CO Dimerization on Cu Nanoparticles under High CO Coverage

Copper has attracted significant interest as a catalyst for thermal and electrochemical CO2 or CO reduction into valuable compounds. These reactions may involve significant quantities of CO adsorbed on the surface of Cu catalysts, whose properties are typically affected by nanostructuring. Here, we applied density functional theory (DFT) calculations to study the effect of CO coverage on the catalytic properties of 0.8 nm large Cu-38 and 1.1 nm large Cu-79 nanocrystallites. Even under mild conditions, CO is calculated to saturate the surface of Cu nanoparticles at an unusually high coverage of 1 ML. At this coverage, CO is calculated to adsorb predominantly on top sites, with some CO molecules occupying bridge sites on the {111} facets. Such high quantities of adsorbed CO led to profound changes in the electronic structure of surface Cu atoms, whose d-band center positions shift to lower energies by more than 0.7 eV. CO coverage was also calculated to have a profound effect on the catalytic properties of Cu particles in the exemplary reaction of CO dimerization into OCCO. Unexpectedly, the barriers for OCCO formation were calculated to increase by similar to 0.6 eV at high CO coverage on Cu nanoparticles due to the intricate effect of coadsorbates on OCCO binding to Cu. Thus, the interplay between nanostructuring and adsorbate coverage is shown to have significant implications for heterogeneous catalysis and electrochemistry that are hard to predict based on chemical intuition.