Single Atom Catalytic Sites Research Articles

Asymmetric CoN3P1 single-atom catalytic sites for enhanced transfer hydrodehalogenation

We present here CoN3P1@NP-PC, a novel asymmetric CoN3P1 single-atom catalyst, which demonstrates outstanding efficiency in transfer hydrodehalogenation (HDH) using just two equivalents of HCOONH4 as a benign and effective reducing agent.

From Porphyrin-Like Rings to High-Density Single-Atom Catalytic Sites: Unveiling the Superiority of p-C2N for Bifunctional Oxygen Electrocatalysis.

With effective utilization of the catalytic site, single-atom catalysts (SACs) supported by nitrogen atoms surrounding built-in pores of two-dimensional (2D) materials, such as porphyrin/phthalocyanine-based covalent organic frameworks, have been highly promising electrocatalysts in the oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) processes for the air electrode of the metal-air battery. However, the number of stable single-atom anchoring sites, i.e., accessible single-atom metal sites, has been concerning as a result of the appearance of heterogeneous or large and even supersized pores in substrate materials. 2D porous graphitic carbon nitride (PGCN) with a stronger stability and smaller component is regarded as a more potential alternative owing to similar controllability and designability. In this work, inspired by the robust coordinated TM-N4 environment of porphyrin/phthalocyanine molecules, novel p-C2N with a high density of porphyrin-like organic units is rationally designed. In well-designed p-C2N, a higher homogeneity and uniformity of coordination sites can enhance the electrocatalytic activity in the whole catalytic material and better prevent SACs from sintering and agglomerating into thermodynamically stable nanoclusters. Utilizing density functional theory (DFT), the stability of the p-C2N monolayer, TM@p-C2N, and OER/ORR catalytic activities of TM@p-C2N (TM including Mn, Fe, Co, Ni, Cu, Ru, Rh, Pd, Ag, Os, Ir, Pt, and Au) are systematically evaluated. Among them, Ir@p-C2N (0.31 V of the OER and 0.36 V of the ORR), Co@p-C2N (0.47 and 0.22 V), and Rh@p-C2N (0.55 and 0.27 V) are screened as promising SACs for the bifunctional ORR and OER. The proposal of p-C2N guides a new direction for the development of TM-N-C-based SAC bifunctional electrocatalysts.

Atomic regulation strategies of dual-metal single-atom catalytic sites supported on 3D N-doped carbon nanotube aerogels for boosting oxygen reduction and zinc-air battery

Dual-metal single-atom catalysts (DSAs) exhibit excellent electrocatalytic properties, holding great promise in energy conversion and storage fields. Their rational design and synthesis are realized by optimizing the types of supporting substrate or regulating the coordination microenvironment. Herein, FeCo DSAs supported on N-doped carbon nanotube aerogels (FeCo DSAs/N-CNAs) were facilely fabricated by a glucose-assisted atomic regulation pyrolysis approach. The morphology and structure were characterized by a series of techniques. The influences of the pyrolysis temperature and types of the metal precursors were carefully investigated, coupled by elaborating the formation mechanism. The resulting FeCo DSAs/N-CNAs catalyst shows a positive onset potential (Eonset = 1.075 V) and half-wave potential (E1/2 = 0.907 V) for oxygen reduction reaction (ORR) in a 0.1 M KOH solution, outperforming those of commercial Pt/C. The obtained catalyst is further exploited for establishing rechargeable Zn-air battery, which shows a larger peak power density of 86.7 mW cm−2 and a longer cycle stability over 144 h. These findings identify low-cost FeCo DSAs/N-CNAs as promising electrocatalysts for advanced rechargeable Zn-air batteries.

Enhancing Photocatalysis: Understanding the Mechanistic Diversity in Photocatalysts Modified with Single-Atom Catalytic Sites.

Surface modification of heterogeneous photocatalysts with single-atom catalysts (SACs) is an attractive approach for achieving enhanced photocatalytic performance. However, there is limited knowledge of the mechanism of photocatalytic enhancement in SAC-modified photocatalysts, which makes the rational design of high-performance SAC-based photocatalysts challenging. Herein, a series of photocatalysts for the aerobic degradation of pollutants based on anatase TiO2 modified with various low-cost, non-noble SACs (vanadate, Cu, and Fe ions) is reported. The most active SAC-modified photocatalysts outperform TiO2 modified with the corresponding metal oxide nanoparticles and state-of-the-art benchmark photocatalysts such as platinized TiO2 and commercial P25 powders. A combination of in situ electron paramagnetic resonance spectroscopy and theoretical calculations reveal that the best-performing photocatalysts modified with Cu(II) and vanadate SACs exhibit significant differences in the mechanism of activity enhancement, particularly with respect to the rate of oxygen reduction. The superior performance of vanadate SAC-modified TiO2 is found to be related to the shallow character of the SAC-induced intragap states, which allows for both the effective extraction of photogenerated electrons and fast catalytic turnover in the reduction of dioxygen, which translates directly into diminished recombination. These results provide essential guidelines for developing efficient SAC-based photocatalysts.

Unlocking the Potential of Sub‐Nanometer Pd Catalysts for Electrochemical Hydrogen Peroxide Production

AbstractThe utilization of nanoscale catalysts represents a valuable and promising strategy for augmenting catalytic performance while mitigating the reliance on expensive noble metals. Nevertheless, a significant knowledge gap persists regarding the intricate interplay between catalyst size, physical properties, and catalytic behavior in the context of the oxygen reduction reaction. In this study, the synthesis of precisely controlled palladium catalysts is presented, spanning a wide range from individual atoms to metal clusters and nanoparticles, followed by a comprehensive evaluation of their performance in acidic conditions. The results show a significant increase in H2O2 selectivity of up to 96% with decreasing catalyst size and strategic approaches are identified to eliminate unselective sites, facilitating the attainment of active and selective catalysts. The enhanced selectivity of the catalysts highlights the potential of single atom catalytic sites and can be adapted to improve the performance of various catalytic processes.

In-situ synthesis of single-atom CoNx clusters-decorated TiO2 for highly efficient charge separation and CO2 photoreduction

Solar-driven CO2 reduction reaction (CO2RR) to produce chemical fuels is an attractive way to alleviate the greenhouse effect and energy crisis. Herein, a novel single-atom CoNx clusters-decorated TiO2 (CoNx/TiO2) is synthesized in situ by calcining a composite derived from immersing a metal organic framework (Mil-125) into cobalt tetra(4-pyridyl)porphyrin (CoPy4) solution. The resultant CoNx/TiO2 delivers an excellent CO2RR activity with CO/CH4 yields of 24.4/119.9 μmol g−1 h−1, corresponding an overall photoactivity of 1007.6 μmol g−1 h−1, 10.6 time higher than that of TiO2 alone. It is found that CoPy4 molecules can enter Mil-125′s micropores, which helps to pyrolyze CoPy4 into highly dispersed single-atom-contained CoNx clusters and to form strong interaction with the primary nanoparticles of TiO2quasi-nanocube-like aggregated particles derived from Mil-125. These factors of CoNx/TiO2 enable efficient photogenerated charge separation, strong chemical adsorption to reactants and high atom utilization, thus providing a new strategy for constructing TiO2-based photocatalysts with highly dispersed single-atom catalytic sites for CO2 photoreduction.

Manipulating orbital hybridization of single-atom catalytic sites in metal-organic framework for high-performance lithium-sulfur batteries

Catalytic single-atom catalysts (SACs) have shown superiority in promoting the sluggish redox reaction kinetics and suppressing the shuttle effect of soluble lithium polysulfides (LiPSs) in lithium-sulfur batteries (LSBs) than traditional catalysts, which are however restricted by the limited ratio of single-atom metal sites. Metal-organic frameworks (MOFs) hold great potential as tunable SACs platforms for their talent in regulating catalytic single-atom sites and manipulating the orbital hybridization with guest molecules through modularized design, which however has not been fully designed and understood in LSBs. In this work, a series of porphyrin-based MOF nanosheets (PCN-222(M)-NSs) possessing rational-designed M-N4 (M= Fe3+, Co2+, Ni2+, and Cu2+) single-atom metal sites were synthesized to manipulate the d-p orbital hybridization between M-N4 center and LiPSs. Systematic in-situ/ex-situ electrochemical experiments and theoretical calculations demonstrate that the Cu-N4 center of PCN-222(Cu)-NS exhibits the best effect for promoting LiPSs conversion and suppressing shuttle effect due to the most effective d-p orbital hybridization between Cu-N4 and sulfur species. The assembled LSBs with PCN-222(Cu)-NS/graphene interlayer show remarkably improved discharge capacity and decreased decay rate at low and high area-sulfur loading.

Mechanism of Particle-Mediated Inhibition of Demetalation for Single-Atom Catalytic Sites in Acidic Electrochemical Environments.

Demetalation, caused by the electrochemical dissolution of metal atoms, poses a significant challenge to the practical application of single-atom catalytic sites (SACSs) in proton exchange membrane-based energy technologies. One promising approach to inhibit SACS demetalation is the use of metallic particles to interact with SACSs. However, the mechanism underlying this stabilization remains unclear. In this study, we propose and validate a unified mechanism by which metal particles can inhibit the demetalation of Fe SACSs. Metal particles act as electron donors, decreasing the Fe oxidation state by increasing the electron density at the FeN4 position, thereby strengthening the Fe-N bond, and inhibiting electrochemical Fe dissolution. Different types, forms, and contents of metal particles increase the Fe-N bond strength to varying extents. A linear correlation between the Fe oxidation state, Fe-N bond strength, and electrochemical Fe dissolution amount supports this mechanism. Our screening of a particle-assisted Fe SACS led to a 78% reduction in Fe dissolution, enabling continuous operation for up to 430 h in a fuel cell. These findings contribute to the development of stable SACSs for energy applications.

Dynamically confined single-atom catalytic sites within a porous heterobilayer for CO oxidation via electronic antenna effects

Suppression of clustering of single-atom catalysts during chemical reaction is a long-standing challenge in heterogeneous catalysis, largely due to the prevailing design scheme that the catalytic atoms are anchored onto the supporting surfaces. Here we use first-principles approaches to establish a different design principle, where the single-atom catalytic centers are dynamically sandwiched between a porous g-${\mathrm{C}}_{3}{\mathrm{N}}_{4}/{\mathrm{MoS}}_{2}$ heterobilayer as a prototypical system. We show that many of the transition metals can be well stabilized as dispersive single atoms within the porous centers. Moreover, the single atoms migrate out of their sandwiched homes in ${\mathrm{O}}_{2}$ activation and CO oxidation, and successfully return home after the reaction is completed. In such a dynamical process the single atoms function as electronic antennas, facilitating the charge donation to or acceptance from the reactants, while effectively lowering the reaction barriers. These findings are instructive in establishing high-performance single-atom catalysts upon two-dimensional porous materials.

A Homing Missile-Like Nanotherapeutic with Single-Atom Catalytic Sites for In Situ Elimination of Intracellular Bacterial Pathogens.

Intracellular bacterial pathogens hiding in host cells tolerate the innate immune system and high-dose antibiotics, resulting in recurrent infections that are difficult to treat. Herein, a homing missile-like nanotherapeutic (FeSAs@Sa.M) composed of a single-atom iron nanozyme (FeSAs) core coated with infected macrophage membrane (Sa.M) is developed for in situ elimination of intracellular methicillin-resistant S. aureus (MRSA). Mechanically, the FeSAs@Sa.M initially binds to the extracellular MRSA via the bacterial recognition ability of the Sa.M component. Subsequently, the FeSAs@Sa.M can be transported to the intracellular MRSA-located regions in the host cell like a homing missile under the guidance of the extracellular MRSA to which it is attached, generating highly toxic reactive oxygen species (ROS) for intracellular MRSA killing via the enzymatic activities of the FeSAs core. The FeSAs@Sa.M is far superior to FeSAs in killing intracellular MRSA, proposing a feasible strategy for treating intracellular infections by in situ generating ROS in bacterial residing regions.

Uncovering Dynamic Edge-Sites in Atomic Co-N-C Electrocatalyst for Selective Hydrogen Peroxide Production.

Understanding the nature of single-atom catalytic sites and identifying their spectroscopic fingerprints are essential prerequisites for the rational design of target catalysts. Here, we apply correlated in situ X-ray absorption and infrared spectroscopy to probe the edge-site-specific chemistry of Co-N-C electrocatalyst during the oxygen reduction reaction (ORR) operation. The unique edge-hosted architecture affords single-atom Co site remarkable structural flexibility with adapted dynamic oxo adsorption and valence state shuttling between Co(2-δ)+ and Co2+ , in contrast to the rigid in-plane embedded Co1 -Nx counterpart. Theoretical calculations demonstrate that the synergistic interplay of in situ reconstructed Co1 -N2 -oxo with peripheral oxygen groups gives a rise to the near-optimal adsorption of *OOH intermediate and substantially increases the activation barrier for its dissociation, accounting for a robust acidic ORR activity and 2e- selectivity for H2 O2 production.

Asymmetric Coordination Environment Engineering of Atomic Catalysts for CO2 Reduction.

Single-atom catalysts (SACs) have emerged as well-known catalysts in renewable energy storage and conversion systems. Several supports have been developed for stabilizing single-atom catalytic sites, e.g., organic-, metal-, and carbonaceous matrices. Noticeably, the metal species and their local atomic coordination environments have a strong influence on the electrocatalytic capabilities of metal atom active centers. In particular, asymmetric atom electrocatalysts exhibit unique properties and an unexpected carbon dioxide reduction reaction (CO2RR) performance different from those of traditional metal-N4 sites. This review summarizes the recent development of asymmetric atom sites for the CO2RR with emphasis on the coordination structure regulation strategies and their effects on CO2RR performance. Ultimately, several scientific possibilities are proffered with the aim of further expanding and deepening the advancement of asymmetric atom electrocatalysts for the CO2RR.

Atomically Precise Integration of Multiple Functional Motifs in Catalytic Metal-Organic Frameworks for Highly Efficient Nitrate Electroreduction.

Ammonia production plays a central role in modern industry and agriculture with a continuous surge in its demand, yet the current industrial Haber-Bosch process suffers from low energy efficiency and accounts for high carbon emissions. Direct electrochemical conversion of nitrate to ammonia therefore emerges as an appealing approach with satisfactory sustainability while reducing the environmental impact from nitrate pollution. To this end, electrocatalysts for efficient conversion of eight-electron nitrate to ammonia require collective contributions at least from high-density reactive sites, selective reaction pathways, efficient multielectron transfer, and multiproton transport processes. Here, we report a catalytic metal-organic framework (two-dimensional (2D) In-MOF In8) catalyst integrated with multiple functional motifs with atomic precision, including uniformly dispersed, high-density, single-atom catalytic sites, high proton conductivity (efficient proton transport channel), high electron conductivity (promoted by the redox-active ligands), and confined microporous environments. These eventually lead to a direct and efficient electrochemical reduction of nitrate to ammonia and record high yield rate, FE, and selectivity for NH3 production. A novel "dynamic ligand dissociation" mechanism provides an unprecedented working principle that allows for the use of a high-quality MOF crystalline structure to function as highly ordered, high-density, single-atom catalyst (SAC)-like catalytic systems and ensures the maximum utilization of the metal centers within the MOF structure. Further, the atomically precise assembly of multiple functional motifs within a MOF catalyst offers an effective and facile strategy for the future development of framework-based enzyme-mimic systems.

A peroxidase-like single-atom Fe-N5 active site for effective killing human lung adenocarcinoma cells

Single-atom catalyst (SAC) is one of the newest catalysts, and attracts people’s wide attention in cancer therapy based on their characteristics of maximum specific catalytic activity and high stability. We designed and synthesized a Fe-N decorated graphene nanosheet (Fe-N5/GN SAC) with the coordination number of five. Through enzymology and theoretical calculations, the Fe-N5/GN SAC has outstanding intrinsic peroxidase-like catalytic activity due to single-atom Fe site with five-N-coordination structure. We explored its potential on lung cancer therapy, and found that it could kill human lung adenocarcinoma cells (A549) by decomposing hydrogen peroxide (H2O2) into toxic reactive oxygen species (ROS) under acidic microenvironment in three-dimensional (3D) lung cancer cell model. Our study demonstrates a promising application of SAC with highly efficient single-atom catalytic sites for cancer treatment.

Engineering at Subatomic Scale: Achieving Selective Catalytic Pathways via Tuning of the Oxidation States in Functionalized Single-Atom Quantum Catalysts.

Regulating the catalytic pathways of single-atom sites in single atom catalysts (SACs) is an exciting debate at the moment, which has redirected the research towards understanding and modifying the single-atom catalytic sites through various strategies including altering the coordination environment of single atom for desirable outcomes as well as increasing their number. One useful aspect concerning the tunability of the catalytic pathways of SACs, which has been overlooked, is the oxidation state dynamics of the single atoms. In this study, iron single-atoms (FeSA) with variable oxidation states, dependent on the precursors, are harnessed inside a nitrogen-rich functionalized carbon quantum dots (CQDs) matrix via a facile one-step and low-temperature synthesis process. Dynamic electronic properties are imparted to the FeSAs by the simpler carbon dots matrix of CQDs in order to achieve the desired catalytic pathways of reactive oxygen species (ROS) generation in different environments, which are explored experimentally and theoretically for an in-depth understanding of the redox chemistry that drives the alternative catalytic pathways in FeSA@CQDs. These alternative and oxidation state-dependent catalytic pathways are employed for specific as well as cascade-like activities simulating natural enzymes as well as biomarkers for the detection of cancerous cells.

Single-metal catalytic sites via high-throughput mechanochemistry enable selective and efficient CO2 photoreduction

In this work, we first report synthesizing a series of single-atom metals (covering main-group, transition, precious, and rare earth metals) photocatalysts MSA/TiO2 using a simple, efficient, and high-yield mechanochemistry (high-energy ball milling) and evaluate their efficiency towards CO2 photoreduction. In the synthesized single-atom catalyst (SAC), the CH4 yield from CO2 photoreduction using PdSA/TiO2 reaches as high as 271.6 μmol·g−1·h−1 with the selectivity of ~98.0%, far surpassing those of conventional Pd clusters and nanoparticles. The experimental results and density functional theory (DFT) calculations reveal that the strong adsorption at single-atom catalytic sites (Pd) leads to significant bending of OCO bond angle from 180.0 to 151.0 ° and length from 1.16 to 1.20 Å. The induced deformation greatly ‘energizes’ the CO2, thus reducing the kinetic energy barrier significantly and offering high catalytic activity. Meanwhile, combined with in-situ Fourier-transform infrared (FT-IR), a rational reaction pathway of CO2 photoreduction over efficient SACs is proposed.

Molecularly Engineered Carbon Platform To Anchor Edge-Hosted Single-Atomic M–N/C (M = Fe, Co, Ni, Cu) Electrocatalysts of Outstanding Durability

A powerful synthetic protocol based on a molecularly engineered anchoring carbon platform (ACP) is reported to stabilize concentrated edge-hosted single-atom catalytic sites of M–N (M = Fe, Co, Ni, Cu) on carbon supports. Polymerization with l-cysteine as an additional organic precursor produces an ACP sheath around the carbon nanotube (CNT)–graphene (GR) hybrid support made of a small domain size with abundant edge sites and doped with sulfur. A few-minute-long microwave pyrolysis anchors strongly the single-atomic M–N moiety on the ACP while suppressing its agglomeration during the high-temperature synthesis and makes the ACP highly graphitized. As a typical example, the edge-hosted single-atomic catalytic sites in Fe–N/S-CNT–GR provide superior pH-independent oxygen reduction reaction (ORR) activity to previously reported Fe–N–C catalysts and commercial Pt/C while demonstrating oxygen evolution reaction (OER) activity in basic conditions similar to known state-of-the-art catalysts. In particular, the Fe–N/S-CNT–GR catalyst is much more stable than commercial Pt/C and Ir/C catalysts during ORR and OER in both base and acid solutions. Inferior stability is a common problem of this type of single-atom heterogeneous catalyst (SAC). An aqueous Zn–air battery with our Fe–N/S-CNT–GR catalyst operates as effectively as the device with the commercial Pt/C–Ir/C catalysts. We believe that our protocol based on the molecularly engineered ACP and microwave pyrolysis can provide a new concept to synthesize a new generation of durable SACs, which could have broad applications in electrochemical energy conversion and storage.

Porphyrin polymer-derived single-atom Fe assisted by Fe2O3 with oxygen vacancy for efficient oxygen reduction reaction

Single-atom catalysts (SACs) have been deemed as one of the most prospective substitutes for high-efficiency oxygen reduction reaction (ORR) catalysts due to its theoretical maximum atomic utilization. However, the convenient preparation and the further improvement in activity of SACs are laborious. Herein, the N-doped porous carbon (NC) material with in site produced Fe-N4 single-atom catalytic sites (FeSA) accompanied by Fe2O3 species with abundant oxygen vacancies (Ov-Fe2O3) as co-catalytic sites (Ov-Fe2O3@FeSA@NC) is successfully obtained by using a well-designed porphyrin conjugated mesoporous polymer (CMP) consisting of iron porphyrin and metal free porphyrin units as a precursor, and followed by pyrolysis. A series of controllable experiments reveal that FeSA assisted by Ov-rich Fe2O3 render Ov-Fe2O3@FeSA@NC outstanding ORR activity in the alkaline medium with the onset and half-wave potentials (Eonset and E1/2) of 0.987 V and 0.901 V vs RHE, which significantly outperformed the electrochemical activity of FeSA@NC (Eonset = 0.962 V, E1/2 = 0.850 V) and Ov-Fe2O3@NC (Eonset = 0.913 V, E1/2 = 0.821 V) with individual FeSA and Ov-Fe2O3 active sites, respectively. This work innovatively demonstrates the importance of oxygen vacancy-assisted single-atom catalysts for oxygen reduction catalysis, and also provides guidance for the design of high-performance SACs.

Automated Image Analysis for Single-Atom Detection in Catalytic Materials by Transmission Electron Microscopy

Single-atom catalytic sites may have existed in all supported transition metal catalysts since their first application. Yet, interest in the design of single-atom heterogeneous catalysts (SACs) only really grew when advances in transmission electron microscopy (TEM) permitted direct confirmation of metal site isolation. While atomic-resolution imaging remains a central characterization tool, poor statistical significance, reproducibility, and interoperability limit its scope for deriving robust characteristics about these frontier catalytic materials. Here, we introduce a customized deep-learning method for automated atom detection in image analysis, a rate-limiting step toward high-throughput TEM. Platinum atoms stabilized on a functionalized carbon support with a challenging irregular three-dimensional morphology serve as a practically relevant test system with promising scope in thermo- and electrochemical applications. The model detects over 20,000 atomic positions for the statistical analysis of important properties for establishing structure-performance relations over nanostructured catalysts, like the surface density, proximity, clustering extent, and dispersion uniformity of supported metal species. Good performance obtained on direct application of the model to an iron SAC based on carbon nitride demonstrates its generalizability for single-atom detection on carbon-related materials. The approach establishes a route to integrate artificial intelligence into routine TEM workflows. It accelerates image processing times by orders of magnitude and reduces human bias by providing an uncertainty analysis that is not readily quantifiable in manual atom identification, improving standardization and scalability.

Co-porphyrin/Ru-pincer complex coupled polymer with Z-scheme molecular junctions and dual single-atom sites for visible light-responsive CO2 reduction

• A new Co-porphyrin/Ru-pincer complex coupled polymer with efficient MMCT is prepared. • Periodic Z-scheme molecular junctions in the polymer promote the charge transfer. • Ru/Co centers in the polymer serve as the reduction/oxidation single-atom sites. • The polymer shows much better Vis-NIR light-driven CO 2 RR activity than its monomers. • A special CO 2 RR mechanism via a pincer-typed N′NN′-Ru-CO intermediate is proposed. Covalent organic polymer has been considered as the promising organic semiconductor for the photocatalytic CO 2 reduction reaction (CO 2 RR) due to its unique features such as adjustable framework, durable stability and feasible bandgap energy, et al . Herein, we report a novel Co II -porphyrin/Ru II -pincer complex coupled polymer (CoPor-RuN 3 ), which exhibits efficient visible light-responsive CO 2 RR activity with the average CO/CH 4 yields of 37.1/1.57 μmol g -1 h −1 and a total photoactivity of 86.8 μmol g -1 h −1 , 25.5 and 4.5 times that of the CoPor and RuN 3 monomers, respectively. It is found that the two metal centers (Co/Ru) and the conjugated framework of the polymer are essential for efficient CO 2 RR. A series of in-situ characterizations prove that periodic Z-scheme molecular junctions are formed by the linkage of amide group in the CoPor-RuN 3 polymer to facilitatie the photogenerated electron transfer from CoPor units to RuN 3 ones, in which Ru and Co serve as the reduction and oxidative single-atom sites, respectively. Moreover, the wavelet transform plots of X-ray absorption spectra of Ru K-edge shows that two CH 3 CN ligands are easily dissociated from the Ru center during the photocatalytic process, leaving empty sites for the adsorption of CO 2 . Based on the experimental observations and theoretical calculations, a plausible photocatalytic CO 2 reduction mechanism involving a pincer-typed N′NN′-Ru-CO intermediate (N′NN′ = 2,6-bis(benzimidazol-2-yl)pyridine) as the real reduction center is clarified. This work gives a new thread for exploring broadband-responsive covalent organic polymers with uniformly dispersed single-atom catalytic sites for CO 2 photoreduction.