Chemoselective Transfer Hydrogenation of Cinnamaldehyde over Activated Charcoal Supported Pt/Fe3O4 Catalyst

A variety of spherical and structured activated charcoal supported Pt/Fe₃O₄ composites with an average particle size of ～100 nm have been synthesized by a self-assembly method using the difference of reduction potential between Pt (IV) and Fe (Ⅱ) precursors as driving force. The formed Fe₃O₄ nanoparticles (NPs) effectively prevent the aggregation of Pt nanocrystallites and promote the dispersion of Pt NPs on the surface of catalyst, which will be favorable for the exposure of Pt active sites for high-efficient adsorption and contact of substrate and hydrogen donor. The electron-enrichment state of Pt NPs donated by Fe₃O₄ nanocrystallites is corroborated by XPS measurement, which is responsible for promoting and activating the terminal C=O bond of adsorbed substrate via a vertical configuration. The experimental results show that the activated charcoal supported Pt/Fe₃O₄ catalyst exhibits 94.8% selectivity towards cinnamyl alcohol by the transfer hydrogenation of cinnamaldehyde with Pt loading of 2.46% under the optimum conditions of 120℃ for 6 h, and 2-propanol as a hydrogen donor. Additionally, the present study demonstrates that a high-efficient and recyclable catalyst can be rapidly separated from the mixture due to its natural magnetism upon the application of magnetic field.     

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.     

Support Morphology Effect on Selective Hydrogenation of 3-Nitrostyrene to 3-Vinylaniline over Pt/α-Fe2O3 Catalysts

Selective hydrogenation of substituted nitroaromatic compounds is an extremely important and challenging reaction. Supported metal catalysts attract much attention in this reaction because the properties of metal nanoparticles (NPs) can be modified by the nature of the support. Herein, the support morphology on the catalytic performance of selective hydrogenation of 3-nitrostyrene to 3-vinylaniline was investigated. Pt NPs supported on octadecahedral α-Fe₂O₃ supports with a truncated hexagonal bipyramid shape (Pt/α-Fe₂O₃-O) and rod-shaped α-Fe₂O₃ supports (Pt/α-Fe₂O₃-R) were prepared by glycol reduction method. Detailed characterizations reveal that the electronic structure and dispersion of Pt NPs can be modified by the supports. The Pt/α-Fe₂O₃-O catalyst exhibited superior catalytic performance for hydrogenation of 3-nitrostyrene because of its low coordinated Pt sites and the small Pt NPs size, which is benefit from the high-index exposed surfaces of truncated hexagonal bipyramid-shaped α-Fe₂O₃ support. The structural evolution during the catalytic reaction was investigated in detail by identical location transmission electron microscopy (IL-TEM) method, which found that the high cycling activity of Pt/α-Fe₂O₃-O catalyst during the cycle experiment results from the stability of Pt NPs.     

Catalytic Performance and Characterization of Pt‐Co/Al2O3 Catalysts for CO2 Reforming of CH4 to Synthesis Gas

Pt‐Co/Al₂O₂ catalyst has been studied for CO₂ reforming of CH₄ to synthesis gas. It was found that the catalytic performance of me catalyst was sensitive to calcination temperature. When Co/Al₂O₃ was calcined at 1473 K prior to adding a small amount of Pt to it, the resulting bimetallic catalyst showed high activity, optimal stability and excellent resistance to carbon deposition, which was more effective to the reaction than Co/Al₂O₃ and Pt/Al₂O₃ catalysts. At lower metal loading, catalyst activity decreased in the following order: Pt‐Co/ Al₂O₃ > Pt/Al₂O₃ > Co/Al₂O₃. With 9% Co, the Co/Al₂O₃ calcined at 923 K was also active for CO₂ reforming of CH₄, however, its carbon formation was much more fast man that of the Pt‐Co/Al₂O₃ catalyst. The XRD results indicated that Pt species well dispersed over the bimetallic catalyst. Its high dispersion was related to the presence of CoAl₂O₄, formed during calcining of Co/Al₂O₃ at high temperature before Pt addition. Promoted by Pt, Co/Al₂O₄ in the catalyst could be reduced partially even at 923 K, the temperature of pre‐reduction for the reaction, confirmed by TPR. Based on these results, it was considered that the zerovalent platinum with high dispersion over the catalyst surface and the zerovalent cobalt resulting from Co/Al₂O₄ reduction are responsible for high activity of the Pt‐Co/Al₂O₃ catalyst, and the remain Co/Al₂O₄ is beneficial to suppression of carbon deposition over the catalyst.     

Selective hydrogenation of phenylacetylene on Pd/Al2O3: Effect of the addition of Pt and particle size

Phenylacetylene hydrogenation on Pd, Pt and Pd–Pt/Al₂O₃ catalysts has been studied. In all catalysts activity was found not to depend on particle size. However, selectivity to styrene was found to depend on Pd/Al₂O₃ catalysts. Carbon deposition in both metal and support explains such a behavior. Nevertheless, in small Pd particles a longer residence time of styrene may control the selectivity.     

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.     

Effect of substrate on phase formation and surface morphology of sol-gel lead-free KNbO3, NaNbO3, and K0.5Na0.5NbO3 thin films

Environmentally acceptable lead-free ferroelectric KNbO₃ (KN) or NaNbO₃ (NN) and K_0.5Na_0.5NbO₃ (KNN) thin films were prepared using a modified sol-gel method by mixing potassium acetate or sodium acetate or both with the Nb-tartrate complex, deposited on the Pt/Al₂O₃ and Pt/SiO₂/Si substrates by a spin-coating method and sintered at 650°C. X-ray diffraction (XRD) analysis indicated that the NN and KNN films on the Pt/SiO₂/Si substrate possessed a single perovskite phase, while NN and KNN films on the Pt/Al₂O₃ substrate contained a small amount of secondary pyrochlore phase, as did KN films on both substrates. Scanning electron microscopic (SEM) and atomic force microscopic (AFM) analyses confirmed that roughness R _q of the thin KNN/Pt/SiO₂/Si film (?? 7.4 nm) was significantly lower than that of the KNN/Pt/Al₂O₃ film (?? 15 nm). The heterogeneous microstructure composed of small spherical and larger needle-like or cuboidal particles were observed in the KN and NN films on both substrates. The homogeneous microstructure of the KNN thin film on the Pt/SiO₂/Si substrate was smoother and contained finer spherical particles (?? 50 nm) than on Pt/Al₂O₃ substrates (?? 100 nm). The effect of different substrates on the surface morphology of thin films was confirmed.     

X射线吸收谱研究碳纳米管内Rh-Mn纳米粒子结构的变化

利用X射线吸收谱技术研究了负载于多壁碳纳米管内的Rh-Mn纳米粒子在不同气氛和温度下的结构. 结果表明,Rh-Mn粒子在空气中是由氧化铑团簇和混合锰氧化物组成. 经过氢气在300 ℃下还原后,混合锰氧化物种转化成MnO. 而氧化铑团簇在He气氛下当温度达到250 ℃时就会发生分解而形成金属铑团簇. 对形成的铑团簇用H₂或CO进行热处理,发现其分散性随温度升高而提高; 同时,X射线吸收谱实验没有观察到Mn和Rh之间存在显著的相互作用,助剂Mn的主要作用是提高了Rh的分散性.     

Gold catalysts supported on ZnO/Al<Subscript>2</Subscript>O<Subscript>3</Subscript> for low-temperature CO oxidation

Gold catalysts with loadings ranging from 0.5 to 7.0 wt% on a ZnO/Al₂O₃ support were prepared by the deposition–precipitation method (Au/ZnO/Al₂O₃) with ammonium bicarbonate as the precipitation agent and were evaluated for performance in CO oxidation. These catalysts were characterized by inductively coupled plasma-atom emission spectrometry, temperature programmed reduction, and scanning transmission electron microscopy. The catalytic activity for CO oxidation was measured using a flow reactor under atmospheric pressure. Catalytic activity was found to be strongly dependent on the reduction property of oxygen adsorbed on the gold surface, which related to gold particle size. Higher catalytic activity was found when the gold particles had an average diameter of 3–5 nm; in this range, gold catalysts were more active than the Pt/ZnO/Al₂O₃ catalyst in CO oxidation. Au/ZnO/Al₂O₃ catalyst with small amount of ZnO is more active than Au/Al₂O₃ catalyst due to higher dispersion of gold particles.     

Influence of Perfluorinated End Groups on the SFRD of [Pt(cod)Me(CnF2n+1)] onto Porous Al2O3 in CO2 under Reductive Conditions

The optimized synthesis of a range of cyclooctadiene‐stabilized Pt complexes that contained different perfluoro‐alkane chains, [Pt(cod)Me(C_nF_2n+1)], is presented. These metal–organic compounds were employed in the so‐called supercritical fluid reactive deposition (SFRD) in CO₂ under reductive conditions to generate metallic nanoparticles on aluminum oxide as a porous support. Thus, Al₂O₃‐supported Pt nanoparticles with a narrow particle‐size distribution were obtained. At a reduction pressure of 15.5 MPa and a temperature of 353 K, particle diameters of d₅₀=2.3–2.8 nm were generated. Decreasing the pressure during the reduction reaction led to slightly larger particles whilst decreasing the amount of organometallic precursor in CO₂ yielded a decrease in the particle size from x₅₀=3.2 nm to 2.6 nm and a particle‐size distribution of 2.2 nm. Furthermore, substitution of the CH₃ end group by the C_nF_2n+1 end groups led to a significant drop in Pt loading of about 50 %. Within the series of perfluorinated end groups that were considered, the Pt complex that contained a branched perfluoro‐isopropyl group showed the most‐interesting results when compared to the control precursor, [Pt(cod)Me₂] ( 1 ).     

General Strategy for Synthesis of Ordered Pt3M Intermetallics with Ultrasmall Particle Size

Controllable synthesis of atomically ordered intermetallic nanoparticles (NPs) is crucial to obtain superior electrocatalytic performance for fuel cell reactions, but still remains arduous. Herein, we demonstrate a novel and general hydrogel‐freeze drying strategy for the synthesis of reduced graphene oxide (rGO) supported Pt₃M (M=Mn, Cr, Fe, Co, etc.) intermetallic NPs (Pt₃M/rGO‐HF) with ultrasmall particle size (about 3 nm) and dramatic monodispersity. The formation of hydrogel prevents the aggregation of graphene oxide and significantly promotes their excellent dispersion, while a freeze‐drying can retain the hydrogel derived three‐dimensionally (3D) porous structure and immobilize the metal precursors with defined atomic ratio on GO support during solvent sublimation, which is not afforded by traditional oven drying. The subsequent annealing process produces rGO supported ultrasmall ordered Pt₃M intermetallic NPs (≈3 nm) due to confinement effect of 3D porous structure. Such Pt₃M intermetallic NPs exhibit the smallest particle size among the reported ordered Pt‐based intermetallic catalysts. A detailed study of the synthesis of ordered intermetallic Pt₃Mn/rGO catalyst is provided as an example of a generally applicable method. This study provides an economical and scalable route for the controlled synthesis of Pt‐based intermetallic catalysts, which can pave a way for the commercialization of fuel cell technologies.     

Ultrathin Coating of Confined Pt Nanocatalysts by Atomic Layer Deposition for Enhanced Catalytic Performance in Hydrogenation Reactions

Metal‐support interfaces play a prominent role in heterogeneous catalysis. However, tailoring the metal‐support interfaces to realize full utilization remains a major challenge. In this work, we propose a graceful strategy to maximize the metal‐oxide interfaces by coating confined nanoparticles with an ultrathin oxide layer. This is achieved by sequential deposition of ultrathin Al₂O₃ coats, Pt, and a thick Al₂O₃ layer on carbon nanocoils templates by atomic layer deposition (ALD), followed by removal of the templates. Compared with the Pt catalysts confined in Al₂O₃ nanotubes without the ultrathin coats, the ultrathin coated samples have larger Pt–Al₂O₃ interfaces. The maximized interfaces significantly improve the activity and the protecting Al₂O₃ nanotubes retain the stability for hydrogenation reactions of 4‐nitrophenol. We believe that applying ALD ultrathin coats on confined catalysts is a promising way to achieve enhanced performance for other catalysts.     

Fabrication of inorganic alumina particles at nanoscale by a pulsed laser ablation technique in liquid and exploring their protein binding,anticancer and antipathogenic activities

The interaction of nanoparticles with biological systems can provide useful information about their therapeutic applications. The aluminum nanoparticles (Al₂O₃ NPs) were synthesized by laser ablation technique and well-characterized by different methods. Fluorescence spectroscopy, circular dichroism (CD) spectroscopy, and molecular docking studies were employed to evaluate the effect of Al₂O₃ NPs on the protein structure. Growth inhibitory and apoptotic effects of the Al₂O₃ NPs against K562 cancer cells and lymphocyte cells were assessed using [3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide] (MTT), flow cytometry, and real time polymerase chain reaction (PCR) assays. The antipathogenic activity of Al₂O₃ NPs against a diverse range of Gram-negative and Gram-positive pathogens was explored through a disk diffusion method. The characterization techniques determined that the Al₂O₃ NPs were successfully synthesized in the nanoscales. Intrinsic, 1-anilino-8-naphthalenesulfonate (ANS) and acrylamide fluorescence spectroscopy studies disclosed that Al₂O₃ NPs can partially change the tertiary structure of human serum albumin (HSA), whereas CD spectroscopy investigation depicted that the secondary structure of HSA remained intact. Molecular docking investigation also manifest that the Al₂O₃ nano-clusters preferably bind to electrostatic residues. Al₂O₃ NPs exhibited promising and selective anticancer features through reactive oxygen species (ROS) production, apoptosis induction, and elevation of Bax/Bcl-2 mRNA ratio. Furthermore, the Al₂O₃ NP showed a remarkable antibacterial activity against both Gram-negative and Gram-positive pathogens. In conclusion, it may be suggested that the synthesized Al₂O₃ NPs can be integrated in the development of anticancer and antipathogenic agents.     

介孔载体负载Pt催化剂上α-酮酸酯的不对称氢化

以介孔材料SBA-15、经或未经Al2O3修饰的具有三维立方孔道结构的SiO2为载体,制备了负载型Pt催化剂,并用于催化α-酮酸酯底物2-氧代-4-苯基-丁酸乙酯(EOPB)和丙酮酸乙酯(Etpy)的不对称氢化反应中.结果表明,当SBA-15孔径由6.2,7.6和9.2nm依次增加时,EOPB不对称氢化的活性和手性选择...     

Effect of the Electric Conductivity of a Catalyst on Methane Activation in a Dielectric Barrier Discharge Reactor

The influence of catalyst electric conductivity on methane activation in a planar-type dielectric barrier discharge reactor is investigated by empirically comparing the degree of methane conversion of bare Al₂O₃ with that of Pt/Al₂O₃; from this, it is determined that the latter catalyst converts less methane owing to the presence of Pt. Calculations and comparisons of electric fields with and without Pt show that the presence of a Pt catalyst results in a lower electric field than does bare Al₂O₃. An analysis of product gases based on the correlation between the fragmentation of radicals and the electric field also indicates that the electric field is decreased by using Pt. From these results, it can be concluded that the synergies between the plasma and the conductive catalysts need to be reassessed for different electric field conditions, and that further studies of non-conductive catalysts that can enhance methane activation and synergistic effects are needed.     

Ag doped α-Fe2O3 nanoparticles: Synthesis,characterization and application as heterogeneous photocatalyst for removal of organic dye from aqueous media without any oxidizing agents

α-Fe₂O₃ and Ag doped α-Fe₂O₃ nanostructures were synthesized by wet chemical reflux method. XRD analysis established formation of α-Fe₂O₃ phase for un-doped nanostructures while for Ag-α-Fe₂O₃ the diffraction peaks shift slightly towards higher angle. FESEM suggests the development of fine nanostructures with particle size order of 40–70 ​nm for pristine α-Fe₂O₃ NPs, whereas comparatively larger size NPs with order of 60–110 ​nm for Ag-α-Fe₂O₃. The NPs were used as photocatalysts for degradation of eosin yellow and malachite green dyes in aqueous medium under visible light irradiation. Ag-α-Fe₂O₃ NPs efficiently decolourize about 98% dye molecules within 90 ​min.     

Synthesis and Characterization of Co3O4/Multiwalled Carbon Nanotubes Nanocomposite for Amperometric Sensing of Hydrazine

Co₃O₄ nanoparticles (NPs) were synthesized and decorated on the multi‐walled carbon nanotubes (MWCNTs) through a simple hydrothermal procedure. The deposited Co₃O₄ NPs on the sidewalls of MWCNTs were found to be cubic crystal structure and homogenously dispersed with a narrow particle size distribution centered at around 6 nm. The Co₃O₄/MWCNTs nanocomposite was then utilized for the electrochemical detection of hydrazine, and exhibited a high sensitivity of 34.5 µA mM^?1, a low detection limit of 0.8 µM (S/N=3), a wide linear range of 20 µM to 1.1 mM along with a short response time of less than 5 s.     

The Metal–Support Interaction Concerning the Particle Size Effect of Pd/Al2O3 on Methane Combustion

The particle size effect of Pd nanoparticles supported on alumina with various crystalline phases on methane combustion was investigated. Pd/θ, α‐Al₂O₃ with weak metal‐support interaction showed a volcano‐shaped dependence of the catalytic activity on the size of Pd particles, and the catalytic activity of the strongly interacted Pd/γ‐Al₂O₃ increased with the particle size. Based on a structural analysis of Pd nanoparticles using CO adsorption IR spectroscopy and spherical aberration‐corrected scanning/transmission electron microscopy, the dependence of catalytic activity on Pd particle size and the alumina crystalline phase was due to the fraction of step sites on Pd particle surface. The difference in fraction of the step site is derived from the particle shape, which varies not only with Pd particle size but also with the strength of metal–support interaction. Therefore, this interaction perturbs the particle size effect of Pd/Al₂O₃ for methane combustion.     

A Vanadium(V) Oxide Nanorod Promoted Platinum/Reduced Graphene Oxide Electrocatalyst for Alcohol Oxidation under Acidic Conditions

A Pt‐V₂O₅/rGO ternary hybrid electrocatalyst was designed by using active vanadium(V) oxide (V₂O₅) nanorods and reduced graphene oxide (rGO) components. The V₂O₅ nanorods were synthesized by a simple polyol‐assisted solvothermal method and were incorporated uniformly onto rGO sheets by intermittent microwave heating. Subsequently, Pt nanoparticles (2–3 nm in size) were deposited over the V₂O₅/rGO composite by the conventional polyol reflux method. The electrocatalytic performance of the Pt‐V₂O₅/rGO ternary hybrid and bare Pt/rGO catalysts towards the oxidation of simple alcohols was evaluated in acidic media. The ternary hybrid catalyst exhibited higher electrocatalytic activity than bare Pt/rGO and also showed good stability. The higher electrocatalytic activity of the Pt‐V₂O₅/rGO ternary hybrid was attributed to a synergistic effect among the Pt, V₂O₅, and rGO components. In addition, oxygen‐containing species, such as OH groups, were generated on V₂O₅ at lower potentials. These groups were able to scavenge intermediate species such as CO_ads on the Pt surfaces and helped to regenerate the active sites on the Pt surface more effectively for the routine alcohol oxidation reaction.     

Pulsed electrodeposition of Pt nanoclusters on carbon nanotubes modified carbon materials using diffusion restricting viscous electrolytes

A simple method for achieving high dispersion and small platinum nanoparticles down to only 2 or 3 nm on structured carbon supports (carbon nanotubes-modified PAN-based carbon fiber and carbon nanotubes-modified graphite foil) is presented. Pulsed electrodeposition of Pt nanoparticles was performed at increased viscosity of the H₂PtCl₆ containing electrolyte by addition of glycerol. The catalyst nanoparticle size can be controlled by varying the amount of glycerol added into the aqueous H₂PtCl₆ solution, and adjusting the number of the potential pulses. The shape and size of the Pt nanoparticles was characterized by scanning electron microscopy and transmission electron microscopy. The electrocatalytic properties of Pt nanoparticles with respect to O₂ and H₂O reduction were investigated by means of cyclic voltammetry, and the improved catalytic activity of the Pt nanoparticles/carbon nanotubes surfaces could be proved.