Selective hydrogenation of cyclopentadiene in mono- and bimetallic catalytic hollow-fiber reactors

The mono- and bimetallic catalytic polymeric hollow-fiber reactors were established with catalytic polymeric cellulose acetate (CA) hollow fibers prepared by supporting the polymer-anchored mono- or bimetallic catalyst in/on the inner wall of the hollow fibers. The selective hydrogenation of cyclopentadiene to cyclopentene was efficiently carried out in the above catalytic polymeric hollow-fiber reactors, especially in the NaBH4 reduced bimetallic PVP-Pd-0.5Co/CA hollow-fiber reactor under mild conditions of 40 degrees C and 0.1 MPa. It was found that there was a remarkable synergic effect of palladium and cobalt reduced by NaBH4 in the bimetallic PVP-Pd-0.5Co/CA hollow-fiber reactor, which results in a 97.5% conversion of cyclopentadiene and a 98.4% selectivity for cyclopentene. (C) 2000 Elsevier Science B.V. All rights reserved.

Hollow fibers of yttria-stabilized zirconia (8YSZ) prepared by calcination of electrospun composite fibers

8YSZ fibers were synthesized by calcination of PVP/zirconium oxychloride/yttrium nitrate composite fibers (PVP-Precursor) obtained by electrospinning. Scanning electron microscopy (SEM) indicated that the 8YSZ fibers are hollow and the gas released during organic binder decomposition resulted in the formation of hollow center in fibers

Magnet-assisted assembly of 1-dimensional hollow PtCo nanomaterials on an electrode surface

In this work, rapid and controllable confinement of one-dimensional (1D) hollow PtCo nanomaterials on an indium tin oxide (ITO) electrode surface was simply realized via magnetic attraction. The successful assembly was verified by scanning electron microscopy (SEM) and cyclic voltammetry, which showed that a longer exposure time of the electrode to the suspension of these 1D hollow nanomaterials (magnetic suspension) led to a larger amount of attached 1D hollow PtCo nanomaterials.

A general method for the rapid synthesis of hollow metallic or bimetallic nanoelectrocatalysts with urchinlike morphology

We have reported a facile and general method for the rapid synthesis of hollow nanostructures with urchinlike morphology. In-situ produced Ag nanoparticles can be used as sacrificial templates to rapidly synthesize diverse hollow urchinlike metallic or bimetallic (such as Au/Pt) nanostructures. It has been found that heating the solution at 100 degrees C during the galvanic replacement is very necessary for obtaining urchinlike nanostructures. Through changing the molar ratios of Ag to Pt, the wall thickness of hollow nanospheres can be easily controlled; through changing the diameter of Ag nanoparticles, the size of cavity of hollow nanospheres can be facilely controlled; through changing the morphologies of Ag nanostructures from nanoparticle to nanowire, hollow Pt nanotubes can be easily designed. This one-pot approach can be extended to synthesize other hollow nanospheres such as Pd, Pd/Pt, Au/Pd, and Au/Pt. The features of this technique are that it is facile, quick, economical, and versatile.

Syntheses of opened hollow clay microspheres through a spray-drying approach and their derivative clay/carbon nanotubes composites

Opened hollow microspheres of organoclays were prepared via spray drying the suspension of modified Na+-montmorillonite (Na+-MMT) with alkylsulfonate. The microstructure and thermal properties of these opened hollow spheres were characterized by means of wide-angle X-ray diffraction, field emission scanning electron microscopy, and thermogravimetric analysis. The results showed that the organoclays had larger interlayer spacing compared with pure Na+-MMT and higher thermal stability relative to the alkylsufonate.

Sintering-resistant hollow fibers of LaMgAl11O19 prepared by electrospinning

Lanthanum magnesium hexaaluminate (LMA) is very important ceramic material for catalytic combustion of natural gas. The sintering-resistant hollow fibers of LMA with diameters ranging from 1 to 3 mu m were fabricated from alcoholic solutions containing polyvinyl pyrrolidone (PVP) and aqueous solution of lanthanum, magnesium and aluminum nitrates. The interaction between PVP and nitrates were studied by X-ray diffraction and Fourier transmission-infrared spectroscopy. The forming mechanism of hollow fibers and the sintering ability of hollow LaMgAl11O19 fibers were discussed.

Strings of interconnected hollow carbon nanoparticles with porous shells prepared using simple solid-phase synthesis

Strings of interconnected hollow carbon nanoparticles with porous shells were prepared by simple heat-treatments of a mixture of resorcinol-formaldehyde gel and transition-metal salts. The sample was characterized by scanning electron microscopy, transmission electron microscopy, X-ray diffraction and nitrogen adsorption. Results show that the sample consisted of relatively uniform hollow particles with sizes ranging from 70 to 80 nm forming a strings-of-pearls-like nanostructure. The material with porous shells possessed well-developed graphitic structure with an interlayer (d(002)) spacing of 0.3369 nm and the stack height of the graphite crystallites of 9 nm.

Novel Hybrid Electrocatalyst with Enhanced Performance in Alkaline Media: Hollow Au/Pd Core/Shell Nanostructures with a Raspberry Surface

In this paper, a hollow Au/Pd core/shell nanostructure with a raspberry surface was developed for methanol, ethanol, and formic acid oxidation in alkaline media. The results showed that it possessed better electrocatalyst performance than hollow Au nanospheres or Pd nanoparticles. The nanostructure was fabricated via a two-step method. Hollow Au nanospheres were first synthesized by a galvanic replacement reaction, and then they were coated with a layer of Pd grains. Several characterizations such as transmission electron microscopy (TEM), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), and X-ray photoelectron spectroscopy (XPS) were used to investigate the prepared nanostructures.

Preparation of Hollow Carbon and Silicon Carbide Fibers with Different Cross-Sections by using Electrospun Fibers as Templates

Hollow carbon nanofibers with circular and rectangular opening were prepared by using electrospun silica fibers as templates. Silica fibers were synthesized by electrospinning, and they were coated with a carbon layer formed by thermal decomposition and carbonization of polystyrene under a nitrogen atmosphere. Hollow carbon nanofibers with circular and rectangular openings were then obtained after the silica core was etched by hydrofluoric acid. The carbon nanofibers with different morphologies also could be used as templates to fabricate silicon carbide fibers. The silicon carbide fibers with circular and rectangular openings could be obtained by using hollow carbon nanofibers and carbon belts as templates, respectively.

General and Facile Method To Prepare Uniform Y2O3:Eu Hollow Microspheres

Well-shaped Y2O3:Eu hollow microspheres have been successfully prepared on a large scale via a urea-based homogeneous precipitation technique in the presence of colloidal carbon spheres as hard templates followed by a subsequent heat treatment process. XRD results demonstrate that all the diffraction peaks of the samples can be well indexed to the pure cubic phase Of Y2O3. TEM and SEM images indicate that the shell of the uniform hollow spheres, whose diameters are about 250 nm, is composed of many uniform nanoparticles with diameters of about 20 nm, basically consistent with the estimation of XRD results. Furthermore, the main process in this method was carried out in aqueous condition, without the use of organic solvents or etching agents. The as-prepared hollow Y2O3:Eu microspheres show a strong red emission corresponding to the D-5(0)-F-7(2) transition of the Eu3+ ions under ultraviolet or low voltage excitation, which might find potential applications in fields such as light phosphor powders, advanced flat panel displays, field emission display devices, and biological labeling.

High-efficiency and low-cost hybrid nanomaterial as enhancing electrocatalyst: Spongelike AWN core/shell nanomaterial with hollow cavity

A high-efficiency and low-cost spongelike Au/Pt core/shell electrocatalyst with hollow cavity has been facilely obtained via a simple two-step wet chemical process. Hollow gold nanospheres were first synthesized via a modified galvanic replacement reaction between Co nanoparticles in situ produced and HAUCl(4). The as-prepared gold hollow spheres were employed as seeds to further grow spongelike Pt shell. It is found that the surface of this hybrid nanomaterial owns many Pt nanospikes, which form a spongelike nanostructure. All experimental data including scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy, and UV-vis-near-infrared spectroscopy have been employed to characterize the obtained Au/Pt hybrid nanomaterial. The rapid development of fuel cell has inspired us to investigate the electrocatalytic properties for dioxygen and methanol of this novel hybrid nanomaterial. Spongelike hybrid nanomaterial mentioned here exhibits much higher catalytic activity for dioxygen reduction and methanol oxidation than the common Pt electrode.

A simple method to prepare titania nanomaterials of core-shell structure, hollow nanospheres and mesoporous nanoparticles

A simple method to prepare titania nanomaterials of core-shell structure, hollow nanospheres and mesoporous nanoparticles has been developed. The core-shell nanostructures with NH4Cl as core and TiO2 center dot xH(2)O-NH4Cl as shell were prepared in nonaqueous system by the deposition on the surface of the aggregated NH4Cl crystals, which could be transformed into mesoporous anatase nanoparticles or hollow nanospheres by calcination at 500A degrees C or extraction with methanol, respectively. The hierarchical mesoporous nanostructures benefited the photocatalytic activities of the resultant titania nanomaterials, demonstrated by the UV light photodegradation of Methyl Orange.

Raspberry-like Hierarchical Au/Pt Nanoparticle Assembling Hollow Spheres with Nanochannels: An Advanced Nanoelectrocatalyst for the Oxygen Reduction Reaction

In this contribution, we for the first time report the synthesis of raspberry-like hierarchical Au/Pt nanoparticle (NP) assembling hollow spheres (RHAHS) with pore structure and complex morphology through one in situ sacrificial template approach without any post-treatment procedure. This method has some clear advantages including simplicity, quickness, high quality, good reproducibility, and no need of a complex post-treatment process (removing templating). Furthermore, the present method could be extended to other metal-based NP assembling hollow spheres. Most importantly, the as-prepared RHAHS exhibited excellent electrocatalytic activity for oxygen reduction reaction (ORR). For instance, the present RHAHS-modified electrode exhibited more positive potential (the half-wave potential at about 0.6 V), higher specific activity, and higher mass activity for ORR than that of commercial platinum black (CPB). Rotating ring-disk electrode (RRDE) voltarnmetry demonstrated that the RHAHS-modified electrode could almost catalyze a four-electron reduction of O-2 to H2O in a 0.5 M air-saturated H2SO4 solution.