Comprehensive activity evaluation of single-atom catalysts

Single-atom catalysts have become one of the hot topics in the heterogeneous catalysis field. However, the acquisition of its catalytic performance should be more rigorous in the next development. Here we discuss how to evaluate the activity of single-atom catalysts by appropriately comparing with their nanoparticle counterparts; we hope this perspective will benefit catalyst design and development in the future. Challenges and opportunities: • The bloom of single-atom catalysts (SACs) brings new opportunity in the field of heterogeneous catalysis on account of their relatively homogenously distributed active sites and maximized atomic efficiency. However, SACs are not necessarily superior to their nanoparticle (NP) counterparts in certain reactions. The catalytic performance of SACs and NPs is determined by not only atomic efficiency but also by their intrinsic activity. • The intrinsic activity is important in fundamental study to tell the catalytic ability of active sites, while in industrial application the apparent activity of a catalyst in consideration of both intrinsic activity and atomic efficiency is more meaningful. A comprehensive comparison is between SACs and NPs in the further development of heterogenous catalysis regarding SACs. • Establishing and meliorating the activity evaluation index is vital in giving feedback for the development of high-performance catalysts, either SACs or NP catalysts. In order to enhance the metal atom utilization efficiency, especially for noble metal, the size of supported metal is decreased from nano to subnano and even to single atomic scale. However, catalytic efficiency is not always increased with decreasing size. Here, we try to answer the question of which kind of metal species, i.e., single atom, cluster, or nanoscale particle, is more suitable for one reaction, from both the micro and macro points of view.