A kinetic model for methanal synthesis and the deactivation of catalyst has been proposed. This model is a Langmuir-Hinshelwood-Hougen-Watson type, which has been obtained from an active-site balance and describes the dynamic behavior of the active sites of a deactivated Cu-ZnO commercial catalyst. The parameters of the proposed kinetic model have been determined by fitting the experimentally obtained mole fractions of all components for a wide variety of conditions to the transient mass conservation equation in a gradientless differential reactor. By using this model, the rates of reactions on deactivated catalyst have been obtained as a function of time. The results show that catalyst deactivation depends on the composition of CO2 and water Also it is found that by enriching synthesis gas with CO, through a dynamic feeding strategy, the conversion of the reactor will be increased.