Dehydrogenation of ethane to ethylene via radical pathways enhanced by alkali metal based catalyst in oxysteam condition

The dehydrogenation of ethane to ethylene in the presence of oxygen and water was conducted using Na₂WO₄/SiO₂ catalyst at high temperatures. At 923 K, the conversion rate without water was proportional to ethane pressure and a half order of oxygen pressure, consistent with a kinetically relevant step where an ethane molecule is activated with dissociated oxygen on the surface. When water was present, the ethane conversion rate was drastically enhanced. An additional term in the rate expression was proportional to a quarter of the oxygen pressure and a half order of the water pressure. This mechanism is consistent with the quasi‐equilibrated OH radical formation with subsequent ethane activation. The attainable yield can be accurately described by taking the water contribution into consideration. At high conversion levels at 1073 K, the C₂H₄ yield exceeded 60% in a single‐pass conversion. The C₂H₄ selectivity was almost insensitive to the C₂H₆ and O₂ pressures. © 2016 American Institute of Chemical Engineers AIChE J, 63: 105–110, 2017     

混合离子液体催化反应精馏合成乙酸正己酯

离子液体催化反应精馏是提高酯交换平衡反应转化率的一种绿色有效方法。以离子液体1-丙基磺酸-3-甲基咪唑三氟甲烷磺酸盐（［PSO₃HMIm］［OTf］）和离子液体1-辛基-2,3-二甲基咪唑双（三氟甲烷磺酰）亚胺盐（［OMMIm］［Tf₂N］）的混合物作为乙酸甲酯和正己醇进行酯交换反应合成乙酸正己酯的催化剂,测定了酯交换反应动力学。探讨了混合比、反应温度、反应物初始摩尔比、催化剂浓度对反应速率和乙酸甲酯转化率的影响,考察了催化剂的回收性能。利用实验数据回归得出混合离子液体催化酯交换反应动力学方程。在反应动力学的基础上进行了乙酸甲酯和正己醇的酯交换反应精馏流程模拟,分析了理论板数、回流比、进料位置及反应段塔板数、催化剂用量、持液量等参数对反应精馏塔的影响。在优化的操作条件下,获得纯度为0.9993的乙酸正己酯产品。     

Ockham's razor for paring microkinetic mechanisms: Electrical analogy vs. Campbell's degree of rate control

Elucidation of the key molecular steps and pathways in an overall reaction is of central importance in developing a better understanding of catalysis. Campbell's degree of rate control (DRC) is the leading methodology currently available for identifying the germane steps and key intermediates in a catalytic mechanism. We contrast Campbell's DRC to our alternate new approach involving an analysis and comparison of the “resistance” and de Donder “affinity,” that is, the driving force, of the various steps and pathways in a mechanism, in a direct analogy to electrical networks. We show that our approach is as just rigorous and more insightful than Campbell's DRC. It clearly illuminates the bottleneck steps within a pathway and allows one to readily discriminate among competing pathways. The example used for a comparison of these two methodologies is a DFT study of the water–gas shift reaction on Pt–Re catalyst published recently. © 2015 American Institute of Chemical Engineers AIChE J, 61: 4332–4346, 2015     

油酸存在下的聚氨酯(脲)固化动力学

采用差示扫描量热法(DSC)研究了油酸存在下聚氨酯(脲)固化过程反应动力学参数.利用Kissinger法求得不同油酸含量固化反应的表观活化能Ea,Crane方程计算该体系的固化反应级数n.结果表明,加入油酸后固化体系的活化能减小,油酸为聚氨酯(脲)固化反应的催化剂;油酸质量分数为0.9%时,固化反应的E.为27.91 ...     

Single‐Molecule Kinetics of an Enzyme in the Presence of Multiple Substrates

Herein, the catalytic activity of a single enzyme in the presence of multiple substrates is studied. Three different mechanisms of bisubstrate binding, namely, ordered sequential, random sequential and ping‐pong nonsequential pathway, are broadly discussed. By means of the chemical master equation approach, exact expressions for the waiting‐time distributions, the mean turnover time and the randomness parameter as a function of the substrate concentration, such that both concentrations are fixed, but one of them is changed quasi‐statically are obtained. The randomness parameter is not equal to unity at intermediate to high substrate concentrations, which indicates the presence of multiple rate‐limiting steps in the reaction pathway in all three modes of bisubstrate binding. This arises due to transitions between the free enzyme and the enzyme–substrate complexes that occur on comparable timescales. Such turnover statistics of the single enzyme can also distinguish between the different types of bisubstrate binding mechanisms.     

Phase-transfer catalysis of the reaction of α-bromo-p-xylene with iron carbonyls

The carbonylation of α-Bromo-p-xylene (BrCH₂C₆H₄CH₃, BX) with iron pentacarbonyl (Fe(CO)₅) by phase-transfer catalysis was studied in an organic solvent/alkaline solution. The reaction mechanism was corrected and clarified. The concentrations of base, reactant and catalyst, volume ratio, the kind of catalysts, organometals and solvents were evaluated to find the optimum condition in this reaction. The technique of phase-transfer catalysis has a dramatic accelerating effect on the reaction. In examining eight kinds of phase-transfer catalysts, tetra-n-butylammonium cation and tetra-n-butylphosphonium cation were found to be the best for increasing the yield of bis(p-methylbenzyl) ketone ((p-CH₃C₆H₄CH₂)₂CO, BMBK). The amount of phase-transfer catalyst, the concentration of NaOH, the molar ratio of BX to Fe(CO)₅ and the volume ratio of aqueous to organic phase affected the product selectivity.     

Expanding the toolbox for development of metal-based dual-functional catalytic membranes

Catalytic membranes offer opportunities to develop modular, process-intensified units. Dual-functional materials, which integrate reactive and separation components in a single material, could play an important role in enabling them. Adapting the various characterization tools that are used to analyze the structures of metal-based catalysts to these integrated structures could provide vital information for their design and implementation. In this perspective, we highlight the ways in which these tools can be used to analyze nonreactive membranes and non-integrated systems where the catalyst and the membrane operate as two separate units. A methodology developed to analyze these comparatively simpler systems could be subsequently extended to integrated dual-functional catalytic membranes. Thus, researchers from the catalysis and membranes communities can work together in a way that will not only lead to fundamental advancements in our understanding of catalytic membranes but also enable their transformation into real, scalable process-intensified units.     

Kinetic study of reaction of hexachlorocyclophosphazene with phenol by triphase catalysis

The kinetics of the substitution reaction of hexachlorocyclotriphosphazene, (NPCl₂)₃, with phenol to synthesize the partially substituted (phenoxy) chlorocyclotriphosphazene was investigated by using triphase catalysis in an organic phase/alkaline solution. The relative reaction-rate constants and the corresponding energies, enthalpies, and entropies of activation of the sequential substitution were also estimated. The diffusional limitations involve both ion diffusion in the aqueous phase and organic reactant diffusion in the organic phase within the catalyst pellet. The particle diffusion and intrinsic reactivity limit the substitution reaction in the organic phase. The diffusion of the aqueous phase in the ion-exchange step is the main rate-limiting factor.     

Kinetics of formation of diphenoxymethane from phenol and dichloromethane using phase-transfer catalysis

The reactions of phenol with dichloromethane using quaternary ammonium salts as a liquid–liquid phase-transfer catalyst in an organic solvent/alkaline solution were investigated. The technique of phase-transfer catalysis had a dramatic accelerating effect on the reaction and increased the yield of diphenoxymethane by more than 95%. The effects of catalysts, temperature, and basic concentration on reaction rate were studied in order to find the optimum operating conditions for this reaction. Experimental results indicated that a potassium hydroxide was preferred over sodium hydroxide in order to enhance the reactivity of the reaction. The reaction rate constant and the distribution coefficient of the intermediate product were obtained. During the reaction, the concentration of the intermediate product was also measured in order to study its behavior in the liquid–liquid system.     

反应条件及陈化过程对氢氧化铬氧化速率的影响

氢氧化铬是含铬二次资源中铬的重要存在形式,也是含六价铬污染物还原时的主要产物,其氧化过程的研究对铬资源的提取和铬污染的控制具有重要意义。以亚硫酸钠还原重铬酸钠制备的氢氧化铬为研究对象,实验考察了氧化温度（室温~200 ℃）、氧化时间（0~168 h）、添加剂种类（碳酸钠、硫酸钠）等因素对氢氧化铬氧化的影响,并进行了氧化方程选取和动力学拟合计算。结果表明,温度越高两种氢氧化铬样品氧化反应越充分、氧化限度越大。在无添加剂条件下,200 ℃时新制、陈化氢氧化铬的氧化速率K值分别是80 ℃时的617、4 375倍;添加剂的加入会促进其氧化反应,140 ℃条件下,新制氢氧化铬添加碳酸钠、硫酸钠为n（Na）∶n（Cr）=0.2时的氧化速率K值分别是无添加时的10、4倍;新制氢氧化铬较陈化氢氧化铬更易氧化,氧化速率K值为陈化氢氧化铬样品的1.4~1.9倍,可能与其所含结合水较多有关。     

Mechanistic and kinetic investigation of Cu(II)-catalyzed controlled radical polymerization enabled by ultrasound irradiation

Controlled radical polymerization (CRP) under external field has been an attractive research area in these years. In this work, a new electron transfer mechanism, that is, sonochemically induced electron transfer (SET) was introduced to mediate polymerization for the first time. The activator Cu^IX/L complex was (re)generated from Cu^IIX₂/L in dimethylsulfoxide (DMSO) by the SET process in the presence of free ligand tris(2-dimethylaminoethyl)amine (Me₆TREN). The investigation of polymerization including the mechanistic insights and effect of experimental conditions on the rate of reaction has been undertaken. Kinetics of Cu(II)-catalyzed CRPs via SET under different conditions (i.e., Me₆TREN concentration, catalyst loading, targeted degree of polymerization, and sonication power) were conducted in an unprecedentedly controlled manner, yielding polymers with predetermined molar masses and low dispersities (Đ < 1.12). Attractively, the polymerization can be performed without the piezoelectric nanoparticles and exogenous reducing agent. Contamination by nonliving chains formed from sonochemically generated radicals is avoided as well. All of these results supported that Cu(II)-based catalyst activation enabled by ultrasonication has a promising potential in scale-up of CRP.     

Formation of Aluminum-Doped Zinc Oxide Nanocrystals via the Benzylamine Route at Low Reaction Kinetics

The influence of essential process parameters on the adjustability of specific process and particulate properties of aluminum-doped zinc oxide (AZO) nanocrystals during synthesis via the benzylamine route at low reaction kinetics is demonstrated by enabling time-resolved access of the selected measurement technique. It is shown that the validity of the pseudo-first-order process kinetics could be extended to the minimum operable reaction kinetics. On the other hand, the impacts of the process temperature and the initial precursor concentration on both the process kinetics and the particle morphology are discussed. The obtained data provide a versatile tool for precise process control by adjusting defined application-specific particle properties of AZO during synthesis.     

Strategic Immobilization of Molecular Catalysts onto Carbon Nanotubes via Noncovalent Interaction for Catalytic Organic Transformations

Since their discovery, carbon nanotubes (CNTs) continue to attract growing interest from scientists in a wide range of fields, likely due to their fascinating nanoarchitecture as well as their electronic and physical properties. From the viewpoint of synthetic chemistry, the chemical and physical stability, high surface area, and π-stacking nature of CNTs are attractive features for their application as solid supports for molecular catalysts. The chemical functionalization of CNTs has been explored for various applications, including covalent and noncovalent grafting of molecular catalysts. Although noncovalent grafting provides less stable immobilized catalysts compared with covalently grafted hybrid molecular catalysts and CNTs, the preparation protocol is expeditious and repetitive use of the catalysts is well demonstrated, confirming their potential broad utility in synthetic organic chemistry.     

明胶的酶降解反应动力学研究——Ⅱ.动力学规律和机理

根据文献[1]中的实验数据,结合化学反应动力学的基础理论,计算了明胶的酶降解反应的反应级数、表观活化能、指前因子等有关动力学参数值。得到反应的总速率方程。所求得的反应速率常数与温度的关系表明,在实验温度范围内,符合Arrhenius公式。最后提出了该反应的酶催化反应机理,实验结果与所推得的机理动力学方程相吻合。     

锂硫电池中的催化应用

锂硫电池以其高理论比容量、环境友好和低成本等优点成为理想的下一代高能量密度储能装置。但活性材料的绝缘特性、多硫化物的穿梭效应和硫物种缓慢的动力学转化过程,导致电池性能持续衰减,是目前阻碍锂硫电池商业化发展的关键。利用催化材料加速硫物种转化,研究催化氧化还原动力学,从而实现高性能锂硫电池的开发、认知硫物种微观转化机制,是近年来受到广泛关注的研究热点。本综述从理解多硫化物产生、转化和硫化锂沉积等角度入手,讨论了锂硫化学中的催化转化特点,综述了近年来锂硫电池催化材料的研究进展,评述了催化剂的设计策略与评价方法,可为高活性锂硫电池催化剂材料提供一定的借鉴。     

乙炔选择性加氢：催化剂结构敏感性分析及调控

Pd催化乙炔选择性加氢是石脑油蒸汽裂解和煤基电石乙炔路径制备聚合级乙烯的关键。传统的Pd基催化剂使用成本较高且选择性和稳定性较差。本文综述了近年来乙炔选择性加氢催化剂结构敏感性及其调控方面的相关研究进展,重点介绍了包括活性金属粒径、纳米颗粒形貌和电子结构等对乙炔选择性加氢反应性能的重要作用,进而阐明了催化剂结构调控的目标与方向。进一步归纳总结了针对该反应特性的催化剂结构定向调控的研究进展,主要包括合金和金属间化合物催化剂、单原子及其合金催化剂的设计。通过合理地调控催化剂结构,优化关键物种的吸脱附和反应动力学行为,能够显著提高乙炔加氢催化剂的选择性及稳定性。在未来的研究中,如何针对该反应特性,构筑高效、稳定和低成本的催化剂将会是该体系催化剂研究的重点与难点。