Unraveling the coordination structure-performance relationship in Pt1/Fe2O3 single-atom catalyst

Dual effect of anchored sulphur and activated oxygen in the catalytic oxidation of organic sulfur over Pt single-atom catalysts

Foul-smelling organic sulfur gases removal of which is crucial for improving environmental quality and protecting human health. Herein, in this study, Pt single-atom (SA) loaded magnesium oxide (MgO) nanosheet catalysts were prepared, which exhibited the dual effects of anchored sulfur and activated oxygen that greatly enhanced the catalytic oxidation efficiency of methyl mercaptan (CH3SH), and 90 % complete oxidation of CH3SH could be achieved by Pt SA/MgO at 325 °C, with an oxidation efficiency that was 8 times higher than that of MgO nanosheets. A series of characterization results indicate that the valence state of Pt in the Pt SA/MgO catalyst ranges between 0 and +4, demonstrating its inherent electron-donating capability. Theoretical calculations show that the oxygen vacancy formation energy is reduced to 4.0 eV after the introduction of Pt SA, and the adsorption energy of atomic groups SH and CH3 is reduced to -1.5 and -2.0 eV. And the bond length of the MgO bond in Pt SA/MgO is shortened to 2.083 Å, forming an asymmetric structure with the PtO bond of 2.142 Å, effectively activating the lattice oxygen. Furthermore, A series of activity tests confirmed that the introduction of Pt SA reduced sulfate deposition, while the reaction pathway of CH3SH catalytic oxidation was optimised by changing the oxidation mechanism. The investigation offers a significant experimental foundation and novel viewpoints for the enhancement of high-performance catalytic oxidation catalysts targeting sulfur-containing volatile organic compounds (VOCs).

Defective Metal-Organic Frameworks Confined PdO with High Resistance to Reduction: An Efficient Photocatalyst for Hydrodeoxygenation of Lignin Derivatives

The positively charged metal species in the supported catalyst is often highly active in various reactions, and stabilization of this state is vital for fabricating catalysts with long-term cycles, particularly under reducing reaction conditions. Herein, we propose a strategy to fabricate reduction-resistant PdO by constructing enhanced metal-support interaction (MSI) using subnanometer nodes in defective metal-organic framework (MOF). Specifically, a photo-induced way was developed to generate defected Zr6O8 nodes for enhanced MSI in nanoconfined space. The obtained Pd/defective-MOF composites not only stabilize PdO via an unsaturated Zr6O8 cluster for a long period under photoreducing conditions but also provide a driving force for substrate enrichment and proton transfer by -OH/-OH2 coordination, leading to a dramatically enhanced catalytic performance in the photocatalytic hydrodeoxygenation of lignin derivatives, which is 4.5 times that of Pd/ideal-MOF composites with weak MSI. This work provides ideas for the selection of ultrasmall support to stabilize positively charged metal and also an avenue to design photocatalysts with tightly connected heterogeneous in MOFs.

Platinum Nanoparticles on Metalloid Antimony Functionalized Graphitic Nanoplatelets for Enhanced Water Electrolysis

Platinum (Pt) nanoparticles are considered to be the most efficient catalyst for acidic hydrogen evolution reaction (HER). However, they are expensive and unstable, because of agglomeration and Ostwald ripening. It is critically necessary for developing a better catalytic support to stabilize the Pt nanoparticles at low loading amounts. One efficient route to improving both catalytic activity and durability is metal catalysts stably anchored on heteroatom functionalized carbon supports via their strong interactions. Nevertheless, the interactions between "metallic" catalysts and "nonmetallic" heteroatom functionalized carbon supports are still unsatisfactory. Here, "metalloid" antimony (Sb) functionalized graphitic nanoplatelets (SbGnP) are reported to stably anchor Pt nanoparticles. The resulting Pt@SbGnP catalyst shows a record high acidic HER performance, attributable to the unique nature of Sb functional groups on SbGnP. Unlike typical low-period nonmetallic heteroatoms on carbon supports, high-period metalloid Sb with various oxidation states of SbOx provided strong binding sites to stably anchor Pt nanoparticles, suppressing particle aggregation, and thus sustaining catalytic activity and stability.

Structural Dynamic Evolution of Pt Nanoclusters in Ultra-Low-Temperature Methane Combustion with Nitrous Oxide

Tailoring and stabilizing the active sites of supported noble-metal catalysts to a semioxidized state with unsaturated coordination remain a long-standing challenge in heterogeneous catalysis. Herein, we develop a reaction-atmosphere-driven evolution approach for dynamic structural tuning of semioxidized metal sites in supported Pt catalysts. N2O as an alternative oxidant is used over Pt/TiO2 in CH4 combustion to dynamically prompt the transformation of Pt0 nanoclusters into Ptδ+ (0 < δ < 2) nanoclusters. Compared to CH4 combustion with O2 that inclines to overoxidize Pt0, the catalytic activity of CH4-N2O combustion is distinctly boosted, achieving complete CH4 combustion at only 200 °C, outperforming the state-of-the-art catalysts using O2 as the oxidant. Computational and experimental studies validate that N2O triggers less electron transfer from Pt than from O2, thereby facilitating the formation and preservation of Ptδ+ species during CH4 combustion. The newly emerged semioxidized Ptδ+ species with oxygen-deficient coordination structures simultaneously enhance lattice oxygen activation and the first C-H bond dissociation of CH4, contributing to ultralow temperature activity. Our work demonstrates that modulating the reaction atmosphere to achieve the structural dynamic evolution of semioxidized metal sites can provide new strategies for designing highly efficient catalysts for low-temperature CH4 combustion.

A d-Electron Deficient Pd Trimer for Exceptional Pyridine Hydrogenation Activity and Selectivity

The selective hydrogenation of pyridines containing reducible groups such as 2-phenylpyridine (PPY) typically has low yields due to strong nitrogen coordination with the metal as well as nonselective and over-hydrogenation. We report the synthesis of a novel Pd trimer catalyst through confined growth on an ordered mesoporous carrier, characterized by a 0.42 d-electron deficiency to address this challenge. This catalyst achieved a nearly complete conversion of 2-phenylpyridine and selectivity to 2-phenylpiperidine (PPD), maintaining its performance across eight batch cycles and continuous flow in the liquid phase for 800 h with negligible loss of activity or selectivity. We discuss the roles of active sites, including Pd d charge and ensemble structure, in relation to activation entropy, a Hammett study, and the adsorption configuration of the reactant. The exceptional 2-phenylpyridine hydrogenation activity and selectivity are attributed to the adsorption constraint of the pyridyl ring and the stabilization of the negatively charged transition state in the rate-determining step produced by the d-electron deficient Pd trimer.

Metal-support frontier orbital interactions in single-atom catalysis

Single-atom catalysts (SACs) with maximized metal use and discrete energy levels hold promise for broad applications in heterogeneous catalysis, energy conversion, environmental science and biomedicine1-7. The activity and stability of SACs are governed by the pair of metal-adsorbate and metal-support interactions8-10. However, the understanding of these interactions with their catalytic performance in nature is challenging. Correlations of activity with the charge state of metal atoms have frequently reached controversial conclusions11-15. Here we report that the activity of palladium (Pd1) SACs exhibits a linear scaling relationship with the positions of the lowest unoccupied molecular orbital (LUMO) of oxide supports across 14 types of semiconductor. Elevation of the LUMO position by reducing the support particle size to a few nanometres boosts a record high activity along with excellent stability in the semi-hydrogenation of acetylene. We show that the elevated LUMO of support reduces its energy gap with the highest occupied molecular orbital (HOMO) of Pd1 atoms, which promotes Pd1-support orbital hybridizations for high stability and further amends the LUMO of anchored Pd1 atoms to enhance Pd1-adsorbate interactions for high activity. These findings are consistent with the frontier molecular orbital theory and provide a general descriptor for the rational selection of metal-support pairs with predictable activity.

Pt nanocluster-Fe single atom pairs dual-regulate charge extraction and interfacial reaction for enhanced photoelectric response

Energy level mismatches between semiconductors and cocatalysts often induce carrier recombination, limiting photocatalytic and photoelectrochemical (PEC) efficiency. Here, we integrate Pt nanocluster-Fe single-atom pairs with CuO to regulate both solid-solid and solid-liquid interfaces in PEC systems. Experimental and theoretical analyses reveal that an Ohmic contact at the CuO/Pt interface accelerates electron extraction, while Pt-to-Fe charge transfer enhances oxygen reduction at Fe sites, collectively boosting reaction kinetics. Leveraging this, we construct a PEC biosensor exploiting chelating effect of glyphosate on CuO to impede electron transfer, achieving a detection limit of 0.41 ng/mL. This interface engineering strategy advances cocatalyst design for enhanced energy conversion and sensing applications by simultaneously addressing carrier dynamics and interfacial reaction barriers.

Tandem reductive amination and deuteration over a phosphorus-modified iron center

Deuterated amines are key building blocks for drug synthesis and the identification of metabolites of new pharmaceuticals, which drives the search for general, efficient, and widely applicable methods for the selective synthesis of such compounds. Here, we describe a multifunctional phosphorus-doped carbon-supported Fe catalyst with highly dispersed isolated metal sites that allow for tandem reductive amination-deuteration sequences. The optimal phosphorus-modified Fe-based catalyst shows excellent performance in terms of both reactivity and regioselectivity for a wide range of deuterated anilines, amines, bioactive complexes, and drugs (>50 examples). Experiments on the gram scale and on catalyst recycling show the application potential of this method. Beyond the direct applicability of the developed method, the described approach opens a perspective for the development of multifunctional single-atom catalysts in other value-adding organic syntheses.

Highly enhanced room-temperature single-atom catalysis of two-dimensional organic-inorganic multiferroics Cr(half-fluoropyrazine)2 for CO oxidation

In modern chemistry, the development of highly efficient room-temperature catalysts is of great significance and remains a long-standing challenge in various typical reactions. Here, we theoretically demonstrate that the two-dimensional (2D) multiferroic, Cr(half-fluoropyrazine)2 [Cr(h-fpyz)2], is a promising single-atom catalyst (SAC) operating at room temperature for CO oxidation. The rate-limiting barrier is merely 0.325 eV, leading to a reaction rate (i.e., 3.47 × 106 s-1) of six orders of magnitude higher than its monoferroic derivative [Cr(pyz)2], due to the synergetic effects of two aspects. First, the more flexible ligand rotations in Cr(h-fpyz)2 facilitate the activation of O2 molecule, simultaneously enhancing the charge transfer and spin-accommodation process. Second, on Cr(h-fpyz)2, O2 adsorption induces a distinctly lower local positive electric field, reducing the electrostatic repulsion of the polar CO molecule. These findings may also pave the way for establishing highly efficient SAC platforms based on 2D multiferroics where multidegree of freedom (e.g., spin, polarity) synergistically matter.

Revealing the catalytic oxidation mechanism of CO on α-Fe2O3 surfaces: an ab initio thermodynamic study

Significant research efforts have been devoted to improving the efficiency of catalytic carbon monoxide (CO) oxidation over α-Fe2O3-based catalysts, but details of the underlying mechanism are still under debate. Here we apply the ab initio thermodynamic method (AITM) within the density functional theory framework to investigate the phase diagram of α-Fe2O3(0001) surfaces with various terminations and the catalytic mechanism of CO oxidation on these surfaces. By extending the conventional AITM to consider the charge state of surface defects, we build the phase diagram of α-Fe2O3(0001) surfaces in relation to the Fermi energy as well as the oxygen chemical potential, which makes it possible to explain the influence of point defects on the surface morphology and to predict the existence of the experimentally observed functional sites such as the ferryl group (FeO) and oxygen vacancies. Our calculations show that the surface with the ferryl-termination exhibits the highest catalytic activity for CO oxidation with remarkably low activation energy (0.05 eV) and the largest exothermic reaction energy, while other surfaces with different terminations are inadequate with relatively high activation energies. Moreover, it is revealed that a Fermi energy increase by means of intrinsic or extrinsic n-type doping is beneficial to the formation of ferryl-termination under both oxygen-rich and oxygen-poor conditions, which promotes the catalytic oxidation of CO via the Eley-Rideal (E-R) mechanism only (O-rich) or in combination with the Mars-van Krevelen (MvK) mechanism (O-poor). Meanwhile, under the O-poor conditions, a Fermi energy decrease by p-type doping facilitates the formation of oxygen vacancies and the CO oxidation might be promoted via the MvK mechanism which is less effective with higher activation energy than the E-R mechanism. Our work provides new fundamental insights into CO oxidation chemistry and mechanisms, thereby contributing to the design of new catalysts with high performance and low cost.

Sintering Evolving Mn2O3-LaMnO3 Perovskite Heterointerfaces as Highly Active and Durable Catalysts for Catalytic Removal of Volatile Organic Compounds

Improving the catalyst performance for the thermal oxidation reaction faces the daunting challenge of the activity-stability trade-off. Herein, an evolved heterointerface was constructed on spherical Mn2O3 nanocatalysts to achieve exceptional stability while maintaining adequate activity by simply introducing La. The generation of the active Mn3O4-Mn2O3 heterointerfaces by La doping was experimentally observed, which further segregates to the surface during thermal aging and forms epitaxially grown heterostructured LaMnO3-Mn2O3 with Mn atoms. The former can act as highly active sites for the deep oxidation of VOCs due to the richness in oxygen vacancies and Mn4+ ions, while the latter acts as the diffusion barrier to inhibit grain growth and produce advantageous reactive electronic structures around the interface. The La-modified Mn2O3 oxide reached 90% conversion in toluene oxidation at 286 °C under the high WHSV of 240,000 mL g-1 h-1 and slightly increased to 327 °C after thermal aging at 800 °C. This work provides a versatile strategy for fabricating effective oxidation catalysts with high low-temperature activity and antisintering properties for industrial applications.

Computational screening on azafullerene-supported bifunctional single-atom catalysts for oxygen evolution and reduction reactions

Developing efficient bifunctional catalysts toward both the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) remains challenging. Herein, we systematically explored the catalytic activity of single-atom catalysts (SACs) for the OER and ORR with 27 transition metal atoms supported on pyrrolic/pyridinic azafullerenes C54N4 and C64N4 using first-principles calculations. The catalytic performance of these single-atom catalysts TM@azafullerenes is highly dependent on the number of electrons in the TM d-orbitals. Azafullerene-supported Rh, Ir, and Co catalysts show overpotentials comparable or even superior to those of TM-N4-graphene, emerging as promising candidates for bifunctional ORR and OER catalysts. Further bonding analysis shows that the TM-N bonds (TM = Rh, Co, and Ir) exhibit ionic characteristics, and ab initio molecular dynamics simulations (AIMD) demonstrate that these catalysts remain stable at 300 K. Descriptors, including the integrated crystal orbital Hamilton population and ϕ incorporating the d-orbital electron count and the electronegativity effectively elucidate the origins of the high catalytic activity for the ORR/OER. Our findings not only enrich the understanding of single-atom catalysts but also stimulate further development of novel fullerene-based SACs.

Metal-support interaction in supported Pt single-atom catalyst promotes lattice oxygen activation to achieve complete oxidation of acetone at low concentrations

A precious metal catalyst with loaded Pt single atoms was prepared and used for the complete oxidation of C3H6O. Detailed results show that the T100 of the 1.5Pt SA/γ-Al2O3 catalyst in the oxidation process of acetone is 250 °C, the TOF of Pt is 1.09 × 10-2 s-1, and the catalyst exhibits good stability. Characterization reveals that the high dispersion of Pt single atoms and strong interaction with the carrier improve the redox properties of the catalyst, enhancing the adsorption and dissociation capability of gaseous oxygen. DFT calculations show that after the introduction of Pt, the oxygen vacancy formation energy on the catalyst surface is reduced to 1.2 eV, and PDOS calculations prove that electrons on Pt atoms can be quickly transferred to O atoms, increasing the number of electrons on the σp * bond and promoting the escape of lattice oxygen. In addition, in situ DRIFTS and adsorption experiments indicate that the C3H6O oxidation process follows the Mars-van Krevelen reaction mechanism, and CH2 =C(CH3)=O(ads), O* (O2-), formate, acetate, and carbonate are considered as the main intermediate species and/or transients in the reaction process. Particularly, the activation rate of O2 and the cleavage of the -C-C- bond are the main rate-determining steps in the oxidation of C3H6O. This work will further enhance the study of the oxidation mechanism of oxygenated volatile organic pollutants over loaded noble metal catalysts.

Regulating Local Coordination Sphere of Ir Single Atoms at the Atomic Interface for Efficient Oxygen Evolution Reaction

Single-atom catalysts dispersed on an oxide support are essential for overcoming the sluggishness of the oxygen evolution reaction (OER). However, the durability of most metal single-atoms is compromised under harsh OER conditions due to their low coordination (weak metal-support interactions) and excessive disruption of metal-Olattice bonds to enable lattice oxygen participation, leading to metal dissolution and hindering their practical applicability. Herein, we systematically regulate the local coordination of Irsingle-atoms at the atomic level to enhance the performance of the OER by precisely modulating their steric localization on the NiO surface. Compared to conventional Irsingle-atoms adsorbed on NiO surface, the atomic Ir atoms partially embedded within the NiO surface (Iremb-NiO) exhibit a 2-fold increase in Ir-Ni second-shell interaction revealed by X-ray absorption spectroscopy (XAS), suggesting stronger metal-support interactions. Remarkably, Iremb-NiO with tailored coordination sphere exhibits excellent alkaline OER mass activity and long-term durability (degradation rate: ∼1 mV/h), outperforming commercial IrO2 (∼26 mV/h) and conventional Irsingle-atoms on NiO (∼7 mV/h). Comprehensive operando X-ray absorption and Raman spectroscopies, along with pH-dependence activity tests, identified high-valence atomic Ir sites embedded on the NiOOH surface during the OER followed the lattice oxygen mechanism, thereby circumventing the traditional linear scaling relationships. Moreover, the enhanced Ir-Ni second-shell interaction in Iremb-NiO plays a crucial role in imparting structural rigidity to Ir single-atoms, thereby mitigating Ir-dissolution and ensuring superior OER kinetics alongside sustained durability.

p-Block metal atom-induced spin state transition of Fe-N-C catalysts for efficient oxygen reduction

A deep understanding of the role of spin configurations of Fe-N-C catalysts in the adsorption and desorption of oxygen intermediates during ORRs is critical for the development of new catalysts for the ORR. Herein, we successfully implanted p-block metal single sites (SnN4, SbN4) into the Fe-N-C system to vary the spin states of Fe species and investigated the ORR performance of active metal centers with varying effective magnetic moments. Through a combination of zero-field cooling (ZFC) temperature-dependent magnetic susceptibility measurements and DFT calculations, we successfully established correlations between the spin state and ORR activity. Magnetic analysis reveals that the p-block metal catalytic sites can effectively induce a low-to-high (or medium) spin state transition of Fe centers. Consequently, the 3d orbital electrons in Fe,M-N-C catalysts penetrate the antibonding π-orbitals of oxygen more easily, thus optimizing the adsorption/desorption of key oxygen intermediates on Fe-N-C catalysts. As a result, the optimized Fe,M-N-C catalyst exhibits a half-wave potential of 0.97 V in a 0.1 M KOH electrolyte, as well as higher durability than conventional Pt/C catalysts. Moreover, the Fe,M-N-C catalysts show encouraging performance in a rechargeable Zn-air battery with high power density and long-term cyclability, indicating the practical applicability of these Fe,M-N-C catalysts.

The Reactivity of Ptn + Clusters With N2O Facilitated by Dual Lewis-Acid Sites

The size dependence of metal cluster reactions frequently reveals valuable information on the mechanism of nanometal catalysis. Here, the reactivity of the Ptn + (n = 1-40) clusters with N2O is studied and a significant dependence on the size of these clusters is noticed. Interestingly, the small Ptn + clusters like Pt3 + and Pt4 + are inclined to form N2O complexes; some larger clusters, such as Pt19 +, Pt21 +, and Pt23 +, appear to be unreactive; however, the others such as Pt3 , 9,15 + and Pt18 + are capable of decomposing N2O. While Pt9 + rapidly reacts with N2O to form a stable quasitetrahedron Pt9O+ product, Pt18 + experiences a series of N2O decompositions to produce Pt18O1-7 +. Utilizing high-precision theoretical calculations, it is shown how the atomic structures and active sites of Ptn + clusters play a vital role in determining their reactivity. Cooperative dual Lewis-acid sites (CDLAS) can be achieved on specific metal clusters like Pt18 +, rendering accelerated N2O decomposition via both N- and O-bonding on the neighboring Pt atoms. The influence of CDLAS on the size-dependent reaction of Pt clusters with N2O is illustrated, offering insights into cluster catalysis in reactions that include the donation of electron pairs.

Advancing Heterogeneous Organic Synthesis With Coordination Chemistry-Empowered Single-Atom Catalysts

For traditional metal complexes, intricate chemistry is required to acquire appropriate ligands for controlling the electron and steric hindrance of metal active centers. Comparatively, the preparation of single-atom catalysts is much easier with more straightforward and effective accesses for the arrangement and control of metal active centers. The presence of coordination atoms or neighboring functional atoms on the supports' surface ensures the stability of metal single-atoms and their interactions with individual metal atoms substantially regulate the performance of metal active centers. Therefore, the collaborative interaction between metal and the surrounding coordination environment enhances the initiation of reaction substrates and the formation and transformation of crucial intermediate compounds, which imparts single-atom catalysts with significant catalytic efficacy, rendering them a valuable framework for investigating the correlation between structure and activity, as well as the reaction mechanism of catalysts in organic reactions. Herein, comprehensive overviews of the coordination interaction for both homogeneous metal complexes and single-atom catalysts in organic reactions are provided. Additionally, reflective conjectures about the advancement of single-atom catalysts in organic synthesis are also proposed to present as a reference for later development.

Foam Ti Supported Pd Catalysts for the Selective Hydrogenation of Nitroaromatics

The selective hydrogenation of nitroaromatics plays an essential role in the chemical industry for the synthesis of anilines and their derivatives, which are known as crucial fine chemicals and pharmaceuticals. In this study, we demonstrate the preparation of Pd/Ti monolith catalyst containing well-isolated metallic Pd sites on Ti substrate through a simple impregnation method, showing remarkable catalytic properties in the selective hydrogenation of nitroaromatics containing various functional groups. Kinetic analyses reveal an apparent activation energy of 61 kJ/mol and the kinetic isotope effect (KH2/KD2) of ~1.7 in the hydrogenation of 3-chloronitrobenzene over Pd/Ti-200 ppm catalyst, indicating the facile dissociation of dihydrogen and the subsequent efficient hydrogenation. The Pd/Ti-200 ppm catalyst also demonstrates good stability and recyclability, maintaining its performance over multiple cycles. This simple but innovative approach not only enhances the efficiency of Pd catalysts in the selective hydrogenation of nitroaromatics but also offers significant potential for industrial applications in aniline production.

High-entropy intermetallics: emerging inorganic materials for designing high-performance catalysts

Alloy materials have been used as promising platforms to upgrade catalytic performance that cannot be achieved with conventional monometallic materials. As a result of numerous efforts, the recent progress in the field of alloy catalysis has been remarkable, and a wide range of new advanced alloys have been considered as potential electro/thermal catalysts. Among advanced alloy materials, high-entropy intermetallics are novel materials, and their excellent catalytic performance has recently been reported. High-entropy intermetallics have several advantages over disordered solid-solution high-entropy alloys, that is, greater structural/thermal stability, more facile site isolation, more precise control of electronic structures, tunability, and multifunctionality. A multidimensional compositional space is indeed limitless, but such a compositional space also provides a well-designed surface configuration because of its ordered nature. In this review, we will provide fundamental insights into high-entropy intermetallics, including thermodynamic properties, synthesis requirements, characterization techniques, roles in catalysis, and reaction examples. The comprehensive information provided in this review will highlight the great application potential of high-entropy intermetallics for catalysis, and will accelerate the development of this newly developed field.

Iron single atoms anchored on ultrathin carbon nitride photocatalyst for visible light-driven water decontamination

Graphitic carbon nitride has gained considerable attention as a visible-light photocatalyst. However, its photocatalytic efficiency is restricted by its limited capacity for absorbing visible light and swift recombination of charge carriers. To overcome this bottleneck, we fabricated an atomic Fe-dispersed ultrathin carbon nitride (Fe-UTCN) photocatalyst via one-step thermal polymerization. Fe-UTCN showed high efficiency in the photodegradation of acetaminophen (APAP), achieving > 90 % elimination within 60-min visible light irradiation. The anchoring of Fe atoms improved the photocatalytic activity of UTCN by narrowing the bandgap from 2.50 eV to 2.33 eV and suppressing radiative recombination. Calculations by density functional theory revealed that the Fe-N4 sites (adsorption energy of - 3.10 eV) were preferred over the UTCN sites (adsorption energy of - 0.18 eV) for the adsorption of oxygen and the subsequent formation of O2•-, the dominant reactive species in the degradation of APAP. Notably, the Fe-UTCN catalyst exhibited good stability after five successive runs and was applicable to complex water matrices. Therefore, Fe-UTCN, a noble-metal-free photocatalyst, is a promising candidate for visible light-driven water decontamination.

Regulating Second-Shell Coordination in Cobalt Single-Atom Catalysts toward Highly Selective Hydrogenation

Manipulating the local coordination environment of central metal atoms in single-atom catalysts (SACs) is a powerful strategy to exploit efficient SACs with optimal electronic structures for various applications. Herein, Co-SACs featured by Co single atoms with coordinating S atoms in the second shell dispersed in a nitrogen-doped carbon matrix have been developed toward the selective hydrogenation of halo-nitrobenzene. The location of the S atom in the model Co-SAC is verified through synchrotron-based X-ray absorption spectroscopy and theoretical calculations. The resultant Co-SACs containing second-coordination shell S atoms demonstrate excellent activity and outstanding durability for selective hydrogenation, superior to most precious metal-based catalysts. In situ characterizations and theoretical results verify that high activity and selectivity are attributed to the advantageous formation of the Co-O bond between p-chloronitrobenzene and Co atom at Co1N4-S moieties and the lower free energy and energy barriers of the reaction. Our findings unveil the correlation between the performance and second-shell coordination atom of SACs.

Stabilizing Few-Atom Platinum Clusters by Zinc Single-Atom-Glue for Efficient Anti-Markovnikov Alkene Hydrosilylation

Few-atom metal clusters (FAMCs) exhibit superior performance in catalyzing complex molecular transformations due to their special spatial environments and electronic states, compared to single-atom catalysts (SACs). However, achieving the efficient and accurate synthesis of FAMCs while avoiding the formation of other species, such as nanoparticles and SACs, still remains challenges. Herein, we report a two-step strategy for synthesis of few-atom platinum (Pt) clusters by predeposition of zinc single-atom-glue (Zn1) on MgO nanosheets (Ptn-Zn1/MgO), where FAMCs can be obtained over a wide range of Pt contents (0.09 to 1.45 wt %). Zn atoms can act as Lewis acidic sites to allow electron transfer between Zn and Pt through bridging O atoms, which play a crucial role in the formation and stabilization of few-atom Pt clusters. Ptn-Zn1/MgO exhibited a high selectivity of 93 % for anti-Markovnikov alkene hydrosilylation. Moreover, an excellent activity with a turnover frequency of up to 1.6×104 h-1 can be achieved, exceeding most of the reported Pt SACs. Further theoretical studies revealed that the Pt atoms in Ptn-Zn1/MgO possess moderate steric hindrance, which enables high selectivity and activity for hydrosilylation. This work presents some guidelines for utilizing atomic-scale species to increase the synthesis efficiency and precision of FAMCs.

Single Mn atom modulated molecular oxygen activation over TiO2 for photocatalytic formaldehyde oxidation

In single-atom catalysts, the atomically dispersed metal sites are pivotal for oxygen molecule activation. We hypothesize that dispersing single Mn atoms on TiO2 nanosheets may improve the photocatalytic oxidation of formaldehyde (HCHO) in the gas phase under ambient conditions. Density function theory (DFT) and experimental experiments were carried out to single Mn atoms not only improved the transfer of localized electrons and photogenerated electrons but also enhanced the activation/dissociation of O2 to generate monoatomic oxygen ions (O-) as the final reactive oxygen species (ROS). In photocatalytic experiments, Mn/TiO2 photocatalyst removed 100 % of HCHO at a low concentration of 7.6 ppm, and reaching excellent mineralization efficiency of over 99.6 %. According to the proposed reaction mechanism, O2 spontaneously adsorbs onto the Mn/TiO2 surface, forming two adsorbed O- after electron donation into the π2p* antibonding orbitals of O2. The adsorbed O- then reacts with gaseous HCHO to produce the key intermediate dioxymethylene (DOM), finally fulfilling a more favorable oxidation process on the Mn/TiO2 surface. This research illustrates the key role of O- in HCHO oxidation and paves the way for practical HCHO removal using TiO2-based photocatalysts.

Post-Formation of Fused Pentagonal Structure on Fjord Region of Polyaromatic Hydrocarbons under Hydrothermal Conditions

This study explores the synthesis of cyclopenta-fused polyaromatic hydrocarbons (CP-PAHs) via Pt-catalyzed cyclization in water, focusing on the formation of fused pentagonal rings within heavily fused PAH frameworks. Utilizing platinum catalysts at lower temperatures (200-260 °C) in water, led to the successful synthesis of singly cyclized CP-PAHs. The reaction conditions facilitated the mono-cyclization of substrates such as dibenzo[g,p]chrysene and its isomers, yielding the desired products while suppressing the formation of bis-cyclized compounds. The use of Fe2O3 as an additive in conjunction with PtO2 was effective to suppress hydrogenation of the substrates and products. The products exhibited a redshift in UV-visible absorption and photoluminescence bands due to a decrease in the HOMO-LUMO energy gap. These findings highlight the potential of Pt-catalyzed cyclization for the controlled synthesis of CP-PAHs, with implications for various applications in materials science.

Pd Single-Atom Loaded Ce-Zr Solid Solution Catalysts Prepared by Flame Spray Pyrolysis for Efficient CO Catalytic Oxidation

Single-atom catalysts (SACs) exhibit remarkable catalytic activity at each metal site. However, conventionally synthesized single-atom catalysts often possess low metal loading, thereby constraining their overall catalytic performance. Here, a flame spray pyrolysis (FSP) method for the synthesis of a single-atom catalyst with a high loading capacity of up to 1.4 wt.% in practice is reported. CeZrO2 acts as a carrier and provides a large number of anchoring sites, which promotes the high-density generation of Pd, and the strong interaction between the metal and the support avoids atom aggregation. Pd-CeZrO2 series catalysts have excellent CO oxidation performance. When 0.97 wt.% Pd is added, the catalytic activity is the highest, and the temperature can be reduced to 120 °C. This work presented here demonstrates that FSP, as an inherently scalable technique, allows for elevating the single-atom loading to achieve an increase in its catalytic performance. The method presented here more options for the preparation of SACs.

Waste Plastic-Supported Pd Single-Atom Catalyst for Hydrogenation

As worldwide plastic pollution continues to rise, innovative ideas for effective reuse and recycling of waste plastic are needed. Single-atom catalysts (SACs), which are known for their high activity and selectivity, present unique advantages in facilitating plastic degradation and conversion. Waste plastic can be used as a support or raw material to create SACs, which reduces waste generation while simultaneously utilizing waste as a resource. This work successfully utilized waste plastic polyurethane (PU) as a support, through a unique Rapid Thermal Processing Reactor (RTPR) to synthesize an efficient Pd1/PU SACs. At 25 °C and 0.5 MPa H2, Pd1/PU displayed outstanding activity and selectivity in the hydrogenation of styrene, as well as remarkable stability. Pd1/PU performed well in hydrogenating a variety of common substrates. These findings highlight the great potential of SACs in plastic waste reuse and recycling, offering intriguing solutions to the global plastic pollution problem.

Linking atomic to mesoscopic scales in multilevel structural tailoring of single-atom catalysts for peroxide activation

A key challenge in designing single-atom catalysts (SACs) with multiple and synergistic functions is to optimize their structure across different scales, as each scale determines specific material properties. We advance the concept of a comprehensive optimization of SACs across different levels of scale, from atomic, microscopic to mesoscopic scales, based on interfacial kinetics control on the coupled metal-dissolution/polymer-growth process in SAC synthesis. This approach enables us to manipulate the multilevel interior morphologies of SACs, such as highly porous, hollow, and double-shelled structures, as well as the exterior morphologies inherited from the metal oxide precursors. The atomic environment around the metal centers can be flexibly adjusted during the dynamic metal-oxide consumption and metal-polymer formation. We show the versatility of this approach using mono- or bi-metallic oxides to access SACs with rich microporosity, tunable mesoscopic structures and atomic coordinating compositions of oxygen and nitrogen in the first coordination-shell. The structures at each level collectively optimize the electronic and geometric structure of the exposed single-atom sites and lower the surface *O formation barriers for efficient and selective peroxidase-type reaction. The unique spatial geometric configuration of the edge-hosted active centers further improves substrate accessibility and substrate-to-catalyst hydrogen overflow due to tunable structural heterogeneity at mesoscopic scales. This strategy opens up new possibilities for engineering more multilevel structures and offers a unique and comprehensive perspective on the design principles of SACs.

Structural Design of Single-Atom Catalysts for Enhancing Petrochemical Catalytic Reaction Process

Petroleum, as the "lifeblood" of industrial development, is the important energy source and raw material. The selective transformation of petroleum into high-end chemicals is of great significance, but still exists enormous challenges. Single-atom catalysts (SACs) with 100% atom utilization and homogeneous active sites, promise a broad application in petrochemical processes. Herein, the research systematically summarizes the recent research progress of SACs in petrochemical catalytic reaction, proposes the role of structural design of SACs in enhancing catalytic performance, elucidates the catalytic reaction mechanisms of SACs in the conversion of petrochemical processes, and reveals the high activity origins of SACs at the atomic scale. Finally, the key challenges are summarized and an outlook on the design, identification of active sites, and the appropriate application of artificial intelligence technology is provided for achieving scale-up application of SACs in petrochemical process.

Atomic Pt Sites Anchored in the Interface between Grains on Vacancy-Enriched CeO2 Nanosheets: One-Step Precursor Combustion Synthesis

Atomic metal catalysts have unique electronic, structural, and catalytic properties, which are widely used in the field of catalysis. However, designing new simple synthesis methods to fabricate atomic metal catalysts is a challenge in catalytic applications. Herein, a one-step precursor combustion strategy is presented that starts directly from precursors of metal salts, using a spontaneous combustion process convert platinum nitrate to atomic Pt sites. The atomic Pt sites with low valence are anchored in the formed interface between grains on vacancy-enriched CeO2 nanosheets. The obtained Pt/CeO2-2 catalyst exhibits much higher three-way catalytic activities at low temperatures than Pt/CeO2-C catalysts prepared using the traditional impregnation method. Density functional theory calculations show that the generated lower valent Pt atoms in the CeO2 interface promote catalytic activity through reducing the energy barrier, and lead to an overall improvement of three-way catalytic activities. This facile strategy provides new insights into the study of the properties and applications of atomic noble metal catalysts.

Selective Orbital Coupling: An Adsorption Mechanism in Single-Atom Catalysis

Quantitative understanding of the chemisorption on single-atom catalysts (SACs) by their electronic properties is crucial for the catalyst design. However, the physical mechanism is still under debate. Here, the CO catalytic oxidation on single transition metal (i.e., Sc, Ti, V, Cr, Mn, Fe, Co, Ni) dopants is used as a theoretical model to explore the correlations between the characteristics of electronic structures and the chemisorption on SACs. For these metal dopants, their atomic d orbitals form several nondegenerate and localized electronic states that are found to be selectively coupled with the π* orbital of the adsorbed O2, which we defined as selective orbital coupling. Based on the selective orbital coupling, we find that the alignment between the selected d state and the π* state determines the bond strength, regardless of the electron occupation number of the selected d states; the electron transfer to form M-O bonding can be provided by the support. Such electron transfer can be related with the electronic metal-support interaction. We attribute the origin of the chemisorption mechanism to the coexistence of the localized orbital of the single transition metal and the continuous energy band of the Au support. Finally, we illustrate how this mechanism dominates the variation trend of the reaction barriers. Our results unravel a fundamental adsorption mechanism in SAC systems.

Emerging single-atom catalysts in the detection and purification of contaminated gases

Single atom catalysts (SACs) show exceptional molecular adsorption and electron transfer capabilities owing to their remarkable atomic efficiency and tunable electronic structure, thereby providing promising solutions for diverse important processes including photocatalysis, electrocatalysis, thermal catalysis, etc. Consequently, SACs hold great potential in the detection and degradation of pollutants present in contaminated gases. Over the past few years, SACs have made remarkable achievements in the field of contaminated gas detection and purification. In this review, we first provide a concise introduction to the significance and urgency of gas detection and pollutant purification, followed by a comprehensive overview of the structural feature identification methods for SACs. Subsequently, we systematically summarize the three key properties of SACs for detecting contaminated gases and discuss the research progress made in utilizing SACs to purify polluted gases. Finally, we analyze the enhancement mechanism and advantages of SACs in polluted gas detection and purification, and propose strategies to address challenges and expedite the development of SACs in polluted gas detection and purification.

Suppressing Metal Leaching and Sintering in Hydroformylation Reaction by Modulating the Coordination of Rh Single Atoms with Reactants

Hydroformylation reaction is one of the largest homogeneously catalyzed industrial processes yet suffers from difficulty and high cost in catalyst separation and recovery. Heterogeneous single-atom catalysts (SACs), on the other hand, have emerged as a promising alternative due to their high initial activity and reasonable regioselectivity. Nevertheless, the stability of SACs against metal aggregation and leaching during the reaction has rarely been addressed. Herein, we elucidate the mechanism of Rh aggregation and leaching by investigating the structural evolution of Rh1@silicalite-1 SAC in response to different adsorbates (CO, H2, alkene, and aldehydes) by using diffuse reflectance infrared Fourier transform spectroscopy, X-ray adsorption fine structure, and scanning transmission electron microscopy techniques and kinetic studies. It is discovered that the aggregation and leaching of Rh are induced by the strong adsorption of CO and aldehydes on Rh, as well as the reduction of Rh3+ by CO/H2 which weakens the binding of Rh with support. In contrast, alkene effectively counteracts this effect by the competitive adsorption on Rh atoms with CO/aldehyde, and the disintegration of Rh clusters. Based on these results, we propose a strategy to conduct the reaction under conditions of high alkene concentration, which proves to be able to stabilize Rh single atom against aggregation and/or leaching for more than 100 h time-on-stream.

Stabilizing Single-Atom Pt on Fe2O3 Nanosheets by Constructing Oxygen Vacancies for Ultrafast H2 Sensing

Single-atom catalysts (SACs) hold great promise in highly sensitive and selective gas sensors due to their ultrahigh atomic efficiency and excellent catalytic activity. However, due to the extremely high surface energy of SACs, it is still a huge challenge to synthesize a stable single-atom metal on sensitive materials. Here, we report an atomic layer deposition (ALD) strategy for the elaborate synthesis of single-atom Pt on oxygen vacancy-rich Fe2O3 nanosheets (Pt-Fe2O3-Vo), which displayed ultrafast and sensitive detection to H2, achieving the stability of Pt single atoms. Gas-sensing investigation showed that the Pt-Fe2O3-Vo materials enabled a significantly enhanced response of 26.5-50 ppm of H2, which was 17-fold higher than that of pure Fe2O3, as well as ultrafast response time (2 s), extremely low detection limit (86 ppb), and improved stability. The experimental and density functional theory (DFT) studies revealed that the abundant oxygen vacancy sites of Fe2O3 contributed to stabilizing the Pt atoms via electron transfer. In addition, the stabilized Pt atoms also greatly promote the electron transfer of H2 molecules to Fe2O3, thereby achieving an excellent H2 sensing performance. This work provides a potential strategy for the development of highly selective and stable chemical sensors.

Probing Coordination Number of Single-Atom Catalysts by d-Band Center-Regulated Luminescence

It is essential to probe the coordination number (CN) because it is a crucial factor to ensure the catalytic capability of single-atom catalysts (SACs). Currently, synchrotron X-ray absorption spectroscopy (XAS) is widely used to measure the CN. However, the scarcity of synchrotron X-ray source and complicated data analysis restrict its wide applications in determining the CN of SACs. In this contribution, we have developed a d-band center-regulated acetone cataluminescence (CTL) probe for a rapid screening of the CN of Pt-SACs. It is disclosed that the CN-triggered CTL is attributed to the fact that the increased CN could induce the downward shift of d-band center position, which assists the acetone adsorption and promotes the subsequent catalytic reaction. In addition, the universality of the proposed acetone-CTL probe is verified by determining the CN of Fe-SACs. This work has opened a new avenue for exploring an alternative to synchrotron XAS for the determination of CN of SACs and even conventional metal catalysts through d-band center-regulated CTL.

Nickel Single Atom Density-Dependent CO2 Efficient Electroreduction

The transition metal-nitrogen-carbon (M─N─C) with MNx sites has shown great potential in CO2 electroreduction (CO2RR) for producing high value-added C1 products. However, a comprehensive and profound understanding of the intrinsic relationship between the density of metal single atoms and the CO2RR performance is still lacking. Herein, a series of Ni single-atom catalysts is deliberately designed and prepared, anchored on layered N-doped graphene-like carbon (x Ni1@NG-900, where x represents the Ni loading, 900 refers to the temperature). By modulating the precursor, the density of Ni single atoms (DNi) can be finely tuned from 0.01 to 1.19 atoms nm-2. The CO2RR results demonstrate that the CO faradaic efficiency (FECO) predominantly increases from 13.4% to 96.2% as the DNi increased from 0 to 0.068 atoms nm-2. Then the FECO showed a slow increase from 96.2% to 98.2% at -0.82 V versus reversible hydrogen electrode (RHE) when DNi increased from 0.068 to 1.19 atoms nm-2. The theoretical calculations are in good agreement with experimental results, indicating a trade-off relationship between DNi and CO2RR performance. These findings reveal the crucial role of the density of Ni single atoms in determining the CO2RR performance of M─N─C catalysts.

Synergistic enhancement of electrocatalytic nitroarene hydrogenation over Mo2C@MoS2 heteronanorods with dual active-sites

Electrocatalytic hydrogenation (ECH) enables the sustainable production of chemicals under ambient conditions, in which catalysts catering for the different chemisorption of reactants/intermediates are desired but still challenging. Here, Mo2C@MoS2 heteronanorods with dual active-sites are developed to accomplish efficient nitroarene ECH according to our theoretical prediction that the binding of atomic H and nitro substrates would be synergistically strengthened on Mo2C-MoS2 interfaces. They afford high faradaic efficiency (>85%), yield (>78%) and selectivity (>99%) for the reduction of 4-nitrostyrene (4-NS) to 4-vinylaniline (4-VA) in neutral electrolytes, outperforming not only the single-component counterparts of Mo2C nanorods and MoS2 nanosheets, but also recently reported noble-metals. Accordingly, in situ Raman spectroscopy combined with electrochemical tests clarifies the rapid ECH of 4-NS on Mo2C-MoS2 interfaces due to the facilitated elementary steps, quickly refreshing active sites for continuous electrocatalysis. Mo2C@MoS2 further confirms efficient and selective ECH toward functional anilines with other well-retained reducible groups in wide substrate scope, underscoring the promise of dual-site engineering for exploring catalysts.

Site-specific metal-support interaction to switch the activity of Ir single atoms for oxygen evolution reaction

The metal-support interactions (MSI) could greatly determine the electronic properties of single-atom catalysts, thus affecting the catalytic performance. However, the typical approach to regulating MSI usually suffers from interference of the variation of supports or sacrificing the stability of catalysts. Here, we effectively regulate the site-specific MSI of Ir single atoms anchored on Ni layered double hydroxide through an electrochemical deposition strategy. Cathodic deposition drives Ir atoms to locate at three-fold facial center cubic hollow sites with strong MSI, while anodic deposition drives Ir atoms to deposit onto oxygen vacancy sites with weak MSI. The mass activity and intrinsic activity of Ir single-atom catalysts with strong MSI towards oxygen evolution reaction are 19.5 and 5.2 times that with weak MSI, respectively. Mechanism study reveals that the strong MSI between Ir atoms and the support stimulates the activity of Ir sites by inducing the switch of active sites from Ni sites to Ir sites and optimizes the adsorption strength of intermediates, thereby enhancing the activity.

Ethylene Methoxycarbonylation over Heterogeneous Pt1/MoS2 Single-Atom Catalyst: Metal-Support Concerted Catalysis

Ethylene methoxycarbonylation (EMC) to methyl propanoate (MP) is an industrially important reaction and commercially uses a homogeneous Pd-phosphine organometallic complex as the catalyst and corrosive strong acid as the promoter. In this work, we develop a Pt1/MoS2 heterogeneous single-atom catalyst (SAC) which exhibits high activity, selectivity, and good recyclability for EMC reaction without need of any liquid acid. The production rate of MP achieves 0.35 gMP gcat-1 h-1 with MP selectivity of 91.1% at 1 MPa CO, 1 MPa C2H4, and 160 °C, which can be doubled at 2 MPa CO and corresponds to 320.1 molMP molPt-1 h-1, at least 1 order of magnitude higher than the earlier reported heterogeneous catalyst and even comparable to some of homogeneous catalyst. Advanced characterizations and DFT calculations reveal that all the Pt single atoms are located at the Mo vacancies along the Mo edge of the MoS2 nanosheets, forming pocket-like Mo-S-Pt1-S-Mo ensembles with uniform and well-defined structure. Methanol is first adsorbed and dissociated on Mo sites, and the produced H spillovers to the adjacent Pt site forming Pt-H species which then activate ethylene, forming Pt-ethyl species. Meanwhile, CO adsorbed on the other Mo site reacts with the Pt-ethyl species, yielding propionyl species, and this carbonylation is the rate-determining step. The final methoxylation step proceeds via the nucleophilic attack of propionyl species by -OCH3 affording the final product MP. Such a metal-support concerted catalysis enabled by the Mo-S-Pt1-S-Mo multisite ensemble opens a new avenue for SACs to promote the multimolecular reactions that prevail in homogeneous catalysis.

A replacement strategy for regulating local environment of single-atom Co-SxN4-x catalysts to facilitate CO2 electroreduction

The performances of single-atom catalysts are governed by their local coordination environments. Here, a thermal replacement strategy is developed for the synthesis of single-atom catalysts with precisely controlled and adjustable local coordination environments. A series of Co-SxN4-x (x = 0, 1, 2, 3) single-atom catalysts are successfully synthesized by thermally replacing coordinated N with S at elevated temperature, and a volcano relationship between coordinations and catalytic performances toward electrochemical CO2 reduction is observed. The Co-S1N3 catalyst has the balanced COOH*and CO* bindings, and thus locates at the apex of the volcano with the highest performance toward electrochemical CO2 reduction to CO, with the maximum CO Faradaic efficiency of 98 ± 1.8% and high turnover frequency of 4564 h-1 at an overpotential of 410 mV tested in H-cell with CO2-saturated 0.5 M KHCO3, surpassing most of the reported single-atom catalysts. This work provides a rational approach to control the local coordination environment of the single-atom catalysts, which is important for further fine-tuning the catalytic performance.

Nanoscale Metal Particle Modified Single-Atom Catalyst: Synthesis, Characterization, and Application

Single-atom catalysts (SACs) have attracted considerable attention in heterogeneous catalysis because of their well-defined active sites, maximum atomic utilization efficiency, and unique unsaturated coordinated structures. However, their effectiveness is limited to reactions requiring active sites containing multiple metal atoms. Furthermore, the loading amounts of single-atom sites must be restricted to prevent aggregation, which can adversely affect the catalytic performance despite the high activity of the individual atoms. The introduction of nanoscale metal particles (NMPs) into SACs (NMP-SACs) has proven to be an efficient approach for improving their catalytic performance. A comprehensive review is urgently needed to systematically introduce the synthesis, characterization, and application of NMP-SACs and the mechanisms behind their superior catalytic performance. This review first presents and classifies the different mechanisms through which NMPs enhance the performance of SACs. It then summarizes the currently reported synthetic strategies and state-of-the-art characterization techniques of NMP-SACs. Moreover, their application in electro/thermo/photocatalysis, and the reasons for their superior performance are discussed. Finally, the challenges and perspectives of NMP-SACs for the future design of advanced catalysts are addressed.

Layer Growth Inhibiting Strategy for Superior-Loading Atomic Metal Sites on Ultrathin Layered Double Hydroxides as the Efficient Chemiluminescence Probes

Owing to the remarkable catalytic attributes, single-atom catalysts (SACs) have exhibited promising application prospects as the substitutes of natural enzymes. However, the low loading amount of atomic sites on typical SACs (no more than 5 wt %) significantly restricts their increased capability. Hereby, a layer growth inhibitor protocol was attempted to optimize anchoring isolated Co atoms efficiently on ultrathin monolayer layered double hydroxides (LDHs). Superior to the conventional multiple-layer LDHs, the synthesized monolayer LDHs (7.29 nm-thick) served as the emerging support for dispersing substantial active sites and featured a dramatic loading content of 32.5 wt %. Through X-ray absorption spectroscopy, the atomically dispersed active centers on Co SACs were verified as Co-N4 moieties. The results of radical scavenger experiments and electron paramagnetic resonance spectroscopy showed that Co SACs were favorable to the high yield of reactive oxygen species originating from the decomposition of H2O2. Therefore, Co SACs functioned as a sensitive enhancer to drastically boost the luminol-H2O2 chemiluminescence intensity by ∼4713-fold, which excelled drastically over these previously reported SACs. Furthermore, Co SACs were adopted as chemiluminescent probes for the quantitation of chlorothalonil, wherein a low detection limit of 49 pg mL-1 (3σ) was achieved. Additionally, the successful application in recovery trials demonstrated the favorable feasibility of Co SACs. The facile layer growth inhibitor protocol affords SACs with improved loading properties and even superior catalytic performances for sensitive luminescent bioassays.

Active sites of atomically dispersed Pt supported on Gd-doped ceria with improved low temperature performance for CO oxidation

"Single - atom" catalysts (SACs) have been the focus of intense research, due to debates about their reactivity and challenges toward determining and designing "single - atom" (SA) sites. To address the challenge, in this work, we designed Pt SACs supported on Gd-doped ceria (Pt/CGO), which showed improved activity for CO oxidation compared to its counterpart, Pt/ceria. The enhanced activity of Pt/CGO was associated with a new Pt SA site which appeared only in the Pt/CGO catalyst under CO pretreatment at elevated temperatures. Combined X-ray and optical spectroscopies revealed that, at this site, Pt was found to be d-electron rich and bridged with Gd-induced defects via an oxygen vacancy. As explained by density functional theory calculations, this site opened a new path via a dicarbonyl intermediate for CO oxidation with a greatly reduced energy barrier. These results provide guidance for rationally improving the catalytic properties of SA sites for oxidation reactions.

Unveiling Interfacial Effects for Efficient and Stable Hydrogen Evolution Reaction on Ruthenium Nanoparticles-Embedded Pentlandite Composites

Heterogenous catalysis is important for future clean and sustainable energy systems. However, an urgent need to promote the development of efficient and stable hydrogen evolution catalysts still exists. In this study, ruthenium nanoparticles (Ru NPs) are in situ grown on Fe5 Ni4 S8 support (Ru/FNS) by replacement growth strategy. An efficient Ru/FNS electrocatalyst with enhanced interfacial effect is then developed and successfully applied for pH-universal hydrogen evolution reaction (HER). The Fe vacancies formed by FNS during the electrochemical process are found to be conducive to the introduction and firm anchoring of Ru atoms. Compared to Pt atoms, Ru atoms get easily aggregated and then grow rapidly to form NPs. This induces more bonding between Ru NPs and FNS, preventing the fall-off of Ru NPs and maintaining the structural stability of FNS. Moreover, the interaction between FNS and Ru NPs can adjust the d-band center of Ru NPs, as well as balance the hydrolytic dissociation energy and hydrogen binding energy. Consequently, the as-prepared Ru/FNS electrocatalyst exhibits excellent HER activity and improved cycle stability under pH-universal conditions. The developed pentlandite-based electrocatalysts with low cost, high activity, and good stability are promising candidates for future applications in water electrolysis.

Coordination engineering of atomically dispersed zirconium on graphene for the oxygen reduction reaction

We study the effect of boron and sulfur doping on graphene with atomically dispersed zirconium as an electrocatalyst for the oxygen reduction reaction (ORR) by using density functional theory (DFT). The use of Zr as a metal center offers a highly stable catalyst due to the high electronegativity difference between Zr and its ligand. The origin of the ORR activity improvement has been investigated thoroughly. Here, we proposed a novel geometric descriptor for an atomically dispersed zirconium on a nitrogen-doped graphene catalyst with an axial oxygen ligand, which is the fractional coordination number of the Zr atom. We found that the fractional coordination number can successfully describe the shift of the dz2 band center in the doped compound, which is related to the binding energy of the Zr to the O ligand. We also found that the oxygen ligand is mobile during the adsorption process of ORR intermediates, and hence it is imperative for the axial oxygen ligand to bind neither too strongly nor too weakly to the Zr atom. The coordination engineering strategy can successfully enhance the ORR activity, shifting the ORR overpotential from 0.75 V and 0.92 V to 0.33 V and 0.32 V. This study provides new insights into the origin of ORR activity by connecting the novel geometric descriptor to the electronic structure and finally it is connected to the ORR activity.

Stabilizing Pt Single Atoms through Pt-Se Electron Bridges on Vacancy-enriched Nickel Selenide for Efficient Electrocatalytic Hydrogen Evolution

Rational design of Pt single-atom catalysts provides a promising strategy to significantly improve the electrocatalytic activity for hydrogen evolution reaction. In this work, we presented a novel and efficient strategy for utilizing the low electron-density region of substrate to effectively trap and confine high electron-density metal atoms. The Pt single-atom catalyst supported by nickel selenide with rich vacancies was prepared via a hydrothermal-impregnation stepwise approach. Through experimental testation and DFT theoretical calculation, we confirm that Pt single atoms are well distributed at cationic vacancies of nickel selenide with loading amount of 3.2 wt. %. Moreover, the atomic Pt combined with the high electronegative Se to form Pt-Se bond as a "bridge" between single atoms and substrate for fast electron translation. This novel catalyst shows an extremely low overpotential of 45 mV at 10 mA cm-2 and an excellent stability over 120 h. Furthermore, the nickel selenide supported Pt SACs exhibits long-term stability for practical application, which maintains a high current density of 390 mA cm-2 over 80 h with a retention of 99 %. This work points a promising direction for designing single atoms catalysts with high catalytic activity and stability for advanced green energy conversion technologies.

Engineering of Local Coordination Microenvironment in Single-Atom Catalysts Enabling Sustainable Conversion of Biomass into a Broad Range of Amines

Utilizing renewable biomass as a substitute for fossil resources to produce high-value chemicals with a low carbon footprint is an effective strategy for achieving a carbon-neutral society. Production of chemicals via single-atom catalysis is an attractive proposition due to its remarkable selectivity and high atomic efficiency. In this work, a supramolecular-controlled pyrolysis strategy is employed to fabricate a palladium single-atom (Pd1 /BNC) catalyst with B-doped Pd-Nx atomic configuration. Owing to the meticulously tailored local coordination microenvironment, the as-synthesized Pd1 /BNC catalyst exhibits remarkable conversion capability for a wide range of biomass-derived aldehydes/ketones. Thorough characterizations and density functional theory calculations reveal that the highly polar metal-N-B site, formed between the central Pd single atom and its adjacent N and B atoms, promotes hydrogen activation from the donor (reductants) and hydrogen transfer to the acceptor (C═O group), consequently leading to exceptional selectivity. This system can be further extended to directly synthesize various aromatic and furonic amines from renewable lignocellulosic biomass, with their greenhouse gas emission potentials being negative in comparison to those of fossil-fuel resource-based amines. This research presents a highly effective and sustainable methodology for constructing C─N bonds, enabling the production of a diverse array of amines from carbon-neutral biomass resources.

Atomic Insights into Synergistic Nitroarene Hydrogenation over Nanodiamond-Supported Pt1 -Fe1 Dual-Single-Atom Catalyst

Fundamental understanding of the synergistic effect of bimetallic catalysts is of extreme significance in heterogeneous catalysis, but a great challenge lies in the precise construction of uniform dual-metal sites. Here, we develop a novel method for constructing Pt1 -Fe1 /ND dual-single-atom catalyst, by anchoring Pt single atoms on Fe1 -N4 sites decorating a nanodiamond (ND) surface. Using this catalyst, the synergy of nitroarenes selective hydrogenation is revealed. In detail, hydrogen is activated on the Pt1 -Fe1 dual site and the nitro group is strongly adsorbed on the Fe1 site via a vertical configuration for subsequent hydrogenation. Such synergistic effect decreases the activation energy and results in an unprecedented catalytic performance (3.1 s-1 turnover frequency, ca. 100 % selectivity, 24 types of substrates). Our findings advance the applications of dual-single-atom catalysts in selective hydrogenations and open up a new way to explore the nature of synergistic catalysis at the atomic level.

Phase-dependent growth of Pt on MoS2 for highly efficient H2 evolution

Crystal phase is a key factor determining the properties, and hence functions, of two-dimensional transition-metal dichalcogenides (TMDs)1,2. The TMD materials, explored for diverse applications3-8, commonly serve as templates for constructing nanomaterials3,9 and supported metal catalysts4,6-8. However, how the TMD crystal phase affects the growth of the secondary material is poorly understood, although relevant, particularly for catalyst development. In the case of Pt nanoparticles on two-dimensional MoS2 nanosheets used as electrocatalysts for the hydrogen evolution reaction7, only about two thirds of Pt nanoparticles were epitaxially grown on the MoS2 template composed of the metallic/semimetallic 1T/1T' phase but with thermodynamically stable and poorly conducting 2H phase mixed in. Here we report the production of MoS2 nanosheets with high phase purity and show that the 2H-phase templates facilitate the epitaxial growth of Pt nanoparticles, whereas the 1T' phase supports single-atomically dispersed Pt (s-Pt) atoms with Pt loading up to 10 wt%. We find that the Pt atoms in this s-Pt/1T'-MoS2 system occupy three distinct sites, with density functional theory calculations indicating for Pt atoms located atop of Mo atoms a hydrogen adsorption free energy of close to zero. This probably contributes to efficient electrocatalytic H2 evolution in acidic media, where we measure for s-Pt/1T'-MoS2 a mass activity of 85 ± 23 A [Formula: see text] at the overpotential of -50 mV and a mass-normalized exchange current density of 127 A [Formula: see text] and we see stable performance in an H-type cell and prototype proton exchange membrane electrolyser operated at room temperature. Although phase stability limitations prevent operation at high temperatures, we anticipate that 1T'-TMDs will also be effective supports for other catalysts targeting other important reactions.

Performance Regulation of Single-Atom Catalyst by Modulating the Microenvironment of Metal Sites

Metal-based catalysts, encompassing both homogeneous and heterogeneous types, play a vital role in the modern chemical industry. Heterogeneous metal-based catalysts usually possess more varied catalytically active centers than homogeneous catalysts, making it challenging to regulate their catalytic performance. In contrast, homogeneous catalysts have defined active-site structures, and their performance can be easily adjusted by modifying the ligand. These characteristics lead to remarkable conceptual and technical differences between homogeneous and heterogeneous catalysts. As a recently emerging class of catalytic material, single-atom catalysts (SACs) have become one of the most active new frontiers in the catalysis field and show great potential to bridge homogeneous and heterogeneous catalytic processes. This review documents a brief introduction to SACs and their role in a range of reactions involving single-atom catalysis. To fully understand process-structure-property relationships of single-atom catalysis in chemical reactions, active sites or coordination structure and performance regulation strategies (e.g., tuning chemical and physical environment of single atoms) of SACs are comprehensively summarized. Furthermore, we discuss the application limitations, development trends and future challenges of single-atom catalysis and present a perspective on further constructing a highly efficient (e.g., activity, selectivity and stability), single-atom catalytic system for a broader scope of reactions.

Single-atomic platinum on fullerene C60 surfaces for accelerated alkaline hydrogen evolution

The electrocatalytic hydrogen evolution reaction (HER) is one of the most studied and promising processes for hydrogen fuel generation. Single-atom catalysts have been shown to exhibit ultra-high HER catalytic activity, but the harsh preparation conditions and the low single-atom loading hinder their practical applications. Furthermore, promoting hydrogen evolution reaction kinetics, especially in alkaline electrolytes, remains as an important challenge. Herein, Pt/C₆₀ catalysts with high-loading, high-dispersion single-atomic platinum anchored on C₆₀ are achieved through a room-temperature synthetic strategy. Pt/C₆₀-2 exhibits high HER catalytic performance with a low overpotential (η₁₀) of 25 mV at 10 mA cm^-2. Density functional theory calculations reveal that the Pt-C₆₀ polymeric structures in Pt/C₆₀-2 favors water adsorption, and the shell-like charge redistribution around the Pt-bonding region induced by the curved surfaces of two adjacent C₆₀ facilitates the desorption of hydrogen, thus favoring fast reaction kinetics for hydrogen evolution.