Single atom catalysts (SACs) are widely researched in various chemical transformations due to the high atomic utilization and catalytic activity. Carbon‐supported SACs are the largest class because of the many excellent properties of carbon derivatives. The single metal atoms are usually immobilized by doped N atoms and in some cases by C geometrical defects on carbon materials. To explore the catalytic mechanisms and improve the catalytic performance, many efforts have been devoted to modulating the electronic structure of metal single atomic sites. Doping with polynary metals and heteroatoms has been recently proposed to be a simple and effective strategy, derived from the modulating mechanisms of metal alloy structure for metal catalysts and from the donating/withdrawing heteroatom doping for carbon supports, respectively. Polynary metals SACs involve two types of metal with atomical dispersion. The bimetal atom pairs act as dual catalytic sites leading to higher catalytic activity and selectivity. Polynary heteroatoms generally have two types of heteroatoms in which N always couples with another heteroatom, including B, S, P, etc. In this Review, the recent progress of polynary metals and heteroatoms SACs is summarized. Finally, the barriers to tune the activity/selectivity of SACs are discussed and further perspectives presented.

As CO 2 emissions are sharply increasing, processes for converting CO 2 into value-added products are becoming more desirable. Ruthenium-based catalysts are the most active for CO 2 methanation; however, their substantially higher cost relative to transition metals makes them prohibitive for industrial application. In this study, we demonstrate porous hexagonal boron nitride (pBN) supports (an ideal support material for thermocatalysts due to the high thermal stability and conductivity) to improve the utilization of Ru and simultaneously enhance the catalytic activity and selectivity for CO 2 methanation. A simple vacuum filtration process is proposed that allows the Ru precursor to quickly locate the defects of pBN, where atomic Ru can be restricted onto the defects via B, N coordination through an annealing treatment. The B and N coordinations reduce the valence state of atomic Ru. The as-prepared catalyst with low Ru loading (0.58 wt %) exhibits CH 4 selectivity up to 93.5%, catalytic stability after 110 h, and a higher reaction rate [1.86 mmol CO 2 /(g cat s)] at 350 °C and 1.0 MPa compared to other nanoparticle catalysts. Both atomic-scale size and low valence state of atomic Ru supported on pBN are responsible for the improvement of CH 4 production rate as confirmed by density functional theory simulation.

Carbon material is a promising electrocatalyst for the oxygen reduction reaction (ORR). Doping of heteroatoms, the most widely used modulating strategy, has attracted many efforts in the past decade. Despite all this, the catalytic activity of heteroatoms‐modulated carbon is hard to compare to that of metal‐based electrocatalysts. Here, a “double‐catalysts” (Fe salt, H3BO3) strategy is presented to directionally fabricate porous structure of crystal graphene nanoribbons (GNs)/amorphous carbon doped by pyridinic NB pairs. The porous structure and GNs accelerate ion/mass and electron transport, respectively. The N percentage in pyridinic NB pairs accounts for ≈80% of all N species. The pyridinic NB pair drives the ORR via an almost 4e− transfer pathway with a half‐wave potential (0.812 V vs reversible hydrogen electrode (RHE)) and onset potential (0.876 V vs RHE) in the alkaline solution. The ORR catalytic performance of the as‐prepared carbon catalysts approximates commercial Pt/C and outperforms most prior carbon‐based catalysts. The assembled Zn–air battery exhibits a high peak power density of 94 mW cm−2. Density functional theory simulation reveals that the pyridinic NB pair possesses the highest catalytic activity among all the potential configurations, due to the highest charge density at C active sites neighboring B, which enhances the interaction strength with the intermediates in the p‐band center.