Adsorption, activation, and conversion of carbon dioxide on small copper-tin nanoclusters

Carbon dioxide (CO₂) conversion to value-added chemicals is an attractive solution to reduce globally accelerating CO₂ emissions. Among the non-precious and abundant metals tested so far, copper (Cu) is one of the best electrocatalysts to convert CO₂ into more than thirty different hydrocarbons and alcohols. However, the selectivity for desired products is often too low. We present a computational investigation of the effects of nanostructuring, doping, and support on the activity and selectivity of Cu-Sn catalysts. Density functional theory calculations were conducted to explore the possibility of using small Cu-Sn clusters, Cu_4-Sn (n = 0-4), isolated or supported on graphene and γ-Al₂O₃, to activate CO₂ and convert it to carbon monoxide (CO) and formic acid (HCOOH). First, a detailed analysis of the structure, stability, and electronic properties of Cu_4-Sn clusters and their ability to absorb and activate CO₂ was considered. Then, the kinetics of the gas phase CO₂ direct dissociation on Cu_4-Sn to generate CO was determined. Finally, the mechanism of electrocatalytic CO₂ reduction to CO and HCOOH on Cu_4-Sn, Cu_4-Sn/graphene and Cu_4-Sn/γ-Al₂O₃ was computed. The selectivity towards the competitive electrochemical hydrogen evolution reaction on these catalysts was also considered. The Cu₂Sn₂ cluster suppresses the hydrogen evolution reaction and is highly selective towards CO, if unsupported, or HCOOH if supported on graphene. This study demonstrates that the Cu₂Sn₂ cluster is a potential candidate for the electrocatalytic conversion of the CO₂ molecule. Moreover, it identifies insightful structure-property relationships in Cu-based nanocatalysts, highlighting the influence of composition and catalyst support on CO₂ activation.