Designing Sites in Heterogeneous Catalysis: Are We Reaching Selectivities Competitive With Those of Homogeneous Catalysts?

Unlocking High Porosity: Post-Synthetic Solvothermal Treatment of Cu-Paddlewheel Based Metal-Organic Cages

Metal-organic cages (MOCs) have garnered significant attention due to their unique discrete structures, intrinsic porosity, designability, and tailorability. However, weak inter-cage interactions, such as van der Waals forces and hydrogen bonding can cause solid-state MOCs to lose structural integrity during desolvation, leading to the loss of porosity. In this work, a novel strategy to retain the permanent porosity of Cu-paddlewheel-based MOCs, enabling their use as heterogeneous catalysts is presented. Post-synthetic solvothermal treatments in non-coordinating solvents, mesitylene, and p-xylene, effectively preserve the packing structures of solvent-evacuated MOCs while preventing cage agglomeration. The resulting MOCs exhibit an exceptional N2 sorption capacity, with a high surface area (SBET = 1934 m2 g-1 for MOP-23), which is among the highest reported for porous MOCs. Intriguingly, while the solvothermal treatment reduced Cu(II) to Cu(I) in the Cu-paddlewheel clusters, the MOCs with mixed-valenced Cu(I)/Cu(II) maintained their crystallinity and permanent porosity. The catalytic activities of these MOCs are successfully examined in copper(I)-catalyzed hydrative amide synthesis, highlighting the prospect of MOCs as versatile reaction platforms.

Use of carboxymethyl cellulose as binder for the production of water-soluble catalysts

Bio-based polymers are materials of high interest given the harmful environmental impact that involves the use of non-biodegradable fossil products for industrial applications. These materials are also particularly interesting as bio-based ligands for the preparation of metal nanoparticles (MNPs), employed as catalysts for the synthesis of high value chemicals. In the present study, Ru (0) and Rh(0) Metal Nanoparticles supported on Sodium Carboxymethyl cellulose (MNP(0)s-CMCNa) were prepared by simply mixing RhCl3x3H2O or RuCl3 with an aqueous solution of CMCNa, followed by NaBH4 reduction. The formation of MNP(0)s-CMCNa was confirmed by FT-IR and XRD, and their size estimated to be around 1.5 and 2.2 nm by TEM analysis. MNP(0)s-CMCNa were employed for the hydrogenation of (E)-cinnamic aldehyde, furfural and levulinic acid. Hydrogenation experiments revealed that CMCNa is an excellent ligand for the stabilization of Rh(0) and Ru(0) nanoparticles allowing to obtain high conversions (>90 %) and selectivities (>98 %) with all substrates tested. Easy recovery by liquid/liquid extraction allowed to separate the catalyst from the reaction products, and recycling experiments demonstrated that MNPs-CS were highly efficiency up to three times in best hydrogenation conditions.

A two-dimensional iron-doped carbon-based nanoenzyme with catalase-like activity for the detection of alkaline phosphatase and ascorbate oxidase

Herein, we successfully synthesized two-dimensional iron-doped carbon-based nanosheets (Fe-N800 CS) with catalase-like activity through doping Fe into Zn MOF and introducing graphitic C3N4 (g-C3N4). The interaction of the Fe-N800 CS with hydrogen peroxide could generated abundant reactive oxygen species (ROS) and further oxidize o-Phenylenediamine (OPD) to 2,3-diaminophenazine (DAP) which has constant fluorescence at 560 nm. Ascorbic acid (AA) could be generated via the hydrolysis reaction between alkaline phosphatase (ALP) and ascorbic acid 2-phosphate (AAP). AA can be oxidized to dehy-droascorbic acid (DHA) by ROS, and then combined with OPD to generate 3-(1,2-dihydroxyethyl)furo[3,4b]-quinoxaline (QXD) with fluorescence at 440 nm, which could increase as the concentration of AA enhanced. DHA could also be generated through oxidation of AA by ascorbate oxidase (AAO). Thus, by monitoring the fluorescence ratio (I560/I440), a ratiometric fluorescence biosensing platform for ALP and AAO was established with the linear ranges in 0.2-10 U/L and 1-60 U/L, respectively. The limit of detection for ALP and AAO were 0.12 U/L and 0.59 U/L. Furthermore, the biosensing platform was successfully applied for the detection of ALP and AAO activity in human serum samples. This work provides a potential tool for future biomedical diagnostics.

Crystalline Olefin-Linked Chiral Covalent Organic Frameworks as a Platform for Asymmetric Catalysis

The construction of olefin-linked chiral covalent organic frameworks (COFs) with high crystallinity is highly desirable while remains great challenge due to the poor reversibility of the formation reaction for the olefin linkages during the in situ structural self-healing process. Herein, we successfully synthesized two sets of enantiomeric olefin-linked COFs. The chiral catalytic groups are uniformly distributed on the pore walls of COFs, resulting in the full exposure of catalytic sites to the reactants in asymmetric catalysis. The as-prepared (R)/(S)-CCOF8 exhibits excellent catalytic performance with exceeding 99 % enantiomeric excess in the enantioselective electrophilic amination reaction. Moreover, the heterogeneous chiral catalysts are conveniently recycled and could maintain the performance after ten catalytic cycles. Our findings expand the scope to construct stable and crystalline chiral COFs for the asymmetric catalysis.

Structural Regulation of Covalent Organic Frameworks for Catalysis

ConspectusChemical reactions can be promoted at lower temperatures and pressures, thereby reducing the energy input, by introducing suitable catalysts. Despite its significance, the quest for efficient and stable catalysts remains a significant challenge. In this context, addressing the efficiency of catalysts stands out as a paramount concern. However, the challenges posed by the vague structure and limited tailorability of traditional catalysts would make it highly desirable to fabricate optimized catalysts based on the understanding of structure-activity relationships. Covalent organic frameworks (COFs), a subclass of fully designed crystalline materials formed by the polymerization of organic building blocks through covalent bonds have garnered widespread attention in catalysis. The precise and customizable structures of COFs, coupled with attributes such as high surface area and facile functional modification, make COFs attractive molecular platforms for catalytic applications. These inherent advantages position COFs as ideal catalysts, facilitating the elucidation of structure-performance relationships and thereby further improving the catalysis. Nevertheless, there is a lack of systematic emphasis on and summary of structural regulation at the atomic/molecular level for COF catalysis. Consequently, there is a growing need to summarize this research field and provide deep insights into COF-based catalysis to promote its further development.In this Account, we will summarize recent advances in structural regulation achieved in COF-based catalysts, placing an emphasis on the molecular design of the structures for enhanced catalysis. Considering the unique components and structural advantages of COFs, we present the fundamental principles for the rational design of structural regulation in COF-based catalysis. This Account starts by presenting an overview of catalysis and explaining why COFs are promising catalysts. Then, we introduce the molecular design principle for COF catalysis. Next, we present the following three aspects of the specific strategies for structural regulation of COF-based catalysts: (1) By designing different functional groups and integrating metal species into the organic unit, the activity and/or selectivity can be finely modulated. (2) Regulating the linkage facilitates charge transfer and/or modulates the electronic structure of catalytic metal sites, and accordingly, the intrinsic activity/selectivity can be further improved. (3) By means of pore wall/space engineering, the microenvironment surrounding catalytic metal sites can be modulated to optimize performance. Finally, the current challenges and future developments in the structural regulation of COF-based catalysts are discussed in detail. This Account provides insight into the structural regulation of COF-based catalysts at the atomic/molecular level toward improving their performance, which would provide significant inspiration for the design and structural regulation of other heterogeneous catalysts.

Solvent-free selective hydrogenation of nitroaromatics to azoxy compounds over Co single atoms decorated on Nb2O5 nanomeshes

The solvent-free selective hydrogenation of nitroaromatics to azoxy compounds is highly important, yet challenging. Herein, we report an efficient strategy to construct individually dispersed Co atoms decorated on niobium pentaoxide nanomeshes with unique geometric and electronic properties. The use of this supported Co single atom catalysts in the selective hydrogenation of nitrobenzene to azoxybenzene results in high catalytic activity and selectivity, with 99% selectivity and 99% conversion within 0.5 h. Remarkably, it delivers an exceptionally high turnover frequency of 40377 h-1, which is amongst similar state-of-the-art catalysts. In addition, it demonstrates remarkable recyclability, reaction scalability, and wide substrate scope. Density functional theory calculations reveal that the catalytic activity and selectivity are significantly promoted by the unique electronic properties and strong electronic metal-support interaction in Co1/Nb2O5. The absence of precious metals, toxic solvents, and reagents makes this catalyst more appealing for synthesizing azoxy compounds from nitroaromatics. Our findings suggest the great potential of this strategy to access single atom catalysts with boosted activity and selectivity, thus offering blueprints for the design of nanomaterials for organocatalysis.

Structure-driven tuning of catalytic properties of core-shell nanostructures

The annual increase in demand for renewable energy is driving the development of catalysis-based technologies that generate, store and convert clean energy by splitting and forming chemical bonds. Thanks to efforts over the last two decades, great progress has been made in the use of core-shell nanostructures to improve the performance of metallic catalysts. The successful preparation and application of a large number of bimetallic core-shell nanocrystals demonstrates the wide range of possibilities they offer and suggests further advances in this field. Here, we have reviewed recent advances in the synthesis and study of core-shell nanostructures that are promising for catalysis. Particular attention has been paid to the structural tuning of the catalytic properties of core-shell nanostructures and to theoretical methods capable of describing their catalytic properties in order to efficiently search for new catalysts with desired properties. We have also identified the most promising areas of research in this field, in terms of experimental and theoretical studies, and in terms of promising materials to be studied.

Formation of Strong Boron Lewis Acid Sites on Silica

Bis(1-methyl-ortho-carboranyl)borane (HBMeoCb2) is a very strong Lewis acid that reacts with the isolated silanols present on silica partially dehydroxylated at 700 °C (SiO2-700) to form the well-defined Lewis site MeoCb2B(OSi≡) (1) and H2. 11B{1H} magic-angle spinning (MAS) nuclear magnetic resonance (NMR) data of 1 are consistent with that of a three-coordinate boron site. Contacting 1 with O═PEt3 (triethylphosphine oxide TEPO) and measuring 31P{1H} MAS NMR spectra show that 1 preserves the strong Lewis acidity of HBMeoCb2. Hydride ion affinity and fluoride ion affinity calculations using small molecules analogs of 1 also support the strong Lewis acidity of the boron sites in this material. Reactions of 1 with Cp2Hf(13CH3)2 show that the Lewis sites are capable of abstracting methide groups from Hf to form [Cp2Hf-13CH3][H313C-B(MeoCb2)OSi≡], but with a low overall efficiency.

Enhancing Precatalyst Performance and Robustness through Aromaticity: Insights from Iridaheteroaromatics

Despite the inherent stability-enhancing benefits of dπ-pπ conjugation-induced aromaticity, metallaaromatic catalysts remain underutilized in this context, despite their reactivity with organic functionalities in stoichiometric reactions. We present a strategy for synthesizing a diverse range of iridaheteroaromatics, (L^L)IrIII(Cp*)I, including iridapyridylidene-indole, iridapyridene-indole, and iridaimidazole, via in situ deprotonation/metalation reactions utilizing [Cp*IrCl2]2 and the respective ligands. These catalysts exhibit enhanced σ-donor and π-acceptor properties, intrinsic σ-π continuum attributes, and versatile binding sites, contributing to stability through enhanced dπ-pπ conjugation-induced aromaticity. Spectroscopic data, X-ray crystallographic data, and density functional theory calculations confirm their aromaticity. These iridaheteroaromatics exhibit formidable catalytic ability across a spectrum of transformations under industrially viable conditions, notably excelling in highly selective cross alkylation and β-alkylation of alcohols and an eco-friendly avenue for quinolone synthesis, achieving remarkably high turnover frequencies (TOFs). Additionally, this method extends to the self-condensation of bioalcohols like ethanol, n-butanol, and n-hexanol in water, replicating conditions frequently encountered in primary fermentation solutions. These iridaheteroaromatics exhibit strong catalytic activity with fast reaction rates, high TOFs, broad substrate compatibility, and remarkable selectivity, displaying their potential as robust catalysts in large-scale applications and emphasizing their practical significance beyond their structural and theoretical importance.

Click nanosponge - A novel amine-rich β-cyclodextrin-based crosslinked polymer for heterogeneous catalysis

Cyclodextrin-based nanosponges are promising materials for heterogeneous catalysis due to their inherent synthetic versatility, tunable porosity and nontoxicity. In this work, a primary amine-rich β-cyclodextrin nanosponge was synthesized via click imine condensation reaction between 1,6-hexamethylamine-functionalized β-cyclodextrin (CDAM) and glutaraldehyde (GLT) to afford CDGLAM, in mild conditions. The crosslinked polymer exhibited a BET surface area of 36.39 m2 g-1, an average pore diameter of 3.09 nm (as assessed by the BJH method), and thermal stability up to 253 °C. CDGLAM was tested as heterogeneous catalyst for the metal-free Henry and Knoevenagel reactions, between aromatic aldehydes and nitromethane or ethyl cyanoacetate, respectively, affording the products in moderate to very high yields. These results show the ease of preparation of β-CD-based nanosponges from a green chemistry perspective, as well as their potential for future use in catalytic systems.

Recent progress in hierarchical nanostructures for Ni-based industrial-level OER catalysts

Exploring efficient and low-cost oxygen evolution reaction (OER) electrocatalysts reaching the industrial level current density is crucial for hydrogen production via water electrolysis. In this feature article, we summarize the recent progress in hierarchical nanostructures for the industrial-level OER. The contents mainly concern (i) the design of a hierarchical structure; (ii) a Ni-based hierarchical structure for the industrial current density OER; and (iii) the surface reconstruction of the hierarchical structure during the OER process. The work provides valuable guidance and insights for the manufacture of hierarchical nanomaterials and devices for industrial applications.

Bridging Together Theoretical and Experimental Perspectives in Single-Atom Alloys for Electrochemical Ammonia Production

Ammonia is an essential commodity in the food and chemical industry. Despite the energy-intensive nature, the Haber-Bosch process is the only player in ammonia production at large scales. Developing other strategies is highly desirable, as sustainable and decentralized ammonia production is crucial. Electrochemical ammonia production by directly reducing nitrogen and nitrogen-based moieties powered by renewable energy sources holds great potential. However, low ammonia production and selectivity rates hamper its utilization as a large-scale ammonia production process. Creating effective and selective catalysts for the electrochemical generation of ammonia is critical for long-term nitrogen fixation. Single-atom alloys (SAAs) have become a new class of materials with distinctive features that may be able to solve some of the problems with conventional heterogeneous catalysts. The design and optimization of SAAs for electrochemical ammonia generation have recently been significantly advanced. This comprehensive review discusses these advancements from theoretical and experimental research perspectives, offering a fundamental understanding of the development of SAAs for ammonia production.

Palladium(II)-immobilized Triptycene based Hypercrosslinked Polymers: An Efficient, Green, and Reusable Heterogenous Catalyst for Suzuki-Miyaura Cross-coupling Reaction

The Suzuki-Miyaura cross-coupling (SMCC) involves the coupling of organohalides and organoboron molecules in the presence of Pd(II)-based catalysts. Often SMCC reactions employ homogenous catalysts. However, such homogenous SMCC reactions are associated with certain limitations which has motivated design of effective and sustainable Pd(II)-based heterogeneous catalytic systems. Herein, we report a systematic development of a Pd(II)-immobilized and triptycene based ionic hyper crosslinked polymer (Pd@TP-iHCP) and explored its application as a heterogeneous catalyst for SMCC reaction. Pd@TP-iHCP has ample N-heterocyclic carbene (NHC) pendants that anchor Pd(II) centres on the polymeric matrix. Pd@TP-iHCP was characterized satisfactorily using FT-IR, 13 C CP-MAS NMR, BET surface area analysis, SEM, EDX and HRTEM. The performance of Pd@TP-iHCP as a heterogeneous catalyst for SMCC reactions was explored using various combinations of aryl boronic acids and aryl halides. Experimental results show that Pd@TP-iHCP is associated with a moderately high surface area. It is an efficient catalyst for SMCC (in aqueous media) with a modest loading of 0.8 mol % Pd(II)-catalyst since high yields of the expected products were obtained in shorter time intervals. Pd@TP-iHCP also features excellent stability and catalyst recyclability since it could be re-used for several cycles without any significant decrease in catalytic efficiency.

Thermally Induced Surface Structure and Morphology Evolution in Bimetallic Pt-Au/HOPG Nanoparticles as Probed Using XPS and STM

Bimetallic nanoparticles expand the possibilities of catalyst design, providing an extra degree of freedom for tailoring the catalyst structure in comparison to purely monometallic systems. The distribution mode of two metal species defines the structure of surface catalytic sites, and current research efforts are focused on the development of methods for their controlled tuning. In light of this, a comprehensive investigation of the factors which influence the changes in the morphology of bimetallic nanoparticles, including the elemental redistribution, are mandatory for each particular bimetallic system. Here we present the combined XPS/STM study of the surface structure and morphology of bimetallic Pt-Au/HOPG nanoparticles prepared by thermal vacuum deposition and show that thermal annealing up to 350 °C induces the alloying process between the two bulk-immiscible metal components. Increasing the treatment temperature enhances the extent of Pt-Au alloying. However, the sintering of nanoparticles starts to occur above 500 °C. The approach implemented in this work includes the theoretical simulation of XPS signal intensities for a more meticulous analysis of the compositional distribution and can be helpful from a methodological perspective for other XPS/STM studies of bimetallic nanoparticles on planar supports.

Observing the Evolution of Metal Oxides in Liquids

Metal oxides with diverse compositions and structures have garnered considerable interest from researchers in various reactions, which benefits from transmission electron microscopy (TEM) in determining their morphologies, phase, structural and chemical information. Recent breakthroughs have made liquid-phase TEM a promising imaging platform for tracking the dynamic structure, morphology, and composition evolution of metal oxides in solution under work conditions. Herein, this review introduces the recent advances in liquid cells, especially closed liquid cell chips. Subsequently, the recent progress including particle growth, phase transformation, self-assembly, core-shell nanostructure growth, and chemical etching are introduced. With the late technical advances in TEM and liquid cells, liquid-phase TEM is used to characterize many fundamental processes of metal oxides for CO2 reduction and water-splitting reactions. Finally, the outlook and challenges in this research field are discussed. It is believed this compilation inspires and stimulates more efforts in developing and utilizing in situ liquid-phase TEM for metal oxides at the atomic scale for different applications.

Thermo-responsive chiral micelles as recyclable organocatalyst for asymmetric Rauhut-Currier reaction in water

Developing eco-friendly chiral organocatalysts with the combined advantages of homogeneous catalysis and heterogeneous processes is greatly desired. In this work, a family of amphiphilic one-handed helical polyisocyanides bearing phosphine pendants is prepared, which self-assembles into well-defined chiral micelles in water and showed thermo-responsiveness with a cloud point of approximately 38.4 °C. The micelles with abundant phosphine moieties at the interior efficiently catalyze asymmetric cross Rauhut-Currier reaction in water. Various water-insoluble substrates are transferred to target products in high yield with excellent enantioselectivity. The yield and enantiomeric excess (ee) of the product generated in water are up to 90% and 96%, respectively. Meanwhile, the yields of the same R-C reaction catalyzed by the polymer itself in organic solvents is <16%, with an ee < 72%. The homogeneous reaction of the chiral micelles in water turns to heterogeneous at temperatures higher than the cloud point, and the catalyst precipitation facilitates product isolation and catalyst recovery. The polymer catalyst is recycled 10 times while maintaining activity and enantioselectivity.

The Role of In Situ/Operando IR Spectroscopy in Unraveling Adsorbate-Induced Structural Changes in Heterogeneous Catalysis

Heterogeneous catalysts undergo thermal- and/or adsorbate-induced dynamic changes under reaction conditions, which consequently modify their catalytic behavior. Hence, it is increasingly crucial to characterize the properties of a catalyst under reaction conditions through the so-called "operando" approach. Operando IR spectroscopy is probably one of the most ubiquitous and versatile characterization methods in the field of heterogeneous catalysis, but its potential in identifying adsorbate- and thermal-induced phenomena is often overlooked in favor of other less accessible methods, such as XAS spectroscopy and high-resolution microscopy. Without detracting from these techniques, and while aware of the enormous value of a multitechnique approach, the purpose of this Review is to show that IR spectroscopy alone can provide relevant information in this field. This is done by discussing a few selected case studies from our own research experience, which belong to the categories of both "single-site"- and nanoparticle-based catalysts.

Development of a chromium oxide loaded mesoporous silica as an efficient catalyst for carbon dioxide-free production of ethylene oxide

Ethylene oxide (EO) is a significant raw material used in many commodities for consumers, particularly ethoxylates, polymers, and certain other glycol derivatives. We synthesized a catalyst by incorporation of chromium oxide into a mesoporous silica material (Cr/MSM) via the hydrothermal method, an effective catalyst for partial ethylene oxidation for producing carbon dioxide (CO2) free EO. Subsequently, XRD, BET, XPS, and TEM were used to analyse the structural characteristics of the Cr/MSM catalyst. The catalytic performance of the synthesized catalyst was assessed in the liquid-phase epoxidation (LPE) of ethylene, utilizing peracetic acid (PAA) as an oxidant. This approach not only circumvented the generation of CO2 but also mitigated the risk of metal leaching. Confirmation of the successful production of EO was achieved through GC chromatography, where the presence of a peak with a retention time (RT) of 8.91 minutes served as conclusive evidence. We systematically explored a range of reaction parameters, including temperature, catalyst concentration, the molar ratio of ethylene to PAA, and solvent effect. This comprehensive investigation aimed to fine-tune the reaction conditions, ultimately improving ethylene conversion and enhancing the selectivity of the catalyst for EO production. This approach can effectively resolve the issues of greenhouse gas emissions and metal leaching that had been associated with previously reported catalysts.

A strategy for high ethylene polymerization performance using titanium single-site catalysts

The synthesis of heterogeneous Ti(IV)-based catalysts for ethylene polymerization following surface organometallic chemistry concepts is described. The unique feature of this catalyst arises from the silica support, KCC-1700. It has (i) a 3D fibrous morphology that is essential to improve the diffusion of the reactants, and (ii) an aluminum-bound hydroxyl group, [(Si-O-Si)(Si-O-)2Al-OH] 2, used as an anchoring site. The [(Si-O-Si)(Si-O-)(Al-O-)TiNp3] 3 catalyst was obtained by reacting 2 with a tetrakis-(neopentyl) titanium TiNp4. The structure of 3 was fully characterized by FT-IR, advanced solid-state NMR spectroscopy [1H, 13C], elemental and gas-phase analysis (ICP-OES and CHNS analysis), and XPS. The benefits of combining these morphological (3D structure) and electronic properties of the support (aluminum plus titanium) were evidenced in ethylene polymerization. The results show a remarkable enhancement in the catalytic performance with the formation of HDPE. Notably, the resulting HDPE displays a molecular weight of 3 200 000 g mol-1 associated with a polydispersity index (PD) of 2.3. Moreover, the effect of the mesostructure (2D vs. 3D) was demonstrated in the catalytic activity for ethylene polymerization.

Automated, Consistent, and Even-Handed Selection of Active Orbital Spaces for Quantum Embedding

A widely used strategy to reduce the computational cost of quantum-chemical calculations is to partition the system into an active subsystem, which is the focus of the computational efforts, and an environment that is treated at a lower computational level. The system partitioning is mostly based on localized molecular orbitals. When reaction paths or energy differences are to be calculated, it is crucial to keep the orbital space consistent for all structures. Inconsistencies in orbital space can lead to unpredictable errors on the potential energy surface. While successful strategies to ensure this consistency have been established for organic and even metal-organic systems, these methods often fail for metal clusters or nanoparticles with a high density of near-degenerate and delocalized molecular orbitals. However, such systems are highly relevant for catalysis. Accurate yet feasible quantum-mechanical ab initio calculations are therefore highly desired. In this work, we present an approach based on the subsystem projected atomic orbital decomposition algorithm that allows us to ensure automated and consistent partitioning even for systems with delocalized and near-degenerate molecular orbitals and demonstrate the validity of this method for the binding energies of small molecules on transition-metal clusters.

An Unusual Microdomain Factor Controls Interaction of Organic Halides with the Palladium Phase and Influences Catalytic Activity in the Mizoroki-Heck Reaction

In this work, using a combination of scanning and transmission electron microscopy (SEM and TEM), the transformations of palladium-containing species in imidazolium ionic liquids in reaction mixtures of the Mizoroki-Heck reaction and in related organic media are studied to understand a challenging question of the relative reactivity of organic halides as key substrates in modern catalytic technologies. The microscopy technique detects the formation of a stable nanosized palladium phase under the action of an aryl (Ar) halide capable of forming microcompartments in an ionic liquid. For the first time, the correlation between the reactivity of the aryl halide and the microdomain structure is observed: Ar-I (well-developed microdomains) > Ar-Br (microphase present) > Ar-Cl (minor amount of microphase). Previously, it is assumed that molecular level factors, namely, carbon-halogen bond strength and the ease of bond breakage, are the sole factors determining the reactivity of aryl halides in catalytic transformations. The present work reports a new factor connected with the nature of the organic substrates used and their ability to form a microdomain structure and concentrate metallic species, highlighting the importance of considering both the molecular and microscale properties of the reaction mixtures.

Construction of Highly Active and Selective Molecular Imprinting Catalyst for Hydrogenation

Surface molecular imprinting (MI) is one of the most efficient techniques to improve selectivity in a catalytic reaction. Heretofore, a prerequisite to fabricating selective catalysts by MI strategies is to sacrifice the number of surface-active sites, leading to a remarkable decrease of activity. Thus, it is highly desirable to design molecular imprinting catalysts (MICs) in which both the catalytic activity and selectivity are significantly enhanced. Herein, a series of MICs are prepared by sequentially adsorbing imprinting molecules (nitro compounds, N) and imprinting ligand (1,10-phenanthroline, L) over the copper surface of Cu/Al2O3. The resulting Cu/Al2O3-N-L MICs not only offer promoted catalytic selectivity but also enhance catalytic activity for nitro compounds hydrogenation by an creating imprinting cavity derived from the presorption of N and forming new active Cu-N sites at the interface of the copper sites and L. Characterizations by means of various experimental investigations and DFT calculations disclose that the molecular imprinting effect (promoted activity and selectivity) originates from the formation of new active Cu-N sites and precise imprinting cavities, endowing promoted catalytic selectivity and activity on the hydrogenation of nitro compounds.

Ternary CdS@MoS2-Co3O4 Multiheterojunction Photocatalyst for Boosting Photocatalytic H2 Evolution

Turning the carrier dynamics in heterojunction photocatalysts is a direct and effective strategy for improving the solar energy conversion efficiency of photocatalysts. Herein, we report a ternary CdS@MoS2-Co3O4 multiheterojunction photocatalyst consisting of the p-n junction of MoS2-Co3O4 and the type-I junction of CdS@MoS2, wherein MoS2 located at the frontier between CdS and Co3O4 acts as an intermediate bridge. The type-I junction allows the directional transfer of photoinduced charge from CdS to MoS2, suppressing the photocorrosion of CdS. Notably, the single-particle photoluminescence technique demonstrates the sequential one-direction hole transfer from MoS2 to Co3O4 aroused by the p-n junction, resulting in a long-lifetime charge separation in the carrier lifetime (54-58 ns). Compared to the bare CdS and type-I CdS@MoS2, the CdS@MoS2-Co3O4 photocatalyst affords a 347-fold and 3.5-fold enhancement of the H2 evolution rate, a quantum efficiency of 28.6% at 450 nm, and a 20 h of long-term stability. This work provides a new understanding of the rational regulation of the charge-transfer mechanism of type-I systems by constructing multiheterojunction photocatalysts.

A Supported Catalyst that Enables the Synthesis of Colorless CO2 -Polyols with Ultra-Low Molecular Weight

Ultra-low molecular weight (ULMW) CO2 -polyols with well-defined hydroxyl end groups represent useful soft segments for the preparation of high-performance polyurethane foams. However, owing to the poor proton tolerance of catalysts towards CO2 /epoxide telomerization, it remains challenging to synthesize ULMW yet colorless CO2 -polyols. Herein, we propose an immobilization strategy of constructing supported catalysts by chemical anchoring of aluminum porphyrin on Merrifield resin. The resulting supported catalyst displays both extremely high proton tolerance (≈8000 times the equivalents of metal centers) and independence of cocatalyst, affording CO2 -polyols with ULMW (580 g mol-1 ) and high polymer selectivity (>99 %). Moreover, the ULMW CO2 -polyols with various architectures (tri-, quadra-, and hexa-arm) can be obtained, suggesting the wide proton universality of supported catalysts. Notably, benefiting from the heterogeneous nature of the supported catalyst, colorless products can be facilely achieved by simple filtration. The present strategy provides a platform for the synthesis of colorless ULMW polyols derived from not only CO2 /epoxides, but also lactone, anhydrides etc. or their combinations.

Single-Atom Catalysis in Organic Synthesis

Single-atom catalysts hold the potential to significantly impact the chemical sector, pushing the boundaries of catalysis in new, uncharted directions. These materials, featuring isolated metal species ligated on solid supports, can exist in many coordination environments, all of which have shown important functions in specific transformations. Their emergence has also provided exciting opportunities for mimicking metalloenzymes and bridging the gap between homogeneous and heterogeneous catalysis. This Review outlines the impressive progress made in recent years regarding the use of single-atom catalysts in organic synthesis. We also illustrate potential knowledge gaps in the search for more sustainable, earth-abundant single-atom catalysts for synthetic applications.

Bottom-Up Design of Photoactive Chiral Covalent Organic Frameworks for Visible-Light-Driven Asymmetric Catalysis

The development of chiral covalentorganic framework catalysts (CCOFs) to synthesize enantiopure organic compounds is crucial and highly desirable in synthetic chemistry. Photocatalytic asymmetric reactions based on CCOFs are eco-friendly and sustainable while they are still elaborate. In this work, we report a general bottom-up strategy to successfully synthesize several photoactive CCOFX (X = 1-5 and 1-Boc). The photoactive porphyrin building blocks are selected as knots and various secondary-amine-based chiral catalytic centers are immobilized on the pore walls of CCOFX through a rational design of benzoimidazole linkers. The porphyrin units act as light-harvesting antennae to generate photo-induced charge carriers for the activation of bromide during the photocatalytic asymmetric alkylation of aldehydes. Meanwhile, various aldehydes are activated by the chiral secondary amine to form the target products with a high yield (up to 97%) and ee value (up to 93%). The results significantly expand the scope to predesign CCOF photocatalysts for visible-light-driven asymmetric catalysis.

Modulating adsorbed hydrogen drives electrochemical CO2-to-C2 products

Electrocatalytic CO₂ reduction is a typical reaction involving two reactants (CO₂ and H₂O). However, the role of H₂O dissociation, which provides active *H species to multiple protonation steps, is usually overlooked. Herein, we construct a dual-active sites catalyst comprising atomic Cu sites and Cu nanoparticles supported on N-doped carbon matrix. Efficient electrosynthesis of multi-carbon products is achieved with Faradaic efficiency approaching 75.4% with a partial current density of 289.2 mA cm^-2 at -0.6 V. Experimental and theoretical studies reveal that Cu nanoparticles facilitate the C-C coupling step through *CHO dimerization, while the atomic Cu sites boost H₂O dissociation to form *H. The generated *H migrate to Cu nanoparticles and modulate the *H coverage on Cu NPs, and thus promote *CO-to-*CHO. The dual-active sites effect of Cu single-sites and Cu nanoparticles gives rise to the catalytic performance.

Silver Supported Nanoparticles on [Mg4 Al-LDH] as an Efficient Catalyst for the α-Alkylation of Nitriles, Oxindoles and Other Carboxylic Acid Derivatives with Alcohols

An efficient heterogeneous silver-catalyzed α-alkylation of nitriles and oxindoles using alcohols via borrowing hydrogen strategy has been developed for the first time. The active nanostructured material, namely [Ag/Mg4 Al-LDH], composed by silver nanoparticles (3-4 nm average particle size) homogeneously stabilized onto a [Mg4 Al-LDH] support with suitable Brønsted basic properties, constitutes a stable catalyst for the sustainable building of novel C-C bonds from alcohols and C-nucleophiles. By applying this catalyst, a broad range of α-functionalized nitriles and oxindoles has been accessed with good to excellent isolated yields and without the addition of external bases. Moreover, the novel silver nanocatalyst has also demonstrated its successful application to the cyclization of N-[2-(hydroxymethyl)phenyl]-2-phenylacetamides to afford 3-arylquinolin-2(1H)-ones, through a one-pot dehydrogenation and intramolecular α-alkylation. Control experiments, kinetic studies, and characterization data of a variety of [Ag/LDH]-type materials confirmed the silver role in the dehydrogenation and hydrogenation steps, while [Mg4 Al-LDH] matrix is able to catalyze condensation. Interestingly, these studies suggest as key point for the successful activity of [Ag/Mg4 Al-LDH], in comparison with other [Ag/LDH]-type nanocatalysts, the suitable acid-base properties of this material.

Multistep Cascade Catalytic Reactions Employing Bifunctional Framework Compounds

Multistep cascade reactions are important to achieve atom as well as step economy over conventional synthesis. This approach, however, is limited due to the incompatibility of the available reactive centers in a catalyst. In the present study, new MOF compounds, [Zn₂(SDBA)(3-ATZ)₂]·solvent, I and II, with tetrahedral Zn centers as good Lewis acidic sites and the free amino group of the 3-amino triazole ligand as a strong Lewis base center were shown to perform 4-step cascade/tandem reaction in a facile manner. Effective conversion of benzaldehyde dimethyl acetal in the presence of excess nitromethane at 100 °C in water to 1-(1,3-dinitropropan-2-yl) benzene was achieved in 10 h with yields of ∼95% (I) and ∼94% (II). This 4-step cascade reaction proceeds via deacetalization (Lewis acid), Henry (Lewis base), and Michael (Lewis base) reactions. The present work highlights the importance of spatially separated functional groups in multistep tandem catalysis─the examples of which are not common.

A Review of the Design and Performance of Catalysts for Hydrothermal Gasification of Biomass to Produce Hydrogen-Rich Gas Fuel

Supercritical water gasification has emerged as a promising technology to sustainably convert waste residues into clean gaseous fuels rich in combustible gases such as hydrogen and methane. The composition and yield of gases from hydrothermal gasification depend on process conditions such as temperature, pressure, reaction time, feedstock concentration, and reactor geometry. However, catalysts also play a vital role in enhancing the gasification reactions and selectively altering the composition of gas products. Catalysts can also enhance hydrothermal reforming and cracking of biomass to achieve desired gas yields at moderate temperatures, thereby reducing the energy input of the hydrothermal gasification process. However, due to the complex hydrodynamics of supercritical water, the literature is limited regarding the synthesis, application, and performance of catalysts used in hydrothermal gasification. Hence, this review provides a detailed discussion of different heterogeneous catalysts (e.g., metal oxides and transition metals), homogeneous catalysts (e.g., hydroxides and carbonates), and novel carbonaceous catalysts deployed in hydrothermal gasification. The article also summarizes the advantages, disadvantages, and performance of these catalysts in accelerating specific reactions during hydrothermal gasification of biomass, such as water-gas shift, methanation, hydrogenation, reforming, hydrolysis, cracking, bond cleavage, and depolymerization. Different reaction mechanisms involving a variety of catalysts during the hydrothermal gasification of biomass are outlined. The article also highlights recent advancements with recommendations for catalytic supercritical water gasification of biomass and its model compounds, and it evaluates process viability and feasibility for commercialization.

Cationic Polymer Coating Increases the Catalytic Activity of Gold Nanoparticles toward Anionic Substrates

Organic coatings on catalytic metal nanoparticles (NPs) typically hinder their activity due to the blocking of active sites. Therefore, considerable effort is made to remove organic ligands when preparing supported NP catalytic materials. Here, cationic polyelectrolyte coatings are shown to increase the catalytic activity of partially embedded gold nanoislands (Au NIs) toward transfer hydrogenation and oxidation reactions with anionic substrates compared to the activity of identical but uncoated Au NIs. Any potential steric hindrance caused by the coating is countered by a decrease in the activation energy of the reaction by half, resulting in overall enhancement. The direct comparison to identical but uncoated NPs isolates the role of the coating and provides conclusive evidence of enhancement. Our findings show that engineering the microenvironment of heterogeneous catalysts, creating hybrid materials that cooperatively interact with the reactants involved, is a viable and exciting path to improving their performance.

Cu-based high-entropy two-dimensional oxide as stable and active photothermal catalyst

Cu-based nanocatalysts are the cornerstone of various industrial catalytic processes. Synergistically strengthening the catalytic stability and activity of Cu-based nanocatalysts is an ongoing challenge. Herein, the high-entropy principle is applied to modify the structure of Cu-based nanocatalysts, and a PVP templated method is invented for generally synthesizing six-eleven dissimilar elements as high-entropy two-dimensional (2D) materials. Taking 2D Cu₂Zn₁Al_0.5Ce₅Zr_0.5O_x as an example, the high-entropy structure not only enhances the sintering resistance from 400 °C to 800 °C but also improves its CO₂ hydrogenation activity to a pure CO production rate of 417.2 mmol g^-1 h^-1 at 500 °C, 4 times higher than that of reported advanced catalysts. When 2D Cu₂Zn₁Al_0.5Ce₅Zr_0.5O_x are applied to the photothermal CO₂ hydrogenation, it exhibits a record photochemical energy conversion efficiency of 36.2%, with a CO generation rate of 248.5 mmol g^-1 h^-1 and 571 L of CO yield under ambient sunlight irradiation. The high-entropy 2D materials provide a new route to simultaneously achieve catalytic stability and activity, greatly expanding the application boundaries of photothermal catalysis.

Three-Component Chemo-Selective Synthesis of N-(o-Alkenylaryl) Pyrazoles by Pyrazole Annulation and Rh-Catalyzed Chemo-Selective Aryl C-H Addition Cascade

By using readily available enaminones, aryl hydrazine hydrochlorides, and alkynes as starting materials, the chemo-selective three-component synthesis of atropisomeric N-(o-alkenylaryl) pyrazoles has been efficiently accessed with rhodium catalysis. Unlike Satoh-Miura reaction leading to the alkyne-based C-H benzannulation by using prior prepared N-phenyl pyrazoles and alkynes as substrates, this three-component protocol displays unprecedented selectivity of C-H alkenylation by blocking the second round metal alkenylation with the key protonation step in the presence of acids.

Advances in CO2 utilization employing anisotropic nanomaterials as catalysts: a review

Anisotropic nanomaterials are materials with structures and properties that vary depending on the direction in which they are measured. Unlike isotropic materials, which exhibit uniform physical properties in all directions, anisotropic materials have different mechanical, electrical, thermal, and optical properties in different directions. Examples of anisotropic nanomaterials include nanocubes, nanowires, nanorods, nanoprisms, nanostars, and so on. These materials have unique properties that make them useful in a variety of applications, such as electronics, energy storage, catalysis, and biomedical engineering. One of the key advantages of anisotropic nanomaterials is their high aspect ratio, which refers to the ratio of their length to their width, which can enhance their mechanical and electrical properties, making them suitable for use in nanocomposites and other nanoscale applications. However, the anisotropic nature of these materials also presents challenges in their synthesis and processing. For example, it can be difficult to align the nanostructures in a specific direction to impart modulation of a specific property. Despite these challenges, research into anisotropic nanomaterials continues to grow, and scientists are working to develop new synthesis methods and processing techniques to unlock their full potential. Utilization of carbon dioxide (CO₂) as a renewable and sustainable source of carbon has been a topic of increasing interest due to its impact on reducing the level of greenhouse gas emissions. Anisotropic nanomaterials have been used to improve the efficiency of CO₂ conversion into useful chemicals and fuels using a variety of processes such as photocatalysis, electrocatalysis, and thermocatalysis. More study is required to improve the usage of anisotropic nanomaterials for CO₂ consumption and to scale up these technologies for industrial use. The unique properties of anisotropic nanomaterials, such as their high surface area, tunable morphology, and high activity, make them promising catalysts for CO₂ utilization. This review article discusses briefly about various approaches towards the synthesis of anisotropic nanomaterials and their applications in CO₂ utilization. The article also highlights the challenges and opportunities in this field and the future direction of research.

A Heterogeneous Single Atom Cobalt Catalyst for Highly Efficient Acceptorless Dehydrogenative Coupling Reactions

A fundamental understanding of metal active sites in single-atom catalysts (SACs) is important and challenging in the development of high-performance catalyst systems. Here, a highly efficient and straightforward molten-salt-assisted approach is reported to create atomically dispersed cobalt atoms supported over vanadium pentoxide layered material, with each cobalt atom coordinated with four neighboring oxygen atoms. The liquid environment and the strong polarizing force of the molten salt at high temperatures potentially favor the weakening of VO bonding and the formation of CoO bonding on the vanadium oxide surface. This cobalt SAC achieves extraordinary catalytic efficiency in acceptorless dehydrogenative coupling of alcohols with amines to give imines, with more than 99% selectivity under almost 100% conversion within 3 h, along with a high turnover frequency (TOF) of 5882 h^-1 , exceeding those of previously reported benchmarking catalysts. Moreover, it delivers excellent recyclability, reaction scalability, and substrate tolerance. Density functional theory (DFT) calculations further confirm that the optimized coordination environment and strong electronic metal-support interaction contribute significantly to the activation of reactants. The findings provide a feasible route to construct SACs at the atomic level for use in organic transformations.

Site-Averaged Ab Initio Kinetics: Importance Learning for Multistep Reactions on Amorphous Supports

Single-atom centers on amorphous supports include catalysts for polymerization, partial oxidation, metathesis, hydrogenolysis, and more. The disordered environment makes each site different, and the kinetics exponentially magnifies these differences to make ab initio site-averaged kinetics calculations extremely difficult. This work extends the importance learning algorithm for efficient and precise site-averaged kinetics estimates to ab initio calculations and multistep reaction mechanisms. Specifically, we calculate site-averaged proton transfer relaxation rates on an ensemble of cluster models representing Brønsted acid sites on silica-alumina. We include direct and water-assisted proton transfer pathways and simultaneously estimate the water adsorption and activation enthalpies for forward and backward proton transfers. We use density functional theory (DFT) to obtain a site-averaged rate, somewhat like a turnover frequency, for the proton transfer relaxation rate. Finally, we show that importance learning can provide orders-of-magnitude acceleration over standard sampling methods for site-averaged rate calculations in cases where the rate is dominated by a few highly active sites.

Geometric and Electronic Engineering of Atomically Dispersed Copper-Cobalt Diatomic Sites for Synergistic Promotion of Bifunctional Oxygen Electrocatalysis in Zinc-Air Batteries

The development of rechargeable zinc-air batteries is heavily dependent on bifunctional oxygen electrocatalysts to offer exceptional oxygen reduction/evolution reaction (ORR/OER) activities. However, the design of such electrocatalysts with high activity and durability is challenging. Herein, a strategy is proposed to create an electrocatalyst comprised of copper-cobalt diatomic sites on a highly porous nitrogen-doped carbon matrix (Cu-Co/NC) with abundantly accessible metal sites and optimal geometric and electronic structures. Experimental findings and theoretical calculations demonstrate that the synergistic effect of Cu-Co dual-metal sites with metal-N₄ coordination induce asymmetric charge distributions with moderate adsorption/desorption behavior with oxygen intermediates. This electrocatalyst exhibits extraordinary bifunctional oxygen electrocatalytic activities in alkaline media, with a half-wave potential of 0.92 V for ORR and a low overpotential of 335 mV at 10 mA cm^-2 for OER. In addition, it demonstrates exceptional ORR activity in acidic (0.85 V) and neutral (0.74 V) media. When applied to a zinc-air battery, it achieves extraordinary operational performance and outstanding durability (510 h), ranking it as one of the most efficient bifunctional electrocatalysts reported to date. This work demonstrates the importance of geometric and electronic engineering of isolated dual-metal sites for boosting bifunctional electrocatalytic activity in electrochemical energy devices.

Schiff base modified starch: A promising biosupport for palladium in Suzuki cross-coupling reactions

Starch can be used in diverse fields because it is a readily available, non-toxic polysaccharide with adaptable functionality and biodegradability. In this study, taking the aforementioned characteristics into consideration, we designed a modified starch (Starch-SB), which serves as supporting material for palladium stabilization. This new air and moisture-stable robust palladium composite [Starch-SB-Pd(II)] was characterized by FT-IR, XRD, TGA, XPS, SEM, EDX, TEM, CP/MAS ¹³C NMR, and ICP-MS analytical techniques. The catalytic studies exhibit high activity (up to 99 %) and stability in Suzuki cross-coupling reactions for this starch supported catalytic system under mild conditions (lower reaction temperature and green solvents) because of the cooperative interactions of multifunctional capturing sites on starch (Schiff base, hydroxy and amine groups) with palladium species. The experiments on reusability demonstrate that Starch-SB-Pd(II), which was prepared from functionalized starch, could be readily recycled several cycles through centrifugation. Moreover, we proposed a possibly multifunctional complex structure. This work presents an appealing and intriguing pathway for the utilization of polysaccharide as crucial support in green chemical transformations.

Oxygen Evolution/Reduction Reaction Catalysts: From In Situ Monitoring and Reaction Mechanisms to Rational Design

The oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) are core steps of various energy conversion and storage systems. However, their sluggish reaction kinetics, i.e., the demanding multielectron transfer processes, still render OER/ORR catalysts less efficient for practical applications. Moreover, the complexity of the catalyst-electrolyte interface makes a comprehensive understanding of the intrinsic OER/ORR mechanisms challenging. Fortunately, recent advances of in situ/operando characterization techniques have facilitated the kinetic monitoring of catalysts under reaction conditions. Here we provide selected highlights of recent in situ/operando mechanistic studies of OER/ORR catalysts with the main emphasis placed on heterogeneous systems (primarily discussing first-row transition metals which operate under basic conditions), followed by a brief outlook on molecular catalysts. Key sections in this review are focused on determination of the true active species, identification of the active sites, and monitoring of the reactive intermediates. For in-depth insights into the above factors, a short overview of the metrics for accurate characterizations of OER/ORR catalysts is provided. A combination of the obtained time-resolved reaction information and reliable activity data will then guide the rational design of new catalysts. Strategies such as optimizing the restructuring process as well as overcoming the adsorption-energy scaling relations will be discussed. Finally, pending current challenges and prospects toward the understanding and development of efficient heterogeneous catalysts and selected homogeneous catalysts are presented.

Optically Controlled Recovery and Recycling of Homogeneous Organocatalysts Enabled by Photoswitches

We address a critical challenge of recovering and recycling homogeneous organocatalysts by designing photoswitchable catalyst structures that display a reversible solubility change in response to light. Initially insoluble catalysts are UV-switched to a soluble isomeric state, which catalyzes the reaction, then back-isomerizes to the insoluble state upon completion of the reaction to be filtered and recycled. The molecular design principles that allow for the drastic solubility change over 10 times between the isomeric states, 87 % recovery by the light-induced precipitation, and multiple rounds of catalyst recycling are revealed. This proof of concept will open up opportunities to develop highly recyclable homogeneous catalysts that are important for the synthesis of critical compounds in various industries, which is anticipated to significantly reduce environmental impact and costs.

Efficient Voltage-Driven Oxidation of Water and Alcohols by an Organic Molecular Catalyst Directly Attached to a Carbon Electrode

The integration of heterogeneous electrocatalysis and molecular catalysis is a promising approach to designing new catalysts for the oxygen evolution reaction (OER) and other processes. We recently showed that the electrostatic potential drop across the double layer contributes to the driving force for electron transfer between a dissolved reactant and a molecular catalyst immobilized directly on the electrode surface. Here, we report high current densities and low onset potentials for water oxidation attained using a metal-free voltage-assisted molecular catalyst (TEMPO). Scanning electrochemical microscopy (SECM) was used to analyze the products and determine faradic efficiencies for the generation of H₂O₂ and O₂. The same catalyst was employed for efficient oxidations of butanol, ethanol, glycerol, and H₂O₂. DFT calculations show that the applied voltage alters the electrostatic potential drop between TEMPO and the reactant as well as chemical bonding between them, thereby increasing the reaction rate. These results suggest a new route for designing next-generation hybrid molecular/electrocatalysts for OER and alcohol oxidations.

A highly robust cluster-based indium(III)-organic framework with efficient catalytic activity in cycloaddition of CO2 and Knoevenagel condensation

The efficient catalytic performance displayed by MOFs is decided by an appropriate charge/radius ratio of defect metal sites, large enough solvent-accessible channels and Lewis base sites capable of polarizing substrate molecules. Herein, the solvothermal self-assembly led to a highly robust nanochannel-based framework of {[In₄(CPDD)₂(μ₃-OH)₂(DMF)(H₂O)₂]·2DMF·5H₂O}_n (NUC-66) with a 56.8% void volume, which is a combination of a tetranuclear cluster [In₄(μ₃-OH)₂(COO)₁₀(DMF)(H₂O)₂] (abbreviated as {In₄}) and a conjugated tetracyclic pentacarboxylic acid ligand of 4,4'-(4-(4-carboxyphenyl)pyridine-2,6-diyl)diisophthalic acid (H₅CPDD). To the best of our knowledge, NUC-66 is a rarely reported {In₄}-based 3D framework with embedded hierarchical triangular-microporous (2.9 Å) and hexagonal-nanoporous (12.0 Å) channels, which are shaped by six rows of {In₄} clusters. After solvent exchange and vacuum drying, the surface of nanochannels in desolvated NUC-66a is modified by unsaturated In³⁺ ions, N_pyridine atoms and μ₃-OH groups, all of which display polarization ability towards polar molecules due to their Lewis acidity or basicity. The catalytic experiments performed showed that NUC-66a had high catalytic activity in the cycloaddition reactions of epoxides with CO₂ under mild conditions, which should be ascribed to its structural advantages including nanoscale channels, rich bifunctional active sites, large surface areas and chemical stability. Moreover, NUC-66a, as a heterogeneous catalyst, could greatly accelerate the Knoevenagel condensation reactions of aldehydes and malononitrile. Hence, this work confirms that the development of rigid nanoporous cluster-based MOFs built on metal ions with a high charge and large radius ratio will be more likely to realize practical applications, such as catalysis, adsorption and separation of gas, etc.

A Priori Design of Dual-Atom Alloy Sites and Experimental Demonstration of Ethanol Dehydrogenation and Dehydration on PtCrAg

Single-atom catalysts have received significant attention for their ability to enable highly selective reactions. However, many reactions require more than one adjacent site to align reactants or break specific bonds. For example, breaking a C-O or O-H bond may be facilitated by a dual site containing an oxophilic element and a carbophilic or "hydrogenphilic" element that binds each molecular fragment. However, design of stable and well-defined dual-atom sites with desirable reactivity is difficult due to the complexity of multicomponent catalytic surfaces. Here, we describe a new type of dual-atom system, trimetallic dual-atom alloys, which were designed via computation of the alloying energetics. Through a broad computational screening we discovered that Pt-Cr dimers embedded in Ag(111) can be formed by virtue of the negative mixing enthalpy of Pt and Cr in Ag and the favorable interaction between Pt and Cr. These dual-atom alloy sites were then realized experimentally through surface science experiments that enabled the active sites to be imaged and their reactivity related to their atomic-scale structure. Specifically, Pt-Cr sites in Ag(111) can convert ethanol, whereas PtAg and CrAg are unreactive toward ethanol. Calculations show that the oxophilic Cr atom and the hydrogenphilic Pt atom act synergistically to break the O-H bond. Furthermore, ensembles with more than one Cr atom, present at higher dopant loadings, produce ethylene. Our calculations have identified many other thermodynamically favorable dual-atom alloy sites, and hence this work highlights a new class of materials that should offer new and useful chemical reactivity beyond the single-atom paradigm.

Crotonaldehyde Adsorption on Cu-Pt Surface Alloys: A Quantum Mechanics Study

The adsorption of crotonaldehyde on Cu-Pt alloy surfaces was characterized by density functional theory (DFT). Two surfaces were considered: Cu2Pt/Cu(111) and Cu3Pt/Cu(111). It was determined that the presence of Pt on the surface, even when isolated as single atoms fully surrounded by Cu, provides additional stability for the adsorbates, increasing the magnitude of the adsorption energy by as much as 40 kJ/mol. The preferred bonding on both surfaces is via multiple coordination, with the most stable configuration being a cis arrangement with di-σ bonding of the C=O bond across a Cu–Cu bridge and an additional π bonding to a Pt atom. The fact that Pt significantly affects the adsorption of unsaturated aldehydes such as crotonaldehyde explains why the kinetics of their hydrogenation using single-atom alloy (SAA) catalysts vary with alloy composition, as we previously reported, and brings into question the simple model in which the role of Pt is only to promote the dissociation of H2.

Engineering the Electronic Structure of Single-Atom Iron Sites with Boosted Oxygen Bifunctional Activity for Zinc-Air Batteries

Rechargeable zinc-air batteries typically require efficient, durable, and inexpensive bifunctional electrocatalysts to support oxygen reduction/evolution reactions (ORR/OER). However, sluggish kinetics and mass transportation challenges must be addressed if the performance of these catalysts is to be enhanced. Herein, a strategy to fabricate a catalyst comprising atomically dispersed iron atoms supported on a mesoporous nitrogen-doped carbon support (Fe SAs/NC) with accessible metal sites and optimized electronic metal-support interactions is developed. Both the experimental results and theoretical calculations reveal that the engineered electronic structures of the metal active sites can regulate the charge distribution of Fe centers to optimize the adsorption/desorption of oxygenated intermediates. The Fe SAs/NC containing Fe₁ N₄ O₁ sites achieves remarkable ORR activity over the entire pH range, with half-wave potentials of 0.93, 0.83, and 0.75 V (vs reversible hydrogen electrode) in alkaline, acidic, and neutral electrolytes, respectively. In addition, it demonstrates a promising low overpotential of 320 mV at 10 mA cm^-2 for OER in alkaline conditions. The zinc-air battery assembled with Fe SAs/NC exhibits superior performance than that of Pt/C+RuO₂ counterpart in terms of peak power density, specific capacity, and cycling stability. These findings demonstrate the importance of the electronic structure engineering of metal sites in directing catalytic activity.

Protein-supported transition metal catalysts: Preparation, catalytic applications, and prospects

The immobilization of transition metal catalysts onto supports enables their easier recycling and improves catalytic performance. Protein supports not only support and stabilize transition metal catalysts but also enable the incorporation of biocompatibility and enzymatic catalysis into these catalysts. Consequently, the engineering of protein-supported transition metal catalysts (PTMCs) has emerged as an effective approach to improving their catalytic performance and widening their catalytic applications. Here, we review the recent development of the preparation and applications of PTMCs. The preparation of PTMCs will be summarized and discussed in terms of the types of protein supports, including proteins, protein assemblies, protein-polymer conjugates, and cross-linked proteins. Then, their catalytic applications including organic synthesis, photocatalysis, polymerization, and biomedicine, will be surveyed and compared. Meanwhile, the established catalytic structures-function relationships will be summarized. Lastly, the remaining issues and prospects will be discussed. By surveying a wide range of PTMCs, we believe that this review will attract a broad readership and stimulate the development of PTMCs.

Green carbon-carbon homocoupling of terminal alkynes by a silica supported Cu(II)-hydrazone coordination compound

A Cu(II) complex, [Cu(HL)(NO₃)(CH₃OH)]·CH₃OH (1), was obtained by the reaction of Cu(NO₃)₂·3H₂O and H2L in methanol solvent (H2L is (E)-4-amino-N'-(2-hydroxy-3-methoxybenzylidene)benzohydrazide). H2L and compound 1 were characterized by various spectroscopic analyses and the molecular structure of [Cu(HL)(NO₃)(CH₃OH)]·CH₃OH was determined by single-crystal X-ray analysis. The results indicated the product is a mononuclear Cu(II) complex and contains a free NH₂ functional group on the structure of the ligand. [Cu(HL)(NO₃)(CH₃OH)]·CH₃OH was used for the preparation of a heterogeneous catalyst by supporting it on functionalized silica gel. The heterogeneous catalyst (Si-Cu) was prepared by an amidification reaction of [Cu(HL)(NO₃)(CH₃OH)]·CH₃OH with functionalized silica gel. The resulting silica-supported catalyst (Si-Cu) was characterized by TGA, FT-IR, EPR, DRS, EDS, XRD, SEM and XPS analyses. Si-Cu was employed in a carbon-carbon coupling reaction and the effects of the amount of Si-Cu and temperature were investigated in the catalytic coupling. The structure of one of the products of the catalytic reactions (C₁₆H₂₂O₂, CP1) was determined by single-crystal X-ray analysis, which proved the formation of a C-C bond and the production of di-acetylene by homocoupling of terminal alkyne. This catalytic system is stable and it can be reused for a coupling reaction without a significant change in its catalytic activity.

In situ identification of surface sites in Cu-Pt bimetallic catalysts: Gas-induced metal segregation

The effect of gases on the surface composition of Cu-Pt bimetallic catalysts has been tested by in situ infrared (IR) and x-ray absorption spectroscopies. Diffusion of Pt atoms within the Cu-Pt nanoparticles was observed both in vacuum and under gaseous atmospheres. Vacuum IR spectra of CO adsorbed on CuPt_x/SBA-15 catalysts (x = 0-∞) at 125 K showed no bonding on Pt regardless of Pt content, but reversible Pt segregation to the surface was seen with the high-Pt-content (x ≥ 0.2) samples upon heating to 225 K. In situ IR spectra in CO atmospheres also highlighted the reversible segregation of Pt to the surface and its diffusion back into the bulk when cycling the temperature from 295 to 495 K and back, most evidently for diluted single-atom alloy catalysts (x ≤ 0.01). Similar behavior was possibly observed under H₂ using small amounts of CO as a probe molecule. In situ x-ray absorption near-edge structure data obtained for CuPt_0.2/SBA-15 under both CO and He pointed to the metallic nature of the Pt atoms irrespective of gas or temperature, but analysis of the extended x-ray absorption fine structure identified a change in coordination environment around the Pt atoms, from a (Pt-Cu):(Pt-Pt) coordination number ratio of ∼6:6 at or below 445 K to 8:4 at 495 K. The main conclusion is that Cu-Pt bimetallic catalysts are dynamic, with the composition of their surfaces being dependent on temperature in gaseous environments.