The catalyst activity was measured in a stainless-steel tube reactor, using 0.05 g of Ru and 0.01 g of Ru+K, placed on quartz wool. All feed gases were high purity (99.9999%), N2, H2, and Ar. The gases were purified to remove oxygen and water before being fed to the catalyst. Before the reaction, all samples were subjected to N2 + 3H2 at 0.1 MPa and raised to the target temperature at 200 °C h -1 . The app Ea were derived based on the Arrhenius equation (see eq. 19) at 380~460°C. The reaction order was obtained based on 𝑟 = 𝑘𝑃 𝑁 2 𝛼 𝑃 𝐻 2 𝛽 𝑃 𝑁𝐻 3 𝛾 (see eq. 17). The gas flow rates (N2, H2, Ar ml min -1 ) were as follows: (20, 60, 0), (15, 45, 0), (10, 30, 0), and (5,15, 0) for NH3 order, (5, 54, 1), , , , and for H2 order, , , , , and (6, 24, 30) for N2 order measurement. The measured reaction rates under these conditions which were used for the reaction order measurements were also used for fitting to the modeled reaction rates (see section 3.1). All ammonia syntheses were performed at 0.1 MPa. Synthesized ammonia was trapped in a 5 mM H2SO4 solution, and the concentration of NH4 + in the solution was measured by ion chromatography (Eco IC, Metrohm). NH3 effluents for all reactions were below 30% of equilibrium of NH3 reaction.