Economic limitation of recent heterogeneous catalysts for ammonia synthesis

The economic performance of newly developed catalysts for ammonia synthesis, Ru/Ca(NH₂)₂ and Ru/Pr₂O₃, are evaluated by process simulation using Aspen Plus©. The results show that the high activity of the new catalysts reduces the electricity cost for pressurizing reactant gases; however, the electricity for lowering the temperature in ammonia separation through liquefaction is significant due to the mitigated pressure and almost compensates for the decreased cost. The results show an economic limitation to current research trends that develop a catalyst for ammonia synthesis under low pressure. It is noted that catalyst costs are high due to expensive ruthenium; thus, the lifetime of catalysts significantly influences the total cost. With the assumption of a long lifetime of catalysts, the new catalysts are advantageous when the electricity cost is high, the characteristics of the case in which renewable energy is employed. As the future direction of the catalyst development, recycling or extending the lifetime of the catalysts and replacing Ru with cheap metal will be crucial from the economic viewpoint. Moreover, effective methods for ammonia collection, such as adsorbents, should be focused on reducing the electricity of ammonia liquefaction in cooling separation and giving a vital meaning to the condition mitigated by the newly developed catalysts.