The interaction of CO2 with K-promoted Mo2C/Mo(100) has been studied with high-resolution electron energy loss spectroscopy, work function measurements and temperature-programmed desorption. Pre-adsorbed potassium dramatically affects the adsorption behavior of CO2 on the Mo2C/Mo(100) surface. It increases the rate of adsorption, the binding energy of CO2 and it induces the dissociation of CO2 through the formation of negatively charged CO2. Potassium adatoms also promote the dissociation of adsorbed CO over Mo2C.