Structure and acidity of Mo/H-MCM-22 catalysts studied by NMR spectroscopy

A comprehensive study on physical and chemical properties of Mo/MCM-22 bifunctional catalysts has been made by using combined analytic and spectroscopic techniques, such as adsorption, elemental analysis, and Xe-129 and P-31 NMR of adsorbed trialkylphosphine oxide probe molecules. Samples prepared by the impregnation method with Mo loadings ranging from 2-10 wt.% have been examined and the results are compared with that obtained from samples prepared by mechanical mixing using MoO3 or Mo2C as agents. Sample calcination treatment is essential in achieving a well-dispersed metal species in Mo/MCM-22. It was found that, upon initial incorporation, the Mo species tend to inactivate both Bronsted and Lewis sites locate predominantly in the supercages rather than the 10-membered ring channels of MCM-22. However, as the Mo loading exceeds 6 wt.%, the excessive Mo species tend to migrate toward extracrystalline surfaces of the catalyst. A consistent decrease in concentrations of acid sites with increasing Mo loading < 6 wt.% was found, especially for those with higher acid strengths. Upon loading of Mo > 6 wt.%, further decreases in both Bronsted and Lewis acidities were observed. These results provide crucial supports for interpreting the peculiar behaviors previously observed during the conversion of methane to benzene over Mo/MCM-22 catalyst under non-oxidative conditions, in which an optimal performance was achieved with a Mo loading of 6 wt.%. The effects of Mo incorporation on porosity and acidity features of the catalyst are discussed. (C) 2004 Published by Elsevier B.V.

Preparation of highly active Pt/C cathode electrocatalysts for DMFCs by an improved aqueous impregnation method

An improved aqueous impregnation method was used to prepare 40 wt% Pt/C electrocatalysts. TEM analysis of the samples showed that the Pt particles impregnated for a short time have a very narrow size distribution in the range of 1-4 nm with an average size of 2.6 nm. UV-vis spectroscopy measurements verified that the redox reaction between PtCl62- and formaldehyde took place with a slow rate at ambient temperature via a two-step reaction path, where PtCl42- serves as an intermediate. The use of the short-time-impregnated 40 wt% Pt/C as cathode electrocatalysts in direct methanol fuel cells yields better performance than that of commercial 40 wt% Pt/C electrocatalyst. Experimental evidence provides clues for the fundamental understanding of elementary steps of the redox reactions, which helps in guiding the design and preparation of highly dispersed Pt catalyst for fuel cells.

Reduction property and catalytic activity of Ce1-XNiXO2 mixed oxide catalysts for CH4 oxidation

Ce1-XNiXO2 oxides with X varying from 0.05 to 0.5 were prepared by different methods and characterized by XRD and TPR techniques. Ce(0.7)Mi(0.3)O(2) sample prepared by sol-gel method shows the highest reducibility and the highest catalytic activity for methane combustion. Three kinds of Ni phases co-exist in the Ce1-XNiXO2 catalysts prepared by sol-gel method: (i) aggregated NiO on the support CeO2, (ii) highly dispersed NiO with strong interaction with CeO2 and (iii) Ni atoms incorporated into CeO2 lattice. The distribution of different Ni species strongly depends on the preparation methods. The highly dispersed NiO shows the highest activity for methane combustion. The NiO aggregated on the support CeO2 shows lower catalytic activity for methane combustion, while the least catalytic activity is found for the Ni species incorporated into CeO2. Any oxygen vacancy formed in CeO2 lattice due to the incorporating of Ni atoms adsorbs and activates the molecular oxygen to form active oxygen species. So the highest catalytic activity for methane combustion on Ce0.7Ni0.3O2 catalyst is attributed not only to the highly dispersed Ni species but also to the more active oxygen species formed. (C) 2002 Elsevier Science B.V. All rights reserved.

Synthesis of carbon nanotube bundles with mesoporous structure by a self-assembly solvothermal route

A kind of carbon nanotube bundle has been synthesized by a simple one-step solvothermal reaction between Na and hexachlorobenzene (HCB) using NiCl2 as catalyst precursor. Before the reaction, NiCl2 was initially dispersed ultrasonically in cyclohexane then prereduced by Na at 230degreesC to produce small Ni particles in reduced state. The tubes thus-produced have a uniform outer diameter of about 20 nm, an inner diameter of 4 nm, and are highly ordered assembled as bundles which have a 2D hexagonal arrangement as proven by SAXS and TEM experiments.

Influence of iron promoter on catalytic properties of Rh-Mn-Li/SiO2 for CO hydrogenation

The effect of iron promoter on the catalytic properties of Rh-Mn-Li/SiO2 catalyst in the synthesis Of C-2 oxygenates from syngas was investigated by means of the following techniques: CO hydrogenation reaction, temperature-programmed reduction (TPR), temperature-programmed desorption and reaction of adsorbed CO (CO-TPD and TPSR) and pulse adsorption of CO. The results showed that the addition of iron promoter could improve the activity of the catalysts. Unexpectedly, the yield of C-2 oxygenates increased greatly from 331.6 up to 457.5 g/(kg h) when 0.05% Fe was added into Rh-Mn-Li/SiO2 catalyst, while no change in the selectivity to C-2 oxygenates was observed. However, the activity and selectivity Of C-2 oxygenates were greatly decreased if the Fe amount exceeded 1.0%. The existence of a little iron decreased the reducibility of Rh precursor, while the reduction of Fe component itself became easier. CO uptake decreased with increasing the quantity of Fe addition. This phenomenon was further confirmed by CO-TPD results. The CO-TPD and TPSR results showed that only the strongly adsorbed CO could be hydrogenated, while the weakly adsorbed CO was desorbed. We propose that Fe is highly dispersed and in close contact with Rh and Mn; such arrangements were responsible for the high yield Of C-2 oxygenates. (C) 2002 Elsevier Science B.V. All rights reserved.

Gold Nanoparticle-based Colorimetric Sensor for pH Sensing

We present a newly designed colormetric sensor sensitive to pH value based on a gold nanocomposite composed of gold nanoparticles and pH-sensitive polymer{dodecylthioether end functionalized poly[2-(diethlamino) ethyl methacrylate], poly(DEAEMA)-DDT}. We have shown that this design can produce stable GNP precipitate under weakly basic condition(pH=7.5) and this precipitate can be dispersed in acidic solution(pH=4.0), due to the 2-(diethylamino) ethyl methacrylate protonated by H+.

Blends of Polypropylene and Syndiotactic 1,2-Polybutadiene: Morphology, Crystallization Behaviors and Mechanical Properties

Morphologies, crystallization behavior and mechanical properties of polypropylene(PP)/syndiotactic 1,2-polybutadiene(s-1,2 PB) blends were investigated. Morphology observation shows the well dispersed domains of s-1,2 PB in PP matrix with the rather small domain sizes from 0.1 to 0.5 mu m when the s-1,2 PB content increases from 5% to 20% (mass fraction) in the blends, and the phase structure tends to become co-continuous as s-1,2 PB content further increases.

Preparation and characterization of polyimide/Al2O3 hybrid films by sol-gel process

A sol-gel process has been developed to prepare polyimide (PI)/Al2O3 hybrid films with different contents of Al2O3 based on pyromellitic dianhydride (PMDA) and 4,4'-oxydianiline (ODA) as monomers. FESEM and TEM images indicated that Al2O3 particles are relatively well dispersed in the polyimide matrix after ultrasonic treatment of the sol from aluminum isopropoxide and thermal imidization of the gel film. The dimensional stability, thermal stability, mechanical properties of hybrid PI films were improved obviously by an addition of adequate Al2O3 content, whereas, dielectric property and the elongation at break decreased with the increase of Al2O3 content. Surprisingly, the corona-resistance property of hybrid film was improved greatly with increasing Al2O3 content within certain range as compared with pure PI film.

Electrospun palladium nanoparticle-loaded carbon nanofibers and their electrocatalytic activities towards hydrogen peroxide and NADH

Palladium nanoparticle-loaded carbon nanofibers (Pd/CNFs) were synthesized by the combination of electrospinning and thermal treatment processes. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) images show that spherical Pd nanoparticles (NPs) are well-dispersed on the surfaces of CNFs or embedded in CNFs. X-ray diffraction (XRD) pattern indicates that cubic phase of Pd was formed during the reduction and carbonization processes, and the presence of Pd NPs promoted the graphitization of CNFs. This nanocomposite material exhibited high electric conductivity and accelerated the electron transfer, as verified by electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV).

Growth mechanism. of synthetic imogolite nanotubes

By controlling the surface effects during droplet evaporation of imogolite solutions, imogolite nanotubes were dispersed individually and directly observed by transmission electron microscopy (TEM), and the structure evolution of imogolite nanotubes in the synthetic process was investigated. It was found that the number of imogolite nanotubes continuously increased with time in the whole reaction. The average length grew slowly over time after a remarkable increase in the initial 24 h, and the length distribution experienced a similar variation with the polydispersity index always below 2. No appreciable changes in tube diameters were detected under TEM observation.

Monodisperse raspberry-like gold submicrometer spheres: Large-scale synthesis and interface assembling for colloid sphere array

We first suggested a one-pot method to synthesize monodisperse raspberry-like submicrometer gold spheres (MRSGS) with high yield. The resulting gold spheres were characterized by scanning electron microscopy, transmission electron microscopy, energy-dispersed X-ray spectroscopy, X-ray photoelectron spectroscopy, X-ray diffraction, and electrochemical technology. It was found that the rough structure provided by raspberry-like gold spheres led to a tremendous electrochemical active area, which was very important because these novel hierarchical gold spheres will probably find important applications in biosensors, electrocatalysis, and others.

One Pot, Facile Synthesis of Hierarchical Silver Nanostrip Assembling Architecture

Here we present a simple wet-chemical approach to synthesize flower-like silver nanostrip assembling architecture at room temperature. Transmission electron microscopy (TEM) and scanning electron microscopy (SEM) images indicate that these microstructures with the diameter of similar to 500nm exhibit hietarchical characteristic. X-ray diffraction (XRD), energy-dispersed X-ray spectroscopy (EDX) and Raman spectroscopy indicate that poly (o-diaminobenzene) (PDB) also exists in the silver hierarchical microstructure.

Near-infrared polymer light-emitting diodes based on infrared dye doped poly(N-vinylcarbazole) film

Infrared light-emitting diodes possess potential applications in optical communication and safety detection. in this paper, we fabricated near-infrared light-emitting diodes possess potential applications in optical communication and safety detection. in this paper, we fabricated near-infrared polymer light-emitting diode employing a commercial near-infrared (NIR) organic dye as an emissive dopant dispersed within poly(N-vinylcarbazole) (PVK) by spin-casting method. The used device structure was indium tin oxide/3,4-polyethylene-dioxythiophene-polystyrene sulfonate/PVK: NIR dye/Al.

Highly active PtRu catalysts supported on carbon nanotubes prepared by modified impregnation method for methanol electro-oxidation

A simple and rapid synthesis method (denoted as modified impregnation method, MI) for PtRu/CNTs (MI) and PtRu/C (MI) was presented. PtRu/CNTs (MI) and PtRu/C (MI) catalysts were characterized by transmission electron microscopy (TEM) and X-ray diffractometry. It was shown that Pt-Ru particles with small average size (2.7 nm) were uniformly dispersed on carbon supports (carbon nanotubes and carbon black) and displayed the characteristic diffraction peaks of Pt face-centered cubic structure.

Uniform YVO4:Ln(3+) (Ln = Eu, Dy, and Sm) nanocrystals: Solvothermal synthesis and luminescence properties

Well-dispersed YVO4:Ln(3+) (Ln = Eu, Dy, and Sm) nanocrystals with uniform morphology and size have been synthesized via a facile solvothermal route. XRD results demonstrate that all of the three samples can be well indexed to the pure tetragonal phase Of YVO4, indicating that the Eu3+, Dy3+, and Sm3+ have been effectively doped into the host lattices of YVO4. TEM images show that the YVO4 nanocrystals exhibit ellipsoid shape and a mean size of about 20 nm, which is in good agreement with the estimation of XRD results.