Coordination numbers for unraveling intrinsic size effects in gold-catalyzed CO oxidation

Geometry-based reactivity descriptors, e.g., regular, generalized, and orbitalwise coordination numbers, were used for unraveling intrinsic size effects of Au nanocatalysts towards CO oxidation. For an ensemble of Au nanoparticles with varying sizes and shapes, s-orbital coordination numbers (CN^s) linearly correlate with *CO and *O adsorption energies at the on-top and hollow sites, respectively, outperforming their regular (CN) and generalized (C[combining macron]N[combining macron]) counterparts attributed to an explicit consideration of interatomic interactions. To take into account the geometric strain of surface atoms, the embedded-atom method (EAM) potential trained with ab initio energies of the bulk, nanoclusters, and extended surfaces at the GGA-PBE level was used for optimizing the Wulff-shaped, free-standing Au nanoparticles up to 7.2 nm. Microkinetic analysis of CO oxidation on extended {111}, {100}, {211}, and {532} surfaces, along with a facile and accurate prediction of *CO and *O adsorption energies at nanoparticles using the herein developed structure-reactivity relationships, captures experimentally measured activity trends of supported Au nanoparticles of varying sizes on a wide variety of metal oxides and illustrates the importance of under-coordinated atoms and insensitivity of surface strains in Au-catalyzed CO oxidation.