Ranting Tao

In Situ Controllable Loading of Ultrafine Noble Metal Particles on Titania

Herein we present a novel and facile approach to controllably load ultrafine noble metal nanoparticles on titania through in situ redox reaction between the reductive titanium(III) oxide support and metal salt precursors in aqueous solution. A series of noble metal/TiO(2) nanocomposites with uniform metal dispersion, tunable metal particle size, and narrow metal particle size distribution were obtained.

The solvent-free selective hydrogenation of nitrobenzene to aniline: an unexpected catalytic activity of ultrafine Pt nanoparticles deposited on carbon nanotubes

In this work, we developed a facile and efficient route to deposit ultrafine Pt particles onto multi-walled carbon nanotubes (MWNTs) with the aid of tip sonication. The loading of Pt on the MWNTs could attain the very high level of 50 wt% and the size of the Pt particles could be controllably tuned in the range 1.9–3.5 nm with narrow size distributions. The resultant nanocomposites were applied to catalyze the hydrogenation of nitrobenzene under solvent-free conditions. It was demonstrated that the Pt/MWNT catalysts showed excellent activity with a high turnover frequency (e.g., 69 900 h−1) as well as superior selectivity to aniline (e.g., >99%) in this reaction.

Pd nanoparticles immobilized on sepiolite by ionic liquids: efficient catalysts for hydrogenation of alkenes and Heck reactions

Palladium-sepiolite catalysts were prepared by immobilizing Pd2+ on sepiolite using an ionic liquid containing a guanidine cation, followed by reduction with hydrogen at 150 °C. The resulting composites were characterized by different techniques. X-Ray photoelectron spectroscopy analysis showed that the loaded Pd existed mainly in the form of Pd0, with a small amount of its oxides, and distributed uniformly on sepiolite with particle size about 5 nm, as confirmed by transmission electron microscopy examination. X-Ray diffraction analysis indicated that the sepiolite retained its original structure after deposition of Pd nanoparticles. The activities of the Pd-sepiolite catalysts for hydrogenations of some alkenes (e.g., cyclohexene and 1,3-cyclohexdiene) and Heck reactions were investigated. It was demonstrated that the as-prepared catalysts exhibited very high efficiency for these reactions.

A simple route to coat mesoporous SiO2 layer on carbon nanotubes

Herein we present a simple method to coat a porous SiO2 layer on carbon nanotubes (CNTs) with the aid of the cationic surfactant cetyltrimethyl ammonium bromide (CTAB). The coating process was studied systematically, and a possible coating mechanism was proposed. Temperature and the ratio of CTAB/CNTs/H2O were found to play key role in the coating process. This method can be applied to both multiwalled carbon nanotubes (MWNTs) and single walled carbon nanotubes (SWNTs). The individualized nature of the CNTs (both MWNTs and SWNTs) was maintained during the coating process. Furthermore, Raman spectroscopy showed that this method is nondestructive to the electronic structure of CNTs. The CNT/porous SiO2 core/shell structure will serve as a platform for further surface functionalization of CNTs.

The Immobilization of Glycidyl-Group-Containing Ionic Liquids and Its Application in CO2 Cycloaddition Reactions

Covalent immobilization of glycidyl-group-containing ionic liquids (ILs) on organic and inorganic supports with functional surfaces was achieved, based on the fact that the glycidyl group can actively react with almost all nucleophilic, electrophilic, neutral, and free-radical species. By using polymer spheres with amino- and carboxyl-group-functionalized surfaces as organic supports and silicas (including SBA15 and silica gel) with amino groups attached as inorganic supports, the ionic liquid 1-glycidyl-butylimidazolium chloride was successfully grafted onto these polymer and silica supports, respectively, through reactions between the glycidyl group in the IL and the polar groups on the support surfaces. The resultant samples were examined by transmission electron microscopy, solid-state (13)C NMR spectroscopy, IR spectroscopy, and ion chromatography. The activities of these resultant polymer- and silica-based catalysts were investigated for CO(2) cycloaddition reactions with epoxides. It was demonstrated that these catalysts could effectively catalyze CO(2) cycloaddition. In particular, the polymer supports generated synergistic effects with the IL in the coupling reaction of CO(2) with propylene oxide, and the turnover frequency could reach about 1700 h(-1) when the IL attached to the NH(2)-functionalized polymer was used as the catalyst.

In-Situ Loading Ultrafine AuPd Particles on Ceria: Highly Active Catalyst for Solvent-Free Selective Oxidation of Benzyl Alcohol

Ce(III) oxide was synthesized under the protection of nitrogen gas, which had strong ability to reduce noble metal ions (e.g., Au, Pd ions) into metallic forms under oxygen-free conditions. On the basis of the surface redox reaction between the Ce(III) oxide support and noble metal ions, an effective and novel approach was presented to prepare noble metal/CeO(2) nanocatalysts, and a series of AuPd/CeO(2) nanocomposites with different Au:Pd molar ratios and metal loadings were obtained in the absence of any extra reducing and protective agents. The resultant composites were characterized by different techniques including X-ray diffraction, transmission electron microspectroscopy, X-ray photoelectron microspectroscopy, and ICP-AES analysis. It was demonstrated that in the AuPd/CeO(2) composites the content of Ce(III) reached about 30%, and the AuPd bimetallic particles with average size of 2.6 or 3.3 nm and narrow size distribution were uniformly distributed on the CeO(2) nanorods. The AuPd/CeO(2) composites were found to be excellent heterogeneous nanocatalysts for the selective oxidation of benzyl alcohol under solvent-free conditions. It was shown that all the AuPd/CeO(2) catalysts exhibited good selectivity toward benzaldehyde; especially, the catalyst with Au:Pd = 1:5 and metal loading of 1.2 wt % displayed extremely high activity with a TOF = 30.1 s(-1) at 160 °C.

Porous Fe3O4 nanoparticles: Synthesis and application in catalyzing epoxidation of styrene

A facile route was employed to synthesize porous magnetite via reaction of FeCl(3)·6H(2)O with N(2)H(4)·H(2)O in ethylene glycol without any structure-directing agent. The resultant Fe(3)O(4) particles were characterized by transmission electron microscopy, N(2) adsorption, X-ray photoelectron spectroscopy, and thermal gravimetric analysis. It was demonstrated that the particle size varied in the range of 40-220 nm, and the pore size of particles was centered around 2 nm. The gases produced in the formation process of the particles played key role in the formation of the porous structure. The obtained porous magnetite was used as support to immobilize Au nanoparticles with size less than 2 nm with the assistance of L-cysteine. The as-prepared Fe(3)O(4) particles can effectively catalyze epoxidation of styrene, and the immobilization of Au nanoparticles on the Fe(3)O(4) support significantly improved the activity of the catalyst.

Thermal-Stable Carbon Nanotube-Supported Metal Nanocatalysts by Mesoporous Silica Coating

A universal strategy was developed for the preparation of high-temperature-stable carbon nanotube (CNT) -supported metal nanocatalysts by encapsulation with a mesoporous silica coating. Specifically, we first showed the design of one novel catalyst, Pt(@)CNT/SiO(2), with a controllable mesoporous silica coating in the range 11-39 nm containing pores ≈3 nm in diameter. The hollow porous silica shell offers a physical barrier to separate Pt nanoparticles from contact with each other, and at the same time the access of reactant species to Pt was not much affected. As a result, the catalyst showed high thermal stability against metal particle agglomeration or sintering even after being subjected to harsh treatments up to 500 °C. In addition, degradation in catalytic activity was minimized for the hydrogenation of nitrobenzene over the catalyst treated at 300 °C for 2 h. The scheme was also extended to coat porous silica onto the surfaces of CuRu(@)CNT and the resultant catalyst thereby can be reusable at least four times without loss of activity for the hydrogenolysis of glycerol. These results suggest that the as-prepared nanostructured CNT-supported catalysts may find promising applications, especially in those processes requiring rigorous conditions.

Imidazolium cation mediated synthesis of polystyrene–polyaniline core–shell structures

Herein we report a novel strategy to fabricate polystyrene–polyaniline (PS–PANi) core–shell structures using cationic PS latex particles without any further surface modification. Imidazolium cation functionalized monodispersed PS particles with diameter ranging from 100 to 700 nm were first prepared via precipitation polymerization and emulsion polymerization processes with the aid of ionic liquids containing imidazolium cations. Subsequently, AuCl4− was immobilized on the surface of PS particles via the imidazolium cations and acted as the oxidant for aniline polymerization, thus directing the core–shell structure formation as aniline hydrochloride was added into the system. PS–PANi core–shell spheres with uniform PANi shells were obtained. Furthermore, a seeded growth method was successfully applied in controlling the thickness of PANi shell. This is the first example in which the oxidant was immobilized on the surface of PS particles to direct the PS–PANi core–shell structure formation.

One-pot solvothermal method to synthesize platinum/W18O49 ultrafine nanowires and their catalytic performance

A simple solvothermal method was developed to prepare platinum/W18O49 ultrafine nanowires (<5 nm in diameter) through hydrolysis of WCl6 in ethanol-water solution in the presence of poly(N-vinyl-2-pyrrolidone) capping with Pt nanoparticles, and a series of Pt/W18O49 nanocomposites were obtained. These Pt/W18O49 composites were characterized by transmission electron microscopy, X-ray diffraction, Fourier-transform infrared spectra, X-ray photoelectron spectroscopy, and photoluminescence spectroscopy. It was demonstrated that PVP not only directed the formation of W18O49 nanowires, but also transferred the metal particles onto the oxide support without any size change. Due to the relatively strong interaction between Pt nanoparticles and the W18O49 nanowires, the as-prepared Pt/W18O49 composites exhibited blue shift in UV emission compared to the W18O49 nanowires, and displayed high activity and excellent stability for hydrogenation of p-chloronitrobenzene to p-chloroaniline with a selectivity of 99.7%.