The catalytic reduction of CO2 to methane, called CO2 methanation or the Sabatier reaction, is a reversible and exothermic reaction. A mean field microkinetic model is developed for the Sabatier reaction on Ru catalyst at atmospheric pressure and validated with reactor simulations in this work. The mechanism comprised of elementary steps occurring on the catalyst surface is devised based on spectroscopic findings and DFT calculations reported in the literature. The initial parameter values are taken from DFT literature or computed using UBI-QEP. The model is fitted to limited experimental data points from only one source in the literature. The resulting model reliably predicts experimental data from multiple sources in the literature for CO2 methanation on Ru at various feed ratios in the temperature range of 250-490 degrees C as well as the equilibrium conversion of CO2. Microkinetic analyses under the relevant conditions revealed that the reaction proceeds via the CO2* -> CO* -> C* -> CHx* pathway on Ru catalyst.