Mass spectrometric analysis of the anionic products of interaction between palladium hydride anions, PdH-, and carbon dioxide, CO2, in a reaction cell shows an efficient generation of the PdHCO2- intermediate and isolated formate product. Multiple isomers of the PdHCO2- intermediates are identified by a synergy between negative ion photoelectron spectroscopy and quantum-chemical calculations. It is shown that a direct mechanism, in which the H atom in PdH- directly activates and hydrogenates CO2, leads to the formation of the formate product. An indirect mechanism, on the other hand, leads to a stable HPdCO2- structure, where CO2 is chemisorbed onto the Pd atom.