Step 2. Simulate the reaction using the current parameters in the repeated steps. The instantaneous reaction rate is derived by Eq. (1). The reaction proceeds according to the obtained reaction rate, and the isothermal and isobaric gas ratio of N2, H2, and NH3 is updated. One reaction step is assumed to be 1 msec. The reaction rate is recalculated by Eq. ( ) based on the updated gas composition. These are repeated until the total reaction time reaches the estimated residence time. The obtained ammonia concentration 𝐶 𝑁𝐻 3 [%] are compared with the experimental results.