Nanoscale Catalysts Research Articles

Determining the Magnetic Status of Active Sites on Nanocatalysts.

Identifying the atomic structure and chemical composition of active sites on nanocatalysts has been a long pursuit in heterogeneous catalysis. Yet, determining the magnetic structure of a well-defined active site is even more challenging. However, explicit morphology and reaction temperature have not been considered in identifying the magnetic behaviors of the nanocatalysts, especially in theoretical studies. Herein, we determined the magnetic status of nanoscale catalysts at finite temperatures by using atomistic spin models. The size dependence of the Curie point and the magnetic premelting have been discussed, indicating that the magnetic properties over a localized active center can greatly differ from the bulk. Therefore, the magnetic phase transitions and its concomitant magneto-catalytic effect can be induced at a considerably low temperature. Our analysis demonstrated that an 8 nm cobalt-based core-shell nanoparticle can achieve the optimal magnetization with Sabatier optimal activity for ammonia synthesis at 523 K, which is in accord with the reaction condition of the Haber-Bosch process. We believe our findings elucidate the importance of determining the localized magnetic configuration for active sites. Furthermore, including this unexcavated dimension in the dynamical simulations of the catalytic process can provide us with a more complete and comprehensive understanding of the reaction mechanism under working conditions.

Factors Influencing Nanoscale Catalysts Prepared Impregnation Method

Factors Influencing Nanoscale Catalysts Prepared Impregnation Method

Dynamic regulation of ferroelectric polarization using external stimuli for efficient water splitting and beyond.

Establishing and regulating the ferroelectric polarization in ferroelectric nano-scale catalysts has been recognized as an emerging strategy to advance water splitting reactions, with the merits of improved surface charge density, high charge transfer rate, increased electronic conductivity, the creation of real active sites, and optimizing the chemisorption energy. As a result, engineering and tailoring the ferroelectric polarization induced internal electric field provides significant opportunities to improve the surface and electronic characteristics of catalysts, thereby enhancing the water splitting reaction kinetics. In this review, an interdisciplinary and comprehensive summary of recent advancements in the construction, characterization, engineering and regulation of the polarization in ferroelectric-based catalysts for water splitting is provided, by exploiting a variety of external stimuli. This review begins with a detailed overview of the classification, benefits, and identification methodologies of the ferroelectric polarization induced internal electric field; this offers significant insights for an in-depth analysis of ferroelectric-based catalysts. Subsequently, we explore the underlying structure-activity relationships for regulating the ferroelectric polarization using a range of external stimuli which include mechanical, magnetic, and thermal fields to achieve efficient water splitting, along with a combination of two or more fields. The review then highlights emerging strategies for multi-scale design and theoretical prediction of the relevant factors to develop highly promising ferroelectric catalysts for efficient water splitting. Finally, we present the challenges and perspectives on the potential research avenues in this fascinating and new field. This review therefore delivers an in-depth examination of the strategies to engineer the ferroelectric polarization for the next-generation of water electrolysis devices, systems and beyond.

Strategies and Mechanisms to Improve the Catalytic Performance of Cu-Based Catalyst for CO2 Electrochemical Reduction Reaction to Methane

This article introduces three significant ways of producing methane by electrocatalytic reduction of carbon dioxide. Electrocatalytic reduction of carbon dioxide can efficiently convert CO2 molecules into various high-energy fuels under ambient conditions. Methane gas, among them, stands out due to its relatively high calorific value, chemical stability, ease of storage and transportation. Therefore, research on electrocatalytic reduction of CO2 to generate methane is crucial. Common methods include adjusting catalyst morphology to expose more active sites, building nanoscale catalysts results in smaller-sized nanostructured copper and combining copper with other metals to form alloys, creating multi-metal catalysts. By optimizing these catalysts, we can efficiently reduce carbon dioxide into methane.

Progress and challenges in structural, in situ and operando characterization of single-atom catalysts by X-ray based synchrotron radiation techniques.

Single-atom catalysts (SACs) represent the ultimate size limit of nanoscale catalysts, combining the advantages of homogeneous and heterogeneous catalysts. SACs have isolated single-atom active sites that exhibit high atomic utilization efficiency, unique catalytic activity, and selectivity. Over the past few decades, synchrotron radiation techniques have played a crucial role in studying single-atom catalysis by identifying catalyst structures and enabling the understanding of reaction mechanisms. The profound comprehension of spectroscopic techniques and characteristics pertaining to SACs is important for exploring their catalytic activity origins and devising high-performance and stable SACs for industrial applications. In this review, we provide a comprehensive overview of the recent advances in X-ray based synchrotron radiation techniques for structural characterization and in situ/operando observation of SACs under reaction conditions. We emphasize the correlation between spectral fine features and structural characteristics of SACs, along with their analytical limitations. The development of IMST with spatial and temporal resolution is also discussed along with their significance in revealing the structural characteristics and reaction mechanisms of SACs. Additionally, this review explores the study of active center states using spectral fine characteristics combined with theoretical simulations, as well as spectroscopic analysis strategies utilizing machine learning methods to address challenges posed by atomic distribution inhomogeneity in SACs while envisaging potential applications integrating artificial intelligence seamlessly with experiments for real-time monitoring of single-atom catalytic processes.

Integration of Facet‐Dependent, Adsorbate‐Driven Surface Reconstruction into Multiscale Models for the Design of Ni‐Based Bimetallic Catalysts for Hydrogen Oxidation

AbstractNi‐based bimetallic catalysts (NiM) show promise to replace expensive Pt‐based catalysts for hydrogen oxidation reaction (HOR). However, the effect of dopant and reaction conditions on the adsorbate‐driven surface reconstruction of NiM nanoparticles remains largely unexplored. Here, we use a multiscale modeling approach – integrating density functional theory, kubic harmonics interpolation, and microkinetic modeling – to investigate the interplay between dopant, reaction conditions, facet, adsorbate type, adsorbate coverage, in situ surface structure, and performance for NiM nanoparticles during HOR. Clear periodic trends appear in dopant effects on key adsorption energies, with dopants showing 7‐fold greater effects when located in the surface as compared to subsurface. Multi‐faceted nanoparticle models showed a non‐uniform correlation between O* coverage and surface reconstruction. HOR performance was facet‐dependent, with the highest performance occurring at reactive fronts formed between regions of high O* and OH* coverage. The nanoparticle averaged performance showed promotional effects for nearly all dopants compared to pure Ni, with the best‐performing dopants located preferentially in the surface layer (e. g. Au, Pd, Ag). Taken together, this work emphasizes the importance of understanding the interplay between reaction conditions, surface reconstruction, and HOR performance for NiM nanoparticles, enabling researchers to both predict and control the working nanoscale catalyst structure.

Thermally Stable Oxide-Capsulated Metal Nanoparticles Structure for Strong Metal-Support Interaction via Ultrafast Laser Plasmonic Nanowelding.

Strong metal-support interaction (SMSI) has drawn much attention in heterogeneous catalysts due to its stable and excellent catalytic efficiency. However, construction of high-performance oxide-capsulated metal nanostructures meets great challenge in materials thermodynamic compatibility. In this work, dynamically controlled formation of oxide-capsulated metal nanoparticles (NPs) structures is demonstrated by ultrafast laser plasmonic nanowelding. Under the strong localized electromagnetic field interaction, metal (Au) NPs are dragged by an optical force toward oxide NPs (TiO2). Intense energy is simultaneously injected into this heterojunction area, where TiO2 is precisely ablated. With the embedding of metal into oxide, optical force on Au gradually turned from attractive to repulsive due to the varied metal-dielectric environment. Meanwhile, local ablated oxides are redeposited on Au NP. Upon the whole coverage of metal NP, the implantation behavior of metal NP is stopped, resulting in a controlled metal-oxide eccentric structure with capsulated oxide layer thickness ≈0.72-1.30nm. These oxide-capsulated metal NPs structures can preserve their configurations even after thermal annealing in air at 600°C for 10min. This ultrafast laser plasmonic nanowelding can also extend to oxide-capsulated metal nanostructure fabrication with broad materials combinations (e.g., Au/ZnO, Au/MgO, etc.), which shows great potential in designing/constructing nanoscale high-performance catalysts.

BioRicinus Communis Seed Extract was Used in the Green Manufacture of Zero-valent Iron Nanoparticles for Photocatalyst Elimination of Chromium

Zero-valent iron was produced in this work utilising BioRicinus communis seed extract. XRD, SEM, and TEM methods were used to characterise the physicochemical characteristics of the finished products. According to TEM analysis, the iron zero-valent nanomaterials with diameters ranging from 20 to 40 nm and shell-core architectures were successfully produced. XRD findings verified the existence of several organic compounds. The photoactivity of the product was investigated by reducing the contaminant. According to the test result, the inclusion of fruit extract as a nanoscale catalyst in the photocatalyst reduced the hexavalent chromium. According to photocatalyst results, when the particulate dose was 0.675 g/L, the trivalent chromium suffered from low was 100%. A pseudo-second-order solution describes this reaction's kinetics. At pH 3 and 0.5 g/L seed extract concentration, the kinetic rate constant is 0.4. As a result, the frequency of the photocatalyst was significantly increased, and a more significant amount of Cr (VI) was eliminated. The accessible sites became progressively constrained and overloaded with bichromate particles as the starting content of Cr (VI) was increased at a consistent dose. Changing the nanoparticle dosage may considerably boost the reaction rate, hence the effectiveness of a photocatalyst's Cr (VI) catalytic cycle.

Ruthenium atoms anchored on oxygen-modified molybdenum disulfide with strong interfacial coupling as efficient and stable catalysts for lithium–oxygen batteries

Rechargeable non-aqueous lithium-oxygen batteries (LOBs) have garnered increasing attention owing to their high theoretical energy density. However, their slow cathodic kinetics hinder efficient battery reactions. Nanoscale catalysts can effectively enhance electrocatalytic activity and atomic utilization efficiency. However, the agglomeration of nanoscale catalysts (such as cluster and single atoms) during continuous discharge/charge cycles leads to decreased electrochemical performance and poor cyclic stability. Herein, the ruthenium (Ru) atomic sites anchored on an O-doped molybdenum disulfide (O-MoS2) catalyst (designated as Ru/O-MoS2) was fabricated using a facile impregnation and calcination method. Strong Ru-O coupling between Ru atoms and the O-MoS2 substrate optimizes the localized electronic structure, resulting in improved electrochemical performance and enhanced resistance to Ostwald ripening. When employed as a cathode catalyst for LOBs, Ru/O-MoS2 catalyst exhibits a high reversible specific capacity (18700.5 (±59.8)mAhg-1), good rate capability, and enhanced long-term stability (115 cycles, 1200h). This study encourages facile and efficient strategies for the development of effective and stable electrocatalysts for use in LOBs.

Site heterogeneity and broad surface-binding isotherms in modern catalysis: Building intuition beyond the Sabatier principle

Site heterogeneity and broad surface-binding isotherms in modern catalysis: Building intuition beyond the Sabatier principle

The Heterogeneity of Turn-over Number in Electrocatalysis

Chemical catalysts dominate the multi-billion global revenue of the chemical industry because they accelerate the time it takes a particular reaction to reach equilibrium without altering the equilibrium constant. Electrocatalysis can provide significant benefits compared to other methods, as it has minimal purification and separation costs, is operational at low temperatures and pressures, replaces hazardous and toxic chemical sources with electric current, and can be integrated with renewable energy sources. From a techno-economical point of view, some considerations are critical during a catalyst design: cost, activity, and durability. One useful metric to quantify catalyst durability is turn-over number (TON), which represents the maximum yield of products attainable from a catalytic center. Mathematically speaking, the TON is defined as: TON = ∫0 ∞ TOF(t) dt, where TOF is the turn-over frequency, which is the rate of turn-overs (N) per active site. Currently, without any exception, the TON is given as a fixed number describing the total amount of substrate converted until the catalysts fully degrade. Our approach studies electrocatalytic deactivation processes at the single catalyst level using a technique entitled single-entity electrochemistry for freely diffusing catalysts. The hydrogen evolution reaction (HER) is investigated with platinum nanoparticles as the model catalyst because it deactivates at the nanoscale when the catalytic activity decreases over time. At specific applied potentials, the current measured when a single platinum nanoparticle impacts the electrode creates a transient spike and decay back to the baseline current. TON is quantified by fitting the current decay response and integrating above the fit to find the charge transferred to catalyze the reaction. Our results show that electrocatalyst degradation and TON have a distribution, where some catalysts are more stable than others, and depends on the applied potential and size of the nanoparticles. In order to study how the surface facets of platinum affect the TON, SECCM was coupled with scanning electron microscopy (SEM) to compare the deactivation of a polycrystalline platinum surface in the macro scale with immobilized platinum nanoparticles on a glassy carbon surface. Combining local structural, electrochemical activity, and durability will bridge our fundamental understanding of macro and nanoscale catalyst deactivation processes to assist in the bottom-up approach of material development and design of large-scale industrial electrocatalysts.

A multi-layer membrane filter made of potassium catalyst and three-way catalyst for a passive after-treatment system

A multi-layer membrane has been fabricated to integrate a Three-Way Catalyst (TWC) and Gasoline Particulate Filter (GPF) into one device, called a four-way catalytic converter. The top layer, made of nano-scale potassium catalyst particles, traps Particulate Matter (PM) with almost 100% filtration efficiency at all times and oxidizes PM (mostly soot) with a significantly reduced temperature of 476°C at the oxidation peak. Moreover, the bottom layer catalyst is comprised of sub-micro TWC particles to combine NO reduction and CO oxidation capabilities. The effective temperature range for the simultaneous removal of all pollutants was between 420°C–500°C.

Synthesis of nanoscale nickel (II) ferrite and a study of its catalytic and sorption activities towards methyl orange

Nanoscale magnetic spinel ferrites are attracting an increased attention as functional materials for catalysis and sorption. Such catalysts and sorbents are advantageous due to their chemical stability in aggressive media, their thermal stability, a large area of specific surface, and high saturation magnetization, which allows using them to create magnetically controlled functional materials. This article presents the results of the synthesis of nickel (II) ferrite nanopowder, its characterization, and a study of its catalytic and sorption activities towards methyl orange dye. X-ray diffraction (XRD), transmission electron microscopy (TEM), and scanning electron microscopy (SEM) were used to characterize nanocrystalline NiFe2O4 synthesized by citrate combustion. The nickel spinel was tested as a catalyst of Fentonlike reaction of oxidative degradation of methyl orange under UV irradiation of l = 270 nm. The study involved differentiation of oxidation during dye sorption on a NiFe2O4 nanoscale catalyst. The oxidative degradation of the pollutant under ultraviolet irradiation in the presence of a catalyst was satisfactorily described by a pseudo-first-order model, the rate constant of the reaction was 0.0191 min–1. The degree of methyl orange destruction reached 99% 150 minutes after the beginning of thereaction. A parallel experiment without the addition of hydrogen peroxide to the dye solution allowed assessing the sorption capacity of nanoscale nickel (II) ferrite. After 150 minutes, the concentration of the dye decreased by 7.5% due to its sorption, the equilibrium sorption capacity of NiFe2O4 was low (0.132 mg/g). This indicates that the methyl orange solution decolorizes mainly due to its catalytic oxidative degradation according to the Fenton reaction. This allows considering nanoscale nickel ferrite as a promising material for wastewater treatment by deep oxidation of organic pollutants

Optimized bimetallic ratios for durable membrane catalyst-film reactors in treating nitrate-polluted water

Nitrate contamination of surface and ground water is a significant global challenge. Most current treatment technologies separate nitrate from water, resulting in concentrated wastestreams that need to be managed. Membrane Catalyst-film Reactors (MCfR), which utilize in-situ produced nanocatalysts attached to hydrogen-gas-permeable hollow-fiber membranes, offer a promising alternative for denitrification without generating a concentrated wastestream. In hydrogen-based MCfRs, bimetallic nano-scale catalysts reduce nitrate to nitrite and then further to di-nitrogen or ammonium. This study first investigated how different molar ratios of indium-to-palladium (In:Pd) catalytic films influenced denitrification rates in batch-mode MCfRs. We evaluated eleven In-Pd bimetallic catalyst films, with In:Pd molar ratios from 0.0029 to 0.28. Nitrate-removal exhibited a volcano-shaped dependence on In content, with the highest nitrate removal (0.19 mgNO3--N-min-1L-1) occurring at 0.045mol In/mol Pd. Using MCfRs with the optimal In:Pd loading, we treated nitrate-spiked tap water in continuous-flow for >60days. Nitrate removal and reduction occurred in three stages: substantial denitrification in the first stage, a decline in denitrification efficiency in the second stage, and stabilized denitrification in the third stage. Factors contributing to the slowdown of denitrification were: loss of Pd and In catalysts from the membrane surface and elevated pH due to hydroxide ion production. Sustained nitrate removal will require that these factors be mitigated.

Research on an in-situ synchronous CO elimination method in blasting operations and engineering experimental application based on nano-CO catalysts

Research on an in-situ synchronous CO elimination method in blasting operations and engineering experimental application based on nano-CO catalysts

Dual Brønsted acidic-basic function immobilized on the 3D mesoporous polycalix [4]resorcinarene: As a highly recyclable catalyst for the synthesis of spiro acenaphthylene/indene heterocycles

Dual Brønsted acidic-basic function immobilized on the 3D mesoporous polycalix [4]resorcinarene: As a highly recyclable catalyst for the synthesis of spiro acenaphthylene/indene heterocycles

Defect engineering enables an advanced separator modification for high-performance lithium-sulfur batteries

Defect engineering enables an advanced separator modification for high-performance lithium-sulfur batteries

Elucidating Local Structure and Positional Effect of Dopants in Colloidal Transition Metal Dichalcogenide Nanosheets for Catalytic Hydrogenolysis.

Tailoring nanoscale catalysts to targeted applications is a vital component in reducing the carbon footprint of industrial processes; however, understanding and controlling the nanostructure influence on catalysts is challenging. Molybdenum disulfide (MoS2), a transition metal dichalcogenide (TMD) material, is a popular example of a nonplatinum-group-metal catalyst with tunable nanoscale properties. Doping with transition metal atoms, such as cobalt, is one method of enhancing its catalytic properties. However, the location and influence of dopant atoms on catalyst behavior are poorly understood. To investigate this knowledge gap, we studied the influence of Co dopants in MoS2 nanosheets on catalytic hydrodesulfurization (HDS) through a well-controlled, ligand-directed, tunable colloidal doping approach. X-ray absorption spectroscopy and density functional theory calculations revealed the nonmonotonous relationship between dopant concentration, location, and activity in HDS. Catalyst activity peaked at 21% Co:Mo as Co saturates the edge sites and begins basal plane doping. While Co prefers to dope the edges over basal sites, basal Co atoms are demonstrably more catalytically active than edge Co. These findings provide insight into the hydrogenolysis behavior of doped TMDs and can be extended to other TMD materials.

Facile Synthesis of Copper Nanocubes in Aqueous Phase for Catalytic Esterification Using Green-Conditions

This work demonstrated a simple and environmentally friendly method for synthesizing silica-supported copper nanocubes (CuNCs/SiO2). The copper nanocubes, with a size of 15 ± 5 nm, were synthesized using green reagents and conditions. Ascorbic acid, water, and di-n-butyl sulfide were employed as reducing agent, solvent, and stabilizing ligand, respectively. The designed nanoscale catalyst was utilized for the esterification of acetic acid to methyl acetate at room temperature. The catalyst exhibited high efficiency, converting 80% of the reactant to the desired product (methyl acetate) after 24 hours of reaction at room temperature. The size and shape of copper nanocubes were characterized by transmission electron microscopy (TEM) and X-ray diffraction to characterize the formation of copper nanocubes, while the esterification product was characterized using gas chromatography-mass spectrometry.

Robust catalyst 3D microarchitectures by digital light printing with ceramic particle–polymer composites

This study entailed the development of an advanced photocatalyst model characterized by high efficiency and ease in dispersion and retrieval processes. This model incorporates a multiscale-hierarchical open-cell structure integrated with nanostructured materials, effectively targeting the removal of organic compounds from wastewater. The fabrication of the specimens was achieved through a combined approach of additive manufacturing and chemical synthesis. The open-cell structure, composed of photopolymerized polymers and synthesized nanocrystals, displays a notable aspect ratio, an extensive surface area, and a significant porosity. These features facilitate the concurrent entry of fluid and light into the core of the framework, leading to enhanced light scattering and activation of photoinduced redox reactions on organic contaminants adhered to the anatase TiO2 surface. The photocatalytic performance was quantified through a spectroscopic analysis, monitoring the absorbance changes associated with organic pollutant degradation. In addition, the influence of open-cell structures on nanomaterial growth under hydrothermal synthesis conditions was explored using finite element method simulations, with findings corroborated by microscopic examination. The functional effectiveness of the novel photocatalyst was assessed through compression tests, analysis of changes pre- and post-reaction, and evaluations of reusability. The developed 3D photocatalyst offers straightforward installation, relocation, and operation, presenting a resilient and effective solution for employing nanoscale catalysts while significantly reducing secondary contamination risks from nanomaterials in aquatic environments. This innovative structure holds potential for application in diverse sectors, including hydrogen production, water decomposition, CO2 capture, and biomedicine.