Shape and Surface Morphology of Copper Nanoparticles under CO2 Hydrogenation Conditions from First Principles

Predicting the state of Cu under a broad range of reaction conditions (pressure and temperature with various adsorbates: CO2, CO, H2O, H*, and O*) is an important property to understand CO2 hydrogenation catalysts. Here, unsupported copper (Cu) nanoparticles (NPs) were modeled in vacuum and under conditions relevant for CO2 hydrogenation conditions from first principles using density functional theory calculations; such models allow precise prediction of particle shapes and surface coverage of the relevant facets of Cu NPs over a large range of conditions relevant to CO2 hydrogenation. This model predicts that the Cu surfaces are fully reduced (in line with experimental results) and free of adsorbed oxygen (O*), H2O*, and CO2* under typical reaction conditions. Furthermore, the Cu(111) facet is at least partially covered with hydrogen (H*) and the Cu(110) facet is partially covered with adsorbed CO* at high reverse-water–gas-shift (RWGS) conversions, while the Cu(100) and Cu(211) facet remain adsorbate-free. Overall, the particle shape of Cu NPs under CO2 hydrogenation conditions is dominated by the (111) facet with a small area of the (100) facet being present (among all the facets considered). The final equilibrium particle shape is set during the initialization of the CO2 hydrogenation reaction and does not change even when the WGS equilibrium is reached.