The reactivity of CO2 with K atoms adsorbed on MgO powders

In this combined quantum chemical and EPR study we have investigated the formation of CO2- radicals by contact of CO2 molecules with a K precovered MgO surface. K atoms have been deposited on polycrystalline MgO samples, and then exposed to CO2. The typical EPR signal of the isolated K atoms disappears when the reaction with CO2 takes place and a new paramagnetic species attributed to CO2- is observed. DFT cluster model calculations show that there is a spontaneous electron transfer from the adsorbed K atom to the CO2 molecule, with formation of K+CO2- surface complexes. These species have the same electronic characteristics and spin distribution of gas-phase M+CO2- (M = Li, Na, K) molecules, but are stabilized by the presence of the ionic surface. The most stable MgO sites where the adsorption of CO2 occurs and the computed EPR properties are discussed.