The hydrogenation of CO2 into value-added complexes is of great importance for both environmental and economic issues. Metal hydrides are good 2 models for the active sites to explore the nature of CO2 hydrogenation; however, the fundamental insights into C-H bond formation are still far from clear because of the ce 10. complexity of real-life catalysts. Herein, gas-phase reactions of the Fe2Hn- (n = 0-3) anions with CO2 were investigated using mass spectrometry and quantum chemical calculations. The experimental results showed that the reduction of CO2 into CO dominates all of these reactions, whereas Fe2H- and Fe2H2- can induce the hydrogenation of CO2 effectively to give rise to products Fe(HCO2)(-) and HFe(HCO2)(-), respectively. The mechanistic aspects and the reactivity of Fe2H2- with an increased number of H atoms in CO2 hydrogenation were rationalized by theoretical calculations.