Since the surface of the site can be partially occupied by dopant metal ion, the surface properties as well as well as the point zero charge (PZC) value may be altered by doping. These changes depend both on the type and amount of dopant metal. Litter and Navio reported that in the case of iron dopant, a concentration higher than 1% leads to Fe2O3, Fe2TiO5 or both insoluble phases formation on surface sites and catalyst is less active [14].