Photoelectron spectroscopy of ammonia via a fast predissociative state

We report a study on resonance enhanced multiphoton ionization photoelectron spectroscopy (REMPI-PES) involving the fast predissociative (A) over tilde state of ammonia, using nano- and femtosecond lasers. The multiphoton scheme involves (1 + 1), (2 + 2), (2 + 2) + 1 and (2 + 2) + 2 photon processes. We have found a progression of stretching vibrations nu(1) in the PE spectrum when pumping NH3 (A) over tilde upsilon(2) = 0, 1 and 3 as intermediate states. The stretching vibration intensity distributions in the photoelectron spectrum are calculated by using the Chebychev method of the wavepacket propagation. The femtosecond spectrum shows a similar feature to the nanosecond spectrum. However, high laser power also causes band broadening and shifting effect as well as above threshold multiphoton ionization.

Highly ordered periodic mesoporous ethanesilica synthesized under neutral conditions

Highly ordered mesoporous ethanesilica (MES) with 2D hexagonal structure was synthesized from 1,2-bis(trimethoxysilyl) ethane under neutral conditions for the first time. Divalent salts, such as NiCl2, MgCl2, ZnCl2, ZnSO4 and Zn(NO3)(2), were used to help the formation of the ordered mesostructure. The MES samples were characterized by powder X-ray diffraction, nitrogen sorption, transmission electron microscopy, FT-IR, C-13 and Si-29 solid-state NMR and thermal gravimetric analysis. A phase transition from a disordered wormhole-like structure to an ordered P6mm structure was observed upon the addition of inorganic salts. The pore size of the MES decreases from 4.7 to 3.9 nm with increasing content of the inorganic salts. Fluoride was also found to be important for the formation of ordered MES under neutral conditions.

HMLH1 gene mutation in gastric cancer patients and their kindred

AIM: To study the status of hMLH1 gene point mutations of gastric cancer kindreds and gastric cancer patients from northern China, and to find out gene mutation status in the population susceptible to gastric cancer.

Development of electrocatalysts for direct alcohol fuel cells

In the present review, we summarize the recent progress in electrocatalysts for direct alcohol fuel cells, focussing on the research of electrocatalysts for both alcohol oxidation and oxygen reduction, which are crucial in the development of fuel cells. A modified EG (ethylene polyol) method to prepare well-dispersed nano-sized Pt-based electrocatalysts with high loadings is reported. By this method, a more active carbon supported PtRu catalyst for methanol oxidation reaction and a PtSn catalyst for ethanol oxidation reaction have been synthesized successfully. Furthermore, a methanol tolerant Pd-based catalyst for cathode oxygen reduction reaction has been developed. HRTEM and HR-EDS have been employed to characterize the microstructure and micro-components of the above electrocatalysts. Results show that the bimetallic electrocatalysts prepared by the modified EG method display uniform size and homogeneous components at nanometer scale.

Size-controllable synthesis of monodispersed SnO2 nanoparticles and application in electrocatalysts

Size-controllable tin oxide nanoparticles are prepared by heating ethylene glycol solutions containing SnCl2 at atmospheric pressure. The particles were characterized by means of transmission electron microscopic (TEM), X-ray diffraction (XRD) studies. TEM micrographs show that the obtained material are spherical nanoparticles, the size and size distribution of which depends on the initial experimental conditions of pH value, reaction time, water concentration, and tin precursor concentration. The XRD pattern result shows that the obtained powder is SnO2 with tetragonal crystalline structure. On the basis of UV/vis and FTIR characterization, the formation mechanism of SnO2 nanoparticles is deduced. Moreover, the SnO2 nanoparticles were employed to synthesize carbon-supported PtSnO2 catalyst, and it exhibits surprisingly high promoting catalytic activity for ethanol electrooxidation.

Structure and chemical composition of supported Pt-Sn electrocatalysts for ethanol oxidation

Carbon supported PtSn alloy and PtSnOx particles with nominal Pt:Sn ratios of 3:1 were prepared by a modified polyol method. High resolution transmission electron microscopy (HRTEM) and X-ray microchemical analysis were used to characterize the composition, size, distribution, and morphology of PtSn particles. The particles are predominantly single nanocrystals with diameters in the order of 2.0-3.0 nm. According to the XRD results, the lattice constant of Pt in the PtSn alloy is dilated due to Sn atoms penetrating into the Pt crystalline lattice. While for PtSnOx nanoparticles, the lattice constant of Pt only changed a little. HRTEM micrograph of PtSnOx clearly shows that the change of the spacing of Pt (111) plane is neglectable, meanwhile, SnO2 nanoparticles, characterized with the nominal 0.264 nm spacing of SnO2 (10 1) plane, were found in the vicinity of Pt particles. In contrast, the HRTEM micrograph of PtSn alloy shows that the spacing of Pt (111) plane extends to 0.234 nm from the original 0.226 nm. High resolution energy dispersive X-ray spectroscopy (HR-EDS) analyses show that all investigated particles in the two PtSn catalysts represent uniform Pt/Sn compositions very close to the nominal one. Cyclic voltammograms (CV) in sulfuric acid show that the hydrogen ad/desorption was inhibited on the surface of PtSn alloy compared to that on the surface of the PtSnOx catalyst. PtSnOx catalyst showed higher catalytic activity for ethanol electro-oxidation than PtSn alloy from the results of chronoamperometry (CA) analysis and the performance of direct ethanol fuel cells (DEFCs). It is deduced that the unchanged lattice parameter of Pt in the PtSnOx catalyst is favorable to ethanol adsorption and meanwhile, tin oxide in the vicinity of Pt nanoparticles could offer oxygen species conveniently to remove the CO-like species of ethanolic residues to free Pt active sites. (C) 2005 Elsevier Ltd. All rights reserved.

Selective oxidations on recoverable catalysts assembled in emulsions

Catalysts assembled in emulsions are found to be potentially recoverable and efficient for a number of catalytic reactions. The catalysts composed of polyoxometalate anions and quaternary ammonium cations have been designed and synthesized according to the catalytic reactions and by optimizing the structures of cations and anions. The catalysts act essentially as surfactants, which are uniformly distributed in the interface of the emulsion droplets, and accordingly behave like homogeneous catalysts. The catalysts show remarkable selectivity and activity in the oxidation of sulfur-containing molecules to sulfones in diesel and the selective oxidation of alcohols to ketones, using H2O2 as oxidant. For an example, the catalyst demonstrated over 96% efficiency of H2O2 and similar to 100% selectivity to sulfones for the selective oxidation of sulfur-containing molecules in real diesel. Moreover, the catalysts can be separated and recycled by a simple demulsification and re-emulsification.