Novel synthesis of Fe2O3–Pt ellipsoids coated by double‐shelled La2O3 as a catalyst for the reduction of 4‐nitrophenol

A facile strategy is reported for the fabrication of Pt‐loaded core–shell nanocomposite ellipsoids (Fe₂O₃‐Pt@DSL) consisting of ellipsoidal Fe₂O₃ cores, double‐layered La₂O₃ shells and deposited Pt nanoparticles (NPs). The formation of the doubled‐shelled structure uses Fe₂O₃‐Pt@mSiO₂ as template sacrificial agent and it involves the re‐deposition of silica and self‐assembly of metal oxide units. The preparation methods of double‐shelled metal oxides avoid repeated coating and etching and could be utilized to fabricate other shaped double‐shelled composites. Characterization results indicated that the Fe₂O₃‐Pt@DSL nanocomposites possessed mesoporous structure and tunable shell thickness. Moreover, due to the formation of Fe₂O₃ and La₂O₃ composites, Pt NPs can also be stabilized via deposition on chemically active oxides with a synergistic effect. Therefore, as a catalyst for the reduction of 4‐nitrophenol, Fe₂O₃‐Pt@DSL showed superior catalytic activity and reusability due to structural superiority and enhanced composite synergy. Finally, well‐dispersed Pt NPs were encapsulated into the void between the shell layers to construct the Fe₂O₃‐Pt@DSL‐Pt catalyst.     

Fabrication and characterization of double‐shelled CeO2‐La2O3/Au/Fe3O4 hollow architecture as a recyclable and highly thermal stability nanocatalyst

A novel magnetic binary‐metal‐oxide‐coated nanocataly composing of a hollow Fe₃O₄ core and CeO₂‐La₂O₃ shells with Au nanoparticles encapsulated has been created in this work. The structural features of catalysts were characterized by several techniques, including SEM, TEM, UV‐vis, FTIR, XRD, XPS and TGA analyses. After the coating of CeO₂‐La₂O₃ layer, CeO₂‐La₂O₃/Au/C/Fe₃O₄ microspheres showed a superior thermal stability and catalytic reactivity compared with a pure CeO₂ or La₂O₃ layer. Accompanied by the burning of carbon layer, the specific surface could be increased by the formation of double‐shelled structure. Besides, the desired samples could be separated by magnet, implying the superior recycle performance. Using the reduction of 4‐nitrophenol by NaBH₄ as a model reaction, the microspheres exhibited highly reusability, superior catalytic activity, thermal stability, which are attributed to the unique double‐shelled structure of the support, uniform distribution of Au nanoparticles, the highly thermal stability of CeO₂‐La₂O₃ layer and mixed oxide synergistic effect. As a consequence, the unique nanocatalyst will open a promising way in the fabrication of the double‐shelled hollow binary‐metal‐oxide materials for future research and has great potential in other applications.     

Pt/oxide nanocatalysts synthesized via the ultrasonic spray pyrolysis process: engineering metal–oxide interfaces for enhanced catalytic activity

We show that Pt nanoparticles synthesized on oxide nanocatalysts exhibit catalytic activity enhancement depending on the type of the oxide support. To synthesize the Pt/oxide nanocatalysts, we employed a versatile synthesis method using Pt nanoparticles (NPs) supported on various metal oxides (i.e., SiO₂, CeO₂, Al₂O₃, and FeAl₂O₄) utilizing ultrasonic spray pyrolysis. Catalytic CO oxidation was carried out on these catalysts, and it was found that the catalytic activity of the Pt NPs varied depending on the supporting oxide. While Pt/CeO₂ exhibited the highest metal dispersion and active surface area, Pt/FeAl₂O₄ exhibited the lowest active surface area. Among the Pt/oxide nanocatalysts, Pt NPs supported on CeO₂ showed the highest catalytic activity. We ascribe the enhancement in turnover frequency of the Pt/CeO₂ nanocatalysts to strong metal–support interactions due to charge transport between the metal catalysts and the oxide support. Such Pt/oxide nanocatalysts synthesized via spray pyrolysis offer potential possibilities for large-scale synthesis of tailored catalytic systems for technologically relevant applications.     

General Synthesis of Multi‐Shelled Mixed Metal Oxide Hollow Spheres with Superior Lithium Storage Properties

Complex hollow structures of transition metal oxides, especially mixed metal oxides, could be promising for different applications such as lithium ion batteries. However, it remains a great challenge to fabricate well‐defined hollow spheres with multiple shells for mixed transition metal oxides. Herein, we have developed a new “penetration–solidification–annealing” strategy which can realize the synthesis of various mixed metal oxide multi‐shelled hollow spheres. Importantly, it is found that multi‐shelled hollow spheres possess impressive lithium storage properties with both high specific capacity and excellent cycling stability. Specifically, the carbon‐coated CoMn₂O₄ triple‐shelled hollow spheres exhibit a specific capacity of 726.7 mA h g^?1 and a nearly 100 % capacity retention after 200 cycles. The present general strategy could represent a milestone in design and synthesis of mixed metal oxide complex hollow spheres and their promising uses in different areas.     

Metallosurfactant Ionogels in Imidazolium and Protic Ionic Liquids as Precursors To Synthesize Nanoceria as Catalase Mimetics for the Catalytic Decomposition of H2O2

The gelation behavior of cationic surfactants with different counterions, Br^?, [FeCl₃Br]^?, and [CeCl₃Br]^?, in imidazolium ionic liquids (ILs) and protic ethylammonium nitrate was investigated. Small‐angle X‐ray scattering measurements and freeze‐fracture transmission electron microscopy observations revealed the lamellar phases of metallosurfactant ionogels. The characteristics of imidazolium ILs, including the size and type, have effects on metallosurfactant ionogel properties, such as transformation temperatures, interlayer spacing, and mechanical strength. Cubic fluorite structured cerium oxide nanoparticles (CeO₂ NPs) were produced by using metallosurfactant ionogels as precursors. Cubic fluorite CeO₂ exhibited good catalase mimetic activity toward H₂O₂ to generate O₂, providing more multiple mimetic enzyme activities of CeO₂ NPs for H₂O₂.     

A Facile Process for the Preparation of Three‐Dimensional Hollow Zn(OH)2 Nanoflowers at Room Temperature

A facile strategy has been developed to synthesize double‐shelled Zn(OH)₂ nanoflowers (DNFs) at room temperature. The nanoflowers were generated via conversion of Cu₂O nanoparticles (NPs) using ZnCl₂ and Na₂S₂O₃ by a simple process. Outward diffusion of the Cu²⁺, produced by an oxidation process on the surface of NPs, and the inward diffusion of Zn²⁺ by coordination and migration, eventually lead to a hollow cavity in the inner NPs with a double‐shelled 3D hollow flower shapes. The thickness of the inner and outer shells is estimated to be about 20 nm, and the thickness of nanopetals is about 7 nm. The nanoflowers have large surface areas and excellent adsorption properties. As a proof of potential applications, the DNFs exhibited an excellent ability to remove organic molecules from aqueous solutions.     

Oxide‐Nanotrap‐Anchored Platinum Nanoparticles with High Activity and Sintering Resistance by Area‐Selective Atomic Layer Deposition

An area‐selective atomic layer deposition (AS‐ALD) method is described to construct oxide nanotraps to anchor Pt nanoparticles (NPs) on Al₂O₃ supports. The as‐synthesized catalysts have exhibited outstanding room‐temperature CO oxidation activity, with a significantly lowered apparent activation energy (ca. 22.17 kJ mol⁻¹) that is half that of pure Pt catalyst with the same loading. Furthermore, the structure shows excellent sintering resistance with the high catalytic activity retention up to 600 °C calcination. The key feature of the oxide nanotraps lies in its ability to anchor Pt NPs via strong metal–oxide interactions while still leaving active metal facets exposed. Our reported method for forming such oxide structure with nanotraps shows great potential for the simultaneous enhancement of thermal stability and activity of precious metal NPs.     

Delivery of Highly Active Noble‐Metal Nanoparticles into Microspherical Supports by an Aerosol‐Spray Method

Noble metal nanoparticles (NPs) with 1–5 nm diameter obtained from NaHB₄ reduction possess high catalytic activity. However, they are rarely used directly. This work presents a facile, versatile, and efficient aerosol‐spray approach to deliver noble‐metal NPs into metal oxide supports, while maintaining the size of the NPs and the ability to easily adjust the loading amount. In comparison with the conventional spray approach, the size of the loaded noble‐metal nanoparticles can be significantly decreased. An investigation of the 4‐nitrophenol hydrogenation reaction catalyzed by these materials suggests that the NPs/oxides catalysts have high activity and good endurance. For 1 % Au/CeO₂ and Pd/Al₂O₃ catalysts, the rate constants reach 2.03 and 1.46 min^?1, which is much higher than many other reports with the same noble‐metal loading scale. Besides, the thermal stability of catalysts can be significantly enhanced by modifying the supports. Therefore, this work contributes an efficient method as well as some guidance on how to produce highly active and stable supported noble‐metal catalysts.     

Tuning the High‐Temperature Wetting Behavior of Metals toward Ultrafine Nanoparticles

The interaction between metal nanoparticles (NPs) and their substrate plays a critical role in determining the particle morphology, distribution, and properties. The pronounced impact of a thin oxide coating on the dispersion of metal NPs on a carbon substrate is presented. Al₂O₃‐supported Pt NPs are compared to the direct synthesis of Pt NPs on bare carbon surfaces. Pt NPs with an average size of about 2 nm and a size distribution ranging between 0.5 nm and 4.0 nm are synthesized on the Al₂O₃ coated carbon nanofiber, a significant improvement compared to those directly synthesized on a bare carbon surface. First‐principles modeling verifies the stronger adsorption of Pt clusters on Al₂O₃ than on carbon, which attributes the formation of ultrafine Pt NPs. This strategy paves the way towards the rational design of NPs with enhanced dispersion and controlled particle size, which are promising in energy storage and electrocatalysis.     

Ultrafine Molybdenum Carbide Nanoparticles Composited with Carbon as a Highly Active Hydrogen‐Evolution Electrocatalyst

The replacement of platinum with non‐precious‐metal electrocatalysts with high efficiency and superior stability for the hydrogen‐evolution reaction (HER) remains a great challenge. Herein, we report the one‐step synthesis of uniform, ultrafine molybdenum carbide (Mo₂C) nanoparticles (NPs) within a carbon matrix from inexpensive starting materials (dicyanamide and ammonium molybdate). The optimized catalyst consisting of Mo₂C NPs with sizes lower than 3 nm encapsulated by ultrathin graphene shells (ca. 1–3 layers) showed superior HER activity in acidic media, with a very low onset potential of ?6 mV, a small Tafel slope of 41 mV dec^?1, and a large exchange current density of 0.179 mA cm^?2, as well as good stability during operation for 12 h. These excellent properties are similar to those of state‐of‐the‐art 20 % Pt/C and make the catalyst one of the most active acid‐stable electrocatalysts ever reported for HER.     

Mild Synthesis of Pt/SnO2/Graphene Nanocomposites with Remarkably Enhanced Ethanol Electro‐oxidation Activity and Durability

We have designed a new Pt/SnO₂/graphene nanomaterial by using L ‐arginine as a linker; this material shows the unique Pt‐around‐SnO₂ structure. The Sn²⁺ cations reduce graphene oxide (GO), leading to the in situ formation of SnO₂/graphene hybrids. L ‐Arginine is used as a linker and protector to induce the in situ growth of Pt nanoparticles (NPs) connected with SnO₂ NPs and impede the agglomeration of Pt NPs. The obtained Pt/SnO₂/graphene composites exhibit superior electrocatalytic activity and stability for the ethanol oxidation reaction as compared with the commercial Pt/C catalyst owing to the close‐connected structure between the Pt NPs and SnO₂ NPs. This work should have a great impact on the rational design of future metal–metal oxide nanostructures with high catalytic activity and stability for fuel cell systems.     

Formation of Hierarchical FeCoS2–CoS2 Double‐Shelled Nanotubes with Enhanced Performance for Photocatalytic Reduction of CO2

Hierarchical FeCoS₂–CoS₂ double‐shelled nanotubes have been rationally designed and constructed for efficient photocatalytic CO₂ reduction under visible light. The synthetic strategy, engaging the two‐step cation‐exchange reactions, precisely integrates two metal sulfides into a double‐shelled tubular heterostructure with both of the shells assembled from ultrathin two‐dimensional (2D) nanosheets. Benefiting from the distinctive structure and composition, the FeCoS₂–CoS₂ hybrid can reduce bulk‐to‐surface diffusion length of photoexcited charge carriers to facilitate their separation. Furthermore, this hybrid structure can expose abundant active sites for enhancing CO₂ adsorption and surface‐dependent redox reactions, and harvest incident solar irradiation more efficiently by light scattering in the complex interior. As a result, these hierarchical FeCoS₂–CoS₂ double‐shelled nanotubes exhibit superior activity and high stability for photosensitized deoxygenative CO₂ reduction, affording a high CO‐generating rate of 28.1 μmol h^?1 (per 0.5 mg of catalyst).     

Propane combustion over supported Pt catalysts

We prepared Pt catalysts supported on various metal oxides, viz., ZrO₂, CeO₂, TiO₂, yttria-stabilized zirconia (YSZ), SiO₂, SiO₂–Al₂O₃, and γ-Al₂O₃, using an incipient wetness method and applied them to propane combustion. In the cases of ZrO₂-, CeO₂-, and TiO₂-supported Pt catalysts, supports with different surface areas were also used. The Pt dispersion in Pt catalysts supported on metal oxides increased with increasing surface area of the support for the same metal oxide. Pt catalysts on supports with lower surface areas (ZrO₂, CeO₂, and TiO₂) showed higher catalytic activities for propane combustion than did Pt catalysts on supports with higher surface areas. The catalytic activity decreased in the following order: Pt/ZrO₂ (2) > Pt/CeO₂ (9) > Pt/TiO₂ (1) = Pt/SiO₂ (350) > Pt/ZrO₂ (18) = Pt/YSZ > Pt/TiO₂ (330) > Pt/SiO₂–Al₂O₃ (350) > Pt/ZrO₂ (73) > Pt/γ-Al₂O₃ (180) > Pt/CeO₂ (160). The catalytic activity is inversely proportional to the amount of O₂ chemisorbed up to the reaction temperature. It can be concluded that metallic Pt is essential for propane combustion and is maintained for the Pt catalysts with large Pt metal particles, which can be prepared by using a support with a low surface area.     

Preparation of disk‐like Pt/CeO2‐p‐TiO2 catalyst derived from MIL‐125(Ti) for excellent catalytic performance

A feasible strategy is reported for the synthesis of a disk‐like Pt/CeO₂‐p‐TiO₂ catalyst derived from the titanium‐based metal–organic framework (MOF) MIL‐125(Ti) through a few valid steps. To verify the successful synthesis and structural features of the Pt/CeO₂‐p‐TiO₂ catalyst, as‐prepared samples were characterized using several techniques. The characterizations demonstrated that MOF‐derived porous TiO₂ was appropriate for application as a support owing to its moderate surface area (101 m² g^?1) and suitable pore size (6 nm). Moreover, to study the effect of calcination temperature on the catalytic performance, the obtained catalyst was calcined at various temperatures. It was found that Pt/CeO₂‐p‐TiO₂ calcined at 550 °C exhibited the highest catalytic performance, evaluated by means of the reduction of 4‐nitrophenol monitored by UV–visible spectra. Furthermore, this catalyst showed good reusability with a conversion of 94% even after six cycles. Finally, a possible reaction mechanism was proposed to explain the reduction of 4‐nitrophenol to 4‐aminophenol over the Pt/CeO₂‐p‐TiO₂ catalyst.     

Ordered mesoporous Pt/Fe3O4–CeO2 heterostructure gel particles with enhanced catalytic performance for the reduction of 4-nitrophenol

The unique physicochemical properties of ordered mesoporous transition metal oxides have attracted more and more attention. The hydrolysis process of metal oxide precursors is difficult to control, and it is difficult to synthesize an ordered mesoporous transition metal oxide material using the conventional template method. Ordered mesoporous Pt/Fe₃O₄–CeO₂ heterostructure gel materials with excellent catalytic properties were successfully prepared using aerogel technology and the chemical deposition method. The Pt/Fe₃O₄–CeO₂ material was an n–n combined heterostructured semiconductor material which consisted of a magnetic Fe₃O₄ layer, a CeO₂ core and Pt noble metal doped nanoparticles. A layer of Fe₃O₄ thin film was formed on the surface of ordered mesoporous Pt/CeO₂ gel matrix material using the chemical deposition method. The intriguing heterostructural features could facilitate reactant diffusion and exposure of active sites which could enhance synergistic catalytic effects between the Pt nanoparticles and CeO₂ nanoparticles. Compared with Pt/CeO₂, the prepared Pt/Fe₃O₄–CeO₂ showed enhanced catalytic activity in the reduction of 4-nitrophenol at room temperature. The catalytic activity of the heterostructure catalysts was systematically investigated using 4-nitrophenol reduction as a model reaction. The results showed that the Pt (0.1%)/Fe₃O₄–CeO₂ sample exhibited the optimal catalytic performance toward catalytic reduction of 4-nitrophenol to 4-aminophenol. The study provided a method for the preparation of heterostructure nanocatalysts with high efficiency, which would be effective for application in various catalytic reactions.     

Constructing magnetic Fe3O4‐Au@CeO2 hybrid nanofibers for selective catalytic degradation of organic dyes

Au nanoparticles (Au NPs) play a vital role in heterogeneous catalytic reactions. However, pristine Au NPs usually suffer from poor selectivity and difficult recyclability. In this work, Fe₃O₄‐Au@CeO₂ hybrid nanofibers were prepared via a simple one‐pot redox reaction between HAuCl₄ and Ce (NO₃)₃ in the presence of Fe₃O₄ nanofibers. CeO₂ shell was uniformly coated on the surface of Fe₃O₄ nanofibers to form a unique core‐shell structure, while Au NPs were encapsulated inside the CeO₂ shell. The as‐prepared Fe₃O₄‐Au@CeO₂ hybrid nanofibers have been proved to be positively surface charged due to the formation of CeO₂ shell, enabling them to be good candidates for predominant selective catalytic activity towards the degradation of negatively charged organic dyes. In addition, the Fe₃O₄‐Au@CeO₂ hybrid nanofibers showed magnetic properties, offering them excellent recyclable usability. This work presents a facile and effective solution to prepare magnetic noble metal/metal oxide hybrid nanomaterials with unique chemical structure and surface characteristic for promising applications in heterogeneous catalysis.     

Facile Synthesis of Platinum–Cerium(IV) Oxide Hybrids Arched on Reduced Graphene Oxide Catalyst in Reverse Micelles with High Activity and Durability for Hydrolysis of Ammonia Borane

Highly dispersed Pt‐CeO₂ hybrids arched on reduced graphene oxide (Pt‐CeO₂/rGO) were facilely synthesized by a combination of the reverse micelle technique and a redox reaction without any additional reductant or surfactant. Under a N₂ atmosphere, the redox reaction between Ce³⁺ and Pt²⁺ occurs automatically in alkaline solution, which results in the formation of Pt‐CeO₂/rGO nanocomposites (NCs). The as‐synthesized Pt‐CeO₂/rGO NCs exhibit superior catalytic performance relative to that shown by the free Pt nanoparticles, Pt/rGO, Pt‐CeO₂ hybrid, and the physical mixture of Pt‐CeO₂ and rGO; furthermore, the nanocomposites show significantly better activity than the commercial Pt/C catalyst toward the hydrolysis of ammonia borane (NH₃BH₃) at room temperature. Moreover, the Pt‐CeO₂/rGO NCs have remarkable stability, and 92 % of their initial catalytic activity is preserved even after 10 runs. The excellent activity of the Pt‐CeO₂/rGO NCs can be attributed not only to the synergistic structure but also to the electronic effects of the Pt‐CeO₂/rGO NCs among Pt, CeO₂, and rGO.     

Formation of Triple‐Shelled Molybdenum–Polydopamine Hollow Spheres and Their Conversion into MoO2/Carbon Composite Hollow Spheres for Lithium‐Ion Batteries

Unique triple‐shelled Mo‐polydopamine (Mo‐PDA) hollow spheres are synthesized through a facile solvothermal process. A sequential self‐templating mechanism for the multi‐shell formation is proposed, and the number of shells can be adjusted by tuning the size of the Mo‐glycerate templates. These triple‐shelled Mo‐PDA hollow spheres can be converted to triple‐shelled MoO₂/carbon composite hollow spheres by thermal treatment. Owing to the unique multi‐shells and hollow interior, the as‐prepared MoO₂/carbon composite hollow spheres exhibit appealing performance as an anode material for lithium‐ion batteries, delivering a high capacity of ca. 580 mAh g^?1 at 0.5 A g^?1 with good rate capability and long cycle life.     

Oxidation behavior of rare earth oxide-coated Fe20Cr and Fe20Cr5Al alloys

This article presents the influence of surface additions of nanocrystalline rare earth (RE) oxides CeO₂, La₂O₃, and CeO₂ + La₂O₃ on the isothermal oxidation behavior of Fe20Cr and Fe20Cr5Al at 1000 °C. Thermogravimetric studies revealed parabolic kinetics in all cases and the scale thickness on specimen surfaces varied with the nature of RE oxide. The oxidation resistance of specimens coated with two RE oxides was significantly higher than those coated with either one of the two oxides. The marked increase in the oxidation resistance of the alloys coated with two RE oxides is due to optimization of RE ion radius and RE oxide grain size/shape.     

Synthesis of ceria nanoparticles for the catalytic activity of cyclohexene epoxidation and selective detection of nitrite

Based on a few noteworthy features, cerium oxide nanoparticles have gained significance in nanotechnology. The effective microwave combustion method (MCM) and the conventional sol–gel (CRSGM) technologies are used in this study to successfully generate the crystalline CeO₂ nanoparticles (NPs). Additionally, using a variety of spectroscopic and analytical methods, the synthesized CeO₂ NPs are examined to assess to understand their structure and morphology. The XRD patterns of CeO₂ NPs show that the structure exhibits a face-centered cubic lattice. Then, with demonstrated good conversion and selectivity, the impact of the epoxidation reaction of cyclohexene was examined. Finally, it can be said that using CeO₂ nanoparticles is an efficient strategy to increase the catalytic activity toward the epoxidation reaction of cyclohexene. In the presence of acetonitrile as a solvent and H₂O₂ as an oxidant, the catalyst samples utilized in the cyclohexene epoxidation reaction were examined. In this study, the CeO₂ catalyst outperformed all other catalysts in terms of cyclohexene maximal conversion and selectivity. After six prolonged cycles, the conversion of cyclohexene oxidation using CeO₂ NPs shows reasonable recyclability and conversion efficiency, making it the best catalyst for an industrial production application.Additionally, the upgraded CeO₂ nanoparticle electrode for nitrite detection has a linear concentration range (0.02–1200 M), a low detection limit (0.22 M), and a higher sensitivity (1.735 A M⁻¹ cm⁻²). CeO₂ NPs, on the other hand, have a quick response time, excellent sensitivity, and high selectivity. Additionally, the manufactured electrode is used to find nitrite in various water samples. Finally, it can be said that using CeO₂ NPs is an efficient strategy to increase the catalytic activity toward cyclohexene oxidation and nitrite.