In an attempt to better understand the decisive role of Ti promoter, the apparent activation energies (Ea) for CO2 methanation are also calculated. They are based on the reaction rates in the temperature range from 200 °C to 300 °C as presented in the Arrhenius plot (Fig. (b)) and then plotted as a function of Ti loading in Fig. ). The obtained Ea values are between 53 and 73 kJ/mol, falling within the range typically reported for Ru-based catalysts . The apparent activation energies for the catalysts with 0% and 4% are about the same but decrease significantly as the Ti loading increases to 8% and 12%, then the value remains similar for 16%. The drop in the apparent activation energy suggests that the nature of the active sites is modified. This modification could affect the CO adsorption energy or even the reaction mechanism (vide infra in the section 3.4.). A change in the reaction mechanism is however rather unlikely, considering a single linear compensation line in the Constable plot in Fig. (In (A) vs. Ea, where A represents the preexponential factor in the Arrhenius equation derived from plots in Fig. )) .