The total concentration of surface reactive sites is set as 4.15×10 -3 mole•L -1 for the volume of the 10 -10 L surface compartment. Assuming 50% of the sites are Ti and 50% of the sites are Obr, then the initial concentrations of Ti and Obr are set as 2.075×10 -3 mole•L -1 for Model 1. Since each O 2-_Ti_Ti_O 2-cluster in Model 2 has four reactive sites, the initial concentration of it is 25% of surface reactive sites, which is 1.0375×10 -3 mole•L -1 .