▎ 摘　　要

A fundamental understanding of the active sites in heterogeneous catalysts is extremely important in the development of effective catalysts. In general, it is difficult to identify the catalytically active sites due to their structural complexity, including the size and specific atomic configurations. In this paper, we prepare different Pt species (single atoms, fully exposed clusters, and nanoparticles) on a nanodiamond/graphene (ND@G) hybrid support to understand their evolution in structure for low-temperature CO oxidation. Remarkably, the atomically dispersed and fully exposed Pt clusters with an ensemble of a few Pt atoms showed the maximum atom utilization of low-coordinated metal sites. As determined by a catalytic performance evaluation, detailed characterizations, and theoretical calculations, the 0.5 wt % Pt-n/ND@G catalyst showed a catalytic performance for CO oxidation at low temperature superior to those of single-atom and nanoparticle catalysts, which was attributed to the weakened CO adsorption and facilitated O-2 dissociative adsorption on these atomically dispersed and fully exposed Pt cluster catalysts.