The term "𝑃 𝑐𝑎𝑡 (𝑑𝑢𝑟𝑎𝑡𝑖𝑜𝑛, 𝑡) × 𝐵𝐷 × 𝑉 𝑟𝑒𝑎𝑐𝑡𝑜𝑟 " calculates the cost of catalyst used in the plant. The catalyst cost is generally estimated by weight and material cost per weight without the economy of scale. 𝑃 𝑐𝑎𝑡 (𝑑𝑢𝑟𝑎𝑡𝑖𝑜𝑛, 𝑡) is the catalyst price [USD/kg] and is determined for each year by Eq. ( ). 𝑃 𝑐𝑎𝑡 (𝑑𝑢𝑟𝑎𝑡𝑖𝑜𝑛, 𝑡) depends on the catalyst durability period (duration), and the cost is incurred when the catalyst is replaced. The influence of duration was evaluated by changing it from 1 to 10 years. BD is the bulk density of the catalyst used [g/cm 3 ] and Vreactor is the volume of the reactor used in the ammonia synthesis loop [m 3 ]. The catalyst prices, bulk densities, and porosities of the four catalysts used in this study are summarized in the Table . BD of KM1R (iron-based catalyst) and Ru/C were obtained from literature values, while the bulk densities of the recent catalysts (Ru/Pr2O3 and Ru/Ba-Ca(NH2)2)