The reactivity of CO2 with K atoms adsorbed on MgO powders

Abstract

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.