Heterogeneous Atomic Catalysts Overcoming the Limitations of Single-Atom Catalysts

Abstract

Recent advances in heterogeneous single-atom catalysts (SACs), which have isolated metal atoms dispersed on a support, have enabled a more precise control of their surface metal atomic structure. SACs could reduce the amount of metals used for the surface reaction and have often shown distinct selectivity, which the corresponding nanoparticles would not have. However, SACs typically have the limitations of low-metal content, poor stability, oxidic electronic states, and an absence of ensemble sites. In this review, various efforts to overcome these limitations have been discussed: The metal content in the SACs could increase up to over 10 wt %; highly durable SACs could be prepared by anchoring the metal atoms strongly on the defective support; metallic SACs are reported; and the ensemble catalysts, in which all the metal atoms are exposed at the surface like the SACs but the surface metal atoms are located nearby, are also reported. Metal atomic multimers with distinct catalytic properties have been also reported. Surface metal single-atoms could be decorated with organic ligands with interesting catalytic behavior. Heterogeneous atomic catalysts, whose structure is elaborately controlled and the surface reaction is better understood, can be a paradigm with higher catalytic activity, selectivity, and durability and used in industrial applications.

Insights into the Mechanism of Methanol Steam Reforming Tandem Reaction over CeO2 Supported Single-Site Catalysts

“…[12][13][14] However, the lack of ensemble sites prevents surface reactions that involve large molecules and some multi-step reactions. [15][16][17] Recent research demonstrated that "ensemble effects" between the metal single atoms and neighboring oxygen vacancies can favor the oxygen transfer and reactants adsorption, promoting the catalytic reaction efficiency with large molecules. [18][19][20] In our previous studies, we demonstrated the enhanced activity and selectivity of methanol dehydrogenation and n-hexane reforming when combining an oxygen vacancy with noble metal atoms.…”

Stepping Out of Transition Metals: Activating the Dual Atomic Catalyst through Main Group Elements

“…In this case, the mono‐atomic structure may face the significant challenge of the competitive adsorptions among reactants. [ 23 ] To overcome this challenge, multi‐atomic catalysts are highly desired. Recently, dual atomic catalysts (DAC) have been reported, where the introduction of the second metal atom enables the simultaneous adsorptions of different reactants, promotes the intermediate conversions, optimizes the binding strength, and supplies ensemble effects, improving the catalytic performances significantly.…”

Single atom catalysts by atomic diffusion strategy

“…The strength of this interaction will affect the interface charge transfer, the electronic structure of the metal, etc., which in turn affects the stability and catalytic performance of SACs. If the force is too weak, a single metal atom is prone to diffusion and agglomeration, and then sintering occurs, resulting in a decrease in the number of catalytic active centers and a decrease in catalytic activity; If the force is too strong, a single metal atom will be loaded on the carrier in a higher oxidation state [103], and its stability will be reduced, resulting in a significant decrease in activity or even loss of activity. In this review, we discuss the synthesis methods of SACs by atomic diffusion strategy based on the diffusion form of the precursor, and explain how individual atoms are carried on the carrier.…”