酸碱处理对ZSM-5分子筛物化性质和反应性能的影响

考察了碱处理、先碱后两步酸处理对HZSM-5分子筛物化性质以及苯与甲醇烷基化反应性能的影响。结果表明,碱处理在脱除分子筛中非骨架硅的同时,提高了晶孔的利用率,也中和了分子筛的强酸中心,使催化剂活化甲醇的能力减弱,苯与甲醇反应活性降低;先碱后两步酸处理既脱除了分子筛中的非骨架铝,也恢复了一部分强酸中心,提高了苯与甲醇的反应活性。进一步考察了先碱后两步酸处理中不同碱浓度的影响,结果表明,适宜浓度的碱处理后再两步酸处理,一方面,能脱除分子筛的非骨架硅铝物种,使分子筛的颗粒粒径更加均匀;另一方面,分子筛的强酸中心有所减少,降低了催化剂的积炭失活速率,苯转化率提高15%以上。     

Experimental study of embedding of attractors in concentration space

The embedding of attractors and their stable and unstable manifolds can be studied experimentally by controlled addition of chemical species to bring about a particular response. For stable small amplitude oscillations near a Hopf bifurcation from a steady state the embedding can be completely determined even in systems where two of the species are not observable. A quenching of the oscillations by dilution candetermine the steady state concentrations. A species that cannot quench the oscillations almost certainly cannot be an essential component of the oscillation. The method can be extended to a study of attractor associated with subharmonic and quasiperiodic bifurcations and of attractors corresponding to nonperiodic motion. We present preliminary results for a subharmonic bifurcation.     

Light activated patterning of dye-labeled molecules on surfaces

This Communication describes a novel method for patterning proteins, ligands, or other organic/inorganic species onto solid substrates. The process works by linking the moiety of interest to a fluorophore that can be subsequently photobleached and bound to the interface. The technique can be performed in aqueous solution and allows several species to be addressed onto the surface simultaneously by using different frequencies of light. Because the method can be used with fluorophores excited by visible light, shorter and more damaging wavelengths can be avoided.     

A new access to Gibbs energies of transfer of ions across liquid|liquid interfaces and a new method to study electrochemical processes at well-defined three-phase junctions

Droplets of polar and nonpolar aprotic solvents containing dissolved electroactive species can be easily attached to paraffin-impregnated graphite electrodes. When the electrode with the attached droplet is introduced into an aqueous electrolyte solution, the electrochemical reactions of the dissolved species can be elegantly studied. Provided the droplet does not contain a dissolved electrolyte, the electrochemical reaction will be confined to the very edge of the three-phase junction droplet|graphite|aqueous electrolyte. When a neutral species is oxidised, two pathways are possible: the oxidised species can remain in the droplet and anions will be transferred from the aqueous solution to the organic solvent, or the oxidised species may leave the droplet and enter the aqueous solution. Depending on the nature of the dissolved species, the nature of the organic solvent, the presence or absence of appropriate anions and cations in the two liquid phases, very different reaction pathways are possible. The new approach allows studies of ion transfer between immiscible solvents to be performed with a three-electrode potentiostat. Electrochemical determinations of the Gibbs energy of ion transfer between aqueous and nonpolar nonaqueous liquids are possible, whereas conventional ion transfer studies require the presence of a dissociated electrolyte in the organic phase. The new method considerably widens the spectrum of accessible ions.     

Characterization of stable aluminium-citrate species as reference substances for aluminium speciation by ion chromatography

Well-defined anionic aluminium-citrate species are accessible from crystalline aluminium complexes. The solution chemistry of those species can be investigated using ion chromatography as a powerful tool for aluminium speciation in aqueous samples. The separation of three anionic aluminium-citrate complexes by anion exchange chromatography is possible within 5 min using isocratic conditions. The element specific detection was done by online coupled ICP-AES. The remaining charge of the complexes after dissolution can be determined by ion chromatography using a retention model. Time-dependent monitoring of the species distribution gave information about the species stabilities and the decomposition pathways. With citric acid as an aluminium chelator partially very stable anionic species are observed. These complexes are important components in biological systems. An example for the practical use of the separation method and the well-defined standards is given for plant sap, which showed two species with similar behavior compared to the investigated stable aluminium-citrate complexes.     

Speciation of aluminum in soil extracts using cation and anion exchangers followed by a flow-injection system with fluorescence detection using lumogallion.

Flow-injection analysis (FIA) with fluorescence detection of aluminum using lumogallion was applied to the chemical speciation of aluminum in soil extracts after the separation of aluminum species with ionic exchangers. Aluminum complexes with organic substances (anion species) can be specified from other species by using a strongly acidic cation exchanger in the pH range of 3 to 5. Furthermore, aluminum can be separated into three categories, namely, (i) the Al3+ and Al-OH complex, (ii) aluminum organic complexes (cation species), and (iii) its anion species by using a strongly acidic and a weakly acidic cation exchanger at around pH 5. A considerable percentage of water-soluble aluminum in soils was found to be complexes with humic substances.     

On the reactivity of surface methoxy species in acidic zeolites

The in situ preparation and isolation of surface methoxy species on acidic zeolites are followed by further investigations of their reactivity in heterogeneously catalyzed reactions. For the first time, the following solid-state NMR evidence for the high reactivity of surface methoxy species has been obtained: (i) Surface methoxy species react readily with ammonia on acidic zeolites at room temperature, by which methylamines and methylammonium cations are formed. (ii) The transformation of surface methoxy species to other alkoxy species can be achieved by the reaction of surface methoxy species and corresponding alkyl halides on acidic zeolites. (iii) Surface methoxy species react readily with hydrochloride, giving methyl chloride as the sole product. (iv) The classic Koch carbonylation reaction and Ritter reaction in solution can be performed with surface methoxy species on acidic zeolites. (v) Carbon monoxide and carbon dioxide are produced by the oxidation of surface methoxy species in the presence of oxygen. The stability and reactivity of surface methoxy species are discussed in comparison with other surface alkoxy species (> C(1) species).     

On the molecular structure of uranium dicarbide: T-shape versus linear isomers

A theoretical study of the molecular structure of uranium dicarbide has been carried out employing DFT, coupled cluster, and multiconfigurational methods. A triangular species, corresponding to a (5)A(2) electronic state, has been found to be the most stable UC(2) species. A triplet linear CUC species, which has been observed in recent infrared spectroscopy experiments, lies much higher in energy. A topological analysis of the electronic density has also been carried out. The triangular species is shown to be in fact a T-shape structure with a U-C interaction which can be considered to be a closed-shell interaction.     

Identification of arsenic species in sheep‐wool extracts by different chromatographic methods

Sheep on the island of North Ronaldsay (Orkney, UK) feed mostly on seaweed, which contains high concentrations of dimethylated arsenoribosides. Wool of these sheep contains dimethylated, monomethylated and inorganic arsenic, in addition to unidentified arsenic species in unbound and complexed form. Chromatographic techniques using different separation mechanisms and detectors enabled us to identify five arsenic species in water extracts of wool. The wool contained 5.2 ± 2.3 µg arsenic per gram wool. About 80% of the arsenic in wool was extracted by boiling the wool with water. The main species is dimethylarsenic, which accounted for about 75 to 85%, monomethylated arsenic at about 5% and the rest is inorganic arsenic. Depending on the separation method and condition, the chromatographic recovery of arsenic species was between 45% for the anion exchange column, 68% for the size exclusion chromatography (SEC) and 82% for the cation exchange column. The SEC revealed the occurrence of two unknown arsenic compounds, of which one was probably a high molecular mass species. Since chromatographic recovery can be improved by either treating the extract with CuCl/HCl (CAT: 90%) or longer storage of the sample (CAT: 105%), in particular for methylated arsenic species, it can be assumed that labile arsenic–protein‐like coordination species occur in the extract, which cannot be speciated with conventional chromatographic methods. It is clear from our study of sheep wool that there can be different kinds of ‘hidden’ arsenic in biological matrices, depending on the extraction, separation and detection methods used. Hidden species can be defined as species that are not recordable by the detection system, not extractable or do not elute from chromatographic columns. Copyright © 2003 John Wiley & Sons, Ltd.     

Reduction of the rotational ambiguity of curve resolution techniques under partial knowledge of the factors. Complementarity and coupling theorems

Multivariate curve resolution techniques allow to uncover from a series of spectra (of a chemical reaction system) the underlying spectra of the pure components and the associated concentration profiles along the time axis. Usually, a range of feasible solutions exists because of the so‐called rotational ambiguity. Any additional information on the system should be utilized to reduce this ambiguity. Sometimes the pure component spectra of certain reactants or products are known, or the concentration profiles of the same or other species are available. This valuable information should be used in the computational procedure of a multivariate curve resolution technique. The aim of this paper is to show how such supplemental information on the components can be exploited. The knowledge of spectra leads to linear restrictions on the concentration profiles of the complementary species and vice versa. Further, affine–linear restrictions can be applied to pairs of a concentration profile and the associated spectrum of a species. These (affine) linear constraints can also be combined with the usual non‐negativity restrictions. These arguments can reduce the rotational ambiguity considerably. In special cases, it is possible to determine the unknown concentration profile or the spectrum of a species only from these constraints. Copyright © 2012 John Wiley & Sons, Ltd.     

High-resolution analysis by nano-electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry for the identification of molecular species of phospholipids and their oxidized metabolites

Nano-electrospray ionization (ESI) Fourier transform ion cyclotron resonance mass spectrometry (FTICRMS) was applied to identify the molecular species of phosphatidylethanolamine of Caenorhabditis elegans, which has a high concentration of phospholipids with a fatty acyl chain having an odd number of carbon atoms. The molecular species of diacyl phosphatidylethanolamine with one fatty acyl chain having an odd number of carbon atoms and one fatty acyl chain having an even number of carbon atoms was identified separately from alkyl-acyl phosphatidylethanolamine with an alkyl chain having an even number of carbon atoms and a fatty acyl chain having an even number of carbon atoms. Furthermore, nano-ESI-FTICRMS was applied to the direct identification of oxidized phosphatidylcholine from soybean. The mass peaks of individual molecular species of oxidative phosphatidylcholine, such as 34:3 diacyl phosphatidylcholine with peroxide (+2O) (m/z 788.544) or 34:2 diacyl phosphatidylcholine with peroxide (+2O) (m/z 790.560), can be separated from the peaks of the molecular species of the non-oxidative phospholipids. This suggests that the mass peaks with a difference of less than 0.1 mass units in their molecular weight can be separated and that their individual exact molecular compositions can be obtained by the FTICRMS analysis. The high resolution and high accuracy of FTICRMS are very effective in the analysis of molecular species of phospholipids and their derivatives.     

催化裂化条件下噻吩与改性Y分子筛的作用机制

以HY、NiY和稀土离子改性的Y分子筛(REY)为研究对象,采用固定床装置评价噻吩模拟油催化裂化性能;运用气相色谱-氢火焰离子发光检测器(GC-FID)、气相色谱-硫化学发光检测器(GC-SCD)和原位红外光谱技术分析产物,关联分子筛的酸性,研究催化裂化条件下噻吩与改性Y分子筛的作用机制。实验结果表明,催化裂化条件下,噻吩与分子筛的作用机制差异主要取决于与B酸或L酸相关的非骨架铝物种或金属离子物种的存在形式。其中,NiY分子筛中,噻吩主要是吸附在与NiOH⁺物种相关的L酸中心,而Ni₄AlO₄³⁺等物种减弱B酸性中心从而降低其裂化性能。对HY来说,噻吩易在与AlO⁺等物种相邻的B酸中心上聚合形成三联噻吩,并发生一定的氢转移和裂化反应;而对REY而言,分子筛中与RE物种相关的L酸位会促进噻吩在与非骨架铝羟基等物种(如Al(OH)₂⁺、Al(OH)²⁺等)相邻的B酸中心形成的二联噻吩发生氢转移和裂化反应。     

Numerical simulation of two-phase partition chromatography in microchannels for moderated log P measurements

A finite element simulation has been used in order to study the partition chromatography process of one species between an aqueous mobile phase and an organic stationary phase located at the bottom of a rectangular microchannel. The transient model incorporates convection--diffusion of the species in the water phase coupled to the diffusion in the stationary organic phase by the way of the partition kinetics at the interface. The time evolution of the injected species concentration is analyzed versus the velocity of the mobile phase, the detecting position and the thickness of the stationary phase. The comparison of simulation results with both experimental data and analytical model confirm its validity. These simulations show that thin channels can be used to measure log P of molecules from their retention time. Finally, we have shown how the sample velocity can be optimized for a given geometry of the channel and diffusion coefficient of the species.     

电子能谱线形分析研究碳物种的化学状态

利用ＸＰＳ的ＣＩｓ携上峰,Ｘ射线激发供歇线形,ＸＰＳ价带谱以及俄歇电子能谱的ＣＫＬＬ线形研究了几处碳材料的化学状态和电子结构。研究结果表明：ＸＰＳ的携上效应可以鉴别不同结构的碳材料。ＸＡＥＳＲ 化学位移和线形也可以有效地研究中不同的碳材料的成像方式。ＸＰＳ的价带谱电子结构的一种有效方法,对碳材料的研究也很有效。ＡＥＳ的ＣＫＬＬ俄歇线形非常适合金属碳化物的鉴别。     

A time-resolved quadrupole mass spectrometric study on 355 nm laser ablated species ejected from LiMn2O4

Mass, velocity and angle distributions of the ablated species generated from 355 nm pulsed laser ablation of a LiMn2O4 target were investigated with an angle- and time-resolved mass spectrometric technique. Both neutral and ionic species of Li, O, LiO, LiO2, Mn, Li2, Li4, Li6, LiMn, MnO and MnO2 were observed at the laser fluence of 0.8 J · cm-2. The yield and variety of the ablated species increase with increasing the laser fluence. The time-of-flight spectra of ablated species can be fitted by a Maxwell-Boltzmann distribution with a center-of-mass velocity. There exist laser fluence thresholds for the ablated LiMn, Li2O and LiO2 species, and the fluence threshold of ionic species is higher than that of neutral species. The angular distributions of the ionic and neutral ablated species can be simulated by a cosnθor a bicosine function αcosθ+(1- α)cos"θ. In addition, the ablation mechanism of LiMn2O4 by a 355 nm pulsed laser is discussed.     

Instrumental Neutron Activation Analysis of Iodine Levels in Fourteen Seaweed Species from the Coastal Belt of Ghana

Fourteen seaweed species were sampled from October 1997 to May 1999 along the rocky shores of Ghana, which is being washed by the Gulf of Guinea (part of the Atlantic Ocean). Instrumental neutron activation analysis (INAA) was used to measure the iodine levels in the species, with the basic aim of selecting seaweed species that are rich in iodine and hence can be used as supplement in the diet of humans. This is to help solve the problems associated with iodine deficiency disorders (IDD). The levels of iodine found in the seaweed species ranged between 55 to 804 ppm. The precision, expressed in terms of relative standard deviation, and accuracy of measurements are within ±5–10%. The results show high variability in and between species and among sampling sites. The high values of iodine concentrations in the macroalgae suggest that these marine organisms can be used as supplement in the diet of humans.     

Fast and stable photochromic oxazines

We have designed and synthesized two photochromic compounds incorporating fused indoline and benzooxazine fragments. Variable-temperature 1H NMR spectroscopy demonstrates that their central [1,3]oxazine ring opens thermally with free energy barriers ranging from 14 to 19 kcal mol(-1). The ring-opened species reverts rapidly to the original isomer and can only be detected after chemical trapping. Specifically, the nucleophilic attack of a hydroxide anion to the indolium cation of the ring-opened species prevents re-isomerization. Laser excitation of both compounds induces the opening of the [1,3]oxazine ring in less than 6 ns with quantum yields up to 0.1. The photoinduced ring opening generates a 4-nitrophenolate chromophore, which absorbs strongly at 440 nm. The photogenerated species reverts to the original form with a lifetime of 22 ns for both compounds. Thus, these transformations can be exploited to interconvert the two isomers of each species with nanosecond switching speeds. Furthermore, thousands of switching cycles can be repeated consecutively without any sign of degradation, even in the presence of molecular oxygen. These processes can be reproduced efficiently in poly(methyl methacrylate) matrixes. Under these conditions, the thermal re-isomerization occurs with biexponential kinetics in submillisecond time scales. In principle, the fast isomerization kinetics and excellent fatigue resistance of both compounds offer the opportunity to modulate rapidly and efficiently a variety of molecular and macroscopic properties. Thus, our molecular design can evolve into the realization of a new family of photochromic compounds and materials with promising photoresponsive character.     

The role of element speciation in environmental and occupational medicine

In order to evaluate the interaction with the environment or to assess absorption, binding mechanisms, reactivity and excretion of elements in humans, element speciation can provide more information than the analysis of element as a whole. Some examples that confirm the importance of speciation depend on the choice of the most appropriate indicator or representative matrix. The determination of As(III), As(V), monomethylarsonic and dimethylarsinic acids can be used to evaluate occupational exposure to As. Exposure to inorganic Hg should be measured by its content in urine, whereas in the case of exposure to alkyl Hg, blood and hair should be considered. Speciation may also be useful in studying element toxicokinetics, since it is well known that hexavalent Cr is taken up more than the trivalent form, and that species of the same metal are differently partitioned in blood. Pentavalent forms of As are absorbed more than trivalent forms, and the organic species of elements are excreted faster than inorganic species. In addition, speciation can play an important role in assessing element toxicodynamics. The toxicity of the three oxidation states of Hg differs considerably; for As a decreasing toxicity from arsenite to dimethylarsinic acid is proposed; for organotin compounds, higher toxicity for ethyl groups than for phenyl groups is reported. However, speciation in biological media is difficult when applied to other elements because of the lack of information on the existence and significance of species whose determination could be valuable. Furthermore, there may be no analytical methods that allow an accurate measurement of the species. The feasibility of speciation in occupational and environmental medicine depends mainly on our capability to solve some problems related to the identification and determination of species and on the demonstration that species measurement represents a clear improvement compared to total element determination.     

CO与蜜勒胺自组装膜协同作用制备Au单原子及多原子物种

金属单原子物种的可控制备对于包括多相催化在内的各种表面化学过程非常重要。在本工作中,我们在Au(111)表面制备了由蜜勒胺分子形成的具有周期性孔道结构的自组装薄膜。这种有机分子薄膜所携载的官能团能与金属原子进行有效作用。通过在室温下暴露CO气体,在表面上成功制备出Au单原子。由于蜜勒胺分子中的杂环氮原子与Au原子作用较强,因此所形成的Au原子具有突出的稳定性,并且具有多种形式的空间分布构型,有望为一些结构敏感性的表面反应提供合适的催化位点。     

Studies on the Adsorption and Dissociation of Methane and Carbon Dioxide on Nickel

The adsorption and dissociation of methane and carbon dioxide for reforming on nickel catalysts were extensively investigated by TPSR, TPD, XPS and pulse reaction methods. These studies showed that the decomposition of methane results in the formation of at least three kinds of surface carbon species on supported nickel catalysts. Carbidic Cα, carbonaceous Cβ and carbidic clusters Cγ surface carbon species formed by the decomposition of methane demonstrated different surface mobility, thermal stability and reactivity. Carbidic Cα is a very active and important intermediate in carbon dioxide reforming with methane, and the carbidic clusters Cγ species might be the precursor of surface carbon deposition. The partially dehydrogenated Cβ species can react with H2 or CO2 to form CH4 or CO. On the other hand, it was proven that CO2 can be weakly adsorbed on supported nickel catalysts, and only one kind of CO2 adsorption state is formed. The interaction mechanism between the species dissociated from CH4 and CO2 during reforming was then hypothesized.