Changliang Huang

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.

Cyclization of o-phenylenediamines by CO2 in the presence of H2 for the synthesis of benzimidazoles

The cyclization of o-phenylenediamines by CO2 in the presence of H2 was presented to directly synthesize benzimidazoles, and a series of benzimidazoles were obtained in excellent yields using RuCl2(dppe)2 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.

Controllable synthesis of supported Cu–M (M =Pt, Pd, Ru, Rh) bimetal nanocatalysts and their catalytic performances

Based on the galvanic replacement reaction between Cu nanoparticles and noble metal ions, a simple and efficient strategy was developed for the preparation of supported Cu–M (M = Pt, Pd, Ru, Rh) bimetallic nanoparticles under intense ultrasonication irradiation at ambient environment. A series of Cu–M/TiO2 bimetal catalysts with controllable composition, metal particle size less than 2 nm and narrow size distribution were obtained, and characterized by transmission electron microscopy (TEM), high resolution transmission electron microscope (HRTEM) with scanning TEM (STEM) mode, energy-dispersive X-ray spectrometers (EDS), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), and ICP-AES analysis. It was demonstrated that most of the metal particles were present in the form of bimetallic state. The mechanism of this strategy was discussed. The resultant Cu–Pd/TiO2 was used to reduce nitrate at room temperature, and it exhibited extremely high activity.

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.

Ionic liquid-stabilized graphene and its use in immobilizing a metal nanocatalyst

A new ionic liquid (IL), 1-butyl-3-methylimidazolium cholate, was first synthesized through an ion exchange reaction of 1-butyl-3-methylimidazolium chloride with sodium cholate. Stable aqueous dispersions of graphene were achieved by exfoliating graphite in the presence of the IL under ultrasonication. Both transmission electron microscopy and Raman measurements showed that the IL-stabilized graphene (IL–G) sheets existed with only a few (<5) layers. Furthermore, the IL–G was used to immobilize noble metal nanoparticles (Pt, Pd, Ru, Rh, etc), and a series of graphene–metal (G–M) composites with metal size ≤2 nm and very narrow size distributions were obtained. The resulting G–M exhibited superior catalytic performance with respect to hydrogenation of arenes. In particular, the as-prepared G–Ru with Ru content of 5% was very active for the hydrogenation of benzene to hexane with a turnover frequency as high as 6000 h−1. The catalysts could be reused without detectable loss of activity, a result of their stable structure.

Diatomite-supported Pd–M (M = Cu, Co, Ni) bimetal nanocatalysts for selective hydrogenation of long-chain aliphatic esters

Diatomite supported Pd-M (M=Cu, Co, Ni) bimetal nanocatalysts with various metal compositions were prepared and characterized by means of X-ray diffraction, transmission electron microscopy, and X-ray photoelectron spectroscopy. It was demonstrated that the metal nanoparticles were uniformly distributed on the support, and their size was centered around 8 nm with a relatively narrow size distribution. The catalysts were used to catalyze hydrogenation of long-chain aliphatic esters, including methyl palmitate, methyl stearate, and methyl laurate. It was indicated that the all diatomite-supported Pd-based bimetal catalysts were active to the selective hydrogenation of long-chain esters to corresponding alcohols at 270°C, originated from the synergistic effect between the metal particles and the diatomite support. For the selective hydrogenation of methyl palmitate, Pd-Cu/diatomite with metal loading of 1% and Pd/Cu=3 displayed the highest performance, giving a 1-hexadecanol yield of 82.9% at the substrate conversion of 98.8%.

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%.

Pt/titania/reduced graphite oxide nanocomposite: An efficient catalyst for nitrobenzene hydrogenation

In this work, a ternary composite, Pt/TiO(2)/RGO (reduced graphite oxide), was prepared via immobilizing Pt particles onto the TiO(2)/RGO composite that was obtained via redox reaction of TiCl(3) and GO. The composite was characterized by different techniques including X-ray diffraction, transmission electron microscopy, and X-ray photoelectron spectroscopy. The TiO(2) particles with size less than 10 nm were uniformly distributed throughout the RGO, and almost each Pt particle with size around 3 nm adhered to TiO(2) particles, resulting in high dispersion of all Pt particles on the support. The Pt particles were in the electron-deficient state due to the strong interactions with the TiO(2) particles and the RGO support. The catalytic performance of the composite for nitrobenzene hydrogenation was investigated under solvent-free condition. It was indicated that the Pt/TiO(2)/RGO catalyst exhibited high activity with a turnover frequency (e.g., 59,000 h(-1)) as well as superior selectivity to aniline (e.g., >99%). Moreover, the catalyst can be reused for six times without any activity loss, which resulted from the stable structure of the catalyst.