Noble metal nanocatalysts have been widely applied in the petrochemical industry,medicine,environmental protection and energy sectors.To decrease the cost and maximize the utilization efficiency,single-atom catalysts (SACs),as a new frontier in heterogeneous catalysis,have attracted considerable attention due to their unique catalytic properties.Unlike traditional nanocatalysts,the catalytic performance of single-atom catalysts is highly dependent on their low-coordination environment,quantum size effects and metal-support interaction.Recently,several methods have been developed for the preparation of single-atom catalysts,including the impregnation method [1],co-precipitation method [2],photo-reduction method [3] and atomic layer deposition (ALD)method [4-6].