Cu-ZnO-ZrO2甲醇水蒸气重整催化剂的原位Raman表征

应用显微Raman光谱对Cu-ZnO-ZrO₂(Zr 24%,w)催化剂催化甲醇水蒸气重整(SRM)反应进行原位表征,并将结果与相同催化剂上的甲醇合成(MS)反应进行对比,结果表明:在SRM反应时,催化剂表面出现四个宽峰,其中544.8和652.8cm^-1分别为CuO-ZnO和ZrO₂的Raman吸收峰,而1361.8 cm^-1为HCOO-Cu对称伸缩振动吸收峰,在1590.3 cm^-1附近的谱峰归属于甲酸物种中OCO的不对称伸缩振动.在由CO-CO₂-H₂合成气合成甲醇时,在1350 cm^-1和分别在1550,1585,1595cm^-1出现两个甲酸根表面物种和甲酸盐的振动吸收谱带.因此,在Cu-ZnO-ZrO₂催化剂上的甲醇合成和甲醇水蒸气重整存在相同的甲酸根中间体,这一结果将有助于对甲醇合成和甲醇水蒸气重整反应机理的理解.     

Ga改性ZSM-5分子筛催化丙烷芳构化性能研究

用离子交换法制备Ga改性ZSM-5双功能催化剂,并结合XRD、SEM、BET、NH₃-TPD、Py-IR及ICP、XPS等多种技术进行表征,考察分子筛硅铝比(Si/Al)和催化剂氧化还原预处理条件对分子筛的酸性质、Ga物种的存在状态及其丙烷芳构化催化性能的影响。研究表明,硅铝比不仅可以改变分子筛的酸性,也会影响分子筛中非骨架Ga物种与分子筛表面的相互作用程度,进而影响含Ga分子筛的丙烷芳构化性能。在质量空速1.0 h^-1、反应温度550℃ 下,Si/Al比为30的Ga-HZSM-5分子筛丙烷转化率和芳烃收率最高。Ga物种的引入可以提高丙烷的转化率和芳烃的选择性,并抑制烷烃、烯烃的裂解。H₂还原处理,将分子筛表面Ga₂O₃还原为低价的Ga⁺和GaH⁺₂物种,促进了Ga物种向分子筛微孔迁移;还原-氧化处理后,Ga⁺和GaH⁺₂物种氧化成GaO⁺,占据分子筛孔道离子交换位,显著提高了催化剂的芳构化活性。     

关于两个氧化一还原反应方程式的配平

我们知道,有的化学反应,当书写反应方程式出现几种配平形式时,应择其一种正确形式。今列举两例[1]浅析之。     

添加气对非平衡等离子体转化低碳烷烃的影响

在常压下, 研究了添加气的种类(N₂, He, Ar, H₂, NH₃, CO和CO₂)对介质阻挡放电低碳烷烃(甲烷、 乙烷和丙烷)转化制低碳烯烃的影响. 结果表明, 以甲烷或乙烷为原料时, N₂, He, Ar和CO的引入有利于提高原料的转化率和总烯烃的选择性; 而CO₂, H₂和NH₃的引入对甲烷、 乙烷的转化率无明显影响, 但H₂和NH₃的引入会使总烯烃的选择性显著降低. 以丙烷为原料时, 所研究的添加气均可提高丙烷的转化率, 而只有CO的引入可提高总烯烃选择性. 综上所述, 80%(摩尔分数) CO添加量最有利于低碳烷烃转化成低碳烯烃, 对应的甲烷、 乙烷和丙烷的转化率分别提高了14.4%, 17.6%和42.8%, 总烯烃的选择性分别提高了19.9%, 25.0%和11.9%. 以CH₄为例, 通过对放电电流波形和等离子体区物种的发射光谱(OES)研究发现, 引入CO能显著增加等离子体的电子密度, 并且体系中出现激发态O^*物种(777.5和844.7 nm), 这种O^*物种能够促进C-H键的断裂, 有利于烯烃的生成. 因此, 等离子体区电子密度的增加和激发态O^*物种的出现可能是CH₄-CO体系中CH₄有效转化的主要原因.     

Ce金属改性对Cu-SAPO-34催化剂水热稳定性能的影响

采用浸渍法制备系列铜铈复合氧化物分子筛催化剂（Cu-Ce/SAPO-34）,探讨了Ce负载量对Cu/SAPO-34催化剂的水热稳定性的影响,通过XRD、SEM、H₂-TPR、XPS和NH₃-TPD等表征手段分析不同催化剂活性和稳定性差异的原因。研究表明,750℃水热老化未造成Cu-Ce/SAPO-34催化剂菱沸石（chabazite,CHA）骨架坍塌,但破坏了部分孔结构和酸性位点,使催化剂表面结晶度下降。水热老化促使催化剂晶格发生拉伸畸变,使Cu²⁺迁移到催化剂表面,Cu²⁺和Ce⁴⁺团簇形成CuO和CeO₂,造成催化剂的Cu活性物种减少和氧空穴浓度降低,所以Cu-Ce/SAPO-34的NH₃选择性催化还原（NH₃-Selective Catalytic Reduction,NH₃-SCR）性能下降。掺杂Ce能提高Cu/SAPO-34催化剂表面的Cu²⁺和Cu⁺活性物种量,减少Cu物种团簇形成CuO,改善催化剂表面活性Cu物种分布性。提高Ce的负载量能稳固Cu-Ce/SAPO-34催化剂的结构,使中、弱强度酸位点得以维持,从而提高其水热稳定性。结果表明,在研究的系列Cu-Ce/SAPO-34催化剂中,Cu/Ce质量比为4：5时具有最佳的水热稳定性。     

·CO3–在基于太阳光驱动的TiO2-贝壳粉降解盐酸四环素中的作用:降解机理和转化路径(英文)

抗生素的滥用和不当排放对水陆生生态系统造成了严重威胁,在世界各地水环境污染物调研中普遍检测到盐酸四环素的存在.如何解决水体中高稳定、难降解的盐酸四环素污染问题是当前环境领域重点研究的课题之一.在各种去除方法中,利用光化学反应生成活性氧物种如·CO₃^–,·OH,·O₂^–,·SO4–和1O₂等实现对有机污染物的降解在众多研究方法中脱颖而出.·CO₃^–在水体中具有较高的稳态浓度且其对有机物降解具有高选择性.CO₃^2–或HCO₃^–与活性物种如·OH, h+,·O₂^–,·SO4–等反应可以生成·CO₃^–.传统的半导体光催化剂TiO₂在光照下会产生·OH,·O₂^–及h⁺等活性物种,能有效...     

两种新型F-荧光化学传感器的合成及其性质研究

本文设计合成了N⁶-对甲苯磺酰胺腺嘌呤(I)和邻苯二对甲苯磺酰胺(Ⅱ)两种主体化合物.通过对其与阴离子物种之间相互作用的研究发现,它们在乙腈溶液中和Cl^-、Br^-、NO₃^-、NO₂^-、HSO₄^-、Ac^-、F^-几种阴离子相互作用时,仅对F^-具有专一的选择性识别作用.F^-离子可使I和Ⅱ主体的荧光吸收猝灭并发生红移.通过试验证明,F^-离子和I、Ⅱ主体的识别作用机理是因形成了激基缔合物.     

Co3V2O8催化剂的合成表征及其催化性能研究

采用共沉淀法制备了Co₃V₂O₈催化剂,并对催化剂进行了BET、XRD、H₂-TPR、XPS、和 TEM等技术表征,研究了其丙烷氧化脱氢 (ODH) 制丙烯反应的催化性能。H₂-TPR和XPS实验结果表明,Co₃V₂O₈催化剂中晶格氧可以较容易转换成可动氧物种(即未完全还原氧物种),使催化剂内各种价态的钒之间易于进行氧化还原反应并形成氧缺位,催化剂的表面含有较多未充分还原氧物种O^-和V⁴⁺ 物种。催化活性结果显示,在425℃和475℃,丙烯选择性分别为49.45%和33.74%,表现了较好的催化性能。     

注意书写离子方程式的几种特殊情况

离子方程式是中学化学教学的重点,同时也是高考热点。从1990年以来的历届高考题中不难发现,几乎届届都涉及到离子方程式书写的考题。那么,如何正确书写离子方程式呢？我们认为除了正确掌握书写离于方程式的一般原则和方法外,还应注意几种特殊情况。     

吡啶在Au电极上吸附的紫外可见反射光谱法研究

电化学调制紫外可见反射光谱技术可用来测定金属电极上吸附物种的取向和吸附物种与金属表面间的相互作用,金属Au与已研究过的Pb、In和Pt^[1～]具有不同形式的能带结构,吸附物种与电极表面间相互作用的电位依赖性可能不同。本文测定了吡啶分子吸附时Au电极的反射差谱,并试图从能带模型角度探讨吡啶分子与Au电极表面原子间的相互作用。     

Approximate solutions of the Bloch-McConnell equations for two-site chemical exchange.

Approximate formulas for the transverse-relaxation rate constant and resonance frequency have been derived for nuclear spins subject to two-site chemical exchange. The new results are more accurate than previous approximations when chemical exchange does not approach the fast-exchange limit or when site populations are not highly asymmetric. Results are derived from an effective average evolution operator that contains contributions from both exact eigenvalues of the Bloch-McConnell equations. These expressions are useful for interpretation of chemical exchange processes in NMR spectroscopy.     

Electric Potential and Reaction Rates at Charged Surfaces in Asymmetric Electrolytes-An Analytic Approach

The electric potential and reaction rates of ions hitting the chemically active surfaces of microcrystals in an asymmetric electrolyte are computed analytically. Following ideas of Debye we start by solving the Poisson-Boltzmann equations and by determining the electric potential of the transport equations. We find distinct deviations when comparing our result with the Gouy-Chapman formula. In a simple model approximating a situation in which lead and hydrogen ions can react at goethite surfaces we compute analytically the currents of ions diffusing to the surfaces of microcrystals where they undergo a chemical reaction. We compute the reaction rates that can be controlled either by chemical reactions at the surface of the microcrystals or by diffusional transport. For realistic parameters of our model we find that the diffusional transport is the rate determining step. Copyright 2001 Academic Press.     

Thermodynamics of electrolytes. III. Activity and osmotic coefficients for 2–2 electrolytes

The peculiar behavior of 2–2 and higher valence type electrolytes is discussed in terms of various theories some of which assume, while others do not, an equilibrium between separated ions and ion pairs as distinct chemical species. It is recognized that in some case a distinct species of inner-shell ion pairs is indicated by spectroscopic or ultrasonic data. Nevertheless, there are many advantages in representing, if possible, the properties of these electrolytes by appropriate virial coefficients and without chemical association equilibria. It is shown that this is possible and is conveniently accomplished by the addition of one term to the equations of Parts I and II of this series. The coefficients of these equations are given for nine solutes. It is also noted that these equations have been successfully applied to mixed electrolytes involving one component of the 2–2-type.     

两相平衡范特霍夫方程的应用

应用相平衡常数讨论了范特霍夫方程在简化一些两相平衡热力学公式推导时的应用。     

Developing Itô stochastic differential equation models for neuronal signal transduction pathways

Mathematical modeling and simulation of dynamic biochemical systems are receiving considerable attention due to the increasing availability of experimental knowledge of complex intracellular functions. In addition to deterministic approaches, several stochastic approaches have been developed for simulating the time-series behavior of biochemical systems. The problem with stochastic approaches, however, is the larger computational time compared to deterministic approaches. It is therefore necessary to study alternative ways to incorporate stochasticity and to seek approaches that reduce the computational time needed for simulations, yet preserve the characteristic behavior of the system in question. In this work, we develop a computational framework based on the It? stochastic differential equations for neuronal signal transduction networks. There are several different ways to incorporate stochasticity into deterministic differential equation models and to obtain It? stochastic differential equations. Two of the developed models are found most suitable for stochastic modeling of neuronal signal transduction. The best models give stable responses which means that the variances of the responses with time are not increasing and negative concentrations are avoided. We also make a comparative analysis of different kinds of stochastic approaches, that is the It? stochastic differential equations, the chemical Langevin equation, and the Gillespie stochastic simulation algorithm. Different kinds of stochastic approaches can be used to produce similar responses for the neuronal protein kinase C signal transduction pathway. The fine details of the responses vary slightly, depending on the approach and the parameter values. However, when simulating great numbers of chemical species, the Gillespie algorithm is computationally several orders of magnitude slower than the It? stochastic differential equations and the chemical Langevin equation. Furthermore, the chemical Langevin equation produces negative concentrations. The It? stochastic differential equations developed in this work are shown to overcome the problem of obtaining negative values.     

糖酵解模型双曲型反应-扩散方程的非线性行为

The Stability and chemical oscillation of the hyperbolic reaction-diffusion equations for glycolysis model are studied and compared with that of the corresponding parabolic equations. The results show that the parabolic equation is the limiting case of the hyperbolic system when the reaction-diffusion number Nrd →∞, and that the divergence of the wave speed, which exists in the parabolic system, does not appear in the hyperbolic one. The stabilities of these two systems are significantly different. The hyperbolic system may exist in chaos state under certain conditions. It is shown that the hyperbolic system is more suitatle to be used as the model for studying chemical oscillations.     

System eigenmobilities in zone electrophoresis: A general moving-boundary approach

System zones in capillary zone electrophoresis represent an important topic, very interesting from the theoretical point but also important for practice. This paper is aimed at contributing to the understanding of system zones as one of the very fundamental properties of electrophoretic systems, by developing an alternative approach to the so far used vector-matrix model of calculation of system mobilities (system eigenmobilities). The presented model is based on the solution of the differential form of the moving-boundary equation. The result for acid-base systems is a single algebraic equation valid universally for a zone comprising any number of constituents (mono- or polyhydric strong or weak acids or bases and/or amphoteric compounds). The value of the described solution against previous models consists in its explicit form, expressing the system eigenmobility of a homogeneous zone of given composition as a function of only known quantities. The obtained equation is shown to be the common source of various simplified equations obtained in the past for particular simple systems. The applicability of the simplified equations is discussed in terms of completeness of the results (number of output system eigenmobilities). For non-buffered systems, the occurrence of a previously unreported non-zero value of system eigenmobility is discussed that is equal to the arithmetic average of mobilities of the solvent ions.     

超微盘电极上统一的稳态伏安曲线方程式——传质时间法

本文提出了传质时间的新概念,并用于推导超微盘电极上同时控制包括Nernst扩散、对流扩散、化学反应和电极反应的稳态伏安曲线方程式,对电流、电位的性质进行了讨论。     

Nuclear magnetic resonance studies of edta in the presence of excess calcium or strontium

The equilibria which exist between metal ions, ethylenediaminetetraacetic acid (EDTA), and the resulting chelates have been thoroughly investigated by many techniques, emphasis being placed on the study of complexes containing a 1:1 ratio of metal ion to ligand. The results presented here are concerned with the observation of the chemical shift of the nonlabile protons of EDTA when excess calcium or strontium ions are present. The results yield evidence for a 2:1 complex. Formation constants for the equilibria believed to be in effect are given and a possible structure of the 2:1 complex is discussed.     

原子簇正负离子的统计分布与生成机理

在分析了实验记录的大量原子簇离子质谱的基础上，发现原子簇的正负离子通常表现为不同的统计分布形式．将它们的分布形式与求解动力学方程得出的分布函数相比，发现由此反映了原子簇正负离子的不同的生成机理：实验所检测的原子簇正离子在许多情况下仅经历了聚合与解离反应，主要是中性原子簇分子电离后的产物；而相应的原子簇负离子则是经历了一系列离子一分子反应后的产物．