Most reaction systems undergo a change of the reaction rate regime when different reaction conditions are present. Therefore, the reaction rate constant of the surface reaction, k S , is used as a proxy to investigate the reaction system from the surface reaction being rate limiting to quasi-equilibrated. Since the reaction network was constructed to be approximately equally fast on all reaction routes at an arbitrarily chosen reference state at T ref = 550 K, the resulting k S is chosen as a reference and denoted with the superscript ref as well (eq. ( )).