Single‐Atom Nano‐Islands (SANIs): A Robust Atomic–Nano System for Versatile Heterogeneous Catalysis Applications

Abstract

and conventional transition metals SACs supported on metal or non-metal carriers) have been developed and upgraded greatly. [3][4][5] Theoretically speaking, the dispersion limit of supported metal catalysts is the uniform distribution of the metal in the form of single atoms on the support: this is not only the ideal state of supported metal catalysts, but also brings the science of catalysis from the "nano age" into the "atomic age". [6][7][8] SACs usually refer to the active sites where isolated metal atoms are loaded onto the surface of the carriers to reach the maximum atomic utilization. These active sites are anchored by adjacent coordination atoms on the carrier (generally through covalent metal-nonmetal bonding) to prevent the thermodynamic diffusion and irreversible aggregation of single metal atoms. However, SACs all along face an unavoidable physicochemical problem: when the metal particles are reduced to the level of single atomic dispersions, the specific surface area increases sharply (reaching the maximum theoretical value), also leading to the maximum value of the metal surface free energy. [9] Therefore, in the actual application environment and catalytic reaction conditions, especially at high temperature or in a reducing atmosphere, the single atomic metal active sites are extremely prone to agglomeration and coupling to form large atomic clusters (even nanoparticles), resulting in the degradation of catalyst performance or even complete inactivation. [10] Recently, however, scientists have found that fully exposed cluster catalysts with low coordination metal bonds (the coordination number of the metal bond is ≈4.4) [11] and local single-atomic agglomeration [12] show more satisfactory performances in specific complex catalytic systems. These works provide a basic understanding of the dynamic stability of SACs under working conditions and call for a reassessment of the reported stability of SACs by considering realistic reaction conditions.Admittedly, it is quite necessary to reevaluate the realistic catalytic stability and dynamic catalysis mechanism of SACs; nevertheless, we hold the opinion that it is more important to design fundamentally a kind of efficient SACs with high activity and high stability at the same time (such as the "moving but not aggregating" design philosophy for metal active sites). On October 26, 2022, in collaboration with Yong Wang's group at Washington State University, Bruce C. Gates's group at the University of California, and Jingyue Liu's group at Arizona Academician Tao Zhang from China and co-workers designed the first Pt 1 / FeO x single-atom catalysts (SACs) in 2011, and they proposed the concept of "single-atom catalysis" in the field of heterogeneous catalysis. Generally, it is easy for active metal single-atom sites on a carrier to migrate and aggregate, which results in poor performance; or the chemical bond between the metal atom and carrier is too strong (immovable), which results in passivation of the active site. Recently, "nano-island" type SACs were...

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