Here, 𝑛̇ , represents the accelerated (or decelerated) response of compound 𝑖 with respect to the expected response according to the RTD and steady-state reaction kinetics. The main reasons for these deviations are interactions of the gaseous compound with the catalyst surface through ad-/desorption and surface reactions. With these transient molar flow rates, the component and elemental balance over the catalyst surface can be drawn, according to eqs. (6) (component) and ( ) (elemental):