Nanoconfinement Effects in Electrocatalysis and Photocatalysis

Recently, the enzyme-inspired nanoconfinement effect has garnered significant attention for enhancing the efficiency of electrocatalysts and photocatalysts. Despite substantial progress in these fields, there remains a notable absence of comprehensive and insightful articles providing a clear understanding of nanoconfined catalysts. This review addresses this gap by delving into nanoconfined catalysts for electrocatalytic and photocatalytic energy conversion. Initially, the effect of nanoconfinement on the thermodynamics and kinetics of reactions is explored. Subsequently, the primary and secondary structures of nanoconfined catalysts are categorized, their properties are outlined, and typical methods for their construction are summarized. Furthermore, an overview of the state-of-the-art applications of nanoconfined catalysts is provided, focusing on reactions of hydrogen and oxygen evolution, oxygen reduction, carbon dioxide reduction, hydrogen peroxide production, and nitrogen reduction. Finally, the current challenges and future prospects in nanoconfined catalysts are discussed. This review aims to provide in-depth insights and guidelines to advance the development of electrocatalytic and photocatalytic energy conversion technology by nanoconfined catalysts.

Exploring the properties, types, and performance of atomic site catalysts in electrochemical hydrogen evolution reactions

Atomic site catalysts (ASCs) have recently gained prominence for their potential in the electrochemical hydrogen evolution reaction (HER) due to their exceptional activity, selectivity, and stability. ASCs with individual atoms dispersed on a support material, offer expanded surface areas and increased mass efficiency. This is because each atom in these catalysts serves as an active site, which enhances their catalytic activity. This review is focused on providing a detailed analysis of ASCs in the context of the HER. It will delve into their properties, types, and performance to provide a comprehensive understanding of their role in electrochemical HER processes. The introduction part underscores HER's significance in transitioning to sustainable energy sources and emphasizes the need for innovative catalysts like ASCs. The fundamentals of the HER section emphasizes the importance of understanding the HER and highlights the key role that catalysts play in HER. The review also explores the properties of ASCs with a specific emphasis on their atomic structure and categorizes the types based on their composition and structure. Within each category of ASCs, the review discusses their potential as catalysts for the HER. The performance section focuses on a thorough evaluation of ASCs in terms of their activity, selectivity, and stability in HER. The performance section assesses ASCs in terms of activity, selectivity, and stability, delving into reaction mechanisms via experimental and theoretical approaches, including density functional theory (DFT) studies. The review concludes by addressing ASC-related challenges in HER and proposing future research directions, aiming to inspire further innovation in sustainable catalysts for electrochemical HER.

An environmentally adaptive gold single-atom catalyst with variable valence states

Single-atom catalysts revolutionize catalysis by maximizing atomic efficiency and enhancing reaction specificity, offering high activity and selectivity with minimal material usage, which is crucial for sustainable processes. However, the unique properties that distinguish single-atom catalysts from other forms, including bulk and nanoparticle catalysts, as well as the physical mechanisms behind their high activity and selectivity, remain unclear, limiting their broader application. Here, through first-principles calculations, we have identified an environmentally adaptive gold single-atom catalyst on a CeO2(111) surface capable of adjusting its valence state in response to different environmental conditions. This adaptability enables the catalyst to simultaneously maintain high stability and activity. In a CO gas atmosphere, numerous oxygen vacancies form on the CeO2(111) surface, where Au single atoms stably adsorb, exhibiting a negative oxidation state that deactivates the catalyst. In an O2 atmosphere, these vacancies are filled, causing the Au single atoms to adsorb onto lattice oxygen and become oxidized to a positive oxidation state, thereby reactivating the catalyst. Under CO oxidation reaction conditions, the Au single atoms oscillate between these positive and negative oxidation states, effectively facilitating the CO oxidation process. These findings provide new insights into the unique properties and high performance of single-atom catalysts, contributing to a better understanding and utilization of these catalysts in various applications.

Light-driven propane dehydrogenation by a single-atom catalyst under near-ambient conditions

Propane dehydrogenation is an energy-intensive industrial reaction that requires high temperatures (550-750 °C) to overcome thermodynamic barriers. Here we overcome these limits and demonstrate that near-ambient propane dehydrogenation can be achieved through photo-thermo-catalysis in a water-vapour environment. We reduce the reaction temperature to 50-80 °C using a single-atom catalyst of copper supported on TiO2 and a continuous-flow fixed-bed reactor. The mechanism differs from conventional propane dehydrogenation in that hydrogen is produced from the photocatalytic splitting of water vapour, surface-bound hydroxyl radicals extract propane hydrogen atoms to form propylene without over-oxidation, and water serves as a catalyst. This route also works for the dehydrogenation of other small alkanes. Moreover, we demonstrate sunlight-driven water-catalysed propane dehydrogenation operating at reaction temperatures as low as 10 °C. We anticipate that this work will be a starting point for integrating solar energy usage into a wide range of high-temperature industrial reactions.

Pt/α-MoC Catalyst Boosting pH-Universal Hydrogen Evolution Reaction at High Current Densities

Constructing subnanometric electrocatalysts is an efficient method to synergistically accelerate H2O dissociation and H+ reduction for pH-universal hydrogen evolution reaction (HER) for industrial water electrolysis to produce green hydrogen. Here, we construct a subnanometric Pt/α-MoC catalyst, where the α-MoC component can dissociate water effectively, with the rapid proton release kinetics of Pt species on Pt/α-MoC to obtain a good HER performance at high current densities in all-pH electrolytes. Quasi-in situ X-ray photoelectron spectroscopy analyses and density functional theory calculations confirm the highly efficient water dissociation capability of α-MoC and the thermodynamically favorable desorption process of hydrolytically dissociated protons on Pt sites at the high current density. Consequently, Pt/α-MoC requires only a low overpotential of 125 mV to achieve a current density of 1000 mA cm-2. Moreover, a Pt/α-MoC-based proton exchange membrane water electrolysis device exhibits a low cell voltage (1.65 V) and promising stability over 300 h with no performance degradation at an industrial-level current density of 1 A cm-2. Notably, even at a current of 100 A, the cell voltage remains low at 2.15 V, demonstrating Pt/α-MoC's promising potential as a scalable alternative for industrial hydrogen production. These findings elucidate the synergistic mechanism of α-MoC and atomically dispersed Pt in promoting efficient HER, offering valuable guidance for the design of electrocatalysts in high current density hydrogen.

Reconstructed rich oxygen defects and Ag0 on Pr6O11 surface through interface-defect engineering for enhanced electrochemical carbon dioxide reduction

The design of catalysts for electrochemical CO2 reduction (ECR) is a key challenge for achieving efficient conversion of CO2 into fuels. By concentrating on the active sites of the surface, the strategy of interface and defect engineering has proven effective in enhancing reactivity. Herein, we developed a new Ag/Pr6O11 nanocomposite catalyst with rich interfaces and oxygen defect structures, which induced the in-situ formation of more oxygen vacancies and Ag0 on Pr6O11 during the initial period of ECR. The catalyst exhibits a Faradaic efficiency of 98% for the conversion of CO2 to CO and a mass activity of 48.4 A g-1 at the overpotential of -1.09 V. The metal-support interface active sites and oxygen vacancy defects at the Ag/Pr6O11 interface enhance interfacial catalytic activity and promote CO2 adsorption and activation. Additionally, in-situ infrared and Raman spectroscopy confirmed that the presence of oxygen vacancies and the interface-modified Ag/Pr6O11 enhanced the local microenvironment on the catalyst surface. This improvement accelerated the adsorption and conversion of the key intermediate *COOH, thereby increasing the intrinsic activity of the ECR process and contributing to the inhibitory effect on the hydrogen evolution reaction (HER). This straight forward strategy of interface integration and surface reconstruction offers a potentially versatile approach for guiding the design of ECR electrocatalysts.

Enhancing hydride formation and transfer for catalytic hydrogenation via electron-deficient single-atom silver

Metal hydrides are sensitive to H2O and O2, which reduces the atom efficiency of the hydride donors. Silver (Ag) is an inexpensive coinage metal; however, its lower activity compared to gold, platinum, and palladium limits its application in catalytic hydrogenation. Here, electron-deficient metallic single-atom Ag (AgSA) was loaded onto γ-Al2O3 using a benzoquinone- and KNO3- assisted photolysis approach. The obtained AgSA/Al2O3 catalyst exhibited high rates, high tolerance to side reactions with O2 and H2O, and high NaBH4 atomic efficiency for the catalytic hydrogenation of nitroaromatics in aqueous media. It showed a low kinetic barrier for B-H activation, leading to silver hydride formation and nitrobenzene hydrogenation, while presenting a high kinetic barrier for OH activation, which inhibited H2 production. This behavior contrasts with that of Ag-nanoparticle-loaded γ-Al2O3. The high activity of AgSA is attributed to its electron-deficient nature and atomic dispersion, whereas its high selectivity is possibly ascribed to the involvement of a dihydrogen bond-containing intermediate. Our findings highlight the potential of AgSA to modulate the formation and reactivity of silver hydrides.

Dry-Solid-Electrochemical Synthesis: A General Method for Large Scale Synthesis of Single-Atom Catalysts with High Metal loadings

Single-atom catalysts (SACs) with high metal loadings are highly desirable but still challenging for large scale synthesis. Here we report a new technique named as dry-solid-electrochemical synthesis (DSES) for a general large-scale synthesis of SACs with high metal loadings in an energy-conservation and environment-friendly way. With it, a series of pure carbon-supported metal SACs (Platinum up to 35.0 wt %, Iridium 21.2 wt %, Ruthenium 20.4 wt % and Iron 17.6 wt %) with high metal loadings were obtained. Particularly, a Pt SAC with Pt 23.9 wt % and remarkable oxygen reduction reaction (ORR) performance in fuel cells is synthesized on kilogram scale. Based on multiple control experiments, a unique redox mechanism for DSES process is proposed: metal precursors on conductive supports are reduced to metals via a homolytic cleavage of metal-halogen bonds by the attacking of electrons flowing through the dry solid phase. Such versatile technique paves a new economical and environment-friendly pathway for fabricating high-metal-loading SACs or atomic dispersion catalysts.

Precisely Tailoring the Second Coordination Sphere of a Cobalt Single-Atom Catalyst for Selective Hydrogenation of Halogenated Nitroarenes

The development of highly efficient and cost-effective nonprecious metal catalysts for the selective hydrogenation of halogenated nitroarenes is very appealing yet challenging. Here, we demonstrate that the hydrogenation activity and selectivity of Co single-atom catalyst (SAC) can be tuned by tailoring the structure of second coordination sphere via P doping. As revealed by synchrotron radiation-based X-ray absorption spectroscopy characterizations, such a P doping on N-coordinated Co SAC results in the unsymmetric Co-N4P1 coordination structure. With a combination of experimental characterizations and theoretical simulations, we find that tailoring the second coordination sphere can greatly improve H2 dissociation and product desorption. As a result, the Co-N4P1 SAC exhibits superior activity, selectivity and stability for the hydrogenation of halogenated nitroarenes to corresponding amines (20 examples, >99 % yields) at 80 °C under 0.5 MPa H2 pressure, significantly outperforming most heterogeneous catalysts reported in the literature. We expect that this work opens a new avenue for the design of highly efficient nonprecious metal SACs for important hydrogenation reactions.

Optimized synergistic effects in sweat glucose detection with a Pt single-atom catalyst on NiO for fingertip wearable biosensors

For the approximately 8.5 % of the global population living with diabetes, puncture-based glucose testing is often an unpleasant experience. Non-invasive sweat glucose testing not only reduces pain and the risk of wound infection but also offers a more suitable method for real-time glucose monitoring. In this study, we developed a fingertip wearable biosensor (FWB) capable of continuously measuring glucose levels in sweat, providing valuable data for assessing glucose concentrations in humans. We successfully synthesized NiO/Pt single-atom catalysts (NiO/Pt SAs) using a UV reduction technique, achieving a detection range of 5 μM to 2 mM that encompasses the full spectrum of physiological glucose levels. Additionally, incorporating 0.075 g of starch enhanced the hydrogel's water absorption and swelling properties, allowing it to absorb over 832 % of its dry weight without breaking, thereby improving sweat absorption efficiency. We also designed an annular microfluidic channel for rapid sweat transport. The circular design fits snugly on the fingertip surface, minimizing footprint and increasing comfort. This makes the device more stable in real-world use and minimizes the effects of external movements or environmental changes. Experimental results confirmed the feasibility of using the FWB to detect glucose in sweat samples from volunteers. We believe our research holds significant promise for advancements in sweat analysis and health monitoring, presenting a novel and efficient approach for continuous glucose monitoring.

Structure-activity relationships in the development of single atom catalysts for sustainable organic transformations

Single atom catalysts (SACs), which can provide the combined benefits of homogeneous and heterogeneous catalysts, are a revolutionary concept in the field of material research. The highly exposed catalytic surfaces, unsaturated sites, as well as unique structural and electronic properties of SACs have the potential to catalyze numerous reactions with unmatched efficiency and durability when stabilized on a suitable support. In this review, we have provided an intuitive insight into the strategies adopted in the last 5 years for morphology control of SACs to know about its impact on metal-support interaction and various organic transformations with special reference to metal oxides, alloys, metal-organic frameworks (MOFs) and carbon-based supports. This review also includes a brief description of unparalleled potentials of SACs and the recent advances in the catalysis of industrially important organic transformations, with special emphasis on the C-C cross-coupling reaction, biomass conversion, hydrogenation, oxidation and click chemistry. This unprecedented and unique perspective will highlight the interactions occurring within SACs that are responsible for their high catalytic efficiency, which will potentially benefit various organic transformations. We have also suggested plausible synergy of various other concepts such as defect engineering and piezocatalysis with SACs, which can provide a new direction to sustainable chemistry. A good understanding of the different types of metal-support interactions will help researchers develop morphology-controlled SACs with tunable properties and establish mechanisms for their exceptional catalytic behaviour in industrially important organic transformations.

Effects of oxygen vacancies on hydrogenation efficiency by spillover in catalysts

Hydrogen spillover is crucial for hydrogenation reactions on supported catalysts. The properties of supports have been reported to be very important for affecting hydrogen spillover and the subsequent hydrogenation process. The introduction of oxygen vacancies offers a promising strategy to enhance efficiency of catalysts. Recent advanced characterization and theoretical modeling techniques have provided us with increasing new insights for understanding hydrogen spillover effects. However, a comprehensive understanding of oxygen vacancy effects on hydrogen spillover and hydrogenation efficiency of catalysts is still lacking. This review focuses on the recent advances in support effects especially oxygen vacancy effects on improving the efficiency of catalysts from three process aspects including hydrogen dissociation, active hydrogen spillover, and hydrogenation by spillover. The challenges in studying the effects on hydrogenations by spillover on the supported catalysts are highlighted at the end of the review. It aims to provide valuable strategies for the development of high-performance catalytic hydrogenation materials.

Recycling Sulfur-Poisoned Pd Catalysts via Thermal Atomization for Semi-Hydrogenation of Acetylene

Palladium catalysts are highly efficient for a variety of chemical industrial processes but are prone to being affected by poisons during practical application. Sulfur is one of the major poisons in Pd-based catalysts. The recycling of deeply poisoned Pd species like Pd sulfides is challenging due to the strong Pd-S bond. Herein, we proposed a top-down strategy to degrade Pd sulfides and create Pd single-atom sites simultaneously by one-step thermal atomization. Pd4S model nanoparticles were successfully converted to Pd single-atom sites supported on nitrogen and sulfur-codoped carbon (Pd1/N, S-C) after loading them on ZIF-8 and thermal treatment. PdZn intermediates were formed during the atomization process. Density functional theory revealed that the formation of PdZn helped the generation of vacancies adjacent to metal nanoparticles, which prompted the atomization process. This strategy can be facilely applied to the atomization of sulfur-poisoned commercial Pd/C, which shows the potential for recycling commercial catalysts. The optimal Pd1/N, S-C catalyst showed good activity and much enhanced selectivity than Pd4S for the semi-hydrogenation of acetylene.

"Suspended" Single Rhenium Atoms on Nickel Oxide for Efficient Electrochemical Oxidation of Glucose

Well-defined single-atom catalysts (SACs) serve as ideal model systems for directly comparing experimental results with theoretical calculations, offering profound insights into heterogeneous catalytic processes. However, precisely designing and controllably synthesizing SACs remain challenging due to the unpredictable structure evolution of active sites and generation of embedded active sites, which may bring about steric hindrance during chemical reactions. Herein, we present the precious nonpyrolysis synthesis of Re SACs with a well-defined phenanthroline coordination supported by NiO (Re1-phen/NiO). Multiple experimental characterizations together with theoretical calculations unravel the idea that the isolated Re atoms are suspended on the NiO surface, connected by phenanthroline ligands standing perpendicular to the surface. This unique structure provides the Re1-phen/NiO SAC with a strong capability to activate glucose molecules, enabling fully exposed Re=O double bonds in an open-ended reaction environment to simultaneously react with hydroxyl and aldehyde groups at both ends of the glucose molecule, rapidly forming glucaric acid.

Efficient Methanol Oxidation Kinetics Enabled by an Ordered Heterocatalyst with Dual Electric Fields

Induced by a sharp-tip-enhanced electric field, periodical nanoassemblies can regulate the reactant flux on the electrode surface, efficiently optimizing the mass transfer kinetics in electrocatalysis. However, when the nanoscale building blocks in homoassemblies are arranged densely, it results in the overlap and reduction of the local electric field. Herein, we present a comprehensive kinetic heteromodel that simultaneously couples the sharp-tip-enhanced electric field and charge transfer electric field between different building blocks with any arrangement densities. The dual electric fields drive the diffusion of reactants from the bulk solution to the electrode surface, significantly enhancing mass transfer kinetics along the horizontal and longitudinal directions, which promotes the electrocatalytic activity significantly. Moreover, the wide generality of the model is further confirmed by electrochemical experiments involving various electrocatalytic systems and catalysts. Therefore, this work highlights the significant role of dual electric fields in electrocatalysis, which is expected to facilitate the development of customized and outstanding catalysts in the future.

Current status of developed electrocatalysts for water splitting technologies: from experimental to industrial perspective

The conversion of electricity into hydrogen (H2) gas through electrochemical water splitting using efficient electrocatalysts has been one of the most important future technologies to create vast amounts of clean and renewable energy. Low-temperature electrolyzer systems, such as proton exchange membrane water electrolyzers, alkaline water electrolyzers, and anion exchange membrane water electrolyzers are at the forefront of current technologies. Their performance, however, generally depends on electricity costs and system efficiency, which can be significantly improved by developing high-performance electrocatalysts to enhance the kinetics of both the cathodic hydrogen evolution reaction and the anodic oxygen evolution reaction. Despite numerous active research efforts in catalyst development, the performance of water electrolysis remains insufficient for commercialization. Ongoing research into innovative electrocatalysts and an understanding of the catalytic mechanisms are critical to enhancing their activity and stability for electrolyzers. This is still a focus at academic institutes/universities and industrial R&D centers. Herein, we provide an overview of the current state and future directions of electrocatalysts and water electrolyzers for electrochemical H2 production. Additionally, we describe in detail the technological framework of electrocatalysts and water electrolyzers for H2 production as utilized by relevant global companies.

Palladium Single Atom-supported Covalent Organic Frameworks for Aqueous-phase Hydrogenative Hydrogenolysis of Aromatic Aldehydes via Hydrogen Heterolysis

Developing a method for the tandem hydrogenative hydrogenolysis of bio-based furfuryl aldehydes to methylfurans is crucial for synthesizing sustainable biofuels and chemicals; however, it poses a challenge due to the easy hydrogenation of the C=C bond and difficult cleavage of the C-O bond. Herein, a palladium (Pd) single-atom-supported covalent organic framework was fabricated and showed a unique 2,5-dimethylfuran yield of up to 98.2 % when reacted with 5-methyl furfuryl aldehyde in an unprecedented water solvent at 30 °C. Furthermore, it exhibited excellent catalytic universality while converting various furfuryl-, benzyl-, and heterocyclic aldehydes at room temperature. The analysis of the catalytic mechanism confirmed that H2 was heterolytically activated on the Pd-N pair and triggered the keto-enol tautomerism of the covalent organic frameworks (COFs) host, resulting in H--Pd⋅⋅⋅O-H+ sites. These sites served as novel asymmetric hydrogenation sites for the C=O group and hydrogenolysis sites for the C-OH group through a scarce SN2 mechanism. This study demonstrated remarkable bifunctional catalysis through the H2-induced keto-enol tautomerism of COF catalysts for the atypical preparation of methyl aromatics in a water solvent at room temperature.

Porous Silicon-Supported Catalytic Materials for Energy Conversion and Storage

Porous silicon (Si) has a tetrahedral structure similar to that of sp3-hybridized carbon atoms in a typical diamond structure, which affords it unique chemical and physical properties including an adjustable intrinsic bandgap, a high-speed carrier transfer efficiency. It has shown great potential in photocatalysis, rechargeable batteries, solar cells, detectors, and electrocatalysis. This review introduces various porous Si-supported electrocatalysts and analyzes the reasons why porous Si is used as a new carrier/active sites from the perspectives of its molecular structure, electronic properties, synthesis methods, etc. The electrochemical applications of porous Si-based electrocatalysts in energy conversion reactions such as hydrogen evolution reaction, oxygen evolution reaction, oxygen reduction reaction, and total water decomposition together with lithium-ion battery and supercapacitor in energy storage are summarized. The challenges and future research directions for porous Si are also discussed. This review aims to deepen the understanding of porous Si and promote the development and applications of this new type of Si material.

A Versatile Strategy for the Controlled Synthesis of Atomically Precise Palladium Nanoclusters

The study of the structures, applications, and structure-property relationships of atomically precise metal nanoclusters relies heavily on their controlled synthesis. Although great progress has been made in the controlled synthesis of Group 11 (Cu, Ag, Au) metal nanoclusters, the preparation of Pd nanoclusters remains a grand challenge. Herein, a new, simple, and versatile synthetic strategy for the controlled synthesis of Pd nanoclusters is reported with tailorable structures and functions. The synthesis strategy involves the controllable transformations of Pd4(CO)4(CH3COO)4 in air, allowing the discovery of a family of Pd nanoclusters with well-defined structure and high yield. For example, by treating the Pd4(CO)4(CH3COO)4 with 2,2-dipyridine ligands, two clusters of Pd4 and Pd10 whose metal framework describes the growth of vertex-sharing tetrahedra have been selectively isolated. Interestingly, chiral Pd4 nanoclusters can be gained by virtue of customized chiral pyridine-imine ligands, thus representing a pioneering example to shed light on the hierarchical chiral nanostructures of Pd. This synthetic methodology also tolerates a wide variety of ligands and affords phosphine-ligated Pd nanoclusters in a simple way. It is believed that the successful exploration of the synthetic strategy would simulate the research enthusiasm on both the synthesis and application of atomically precise Pd nanoclusters.

Boosting Enzyme-Like Activity Through Controlled Coordination of Metal Single-Atoms in Rhombic Cavity of Graphyne

The coordination number of metal single-atoms, being an important factor, should be precisely controlled as it affects both activity and specificity. Herein, the introduction of nitrogen into the para position of benzene in graphyne (2N-GY) is proposed as a carrier for anchoring metal single-atoms onto pyrazine nitrogen. These atoms are then coordinated to the center of the rhombic cavity, ensuring precisely controlled coordination numbers. Inspired by natural enzymes, a series of transition metal single-atom nanozymes (SANs) are constructed utilizing 2N-GY. Both theory calculations and experiments demonstrated that the incorporation of metal single-atoms of Fe, Mn, and Mo effectively augmented the enzyme-like activity, with Mo/GY exhibiting the highest peroxidase -like activity. Based on the differing activities of M/GY (M = Fe, Mn, Mo) and the varying abilities of sulfhydryl groups in biothiols to occupy metal active sites, sensing arrays for the high-throughput identification of six biothiols are constructed. After combining the fingerprint feature responses of biothiols and SANs with machine learning algorithms, the efficient distinction of the six biothiols is achieved. This study introduces a novel pathway for designing and synthesizing SANs that mimic natural enzymes.

Photocatalytic Methanol Dehydrogenation with Switchable Selectivity

Switchable selectivity achieved by altering reaction conditions within the same photocatalytic system offers great advantages for sustainable chemical transformations and renewable energy conversion. In this study, we investigate an efficient photocatalytic methanol dehydrogenation with controlled selectivity by varying the concentration of nickel cocatalyst, using zinc indium sulfide nanocrystals as a semiconductor photocatalyst, which enables the production of either formaldehyde or ethylene glycol with high selectivity. Control experiments revealed that formaldehyde is initially generated and can either serve as a terminal product or intermediate in producing ethylene glycol, depending on the nickel concentration in the solution. Mechanistic studies suggest a unique role of ionic nickel as an additional photoelectron competitor that can significantly influence selectivity, alongside its well-established function as a hydrogen evolution reaction cocatalyst under photocatalytic conditions. The demonstrated switchable selectivity provides a new tool for producing diverse products from methanol, while advancing the understanding of cocatalyst behavior for versatile catalytic performance.

Ferromagnetic Fe-TiO2 spin catalysts for enhanced ammonia electrosynthesis

Magnetic field effects (MFE) of ferromagnetic spin electrocatalysts have attracted significant attention due to their potential to enhance catalytic activity under an external magnetic field. However, no ferromagnetic spin catalysts have demonstrated MFE in the electrocatalytic reduction of nitrate for ammonia (NO3RR), a pioneering approach towards NH3 production involving the conversion from diamagnetic NO3- to paramagnetic NO. Here, we report the ferromagnetic Fe-TiO2 to investigate MFE on NO3RR. Fe-TiO2 possesses a high density of atomically dispersed Fe sites and exhibits an intermediate-spin state, resulting in magnetic ordering through ferromagnetism. Assisted by a magnetic field, Fe-TiO2 achieves a Faradaic efficiency (FE) of up to 97% and an NH3 yield of 24.69 mg mgcat-1 at -0.5 V versus reversible hydrogen electrode. Compared to conditions without an external magnetic field, the FE and NH3 yield for Fe-TiO2 under an external magnetic field is increased by ~21.8% and ~ 3.1 times, respectively. In-situ characterization and theoretical calculations show that spin polarization enhances the critical step of NO hydrogenation to NOH by optimizing electron transfer pathways between Fe and NO, significantly boosting NO3RR activity.

Isolated Metal Centers Activate Small Molecule Electrooxidation: Mechanisms and Applications

Electrochemical oxidation of small molecules shows great promise to substitute oxygen evolution reaction (OER) or hydrogen oxidation reaction (HOR) to enhance reaction kinetics and reduce energy consumption, as well as produce high-valued chemicals or serve as fuels. For these oxidation reactions, high-valence metal sites generated at oxidative potentials are typically considered as active sites to trigger the oxidation process of small molecules. Isolated atom site catalysts (IASCs) have been developed as an ideal system to precisely regulate the oxidation state and coordination environment of single-metal centers, and thus optimize their catalytic property. The isolated metal sites in IASCs inherently possess a positive oxidation state, and can be more readily produce homogeneous high-valence active sites under oxidative potentials than their nanoparticle counterparts. Meanwhile, IASCs merely possess the isolated metal centers but lack ensemble metal sites, which can alter the adsorption configurations of small molecules as compared with nanoparticle counterparts, and thus induce various reaction pathways and mechanisms to change product selectivity. More importantly, the construction of isolated metal centers is discovered to limit metal d-electron back donation to CO 2p* orbital and reduce the overly strong adsorption of CO on ensemble metal sites, which resolve the CO poisoning problems in most small molecules electro-oxidation reactions and thus improve catalytic stability. Based on these advantages of IASCs in the fields of electrochemical oxidation of small molecules, this review summarizes recent developments and advancements in IASCs in small molecules electro-oxidation reactions, focusing on anodic HOR in fuel cells and OER in electrolytic cells as well as their alternative reactions, such as formic acid/methanol/ethanol/glycerol/urea/5-hydroxymethylfurfural (HMF) oxidation reactions as key reactions. The catalytic merits of different oxidation reactions and the decoding of structure-activity relationships are specifically discussed to guide the precise design and structural regulation of IASCs from the perspective of a comprehensive reaction mechanism. Finally, future prospects and challenges are put forward, aiming to motivate more application possibilities for diverse functional IASCs.

Coordination Equilibrium-Assisted Coprecipitation Synthesis of Atomically Dispersed 3d Metal Catalysts

As a frontier of heterogeneous catalysis, single-atom catalysts (SACs) have been extensively studied fundamentally. One obstacle that limits the industrial application of SACs is the lack of a synthetic method that can prepare the catalysts on a large scale. Wet-chemistry methods that are conventionally used to prepare nanoparticle-based industrial catalysts might be a solution. In this work, we report a coprecipitation method using ethylenediaminetetraacetic acid (EDTA) as an equilibrium regulator to synthesize a series of atomically dispersed 3d metal over the Mg(OH)2 support. Mg(OH)2 is formed from the spontaneous dissolution of MgO, which is also the alkali source for coprecipitation to occur. The dissolution-precipitation equilibria of metal hydroxides compete with the coordination equilibria of EDTA-coordinated metal cations, leading to the coprecipitation of loaded metal and Mg2+ cations. The synthetic strategy is applicable for Fe, Co, Ni, and Cu, forming four catalysts that are active for the photodegradation of methylene blue under visible light.

Asymmetric Coupled Binuclear-Site Catalysts for Low-Temperature Selective Acetylene Semi-Hydrogenation

Heterogeneous metal catalysts with bifunctional active sites are widely used in chemical industries. Although their improvement process is typically based on trial-and-error, it is hindered by the lack of model catalysts. Herein, we report an effective vacancy-pair capturing strategy to fabricate 12 heterogeneous binuclear-site catalysts (HBSCs) comprising combinations of transition metals on titania. During the synthesis of these HBSCs, proton-passivation treatment and step-by-step electrostatic anchorage enabled the suppression of single-atom formation and the successive capture of two target metal cations on the titanium-oxygen vacancy-pair site. Additionally, during acetylene hydrogenation at 20 °C, the HBSCs (e.g., Pt1Pd1-TiO2) consistently generated more than two times the ethylene produced by their single-atom counterparts (e.g., Pd1-TiO2). Furthermore, the Pt1Pd1 binuclear sites in Pt1Pd1-TiO2 were demonstrated to catalyze C2H2 hydrogenation via a bifunctional active-site mechanism: initially C2H2 chemisorb on the Pt1 site, then H2 dissociates and migrates from Pd1 to Pt1, and finally hydrogenation occurs at the Pt1-Pd1 interface.

Bottom-up approaches to prepare ultrathin TiO2 nanosheets

Atomically thin two-dimensional (2D) materials are promising platforms to explore the unusual physical and chemical properties in surface chemistry, various catalysis, and devices. Most 2D materials derive from inherently layer-structured compounds through top-down exfoliation, but it is usually challenging to directly prepare ultrathin nanosheets of non-layered materials. TiO2 contains at least 8 non-layered polymorphs, and some of them have found wide applications in heterogeneous catalysis, photocatalysis, solar cells, lithium-ion batteries, etc. In this review, we summarize typical bottom-up wet-chemistry synthetic systems of atomically thin TiO2 nanosheets. The synthesis protocols are discussed in groups of different phases, and the growth mechanisms are classified into three approaches of strong ligand confinement, layered intermediate, and templated synthesis.

Crystallization of 2D TiO2 Nanosheets via Oriented Attachment of 1D Coordination Polymer

Demystifying the molecular mechanism of growth is vital for the rational design, synthesis, and optimization of functional nanomaterials. Despite the promising perspectives and extensive efforts, the growth mechanism of atomically thin TiO2(B) nanosheets remains unclear, hence it is difficult to tune their band and surface structures. Herein, we report an oriented attachment-based crystallization mechanism of TiO2(B) nanosheets from a 1D titanium glycolate coordination polymer through hydrolysis and condensation. With time-tracking experiments, this 1D coordination polymer is found to be an intermediate in the synthesis of TiO2(B) nanosheets by using Ti alkoxides and chlorides as precursors, suggesting the universality of the 1D-to-2D growth mechanism. Such a side-to-side attachment pathway bridges the classical and nonclassical interpretations of crystallization, and meanwhile hints at the possibility of other 1D complexes as potential precursors for 2D materials.

General synthesis of neighboring dual-atomic sites with a specific pre-designed distance via an interfacial-fixing strategy

A potential non-precious metal catalyst for oxygen reduction reaction should contain metal-N4 moieties. However, most of the current strategies to regulate the distances between neighboring metal sites are not pre-designed but depend on the probability by tuning the metal loading or the support. Herein, we report a general method for the synthesis of neighboring metal-Nx moieties (metal = Fe, Cu, Co, Ni, Zn, and Mn) via an interfacial-fixing strategy. Specifically, polydopamine is used to coat nanotemplates made of metal oxides, followed by pyrolysis to form a metal-oxide skeleton coated by rich nitrogen-doped carbon shells. After chemically etching the skeleton, only interfacial metal atoms strongly bonded with the support via nitrogen atoms are retained. The high purity (>95%) of dual Fe sites was confirmed by both the direct visualization of local regions and the indirect evidence of the averaged information. When these neighboring metal-Nx moieties are applied for oxygen reduction reaction, Fe-Nx moieties exhibit the superior activity, even outperforming commercial Pt/C in the aspects of the half-wave potential, methanol tolerance, carbon monoxide tolerance, and robustness.

Synergetic Modulation of Electronic Properties of Cobalt Oxide via "Tb" Single Atom for Uphill Urea and Water Electrolysis

Exploring single-atom (SA) catalysts in hybrid urea-assisted water electrolysis offers a viable alternative to both Hydrogen (H2) generation and polluted water treatment. However, the unfavorable electronic stabilization, low SA content, intrinsically slow kinetics, and imbalanced adsorption-desorption steps are the bottleneck for its scale-up implementation. Herein, a rare-earth Terbium single atom (TbSA) is topologically stabilized on defect-rich Co3O4 (TbSA@d-Co3O4) by Tb─O co-ordination for urea oxidation reaction (UOR) and H2 evolution reaction (HER). Benefitting from the strong TbSA interaction with the d-Co3O4, the TbSA@d-Co3O4 achieves a 10 mA cm-2 current density at 1.27 V and -35 mV for UOR and HER, respectively. Remarkably, when TbSA@d-Co3O4 is applied as a bi-functional catalyst in a two-electrode system, it merely requires 1.22 V to acquire 10 mA cm-2 with excellent operational stability for 100 h. The hybrid electrolyzer can be successfully empowered by the triboelectric nanogenerator, AA battery, and solar panel with a nominal potential of 1.5 V. The mechanistic investigation predicts "TbSA" insertion in d-Co3O4 lowered the potential determining step, attributed to balanced reaction energetics for adsorption-desorption of intermediates and favorable charge transfer characteristics for UOR. This work offers a new paradigm to explore the catalytic properties of rare-earth "f-block" elements to create advanced electrocatalysts via structural modulation.

Converting CO2 Into Natural Gas Within the Autoclave: A Kinetic Study on Hydrogenation of Carbonates in Aqueous Solution

Catalytic conversion of carbon dioxide (CO2) into value-added chemicals is of pivotal importance, well the cost of capturing CO2 from dilute atmosphere is super challenge. One promising strategy is combining the adsorption and transformation at one step, such as applying alkali solution that could selectively reduce carbonate (CO3 2-) as consequences of CO2 adsorption. Due to complexity of this system, the mechanistic details on controlling the hydrogenation have not been investigated in depth. Herein, Ru/TiO2 catalyst was applied as a probe to elucidate the mechanism of CO3 2- activation, in which with thermodynamic and kinetic investigations, a compact Langmuir-Hinshelwood reaction model was established which suggests that the overall rate of CO3 2- hydrogenation was controlled by a specific C-O bond rupture elementary step within HCOO- and the Ru surface was mainly covered by CO3 2- or HCOO- at independent conditions. This assumption was further supported by negligible kinetic isotope effects (kH/kD≈1), similarity on reaction barriers of CO3 2- and HCOO- hydrogenation (ΔH≠ hydr,Na2CO3 and ΔH≠ hydr,HCOONa) and a non-variation of entropy (ΔS≠ hydr≈0). More interestingly, the alkalinity of the solution is certainly like a two sides in a sword and could facilitate the adsorption of CO2 while hold back catalysis during CO3 2- hydrogenation.

Ring-shaped cavity anchor Pt to derive Pt/WO3-x heterointerfaces for efficient hydrogen evolution in acidic water and seawater

Developing novelplatinum (Pt)-based hydrogen evolution reaction (HER) catalysts with high activity and stability is significant for the ever-broader applications of hydrogen energy. However, achieving precise modulation of the ultrafine Pt nanoparticles coordination environment in conventional catalysts is challenging. In this work, we developed a unique "ring-shaped cavity induced" strategy to anchor the Ptx through the ring-shaped cavity of polyoxometalates (POMs) Na33H7P8W48O184 (denoted as P8W48). The NayPtx[P8W48O184] (PtxP8W48) was in-situ converted into abundant Pt/WO3-x heterostructure with Pt (∼2 nm) and highly depressed Pt-O-W heterointerfaces. Pt/WO3-x nanoparticles supported on highly conductive rGO exhibit superior HER activity. The overpotentials of the catalyst are only 2.8 mV and 4.7 mV at 10 mA·cm-2 in acidic water and seawater, far superior to commercial 20 % Pt/C catalyst. Additionally, the catalyst can be stabilized at a current density of 30 mA·cm-2 for 180 h. This study provides a feasible strategy for rational design of Pt-based catalysts for renewable energy applications.

Single-Atom Electron Pumps Over Transition Metal Chalcogenides Boosting Photocatalysis

Cocatalyst is of paramount significance to provide fruitful active sites for suppressing the spatial charge recombination toward boosted photocatalysis. Up to date, exploration of robust and stable cocatalysts is remained challenging. Inspired by the intrinsic merits of single-atom catalysts (SACs), such as distinctive electronic structure and high atomic utilization efficiency, single-atom/transition metal chalcogenides (TMCs) is utilized as a model to synthesize CdS-Pd single-atom catalyst (CdS-PdSA) heterostructures. This demonstrates the precise anchoring of isolated metal single-atom catalysts (SACs) onto TMCs through a simple yet effective wet-chemical strategy. The resulting heterostructures exhibit significantly enhanced and stable photocatalytic activity for selective anaerobic organic transformations and hydrogen production under visible light. This enhancement is primarily inferred due to the role of Pd SACs as electron pumps, which directionally trap the electrons photoexcited over CdS, accelerating the spatial charge separation and prolonging the carrier lifespan. The charge transport route and photocatalytic mechanism are elucidated. This work underscores the potential of SACs as cocatalysts in heterogeneous photocatalysis, offering valuable insights for the rational design of atomic-level cocatalysts for solar-to-chemical energy conversion and beyond.

Evolution of Nitrogen-Coordinated Metal Single Atoms Toward Single-Atom Alloys on MgH₂ as Efficient and Stable Hydrogen Spillover Catalysts

M-N-C catalysts with nitrogen-coordinated metal single-atom active sites have demonstrated high activity for hydrogen storage materials, but their stability in this application remains uncertain. This study addresses this issue by using nickel phthalocyanine (NiPc) molecules on MgH₂ particles as a model system. It is found that the N-coordinated high-valence Ni single atoms in the NiN₄ active site are unstable in the reducing environment of hydrogen storage, spontaneously evolving into zero-valence Ni, forming a Ni₁-Mg single-atom alloy (SAA). The Ni₁-Mg SAA exhibits remarkable stability in catalyzing Mg hydrogen storage reactions. Furthermore, it demonstrates comprehensive catalytic activity for each step of hydrogen absorption and desorption from Mg, surpassing the efficiency of the NiN₄ active site, especially in the critical steps of hydrogenation and dehydrogenation. Overall, the catalytic performance of Ni₁-Mg SAA is superior to most known nickel-based catalysts. This evolutionary process is also observed in FePc, CoPc, and tetraphenylporphyrin nickel (Ni-TPP), suggesting that this reducing transformation is a universal phenomenon for MN₄-type active sites in hydrogen storage catalysis.

Sabatier Principle Driving Interface Defect Engineering on 3D Graphene-Like Encapsulated Cobalt Structure for Hydrogenation Reaction

Establishing structural defects is a perspective way to increase the catalytic hydrogenation reaction. Toward Sabatier optimization for hydrogenation reaction with defect density offers guidance for designing optimal catalysts with the highest performance. A controllable synthesis strategy is reported for Co@NC-x catalyst induced by defect density. A series of N-doped carbon-based defective Co@NC-x catalysts with different defect densities ranging from 1.5 × 1011 to 1.9 × 1011 cm-2 via high-temperature sublimation strategy is obtained. The results show that the volcano curves are observed between defect density and catalytic hydrogenation performance with a summit at a moderate defect density of 1.7 × 1011 cm-2, matched well with Sabatier phenomenon. Remarkably, the defect density on the graphene-like shell serves as descriptor to the adsorbate state and consequently the catalytic activity. However, to the best of knowledge, the Sabatier phenomenon in hydrogenation reactions at the defect scale in 3D graphene-like encapsulated metal (3D-GEM) catalysts has not been reported. This work highlights the meaning of defect-density effect on catalytic hydrogenation reaction, supplying meaningful guidance for the rational design of more efficient and durable defective 3D-GEM catalyst.

Reticular Materials for Photocatalysis

Photocatalysis leverages solar energy to overcome the thermodynamic barrier, enabling efficient chemical reactions under mild conditions. It can greatly reduce reliance on traditional energy sources and has attracted significant research interest. Reticular materials, including metal-organic frameworks (MOFs) and covalent organic frameworks (COFs), represent a class of crystalline materials constructed from molecular building blocks linked by coordination and covalent bonds, respectively. Reticular materials function as heterogeneous catalysts, combining well-defined structures and high tailorability akin to homogeneous catalysts. In this review, the regulation of light absorption, charge separation, and surface reactions in the photocatalytic process through precise molecular-level design based on the features of reticular materials is elaborated. Notably, for MOFsmicroenvironment modulation around catalytic sites affects photocatalytic performance is delved, with emphasis on their unique dynamic and flexible microenvironments. For COFs, the inherent excitonic effects due to their fully organic nature is discussed and highlight the strategies to regulate excitonic effects for charge- and/or energy-transfer-mediated photocatalysis. Finally, the current challenges and future directions in this field, aiming to provide a comprehensive understanding of how reticular materials can be optimized for enhanced photocatalysis is discussed.

Oxygen Vacancy-Enriched Alumina Stabilized Pd Nanocatalysts for Selective Hydrogenation of Phenols

The prevalence of electronic defects has not been successfully demonstrated in nonreducible oxides. This work presents a straightforward approach to the preparation of a yellow alumina rich in F-centers (oxygen vacancies containing free electrons), which is well characterized by systematic spectral methods. The surface electron density of the as-prepared F-center enriched alumina sample was estimated to be approximately 0.35 mmol·g-1. Free electrons on the surface can reduce palladium precursors in situ, leading to the deposition of fine Pd nanoparticles on alumina. The produced Pd nanocatalysts are highly effective in the selective hydrogenation of phenol to cyclohexanone, achieving a high catalytic performance under mild conditions (30 °C and 0.1 MPa of H2). Systematic mechanism investigations reveal that hydroxyl radicals generated at the catalyst interfaces facilitate the activation of phenol. The activated phenol is then sequentially hydrogenated to give the intermediate 2-cyclohexenone and then the desired cyclohexanone. The catalyst system demonstrates efficacy in selectively hydrogenating substituted phenols into a wide array of functional ketones.

Improving the Chemical Utilization Efficiency of Pd Hydrodechlorination Catalysts through Hydrogen-Spillover Empowered Synergy between Pd and TiNiN Support

The sustainable and affordable environmental application of Pd catalysis needs further improvement of Pd mass activity. Besides the well-recognized importance of physical utilization efficiency─the ratio of surface atoms forming reactant-accessible reactive sites─a lesser-known fact is that the congestion of these reactive sites, which we term as the chemical utilization efficiency, also influences the mass activity. Herein, by leveraging the 100% physical utilization efficiency of a fully exposed Pd cluster (Pdn) and the hydrogenation activity of TiNiN, we developed Pdn/TiNiN as a high physical and chemical utilization efficiency catalyst. During the catalytic hydrodechlorination of 4-chlorophenol and the subsequent hydrogenation of phenol, Pdn focuses on H2 dissociation and C-Cl cleavage, while TiNiN facilitates the subsequent hydrogenation of phenol into less toxic cyclohexanone via H-spillover. This synergy results in a 20-40-fold increase in the hydrodechlorination rate. The enhanced chemical utilization efficiency of Pd informs the design of Pdn/TiNiN microspheres for the conversion of halogenated organics from pharmaceutical wastewater and the design of a fixed-bed reactor to transfer trace amounts of 4-CP from river water. Ultimately, this approach decentralizes the use of Pd in environmental catalysis and reduction processes.

Satellite Pd Single-Atom Embraced AuPd Alloy Nanoclusters for Enhanced Hydrogen Evolution

The fabrication of hybrid active sites that synergistically contain nanoclusters and single atoms (SAs) is vital for electrocatalysts to achieve excellent activity and durability. Herein, we develop a ligand-assisted pyrolysis strategy using nanoclusters (Au4Pd2(SC2H4Ph)8) with alloy cores and protected ligands to build AuPd cluster sites embraced by satellite Pd SAs. In the thermal drive control process, different thermodynamic properties of the alloy atoms and the confinement effects of organic ligands allow for the mild spillover of the single-component metal Pd, resulting in the formation of AuPd alloy nanoclusters tightly encompassed by isolated Pd atoms. Experiments and theoretical calculations indicated that the satellite Pd atoms can optimize the electronic structure of the AuPd nanoclusters and Au sites in the alloy to facilitate the adsorption and dissociation of H2O, thus enhancing the hydrogen evolution reaction (HER) activity. The optimal AuPdNCs/PdSAs-600 exhibits outstanding electrocatalytic activity toward HER, with overpotentials of 21 and 38 mV at 10 mA cm-2 in acidic and alkaline media, respectively. Moreover, the mass activity and turnover frequency of AuPdNCs/PdSAs-600 are one order of magnitude higher than those of commercial Pd/C and Pt/C catalysts. This facile strategy for constructing hybrid catalytic centers using ligand-protected nanoclusters provides efficient insights for the further design of nanocluster-based electrocatalysts synergized by SAs.

Utilisation of in situ formed cyano-bridged coordination polymers as precursors of supported Ir-Ni alloy nanoparticles with precisely controlled compositions and sizes

Ir-Ni alloys supported on SiO2 have been reported to show high catalytic activity for styrene hydrogenation; however, precise control of compositions and sizes of the Ir-Ni alloys is difficult when conventional metal salts are used as precursors. Furthermore, the concomitant formation of unalloyed Ni nanoparticles disturbs quantitative discussion about Ir-Ni alloy compositions. We report herein a preparation method of Ir-Ni alloys with precisely controlled compositions on SiO2 using Ni(NO3)2 and an Ir complex possessing CN- ligands, [Ir(CN)6]3- or [Ir(ppy)2(CN)2]- (ppy = 2-phenylpyridine), as precursors. The in situ formation of cyano-bridged coordination polymers involving Ir and Ni promotes the formation of Ir-Ni alloys, whose compositions are virtually the same as expected from the amounts of Ir and Ni used for the preparation, after heat treatment under H2. The use of [Ir(ppy)2(CN)2]- as the precursor resulted in the formation of smaller Ir-Ni alloy particles than those with [Ir(CN)6]3- related to the structures of the formed coordination polymers.

Sulfate residuals on Ru catalysts switch CO2 reduction from methanation to reverse water-gas shift reaction

Efficient heterogeneous catalyst design primarily focuses on engineering the active sites or supports, often neglecting the impact of trace impurities on catalytic performance. Herein, we demonstrate that even trace amounts of sulfate (SO42-) residuals on Ru/TiO2 can totally change the CO2 reduction from methanation to reverse-water gas shift (RWGS) reaction under atmospheric pressure. We reveal that air annealing causes the trace amount of SO42- to migrate from TiO2 to Ru/TiO2 interface, leading to the significant changes in product selectivity from CH4 to CO. Detailed characterizations and DFT calculations show that the sulfate at Ru/TiO2 interface notably enhances the H transfer from Ru particles to the TiO2 support, weakening the CO intermediate activation on Ru particles and inhibiting the further hydrogenation of CO to CH4. This discovery highlights the vital role of trace impurities in CO2 hydrogenation reaction, and also provides broad implications for the design and development of more efficient and selective heterogeneous catalysts.

Elucidating Synergies of Single-Atom Catalysts in a Model Thin Film Photoelectrocatalyst to Maximize Hydrogen Evolution Reaction

Realization of the full potential of single-atom photoelectrocatalysts in sustainable energy generation requires careful consideration of the design of the host material. Here, a comprehensive methodology for the rational design of photoelectrocatalysts using anodic titanium dioxide (TiO2) nanofilm as a model platform is presented. The properties of these nanofilms are precisely engineered to elucidate synergies across structural, chemical, optoelectronic, and electrochemical properties to maximize the efficiency of the hydrogen evolution reaction (HER). These findings clearly demonstrate that thicker TiO2 nanofilms in anatase phase with pits on the surface can accommodate single-atom platinum catalysts in an optimal configuration to increase HER performance. It is also evident that the electrolyte temperature can further enhance HER output through thermochemical effect. A judicious design incorporating all these factors into one system gives rise to a ten-fold HER enhancement. However, the reusability of the host photoelectrocatalyst is limited by the leaching of the Pt atom, worsening HER. Density-functional theory calculations have provided insights into the mechanism underlying the experimental observations in terms of moderate hydrogen adsorption and enhanced gas generation. This improved understanding of the critical factors determining HER performance in a model photoelectrocatalyst paves the way for future advances in scalable and translatable photoelectrocatalyst technologies.

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.

Universal and scalable synthesis of photochromic single-atom catalysts for plastic recycling

Metal oxide nanostructures with single-atomic heteroatom incorporation are of interest for many applications. However, a universal and scalable synthesis approach with high heteroatom concentrations represents a formidable challenge, primarily due to the pronounced structural disparities between Mhetero-O and Msub-O units. Here, focusing on TiO2 as the exemplified substrate, we present a diethylene glycol-assisted synthetic platform tailored for the controlled preparation of a library of M1-TiO2 nanostructures, encompassing 15 distinct unary M1-TiO2 nanostructures, along with two types of binary and ternary composites. Our approach capitalizes on the unique properties of diethylene glycol, affording precise kinetic control by passivating the hydrolytic activity of heteroatom and simultaneously achieving thermodynamic control by introducing short-range order structures to dissipate the free energy associated with heteroatom incorporation. The M1-TiO2 nanostructures, characterized by distinctive and abundant M-O-Ti units on the surface, exhibit high efficiency in photochromic photothermal catalysis toward recycling waste polyesters. This universal synthetic platform contributes to the preparation of materials with broad applicability and significance across catalysis, energy conversion, and biomedicine.

Ethylene Glycol (EG)-Derived Chlorine-Resistant Cu0/TiO2-x for Efficient Photocatalytic Degradation of Nitrate to N2 without Sacrificial Agents at Near-Neutral pH Conditions: The Synergistic Effects of Cu0 and EG Radicals

The selective photoreduction of nitrate to nontoxic nitrogen gas has emerged as an energy-efficient and environmentally friendly route for nitrate removal. However, the coexisting high-concentration chloride ions in wastewater can exert a significant influence on nitrate reduction due to the competitive adsorption and corrosion of Cl- on photocatalysts. Herein, we prepared ethylene glycol-Cu/TiO2-x (EG-Cu/TiO2-x) through a solvothermal reaction of Cu-doped TiO2 in an EG solution. The photodegradation of nitrate using EG-Cu/TiO2-x without adding sacrificial agents can efficiently occur in near-neutral pH solutions containing 50 mM Cl- with 95.26% of NO3- removal and 76.52% of N2 selectivity. Moreover, the photocatalyst performance remained at a high level after 8 cycles. In this work, NO3- was first converted to NH4+ by Cu0 and Ti3+, followed by the NH4+-to-N2 conversion by photogenerated chlorine free radicals. Compared to HO•, Cl•, and Cl2•-, ClO• is proved to play the predominant role in transforming NH4+ to N2. The EG radicals produced by UV light impede Cl- adsorption on Cu, protecting Cu0 from being corroded. What's more, photoelectrons can reduce Ti4+ to Ti3+ and protect Cu0 from being oxidized, enabling the stability of reactive sites. This work provides novel insights and understanding on designing photocatalysts for NO3- removal in solutions containing chloride ions, highlighting the significance of eliminating Cl- by EG radicals and adjusting the conversion process of NO3- for the efficient removal of NO3-.

Selective hydrogenolysis of the Csp2-O bond in the furan ring using hydride-proton pairs derived from hydrogen spillover

Selective hydrogenolysis of biomass-derived furanic compounds is a promising approach for synthesizing aliphatic polyols by opening the furan ring. However, there remains a significant need for highly efficient catalysts that selectively target the Csp2-O bond in the furan ring, as well as for a deeper understanding of the fundamental atomistic mechanisms behind these reactions. In this study, we present the use of Pt-Fe bimetallic catalysts supported on layered double hydroxides [PtFe x /LDH] for the hydrogenolysis of furanic compounds into aliphatic alcohols, achieving over 90% selectivity toward diols and triols. Our findings reveal that the synergy between Pt nanoparticles, atomically dispersed Pt sites and the support facilitates the formation of hydride-proton pair at the Pt δ+⋯O2- Lewis acid-base unit of PtFe x /LDH through hydrogen spillover. The hydride specifically targets the Csp2-O bond in the furan ring, initiating an SN2 reaction and ring cleavage. Moreover, the presence of Fe improves the yield of desired alcohols by inhibiting the adsorption of vinyl groups, thereby suppressing the hydrogenation of the furan ring.

Hidden Impurities Generate False Positives in Single Atom Catalyst Imaging

Single-atom catalysts (SACs) are an emerging class of materials, leveraging maximum atom utilization and distinctive structural and electronic properties to bridge heterogeneous and homogeneous catalysis. Direct imaging methods, such as aberration-corrected high-angle annular dark-field scanning transmission electron microscopy, are commonly applied to confirm the atomic dispersion of active sites. However, interpretations of data from these techniques can be challenging due to simultaneous contributions to intensity from impurities introduced during synthesis processes, as well as any variation in position relative to the focal plane of the electron beam. To address this matter, this paper presents a comprehensive study on two representative SACs containing isolated nickel or copper atoms. Spectroscopic techniques, including X-ray absorption spectroscopy, were employed to prove the high metal dispersion of the catalytic atoms. Employing scanning transmission electron microscopy imaging combined with single-atom-sensitive electron energy loss spectroscopy, we scrutinized thin specimens of the catalysts to provide an unambiguous chemical identification of the observed single-atom species and thereby distinguish impurities from active sites at the single-atom level. Overall, the study underscores the complexity of SACs characterization and establishes the importance of the use of spectroscopy in tandem with imaging at atomic resolution to fully and reliably characterize single-atom catalysts.

Energetic and Kinetic Competition on the Stability of Pd13 Clusters: Ab Initio Molecular Dynamics Simulations

Material stability is the focus on both experiments and calculations, which includes the energetic stability at the static state and the thermodynamic stability at the kinetic state. To show whether energetics or kinetics dominates on material stability, this study focuses on the Pd13 clusters, because of their observable magnetic moment in experiment. Energetically, the CALYPSO searching method and first-principles calculations find that Pd13(C2) is the ground state at 0 K while the static frequency calculations demonstrate that the icosahedron Pd13(Ih) becomes more favorable on free energy as temperature increases. However, their magnetic moments (8 μB) are not in agreement with the experimental value (<5.2 μB). Kinetically, ab initio molecular dynamics simulations reveal that Pd13(C3v) (6 μB) has supreme isomerization temperature and the other 11 low-lying isomers transform to Pd13(C3v) directly or indirectly, demonstrating that Pd13(C3v) has the maximum probability to be observed in experiment. The magnetic moment difference between experiment (<5.2 μB) and this calculation (6 μB) may be due to the spin multiplicities. Our result suggests that the magnetic moment disparity between theory and experiment (in Pd13 clusters) originates from the kinetic stability.

Incorporation of Pd Single-Atom Sites in Perovskite with an Excellent Selectivity toward Photocatalytic Semihydrogenation of Alkynes

Semihydrogenation is a crucial industrial process. Noble metals such as Pd have been extensively studied in semihydrogenation reactions, owing to their unique catalytic activity toward hydrogen activation. However, the overhydrogenation of alkenes to alkanes often happens due to the rather strong adsorption of alkenes on Pd active phases. Herein, we demonstrate that the incorporation of Pd active phases as single-atom sites in perovskite lattices such as SrTiO3 can greatly alternate the electronic structure and coordination environment of Pd active phases to facilitate the desorption of alkenes rather than further hydrogenation. Furthermore, the incorporated Pd sites can be well stabilized without sintering by a strong host-guest interaction with SrTiO3 during the activation of H species in hydrogenation reactions. As a result, the Pd incorporated SrTiO3 (Pd-SrTiO3) exhibits an excellent time-independent selectivity (>99.9 %) and robust durability for the photocatalytic semihydrogenation of phenylacetylene to styrene. This strategy based on incorporation of active phases in perovskite lattices will have broad implications in the development of high-performance photocatalysts for selective hydrogenation reactions.

Intermetallics triggering pyroptosis and disulfidptosis in cancer cells promote anti-tumor immunity

Pyroptosis, an immunogenic programmed cell death, could efficiently activate tumor immunogenicity and reprogram immunosuppressive microenvironment for boosting cancer immunotherapy. However, the overexpression of SLC7A11 promotes glutathione biosynthesis for maintaining redox balance and countering pyroptosis. Herein, we develop intermetallics modified with glucose oxidase (GOx) and soybean phospholipid (SP) as pyroptosis promoters (Pd2Sn@GOx-SP), that not only induce pyroptosis by cascade biocatalysis for remodeling tumor microenvironment and facilitating tumor cell immunogenicity, but also trigger disulfidptosis mediated by cystine accumulation to further promote tumor pyroptosis in female mice. Experiments and density functional theory calculations show that Pd2Sn nanorods with an intermediate size exhibit stronger photothermal and enzyme catalytic activity compared with the other three morphologies investigated. The peroxidase-mimic and oxidase-mimic activities of Pd2Sn cause potent reactive oxygen species (ROS) storms for triggering pyroptosis, which could be self-reinforced by photothermal effect, hydrogen peroxide supply accompanied by glycometabolism, and oxygen production from catalase-mimic activity of Pd2Sn. Moreover, the increase of NADP+/NADPH ratio induced by glucose starvation could pose excessive cystine accumulation and inhibit glutathione synthesis, which could cause disulfidptosis and further augment ROS-mediated pyroptosis, respectively. This two-pronged treatment strategy could represent an alternative therapeutic approach to expand anti-tumor immunotherapy.

Preparation of PdNi bimetallic loaded amino modified porous carbon material catalyst based on chitosan and its applications

The utilization efficiency of palladium-based catalysts has sharply increased in many catalytic reactions. However, numerous studies have shown that preparing alloys of palladium with other metals has superior catalytic activity than pure palladium. Additionally, hierarchical porous carbon has gradually developed into an excellent carrier for loading bimetallic nanoparticles. In this study, we firstly pyrolyzed chitosan, sodium bicarbonate and nickel nitrate to create highly dispersed porous carbon materials doped with Ni NPs. The carbon materials were then grafted with silane coupling agent (APTMS) to afford them with amino groups on the surface. Taking advantage of the fact that Pd2+ can react with Ni in spontaneous reduction reaction, Pd was deposited on the surface of Ni to produce PdNi bimetallic-loaded carbon catalysts containing amino groups. The resulting catalysts were examined by a series of characterizations and were found to have a hierarchically porous structure and large specific surface area, which increased the number of active sites of the catalysts. In comparison to other Pd catalysts, the PdNi/HPCS-NH2 catalysts displayed remarkable activity for Suzuki coupling reaction and hydro reduction of nitroaromatics, which exhibited a high turnover frequency value (TOF) of 37,857 h-1 and 680.9 h-1, respectively. These were mainly due to the high dispersion of the PdNi NPs and the superior structure of the carriers. Moreover, the catalysts did not experience a significant decline in activity after ten cycles. All in all, this investigation has created a new approach for the fabrication of novel carriers for Pd catalysts, which is in line with the concept of green chemistry and recyclable.