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

Abstract

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−nSn_n (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−nSn_n clusters and their ability to absorb and activate CO₂ was considered. Then, the kinetics of the gas phase CO₂ direct dissociation on Cu_4−nSn_n to generate CO was determined. Finally, the mechanism of electrocatalytic CO₂ reduction to CO and HCOOH on Cu_4−nSn_n, Cu_4−nSn_n/graphene and Cu_4−nSn_n/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.