Increased Silver Activity for Direct Propylene Epoxidation via Subnanometer Size Effects

Low-Temperature Direct Oxidation of Propane to Propylene Oxide Using Supported Subnanometer Cu Clusters

Propylene oxide, a key commodity of the chemical industry for a wide range of consumer products, is synthesized through sequential propane dehydrogenation and epoxidation reactions. However, the lack of a direct catalytic route from propane to propylene oxide reduces efficiency and represents a major challenge for catalysis science. Herein, we report the discovery of a highly active and selective catalyst, made of alumina-supported subnanometer copper clusters, which can directly convert propane to propylene oxide at temperatures as low as 150 °C. Moreover, at higher temperatures, on the same catalysts, the selectivity is switched to propylene. Accompanying theoretical calculations indicate that partially oxidized and/or hydroxylated clusters have low activation energies for both propane dehydrogenation and propylene epoxidation pathways, enabling direct conversion with very high selectivity for propylene oxide. The discovery of a low-temperature catalyst that can convert propane directly to propylene oxide provides an important opportunity for the development of energy-efficient and economic catalysts for this industrially critical process. Similarly, when operating at higher temperatures, these catalysts are posed as potent oxidative dehydrogenation catalysts.

V activated electro-epoxidation catalyst in membrane electrode assembly system for the production of propylene oxide

Direct electro-epoxidation of propylene (D-EOPO) with a membrane electrode assembly (MEA) system represents a sustainable approach for producing propylene oxide, which can reduce ohmic losses and simplify product separation. To address the challenges of selectivity and activity, we develop an Ag/V catalyst and integrate it into the "liquid-free" MEA reactor for continues D-EOPO. The V in the catalyst facilitates the formation of Ag-O active centers, thereby reducing the generation energy of *O radicals. Meanwhile, V doping also results in a downshift of the d-band center of the Ag sites. Consequently, the formation of the crucial intermediate (*OC3H6) is significantly accelerated through the coupling *O with adsorbed propylene, thereby markedly improving propylene oxide (PO) production. The MEA reactor, integrated with the developed Ag/V catalyst, can maintain a stable production rate of PO at 227 μmol/h over a period of 78 hours. Thus, the "liquid-free" electro-epoxidation protocol developed here exhibits greater industrial applicability.

Research Progress in Epoxidation of Light Small-Molecule Olefins

Light olefins, as important bulk raw materials in the petrochemical industry, play an irreplaceable role in the development of the manufacturing industry and the economy. The epoxides of light olefins are important intermediates for the synthesis of polymers, drugs, and fine chemicals, and their green, efficient, and safe synthesis has attracted much attention. This review focuses on the research progress of light olefin epoxidation and elucidates traditional epoxidation methods, such as the chlorohydrin method. Although these processes have mature processes, they have drawbacks, including equipment corrosion, environmental pollution, poor safety, and high waste emissions. Special emphasis is placed on catalytic epoxidation systems using oxygen or organic peroxides as oxygen sources. For homogeneous catalytic systems, certain metal complexes exhibit high activity and selectivity yet are difficult to separate and recycle. Moreover, heterogeneous catalytic systems have become a research hotspot due to their advantages of easy separation and reusability, with supported metal catalysts being a prime example. Meanwhile, the effects of reaction temperature, pressure, solvent, etc., on epoxidation are explored. The specific reaction mechanisms are also studied and analyzed. Current research challenges, including enhancing catalyst stability and reducing costs, are summarized. In the future, developing highly efficient, green, and economically viable epoxidation technologies for large-scale industrial applications represents an important research direction in this field.

Ultrafine Nanoparticle Rh/CeO2-ZrO2 Catalysts Synthesized via Spatial Confinement: Higher Three-Way Catalytic Activity Compared to Rh Single-Atom Catalyst

The synthesis of size-controlled ultrafine metal-based catalysts is vitally important for chemical conversion technologies. This study presents a spatial confinement strategy for the synthesis of Rh/CeO2-ZrO2 (0.5 wt % Rh) three-way catalysts with ultrafine Rh nanoparticles (1-3 nm). This strategy utilizes the self-confinement effect of Rh ions through the strong electrostatic adsorption between Rh ions and the surface of CeO2-ZrO2, as well as the spatial hindrance provided by the mesopores of the support during Rh particle growth. The nanoparticle catalyst (NPC) with a size of ∼2.19 nm exhibits high catalytic performance, surpassing the Rh single-atom catalyst (SAC) and the other NPCs with different Rh sizes in the three-way catalytic reaction under a gas mixture of carbon monoxide (CO), hydrocarbons (HCs), and nitric oxide (NO). Rh SAC displays higher CO oxidation activity and comparable C3H6 oxidation activity compared with Rh NPC in reaction atmospheres without NO gas molecules. However, the presence of NO molecules hinders the adsorption and reaction of CO and HCs on the Rh single-atom sites. The impact of NO on Rh NPC is weaker due to the multiatomic active center structure of the Rh nanoparticles, resulting in enhanced low-temperature catalytic activity in three-way reaction atmospheres. Additionally, NPC demonstrates better stability than SAC under hydrothermal aging condition.

The roles of various Fe-Cu bimetallic nanoclusters in controlling the C2 selectivity for the CO reduction reaction - a DFT study

The unique microstructure of the Cu13 nanocluster with distinct catalytic properties from general metals has been used to study the selectivity effect on oxygenated hydrocarbons. The strong synergistic promotion of Fe-Cu bimetallic nanocatalysts has been used to convert CO2 or CO to olefins via selective reduction. Unveiled using DFT, we have characterized the CO reduction capabilities of a series of Fe-Cu bimetallic nanocatalysts and further investigated to search for the possible intermediates along the CO reduction pathway. FenCu13-n clusters with different compositions (n = 1, 2, 7, 11 and 12) are selected to represent the Cu dominant, the equal ratios, and the Fe dominant conditions in the simulations. Only the Fe-dominant clusters, particularly Fe7Cu6 and Fe11Cu2, show a preference for the formation of the COCHO intermediate. The improvement in selectivity is crucial to the successful design of catalytic systems for carbon-neutral processes. Thus, we incorporated carbon nanotubes (CNTs) to stabilize Fe7Cu6 and Fe11Cu2 nanoclusters, with the goal of enhancing the reactivity of the CORR. Compared to the isolated nanoclusters, the Fe11Cu2/CNT not only reduces the activation energy for CO⋯CHO bond formation and the reaction energy for COCHO intermediate formation but also exhibits more stable thermodynamic properties for ethanol generation.

Effect of Cu/Au for propylene epoxidation over the Ag2O(111) surface: a DFT study

Catalysts belonging to the IB group for propylene epoxidation have garnered significant attention and have been extensively developed in the chemical industry. In this study, spin-polarized density functional theory (DFT) calculations combined with a U correction were performed to study propylene epoxidation on the Ag2O(111) surface with and without Cu or Au doping. Our calculations revealed a dual propylene epoxidation mechanism: the allylic hydrogen stripping (AHS) route and the intermediary propylene oxametallacycle (OMMP) route. The doped Cu or Au sites on the Ag2O(111) surface exhibited superior adsorbate activity, which also influenced the activity of adjacent surface Osuf sites. On the Cu-Ag2O(111) surface, the Osuf site exhibited the lowest basicity, favoring the OMMP route. Conversely, on the Au-Ag2O(111) surface, the Osuf site had relatively stronger basicity, which favored the AHS route. Furthermore, energetic span model analysis was carried out and showed that product selectivity followed different patterns depending on the doping: acrolein > acetone > propanal ≅ PO on the pure surface, acrolein > PO > propanal ≅ acetone on the Cu-doped surface, and acrolein > acetone > propanal > PO on the Au-doped surface. Notably, acrolein was prone to complete combustion to carbon dioxide, which became the primary product on both doped and undoped Ag2O(111) surfaces. While the selectivity of PO can be enhanced slightly by the doping of Cu, unfortunately, the selectivity of PO can be reduced by the doping of Au. This study aims to provide insights into the nature of IB group catalysts for propylene epoxidation, which mainly regulate the lower basicity of lattice oxygen through doping promoters and optimize the industrial yield of PO.

Exploring nitrogen-mediated effects on Fe and Cu cluster development in graphene: a DFT study

The controlled growth and stability of transition metal clusters on N-doped materials have become the subject of intense investigation for unveiling comprehension on the cluster growth evolution. In this study, we investigated the growth mechanisms of non-magnetic (copper) and magnetic (iron) clusters on graphene with two atomic vacancies, with and without pyridinic nitrogen (N). Our results determine the role of pyridinic N in the growth and physicochemical properties of the mentioned metal clusters. In an N environment, Cu grows perpendicularly, whereas under N-deficient conditions, the clusters agglomerate. Fe cumulate-type clusters are formed regardless of the presence of N. However, N causes the Fe clusters to rise over one side of the surface without deforming the monolayer; meanwhile, in the absence of N, the Fe clusters protrude from both sides of the monolayer. Remarkably, the presence of N makes it feasible to induce magnetization in the Cun-N4V2 systems and aid in focalizing the magnetic properties on the Fe clusters for the Fen-N4V2 case. These findings offer insights into the role of N in cluster growth, with potential implications for diverse applications, including magnetic and electrocatalytic materials.

In Situ Deprotection-Free Synthesis of Silver/Graphdiyne with a High Raman Sensing Effect for Detection of Polychlorophenols and Microplastics

Since the first synthesis of graphdiyne (GDY), it has been widely receiving a lot of attention and has great application prospects in many fields, such as energy storage, catalysis, and sensing. However, the complex deprotection treatment and long reaction time limit its mass production and applications. Here, we present a strategy for the silver-catalyzed deprotection-free rapid synthesis of GDY. Crystalline GDY was synthesized in 8 h at room temperature and atmospheric pressure, and after the reaction, Ag nanoparticles with an ultrathin diameter of 2-3 nm were formed in situ inside and on the surface of GDY. This Ag/GDY composite exhibits a high specific surface area of 672.3 m2 g-1 and strong surface plasmon resonance behavior, showing a strong surface-enhanced Raman scattering effect. The enhancement factor and the lowest detection limit for rhodamine 6G are 3.54 × 108 and 1 × 10-14 M, respectively. The Ag/GDY achieves the simultaneous enrichment and detection of polychlorophenols and ultrafine nanoplastics.

Direct propylene epoxidation with molecular oxygen over titanosilicate zeolites

The direct epoxidation of propylene with molecular oxygen represents a desired route for propylene oxide (PO) production with 100% theoretical atomic economy. However, this aerobic epoxidation reaction suffers from the apparent trade-off between propylene conversion and PO selectivity, and remains a key challenge in catalysis. We report that Ti-Beta zeolites containing isolated framework Ti species can efficiently catalyze the aerobic epoxidation of propylene. Stable propylene conversion of 25% and PO selectivity of up to 90% are achieved at the same time, matching the levels of industrial ethylene aerobic epoxidation processes. H-terminated pentacoordinated Ti species in Beta zeolite frameworks are identified as the preferred active sites for propylene aerobic epoxidation and the reaction is initiated by the participation of lattice oxygen in Ti-OH. These results are expected to spark new technology for the industrial production of PO toward more sustainable chemistry and chemical engineering.

Fabrication of bio-inorganic metal nanoparticles by low-cost lychee extract for wastewater remediation: a mini-review

INTRODUCTION

This review article gives an overview of the biogenic synthesis of metal nanoparticles (mNPs) while using Litchi chinensis extract as a reducing and stabilizing agent. The subtropical fruit tree i.e lychee contains phytochemicals such as flavonoids, terpenoids, and polyphenolic compounds which act as reducing agents and convert the metal ions into metal atoms that coagulate to form mNPs.

METHODOLOGY

Different methodologies adopted for the synthesis of lychee extract and its use in the fabrication of mNPs under different reaction conditions such as solvent, extract amount, temperature, and pH of the medium have also been discussed critically in detail.

TECHNIQUES

Different techniques such as FTIR, UV-visible, XRD, SEM, EDX, and TEM adopted for the analysis of biogenic synthesis of mNPs have also been discussed in detail. Applications of mNPs: Applications of these prepared mNPs in various fields due to their antimicrobial, antiinflammatory, anticancer, and catalytic activities have also been described in detail.

Chemical and engineering bases for green H2O2 production and related oxidation and ammoximation of olefins and analogues

Plastics, fibers and rubber are three mainstream synthetic materials that are essential to our daily lives and contribute significantly to the quality of our lives. The production of the monomers of these synthetic polymers usually involves oxidation or ammoximation reactions of olefins and analogues. However, the utilization of C, O and N atoms in current industrial processes is <80%, which represents the most environmentally polluting processes for the production of basic chemicals. Through innovation and integration of catalytic materials, new reaction pathways, and reaction engineering, the Research Institute of Petroleum Processing, Sinopec Co., Ltd. (RIPP) and its collaborators have developed unique H2O2-centered oxidation/ammoximation technologies for olefins and analogues, which has resulted in a ¥500 billion emerging industry and driven trillions of ¥s' worth of downstream industries. The chemical and engineering bases of the production technologies mainly involve the integration of slurry-bed reactors and microsphere catalysts to enhance H2O2 production, H2O2 propylene/chloropropylene epoxidation for the production of propylene oxide/epichlorohydrin, and integration of H2O2 cyclohexanone ammoximation and membrane separation to innovate the caprolactam production process. This review briefly summarizes the whole process from the acquisition of scientific knowledge to the formation of an industrial production technology by RIPP. Moreover, the scientific frontiers of H2O2 production and related oxidation/ammoximation processes of olefins and analogues are reviewed, and new technological growth points are envisaged, with the aim of maintaining China's standing as a leader in the development of the science and technologies of H2O2 production and utilization.

Electrifying oxidation of ethylene and propylene

Ethylene and propylene, as essential precursors in the chemical industry, have been playing a pivotal role in the production of various value-added chemicals that find wide applications in diverse sectors, such as polymer synthesis, lithium-ion battery electrolytes, antifreeze agents and pharmaceuticals. Nevertheless, traditional methods for olefin functionalization including chlorohydrination and epoxidation involve energy-intensive steps and environment-detrimental by-products. In contrast, electrocatalysis is emerging as a promising and sustainable approach for olefin oxidation via utilizing renewable electricity. Recent advancements in energy storage and conversion technologies have intensified the research efforts toward designing efficient electrocatalysts for the selective oxidation of ethylene and propylene, highlighting the shift towards more sustainable production methods. Herein, we summarize recent progress in the electrocatalytic oxidation of ethylene and propylene, focusing on achievement in catalyst design, reaction system selection and mechanism exploration. We figure out the advantages of different oxidation methods for improved performance and discuss the various types of catalysts like noble metals, non-noble metals, metal oxides and carbon-based materials, in facilitating the electrochemical oxidation of ethylene and propylene. Finally, we also provide an overview of current challenges and problems requiring further works.

Molten-Salt Electrochemical-Assisted Synthesis of the CeO2-OV@GC Composite-Supported Pt Clusters with a Pt-O-Ce Structure for the Oxygen Reduction Reaction

Highly active and robust Pt-based electrocatalysts for an oxygen reduction reaction (ORR) are of crucial significance for the development of proton exchange membrane fuel cells (PEMFCs). Herein, the high-loading and well-dispersive Pt clusters on graphitic carbon-supported CeO2 with abundant oxygen vacancies (PtAC/CeO2-OV@GC) were successfully fabricated by a molten-salt electrochemical-assisted method. The bonding of Pt with the highly electronegative O induces charge redistribution through the Pt-O-Ce structure, thus reducing the adsorption energies of oxygen-containing species. Such a PtAC/CeO2-OV@GC electrocatalyst exhibits a greatly enhanced ORR performance with a mass activity of 0.41 ± 0.02 A·mg-1Pt at 0.9 V versus a reversible hydrogen electrode, which is 2.7 times the value of a commercial Pt/C catalyst and shows negligible activity decay after 20000 cycles of accelerated degradation tests. It is anticipated that this work will provide enlightening guidance on the controllable synthesis and rational design of high-performance Pt-based electrocatalysts for PEMFCs.

Advances in Naked Metal Clusters for Catalysis

The properties of sub-nano metal clusters are governed by quantum confinement and their large surface-to-bulk ratios, atomically precise compositions and geometric/electronic structures. Advances in metal clusters lead to new opportunities in diverse aspects of sciences including chemo-sensing, bio-imaging, photochemistry, and catalysis. Naked metal clusters having synergic multiple active sites and coordinative unsaturation and tunable stability/activity enable researchers to design atomically precise metal catalysts with tailored catalysis for different reactions. Here we summarize the progress of ligand-free naked metal clusters for catalytic applications. It is anticipated that this review helps to better understand the chemistry of small metal clusters and facilitates the design and development of new catalysts for potential applications.

Capture of single Ag atoms through high-temperature-induced crystal plane reconstruction

The "terminal hydroxyl group anchoring mechanism" has been studied on metal oxides (Al2O3, CeO2) as well as a variety of noble and transition metals (Ag, Pt, Pd, Cu, Ni, Fe, Mn, and Co) in a number of generalized studies, but there is still a gap in how to regulate the content of terminal hydroxyl groups to influence the dispersion of the active species and thus to achieve optimal catalytic performance. Herein, we utilized AlOOH as a precursor for γ-Al2O3 and induced the transformation of the exposed crystal face of γ-Al2O3 from (110) to (100) by controlling the calcination temperature to generate more terminal hydroxyl groups to anchor Ag species. Experimental results combined with AIMD and DFT show that temperature can drive the atomic rearrangement on the (110) crystal face, thereby forming a structure similar to the atomic arrangement of the (100) crystal face. This resulted in the formation of more terminal hydroxyl groups during the high-temperature calcination of the support (Al-900), which can capture Ag species to form single-atom dispersions, and ultimately develop a stable and efficient single-atom Ag-based catalyst.

Spatial decoupling of bromide-mediated process boosts propylene oxide electrosynthesis

The electrochemical synthesis of propylene oxide is far from practical application due to the limited performance (including activity, stability, and selectivity). In this work, we spatially decouple the bromide-mediated process to avoid direct contact between the anode and propylene, where bromine is generated at the anode and then transferred into an independent reactor to react with propylene. This strategy effectively prevents the side reactions and eliminates the interference to stability caused by massive alkene input and vigorously stirred electrolytes. As expected, the selectivity for propylene oxide reaches above 99.9% with a remarkable Faradaic efficiency of 91% and stability of 750-h (>30 days). When the electrode area is scaled up to 25 cm2, 262 g of pure propylene oxide is obtained after 50-h continuous electrolysis at 6.25 A. These findings demonstrate that the electrochemical bromohydrin route represents a viable alternative for the manufacture of epoxides.

Construction of novel Ag(0)-containing silver nanoclusters by regulating auxiliary phosphine ligands

Controlled synthesis of metal clusters through minor changes in surface ligands holds significant interest because the corresponding entities serve as ideal models for investigating the ligand environment's stereochemical and electronic contributions that impact the corresponding structures and properties of metal clusters. In this work, we obtained two Ag(0)-containing nanoclusters (Ag17 and Ag32) with near-infrared emissions by regulating phosphine auxiliary ligands. Ag17 and Ag32 bear similar shells wherein Ag17 features a trigonal bipyramid Ag5 kernel while Ag32 has a bi-icosahedral interpenetrating an Ag20 kernel. Ag17 and Ag32 showed a near-infrared emission (NIR) of around 830 nm. Benefiting from the rigid structure, Ag17 displayed a more intense near-infrared emission than Ag32. This work provides new insight into the construction of novel superatomic silver nanoclusters by regulating phosphine ligands.

Reactivity of cationic silver clusters with O2: a probe of interplay between clusters' geometric and electronic structures

We explored the size-dependent reactivity of Agn+ (n = 2-22) with O2 under mild conditions and found that only a few sizes of Agn+, with even values of n = 4, 6, 12, 16, 18, and 22, are reactive. Possible structures of Agn+ (n = 2-22) were determined using a genetic algorithm with incomplete local optimizations at the DFT level, and the calculated bonding strengths of O2 on these structures are consistent with experimental observations. Analyses revealed a close relationship between the reactivity of Agn+ with O2 and its HOMO-LUMO gap: cationic silver clusters with a small HOMO-LUMO gap are reactive, which can be rationalized by the covalent character of chemical bonds between Agn+ and O2 involving their frontier orbitals. The peculiar size-dependent HOMO-LUMO gaps and reactivity with O2 correlate with the subtle interplay between the electronic configurations and geometric structures of these silver cluster cations.

Computational Screening of a Single-Atom Catalyst Supported by Monolayer Nb2S2C for Oxygen Reduction Reaction

The search for high-performance catalysts to improve the catalytic activity for an oxygen reduction reaction (ORR) is crucial for developing a proton exchange membrane fuel cell. Using the first-principles method, we have performed computational screening on a series of transition metal (TM) atoms embedded in monolayer Nb2S2C to enhance the ORR activity. Through the scaling relationship and volcano plot, our results reveal that the introduction of a single Ni or Rh atom through substitutional doping into monolayer Nb2S2C yields promising ORR catalysts with low overpotentials of 0.52 and 0.42 V, respectively. These doped atoms remain intact on the monolayer Nb2S2C even at elevated temperatures. Importantly, the catalytic activity of the Nb2S2C doped with a TM atom can be effectively correlated with an intrinsic descriptor, which can be computed based on the number of d orbital electrons and the electronegativity of TM and O atoms.

Quantitative in situ synchrotron X-ray analysis of the ALD/MLD growth of transition metal dichalcogenide TiS2 ultrathin films

We present the results of a full quantitative analysis of X-ray absorption spectroscopy (XAS) performed in situ during the growth of ultrathin titanium disulfide (TiS2) films via an innovative two-step process, i.e. atomic layer deposition/molecular layer deposition (ALD/MLD) followed by annealing. This growth strategy aims at separating the growth process from the crystallization process by first creating an amorphous Ti-thiolate that is converted later to crystalline TiS2via thermal annealing. The simultaneous analysis of Ti and S K-edge XAS spectra, exploiting the insights from density functional theory calculations, allows us to shed light on the chemical and structural mechanisms underlying the main steps of growth. The nature of the bonding at the base of the interface creation with the SiO2 substrate is disclosed in this study. Evidence of a progressive incorporation of S in the amorphous Ti-thiolate is given. Finally, it is shown that the annealing step plays a critical role since the transformation of the Ti-thiolate into nanocrystalline TiS2 and the loss of S are simultaneously induced, validating the two-step synthesis approach, which entails distinct growth and crystallization steps. These observations contribute to a deeper understanding of the bonding mechanism at the interface and provide insights for future research in this field and the generation of ultra-thin layered materials.

2D nanocomposite materials for HER electrocatalysts - a review

Hydrogen energy has the potential to be a cost-effective and strong technology for brighter development. Hydrogen fuel production by water electrolyzers has attracted attention. 2D nanocomposites with distinctive properties have been extensively explored for various applications from hydrogen evolution reactions to improving the efficiency of water electrolyzer, which is the most eco-friendly, and high-performance for hydrogen production. Recently, typical 2D nanocomposites such as Metal-Free 2D, TMDs, Mxene, LDH, organic composites, and Heterostructure have recently been thoroughly researched for use in the HER. We discuss effective ways for increasing the HER efficiency of 2D catalysts in this paper, And the unique advantages and mechanisms for specific applications are highlighted. Several essential regulating strategies for developing 2D nanocomposite-based HER electrocatalysts are included such as interface engineering, defect engineering, heteroatom doping, strain & phase engineering, and hybridizing which improve HER kinetics, the electrical conductivity, accessibility to catalytic active sites, and reaction energy barrier can be optimized. Finally, the future prospects for 2D nanocomposites in HER are discussed, as well as a thorough overview of a variety of methodologies for designing 2D nanocomposites as HER electrocatalysts with excellent catalytic performance. We expect that this review will provide a thorough overview of 2D nanocatalysts for hydrogen production.

Direct propylene epoxidation via water activation over Pd-Pt electrocatalysts

Direct electrochemical propylene epoxidation by means of water-oxidation intermediates presents a sustainable alternative to existing routes that involve hazardous chlorine or peroxide reagents. We report an oxidized palladium-platinum alloy catalyst (PdPtOx/C), which reaches a Faradaic efficiency of 66 ± 5% toward propylene epoxidation at 50 milliamperes per square centimeter at ambient temperature and pressure. Embedding platinum into the palladium oxide crystal structure stabilized oxidized platinum species, resulting in improved catalyst performance. The reaction kinetics suggest that epoxidation on PdPtOx/C proceeds through electrophilic attack by metal-bound peroxo intermediates. This work demonstrates an effective strategy for selective electrochemical oxygen-atom transfer from water, without mediators, for diverse oxygenation reactions.

Investigation of the oxygen coverage effect on the direct epoxidation of propylene over copper through DFT calculations

The direct epoxidation of propylene is one of the most important selective oxidation reactions in industry. The development of high-performance copper-based catalysts is the key to the selective oxidation technology and scientific research of propylene. The mechanism of propylene's partial oxidation catalyzed by Cu(111) under different oxygen coverage conditions was studied using density functional theory calculations and microkinetic modeling. We report here in detail two parallel reaction pathways: dehydrogenation and epoxidation. The transition states and energy distributions of the intermediates and products were calculated. The present results showed that propylene oxide (PO) selectivity was high under low oxygen coverage, and increasing the oxygen coverage would decrease the PO selectivity but increase the PO activity, and there was an inverse relationship between PO selectivity and activity. Increasing oxygen coverage would reduce the energy barrier for the C-O bond formation of C3H5O due to the weaker adsorption strength of C3H5, thus decreasing the PO formation selectivity. On the other hand, increasing oxygen coverage would reduce the energy barrier for the possible reaction steps of propylene epoxidation in general, and thus increasing the catalytic activity. It might be proposed that the active site for propylene epoxidation is the metallic copper or partially oxidized copper in terms of the change of PO formation selectivity with oxygen coverage.

Silver-Exchanged Zeolite Y Catalyzes a Selective Insertion of Carbenes into C-H and O-H Bonds

Commercially available zeolite Y modulates the catalytic activity and selectivity of ultrasmall silver species during the Buchner reaction and the carbene addition to methylene and hydroxyl bonds, by simply exchanging the counter cations of the zeolite framework. The zeolite acts as a macroligand to tune the silver catalytic site, enabling the use of this cheap and recyclable solid catalyst for the in situ formation of carbenes from diazoacetate and selective insertion in different C-H (i.e., cyclohexane) and C-O (i.e., water) bonds. The amount of catalyst in the reaction can be as low as ≤0.1 mol % silver. Besides, this reactivity allows deeply drying the HY zeolite framework by making the strongly adsorbed water molecules react with the in situ formed carbenes.

Advances in heterogeneous single-cluster catalysis

Heterogeneous single-cluster catalysts (SCCs) comprising atomically precise and isolated metal clusters stabilized on appropriately chosen supports offer exciting prospects for enabling novel chemical reactions owing to their broad structural diversity with unparalled opportunities for engineering their properties. Although the pioneering work revealed intriguing performance trends of size-selected metal clusters deposited on supports, synthetic and analytical challenges hindered a thorough understanding of surface chemistry under realistic conditions. This Review underscores the importance of considering the cluster environment in SCCs, encompassing the development of robust metal-support interactions, precise control over the ligand sphere, the influence of reaction media and dynamic behaviour, to uncover new reactivities. Through examples, we illustrate the criticality of tailoring the entire catalytic ensemble in SCCs to achieve stable and selective performance with practically relevant metal coverages. This expansion in application scope transcends from model reactions to complex and technically relevant reactions. Furthermore, we provide a perspective on the opportunities and future directions for SCC design within this rapidly evolving field.

Transition from monolayer-thick 2D to 3D nano-clusters on α-Al2O3(0001)

This paper reports on the long-standing puzzle of the atomic structure of the Ag/α-Al2O3(0001) interface by combining X-ray absorption spectroscopy, to determine Ag local environment [i.e. average Ag-Ag (dAg-Ag) and Ag-O (dAg-O) interatomic distances and Ag coordination numbers (CN)], and numerical simulations on nanometric-sized particles. The experimental key was the capability of a structural study of clusters involving only a few atoms. The concomitant decrease of dAg-Ag and CN with decreasing cluster size provides unambiguous fingerprints for the dimensionality of the Ag clusters in the subnanometric regime leading to a series of unexpected results regarding the size-dependent interface structures. At low coverage, Ag atoms sit on surface Al sites to form buckled monolayer-thick islands associated with a Ag-Ag distance (2.75 Å) which fits the alumina lattice. Upon increasing Ag coverage, as 3D clusters appear, the Ag interface atoms tend to leave Al sites to sit atop O atoms as dAg-Ag increases. The then highlighted size-dependent evolution, is built on structural models which seemed so far contradictory in a static vision of the interface. Theory generalizes the case as it predicts the existence of alumina-supported 2D clusters of Pd and Pt at small coverage and a similar 2D-3D transition upon increasing the size. The structural transformation from 2D Ag clusters to macroscopic 3D islands is accompanied by a noticeable reduction of adhesion energy at the Ag/α-Al2O3(0001) interface.

Coalescing Dynamics between Ag55 and Cu55 Clusters as Well as Thermodynamics during Cooling the Coalesced Clusters from Atomic Simulations

Molecular dynamics simulations are performed to investigate the coalescing processes between a Cu55 cluster with a liquid, FCC, or Ih structure and a Ag55 cluster in liquid, as well as the structural changes of the coalesced clusters during the cooling process. The simulation results show that the initial structure of the Ag and Cu clusters significantly affects the coalescence stages and the structures after coalescence. There are apparent rotations of the Ag cluster with the liquid structure relative to the Cu cluster with the liquid structure when they are approaching. Before the formation of a neck, the Cu cluster with the Ih structure is more stable and less likely to lose its structure compared to the Cu cluster with the FCC structure. During the cooling process, the coalesced clusters will form different packing structures, including Ih and metastable core/shell structures. The Lode-Nadai values reveal the loading states on the atoms when the two clusters collide. The thermodynamic behaviors during the cooling process were investigated to better understand the order degree of the packing structures and the structural transition processes.

Room temperature epoxidation of ethylene over delafossite-based AgNiO2 nanoparticles

A mixed oxide of silver and nickel AgNiO2 was obtained via co-precipitation in alkaline medium. This oxide demonstrates room temperature activity in the reaction of ethylene epoxidation with a high selectivity (up to 70%). Using the PDF method, it was found that the initial structure of AgNiO2 contains stacking faults and silver vacancies, which cause the nonstoichiometry of the oxide (Ag/Ni < 1). It has been established that on the initial surface of AgNiO2 oxide, silver state can be considered as an intermediate between Ag2O and Ag0 (i.e. Agδ+-like), while nickel is characterized by signs of a deeply oxidized state (Ni3+-like). The interaction of AgNiO2 with C2H4 at room temperature leads to the simultaneous removal of two oxygen species with Eb(O 1s) = 529.0 eV and 530.5 eV considered as nucleophilic and electrophilic oxygen states, respectively. Nucleophilic oxygen was attributed to the lattice oxygen (Ag-O-Ni), while the electrophilic species with epoxidation activity was associated with the weakly bound oxygen stabilized on the surface. According to the TPR-C2H4 data, a large number of weakly bound oxygen species were found on the pristine AgNiO2 surface. The removal of such species at room temperature didn't result in noticeable structural transformation of delafossite. As the temperature of ethylene oxidation over AgNiO2 increased, the appearance of Ag0 particles was first observed below 200 °C followed by the complete destruction of the delafossite structure at higher temperatures.

In situ infrared CO detection using silver loaded EMT zeolite films

Ag cluster catalyst-based oxidation of CO to CO2 is an important way to remove CO at low temperatures. However, the instability of silver clusters seriously limits the catalytic application. Herein, sub-nanosized EMT zeolite nanoparticles served as Ag cluster carriers with high selectivity, low coordination, and unsaturated atom active sites. The silver clusters with sub-nanometer size can be controlled with different charge states and loading rates. A detection film with 500 nm was further prepared by assembling the Ag-EMT composites with a small amount of Nalco as an adhesive. For CO detection, a completely enclosed gas sensing device based on in situ infrared spectroscopy was employed without air interference. CO was accurately introduced into the detection chamber and catalysed into CO2 by silver loaded EMT zeolite films, and the whole process was accurately recorded by infrared spectroscopy. CO with a detection range of 2-50 ppm was realized, showing great application potential in gas monitoring.

Mechanistic Understanding of the Use of Single-Atom and Nanocluster Catalysts for Syngas Production via Partial Oxidation of Methane

Single-atom and nanocluster catalysts presenting potent catalytic activity and excellent stability are used in high-temperature applications such as in structural composites, electrical devices, and catalytic chemical reactions. Recently, more attention has been drawn to application of these materials in clean fuel processing based on oxidation in terms of recovery and purification. The most popular media for catalytic oxidation reactions include gas phases, pure organic liquid phases, and aqueous solutions. It has been proven from the literature that catalysts are frequently selected as the finest in regulating organic wastewater, solar energy utilization, and environmental treatment applications in most catalytic oxidation of methane vis-à-vis photons and in environmental treatment applications. Single-atom and nanocluster catalysts have been engineered and applied in catalytic oxidations considering metal-support interactions and mechanisms facilitating catalytic deactivation. In this review, the present improvements on engineering single-atom and nano-catalysts are discussed. In detail, we summarize structure modification strategies, catalytic mechanisms, methods of synthesis, and application of single-atom and nano-catalysts for partial oxidation of methane (POM). We also present the catalytic performance of various atoms in the POM reaction. Full knowledge of the use of remarkable POM vis-à-vis the excellent structure is revealed. Based on the review conducted on single-atom and nanoclustered catalysts, we conclude their viability for POM reactions; however, the catalyst design must be carefully considered not only for isolating the individual influences from the active metal and support but also for incorporating the interactions of these components.

Design Rules for Obtaining Narrow Luminescence from Semiconductors Made in Solution

Solution-processed semiconductors are in demand for present and next-generation optoelectronic technologies ranging from displays to quantum light sources because of their scalability and ease of integration into devices with diverse form factors. One of the central requirements for semiconductors used in these applications is a narrow photoluminescence (PL) line width. Narrow emission line widths are needed to ensure both color and single-photon purity, raising the question of what design rules are needed to obtain narrow emission from semiconductors made in solution. In this review, we first examine the requirements for colloidal emitters for a variety of applications including light-emitting diodes, photodetectors, lasers, and quantum information science. Next, we will delve into the sources of spectral broadening, including "homogeneous" broadening from dynamical broadening mechanisms in single-particle spectra, heterogeneous broadening from static structural differences in ensemble spectra, and spectral diffusion. Then, we compare the current state of the art in terms of emission line width for a variety of colloidal materials including II-VI quantum dots (QDs) and nanoplatelets, III-V QDs, alloyed QDs, metal-halide perovskites including nanocrystals and 2D structures, doped nanocrystals, and, finally, as a point of comparison, organic molecules. We end with some conclusions and connections, including an outline of promising paths forward.

Size-Controlled Synthesis of Luminescent Few-Atom Silver Clusters via Electron Transfer in Isostructural Redox-Active Porous Ionic Crystals

Ag clusters with a controlled number of atoms have received significant interest because they show size-dependent catalytic, optical, electronic, or magnetic properties. However, the synthesis of size-controlled, ligand-free, and air-stable Ag clusters with high yields has not been well-established. Herein, it is shown that isostructural porous ionic crystals (PICs) with redox-active polyoxometalates (POMs) can be used to synthesize Ag clusters via electron transfer from POMs to Ag⁺ . Ag clusters with average numbers of three, four, or six atoms emitting blue, green, or red colors, respectively, are formed and stabilized in the PICs under ambient conditions without any protecting ligands. The cluster size solely correlates with the degree of electron transfer, which is controlled by the reduction time and types of ions or elements of the PICs. Thus, advantages have been taken of POMs as electron sources and PICs as scaffolds to demonstrate a convenient method to obtain few-atom Ag clusters.

Br-/BrO--mediated highly efficient photoelectrochemical epoxidation of alkenes on α-Fe2O3

Epoxides are significant intermediates for the manufacture of pharmaceuticals and epoxy resins. In this study, we develop a Br^-/BrO^- mediated photoelectrochemical epoxidation system on α-Fe₂O₃. High selectivity (up to >99%) and faradaic efficiency (up to 82 ± 4%) for the epoxidation of a wide range of alkenes are achieved, with water as oxygen source, which are far beyond the most reported electrochemical and photoelectrochemical epoxidation performances. Further, we can verify that the epoxidation reaction is mediated by Br^-/BrO^- route, in which Br^- is oxidized non-radically to BrO^- by an oxygen atom transfer pathway on α-Fe₂O₃, and the formed BrO^- in turn transfers its oxygen atom to the alkenes. The non-radical mediated characteristic and the favorable thermodynamics of the oxygen atom transfer process make the epoxidation reactions very efficient. We believe that this photoelectrochemical Br^-/BrO^--mediated epoxidation provides a promising strategy for value-added production of epoxides and hydrogen.

Bridging the gas and condensed phases for metal-atom encapsulating silicon- and germanium-cage superatoms: electrical properties of assembled superatoms

With the development of nanocluster (NC) synthesis methods in the gas phase, atomically precise NCs composed of a finite number of metal and semiconductor atoms have emerged. NCs are expected to be the smallest units for nanomaterials with various functions, such as catalysts, optoelectronic materials, and electromagnetic devices. The exploration of a stable NC called a magic number NC has revealed a couple of important factors, such as a highly symmetric geometric structure and an electronic shell closure, and a magic number behavior is often enhanced by mixing additional elements. A synergetic effect between geometric and electronic structures leads to the formation of chemically robust NC units called superatoms (SAs), which act as individual units assembled as thin films. The agglomeration of non-ligated bare SAs is desirable in fabricating the assembled SAs associated with intrinsic SA nature. The recent development of an intensive pulsed magnetron sputtering method opens up the scalable synthesis of SAs in the gas phase, enabling the fabrication of SA assembly coupled with the non-destructive deposition of a soft-landing technique. This perspective describes our recent progress in the investigation of the formation of binary cage SA (BCSA) assembled thin films composed of metal-atom encapsulating silicon-cage SAs (M@Si₁₆) and germanium-cage SAs (M@Ge₁₆), with a focus on their electrical properties associated with a conduction mechanism toward the development of new functional nanoscale materials.

Confinement Effects in Well-Defined Metal-Organic Frameworks (MOFs) for Selective CO2 Hydrogenation: A Review

Decarbonization has become an urgent affair to restrain global warming. CO₂ hydrogenation coupled with H₂ derived from water electrolysis is considered a promising route to mitigate the negative impact of carbon emission and also promote the application of hydrogen. It is of great significance to develop catalysts with excellent performance and large-scale implementation. In the past decades, metal-organic frameworks (MOFs) have been widely involved in the rational design of catalysts for CO₂ hydrogenation due to their high surface areas, tunable porosities, well-ordered pore structures, and diversities in metals and functional groups. Confinement effects in MOFs or MOF-derived materials have been reported to promote the stability of CO₂ hydrogenation catalysts, such as molecular complexes of immobilization effect, active sites in size effect, stabilization in the encapsulation effect, and electron transfer and interfacial catalysis in the synergistic effect. This review attempts to summarize the progress of MOF-based CO₂ hydrogenation catalysts up to now, and demonstrate the synthetic strategies, unique features, and enhancement mechanisms compared with traditionally supported catalysts. Great emphasis will be placed on various confinement effects in CO₂ hydrogenation. The challenges and opportunities in precise design, synthesis, and applications of MOF-confined catalysis for CO₂ hydrogenation are also summarized.

Computational screening of chemically active metal center in coordinated dipyridyl tetrazine network

Creation, stabilization, characterization, and control of single transition metal (TM) atoms may lead to significant advancement of the next-generation catalyst. Metal organic network (MON) in which single TM atoms are coordinated and separated by organic ligands is a promising class of material that may serve as a single atom catalyst. Our density functional theory-based calculations of MONs in which dipyridyl tetrazine (DPTZ) ligands coordinate with a TM atom to form linear chains leads to two types of geometries of the chains. Those with V, Cr, Mo, Fe, Co, Pt, or Pd atoms at the coordination center are planar while those with Au, Ag, Cu, or Ni are non-planar. The formation energies of the chains are high (∼2.0-7.9 eV), suggesting that these MON can be stabilized. Moreover, the calculated adsorption energies of CO and O₂on the metal atom at center of the chains with the planar configuration lie in the range 1.0-3.0 eV for V, Cr, Mo, Fe, and Co at the coordination center, paving the way for future studies of CO oxidation on TM-DPTZ chains with the above five atoms at the coordination center.

Prediction of Three-Metal Cluster Catalysts on Two-Dimensional W2N3 Support with Integrated Descriptors for Electrocatalytic Nitrogen Reduction

In the electrocatalytic nitrogen reduction reaction (NRR), nitrogen (N2) is chemically inert, it is difficult to break the triple bond, and the subsequent protonation step is very challenging. Suitable catalysts with high selectivity and high activity are needed to promote the electrocatalytic NRR. We screen a large number of clusters composed of three metal atoms embedded into a two-dimensional metal nitride, W2N3, with a N vacancy, and calculate the reaction energetics. The VNiCu cluster has the best catalytic activity among all the catalysts proposed so far. The Fe3 and Fe2Co clusters are excellent catalysts as well. In all cases, spin polarization is needed to observe the catalytic effect. We establish the optimal NRR path and confirm that it remains unchanged in the presence of a solvent. We find three groups of descriptors that can well predict the materials' properties and exhibit linear relationships with the NRR limiting potential.

Propylene Oxide Addition Effect on the Chemical Speciation of a Fuel-Rich Premixed n-Heptane/Toluene Flame

1,2-Propylene oxide (PO, C₃H₆O) is considered as a promising agent for improving fuel. In this work, the effect of PO additives on the species pool in a premixed burner-stabilized fuel-rich (ϕ = 1.6) flame fueled by n-heptane/toluene mixture (7/3 by volume of liquids) at atmospheric pressure is studied by the flame-sampling molecular beam mass spectrometry and numerical modeling in order to get insight into the chemical aspects of the influence of oxygenates with an epoxy group on the formation of abundant intermediates (including PAH precursors) during combustion of fossil fuels. The flames with various loadings of PO in the fuel blend (from 0 to 16.3% in mole basis) are examined, and detailed kinetic mechanisms available in the literature are validated against the measurements of mole fraction profiles of reactants, major products, and many intermediate species. A higher reactivity of the fresh mixture and a reduction in the peak mole fractions of intermediates playing an important role in PAH formation (benzene, styrene, ethylbenzene, phenol, acetylene, diacetylene, etc.) are observed when PO is added. This was found to be due to simultaneously two factors: the partial replacement of "sooting" fuel (toluene, which is the main precursor of these species) with oxygenated additive, and the changes in the flame radical pool caused by PO addition. Propylene oxide additive was found to change the ratio between H, OH, O, and CH₃ toward an increase in the proportion of O and CH₃. The detailed kinetic mechanisms considered in the work are found to overpredict the peak mole fraction of acetylene, a key species playing a crucial role in PAH growth. Its chemistry is revisited in order to provide a better prediction of C₂H₂ and, as a result, PAHs.

Green synthesis of propylene oxide directly from propane

The chemical industry faces the challenge of bringing emissions of climate-damaging CO₂ to zero. However, the synthesis of important intermediates, such as olefins or epoxides, is still associated with the release of large amounts of greenhouse gases. This is due to both a high energy input for many process steps and insufficient selectivity of the underlying catalyzed reactions. Surprisingly, we find that in the oxidation of propane at elevated temperature over apparently inert materials such as boron nitride and silicon dioxide not only propylene but also significant amounts of propylene oxide are formed, with unexpectedly small amounts of CO₂. Process simulations reveal that the combined synthesis of these two important chemical building blocks is technologically feasible. Our discovery leads the ways towards an environmentally friendly production of propylene oxide and propylene in one step. We demonstrate that complex catalyst development is not necessary for this reaction.

Advanced nanomaterials for highly efficient CO2 photoreduction and photocatalytic hydrogen evolution

At present, CO₂ photoreduction to value-added chemicals/fuels and photocatalytic hydrogen generation by water splitting are the most promising reactions to fix two main issues simultaneously, rising CO₂ levels and never-lasting energy demand. CO₂, a major contributor to greenhouse gases (GHGs) with about 65% of the total emission, is known to cause adverse effects like global temperature change, ocean acidification, greenhouse effects, etc. The idea of CO₂ capture and its conversion to hydrocarbons can control the further rise of CO₂ levels and help in producing alternative fuels that have several further applications. On the other hand, hydrogen being a zero-emission fuel is considered as a clean and sustainable form of energy that holds great promise for various industrial applications. The current review focuses on the discussion of the recent progress made in designing efficient photocatalytic materials for CO₂ photoreduction and hydrogen evolution reaction (HER). The scope of the current study is limited to the TiO₂ and non-TiO₂ based advanced nanomaterials (i.e. metal chalcogenides, MOFs, carbon nitrides, single-atom catalysts, and low-dimensional nanomaterials). In detail, the influence of important factors that affect the performance of these photocatalysts towards CO₂ photoreduction and HER is reviewed. Special attention is also given in this review to provide a brief account of CO₂ adsorption modes on the catalyst surface and its subsequent reduction pathways/product selectivity. Finally, the review is concluded with additional outlooks regarding upcoming research on promising nanomaterials and reactor design strategies for increasing the efficiency of the photoreactions.

"Magic" Sinter-Resistant Cluster Sizes of Ptn Supported on Alumina

Subnano cluster catalysts, while highly promising due to unique activity, selectivity, and atom-efficiency, are limited in wider applications, as they are prone to deactivation via sintering. Even size-selection, which was previously shown to reduce sintering of nanoparticles, cannot reduce the sintering of highly fluxional subnano clusters due to their inherent isomeric diversity. Here, we use a combination of theory and experiment to show that Pt clusters on Al₂O₃ exhibit size-dependent sintering resistance. We furthermore show that Pt₄/Al₂O₃ and Pt₇/Al₂O₃ are "magic" sinter-resistant cluster sizes. Their stability is attributed to the greater degree of bulk-like crystallinity of the dominant isomers. In addition, we identify different spatial signatures characteristic of the sintering of clusters with differing sintering stabilities.

Effect of ZrS2 load single/dual-atom catalysts on the hydrogen evolution reaction: A first-principles study

The hydrogen evolution effect of ZrS₂ carrier loaded with transition metal single-atom (SA) was explored by first-principles method. ZrS₂ was constructed with transition metal single-atom and dual-atom. The structure-activity relationship of supported single-atom catalysts was described by electronic properties and hydrogen evolution kinetics. The results show that the ZrS₂ carrier-loaded atomic-level catalysts are more likely to occur in acidic environments, where the Mo SA load has a higher hydrogen precipitation capacity than the Pt SA. In the case of dual-atom adsorption, most of the hydrogen reduction processes are higher than that of single atom loading, which indicates that the outer orbital hybridization is more likely to lead to the interfacial charge recombination of the catalyst. Thereinto, Ni/Pt @ZrS₂ has the lowest Gibbs free energy (0.08 eV), and the synergistic effect of transition metals induces the deviation of the center of the d-band from the Fermi level and improves the dissociation ability of H ions. The design provides a new catalytic model for the HER and provides some ideas for understanding the two-site catalysis.

Recent progress of sub-1 nm nanomaterials: synthesis, polymer-analogue properties and applications in redox catalysis

Sub-1 nm nanomaterials (SNMs) have attracted attention for their novel structures and size-related properties. In the past decade, various SNMs were synthesized, such as nanowires, nanorings, nanosheets, nanobelts, nanotubes, and other superstructures. We discussed their synthetic strategies systematically, including the ligand pathway and the cluster-nuclei co-assembly pathway. In addition, SNMs exhibit unique size-related properties. Firstly, SNWs show polymer-analogue properties due to their sub-nanometric size and ultrahigh aspect ratio. We illustrate the polymer-analogue properties on both microscopic and macroscopic scales. The macroscopic assemblies of SNWs can be widely applied for organic liquid storage, energy, and optical applications. Finally, we summarized the applications of SNMs in redox catalysis. Their extraordinary catalytic activity is attributed to their large specific surface area and electronic delocalization at the sub-nanometric scale. We hope this feature article can provide new viewpoints on the design and applications of SNMs.