The Role of Organic Capping Layers of Platinum Nanoparticles in Catalytic Activity of CO Oxidation

It is shown that the conversion of ethanol-to-gasoline over an HZSM-5 catalyst yields essentially the same product distribution as for methanol-to-gasoline performed over the same catalyst. Interestingly, there is a significant difference between the identity of the hydrocarbon molecules trapped inside the HZSM-5 catalyst when ethanol is used as a feed instead of methanol. In particular, the hydrocarbon pool contains a significant amount of ethylsubstituted aromatics when ethanol is used as feedstock, but there remains only methyl-substituted aromatics in the product slate.     

Nitric Oxide Reduction Using Hydrogen Over Perovskite Catalysts with Promotional Effect of Platinum on Catalytic Activity

The catalytic activities of strontium substituted La_0.7Sr_0.3MnO₃ type perovskite catalysts for NO reduction using H₂ as reducing agent has been studied, which is further improved by incorporation of Pt outside (0.1 wt.%Pt/La_0.7Sr_0.3MnO₃) and inside (La_0.7Sr_0.3Mn_0.97Pt_0.03O₃) the perovskite lattice structure. Pt shows excellent enhancement in catalytic selectivity towards N₂ when supported on the perovskite. The catalysts were characterized using thermo-gravimetric analysis (TGA), X-ray diffraction (XRD), scanning electron microscopy (SEM) and specific surface area. Catalysts evaluations were carried out using thermo-gravimetric analysis coupled with mass spectra (TG-MS).     

纳米银粒子的制备及其催化性能的研究

采用化学还原的方法,以聚乙烯吡咯烷酮为稳定剂,硼氢化钠为还原剂合成了纳米级银粒子。TEM和XRD分析表明所制备的银纳米粒子粒径分布窄,其平均粒径为15nm左右,且具有较高的结晶度。进一步催化硼氢化钠还原甲苯胺蓝的实验表明该银溶胶具有较高的催化活性。     

Preparation of Raspberry-Like Adsorbed Silica Nanoparticles via Miniemulsion Polymerization Using a Glycerol-Functionalized Silica Sol

A series of polymer/SiO₂ organic-inorganic composite microspheres were successfully prepared through miniemulsion polymerization. A TEM study indicated that the composite microspheres had raspberry-like morphology and silica particles were successfully deposited onto the surfaces of organic polymer microspheres. The average particle size and the silica content of composite microspheres could range from 180 nm to 240 nm and 15 ～ 35 wt%, respectively. The influence of reaction conditions such as the amount of emulsifier, the sonification frequency and sonification time, the amount of silica sol, butyl acrylate (BA) on the particle size, silica content and morphology of composite microspheres have been studied.     

Synthesis of Multifunctional Silica Composites Encapsulating a Mixture Layer of Quantum Dots and Magnetic Nanoparticles

Multifunctional silica colloidal composites with enhanced photoluminescence (PL) and superparamagnetism are reported. Enhanced PL and superparamagnetism were achieved by encapsulating a mixture layer of quantum dots (QDs) and superparamagnetic iron oxide nanoparticles (SPIONs) within a silica sphere, wherein QDs and SPIONs were capped by 3-mercaptopropionic acid (MPA) and 2-carboxy ethyl phosphonic acid (CEPA), respectively. The silica composites encapsulating a mixture layer of QDs and SPIONs, i.e., S(Q,M)S core(layer)shell architectures with various diameters (80, 360, and 900 nm) were successfully prepared by utilizing electrostatic interaction between positively charged amine-functionalized silica (S) and negatively charged mixture of QD–MPA (Q) and SPION–CEPA (M) and then, by forming a silica shell of 10–20 nm. The S(Q,M)S showed more than twice higher PL intensity than MPA-capped QD with the same QD concentration. Increasing the molar ratio of M/Q from 0.02 to 0.05 in the S(Q,M)S increased the saturation magnetization value from 0.15 to 0.62 emu/g. The S(Q,M)S composites with enhanced PL intensity and superparamagnetism are expected to be a plausible probe material for bioimaing and sensing application. Also, the current synthetic strategy for S(Q,M)S composites is expected to be extendible to include other functional nanoparticles.     

Novel Two-Step Synthesis of Controlled Size and Shape Platinum Nanoparticles Encapsulated in Mesoporous Silica

Uniform shape and size platinum nanoparticles encapsulated in mesoporous silica (SBA-15) were prepared in the same solution by a novel two-step method. Platinum nanoparticles were prepared in aqueous solution of K₂PtCl₄, the reduction was carried out by bubbling hydrogen, the capping material was tri-block poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) copolymer. The mesoporous silica was synthesized using the same copolymer as template from tetraethyl orthosilicate by hydrolysis in acidic conditions. The Pt-nanoparticles-in-mesoporous-silica system was characterized by a combination of low-angle powder X-ray diffraction, transmission electron microscopy and N₂ porosimetry. The platinum nanoparticles are encapsulated in the mesopores and retained their size and morphology. It appears that this hybrid material should be a superior three-dimensional high-surface-area catalyst for selective platinum-catalyzed reactions.     

Cefditorene-Mediated Synthesis of Silver Nanoparticles and Its Catalytic Activity

Ag(0) NPs were prepared by chemical reduction method in which silver nitrate was taken as the metal precursor and cefditorene as a reducing/capping agent and NaOH as the catalyst for reaction enhancement. The formation of the Ag(0) NPs was monitored using UV–Vis absorption spectroscopy confirmed the formation of Ag(0) NPs by exciting the typical surface plasmon absorption maxima at 405 nm. Transmission electron microscopy (TEM) confirmed the spherical morphology of the (Ag(0) NPs). The crystallite (11 ± 3 nm) and particle size (14.1 ± 2.2 nm) obtained from TEM and XRD analysis were coinciding with each other. Prepared Ag(0) NPs were then used as catalyst against 2-nitroaniline, 3-nitroaniline and 4-nitroaniline, which all showed best catalytic activity.     

不同硅源合成Bi-MCM-41分子筛及其催化性能

分别以硅酸钠、正硅酸乙酯和硅溶胶为硅源,十六烷基三甲基溴化铵为模板剂,硝酸铋为铋源,在弱碱性的务件下用水热法合成了Bi-MCM-41中孔分子筛,通过XRD、UV-Vis等表征手段对其进行结构、性质分析,结果表明：不同的硅源所合成的分子筛质量有所不同,以正硅酸乙酯和硅酸钠为硅源所合成的分子筛具有良好的长程有序结构和孔结构,并且铋高度分散于MCM-41分子筛骨架中。它们在苯乙烯催化氧化制苯甲醛的反应中有很好的催化活性,实验考察了不同硅源对肼．MCM-41中孔分子筛催化活性的影响并对其原因进行了探讨。     

Green Chemical Synthesis of Silver Nanoparticles and its Catalytic Activity

Silver nanoparticles (Ag(0) NPs) were synthesized by the chemical reduction method, in which ceftriaxone (antibiotic) used as reducing (to convert Ag⁺ to Ag(0)) and capping agent. UV–Visible spectroscopy revealed the first indication of formation of Ag(0) NPs. FT-IR spectroscopy showed the interaction of formation of bonding between antibiotic standard and silver. X-ray powder diffraction powder pattern confirmed the crystalline nature of prepared Ag(0) NPs. These Ag(0) NPs were used as catalyst for three organic hazardous chemicals i.e., 4-nitro-1,3-Phenylene diamine, 6-methyl-2-nitroanilline, 4-methyle-2-nitroanilline. The prepared Ag(0) NPs showed good catalytic activity against these compounds.     

Catalytic Activity of Supported Platinum and Metal Oxide Catalysts for Toluene Oxidation

Oxidation of toluene has been investigated over supported platinum as well as over a variety metal oxide (M _x O _y ) catalysts dispersed on high surface area γ-Al₂O₃. Catalysts were characterized with respect to their specific surface area (BET), metal dispersion (selective chemisorption of CO), phase composition and M _x O _y crystallite size (XRD) and reducibility (H₂-TPR). Catalytic performance for the title reaction was investigated in the temperature range of 100–500 °C, using a feed composition consisting of 0.1% toluene in air. For Pt/M _x O _y catalysts, it has been found that catalytic performance depends on the nature of the support, with Pt/CeO₂ being the most active catalyst at low temperatures. The intrinsic reaction rate per surface platinum atom does not depend on Pt loading (0.5–5 wt%), at least for Pt/Al₂O₃. Reducible metal oxides, such as ceria, are active for the title reaction and catalytic performance is improved significantly with increase of specific surface area (SSA). However, the intrinsic reaction rate per unit surface area is invariant with SSA. Dispersion of M _x O _y on high surface area inert supports, such as Al₂O₃, results in materials with relatively high catalytic activity, which seems to correlate well with the reducibility of metal oxides. Catalytic performance of M _x O _y /Al₂O₃ catalysts can be optimized by proper selection of M _x O _y loading. Best performing catalysts of this series include 60% MnO, 90% CeO₂ and 5% CuO on Al₂O₃ which, under the present experimental conditions, are able to completely convert toluene toward CO₂ at temperatures lower than 350 °C. Dispersion of Pt on M _x O _y /Al₂O₃ catalysts improves significantly the catalytic performance of irreducible M _x O _y but does not alter appreciably the activity of reducible M _x O _y /Al₂O₃ catalysts.     

Preparation of ZSM-5 Zeolite Honeycomb Monoliths Using Microporous Silica Obtained from Metakaolinite

Zeolite honeycomb monoliths were prepared from ZSM-5 powders synthesized under hydrothermal conditions using microporous silica obtained by selective leaching of metakaolinite. This honeycomb material was compared with those prepared using alkoxides (TEOS) as the silica source. The honeycomb monoliths were formed by extrusion of paste made from the synthesized powders through a multi-channel honeycomb die. The morphology and porous properties of these materials were studied using XRD, FTIR, SEM and N₂/Ar adsorption. ZSM-5 grains in the monoliths prepared from metakaolinite showed platy morphology with preferred orientation of the crystals in the extruded surface, and displayed an absence of secondary growth. The twinned morphology of ZSM-5 crystals was observed in the monoliths prepared using TEOS and this contributed to an increase in the external surface area even though the total surface area was identical to that of samples prepared from metakaolinite. The physical properties, thermal stability and mechanical strength of the monoliths was compared with zeolite-coated honeycombs. The results show that microporous silica prepared by acid leaching of metakaolinite is a cost-effective raw material for preparing ZSM-5 honeycomb monoliths with controlled morphology and tunable SiO₂/Al₂O₃ ratios.     

Synthesis of Silver Nanoparticles Using Syzygium malaccense Fruit Extract and Evaluation of Their Catalytic Activity and Antibacterial Properties

Journal of Inorganic and Organometallic Polymers and Materials - In this study, green synthesis of silver nanoparticles, an aqueous Syzygium malaccense fruit extract, was employed...     

Molecular Interactions of Silica Nanoparticles and Biomolecule-Functionalized Silica Nanoparticles with Bixa orellana L. Plant DNA

Silicon - Surface functionalization of silica nanoparticles (SiNPs) with biomolecules, such as amino acids, amino sugars and carbohydrates was performed to produce surface-functionalized silica...     

Preparation,XAFS Characterization,and Catalysis of Platinum Nanowires and Nanoparticles in Mesoporous Silica FSM-16

Pt nanowires are prepared in mesoporous FSM-16 by photoreduction of H₂PtCl₆, while H₂-reduction of H₂PtCl₆/FSM-16 at 673 K gives Pt nanoparticles in FSM-16. The Pt nanowires and nanoparticles are characterized by physicochemical methods such as XAFS, TEM, XRD, and XPS. The formation mechanism of the Pt nanowires and the catalytic performance in the water–gas-shift reaction are also investigated.     

The Effect of Water Vapor on the Particle Structure and Size of Silica Nanoparticles During Sintering

In this article, the influence of the water vapor concentration on structural changes of SiO₂ aerosol nanoparticle agglomerates during tempering was studied. The presence of water vapor in the carrier gas was shown to strongly accelerate the kinetics of sintering. While dry sintering at temperatures between 1100°C and 1500°C generated aggregates only, the addition of water to the process yields individual, completely coalesced nanoparticles at a temperature of 1300°C. Furthermore, depending on the water vapor concentration and temperature of the process, evaporation and condensation processes could be observed, leading to bimodal size distributions. The results prove the significant role of the water concentration in high temperature synthesis of silica and may be used to improve the control over morphology and specific surface area in these processes.     

Unique Catalytic Activity of Platinum Eluted into Perovskite in the Solid Phase

It has been found that Pt eluted into the (La_0.7Sr_0.2Ba_0.1)ScO_3-δ perovskite oxide exhibited higher catalytic activity for CO oxidation than for H₂ oxidation under separate reaction conditions, a behaviour which differs from that of conventional Pt catalysts. The unique activity appeared when ionic Pt in the perovskite lattice was partly reduced, forming Pt nanoparticles on the surface.