To investigate the effect of coverage on app Ea, app Ea was measured by varying the reactant gas flow rate. At a total flow rate of 80 cm 3 min-1 , the app Ea of Ru and Ru+K were 130.6 and 115.9 kJ mol -1 , respectively, but at a total flow rate of 20 cm 3 min-1 they decreased to 107.9 and 92.2 kJ mol -1 , respectively (Figure ). Therefore, the lower the gas flow rate, the smaller the app Ea.