The reaction mechanism of CO2 on PuO2 and α-Pu2O3 surfaces

Abstract

Within DFT+U-D3 scheme, we systematically investigate the major steps of CO₂ reaction on Pu-oxide surfaces, including CO₂ adsorption, dissociation and CO releasing. On intact Pu-oxide surfaces, the chemical adsorption of CO₂ needs to be activated, while the dissociation is unlikely to happen. Interestingly, both steps can be notably promoted when Pu-oxide surfaces are covered with *H or *OH from dissociated H₂O, which is fully consistent with the experimental findings that moisture can boosting CO₂ adsorption on PuO₂ surface. Specifically, the polarons induced by *H or *OH show strong couplings with CO₂, which first activate the barrier-less chemisorption of CO₂ and then promote the dissociation of CO₂ by weaken the CO bond. Furthermore, we find that the oxidation state of Pu in its oxides determines the tendency of CO releasing step, which is endothermic and exothermic on PuO₂ and α-Pu₂O₃ surfaces, respectively. Thus, we predict the reaction of CO₂ on Pu-oxide surface is not impossible, especially when PuO₂ is reducing to α-Pu₂O₃ during the long-term storage. This work reveals the reaction mechanism and possible reactive pathway of CO₂ on Pu-oxides, which provides a significant step forward in the understanding of the surface reactions of actinide oxides.