For the experiments using bed configuration d) the total molar flow rate at the reactor outlet, 𝑛̇ , , was calculated based on the measured molar fraction, 𝑦 , and the constant molar flow rate, 𝑛̇ , , of the external standard He as given in Eq. . The molar flow rate of NH3 at the reactor outlet, 𝑛̇ , , was calculated based on the total molar flow rate and the measured molar fraction of NH3 in the gas phase (Eq. ( )).