Dealuminated Beta zeolite reverses Ostwald ripening for durable copper nanoparticle catalysts

Dynamic evolution of metal structures on/in zeolites for catalysis

Dynamic changes of metal species always occur during catalysis, and primarily rely on forming mobile metal species initiated by thermal or chemical conditions. During these processes, a support is important in affecting the catalyst stability and dynamic change pathways. Among several supports, zeolites provide ideal features for regulating the migration of metal species due to their unique pore structures and specific defect sites. This review provides a comprehensive summary of typical cases about dynamic migration of metal species on/in metal-zeolite catalysts, analyzing the mechanisms and driving factors of metal migration under different reaction conditions. We discuss the roles of zeolite supports in the migration process of metal species, particularly their crucial contributions to the stability of metal species and the optimization of active sites. In addition, the potential mechanism of the dynamic migration of metal species, theoretical studies, and practical guidance for designing highly efficient catalysts are also included in this review.

Carbon doped cobalt nanoparticles encapsulated in graphitic carbon shells: Efficient bifunctional oxygen electrocatalysts for ultrastable Zn-air batteries

Rational design of low-cost, highly active and robust bifunctional oxygen electrocatalysts is essential for advancing the performance of rechargeable Zn-air batteries (ZABs). Herein, a facile one-step pyrolysis approach is reported to synthesize cobalt nanoparticles encapsulated in N-doped graphitic carbon with a core-shell structure. The temperature-dependent interdiffusion of C and Co atoms at the interface was observed. The catalyst prepared at an optimized temperature of 800 °C (Co@NC-800) exhibited a half-wave potential of 0.82 V for oxygen reduction reaction and an overpotential of 350 mV at 10 mA cm-2 for oxygen evolution reaction. Density functional theory calculations demonstrated the electron redistribution of the metallic active sites and provided insights into the origin of bifunctional activity. The rechargeable ZAB assembled using Co@NC-800 demonstrated superior performance compared to precious metal based electrocatalysts, achieving a peak power density up to 213.6 mW cm-2, a specific capacity of 774.1 mAh gZn-1, and notable durability. This work provides a strategy for rational design of highly efficient and durable non-noble metal catalysts for rechargeable ZAB technologies.

Anchoring Cu sites in a hierarchical single-crystalline ZSM-5 zeolite for enhanced diffusion and benzene oxidation

Phenol is an important intermediate for high-value chemicals. Current phenol production via the three-step cumene process leads to significant energy waste and environmental problems. The conversion of benzene to phenol under mild conditions can be achieved by oxidation with Cu-based zeolites. However, conventional microporous zeolites suffer from severe diffusion limitations, especially when bulky molecules, such as benzene, are involved. In this work, we used a hierarchically macro-meso-microporous ZSM-5 single crystal (Hier-ZSM-5) as a substrate for Cu species (Cu@Hier-ZSM-5). The irregular morphology of the opal-like Hier-ZSM-5 exhibited abundant surface Si-OH groups and provided a platform for stabilizing Cu2+ sites. Meanwhile, hierarchical porosity significantly improved the diffusion ability of bulky molecules. As a result, excellent selective oxidation performance of benzene was obtained with Cu@Hier-ZSM-5, achieving a conversion of 77% and a phenol selectivity of 73%, which were 1.5 times and 2 times higher than those obtained with a catalyst based on microporous ZSM-5, respectively. CuOOH species were identified as an important intermediate in benzene oxidation. This hierarchical zeolite system, with a synergistic effect of site anchoring and molecular diffusion, provides an excellent platform for catalyst design.

Particle Hopping and Coalescence of Supported Au Nanoparticles in Harsh Reactive Environments

Sintering of supported metal nanoparticles (NPs) is a general and important phenomenon in materials and catalysis science. A consensus view is that it takes place either via the Ostwald ripening (OR) or particle migration and coalescence (PMC) mechanism through the substrate, but how sintering occurs under high gas pressure and high temperature has not been addressed. Here, we perform millisecond-scale environmental kinetic Monte Carlo (EKMC) simulations combined with density functional theory (DFT) calculations to reveal a unique through-space sintering mechanism, particle hopping and coalescence (PHC). Under high CO pressure and high temperature, the coalescence of Au NPs takes place through NP hopping up from the anatase TiO2(101) substrate and mass transfer via the gas phase. When the sintered floating NP reaches a critical size, it spontaneously redeposits onto the substrate. This process is driven by the preference of interfacial Au atoms of small NPs to interact with CO rather than the substrate at a high CO chemical potential. The PHC mechanism implies that NP sintering and intersubstrate catalyst transfer may occur easier than expected during reactions and provides a distinct perspective to understand catalyst thermal deactivation under harsh operando conditions.

A self-regenerating Pt/Ge-MFI zeolite for propane dehydrogenation with high endurance

Supported noble metal cluster catalysts are typically operated under severe conditions involving switching between reducing and oxidizing atmospheres, causing irreversible transformation of the catalyst structure and thereby leading to permanent deactivation. We discovered that various platinum (Pt) precursors spontaneously disperse in a germanium-MFI (Ge-MFI) zeolite, which opposes the Ostwald ripening phenomenon, producing self-regenerating Pt/Ge-MFI catalysts for propane dehydrogenation. These catalysts reversibly switch between Pt clusters and Pt single atoms in response to reducing reaction and oxidizing regeneration conditions. This environmental adaptability allows them to completely self-regenerate over 110 reaction and regeneration cycles in propane dehydrogenation, and they exhibited unprecedented sintering resistance when exposed to air at 800°C for 10 days. Such spontaneous metal dispersion in a Ge-MFI zeolite is a robust and versatile methodology for fabricating various rhodium, ruthenium, iridium, and palladium cluster catalysts.

Stable Cobalt-Zeolite Propane-Dehydrogenation Catalysts Enabled by Reaction-Driven Reconstruction

Cobalt-based catalysts have emerged as promising substitutes for Pt- and Cr-based propane dehydrogenation (PDH) catalysts. However, controlling the distribution of Co species and achieving stable active centers remains challenging. Here, we report that reaction-driven reconstruction of metallic cobalt (Co0) species within pure silica MFI zeolite (S-1) into CoOx clusters within silanol nests during PDH yields efficient and durable performance. Atomically dispersed CoOx clusters exhibit exceptional durability and high propylene space-time yield (STY), maintaining an ultrahigh propylene STY of 17.2 mmolC3H6 gcat -1 h-1 for over 260 h under industrially relevant conditions, surpassing previous cobalt-based PDH catalysts. Moreover, the catalyst operates stably at 520 °C for 170 h with near-equilibrium propane conversions. Comprehensive characterizations indicate the dynamic evolution process from the silanol nests effectively capturing and stabilizing Co0 species within S-1 zeolite, thereby promoting the dynamic formation of CoOx clusters during the PDH process. We also demonstrate that stable Co─O active centers formed by this unique anchoring strategy improve catalyst stability by suppressing coke formation and promoting efficient propane dehydrogenation.

Upcycling Spent Lithium-Ion Batteries: Constructing Bifunctional Catalysts Featuring Long-Range Order and Short-Range Disorder for Lithium-Oxygen Batteries

Upcycling of high-value metals (M = Ni, Co, Mn) from spent ternary lithium-ion batteries to the field of lithium-oxygen batteries is highly appealing, yet remains a huge challenge. In particular, the alloying of the recovered M components with Pt and applied as cathode catalysts have not yet been reported. Herein, a fresh L12-type Pt3 M medium-entropy intermetallic nanoparticle is first proposed, confined on N-doped carbon matrix (L12-Pt3(Ni1/3Co1/3Mn1/3)@N-C) based on spent 111 typed LiNi1-x-yMnxCoyO2 cathode. This well-defined catalyst combines both features of long-range order L12 face-centered cubic structure and short-range disorder in M sites. The former contributes to enhancing the structural stability, and the latter further facilitates deeply activating the catalytic activity of Pt sites. Experiments and theoretical results demonstrate that the local coordination environment and electronic distribution of Pt are both fundamentally modulated via surrounding disordered Ni, Co, and Mn atoms, which greatly optimize the affinity toward oxygen-containing intermediates and facilitate the deposition/decomposition kinetics of the thin-film Li2O2 discharge products. Specifically, the L12-Pt3(Ni1/3Co1/3Mn1/3)@N-C catalyst exhibits an ultra-low overpotential of 0.48 V and achieves 220 cycles at 400 mA g-1 under 1000 mAh g-1. The work provides important insights for the recycling of spent lithium-ion batteries into advanced catalyst-related applications.

Structurally Engineering Multi-Shell Hollow Zeolite Single Crystals via Defect-Directed Oriented-Kinetics Transformation and Their Heterostructures for Hydrodeoxygenation Reaction

Single-crystalline multi-shell hollow porous materials with high compartment capacity, large active surface area, and superior structural stability are expected to unlock tremendous potential across diverse critical applications. However, their synthetic methodology has not yet been well established. Here, we develop a defect-directed oriented-kinetics transformation approach to prepare multi-shell hollow aluminosilicate ZSM-5 zeolite (MFI) crystals with single-crystalline feature, hierarchical macro-/mesoporosity, controllable shell number, and high structural stability. The methodology lies in the creation of zeolite precursors consisting of multiple inhomogeneous layers with gradient-distributed defects along the [100] and [010] directions and irregularly discrete defects-rich regions along the [001] direction via continuous epitaxial growth. Subsequently, the locations with more defects could be preferentially etched to form voids or mesopores, meanwhile oriented recrystallization interconnects the nanoshells into a unified architecture along the [001] direction. Benefiting from the easily accessible bifunctional metal/acid sites and the capability for reactant accumulation, the resultant multi-shell hollow Ni-loaded zeolite catalysts show significantly enhanced catalytic activity in the hydrodeoxygenation of stearic acid into liquid fuels. The insight gained from this systematic study will facilitate the rational design and synthesis of diverse multi-shell hollow structured single-crystalline porous materials for a broad range of potential applications.

'Tearing Effect' of Alloy-Support Interaction for Alloy Redispersion in NiRu/TiO2 Hydrogenation Catalysts

Supported alloy catalysts have been extensively applied to many significant industrial chemical processes due to the abundant active sites with distinguishable geometry and electron states. However, a detailed in situ investigation of the interaction between support and alloy nanoparticles is still lacking. Here, a subversive 'tearing effect' on the interface of TiO2-supported NiRu alloy nanoparticles is in situ discovered by environmental transmission electron microscopy (ETEM) with a dramatic redispersion process of alloy nanoparticles from ~25 nm to 2-3 nm under the repeated hydrogen reduction. Dual-driven by the distinct alloy-support interaction involving the restructuring of alloy nanoparticles and growth of TiOx overlayer, larger NiRu alloy nanoparticles spontaneously disintegrate into atoms migrating on support. Atoms are finally captured by the defects generated on TiO2 during the repeat reduction, which also confines the further growth of the newly alloy nanoparticles. Owing to this specific alloy-support interaction, smaller alloy nanoparticles on TiO2 support are much more stable than the bigger ones, which holds promise for industrial applications as durable catalysts. This novel metal-support interaction with the 'tearing effect' revealed on supported alloy catalysts provides new knowledge on the structure-performance relationships in all the alloy catalysts for hydrogenation reactions.

Construction of Pt─O Sites on Pt Nanoclusters in Silicalite-1 Zeolite for Efficient Catalytic Oxidation of Hydrogen Isotope Gases

The construction, use, and maintenance of tritium-related equipment will inevitably produce tritium-containing radioactive waste gas, and the production of efficient catalysts for tritium removal remains a difficult problem. Herein, silicalite-1 zeolite with entrapped Pt nanoclusters is skillfully post-oxidized at an appropriate temperature, building highly active Pt─O sites on the nanoclusters to achieve efficient oxidation of hydrogen isotopes at low temperatures. The designed Pt─O sites can directly participate in the oxidation reaction of hydrogen isotopes. Compared to the case without Pt─O sites, the presence of these sites significantly reduces the reaction energy barrier to 0.55 eV, enabling the catalyst to achieve a hydrogen conversion rate of 99% at a low temperature of 40 °C. Specifically, the O atoms consumed by the Pt─O sites in the reaction are replaced by O2 gas and this cycle repeats, which is consistent with the Mars-van Krevelen (M-K) theory. This ensures efficient catalytic oxidation of hydrogen isotopes, and provides an astonishingly high conversion rate of 99% in the nearly 34 days restart performance test. The results of this study provide insights into the strategic design of efficient catalysts for hydrogen isotope oxidation.

Advances in Programmable Control of Ostwald Ripening for Tailoring Material Properties: Challenges, Applications, and Future Perspectives

During the past decade, enlightened by the better understanding of the mechanism of Ostwald ripening (OR), programmable control of OR process have gained popularity in the fields from nanocrystals to bulk materials in virtue of its important on regulating the structural and chem-physical properties. In this perspective, we systematically summarize the up-to date advanced applications of OR process involved in nanomaterials and bulk material properties. The potential challenges and perspectives for further research are highlighted. We envision that such research directions will be a base for future work and have a bright future especially for material science.

Dynamically Confined Active Silver Nanoclusters with Ultrawide Operating Temperature Window in CO oxidation

Supported metal nanoclusters are often highly active in many catalytic reactions but less stable particularly under harsh reaction conditions. Here, we demonstrate that this activity-stability trade-off can be efficiently broken through rational design of surrounding microenvironment of the supported nanocatalyst including gas adsorbate overlayer and underneath support surface chemistry. Our studies reveal that chemisorbed oxygen species on Ag surface and surface hydroxyl groups on oxide support, which are dynamically consumed during reaction but sustained by reaction environment (O2 and H2O vapor), drive spontaneous redispersion of Ag particles and stabilization of highly active Ag nanoclusters. Such a dynamic confinement effect from gas-catalyst-support interaction enables the Ag nanoclusters to exhibit complete catalytic oxidation of CO over a wide temperature window of 25-500 °C under dry conditions and 200-800 °C under wet conditions as well as remarkable stability at 300 °C over 1000 h.

Advances and Challenges in Speciation Measurement and Microkinetic Modeling for Gas-Solid Heterogeneous Catalysis

Microkinetic modeling of heterogeneous catalysis serves as an efficient tool bridging atom-scale first-principles calculations and macroscale industrial reactor simulations. Fundamental understanding of the microkinetic mechanism relies on a combination of experimental and theoretical studies. This Perspective presents an overview of the latest progress of experimental and microkinetic modeling approaches applied to gas-solid catalytic kinetics. Then, opportunities and challenges are presented based on recent research progress in gas-solid catalysis and combustion chemistry. For experimental approaches, the importance of ideal catalytic reactors, structured catalysts, and precise elementary rate measurements is emphasized. Additionally, integrating spatiotemporally resolved operando gas-phase diagnostics with surface-adsorbed species characterization methods offers new opportunities for gaining deeper insights into gas-surface reactions. In microkinetic modeling, a hybrid rate parameter evaluation approach that combines first-principles calculations with semiempirical methods, followed by automated mechanism generation and data-driven optimization, opens new avenues for efficiently constructing surface mechanisms. Furthermore, extending microkinetic modeling beyond mean-field approximations allows simulations under realistic catalyst operating conditions. Finally, the critical role of gas-phase mechanisms and comprehensive microkinetic modeling analyses in advancing our fundamental understanding of gas-solid catalytic processes is highlighted.

Low loading of Pt on MoB Constructed by microwave Quasi-solid approach with solvent Regulation for hydrogen evolution reaction

The interaction between metal nanoclusters and the carrier can enhance the electron transfer rate to optimize the hydrogen evolution reaction (HER) performance, but the common synthesis approaches often lead to metal particle agglomeration, and then blocking active sites. Herein, highly-dispersed Pt nanoclusters supported onto molybdenum boride (MoB) is developed through microwave approach with various solvent to regulate the catalytic performance. The synthesized electrocatalyst with the addition of methanol (Pt/MoB-M) exhibits excellent electrocatalytic performance towards HER with low overpotential (13 mV at 10 mA cm-2), small Tafel slope (24 mV dec-1), and high mass activity (10.06 A/mgPt at 50 mV). This work presents a novel approach to prepare highly-efficient electrocatalysts for renewable energy-related applications of non-carbon supported low loading of precious metals.

Enhanced NH3-SCR activity of Cu-SAPO-34 by regulating Si distribution via an interzeolite conversion strategy

An interzeolite conversion (IZC) method was developed for the rapid synthesis of Cu-SAPO-34 from SAPO-37, achieving isolated Si distribution and optimized Cu states. The resulting Cu-SAPO-34 exhibited exceptional NH3-SCR performance, with over 90% NO conversion from 200-600 °C due to proper acidity and Cu status generated from the isolated Si.

Embedding Reverse Electron Transfer Between Stably Bare Cu Nanoparticles and Cation-Vacancy CuWO4

Cu nanoparticles (NPs) have attracted widespread attention in electronics, energy, and catalysis. However, conventionally synthesized Cu NPs face some challenges such as surface passivation and agglomeration in applications, which impairs their functionalities in the physicochemical properties. Here, the issues above by engineering an embedded interface of stably bare Cu NPs on the cation-vacancy CuWO4 support is addressed, which induces the strong metal-support interactions and reverse electron transfer. Various atomic-scale analyses directly demonstrate the unique electronic structure of the embedded Cu NPs with negative charge and anion oxygen protective layer, which mitigates the typical degradation pathways such as oxidation in ambient air, high-temperature agglomeration, and CO poisoning adsorption. Kinetics and in situ spectroscopic studies unveil that the embedded electron-enriched Cu NPs follow the typical Eley-Rideal mechanism in CO oxidation, contrasting the Langmuir-Hinshelwood mechanism on the traditional Cu NPs. This mechanistic shift is driven by the Coulombic repulsion in anion oxygen layer, enabling its direct reaction with gaseous CO to form the easily desorbed monodentate carbonate.

Chiral Ligand-Decorated Rhodium Nanoparticles Incorporated in Covalent Organic Framework for Asymmetric Catalysis

While metal nanoparticles (NPs) have demonstrated their great potential in catalysis, introducing chiral microenvironment around metal NPs to achieve efficient conversion and high enantioselectivity remains a long-standing challenge. In this work, tiny Rh NPs, modified by chiral diene ligands (Lx) bearing diverse functional groups, are incorporated into a covalent organic framework (COF) for the asymmetric 1,4-addition reactions between arylboronic acids and nitroalkenes. Though Rh NPs hosted in the COF are inactive, decorating Rh NPs with Lx creates the active Rh-Lx interface and induces high activity. Moreover, chiral microenvironment modulation around Rh NPs by altering the groups on chiral diene ligands greatly optimizes the enantioselectivity (up to 95.6 % ee). Mechanistic investigations indicate that the formation of hydrogen-bonding interaction between Lx and nitroalkenes plays critical roles in the resulting enantioselectivity. This work highlights the significance of chiral microenvironment modulation around metal NPs by chiral ligand decoration for heterogeneous asymmetric catalysis.

Thermal Effect Management via Entropy Variation Strategy to Improve the Catalyst Stability in Acetylene Hydrogenation

The dynamic structure evolution of heterogeneous catalysts during reaction has gained great attention recently. However, controllably manipulating dynamic process and then feeding back catalyst design to extend the lifetime remains challenging. Herein, we proposed an entropy variation strategy to develop a dynamic CuZn-Co/HEOs catalyst, in which the non-active Co nano-islands play a crucial role in controlling thermal effect via timely capturing and utilizing reaction heat generated on the adjacent active CuZn alloys, thus solving the deactivation problem of Cu-based catalysts. Specifically, heat sensitive Co nano-islands experienced an entropy increasing process of slowly redispersion during the reaction. Under such heat dissipation effect, the CuZn-Co/HEOs catalyst exhibited 95.7 % ethylene selectivity and amazing long-term stability (>530 h) in the typical exothermic acetylene hydrogenation. Aiming at cultivating it as a catalyst with promising industrial potential, we proposed a simple regeneration approach via an entropy decreasing process.

Ostwald-Ripening Induced Interfacial Protection Layer Boosts 1,000,000-Cycled Hydronium-Ion Battery

Collapsing and degradation of active materials caused by the electrode/electrolyte interface instability in aqueous batteries are one of the main obstacles that mitigate the capacity. Herein by reversing the notorious side reactions include the loss and dissolution of electrode materials, as we applied Ostwald ripening (OR) in the electrochemical cycling of a copper hexacyanoferrate electrode in a hydronium-ion batteries, the dissolved Cu and Fe ions undergo a crystallization process that creates a stable interface layer of cross-linked cubes on the electrode surface. The layer exposed the low-index crystal planes (100) and (110) through OR-induced electrode particle growth, supplemented by vacancy-ordered (100) superlattices that facilitated ion migration. Our design stabilized the electrode-electrolyte interface considerably, achieving a cycle life of one million cycles with capacity retention of 91.6 %, and a capacity retention of 91.7 % after 3000 cycles for a full battery.

Oxidation of Ammonia in Water Microdroplets Produces Nitrate and Molecular Hydrogen

Water microdroplets containing dissolved ammonia (30-300 μM) are sprayed through a copper oxide mesh with a 200 μm average pore size, resulting in the formation of nitrate (NO3-) and the release of molecular hydrogen (H2). The products result from a redox process that takes place at the liquid-solid interface through contact electrification, where no external potential is applied. Oxidation is initiated by superoxide radical anions (O2-) that originate from the oxygen in the air surrounding the microdroplets and from the hydroxyl radicals (OH•) originating from the water-air interface. Two spin traps (TEMPO and DMPO) capture these radicals as well as NH2OH+•, HNO, NO•, NO2•, and NOOH, which are detected by mass spectrometry. We also directly observed N2O2-• by the same means. We found that the hydrogen atom from the ammonia molecule can be set free not only in the form of H• but also as H2, which is detected using a residue gas analyzer. The oxidation process can be significantly enhanced by a factor of 3 when the sprayed microdroplets are irradiated with ultraviolet light (265 nm, 5 W). 35% of 300 μM ammonia can be degraded within 20 μs, and the nitrate conversion rate is estimated to be 15 nmol·mg-1·h-1.

Hydrogenation of the benzene rings in PET degraded chemicals over meso-HZSM-5 supported Ru catalyst

Chemical upcycling of waste polyethylene terephthalate (PET) to value-added products can reduce the emission of CO2, microplastics and toxic chemicals. In this work, mesoporous H-type Zeolite Socony Mobil-5 (HZSM-5) supported Ru catalyst (Ru/m-HZSM-5) was synthesized and tested in the hydrogenation of PET degraded chemicals (bis(2-hydroxyethyl) terephthalate, dimethyl terephthalate, diethyl terephthalate, and terephthalic acid). Characterizations disclosed that Ru/m-HZSM-5 catalyst possesses mesopores (a dominant channel of 5.32 nm), enlarged specific surface area (404 m2·g-1), and Ru NPs dispersed highly (40.6 %) compared to that of Ru/HZSM-5. And also, it was found that Ru/m-HZSM-5 was capable for the hydrogenation of benzene rings in these PET degraded chemicals with large sizes (1.09-1.82 nm). In particular, the conversion of BHET and the selectivity of BHCD over Ru/m-HZSM-5 reached 95.5 % and 95.6 % at 120 °C within 2 h. And Ru/m-HZSM-5 could be recycled at least five times without obvious loss of activity and selectivity.

Silanol-Stabilized Atomically Dispersed Ptδ+-Ox-Sn Active Sites in Protozeolite for Propane Dehydrogenation

Crystalline zeolites have been proven to be excellent supports for confining subnanometric metal catalysts to boost the propane dehydrogenation (PDH) reaction. However, the introduced metallic species may suffer from severe sintering and limited stability during the catalytic process, especially when utilizing an industrial impregnation method for metal incorporation. In this study, we developed a new type of support based on amorphous protozeolite (PZ), taking advantage of its adjustable silanol chemistry and zeolitic microporous characteristic for stabilizing atomically dispersed PtSn catalyst via a simple, cost-effective coimpregnation process. The combination of X-ray absorption spectroscopy, X-ray photoelectron spectroscopy, in situ diffuse reflectance infrared Fourier transform spectroscopy under CO atmosphere, and density functional theory calculations confirmed the formation of highly dispersed active Ptδ+-Ox-Sn species in PtSn/PZ. The PtSn/PZ catalyst exhibited a high propane conversion of 45.4% and a high propylene selectivity of 99% (WHSV= 3.6 h-1, 550 °C), with a high apparent rate coefficient of 565 molC3H6·gPt-1·h-1·bar-1 at a high WHSV of 108 h-1, presenting a top-level performance among the state-of-the-art Pt-based catalysts prepared by in situ synthesis and impregnation methods. The silanol density determined the chemical state of PtSn species, showing a change from atomically dispersed Ptδ+-Ox-Sn sites to PtSn alloy with decreasing silanol density of supports. This work provides a general strategy using silanol-rich amorphous protozeolite as support for stabilizing various metal catalysts by the simple impregnation method and also offers an effective way for fine tailoring the chemical state of metallic species via a silanol-engineered approach.

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

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

Water-assisted oxidative redispersion of Cu particles through formation of Cu hydroxide at room temperature

Sintering of active metal species often happens during catalytic reactions, which requires redispersion in a reactive atmosphere at elevated temperatures to recover the activity. Herein, we report a simple method to redisperse sintered Cu catalysts via O2-H2O treatment at room temperature. In-situ spectroscopic characterizations reveal that H2O induces the formation of hydroxylated Cu species in humid O2, pushing surface diffusion of Cu atoms at room temperature. Further, surface OH groups formed on most hydroxylable support surfaces such as γ-Al2O3, SiO2, and CeO2 in the humid atmosphere help to pull the mobile Cu species and enhance Cu redispersion. Both pushing and pulling effects of gaseous H2O promote the structural transformation of Cu aggregates into highly dispersed Cu species at room temperature, which exhibit enhanced activity in reverse water gas shift and preferential oxidation of carbon monoxide reactions. These findings highlight the important role of H2O in the dynamic structure evolution of supported metal nanocatalysts and lay the foundation for the regeneration of sintered catalysts under mild conditions.

Optimizing Nanosuspension Drug Release and Wound Healing Using a Design of Experiments Approach: Improving the Drug Delivery Potential of NDH-4338 for Treating Chemical Burns

NDH-4338 is a highly lipophilic prodrug comprising indomethacin and an acetylcholinesterase inhibitor. A design of experiments approach was used to synthesize, characterize, and evaluate the wound healing efficacy of optimized NDH-4338 nanosuspensions against nitrogen mustard-induced skin injury. Nanosuspensions were prepared by sonoprecipitation in the presence of a Vitamin E TPGS aqueous stabilizer solution. Critical processing parameters and material attributes were optimized to reduce particle size and determine the effect on dissolution rate and burn healing efficacy. The antisolvent/solvent ratio (A/S), dose concentration (DC), and drug/stabilizer ratio (D/S) were the critical sonoprecipitation factors that control particle size. These factors were subjected to a Box-Behnken design and response surface analysis, and model quality was assessed. Maximize desirability and simulation experiment optimization approaches were used to determine nanosuspension parameters with the smallest size and the lowest defect rate within the 10-50 nm specification limits. Optimized and unoptimized nanosuspensions were prepared and characterized. An established depilatory double-disc mouse model was used to evaluate the healing of nitrogen mustard-induced dermal injuries. Optimized nanosuspensions (A/S = 6.2, DC = 2% w/v, D/S = 2.8) achieved a particle size of 31.46 nm with a narrow size range (PDI = 0.110) and a reduced defect rate (42.2 to 6.1%). The optimized nanosuspensions were stable and re-dispersible, and they showed a ~45% increase in cumulative drug release and significant edema reduction in mice. Optimized NDH-4338 nanosuspensions were smaller with more uniform sizes that led to improved physical stability, faster dissolution, and enhanced burn healing efficacy compared to unoptimized nanosuspensions.

Fabrication of a ZIF-on-lamella-zeolite architecture as a highly efficient catalyst for aldol condensation

Designing composite catalysts that harness the strengths of individual components while mitigating their limitations is a fascinating yet challenging task in catalyst engineering. In this study, we aimed to enhance the catalytic performance by anchoring ZIF-67 nanoparticles of precise sizes onto lamella Si-MWW zeolite surfaces through a stepwise regrowth process. Co ions were initially grafted onto the zeolite surface using ultrasonication, followed by a seed-assisted secondary growth method. Si-MWW proved to be the ideal zeolite support due to its thin layered structure, large external surface area and substantial lateral dimensions. The abundant Si-OH groups on its surface played a crucial role in securely binding Co ions, limiting size growth and preventing undesirable ZIF-67 aggregation. The resulting ZIF-67/MWW composite with finely dispersed nano-scale ZIF-67 particles exhibited a remarkable catalytic performance and stability in the aldol condensation reactions involving acetone and various aldehydes. This approach holds promise for designing MOF/zeolite composite catalysts.