method. • Optimal pH conditions are suggested to obtain proper catalysts for NH 3 decomposition. • Surface metallic Ni is the most important factor in determining the catalytic activity of the catalyst. • The good catalytic performance is due to the synergy of active Ni, porosity, particle size, and catalyst basicity. • The Ni/Al 2 O 3 catalyst maintained excellent activity and stability at 600 °C and WHSV 54000 mL/g cat. /h for 200 hours. In this study, the influence of solution pH (6.0–12.5) of the cation–anion double hydrolysis (CADH) method in the formation of Ni/Al 2 O 3 catalyst and its catalytic performance for green hydrogen production from NH 3 decomposition was studied for the first time. The physicochemical properties of the prepared catalysts were systematically characterized by various analysis techniques. The results indicated that pH conditions significantly influenced both the structural properties and catalytic activity of the derived Ni/Al 2 O 3 catalysts. The better catalytic activity for NH 3 decomposition over catalysts prepared under high pH conditions (pH ≥ 10.0) is mainly due to the appropriate synergic effect of the interaction between Ni and Al 2 O 3 support, large active Ni surface area, and suitable porosity, particle size, and basicity of the catalyst. The correlation analysis and density functional theory (DFT) calculations confirm that the percentage of surface metallic Ni plays a crucial role in controlling the catalytic activity of Ni/Al 2 O 3 catalysts. The 40Ni/Al 2 O 3 catalyst (Ni = 40 wt%) could achieve over 94.5% NH 3 conversion under the harsh reaction conditions of 600 °C and NH 3 WHSV of 54000 mL/g cat. /h, and that stably maintained for 200 h without any obvious deactivation. Overall, our work not only highlights the critical role of pH conditions in the CADH solution for cost-effective Ni/Al 2 O 3 catalyst preparation but also proposes a promising strategy for developing a highly active, stable, and Ru-free catalyst for practical hydrogen production via NH 3 decomposition.