Size Dependence of Molar Absorption Coefficients of CdSe Semiconductor Quantum Rods

Fundamental properties: The molar absorption coefficients of CdSe quantum rods are determined experimentally as a function of their dimensions (see figure). Far above the band gap a simple dependence on volume is seen. The behavior at the band gap manifests a concentration of oscillator strength with decreased diameter in agreement with strong quantum confinement behavior.

     

Extraction of Chemical Speciation and Molar Absorption Coefficients with Well-Posed Solutions of Beer's Law

The performance of different types of solutions of Beer's law was evaluated on a suite of synthetic uv-vis spectra generated at various degrees of random error. Solutions making use of absorbance matrices filtered from random noise were the most successful at retrieving the properties of chemical species at larger errors. Repeated automated simulations, however, indicated that such solutions display a number of occurrences associated with poor fits to the synthetic data. Solutions to Beer's law starting from the raw absorbance matrices including random errors produced more consistent sets of values of rather poorer quality. A bootstrap statistical analysis of the repeated simulations showed the median quality of the fit (e.g., sum-of-squares of the deviations) nonetheless to be far superior for solutions making use of error/noise filtration. These resulting absorbance matrices when reduced dimensionality, moreover, gave better values of the molar absorption coefficients and formation constant if solved numerically using orthogonal-triangular (QR) factorizations. These solutions are therefore recommended for the extraction of spectroscopic and thermodynamic/kinetic properties of chemical species from spectroscopic data, however, not without a rigorous validation of the model. All the solutions to Beer's law are provided in the computational language of Matlab 7.0 and may be readily implemented for any quantitative spectroscopic analyses.     

稀土金属在不对称催化中的应用:从均相催化到异相催化

稀土金属的配位数较高,可通过容纳大型手性配体,构筑手性环境,催化不对称反应的定向发生,在工业生产特别是制药工程中具有重要应用价值.本文以Henry反应、Mannich反应和Strecker反应为例,总结回顾了稀土金属催化剂在此类反应中的设计思路、性能特点与应用前景,旨在展现稀土金属催化剂兼具融合均相催化与异相催化的优势...     

Frustrated Lewis Pairs in Heterogeneous Catalysis: Theoretical Insights

Frustrated Lewis pair (FLP) catalysts have attracted much recent interest because of their exceptional ability to activate small molecules in homogeneous catalysis. In the past ten years, this unique catalysis concept has been extended to heterogeneous catalysis, with much success. Herein, we review the recent theoretical advances in understanding FLP-based heterogeneous catalysis in several applications, including metal oxides, functionalized surfaces, and two-dimensional materials. A better understanding of the details of the catalytic mechanism can help in the experimental design of novel heterogeneous FLP catalysts.     

Monte Carlo Simulations of Adsorbed Solutions in Heterogeneous Porous Materials

We present results of a Monte Carlo simulation study of binary mixtures of ethane and methane in silica gel. The molecular model treats the adsorbent as a matrix of silica microspheres. The adsorption isotherms, adsorption selectivities and isosteric heats of adsorption have been determined for these systems. The results are compared with predictions from the ideal adsorbed solution (IAS) theory and with experiment. The heats of adsorption are accurately described by the IAS theory. The adsorption isotherms are accurately described by the IAS theory at low bulk pressure but the IAS theory overpredicts the density at high bulk pressure. This latter effect is opposite to that observed in bulk mixtures of this type where nonidealities generally lead to a density increase on mixing. The pressure dependence of the selectivity does not exhibit a maximum at low pressure. We discuss this effect in terms of the adsorbent microstructure.     

Inter-Metal Interaction of Dual-Atom Catalysts in Heterogeneous Catalysis

Dual-atom catalysts (DACs) have been a new frontier in heterogeneous catalysis due to their unique intrinsic properties. The synergy between dual atoms provides flexible active sites, promising to enhance performance and even catalyze more complex reactions. However, precisely regulating active site structure and uncovering dual-atom metal interaction remain grand challenges. In this review, we clarify the significance of the inter-metal interaction of DACs based on the understanding of active center structures. Three diatomic configurations are elaborated, including isolated dual single-atom, N/O-bridged dual-atom, and direct dual-metal bonding interaction. Subsequently, the up-to-date progress in heterogeneous oxidation reactions, hydrogenation/dehydrogenation reactions, electrocatalytic reactions, and photocatalytic reactions are summarized. The structure-activity relationship between DACs and catalytic performance is then discussed at an atomic level. Finally, the challenges and future directions to engineer the structure of DACs are discussed. This review will offer new prospects for the rational design of efficient DACs toward heterogeneous catalysis.     

荧光摩尔吸收系数法测定洗护用品中烷基酚聚氧乙烯醚

建立了洗涤用品和化妆品护理用品中烷基酚聚氧乙烯醚(NPnEO和OPnEO,n=0～30)的高效液相色谱分析方法。采用乙腈水溶液超声提取不同基质类型的洗涤用品和化妆品护理用品,利用快速反相C18柱(Poroshell 120 EC-C18,75 mm×4.6 mm,2.7μm)串联HILIC硅胶色谱柱(Atlantis HILIC Slica,250 mm×4.6 mm,5μm)对NPnEO和OPnEO的各单体及样品杂质进行有效分离,以乙腈-10 mmol/L醋酸铵溶液为流动相进行梯度洗脱,荧光检测器进行检测,建立了荧光摩尔吸收系数定量校正NPnEO和OPnEO的计算模型。通过测定NPnEO和OPnEO混合标准溶液,计算得到两者的荧光摩尔吸收系数。对样品中NPnEO和OPnEO的平均分子量进行测定,并利用荧光摩尔吸收系数对总峰面积进行校正定量。方法的回收率为99.0%～105.7%,相对标准偏差不大于12.5%,定量下限为40.0 mg/kg。该方法快速、准确、适用范围广,可用于各类洗涤用品和化妆品护理用品中烷基酚聚氧乙烯醚(NPnEO和OPnEO)含量的检测。     

Perylene-Grafted Silicas: Mechanistic Study and Applications in Heterogeneous Photoredox Catalysis

A mechanistic study is herein presented for the use of heterogeneous photocatalysts based on perylene moieties. First, the successful immobilization of perylene diimides (PDI) on silica matrices is demonstrated, including their full characterization by means of electronic microscopy, surface area measurements, powder XRD, thermogravimetric analysis, and FTIR, ²⁹Si and ¹³C solid-state NMR, fluorescence, and diffuse reflectance spectroscopies. Then, the photoredox activity of the material was tested by using two model reactions, alkene oxidation and 4-nitrobenzylbromide reduction, and mechanistic studies were performed. The mechanistic insights into their photoredox activity show they have promising dual photocatalytic activity for both organic oxidations and reductions.     

Spectroscopic Identification of Hydrogen Bond Vibrations and Quasi-Isostructural Polymorphism in N-Salicylideneaniline

The ortho-hydroxy aryl Schiff base 2-[(E)-(phenylimino)methyl]phenol and its deutero-derivative have been studied by the inelastic incoherent neutron scattering (IINS), infrared (IR) and Raman experimental methods, as well as by Density Functional Theory (DFT) and Density-Functional Perturbation Theory (DFPT) simulations. The assignments of vibrational modes within the 3500–50 cm⁻¹ spectral region made it possible to state that the strong hydrogen bond in the studied compound can be classified as the so-called quasi-aromatic bond. The isotopic substitution supplemented by the results of DFT calculations allowed us to identify vibrational bands associated with all five major hydrogen bond vibrations. Quasi-isostructural polymorphism of 2-[(E)-(phenylimino)methyl]phenol (SA) and 2-[(E)-(phenyl-D₅-imino)methyl]phenol (SA-C₆D₅) has been studied by powder X-ray diffraction in the 20–320 K temperature range.     

蒙特卡罗方法及其在多相催化中的应用

1　蒙特卡罗方法简介足球比赛开始前 ,裁判往往用掷硬币的方法决定双方进攻的方向。这种方法两方都能接受 ,因为正面朝上和朝下的机会是相同的 ,也就是说概率都是 50 %。现在 ,假如我们往地上掷一个密度不均匀、形状不规则的多面体 ,问某一个面朝地的概率是多少 ?恐怕没有人能知道。找到答案的方法其实很简单 :把这个多面体一次又一次地往地上投 ,数出该面朝地的次数 ,然后再除以总的投掷次数。这种解决问题的方法实际上就是蒙特卡罗方法。但它真正成为一种研究科学问题的方法 ,则要归功于ｖｏｎＮｅｕｍａｎｎ、Ｕｌａｍ以及Ｍｅｔｒｏｐｌ…     

A Laboratory Study of Heterogeneous Catalysis in Ultrahigh Vacuum

A surface science experiment has been developed that can be used in both the undergraduate and graduate curriculum. Students study the mechanism of carbon monoxide oxidation using a platinum foil catalyst, and they also get hands-on experience with ultrahigh vacuum equipment. Using temperature programmed desorption, students study the desorption of carbon monoxide and oxygen from platinum foil in vacuum. The study allows students to determine that the Langmuir-Hinshelwood reaction mechanism operates in this catalytic system.     

多相催化研究中化学动力学的作用(英文)

The paper presents shortly some of the important elements of the theory and of the practical applications of the kinetics of heterogeneous catalytic reactions. Discussed are some of the most important concepts of the kinetics of complex heterogeneous catalytic reactions,methodology of building kinetic models and mathematical treatment of experimental data,influence of heat and mass transfer,types of laboratory reactors,kinetics and nanosized catalysts and others. Examples for use of the kinetic studies for the development and application of industrial catalysts and modeling of industrial reactors are presented.     

The Study of the Nature of Adsorbed Species to Build a Bridge between Surface Science and Catalysis: Problems of Pressure and Material Gap

This review substantiates the molecular approach to the study of the catalytic action of various systems, which consists in the comparative study of the nature and reactivity of adsorbed species and considering the problems of pressure and material gaps. The pressure gap problem can be solved by a continuous increase in the pressure of the reaction mixture, including carrying out in situ studies. The solution to the problem of material gap is possible when one passes from bulk to dispersed samples, which model real supported catalysts. As the last step that can build a bridge between surface science and catalysis, the study of nanoparticle reactivity toward the reactants of a catalytic reaction with varying sizes of nanoparticles is proposed. The scope of such an approach is demonstrated by the study of silver catalysts of ethylene epoxidation. It was found that the catalytic action of silver in the process of ethylene oxide synthesis is determined by the possibility of formation of electrophilic adsorbed atomic oxygen. Its formation is more efficient under the action of reaction mixtures at high pressures and on the surfaces of silver species with sizes smaller than 50 nm. It is shown that the reaction center should also contain the nucleophilic form of O_ads, which itself is only active in the complete oxidation of ethylene but creates the Ag¹⁺ sites for ethylene adsorption. The disappearance of O_nucl with a decrease in the size of silver particles below 50 nm leads to a drastic decrease in the rate of ethylene epoxidation. The reaction mechanism made it possible to propose systems with an abnormally high value of selectivity to ethylene oxide (>90%).     

Molar Entropy and Enthalpy of CO Adsorbed in Zeolites as Derived from VTIR Data: Role of Intermolecular Modes

Detailed analysis of recently reported variable-temperature IR (VTIR) spectra of carbon monoxide adsorbed in alkaline zeolites shows how, not only the corresponding values of standard adsorption enthalpy ( ) and entropy ( ) can be obtained, but also the thermodynamic values of molar entropy and enthalpy which characterize the adsorbed gas phase. In addition, it is shown that the so obtained molar entropy data can lead to new insights into soft molecular modes, which would be hardly accessible by conventional IR spectroscopic techniques.     

Nanoporous Metals for Heterogeneous Catalysis: Following the Success of Raney Nickel

Nanoporous metals (NPMs) with diversified shapes and compositions can be readily fabricated by dealloying monolithic alloys through chemical or electrochemical processes. Benefited from their high surface area, high density of low-coordinated sites on the ligament surface, and unsupported character, NPMs have attracted increasing attentions as a new class of heterogeneous catalysts with high activity, selectivity, and long-term stability, reminiscent of the great success of Raney nickel. In the present minireview, we summarize the recent advances in this exciting field and provide a critical discussion of the nature of their active sites and the structure–property correlation.     

Hydrodeoxygenation Using Magnetic Induction: High‐Temperature Heterogeneous Catalysis in Solution

Magnetic heating has recently been demonstrated as an efficient way to perform catalytic reactions after deposition of the heating agent and the catalyst on a support. Here we show that in solution, and under mild conditions of mean temperature and pressure, it is possible to use magnetic heating to carry out transformations that are otherwise performed heterogeneously at high pressure and/or high temperature. As a proof of concept, we chose the hydrodeoxygenation of acetophenone derivatives and of biomass‐derived molecules, namely furfural and hydroxymethylfurfural. These reactions are difficult, require heterogeneous catalysts and high pressures, and, to the best of our knowledge, have no precedent in standard solution. Here, hydrodeoxygenations are fully selective under mild conditions (3 bar H₂, moderate mean temperature of the solvent). The reason for this reactivity is the fast heating of the particles well above the boiling temperature of the solvent and the local creation of hot spots surrounded by a vapor layer, in which high temperature and pressure may be present. This technology may be practicable for many organic transformations.     

微乳液法制备固体催化剂在多相催化领域中的应用

采用微乳液法制备纳米粒子具有粒径可控、粒度分布均匀、粒子不易团聚等优点,在一些反应中表现出优良的催化性能.本文介绍了微乳液的概念,阐述了反相微乳体系(W/O)作为纳米反应器的原理以及用于制备固体催化剂的方法.综述了反相微乳液法制备固体催化剂在多相催化领域中的应用,并指出该技术存在的问题和发展趋势.