Oxygen Species Enhanced Catalytic Efficiency of Au1Agx/SiO2 Catalysts for CO Oxidation

A series of Au1Agx alloys (x = 0, 0.2, 0.3, 1.0, and 3.0) supported over SiO2 has been prepared and pretreated via different atmospheric processes. The physical-chemical properties of these materials have been systematically characterized using X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), ultraviolet-visible (UV-vis) spectroscopy, and transmission electron microscopy (TEM). The results reveal that oxygen species are doped into the alloy structure by the oxygen-involved pretreatment, leading to lattice expansion as well as a significant increase in catalytic activity. Improvement in the catalytic activity of Au1Ag0.3/SiO2 through sequential reduction and oxidation pretreatment was evidenced by a decrease in the temperature of 100% CO conversion by approximately 500 K. A volcano trend in catalytic activity is found as the Ag composition is increased in the alloy structure. Density-functional theory (DFT) calculations suggest that the introduced oxygen species are likely present at the subsurface of the AuAg alloy and involved in the reaction or in modifying the electronic structure of surface Ag, thereby enhancing the catalytic activity for CO oxidation.

A General Approach for Metal Nanoparticle Encapsulation Within Porous Oxides

Encapsulation of metal nanoparticles within oxide materials has been shown as an effective strategy to improve activity, selectivity, and stability in several catalytic applications. Several approaches have been proposed to encapsulate nanoparticles, such as forming core-shell structures, growing ordered structures (zeolites or metal-organic frameworks) on nanoparticles, or directly depositing support materials on nanoparticles. Here, a general nanocasting method is demonstrated that can produce diverse encapsulated metal@oxide structures with different compositions (Pt, Pd, Rh) and multiple types of oxides (Al2O3, Al2O3-CeO2, ZrO2, ZnZrOx, In2O3, Mn2O3, TiO2) while controlling the size and dispersion of nanoparticles and the porous structure of the oxide. Metal@polymer structures are first prepared, and then the oxide precursor is infiltrated into such structures and the resulting material is calcined to form the metal@oxide structures. Most Pt@oxides catalysts show similar catalytic activity, demonstrating the availability of surface Pt sites in the encapsulated structures. However, the Pt@Mn2O3 sample showed much higher CO oxidation activity, while also being stable under aging conditions. This work demonstrated a robust nanocasting method to synthesize metal@oxide structures, which can be utilized in catalysis to finely tune metal-oxide interfaces.

Sustainable carbonaceous nanomaterial supported palladium as an efficient ligand-free heterogeneouscatalyst for Suzuki-Miyaura coupling

A novel ligand-free heterogeneous catalyst was synthesized via pyrolysis of Samanea saman pods to produce carbon nanospheres (SS-CNSs), which served as a carbon support for immobilizing palladium nanoparticles through an in situ reduction technique (Pd/SS-CNS). The SS-CNSs effectively integrated 3% of Pd on their surfaces with no additional activation procedures needed. The nanomaterials obtained underwent thorough characterization employing various techniques such as FT-IR, XRD, FE-SEM, TEM, EDS, ICP-AES, and BET. Subsequently, the efficiency of this Pd/SS-CNS catalyst was assessed for the synthesis of biaryl derivatives via Suzuki coupling, wherein different boronic acids were coupled with various aryl halides using an environmentally benign solvent mixture of EtOH/H2O and employing only 0.1 mol% of Pd/SS-CNS. The catalytic system was conveniently recovered through centrifugation and demonstrated reusability without any noticeable decline in catalytic activity. This approach offers economic viability, ecological compatibility, scalability, and has the potential to serve as an alternative to homogeneous catalysis.

Enhancing the Green Synthesis of Glycerol Carbonate: Carboxylation of Glycerol with CO2 Catalyzed by Metal Nanoparticles Encapsulated in Cerium Metal-Organic Frameworks

The reaction of glycerol with CO2 to produce glycerol carbonate was performed successfully in the presence of gold nanoparticles (AuNPs) supported by a metal-organic framework (MOF) constructed from mixed carboxylate (terephthalic acid and 1,3,5-benzenetricarboxylic acid). The most efficient were two AuNPs@MOF catalysts prepared from pre-synthesized MOF impregnated with Au3+ salt and subsequently reduced to AuNPs using H2 (catalyst 4%Au(H2)@MOF1) or reduced with NaBH4 (catalyst 4%Au@PEI-MOF1). Compared to existing catalysts, AuNPs@MOFs require simple preparation and operate under mild and sustainable conditions, i.e., a much lower temperature and the lowest CO2 overpressure ever reported, with MgCO3 having been found to be the optimal dehydrating agent. Although the yield of the process is still not competitive with previously developed systems, the most promising advantage is the highest TOF (78 h-1) ever reported for this reaction. The optimal parameters observed for AuNPs were also tested on AgNPs and CuNPs with promising results, suggesting their great potential for industrial application. The catalysts were characterized by XRD, TEM, SEM-EDS, ICP-MS, XPS, and porosity measurements, confirming that AuNPs are present in low concentration, uniformly distributed, and confined to the cavities of the MOF.

Effect of Ligand Attachment at Ag11 for CO Oxidation: A Computational Investigation

Heterogeneous CO oxidation is a demanding reaction at room temperature due to the high activation energy required to break the O=O bond. While several metal clusters are reported to oxidize CO successfully, they fall short of their selectivity for the reaction and recyclability. In this regard, there is a need for economic catalysts with high catalytic activity, low activation barrier, and reusability. In this study, we have investigated the catalytic activity of the neutral pristine and ligated Ag11 cluster toward CO oxidation. We investigated the attachment effect of three organic donor ligands: trimethylphosphine, triethylphosphine, and N-ethyl pyrrolidone to the Ag11 cluster. Our results show that including donor ligands on the Ag11 cluster surface can significantly reduce the barrier heights for CO oxidation. The minimum barrier heights with the system coordinated with triethylphosphine showed the lowest activation barrier of 1.06 kcal/mol compared to the high activation barrier of 14.77 kcal/mol recorded for the pristine cluster. Exploration of the reaction mechanism and charge analysis showed that the electron donor ligands activate O2 via charge donation, thereby reducing the barrier heights of CO oxidation.

The phenomenon of "dead" metal in heterogeneous catalysis: opportunities for increasing the efficiency of carbon-supported metal catalysts

This review addresses the largely overlooked yet critical issue of "dead" metal in heterogeneous metal catalysts. "Dead" metal refers to the fraction of metal in a catalyst that remains inaccessible to reactants, significantly reducing the overall catalyst performance. As a representative example considered in detail here, this challenge is particularly relevant for carbon-supported metal catalysts, extensively employed in research and industrial settings. We explore key factors contributing to the formation of "dead" metal, including the morphology of the support, metal atom intercalation within the support layers, encapsulation of metal nanoparticles, interference by organic molecules during catalyst preparation, and dynamic behavior under microwave irradiation. Notably, the review outlines a series of strategic approaches to mitigate the occurrence of "dead" metal during catalyst preparation, thus boosting the catalyst efficiency. The knowledge gathered is important for enhancing the preparation of catalysts, especially those containing precious metals. Beyond the practical implications for catalyst design, this study introduces a novel perspective for understanding and optimizing the catalyst performance. The insights are expected to broadly impact different scientific disciplines, empowered with heterogeneous catalysis and driving innovation in energy, environmental science, and materials chemistry, among others. Exploring the "dead" metal phenomenon and potential mitigation strategies brings the field closer to the ultimate goal of high-efficiency, low-cost catalysis.

A mini review on recent progress of steam reforming of ethanol

H2 is one of the promising renewable energy sources, but its production and transportation remain challenging. Distributed H2 production using liquid H2 carriers is one of the ideal ways of H2 utilization. Among common H2 carriers, ethanol is promising as it has high H2 content and can be derived from renewable bio-energy sources such as sucrose, starch compounds, and cellulosic biomass. To generate H2 from ethanol, steam reforming of ethanol (SRE) is the most common way, while appropriate catalysts, usually supported metal catalysts, are indispensable. However, the SRE process is quite complicated and always accompanied by various undesirable by-products, causing low H2 yield. Moreover, the catalysts for SRE are easy to deactivate due to sintering and carbon deposition under high reaction temperatures. In recent years, lots of efforts have been made to reveal SRE mechanisms and synthesize catalysts with high H2 yield and excellent stability. Both active metals and supports play an important role in the reaction. This mini-review summarizes the recent progress of SRE catalysts from the view of the impacts of active metals and supports and draws an outlook for future research directions.

A hollow void catalyst of Co@C(Z-d)@void@CeO2 for enhancing the performance and stability of the Fischer-Tropsch synthesis

To enhance the catalyst performance of Fischer-Tropsch synthesis (FTS), removing the mass-transfer restriction in the catalysis synthesis is essential. Although the core-shell nanostructures can improve the activity and stability of the catalyst, they can restrict the reactants' diffusion towards the active sites and the transfer of the products from these sites in FTS. Creating an adequate porosity between the core and the outer shell of the catalyst structure can tackle this issue. In this work, the synthesized cobalt-based nano-catalyst is encapsulated with two shells and a middle porous shell. The first shell is a carbon shell at the core of the catalyst derived from ZIF-67, the second one is the outer shell of ceria, and the middle porous shell is formed by removing the sacrificial silica shell through the etching technique. The characterization and performance tests represent significant evidence of the etching treatment's impact on the FTS catalyst performance. Besides, molecular dynamics simulation is also utilized to clarify its effect. The FTS catalytic performance is enhanced more than 2 times with the etched catalyst versus the catalyst without it at 17.5 bar and a (H2/CO) ratio of 1.2. In addition, not only does the etched catalyst with high porosity play the role of a nanoreactor and intensify its catalytic performance, but it also has higher stability.

Platinum Nanoparticles Immobilized on Electrospun Membranes for Catalytic Oxidation of Volatile Organic Compounds

Structured catalytic membranes with high porosity and a low pressure drop are particularly suitable for industrial processes carried out at high space velocities. One of these processes is the catalytic total oxidation of volatile organic compounds, which is an economically feasible and environmentally friendly way of emission abatement. Noble metal catalysts are typically preferred due to high activity and stability. In this paper, the preparation of a thermally stable polybenzimidazole electrospun membrane, which can be used as a support for a platinum catalyst applicable in the total oxidation of volatile organic compounds, is reported for the first time. In contrast to commercial pelletized catalysts, high porosity of the membrane allowed for easy accessibility of the platinum active sites to the reactants and the catalytic bed exhibited a low pressure drop. We have shown that the preparation conditions can be tuned in order to obtain catalysts with a desired platinum particle size. In the gas-phase oxidation of ethanol, acetone, and toluene, the catalysts with Pt particle sizes 2.1 nm and 26 nm exhibited a lower catalytic activity than that with a Pt particle size of 12 nm. Catalysts with a Pt particle size of 2.1 nm and 12 nm were prepared by equilibrium adsorption, and the higher catalytic activity of the latter catalyst was ascribed to more reactive adsorbed oxygen species on larger Pt nanoparticles. On the other hand, the catalyst with a Pt particle size of 26 nm was prepared by a solvent evaporation method and contained less active polycrystalline platinum. Last but not least, the catalyst containing only 0.08 wt.% of platinum achieved high conversion (90%) of all the model volatile organic compounds at moderate temperatures (lower than 335 °C), which is important for reducing the costs of the abatement technology.

Structural Evolution of Anatase-Supported Platinum Nanoclusters into a Platinum-Titanium Intermetallic Containing Platinum Single Atoms for Enhanced Catalytic CO Oxidation

Strong metal-support interactions characteristic of the encapsulation of metal particles by oxide overlayers have been widely observed on large metal nanoparticles, but scarcely occur on small nanoclusters (<2 nm) for which the metal-support interactions remain elusive. Herein, we study the structural evolution of Pt nanoclusters (1.5 nm) supported on anatase TiO₂ upon high-temperature H₂ reduction. The Pt nanoclusters start to partially evolve into a CsCl-type PtTi intermetallic compound when the reduction temperature reaches 400 °C. Upon 700 °C reduction, the PtTi nanoparticles are exclusively formed and grow epitaxially along the TiO₂ (101) crystal faces. The thermodynamics of the formation of PtTi via migration of reduced Ti atoms into Pt cluster is unraveled by theoretical calculations. The thermally stable PtTi intermetallic compound, with single-atom Pt isolated by Ti, exhibits enhanced catalytic activity and promoted catalytic durability for CO oxidation.

Multi-Compartmentalized Cellulose Macrobead Catalysts for In Situ Organic Reaction in Aqueous Media

This study reports a promising approach to fabricate bacterial cellulose (BC)-based macrobead catalysts with improved catalytic activities and recyclability for organic reactions in aqueous media. To this end, the consecutive extrusion and gelation of BC precursor fluids is conducted using a combined micronozzle device to compartmentalize the resulting BC macrobeads in a programmed manner. The use of BCs laden with Au and Pd nanoparticles (NPs), and Fe₃ O₄ NPs led to the production of catalytically and magnetically compartmentalized BC macrobeads, respectively. Through the model reduction reaction of 4-nitrophenol to 4-aminophenol using NaBH₄ , it is finally demonstrated that the BC macrobead catalysts not only enhance catalytic activities while exhibiting high reaction yields (>99%) in aqueous media, but also repeatedly retrieve the products with ease in response to the applied magnetic field, enabling the establishment of a useful green catalyst platform.

Nano-architectural design of TiO2 for high performance photocatalytic degradation of organic pollutant: A review

In the past several decades, significant efforts have been paid toward photocatalytic degradation of organic pollutants in environmental research. During the past years, titanium dioxide nano-architectures (TiO2 NAs) have been widely used in water purification applications with photocatalytic degradation processes under Uv/Vis light illumination. Photocatalysis process with nano-architectural design of TiO2 is viewed as an efficient procedure for directly channeling solar energy into water treatment reactions. The considerable band-gap values and the subsequent short life time of photo-generated charge carriers are showed among the limitations of this approach. One of these effective efforts is the using of oxidation processes with advance semiconductor photocatalyst NAs for degradation the organic pollutants under UV/Vis irradiation. Among them, nano-architectural design of TiO2 photocatalyst (such as Janus, yolk-shell (Y@S), hollow microspheres (HMSs) and nano-belt) is an effective way to improve oxidation processes for increasing photocatalytic activity in water treatment applications. In the light of the above issues, this study tends to provide a critical overview of the used strategies for preparing TiO2 photocatalysts with desirable physicochemical properties like enhanced absorption of light, low density, high surface area, photo-stability, and charge-carrier behavior. Among the various nanoarchitectural design of TiO2, the Y@S and HMSs have created a great appeal given their considerable large surface area, low density, homogeneous catalytic environment, favorable light harvesting properties, and enhanced molecular diffusion kinetics of the particles. In this review was summarized the developments that have been made for nano-architectural design of TiO2 photocatalyst. Additional focus is placed on the realization of interfacial charge and the possibility of achieving charge carriers separation for these NAs as electron migration is the extremely important factor for increasing the photocatalytic activity.

The preparation of ultrastable Al3+ doped CeO2 supported Au catalysts: Strong metal-support interaction for superior catalytic activity towards CO oxidation

The classical strong metal-support interaction (SMSI) plays a key role in improving thermal stability for supported Au catalysts. However, it always decreases the catalytic activity because of the encapsulation of Au species by support. Herein, we demonstrate that Al³⁺ is a functional additive which could effectively improve both catalytic activity and sintering resistant property for H₂ pretreated Al³⁺ doped CeO₂ supported Au (AuCeAl) catalyst at high temperature. The physical characterization and in-situ DRIFTS results provide insight that more oxygen vacancies generated by Al³⁺ doping could be as preferential adsorption sites for CO molecules when the encapsulation of Au species occurred, which is certificated by an accelerated formation of bicarbonate species. In the meantime, smaller Au nanoparticles with higher dispersion (2.8 nm, 85.63%) is achieved in AuCeAl catalysts, compared with that in CeO₂ supported Au (AuCe) catalysts (5.1 nm, 36.17%). Additionally, the as-prepared AuCeAl catalysts also have superior catalytic performance even after calcination at 800 °C in air.

Solid-State Reaction Synthesis of Nanoscale Materials: Strategies and Applications

Nanomaterials (NMs) with unique structures and compositions can give rise to exotic physicochemical properties and applications. Despite the advancement in solution-based methods, scalable access to a wide range of crystal phases and intricate compositions is still challenging. Solid-state reaction (SSR) syntheses have high potential owing to their flexibility toward multielemental phases under feasibly high temperatures and solvent-free conditions as well as their scalability and simplicity. Controlling the nanoscale features through SSRs demands a strategic nanospace-confinement approach due to the risk of heat-induced reshaping and sintering. Here, we describe advanced SSR strategies for NM synthesis, focusing on mechanistic insights, novel nanoscale phenomena, and underlying principles using a series of examples under different categories. After introducing the history of classical SSRs, key theories, and definitions central to the topic, we categorize various modern SSR strategies based on the surrounding solid-state media used for nanostructure growth, conversion, and migration under nanospace or dimensional confinement. This comprehensive review will advance the quest for new materials design, synthesis, and applications.

Visualization of the Final Stage of Sintering in Nanoceramics with Atomic Resolution

The deep understanding of the sintering mechanism is pivotal to optimizing denser ceramics production. Although several models explain the sintering satisfactorily on the micrometric scale, the extrapolation for nanostructured systems is not trivial. Aiming to provide additional information about the particularities of the sintering at the nanoscale, we performed in situ experiments using high-resolution transmission electron microscopy (HRTEM). We studied the pore elimination process in a ZrO₂ thin film and identified a high anisotropic pore elimination. Interestingly, there is a redistribution of the atoms from the rough surface in the solid-gas surface, followed by the atom attachment in a faceted surface. Finally, we found evidence of the pore acting as a pin, reducing the GB mobility. These findings certainly can contribute to enhance the kinetic models to describe the densification process of systems at the nanoscale.

Dilute Alloys Based on Au, Ag, or Cu for Efficient Catalysis: From Synthesis to Active Sites

The development of new catalyst materials for energy-efficient chemical synthesis is critical as over 80% of industrial processes rely on catalysts, with many of the most energy-intensive processes specifically using heterogeneous catalysis. Catalytic performance is a complex interplay of phenomena involving temperature, pressure, gas composition, surface composition, and structure over multiple length and time scales. In response to this complexity, the integrated approach to heterogeneous dilute alloy catalysis reviewed here brings together materials synthesis, mechanistic surface chemistry, reaction kinetics, in situ and operando characterization, and theoretical calculations in a coordinated effort to develop design principles to predict and improve catalytic selectivity. Dilute alloy catalysts─in which isolated atoms or small ensembles of the minority metal on the host metal lead to enhanced reactivity while retaining selectivity─are particularly promising as selective catalysts. Several dilute alloy materials using Au, Ag, and Cu as the majority host element, including more recently introduced support-free nanoporous metals and oxide-supported nanoparticle "raspberry colloid templated (RCT)" materials, are reviewed for selective oxidation and hydrogenation reactions. Progress in understanding how such dilute alloy catalysts can be used to enhance selectivity of key synthetic reactions is reviewed, including quantitative scaling from model studies to catalytic conditions. The dynamic evolution of catalyst structure and composition studied in surface science and catalytic conditions and their relationship to catalytic function are also discussed, followed by advanced characterization and theoretical modeling that have been developed to determine the distribution of minority metal atoms at or near the surface. The integrated approach demonstrates the success of bridging the divide between fundamental knowledge and design of catalytic processes in complex catalytic systems, which can accelerate the development of new and efficient catalytic processes.

Tailoring Single-Atom Platinum for Selective and Stable Catalysts in Propane Dehydrogenation

Propane dehydrogenation has been a promising method for producing propylene that has the potentials to meet the increasing global demand for propylene. However, owing to the restricted equilibrium conversion caused by the high endothermicity, even the Pt-based catalysts, which exhibit high activity and selectivity, severely suffer significantly from coke formation and/or nanoparticle sintering at realistic reaction temperatures, resulting in a short catalyst lifetime. As a result, few innovative catalysts in terms of catalytic activity, selectivity, and stability, have been produced. In this Review, we focus on the characteristics of single-atom-like Pt sites for PDH and attempt to provide suggestions for developing highly efficient catalysts. First, we briefly describe the fundamental strategies. Following that, the remarkable catalysis is addressed by three different distinct sorts of state-of-the-art single-atom-like Pt catalysts are discussed. Additionally, we present other promising catalyst design approaches that are not based on single-atom-like Pt catalysts, as well as future research challenges in this field.

Ionic liquid and lysine co-assisted synthesis of the highly dispersed Ni/SAPO-11 catalyst

The synthesis of highly-dispersed non-noble based catalysts and its application on hydrogenation /dehydrogenation still remains challenging. Therefore, it is of great importance to protect metal from aggregation in both calcination...

Direct electrochemistry of silver nanoparticles-decorated metal-organic frameworks for telomerase activity sensing via allosteric activation of an aptamer hairpin

A direct electrochemistry of silver nanoparticles (AgNPs)-anchored metal-organic frameworks (MOFs) is developed for detection of telomerase activity based on allosteric activation of an aptamer hairpin. AgNPs in situ decorated on PCN-224 (AgNPs/PCN-224) constituted the direct electrochemical labels that were further biofunctionalized by recognition moiety of streptavidin (SA). To achieve the target biosensing, an allosteric hairpin-structured DNA was elaborately designed for signal transduction. The presence of telomerase elongated its primer in the hairpin to displace partial stem strand, thus resulted in the formation of SA aptamer-open structure. Through the specific interaction with aptamer, SA-biofunctionalized AgNPs/PCN-224 probe was attached onto the electrode surface, generating electrochemical signal at + 0.072 V of AgNPs centralized by MOF structure. The direct electrochemical biosensor showed target activity-dependent response from 1.0 × 10^-7 to 1.0 × 10^-1 IU L^-1 with a detection limit of 5.4 × 10^-8 IU L^-1. Moreover, the sensor was applied in evaluation of telomerase activity in living cancer cells. The established electrochemical detection approach in this work avoids the critical deoxygenation conditions and additional electrocatalytic reagents, which opens a novel biosensing perspective for direct electrochemistry of MOF-based nanocomposites.

CoNi Nanoparticles Supported on N-Doped Bifunctional Hollow Carbon Composites as High-Performance ORR/OER Catalysts for Rechargeable Zn-Air Batteries

Searching for high-quality air electrode catalysts is the long-term goal for the practical application of Zn-air batteries. Here, a series of coexistent composite materials (CoNi/NHCS-TUC-x) of cobalt-nickel supported on nitrogen-doped hollow spherical carbon and tubular carbon are obtained using a simple pyrolysis strategy. Co and Ni in the composites are mainly present in the form of alloy nanoparticles, M-N_x and M-C_x (M = Co or Ni) species, with high oxygen reduction reaction (ORR)/oxygen evolution reaction (OER) electroactivity. The materials containing different proportions of spherical carbon and tubular carbon obtained by simply adjusting the raw materials for generating tubular carbon exhibit interesting bifunctional performance: samples with an abundant tubular content have the highest ORR onset potential (0.91 V vs reversible hydrogen electrode), while those with a rich spherical content have the highest ORR current density (5.13 mA·cm^-2). Furthermore, CoNi/NHCS-TUC-3 provides the lowest potential difference (ΔE = E_j=10 - E_1/2) of 0.806 V. We then test the potential possibility of CoNi/NHCS-TUC-3 as an air electrode for primary and rechargeable Zn-air batteries. The primary battery delivers an open-circuit potential of 1.59 V, a peak power density of 361.8 mA·cm^-2, and a specific capacity of 756.5 mA h·g_Zn^-1. The rechargeable battery could be cycled stably for more than 55 h at 10 mA·cm^-2. These characteristics make CoNi/NHCS-TUC-3 a superior electrocatalyst for both the ORR and OER, as well as a suitable bifunctional electrode applied to a rechargeable Zn-air battery.

A Perspective on Modelling Metallic Magnetic Nanoparticles in Biomedicine: From Monometals to Nanoalloys and Ligand-Protected Particles

The focus of this review is on the physical and magnetic properties that are related to the efficiency of monometallic magnetic nanoparticles used in biomedical applications, such as magnetic resonance imaging (MRI) or magnetic nanoparticle hyperthermia, and how to model these by theoretical methods, where the discussion is based on the example of cobalt nanoparticles. Different simulation systems (cluster, extended slab, and nanoparticle models) are critically appraised for their efficacy in the determination of reactivity, magnetic behaviour, and ligand-induced modifications of relevant properties. Simulations of the effects of nanoscale alloying with other metallic phases are also briefly reviewed.

Thermal Stability of Ru–Re NPs in H2 and O2 Atmosphere and Their Activity in VOCs Oxidation: Effect of Ru Precursor

The thermal stability of Ru–Re NPs on γ-alumina support was studied in hydrogen at 800 °C and in air at 250–400 °C. The catalysts were synthesized using Cl-free and Cl-containing Ru precursors and NH4ReO4. Very high sintering resistance of Ru–Re NPs was found in hydrogen atmosphere and independent of Ru precursors and Re loading, the size of them was below 2–3 nm. In air, metal segregation occurred at 250 °C, leading to formation of RuO2 and highly dispersed ReOx species. Ruthenium agglomeration was hindered at higher Re loading and in presence of residual Cl species. Propane oxidation rate was higher with the Ru(N)–Re catalysts than with Ru(N) and that containing Cl species. The Ru(N)–Re (3:1) catalyst exhibited the highest activity and the lowest activation energy (91.6 kJ mol−1) what is in contrast to Ru(Cl)–Re (3:1) which had the lowest activity and the highest activation energy (119.3 kJ mol−1). Thus, the synergy effect was not observed in Cl-containing catalysts.

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Prospects and Applications of Palladium Nanoparticles in the Cross-coupling of (hetero)aryl Halides and Related Analogues

Discovering efficient methods for the formation of carbon-carbon bonds is a central ongoing theme in organic synthesis. Cross-coupling reactions catalysed by metal nanoparticles are attractive alternatives to the traditional use of metal counterparts due to the catalytic tunability, selectivity, recyclability and reusability of the nanoparticles. The ongoing search for sustainable processes demands that reusable and environmentally benign catalysts are used. While the advantages of nanoparticles catalysts over bulk catalysts cannot be overemphasised, the problem of sintering, agglomeration and leaching are drawbacks to their full industrial applications. Hence, efforts are being made towards advancing the efficiency of the catalytic nanoparticle systems over the years. This review presents the progress, the challenges and the prospects of palladium nanoparticle with focus on Heck, Suzuki, Hiyama and Sonogashira cross-coupling reactions involving (hetero) aryl halides and the analogues.

Dextran mediated MnFe2O4/ZnS magnetic fluorescence nanocomposites for controlled self-heating properties

Dextran mediated MnFe2O4/ZnS opto-magnetic nanocomposites with different concentrations of ZnS were competently synthesized adopting the co-precipitation method. The structural, morphological, magnetic, and optical properties of the nanocomposites were exhaustively characterized by XRD, HRTEM, FTIR, VSM techniques, and PL spectroscopy. XRD spectra demonstrate the existence of the cubic spinel phase of MnFe2O4 and the cubic zinc blend phase of ZnS in the nanocomposites. HRTEM images show the average crystallite size ranges of 15-21 nm for MnFe2O4 and 14-45 nm for ZnS. Investigation of the FTIR spectra reveals the incorporation of ZnS nanoparticles on the surface of MnFe2O4 nanoparticles by dint of biocompatible surfactant dextran. The nanocomposites exhibit both magnetic and photoluminescence properties. Photoluminescence analysis confirmed the redshift of the emission peaks owing to the trap states in the ZnS nanocrystals. The room temperature VSM analysis shows that the saturation magnetization and coercivity of MnFe2O4 nanoparticles initially increase then decrease with the increasing concentration of ZnS in the nanocomposite. The induction heating analysis shows that the presence of dextran enhances the self heating properties of the MnFe2O4/ZnS nanocomposites which can also be controlled by tailoring the concentration of the ZnS nanoparticles. These suggest that MnFe2O4/Dex/ZnS is a decent candidate for hyperthermia applications.

Localization model description of the interfacial dynamics of crystalline Cu and Cu 64 Zr 36 metallic glass nanoparticles

Many of the special properties of nanoparticles (NPs) and nanomaterials broadly derive from the significant fraction of particles (atoms, molecules or segments of polymeric molecules) in the NP interfacial region in which the interparticle interactions are characteristically highly anharmonic in comparison to the bulk material. This leads to relatively large mean square particle displacements relative to the material interior, often resulting in a strong increase interfacial mobility and reactivity in both crystalline and glass NPs. The 'Debye-Waller factor', or the mean square particle displacement< u 2 > on a ps 'caging' timescale relative to the square of the average interparticle distanceσ 2 , provides an often experimentally accessible measure of the strength of this anharmonic interaction. The Localization Model (LM) of the dynamics of condensed materials relates this thermodynamic property to the structural relaxation timeτ α , determined from the intermediate scattering function, without any free parameters. Moreover, the LM allows for the prediction of the diffusion coefficient D when combined with the 'decoupling' or Fractional Stokes-Einstein relation linkingτ α to D. In the current study, we employed classical molecular dynamics simulation to investigate the structural relaxation and diffusion of modelCu 64 Zr 36 metallic glass and Cu crystalline NPs with different sizes. As with previous studies validating the LM on model bulk and crystalline materials, and for the interfacial dynamics of thin crystalline and metallic glass films, we find the LM model also describes the interfacial dynamics of model crystalline metal (Cu) and metallic glass (Cu 64 Zr 36 ) NPs to a good approximation, further confirming the generality of the model.

Ru-containing magnetic yolk-shell structured nanocomposite: a powerful, recoverable and highly durable nanocatalyst

A novel method was used to prepare a magnetic phenylene-based periodic mesoporous organosilica nanocomposite with yolk-shell structure (Fe3O4@YSPMO). The Fe3O4@YSPMO nanomaterial was prepared by using easily accessible pluronic-P123 and cetyltrimethylammonium bromide (CTAB) surfactants under basic conditions. This material was employed for effective immobilization of potassium perruthenate to prepare an Fe3O4@YSPMO@Ru nanocatalyst for the aerobic oxidation of alcohols. The physiochemical properties of the designed Fe3O4@YSPMO@Ru nanocomposite were studied using PXRD, FT-IR, TGA, SEM, TEM, ICP, VSM and XPS analyses. Fe3O4@YSPMO@Ru was effectively employed as a highly recoverable nanocatalyst in the selective aerobic oxidation of alcohols.

Effects of Hydrothermal Aging on CO and NO Oxidation Activity over Monometallic and Bimetallic Pt-Pd Catalysts

By combining scanning transmission electron microscopy, CO chemisorption, and energy dispersive X-ray spectroscopy with CO and NO oxidation light-off measurements we investigated deactivation phenomena of Pt/Al2O3, Pd/Al2O3, and Pt-Pd/Al2O3 model diesel oxidation catalysts during stepwise hydrothermal aging. Aging induces significant particle sintering that results in a decline of the catalytic activity for all catalyst formulations. While the initial aging step caused the most pronounced deactivation and sintering due to Ostwald ripening, the deactivation rates decline during further aging and the catalyst stabilizes at a low level of activity. Most importantly, we observed pronounced morphological changes for the bimetallic catalyst sample: hydrothermal aging at 750 °C causes a stepwise transformation of the Pt-Pd alloy via core-shell structures into inhomogeneous agglomerates of palladium and platinum. Our study shines a light on the aging behavior of noble metal catalysts under industrially relevant conditions and particularly underscores the highly complex transformation of bimetallic Pt-Pd diesel oxidation catalysts during hydrothermal treatment.

High energy surface x-ray diffraction applied to model catalyst surfaces at work

Catalysts are materials that accelerate the rate of a desired chemical reaction. As such, they constitute an integral part in many applications ranging from the production of fine chemicals in chemical industry to exhaust gas treatment in vehicles. Accordingly, it is of utmost economic interest to improve catalyst efficiency and performance, which requires an understanding of the interplay between the catalyst structure, the gas phase and the catalytic activity under realistic reaction conditions at ambient pressures and elevated temperatures. In recent years efforts have been made to increasingly develop techniques that allow for investigating model catalyst samples under conditions closer to those of real technical catalysts. One of these techniques is high energy surface x-ray diffraction (HESXRD), which uses x-rays with photon energies typically in the range of 70-80 keV. HESXRD allows a fast data collection of three dimensional reciprocal space for the structure determination of model catalyst samples under operando conditions and has since been used for the investigation of an increasing number of different model catalysts. In this article we will review general considerations of HESXRD including its working principle for different model catalyst samples and the experimental equipment required. An overview over HESXRD investigations performed in recent years will be given, and the advantages of HESXRD with respect to its application to different model catalyst samples will be presented. Moreover, the combination of HESXRD with other operando techniques such as in situ mass spectrometry, planar laser-induced fluorescence and surface optical reflectance will be discussed. The article will close with an outlook on future perspectives and applications of HESXRD.

Photosynthesis of a Photocatalyst: Single Atom Platinum Captured and Stabilized by an Iron(III) Engineered Defect

Single atom (SA), noble metal catalysts are of interest due to high projected catalytic activity while minimizing cost. Common issues facing many synthesis methodologies include complicated processes, low yields of SA product, and production of mixtures of SA and nanoparticles (NPs). Herein we report a simple, room-temperature synthesis of single Pt-atom decorated, anatase Fe-doped TiO₂ particles that leverages the Fe dopant as an engineered defect site to photodeposit and stabilize atomically dispersed Pt. Both particle morphology and Fe dopant location are based on thermodynamic principles (Gibbs-Wulff construction). CO-DRIFTS (diffuse reflectance infrared Fourier transform spectroscopy) reveals absence of bridge-bonded CO signal, confirming atomically dispersed Pt. XAS (X-ray absorption spectroscopy) of both Pt and Fe indicates Fe-O-Pt bonding that persists through catalytic cycling. Mass balance indicates that the Pt loading on single particles is 2.5 wt % Pt; the single Pt-atom decorated nanoparticle yield is 17%. Pt-containing particles show more than an order-of-magnitude increased photooxidation efficiency relative to particles containing only Fe. High single-atom-Pt yield, ease of synthesis, and high catalytic activity demonstrate the utility and promise of this method. The principles of this photodeposition synthesis allow for its generalizability toward other SA metals of catalytic interest.

Palladium supported on structurally stable phenanthroline-based polymer nanotubes as a high-performance catalyst for the aqueous Suzuki–Miyaura coupling reaction

One-dimensional Pd-supported catalyst exhibits excellent catalytic activity since its TOF value is 3077 h⁻¹ for the Suzuki–Miyaura coupling reaction of bromobenzene and phenylboronic acid under ambient conditions.

Spray-Dried Ni Catalysts with Tailored Properties for CO2 Methanation

A catalyst production method that enables the independent tailoring of the structural properties of the catalyst, such as pore size, metal particle size, metal loading or surface area, allows to increase the efficiency of a catalytic process. Such tailoring can help to make the valorization of CO2 into synthetic fuels on Ni catalysts competitive to conventional fossil fuel production. In this work, a new spray-drying method was used to produce Ni catalysts supported on SiO2 and Al2O3 nanoparticles with tunable properties. The influence of the primary particle size of the support, different metal loadings, and heat treatments were applied to investigate the potential to tailor the properties of catalysts. The catalysts were examined with physical and chemical characterization methods, including X-ray diffraction, temperature-programmed reduction, and chemisorption. A temperature-scanning technique was applied to screen the catalysts for CO2 methanation. With the spray-drying method presented here, well-organized porous spherical nanoparticles of highly dispersed NiO nanoparticles supported on silica with tunable properties were produced and characterized. Moreover, the pore size, metal particle size, and metal loading can be controlled independently, which allows to produce catalyst particles with the desired properties. Ni/SiO2 catalysts with surface areas of up to 40 m2 g−1 with Ni crystals in the range of 4 nm were produced, which exhibited a high activity for the CO2 methanation.

The Origin of Au/Ce1-xZrxO2 Catalyst’s Active Sites in Low-Temperature CO Oxidation

Gold catalysts have found applications in many reactions of both industrial and environmental importance. Great interest has been paid to the development of new processes that reduce energy consumption and minimize pollution. Among these reactions, the catalytic oxidation of carbon monoxide (CO) is an important one, considering that a high concentration of CO in the atmosphere creates serious health and environmental problems. This paper examines the most important achievements and conclusions arising from the own authorship contributions concerning (2 wt. % Au)/Ce1−xZrxO2 catalyst’s active sites in low-temperature CO oxidation. The main findings of the present review are: (1) The effect of preparing conditions on Au crystallite size, highlighting some of the fundamental underpinnings of gold catalysis: the Au surface composition and the poisoning effect of residual chloride on the catalytic activity of (2 wt. % Au)/Ce1−xZrxO2 catalysts in CO oxidation; (2) The identification of ion clusters related to gold and their effect on catalyst’ surface composition; (3) The importance of physicochemical properties of oxide support (e.g., its particle size, oxygen mobility at low temperature and redox properties) in the creation of catalytic performance of Au catalysts; (4) The importance of oxygen vacancies, on the support surface, as the centers for oxygen molecule activation in CO reaction; (5) The role of moisture (200–1000 ppm) in the generation of enhanced CO conversion; (6) The Au-assisted Mars-van Krevelen (MvK) adsorption–reaction model was pertinent to describe CO oxidation mechanism. The principal role of Au in CO oxidation over (2 wt. % Au)/Ce1−xZrxO2 catalysts was related to the promotion in the transformation process of reversibly adsorbed or inactive surface oxygen into irreversibly adsorbed active species; (7) Combination of metallic gold (Au0) and Au-OH species was proposed as active sites for CO adsorption. These findings can help in the optimization of Au-containing catalysts.

Stable and Catalytically Active Shape-Engineered Cerium Oxide Nanorods by Controlled Doping of Aluminum Cations

Shape-engineered nanocrystals (SENs) promise a better selectivity and a higher activity in catalytic reactions than the corresponding non-shape-engineered ones because of their larger specific surface areas and desirable crystal facets. However, often, it is challenging to apply SENs in practical catalytic applications at high reaction temperatures, where SENs deforms into more stable, less active nanoparticles. In this paper, we show that atomic layer deposition (ALD) of Al₂O₃ at 200 °C can controllably dope Al cations into the shape-engineered CeO₂ nanorods (NRs) to not only increase their shape transition temperature from 400 °C to beyond 700 °C but also greatly increase their specific reversible oxygen storage capacity (srOSC). The substituted Al³⁺ ions impede the surface diffusion of Ce ions and therefore improve the thermal stability of CeO₂ NRs. These Al³⁺ dopants form -Al-O-Ce-O- clusters, which are new Ce species and can be reversibly reduced and oxidized at 500-700 °C. This low-temperature chemical doping method decouples the synthesis process of SENs from the doping process and maintains the shape of the SENs during the activation of dopants. This concept could be adopted to enable the applications of other SENs in challenging high-temperature environments.

A sinter-resistant catalytic system based on ultra-small Ni-Cu nanoparticles encapsulated in Ca-SiO2 for high-performance ethanol steam reforming

To enhance the catalytic performance of catalysts for the ethanol steam reforming (ESR) reaction, a facile reverse micelle strategy was adopted to prepare a core@shell Ni-Cu@Ca-SiO2 (Ni-Cu@CS) nanoreactor composed of an ultra-small Ni-Cu alloy (∼2.8 nm) encapsulated in Ca-functionalized SiO2 nanoparticles. Benefiting from its core@shell structural features and unique components, the Ni-Cu@CS nanoreactor exhibited superior activity (69.91% H2 selectivity and 99.99% ethanol conversion) and stability compared to reference samples. The regenerated Ni-Cu@CS nanoreactor showed high stability, maintaining 98.14% ethanol conversion and only 1.98 mg gcat-1 h-1 in carbon deposition. The high catalytic performance of Ni-Cu@CS is attributed to not only its encapsulated structure, which effectively prevented the sintering of neighboring Ni-Cu alloy nanoparticles, but also to its Ca-functionalized porous SiO2 shell, suppressing the carbon deposition. Moreover, its porous thin shell facilitated the mass transfer and diffusion of reactants and products. Thus, the Ni-Cu@CS nanoreactor is expected to become a new type of high-efficiency nanoreactor for the ESR reaction.