STUDIES OF MULTICOMPONENT COMPLEX OXIDE CATALYSTS FOR OXIDATIVE COUPLING OF METHANE VI.SURFACE BASICITY AND SURFACE ACTIVE OXYGEN SPECIES OF LiTi_xLa_(1-x)O_2 λ MULTICOMPONENT OXIDE CATALYSTS

The surface basicity of Ti-La-Li multicoinponent oxides has been investigated by means of CO2-TPD. The experiment results show that C2 (C2H6 C2H4) selectivity is related to surface basic strength. The surface active oxygen species have also been characterized by means of XPS, O2-TPD and so on. It has been indicated that C2 selectivity and CH4 conversion are correlated with lattice oxygen and the adsorbed oxygen on the surface of the catalyst respectively In the O2-TPD experiments, it has also been found that there are three kinds of oxygen species on the surface of the series catalvsts, which are a (100℃ 750℃) Among them α-oxvgen causes deep oxidation whileβand γ oxygen species are related to oxidalive coupling of methane (OCM).     

Separation of chlamydosporol epimers by reversed-phase HPLC using commercial solvent optimisation software

Summary Two epimers of the mycotoxin chlamydosporol were separated by HPLC on an RP-18 column using a quaternary mobile phase consisting of water (79.1%), methanol (10.0%), acetonitrile (10.4%) and tetrahydrofuran (0.5%), with a flow rate of 1 ml min^–1. This optimal composition of mobile phase, with which the resolution value for the two epimers (1 and2) was 2.73 with retention times of 5.88 and 7.12 min, respectively, was achieved by the application of Philips Solvent Optimisation Software PU 6100. The presence of free silanols on the stationary phase was shown to be an essential requirement for the separation of the chlamydosporol epimers.     

Determination of Inorganic Arsenic Species by Electrochemical Hydride Generation Atomic Absorption Spectrometry with Selective Electrochemical Reduction

A new direct procedure for the determination of inorganic arsenic species was developed by electrochemical hydride generation atomic absorption spectrometry （EcHG-AAS） with selective electrochemical reduction. The determination of inorganic arsenic species is based on the fact that As（Ⅲ） shows significantly higher absorbance at low electrolytic currents than As（Ⅴ） in 0.3 mol·L^-1 H2SO4. The electrolytic current used for the determination of As（Ⅲ） without considerable interferences of As（Ⅴ） was 0.4 A, whereas the current for the determination of As（Ⅲ） and As（Ⅴ） was 1.2 A. For equal concentrations of As（Ⅲ） and As（Ⅴ） in a sample, the interferences of As（Ⅴ） during the As（Ⅲ） determination were smaller than 5%. The absorbance for As（Ⅴ） could be calculated by subtracting that for As（Ⅲ） measured at 0.4 A from the total absorbance for As（Ⅲ） and As（Ⅴ） measured at 1.2 A, and then the concentration of As（Ⅴ） can be obtained by its calibration curve at 1.2 A. The methodology developed provided the detection limits of 0.3 and 0.6 ng·mL^-1 for As（Ⅲ） and As（Ⅴ）, respectively. The relative standard deviations were of 3.5% for 20 ng·mL^-1 As（Ⅲ） and 3.2% for 20 ng·mL^-1 As（Ⅴ）. The method was successfully applied to determination of soluble inorganic arsenic species in Chinese medicine.     

Copper-catalyzed addition reaction of γ,γ-dialkoxyallylic zirconium species with imines

In the presence of CuCN, reaction of γ,γ-dialkoxyallylic zirconium species 1 with imines proceeded at the γ-position of 1 to give gem-dialkoxyhomoallylic amines 3 in high yield. In this reaction, γ,γ-dialkoxyallylic zirconium species 1 acts as an α,β-unsaturated acyl anion equivalent.     

Comparative analysis of the underground parts ofGentiana species by HPLC with diode-array and mass spectrometric detection

Summary The aim of this work was to compare the chemical composition of the underground parts (roots and rhizomes) ofGentiana cruciata L.,Gentiana pneumonanthe L., andGentiana asclepiadea L.— the three gentians native to Hungary—with that of the widely used stomachicGentiana lutea L., to determine which of the three Hungarian species could be used as a substitute forGentiana lutea in pharmaceutical preparations. The four gentians were compared by means of RPHPLC with diode-array detection (DAD) and electrospray ionization-mass spectrometric detection (ESI-MSD). The quantities of the lead compounds, the secoiridoid-glycosides, in 220 samples of the underground parts of gentians originating from several locations in Hungary, were determined by a more economical RPHPLC-DAD method. The occurrence of the characteristic compounds investigated—bitter principles and xanthones—in the underground parts of the speciesGentiana asclepiadea L. suggest it might be a potential replacement forGentiana lutea L. in pharmaceutical products. Presented at Balaton Symposium '01 on High-Performance Separation Methods, Siófok, Hungary, September 2–4, 2001     

甲烷氧化偶联催化剂La2O3／SrCO3—BaCO3的催化活性与表征

在甲烷氧化偶联制Ｃ２烃的研究中，人们发现碱土金属与稀土金属组成的复合氧化物催化剂具有高的催化活性［１，２］．稀土化合物作为有希望的工业催化剂之一，已受到广泛的关注．一般认为，它们含有的氧空位对活化甲烷的有效氧物种有利．Ｄｅｂｅｙ等在１％Ｓｒ／Ｌａ２Ｏ...     

Visual observation of contact-induced intercrystalline migration of aromatic species adsorbed in zeolites by fluorescence microscopy.

Intercrystalline migration and a migration-assisted chemical reaction of adsorbed aromatic species between zeolite particles in physical contact were visualized by fluorescence microscopy coupled with a particle manipulation technique. The luminescence color characteristics of particular zeolite particles originating from the specific photochemistry of adsorbed species was exploited to follow the migration of the molecules. Two examples are shown that are relevant to the visualization of the time-dependent migration process: A one guest-two sets of zeolite crystals system: chrysene (Chry)-loaded zeolite Na+ -X (the sodium form of zeolite X) crystals were placed in contact with unloaded Tl+ -X (thallium-exchanged X) crystals and allowed to stand at room temperature. Initially, the blue fluorescence of Chry was detected only from the Na+ -X particles, but later, the development of green phosphorescence emission was discernible from the Tl+ -X which suggests that Chry migrated from the Na+ -X to the Tl+ -X crystals. A two guest-species systems: Electron-donating Chry-loaded Na+ -X crystals were placed in contact with electron-accepting 1,2,4,5-tetracyanobenzene (TCNB)-loaded Na+ -X or Na+ -Y crystals. With time, the former system (Chry/Na+ -X and TCNB/Na+ -X) gave rise to the emission of Chry-TCNB charge-transfer complexes resulting mainly from the migration of Chry while the latter system (Chry/Na+ -X and TCNB/Na+ -Y) afforded the same emission resulting largely from the migration of TCNB. The present investigation reveals that there is a certain direction for guest migration depending on the zeolite host and the nature of host-guest or guest-guest interaction.     

Variable low-mass filtering using an electrodynamic ion funnel

An adjustable low-mass filter has been developed for an electrospray ionization (ESI) source to block ions associated with unwanted background species from entering the mass spectrometer. The low-mass filter is made by using an adjustable potential energy barrier from the conductance-limiting plate of an electrodynamic ion funnel, which prohibits species with higher ion mobilities from exiting the ESI source. We show that this arrangement provides a linear voltage adjustment for low-mass filtering from m/z 0 to 500. Mass filtering above m/z 500 is also performed; however, higher-mass species are attenuated. The mass filter was tested with a liquid chromatography/mass spectrometry (LC/MS) analysis of a bovine serum albumin (BSA) tryptic digest and resulted in the ability to block low-mass, background species, which accounted for 40-70% of the total ion current immediately behind the ESI source during peak elution and detection.     

HPLC-ICP-MS在紫菜中砷形态分析的应用

通过HPLC－ICP－MS联用技术初步探讨了紫菜中砷的形态；选用了纯水萃取，再用甲醇稀释，用阴离子交换色谱柱经HPLC分离，再用ICP－MS测定，实验发现了2个未知形态色谱峰；该技术将液相色谱的分离技术与ICP－MS高灵敏度的检测方式相结合，具有分离效果好，灵敏度高，耗样量少，速度快，线性范围宽等优点。     

Dehydrogenation of ethylbenzene with CO2 over Cr-MCM-41 catalyst

M-MCM-41 catalysts (M: V, Cr, Fe, and Ga) prepared by direct hydrothermal synthesis (DHT) have been tested for dehydrogenation of ethylbenzene with CO₂. The synthesized materials were characterized by X-ray diffraction (XRD), N₂ adsorption (77 K), and diffuse reflectance UV–vis spectroscopic measurements. Cr-MCM-41 showed the highest activity among M-MCM-41 catalysts tested, resulting in the production of styrene with the conversion of 65% and the selectivity above 90%. The rate of styrene formation increased with increasing Cr loading up to 1.7 wt.%. It is suggested that Cr(VI)O₄ in tetrahedral coordination is formed as an active monochromate species and reduced to Cr(III)O₆ in octahedral coordination as a less active polychromate species during the reaction. Deactivated catalyst was regenerated by a treatment with gaseous oxygen or CO₂, during which redistribution as well as reoxidation of polymeric Cr(III)O₆ octahedra to monomeric Cr(VI)O₄ tetrahedra was observed. The rate of CO formation increased together with that of styrene formation, while the rate of H₂ formation decreased, with increasing partial pressure of CO₂. It was confirmed that reverse water-gas shift reaction took place over Cr-MCM-41 by a separate experiment. The rate of CO formation during the dehydrogenation of ethylbenzene with CO₂ over Cr-MCM-41 was well accounted for by assuming parallel occurrence of two reactions, i.e., direct oxidative dehydrogenation of ethylbenzene with CO₂ and simple dehydrogenation of ethylbenzene thermodynamically assisted by reverse water-gas shift reaction.