The effects of K2O cluster size and exposed facets on CO2 binding energetics

The increasing concentration of atmospheric CO2 is a major contributor to global increase in temperature, which motivates the development of efficient materials for car- bon capture. Alkali metal oxides, due to their intrinsic surface basicity and low cost, have emerged as promising candidates for CO2 adsorption. However, the exception- ally strong binding of CO2 to bulk alkali oxides hinders its controlled desorption as a concentrated stream for sequestration. In this study, we investigate the interaction of CO2 with potassium oxide K2O clusters of varying sizes ranging from monomoer to tetramer through density functional theory modeling to understand the role of clus- ter size on adsorption strength. The resulting models show that CO2 adsorption is weaker on exceedingly small K2O clusters than on bulk K2O. Empirical thermogravi- metric and differential scanning calorimetry measurements similarly showed stronger COadsorptionon larger K2O clusters. The cooperative electronic and geometric effects that cause strong CO2 binding on continuous surfaces may be beneficially disrupted on highly constrained active surfaces, allowing controlled desorption of captured emis- sions with lower process energy input. K2O clusters on γ-alumina were evaluated to understand the effect of metal oxide supports used in practice to achieve high active site dispersion. Incorporation of a γ-alumina support significantly strengthened CO2 binding energies, which highlights the significant influence of underlying supports on the adsorption chemistry of highly dispersed active clusters.