Materials Science › Materials Chemistry

Catalytic Processes in Materials Science

Description

This cluster of papers covers advances in the research of catalytic nanomaterials, particularly focusing on the catalytic properties of nanoparticles, metal-support interactions, low-temperature oxidation reactions, selective oxidation processes, NOx reduction, and methane activation. The studies explore the use of various materials such as ceria and gold in catalysis, with a strong emphasis on understanding the mechanisms and optimizing the performance of these nanomaterials.

Keywords

Catalysis; Nanoparticles; Oxidation; Ceria; Gold; Metal-Support Interactions; Low-Temperature; Selective Oxidation; NOx Reduction; Methane Activation

Abstract Over the past several years, cerium oxide and CeO2-containing materials have come under intense scrutiny as catalysts and as structural and electronic promoters of heterogeneous catalytic reactions. Recent developments … Abstract Over the past several years, cerium oxide and CeO2-containing materials have come under intense scrutiny as catalysts and as structural and electronic promoters of heterogeneous catalytic reactions. Recent developments regarding the characterization of ceria and CeO2-containing catalysts are critically reviewed with a special focus towards catalyst interaction with small molecules such as hydrogen, carbon monoxide, oxygen, and nitric oxide. Relevant catalytic and technological applications such as the use of ceria in automotive exhaust emission control and in the formulation of SO x reduction catalysts is described. A survey of the use of CeO2-containing materials as oxidation and reduction catalysts is also presented.
Supported metal nanostructures are the most widely used type of heterogeneous catalyst in industrial processes. The size of metal particles is a key factor in determining the performance of such … Supported metal nanostructures are the most widely used type of heterogeneous catalyst in industrial processes. The size of metal particles is a key factor in determining the performance of such catalysts. In particular, because low-coordinated metal atoms often function as the catalytically active sites, the specific activity per metal atom usually increases with decreasing size of the metal particles. However, the surface free energy of metals increases significantly with decreasing particle size, promoting aggregation of small clusters. Using an appropriate support material that strongly interacts with the metal species prevents this aggregation, creating stable, finely dispersed metal clusters with a high catalytic activity, an approach industry has used for a long time. Nevertheless, practical supported metal catalysts are inhomogeneous and usually consist of a mixture of sizes from nanoparticles to subnanometer clusters. Such heterogeneity not only reduces the metal atom efficiency but also frequently leads to undesired side reactions. It also makes it extremely difficult, if not impossible, to uniquely identify and control the active sites of interest.The ultimate small-size limit for metal particles is the single-atom catalyst (SAC), which contains isolated metal atoms singly dispersed on supports. SACs maximize the efficiency of metal atom use, which is particularly important for supported noble metal catalysts. Moreover, with well-defined and uniform single-atom dispersion, SACs offer great potential for achieving high activity and selectivity.In this Account, we highlight recent advances in preparation, characterization, and catalytic performance of SACs, with a focus on single atoms anchored to metal oxides, metal surfaces, and graphene. We discuss experimental and theoretical studies for a variety of reactions, including oxidation, water gas shift, and hydrogenation. We describe advances in understanding the spatial arrangements and electronic properties of single atoms, as well as their interactions with the support. Single metal atoms on support surfaces provide a unique opportunity to tune active sites and optimize the activity, selectivity, and stability of heterogeneous catalysts, offering the potential for applications in a variety of industrial chemical reactions.
To investigate the initial chemical events associated with high-temperature gas-phase oxidation of hydrocarbons, we have expanded the ReaxFF reactive force field training set to include additional transition states and chemical … To investigate the initial chemical events associated with high-temperature gas-phase oxidation of hydrocarbons, we have expanded the ReaxFF reactive force field training set to include additional transition states and chemical reactivity of systems relevant to these reactions and optimized the force field parameters against a quantum mechanics (QM)-based training set. To validate the ReaxFF potential obtained after parameter optimization, we performed a range of NVT-MD simulations on various hydrocarbon/O2 systems. From simulations on methane/O2, o-xylene/O2, propene/O2, and benzene/O2 mixtures, we found that ReaxFF obtains the correct reactivity trend (propene > o-xylene > methane > benzene), following the trend in the C-H bond strength in these hydrocarbons. We also tracked in detail the reactions during a complete oxidation of isolated methane, propene, and o-xylene to a CO/CO2/H2O mixture and found that the pathways predicted by ReaxFF are in agreement with chemical intuition and our QM results. We observed that the predominant initiation reaction for oxidation of methane, propene, and o-xylene under fuel lean conditions involved hydrogen abstraction of the methyl hydrogen by molecular oxygen forming hydroperoxyl and hydrocarbon radical species. While under fuel rich conditions with a mixture of these hydrocarbons, we observed different chemistry compared with the oxidation of isolated hydrocarbons including a change in the type of initiation reactions, which involved both decomposition of the hydrocarbon or attack by other radicals in the system. Since ReaxFF is capable of simulating complicated reaction pathways without any preconditioning, we believe that atomistic modeling with ReaxFF provides a useful method for determining the initial events of oxidation of hydrocarbons under extreme conditions and can enhance existing combustion models.
The infrared spectral performance of the N x O y species observed on oxide surfaces [N2O, NOāˆ’, NO, (NO)2, N2O3, NO+, NO2 āˆ’ (different nitro and nitrito anions), NO2, N2O4, … The infrared spectral performance of the N x O y species observed on oxide surfaces [N2O, NOāˆ’, NO, (NO)2, N2O3, NO+, NO2 āˆ’ (different nitro and nitrito anions), NO2, N2O4, N2O5, NO2, and NO3 āˆ’ (bridged, bidentate, and monodentate nitrates)] is considered. The spectra of related compounds (N2, H-, and C-containing nitrogen oxo species, C─N species, NH x species) are also briefly discussed. Some guidelines for spectral identification of N x O y adspecies are proposed and the transformation of the nitrogen oxo species on catalyst surfaces are regarded.
Most catalysts consist of nanometer-sized particles dispersed on a high-surface-area support. Advances in characterization methods have led to a molecular-level understanding of the relationships between nanoparticle properties and catalytic performance. … Most catalysts consist of nanometer-sized particles dispersed on a high-surface-area support. Advances in characterization methods have led to a molecular-level understanding of the relationships between nanoparticle properties and catalytic performance. Together with novel approaches to nanoparticle synthesis, this knowledge is contributing to the design and development of new catalysts.
The energy of a large number of oxidation reactions of $3d$ transition metal oxides is computed using the generalized gradient approach (GGA) and $\mathrm{GGA}+\mathrm{U}$ methods. Two substantial contributions to the … The energy of a large number of oxidation reactions of $3d$ transition metal oxides is computed using the generalized gradient approach (GGA) and $\mathrm{GGA}+\mathrm{U}$ methods. Two substantial contributions to the error in GGA oxidation energies are identified. The first contribution originates from the overbinding of GGA in the ${\mathrm{O}}_{2}$ molecule and only occurs when the oxidant is ${\mathrm{O}}_{2}$. The second error occurs in all oxidation reactions and is related to the correlation error in $3d$ orbitals in GGA. Strong self-interaction in GGA systematically penalizes a reduced state (with more $d$ electrons) over an oxidized state, resulting in an overestimation of oxidation energies. The constant error in the oxidation energy from the ${\mathrm{O}}_{2}$ binding error can be corrected by fitting the formation enthalpy of simple nontransition metal oxides. Removal of the ${\mathrm{O}}_{2}$ binding error makes it possible to address the correlation effects in $3d$ transition metal oxides with the $\mathrm{GGA}+\mathrm{U}$ method. Calculated oxidation energies agree well with experimental data for reasonable and consistent values of U.
Traditional analysis of reactions catalyzed by supported metals involves the structure of the metallic particles. However, we report here that for the class of nanostructured gold- or platinum-cerium oxide catalysts, … Traditional analysis of reactions catalyzed by supported metals involves the structure of the metallic particles. However, we report here that for the class of nanostructured gold- or platinum-cerium oxide catalysts, which are active for the water-gas shift reaction, metal nanoparticles do not participate in the reaction. Nonmetallic gold or platinum species strongly associated with surface cerium-oxygen groups are responsible for the activity.
Tungsten carbide catalyzes the formation of water from hydrogen and oxygen at room temperature, the reduction of tungsten trioxide by hydrogen in the presence of water, and the isomerization of … Tungsten carbide catalyzes the formation of water from hydrogen and oxygen at room temperature, the reduction of tungsten trioxide by hydrogen in the presence of water, and the isomerization of 2,2-dimethylpropane to 2-methylbutane. This catalytic behavior, which is typical of platinum, is not exhibited at all by tungsten. The surface electronic properties of the latter are therefore modified by carbon in such a way that they resemble those of platinum.
One of the main stumbling blocks in developing rational design strategies for heterogeneous catalysis is that the complexity of the catalysts impairs efforts to characterize their active sites. We show … One of the main stumbling blocks in developing rational design strategies for heterogeneous catalysis is that the complexity of the catalysts impairs efforts to characterize their active sites. We show how to identify the crucial atomic structure motif for the industrial Cu/ZnO/Al(2)O(3) methanol synthesis catalyst by using a combination of experimental evidence from bulk, surface-sensitive, and imaging methods collected on real high-performance catalytic systems in combination with density functional theory calculations. The active site consists of Cu steps decorated with Zn atoms, all stabilized by a series of well-defined bulk defects and surface species that need to be present jointly for the system to work.
Gold nanocrystals absorbed on metal oxides have exceptional properties in oxidation catalysis, including the oxidation of carbon monoxide at ambient temperatures, but the identification of the active catalytic gold species … Gold nanocrystals absorbed on metal oxides have exceptional properties in oxidation catalysis, including the oxidation of carbon monoxide at ambient temperatures, but the identification of the active catalytic gold species among the many present on real catalysts is challenging. We have used aberration-corrected scanning transmission electron microscopy to analyze several iron oxide–supported catalyst samples, ranging from those with little or no activity to others with high activities. High catalytic activity for carbon monoxide oxidation is correlated with the presence of bilayer clusters that are ∼0.5 nanometer in diameter and contain only ∼10 gold atoms. The activity of these bilayer clusters is consistent with that demonstrated previously with the use of model catalyst systems.
Gold clusters ranging in diameter from 1 to 6 nanometers have been prepared on single crystalline surfaces of titania in ultrahigh vacuum to investigate the unusual size dependence of the … Gold clusters ranging in diameter from 1 to 6 nanometers have been prepared on single crystalline surfaces of titania in ultrahigh vacuum to investigate the unusual size dependence of the low-temperature catalytic oxidation of carbon monoxide. Scanning tunneling microscopy/spectroscopy (STM/STS) and elevated pressure reaction kinetics measurements show that the structure sensitivity of this reaction on gold clusters supported on titania is related to a quantum size effect with respect to the thickness of the gold islands; islands with two layers of gold are most effective for catalyzing the oxidation of carbon monoxide. These results suggest that supported clusters, in general, may have unusual catalytic properties as one dimension of the cluster becomes smaller than three atomic spacings.
Aluminosilicate zeolites such as UTD-1 (structure shown) belong to a family of nanoporous inorganic materials that find utility in catalysis, separation, and ion exchange. During the last decade, the rate … Aluminosilicate zeolites such as UTD-1 (structure shown) belong to a family of nanoporous inorganic materials that find utility in catalysis, separation, and ion exchange. During the last decade, the rate of discovery of new open-framework materials based, for example, on phosphates, sulfides, halides, nitrides, and coordination compounds has increased dramatically. The synthesis, structures, and properties of this remarkable class of materials are reviewed.
Single-crystalline and uniform nanopolyhedra, nanorods, and nanocubes of cubic CeO2 were selectively prepared by a hydrothermal method at temperatures in the range of 100āˆ’180 °C under different NaOH concentrations, using … Single-crystalline and uniform nanopolyhedra, nanorods, and nanocubes of cubic CeO2 were selectively prepared by a hydrothermal method at temperatures in the range of 100āˆ’180 °C under different NaOH concentrations, using Ce(NO3)3 as the cerium source. According to high-resolution transmission electron microscopy, they have different exposed crystal planes: {111} and {100} for polyhedra, {110} and {100} for rods, and {100} for cubes. During the synthesis, the formation of hexagonal Ce(OH)3 intermediate species and their transformation into CeO2 at elevated temperature, together with the base concentration, have been demonstrated as the key factors responsible for the shape evolution. Oxygen storage capacity (OSC) measurements at 400 °C revealed that the oxygen storage takes place both at the surface and in the bulk for the as-obtained CeO2 nanorods and nanocubes, but is restricted at the surface for the nanopolyhedra just like the bulk one, because the {100}/{110}-dominated surface structures are more reactive for CO oxidation than the {111}-dominated one. This result suggests that high OSC materials might be designed and obtained by shape-selective synthetic strategy.
ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTDoped LaGaO3 Perovskite Type Oxide as a New Oxide Ionic ConductorTatsumi Ishihara, Hideaki Matsuda, and Yusaku TakitaCite this: J. Am. Chem. Soc. 1994, 116, 9, 3801–3803Publication Date … ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTDoped LaGaO3 Perovskite Type Oxide as a New Oxide Ionic ConductorTatsumi Ishihara, Hideaki Matsuda, and Yusaku TakitaCite this: J. Am. Chem. Soc. 1994, 116, 9, 3801–3803Publication Date (Print):May 1, 1994Publication History Published online1 May 2002Published inissue 1 May 1994https://pubs.acs.org/doi/10.1021/ja00088a016https://doi.org/10.1021/ja00088a016research-articleACS PublicationsRequest reuse permissionsArticle Views6405Altmetric-Citations1294LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InRedditEmail Other access optionsGet e-Alertsclose Get e-Alerts
Abstract A variety of gold catalysts can be used to catalyze the oxidation of carbon monoxide at temperatures as low as āˆ’70 °C and are stable in a moistened gas … Abstract A variety of gold catalysts can be used to catalyze the oxidation of carbon monoxide at temperatures as low as āˆ’70 °C and are stable in a moistened gas atmosphere. The novel catalysts, prepared by coprecipitation, are composed of ultra-fine gold particles and one of the oxides of 3d transition metals of group VIII, namely, Fe, Co, and Ni.
ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTStrong metal-support interactions. Group 8 noble metals supported on titanium dioxideS. J. Tauster, S. C. Fung, and R. L. GartenCite this: J. Am. Chem. Soc. 1978, 100, … ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTStrong metal-support interactions. Group 8 noble metals supported on titanium dioxideS. J. Tauster, S. C. Fung, and R. L. GartenCite this: J. Am. Chem. Soc. 1978, 100, 1, 170–175Publication Date (Print):January 1, 1978Publication History Published online1 May 2002Published inissue 1 January 1978https://pubs.acs.org/doi/10.1021/ja00469a029https://doi.org/10.1021/ja00469a029research-articleACS PublicationsRequest reuse permissionsArticle Views13859Altmetric-Citations2434LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InRedditEmail Other access optionsGet e-Alertsclose Get e-Alerts
Interest in catalysis by metal nanoparticles (NPs) is increasing dramatically, as reflected by the large number of publications in the last five years. This field, "semi-heterogeneous catalysis", is at the … Interest in catalysis by metal nanoparticles (NPs) is increasing dramatically, as reflected by the large number of publications in the last five years. This field, "semi-heterogeneous catalysis", is at the frontier between homogeneous and heterogeneous catalysis, and progress has been made in the efficiency and selectivity of reactions and recovery and recyclability of the catalytic materials. Usually NP catalysts are prepared from a metal salt, a reducing agent, and a stabilizer and are supported on an oxide, charcoal, or a zeolite. Besides the polymers and oxides that used to be employed as standard, innovative stabilizers, media, and supports have appeared, such as dendrimers, specific ligands, ionic liquids, surfactants, membranes, carbon nanotubes, and a variety of oxides. Ligand-free procedures have provided remarkable results with extremely low metal loading. The Review presents the recent developments and the use of NP catalysis in organic synthesis, for example, in hydrogenation and C--C coupling reactions, and the heterogeneous oxidation of CO on gold NPs.
Hydrogen peroxide (H2O2) is widely used in almost all industrial areas, particularly in the chemical industry and environmental protection. The only degradation product of its use is water, and thus … Hydrogen peroxide (H2O2) is widely used in almost all industrial areas, particularly in the chemical industry and environmental protection. The only degradation product of its use is water, and thus it has played a large role in environmentally friendly methods in the chemical industry. Hydrogen peroxide is produced on an industrial scale by the anthraquinone oxidation (AO) process. However, this process can hardly be considered a green method. It involves the sequential hydrogenation and oxidation of an alkylanthraquinone precursor dissolved in a mixture of organic solvents followed by liquid-liquid extraction to recover H2O2. The AO process is a multistep method that requires significant energy input and generates waste, which has a negative effect on its sustainability and production costs. The transport, storage, and handling of bulk H2O2 involve hazards and escalating expenses. Thus, novel, cleaner methods for the production of H2O2 are being explored. The direct synthesis of H2O2 from O2 and H2 using a variety of catalysts, and the factors influencing the formation and decomposition of H2O2 are examined in detail in this Review.
The high catalytic activity of gold clusters on oxides has been attributed to structural effects (including particle thickness and shape and metal oxidation state), as well as to support effects. … The high catalytic activity of gold clusters on oxides has been attributed to structural effects (including particle thickness and shape and metal oxidation state), as well as to support effects. We have created well-ordered gold mono-layers and bilayers that completely wet (cover) the oxide support, thus eliminating particle shape and direct support effects. High-resolution electron energy loss spectroscopy and carbon monoxide adsorption confirm that the gold atoms are bonded to titanium atoms. Kinetic measurements for the catalytic oxidation of carbon monoxide show that the gold bilayer structure is significantly more active (by more than an order of magnitude) than the monolayer.
Cerium dioxide (CeO2, ceria) is becoming an ubiquitous constituent in catalytic systems for a variety of applications. 2016 sees the 40(th) anniversary since ceria was first employed by Ford Motor … Cerium dioxide (CeO2, ceria) is becoming an ubiquitous constituent in catalytic systems for a variety of applications. 2016 sees the 40(th) anniversary since ceria was first employed by Ford Motor Company as an oxygen storage component in car converters, to become in the years since its inception an irreplaceable component in three-way catalysts (TWCs). Apart from this well-established use, ceria is looming as a catalyst component for a wide range of catalytic applications. For some of these, such as fuel cells, CeO2-based materials have almost reached the market stage, while for some other catalytic reactions, such as reforming processes, photocatalysis, water-gas shift reaction, thermochemical water splitting, and organic reactions, ceria is emerging as a unique material, holding great promise for future market breakthroughs. While much knowledge about the fundamental characteristics of CeO2-based materials has already been acquired, new characterization techniques and powerful theoretical methods are deepening our understanding of these materials, helping us to predict their behavior and application potential. This review has a wide view on all those aspects related to ceria which promise to produce an important impact on our life, encompassing fundamental knowledge of CeO2 and its properties, characterization toolbox, emerging features, theoretical studies, and all the catalytic applications, organized by their degree of establishment on the market.
Atomically dispersed noble metal catalysts often exhibit high catalytic performances, but the metal loading density must be kept low (usually below 0.5%) to avoid the formation of metal nanoparticles through … Atomically dispersed noble metal catalysts often exhibit high catalytic performances, but the metal loading density must be kept low (usually below 0.5%) to avoid the formation of metal nanoparticles through sintering. We report a photochemical strategy to fabricate a stable atomically dispersed palladium-titanium oxide catalyst (Pd1/TiO2) on ethylene glycolate (EG)-stabilized ultrathin TiO2 nanosheets containing Pd up to 1.5%. The Pd1/TiO2 catalyst exhibited high catalytic activity in hydrogenation of C=C bonds, exceeding that of surface Pd atoms on commercial Pd catalysts by a factor of 9. No decay in the activity was observed for 20 cycles. More important, the Pd1/TiO2-EG system could activate H2 in a heterolytic pathway, leading to a catalytic enhancement in hydrogenation of aldehydes by a factor of more than 55.
Hot single-atom catalysts For heterogeneous catalysts made from precious metal nanoparticles adsorbed on metal oxides, high temperatures are the enemy. The metal atoms become mobile and the small particles grow … Hot single-atom catalysts For heterogeneous catalysts made from precious metal nanoparticles adsorbed on metal oxides, high temperatures are the enemy. The metal atoms become mobile and the small particles grow larger, causing a loss in surface area and hence in activity. Jones et al. turned this process to their advantage and used these mobile species to create single-atom platinum catalysts. The platinum on alumina supported transfers in air at 800°C to ceria supports to form highly active catalysts with isolated metal cations. Science , this issue p. 150
Platinum group metal-free (PGM-free) metal-nitrogen-carbon catalysts have emerged as a promising alternative to their costly platinum (Pt)-based counterparts in polymer electrolyte fuel cells (PEFCs) but still face some major challenges, … Platinum group metal-free (PGM-free) metal-nitrogen-carbon catalysts have emerged as a promising alternative to their costly platinum (Pt)-based counterparts in polymer electrolyte fuel cells (PEFCs) but still face some major challenges, including (i) the identification of the most relevant catalytic site for the oxygen reduction reaction (ORR) and (ii) demonstration of competitive PEFC performance under automotive-application conditions in the hydrogen (H2)-air fuel cell. Herein, we demonstrate H2-air performance gains achieved with an iron-nitrogen-carbon catalyst synthesized with two nitrogen precursors that developed hierarchical porosity. Current densities recorded in the kinetic region of cathode operation, at fuel cell voltages greater than ~0.75 V, were the same as those obtained with a Pt cathode at a loading of 0.1 milligram of Pt per centimeter squared. The proposed catalytic active site, carbon-embedded nitrogen-coordinated iron (FeN4), was directly visualized with aberration-corrected scanning transmission electron microscopy, and the contributions of these active sites associated with specific lattice-level carbon structures were explored computationally.
Metal species with different size (single atoms, nanoclusters, and nanoparticles) show different catalytic behavior for various heterogeneous catalytic reactions. It has been shown in the literature that many factors including … Metal species with different size (single atoms, nanoclusters, and nanoparticles) show different catalytic behavior for various heterogeneous catalytic reactions. It has been shown in the literature that many factors including the particle size, shape, chemical composition, metal–support interaction, and metal–reactant/solvent interaction can have significant influences on the catalytic properties of metal catalysts. The recent developments of well-controlled synthesis methodologies and advanced characterization tools allow one to correlate the relationships at the molecular level. In this Review, the electronic and geometric structures of single atoms, nanoclusters, and nanoparticles will be discussed. Furthermore, we will summarize the catalytic applications of single atoms, nanoclusters, and nanoparticles for different types of reactions, including CO oxidation, selective oxidation, selective hydrogenation, organic reactions, electrocatalytic, and photocatalytic reactions. We will compare the results obtained from different systems and try to give a picture on how different types of metal species work in different reactions and give perspectives on the future directions toward better understanding of the catalytic behavior of different metal entities (single atoms, nanoclusters, and nanoparticles) in a unifying manner.
It is well known that urbanization and industrialization have resulted in the rapidly increasing emissions of volatile organic compounds (VOCs), which are a major contributor to the formation of secondary … It is well known that urbanization and industrialization have resulted in the rapidly increasing emissions of volatile organic compounds (VOCs), which are a major contributor to the formation of secondary pollutants (e.g., tropospheric ozone, PAN (peroxyacetyl nitrate), and secondary organic aerosols) and photochemical smog. The emission of these pollutants has led to a large decline in air quality in numerous regions around the world, which has ultimately led to concerns regarding their impact on human health and general well-being. Catalytic oxidation is regarded as one of the most promising strategies for VOC removal from industrial waste streams. This Review systematically documents the progresses and developments made in the understanding and design of heterogeneous catalysts for VOC oxidation over the past two decades. It addresses in detail how catalytic performance is often drastically affected by the pollutant sources and reaction conditions. It also highlights the primary routes for catalyst deactivation and discusses protocols for their subsequent reactivation. Kinetic models and proposed oxidation mechanisms for representative VOCs are also provided. Typical catalytic reactors and oxidizers for industrial VOC destruction are further discussed. We believe that this Review will provide a great foundation and reference point for future design and development in this field.
Ammonia fuel is regarded as a promising zero-carbon alternative to diesel in next-generation marine engines. However, the high-temperature ammonia-rich environment poses significant corrosion challenges to hot-end components such as valves. … Ammonia fuel is regarded as a promising zero-carbon alternative to diesel in next-generation marine engines. However, the high-temperature ammonia-rich environment poses significant corrosion challenges to hot-end components such as valves. This study investigates the corrosion behavior of Ni80A alloy marine valves under the coupled effects of a high temperature and ammonia atmosphere. Using computational fluid dynamics (CFD), the service temperature of the valve and the ammonia concentration distribution inside the engine cylinder were identified. High-temperature corrosion experiments were conducted with a custom-designed setup. Results show that corrosion kinetics accelerated markedly with temperature: the initial corrosion rate at 800 °C was four times that at 500 °C, and the maximum corrosion layer thickness reached 37 μm—double that at lower temperatures. Microstructural analysis revealed a transition from a dense, defect-free corrosion layer at 500 °C to a non-uniform layer with coarse CrN particles and aggregated nitrides at 800 °C. Notably, surface hardness increased at both temperatures, peaking at 590 HV at 500 °C, while matrix hardness at 800 °C declined due to γ′ phase coarsening and grain growth. This work provides detailed insight into the temperature-dependent ammonia corrosion mechanisms of marine Ni-based alloy valves, offering essential data for material design and durability assessment in ammonia-fueled marine engines.
Blocked electron transfer in the catalyst during advanced oxidation processes causes sluggish singlet oxygen (1O2) generation efficiency and sacrifices catalyst stability. In this work, we propose an electron‐delocalization strategy that … Blocked electron transfer in the catalyst during advanced oxidation processes causes sluggish singlet oxygen (1O2) generation efficiency and sacrifices catalyst stability. In this work, we propose an electron‐delocalization strategy that unlocks ATd2+‐O‐BOh3+ electron‐transfer pathways within spinel oxide (Cu0.8Fe2.2O4), inducing the intermolecular electron transfer of peroxymonosulfate (PMS) for selective 1O2 generation. In‐situ characterizations and theoretical calculations confirm that the electron‐delocalized Cu2+ triggers a high spin‐state of O in FeTd2+‐O‐FeOh3+, thus creating a spin channel for the spontaneous intermolecular electron transfer of PMS from the FeOh3+ adsorption site to the FeTd2+ adsorption site through FeTd2+‐O‐FeOh3+. This process allows for the simultaneous oxidation and reduction of PMS, thereby reducing the energy barriers for the formation of SO4•– and SO5•– radicals. Subsequently, the interfacial SO4•– rapidly oxidizes SO5•– into 1O2, enhancing 1O2 generation efficiency without sacrificing catalyst stability. The selectivity of 1O2 in the Cu0.8Fe2.2O4/PMS system reaches 98.4%. Multiple pollutants are removed in the Cu0.8Fe2.2O4/PMS system without interference from coexisting substances. The scale‐up experiment realizes 100% contaminant removal during the continuous operation process (48 h). This work exhibits a novel strategy for selective 1O2 generation to achieve the goal of practical applications.
Pharmaceuticals such as diclofenac (DCF), a widely used anti-inflammatory drug, are frequently detected in water bodies and pose serious environmental and health risks due to their persistence and low biodegradability. … Pharmaceuticals such as diclofenac (DCF), a widely used anti-inflammatory drug, are frequently detected in water bodies and pose serious environmental and health risks due to their persistence and low biodegradability. Although ozonation is an effective method for pollutant removal, its efficiency is often limited by low ozone utilization and incomplete mineralization. In this work, CuO/Al2O3- and MnO2/Al2O3-supported catalysts were prepared via an impregnation method and evaluated for their performance in catalytic ozonation of diclofenac (DCF) in an aqueous solution. The catalysts were characterized by TEM, N2 adsorption–desorption, FTIR, and XPS analyses. The effects of catalyst type, dosage, initial pH, and ozone flow rate on degradation efficiency were systematically investigated. Under optimal conditions, the DCF removal efficiencies reached 73.99% and 76.33% using CuO/Al2O3 and MnO2/Al2O3, respectively, while COD removal efficiencies were 77.6% and 89.3%. Quenching experiments indicated that hydroxyl radicals (•OH) were the predominant reactive species involved in the catalytic ozonation process. The results demonstrate that supported CuO and MnO2 catalysts can effectively enhance diclofenac degradation by ozone, offering potential for advanced water treatment applications.
Recent advances in the photocatalytic activation of dry reforming of methane (DRM: CO2 + CH4 → 2CO + 2H2) at low temperature and ambient pressure have generated considerable interest as … Recent advances in the photocatalytic activation of dry reforming of methane (DRM: CO2 + CH4 → 2CO + 2H2) at low temperature and ambient pressure have generated considerable interest as a promising route to convert greenhouse gases into valuable synthetic gas (syngas). While detailed studies have revealed the mechanisms involved in photocatalytic DRM at metal-semiconductor interfaces, less attention has been devoted to how high-surface-area semiconductor supports may enhance such conversions. Here, we structure triblock terpolymer self-assembly directed sol-gel-derived transition metal oxide (Ta2O5 or TiO2) supports of Rh-loaded photocatalysts into various equilibrium and nonequilibrium derived porous morphologies and show how they modulate single-pass conversion, total production rate, and material efficiency. Supported by in-depth materials characterization, flow, and optics simulations rationalizing observed trends, results reveal record catalyst performance. Our work suggests that asymmetric pore structures simultaneously optimizing mass transport and surface area may be well-suited to maximize photocatalyst performance.
The selective oxidation of methane (CH4) has attractive potentials for mitigating global warming and producing value‐added chemicals, while the efficient generation of multicarbon products such as ethanol remains challenging, due … The selective oxidation of methane (CH4) has attractive potentials for mitigating global warming and producing value‐added chemicals, while the efficient generation of multicarbon products such as ethanol remains challenging, due to the short lifetimes and high unpaired concentrations of reactive intermediates (like •OH, •CH3, •OCH3, •CH2OH). Herein, we developed a medium‐spin Zn‐O‐Fe(MS) catalyst with tunable Fe(III) spin states, which can efficiently photo‐oxidize CH4 to ethanol at ambient conditions. The unpaired electrons in d‐orbitals of Fe sites allow for efficient adsorption of •OH, and the eg‐orbital occupancy enables stabilizing different key carbon‐containing intermediates (•OCH3 vs. •CH2OH). By balancing those two descriptors, the medium‐spin Zn‐O‐Fe(MS) catalyst allows to achieve selective generation of •CH2OH intermediates with a moderate *OH coverage, and subsequent coupling of •CH3 and •CH2OH to ethanol. With a light intensity of 100 mWĀ·cm‐2 and water as a weak oxidant, the Zn‐O‐Fe(MS) catalyst exhibited a peak photocatalytic CH4‐to‐ethanol yield of 372 μmolĀ·g‐1Ā·h‐1 without the use of photosensitizers or sacrificial reagents, which is ~ 3 times higher than the previously best reported photocatalytic CH4 oxidation to ethanol under similar conditions. Our study suggests an attractive potential of converting CH4 to multicarbon products by modulating spin states of the catalytic sites.
Nitric oxide binding to and/or dissociation on isolated cobalt cluster cations, Con+ (n = 3-14), has been investigated using a combination of infrared multiple photon dissociation spectroscopy and density functional … Nitric oxide binding to and/or dissociation on isolated cobalt cluster cations, Con+ (n = 3-14), has been investigated using a combination of infrared multiple photon dissociation spectroscopy and density functional theory. Rich vibrational structure in the 300-800 cm-1 spectral region reflects predominantly dissociative adsorption, though a minor molecularly bound isomer cannot be ruled out. Inert messenger tagging reveals nitrogen and oxygen atoms bound in bridged and/or three-atom sites. The calculated potential energy surface associated with the reaction between NO and Co3+ confirms only submerged barriers to dissociation and unusual full insertion of the N atom, which binds to all three metal atoms. The second NO adsorbed also dissociates on all clusters studied here, with the smallest cluster, [Co3N2O2]+-Arm, adopting an unusual planar cyclic structure with O atoms and an N2 molecule inserted between adjacent Co atoms.
Proton-coupled electron transfer (PCET) has emerged as a promising strategy for boosting hydrogen peroxide (H2O2) production through the two-electron oxygen reduction reaction (ORR). To achieve efficient H2O2 production, a specific … Proton-coupled electron transfer (PCET) has emerged as a promising strategy for boosting hydrogen peroxide (H2O2) production through the two-electron oxygen reduction reaction (ORR). To achieve efficient H2O2 production, a specific C═N-NH-C═O structure was engineered on CQDs through Schiff-base addition reaction, creating an ideal catalytic microenvironment within the molecule via the integration of a proton donor and oxygen adsorption site. Benefiting from that, the obtained benzohydrazide-modified CQDs (BD-CQDs) exhibited a H2O2 production efficiency of 1562 μmol g-1 h-1 even without an external oxygen supply and electron donor, nearly three times that of the pristine CQDs. Mechanism investigation verified that oxygen adsorption shifted from a side-on type to an end-on type after modification, and the O═O bond was stretched on the C═O adjacent to -NH-, improving H2O2 selectivity to 92.5%. Identification of active sites revealed that -NH- provided sustainable proton flux for PCET, while the C═N bridge boosted the charge separation and transfer. Owing to the spatial proximity within the integrated catalytic microenvironment, the proton transfer energy barrier was significantly decreased, thermodynamically favoring H2O2 production. BD-CQDs retained an efficiency of over 88% after five successive cycles or in an ionic environment, highlighting their practical application potential in photocatalytic energy conversion.
The development of efficient catalysts to regulate the thermal decomposition and combustion behavior of ammonium perchlorate (AP) is essential for improving the energy output of solid propellants. In this study, … The development of efficient catalysts to regulate the thermal decomposition and combustion behavior of ammonium perchlorate (AP) is essential for improving the energy output of solid propellants. In this study, a LaFe0.5Co0.5O3/Ni-Fe Prussian Blue Analogue (PBA) composite was designed to synergistically enhance the decomposition kinetics and combustion performance of AP. The composite integrates perovskite-type oxides with a conductive PBA framework, forming a bifunctional electronic-geometric catalytic interface. Systematic characterization revealed that the optimized Ni-Fe PBA effectively balanced oxygen vacancy generation, Fe2+/Fe3+ redox cycling, and a multistage pore structure. This led to a 106.9 °C reduction in AP's thermal decomposition temperature and a 56.2% decrease in activation energy. Combustion tests demonstrated a 48.1% increase in burning rate, a 35.0% increase in flame area, and a 45.8% increase in luminescence intensity, which may be attributed to improved charge transfer and gas diffusion facilitated by interfacial synergy between the two components. This work offers a strategy for designing high-performance catalysts via interfacial engineering, with promising potential for broad applications in fuel energy modulation.
Direct degradation of pollutants by free radicals generated from a photocatalytic oxygen reduction reaction (ORR) has advantages of both thermodynamics and kinetics, but realizing the high degradation activity and selectivity … Direct degradation of pollutants by free radicals generated from a photocatalytic oxygen reduction reaction (ORR) has advantages of both thermodynamics and kinetics, but realizing the high degradation activity and selectivity still remains a great challenge. In this study, we successfully designed donor-acceptor (D-A) UiO-68 metal-organic frameworks (MOFs) by introducing different electron-withdrawing groups for enhanced photocatalytic degradation of pollutants. The electron-withdrawing group-functionalized UiO-68 was able to generate singlet oxygen (1O2) rather than hydrogen peroxide (H2O2) via the ORR process in the absence of a sacrificial agent. Theoretical and experimental results showed that the introduction of electron-withdrawing groups widened the visible-light absorption range and improved the intramolecular charge transfer, thus generating highly active and selective 1O2 for the degradation of Rhodamine B and methyl orange within 10 min. This study highlights the important role of the synergistic interaction between donor and acceptor units in promoting intramolecular charge transfer to increase the production efficiency of reactive oxygen species, providing a promising strategy for designing efficient photocatalysts and beyond.
ABSTRACT Laser light scattering (LLS), manual counting of scanning electron microscopy (SEM) images, and reduction of SEM images using ImageJ (open source program) to determine Feret (caliper) diameters were applied … ABSTRACT Laser light scattering (LLS), manual counting of scanning electron microscopy (SEM) images, and reduction of SEM images using ImageJ (open source program) to determine Feret (caliper) diameters were applied to determine particle size distribution (PSD) of four preparations of 1,3,5‐triamino‐2,4,6‐trinitrobenzene (TATB) and yttria‐stabilized zirconia (YSZ), an SEM certified standard. Mie theory was used to reduce the LLS data. The spherical nature of the YSZ made it a good candidate for LLS. Variations in n , the refractive index, and iĪŗ, the imaginary component, produced very little change in the PSD. However, changing the carrier liquid from H 2 O to a 40% aqueous sucrose solution, thereby changing the carrier refractive index, n 0 , substantially affected the PSD. The Mie complex refractive indices for the YSZ were n = 2.200, iĪŗ = 0.100, with a 40% aqueous sucrose solution, n 0 = 1.400. The triclinic crystal structure of TATB made refractive index determinations more difficult, so a study was conducted varying Mie parameters and comparing them to the same data reduced using the Fraunhofer theory. Changing the n and Īŗ parameters produced PSD with a small concentration of particles less than 1 µm in size or none in this range. SEM images, Feret data, manual counting, and Fraunhofer data reduction indicate particles less than 1 µm are probably < 5% in concentration. The final selection of Mie parameters for TATB was n = 2.283, iĪŗ = 0.1, and suspension medium, n 0 = 1.330. Computations, using density functional theory produced similar parameters.
Abstract A series of copper (Cu) exchanged chabazite zeolite with different Cu content were investigated to elucidate the effect of SO 2 poisoning and regeneration of the Cu species. The … Abstract A series of copper (Cu) exchanged chabazite zeolite with different Cu content were investigated to elucidate the effect of SO 2 poisoning and regeneration of the Cu species. The distribution and redox ability of Cu species were determined by in situ electron paramagnetic resonance (EPR) measurements. After exposure of the catalyst to SO 2 , a large amount of redox active Cu sites disappeared and were replaced with redox inactive sulfated Cu species. The redox window, that is, the amount of Cu able to change oxidation state in the catalyst decreased significantly and was only partially regained by regeneration of the catalyst. This work provides a deeper knowledge of the effect of sulfation and regeneration of the copper sites by characterizing the redox activity of the individual Cu sites.
The regulation of single‐atom catalyst (SAC) through microenvironment engineering, particularly via peripheral species, has recently garnered significant attention in the fields of materials science and heterogeneous catalysis. Nevertheless, establishing unambiguous … The regulation of single‐atom catalyst (SAC) through microenvironment engineering, particularly via peripheral species, has recently garnered significant attention in the fields of materials science and heterogeneous catalysis. Nevertheless, establishing unambiguous structure‐property relationships for SAC, especially concerning peripheral effects, remains a significant challenge. Herein, we propose a strategy for the design of N‐doped carbon‐supported Fe SACs for CO2 reduction reaction (CO2RR). Density functional theory calculations reveal that installing five‐ or six‐membered ring in the outer shell modulates the electronic properties of the inner‐shell coordination N species, altering their electron transfer capabilities while fine‐tuning the d‐p coupling between the Fe center and adjacent N atoms. Notably, five‐membered rings induce stronger d‐p coupling compared to their six‐membered counterparts, leading to higher Fe valance state. This electronic modulation optimizes the adsorption strength of key CO2RR intermediates (COOH* and CO*), enhancing catalytic performance for CO production. Extensive experimental studies corroborate these theoretical findings. The proposed ā€œoutside‐inā€ design strategy can be extended to Ni SACs, offering new insights into the exploration of highly efficient single‐atom centers through peripheral geometric effects.
Dry reforming of methane (DRM) used two greenhouse gases (CO2 and CH4) as reactants to produce hydrogen and syngas, which is considered to be an effective means to address the … Dry reforming of methane (DRM) used two greenhouse gases (CO2 and CH4) as reactants to produce hydrogen and syngas, which is considered to be an effective means to address the greenhouse effect. In this paper, a series of nano core-shell structure La2Ni2-xFexO6@CeO2 composite catalysts with Ni and Fe double regulation at the B-site were prepared by the sol-gel method and applied to the DRM reaction. The experimental results showed that the addition of the Ni ion at the B position of double perovskite can boost the active sites on the prepared catalyst surface and thereby promote the activation and decomposition of reactants. Simultaneously, the incorporation of Fe ions can also increase the lattice oxygen migration and internal oxygen vacancy concentration of the perovskite, and the La2Ni1.6Fe0.4O6@CeO2 sample has the highest surface chemisorbed oxygen content (53.37%). Moreover, the strong interaction between the La2Ni2-xFexO6 core and the CeO2 shell can enlarge the specific surface area and pore volume, which could further improve the oxygen vacancy concentration and coke resistance ability and thus may stimulate the adsorption and dissociation of CH4 and CO2. Meanwhile, the suitable doping ratio of Ni and Fe can effectively enhance the redox performance of the catalyst, and the synergistic effect between Ni and Fe can markedly improve its thermal stability and carbon resistance. The density functional theory was employed to reveal the CH4 adsorption kinetics, and the calculation results convinced us that the La2Ni1.6Fe0.4O6@CeO2 catalyst possessed a lower energy barrier and carbon elimination effect in DRM as expected. Moreover, a fixed-bed tubular reactor was employed to evaluate the catalytic performance of the as-prepared samples, and the 6 h experiment results indicate that the La2Ni1.6Fe0.4O6@CeO2 catalyst achieves top reaction performance with the desired H2/CO of 1, with conversions of CH4 and CO2 reaching 93.12% and 89.95%, respectively. Finally, 41 h continuous stability experiments exhibit a slight decrease of CH4 and CO2 conversions (average: 89.25% and 84.37%), and the average H2/CO ratio still remained at 1.01.
Abstract Thin films of BaZrO 3 , 0.5- and 1.0-nm thick, were prepared on high-surface-area MgAl 2 O 4 (MAO) by Atomic Layer Deposition (ALD) and examined as supports for … Abstract Thin films of BaZrO 3 , 0.5- and 1.0-nm thick, were prepared on high-surface-area MgAl 2 O 4 (MAO) by Atomic Layer Deposition (ALD) and examined as supports for Ni catalysts in Methane Steam Reforming (MSR). Scanning Transmission Electron Microscopy (STEM) showed that the films were conformal with the MAO surface. X-Ray Diffraction (XRD) with Rietveld Analysis indicated that the 1.0-nm film had a perovskite structure. A catalyst with 1-wt% Ni on the BaZrO 3 /MAO support exhibited similarities to exsolution catalysts in that catalysts oxidized at 1073 K and reduced at only 773 K were nearly 4 orders of magnitude less active than catalysts oxidized and reduced at 1073 K. Rates on Ni/BaZrO 3 /MAO catalyst were higher than those on Ni/MAO and exhibited a significantly different activation energy. Because BaZrO 3 is a proton conductor, it is suggested that MSR rates on Ni/BaZrO 3 /MAO are enhanced by proton transfer at the Ni-perovskite interface. Graphical Abstract
The selective catalytic reduction of NOx with CH4 (CH4-SCR) holds the potential to simultaneously abate harmful NOx and CH4 greenhouse gases. In this study, a series of bimetallic M-In/H-SSZ-39 catalysts … The selective catalytic reduction of NOx with CH4 (CH4-SCR) holds the potential to simultaneously abate harmful NOx and CH4 greenhouse gases. In this study, a series of bimetallic M-In/H-SSZ-39 catalysts (where M represents Cr, Co, Ce, and Fe) were prepared via an ion exchange method and subsequently evaluated for their CH4-SCR activity. The influences of the preparation parameters, including the metal ion concentration and calcination temperature, as well as the operating conditions, such as the CH4/NO ratio, O2 concentration, water vapor content, and gas hourly space velocity (GHSV), on the catalytic activity of the optimal Cr-In/H-SSZ-39 catalyst were meticulously examined. The results revealed that the Cr-In/H-SSZ-39 catalyst exhibited peak CH4-SCR catalytic performance when the Cr(NO3)3 concentration was 0.0075 M, the In(NO3)3 concentration was 0.066 M, and the calcination temperature was 500 °C. Under optimal operating conditions, namely GHSV of 10,000 hāˆ’1, 400 ppm NO, 800 ppm CH4, 15 vol% O2, and 6 vol% H2O, the NOx conversion rate reached 93.4%. To shed light on the excellent performance of Cr-In/H-SSZ-39 under humid conditions, a comparative analysis of the crystalline phase, chemical composition, pore structure, surface chemical state, surface acidity, and redox properties of Cr-In/H-SSZ-39 and In/H-SSZ-39 was conducted. The characterization results indicated that the incorporation of Cr into In/H-SSZ-39 enhanced its acidity and also facilitated the generation of InO+ active species, which promoted the oxidation of NO and the activation of CH4, respectively. A synergistic effect was observed between Cr and In species, which significantly improved the redox properties of the catalyst. Consequently, the activated CH4 could further interact with InO+ to produce carbon-containing intermediates such as HCOOāˆ’, which ultimately reacted with nitrate-based intermediates to yield N2, CO2, and H2O.
The partial oxidation of methane to methanol over copper-exchanged zeolites offers a promising avenue for methane valorization. Numerous zeolites have been demonstrated to be active for the selective oxidation of … The partial oxidation of methane to methanol over copper-exchanged zeolites offers a promising avenue for methane valorization. Numerous zeolites have been demonstrated to be active for the selective oxidation of methane, with the methanol yield varying significantly depending on the zeolite framework, Si/Al ratio, and copper loading. Herein, we present a comprehensive study of one of the most active Cu-erionite (Cu-ERI) zeolites with different compositions for the stepwise conversion of methane to methanol, aiming to elucidate the relationship between the methanol yield and the nature of copper species in Cu-ERI zeolites. Operando X-ray absorption spectroscopy (XAS), combined with Fourier-transform infrared spectroscopy (FTIR), allows us to establish a correlation that reveals the dependence of the methanol yield on the reduction rate of copper species. Our findings demonstrate that the Cu/Al ratio plays a crucial role in determining the reducibility of copper species in Cu-ERI zeolites, which in turn governs methanol yield normalized to the copper content. While the Si/Al ratio of the parent zeolite determines the achievable copper loading and the maximal methanol yield, it does not influence the normalized methanol yield. This work suggests that controlling the Cu/Al ratio is essential for maximizing copper efficiency and achieving selective methane partial oxidation. At a fixed optimal Cu/Al ratio, increasing the Al content enhances the total methanol yield by providing more copper exchange sites. The structure-activity relationship of Cu-ERI zeolites in the direct conversion of methane to methanol offers valuable insights into the interplay between the zeolite host and copper species, highlighting the importance of both Cu/Al and Si/Al ratios in designing selective, high-performance materials for this challenging reaction.
The present study investigates the influence of fuel type and combustion parameters on the synthesis efficiency and material characteristics of zinc-based nano metal oxides via the solution combustion process (SCP). … The present study investigates the influence of fuel type and combustion parameters on the synthesis efficiency and material characteristics of zinc-based nano metal oxides via the solution combustion process (SCP). Urea and citric acid were employed as organic fuels to facilitate redox reactions with zinc nitrate serving as the oxidizer. The thermal behavior, combustion reaction kinetics, fuel-to-oxidizer ratios (Φ), and their impact on combustion temperature, product morphology, and phase purity were systematically analyzed. Characterization techniques including flame observation, XRD, SEM and UV-Vis spectroscopy were employed to evaluate crystallinity, particle size range of the synthesized nanoparticles, along with efficiency of fuels used for combustion process. Results indicate that fuel type significantly affects the combustion flame temperature and reaction exothermicity, thereby influencing the structural and morphological attributes of the final oxide product. Urea-based synthesis exhibited rapid combustion and smaller particle sizes, while citric acid yielded more homogeneous and porous structures. The study underscores the role of fuel chemistry in tailoring nanomaterial properties and optimizing energy efficiency in SCP-based synthesis routes.
Single-atom catalysts (SACs) offer superior catalytic performance compared with traditional nanoparticle catalysts but are challenging to develop because of the need for extensive optimization and specialized characterization techniques. This study … Single-atom catalysts (SACs) offer superior catalytic performance compared with traditional nanoparticle catalysts but are challenging to develop because of the need for extensive optimization and specialized characterization techniques. This study presents a rapid and versatile method for detecting synthesis conditions and elucidating the deposition mechanisms of SACs on various substrates. By depositing active elements (Au, Cu, Ni, and Rh) on facet-specific single-crystalline substrates (CeO2, TiO2, MgO, and Al2O3) and employing time-of-flight secondary ion mass spectroscopy (ToF-SIMS), we assessed facet-dependent deposition behaviors and identified optimal conditions for solution-based SAC synthesis. ToF-SIMS revealed diverse deposition behaviors depending on the active element, substrate type, and facet, including the formation of single-atom sites, aggregation into clusters, or absence of deposition altogether. These findings, which align with previous reports on specific systems, highlight the technique's ability to rapidly differentiate these outcomes across various materials. Our study demonstrates that ToF-SIMS is a viable tool for the rapid screening of synthesis conditions, contributing to the faster and more efficient development of next-generation single-atom catalysts.
Ammonia is cogitated as a future fuel due to the carbon-free emission during its combustion. However, for obtaining high efficiency and low emissions while using ammonia as fuel, optimizing the … Ammonia is cogitated as a future fuel due to the carbon-free emission during its combustion. However, for obtaining high efficiency and low emissions while using ammonia as fuel, optimizing the operational parameters of the engine is necessary. Therefore, the present study focuses on evaluating the performance, emission, and combustion characteristics of a diesel engine fueled with ammonia with diesel fuel under dual-fuel mode. The novelty of the present work lies in the fact that optimizing the operating parameters was conducted through the experimental results based on the variation of pilot-fuel injection timing (PFIT) and engine load, as well as the implementation of response surface methodology (RSM) for determining the optimized conditions. In the first stage, the experimental analysis was conducted on a 3.5-kW diesel engine with a PFIT variation (23°, 26°, 29°, and 32°bTDC) and engine load (20%, 40%, 60%, 80%, and 100%) by inducting ammonia directly into the inlet manifold with the help of a solenoid valve through port injection. The findings indicated the ideal PFIT for an ammonia-powered diesel engine of 29°bTDC. In the second stage, engine performance and emission parameters were optimized using desirability optimization in RSM. Resultantly, an engine load of 74.5% and PFIT of 31°bTDC could produce optimal brake thermal efficiency of 17.3%, liquid fuel ratio of 62.99%, and peak cylinder pressure of 48.43 bar. Moreover, emission parameters like 11.74 ppm CO, 0.49 vol.% CO 2 , 12.46 ppm HC, and 127.82 ppm NO x were also achieved. Interestingly, the as-used model could offer high efficiency and accuracy (<5% error) compared to experimental results. It could be generally concluded that ammonia-powered diesel engines should be operated at high engine loads and advanced PFIT to obtain better performance and emission characteristics.
Epoxide deoxygenation by photocatalysis was explored using Au-Co alloy nanoparticles supported on ZrO2 under visible light irradiation. The active metals were deposited on commercial monoclinic ZrO2 by chemical impregnation to … Epoxide deoxygenation by photocatalysis was explored using Au-Co alloy nanoparticles supported on ZrO2 under visible light irradiation. The active metals were deposited on commercial monoclinic ZrO2 by chemical impregnation to achieve controlled mass ratios of gold and cobalt in the alloy nanoparticles. The characterisation of the alloy nanoparticles confirmed the technique produced an average particle size of 4.50 ± 0.29 nm. Catalysts containing pure 3% Au and different Au-Co metal ratios attached to the ZrO2 induced the deoxygenation of styrene oxide in an isopropanol solvent medium. Only 20 mg of pure Au/ZrO2 catalyst gave a 99% yield of styrene at an 80 °C temperature within 16 h under visible light irradiation (400–800 nm). Au-Co/ZrO2 catalysts generally induced conversion to styrene under the same conditions below 60 °C. Above 60 °C, a new reaction pathway was observed to favour a different product over Au-Co/ZrO2, which was identified as styrene glycol. This study developed a new approach to the synthesis of styrene glycol, a molecule that has many useful applications in the chemical and polymer industries. Surface-enhanced Raman spectroscopic (SERS) studies and electron paramagnetic resonance spectroscopic (EPR) studies identified changes in the reaction mechanism and pathway upon increasing the cobalt molar ratio in the Au-Co alloy catalysts.
Strong metal-support interaction (SMSI) is one of the most important phenomena in the history of heterogeneous catalysis and has gained renewed attention in the past decade due to the emergence … Strong metal-support interaction (SMSI) is one of the most important phenomena in the history of heterogeneous catalysis and has gained renewed attention in the past decade due to the emergence of various new types of SMSI. However, the origin of SMSI still remains in debate. Both minimizing surface energy and electron transfer have been regarded as the origin of SMSI because these two are hard to decouple in traditional supported metal catalysts. In this work, a TiOx/Au/Al2O3 quasi-model catalyst was fabricated by inversely depositing a minimal amount of TiOx on the surface of Au nanoparticles, where the charge transfer between TiOx and Au was minimized. As experimentally demonstrated, under high-temperature reduction-reoxidation treatment, the surface TiOx undergoes a wetting-dewetting process, accompanied by the reversible suppression and recovery of the adsorption capability, during which the electron transfer between TiOx and Au is negligible. This work suggests that charge transfer may not be the driving force for the occurrence of SMSI, contributing to a deeper understanding of the SMSI mechanism.
Heterogeneous bimetallic catalysts demonstrate enhanced catalytic performance compared with monometallic systems, as evidenced by flame spray pyrolysis synthesized Pd-Ru/CeO2 nanoalloys. Through precise control of Pd/Ru ratios, the optimized Pd0.5Ru0.5/CeO2 catalyst … Heterogeneous bimetallic catalysts demonstrate enhanced catalytic performance compared with monometallic systems, as evidenced by flame spray pyrolysis synthesized Pd-Ru/CeO2 nanoalloys. Through precise control of Pd/Ru ratios, the optimized Pd0.5Ru0.5/CeO2 catalyst achieves complete CO oxidation at 120 °C. Advanced characterization uncovers two synergistic mechanisms─alloy-induced electronic redistribution confirmed by XPS analysis reveals interfacial charge transfer between Pd and Ru, while CO-TPD measurements demonstrate complementary adsorption behavior with Ru-dominated CO chemisorption and Pd-enhanced oxygen activation. The flame synthesis process simultaneously establishes strong metal-support interactions via CeO2 oxygen vacancy anchoring, stabilizing highly dispersed alloy nanoclusters. This study establishes flame spray pyrolysis as an effective strategy for engineering bimetallic catalysts with tailored electronic and structural synergy, providing a rational design framework for alloy-based oxidation systems.
Volatile Organic Compounds (VOCs) pollution poses significant threats to both environmental quality and human health, while conventional purification technologies such as photocatalysis and adsorption exhibit limitations, including low efficiency and … Volatile Organic Compounds (VOCs) pollution poses significant threats to both environmental quality and human health, while conventional purification technologies such as photocatalysis and adsorption exhibit limitations, including low efficiency and high operational costs. This study implements Nano Water Ion Technology (NWIT) for efficient VOCs degradation under ambient conditions (20 °C). Through a customized reaction system, we systematically investigated the degradation performance and mechanistic pathways of NWIT toward representative VOCs (formaldehyde and toluene). Experimental analysis revealed significant correlations between NWIT operation and VOCs degradation: degradation efficiency decreased with elevated airflow velocity, increased with higher relative humidity, and demonstrated concentration-dependent kinetics influenced by ambient VOCs levels. Mechanistic studies identified the co-existing state of O2 and H2O as a decisive factor in NWIT efficacy, with non-hydrogen-containing reactive oxygen species exhibiting dominant regulatory roles in VOCs degradation processes, demonstrating superior efficiency enhancement contributions compared to hydrogen-containing reactive oxygen species.
Abstract Modulating the synthesis method to construct structural defects is significant for designing MnO 2 ‐based catalysts that exhibited superior performance. In this paper, a Ce‐α‐MnO 2 ‐Γ catalyst with … Abstract Modulating the synthesis method to construct structural defects is significant for designing MnO 2 ‐based catalysts that exhibited superior performance. In this paper, a Ce‐α‐MnO 2 ‐Γ catalyst with temperature‐induced phase reconstruction is successfully designed and prepared. During the high‐temperature calcination process, Ce‐α‐MnO 2 ‐Γ underwent a phase transition from Γ‐MnO 2 to α‐MnO 2 . This structural reconstruction created numerous defects, redistributed surface charges, increased the contents of active Mn 3+ and Ce 4+ . The introduction of oxygen vacancies improved the adsorption and reactivation of toluene and gaseous oxygen and sped up the depletion and replacement period of lattice oxygen. Compared with the Ce‐α‐MnO 2 catalyst prepared by ordinary hydrothermal method, Ce‐α‐MnO 2 ‐Γ has better catalytic performance and excellent durability, reaching 90% of toluene conversion at 229 °C. Furthermore, in situ DRIFTS tests illustrated that the toluene oxidation reaction adhered to the MvK mechanism, revealing the essential role of lattice oxygen in Ce‐α‐MnO 2 ‐Γ in the catalytic oxidation of toluene.
Nitrogen oxides (NOx), harmful pollutants primarily from fossil fuel combustion, pose significant environmental and health risks. Among mitigation technologies, NH3-SCR is widely adopted due to its high efficiency and industrial … Nitrogen oxides (NOx), harmful pollutants primarily from fossil fuel combustion, pose significant environmental and health risks. Among mitigation technologies, NH3-SCR is widely adopted due to its high efficiency and industrial viability. MnO2-based catalysts, particularly α-MnO2, have gained attention for low-temperature NH3-SCR owing to their redox properties, low-temperature activity, and environmental compatibility. In this study, α-MnO2 catalysts with tunable oxygen vacancy concentrations were synthesized by varying calcination atmospheres. Compared to α-MnO2-Air, the oxygen vacancy-rich α-MnO2-N2 exhibited stronger acidity, enhanced redox properties, and superior NH3/NO adsorption and activation, achieving 98% NO conversion at 125–250 °C. Oxygen vacancies promoted NH3 adsorption on Lewis/BrĆønsted acid sites, facilitating -NH2 intermediate formation, while enhancing NO oxidation to reactive nitrates. In situ DRIFTS revealed a dual E-R and L-H reaction pathway, with oxygen vacancies crucial for NO activation, intermediate formation, and N2 generation. These findings underscore the importance of oxygen vacancy engineering in optimizing Mn-based SCR catalysts.
The application of discharge plasma in catalyst preparation and modification is reviewed in this paper. Catalysts play a crucial role in various fields, and discharge plasma, with its unique physicochemical … The application of discharge plasma in catalyst preparation and modification is reviewed in this paper. Catalysts play a crucial role in various fields, and discharge plasma, with its unique physicochemical properties and environmental friendliness, shows great potential in the preparation and surface engineering of catalysts. Plasma can effectively activate reactant molecules under mild conditions, thereby enhancing the reaction rate, and regulate the microstructure and active site distribution of the catalysts, thereby improving the performance of specific catalytic reactions. In this paper, different plasma sources and discharge fundamentals are reviewed, mainly emphasising on the application of plasma in catalysts preparation and surface modification. The advantages and applications of plasma-assisted catalyst synthesis, plasma chemical vapor deposition and plasma atomic layer deposition are discussed. The modification effects of plasma on the physical and chemical properties of catalysts are analyzed, and the effects of these modifications on different reaction types and their mechanisms are outlined. Finally, future research directions and challenges are discussed to offer reference for the development of discharge plasma technology in material and catalysis sciences.
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