自然氧化偶联及其在碳氢功能化反应中的应用

氧化偶联作为一种经济、高效的化学键构建模式,在有机合成化学中得到了广泛的应用.近年来, Klussmann、焦宁和霍聪德等课题组通过发展简单、直接的自然氧化偶联反应,成功实现了一些Csp³-H和Csp²-H功能化反应,在该领域中取得了重要进展.我们就他们近年来在该领域的研究进展作一亮点评述.     

脂肪醇氨氧化反应制备脂肪腈研究进展北大核心CSCD

脂肪腈是一类非常重要的化工原料和中间体,被广泛应用于医药、农用化学品、染料和合成树脂等领域.在诸多合成脂肪腈的路线中,脂肪醇氨氧化制备脂肪腈的路线使用可源于生物质资源的脂肪醇为原料,有助于“碳中和”和“碳达峰”目标的实现;同时,该反应副产物为水或氢气,符合“绿色”可持续发展的要求,具有重要的研究价值.根据脂肪醇氨氧化制备脂肪腈的过程中是否需要向体系中提供氧气,氨氧化过程可分为需氧氧化-氨化反应和脱氢氧化-氨化反应两类.需氧氧化-氨化反应在均相催化体系和非均相催化体系中均具有相关研究,而脱氢氧化-氨化反应的研究则主要集中在非均相体系中.按照以上分类,综述了脂肪醇氨氧化制备脂肪腈催化体系的研究进展,分析了不同种类催化体系的优势与尚存在的不足,并展望了该反应催化体系未来发展的方向.     

过氧化脲在氧化反应中的应用研究进展

氧化反应是重要的有机合成单元反应,常采用H2O2或过氧酸等为氧化剂.近年来,过氧化脲作为一种清洁环保的固态H2O2,以其性质稳定、H2O2含量高(36.2%)且释放可控等优点,在众多氧化反应中得到了广泛应用.对过氧化脲在氧化反应中的应用进行了总结和概述,重点介绍了环氧化、Baeyer-Villiger氧化、N-氧化、硫醚氧化成砜和亚砜、氧化卤化等反应.     

生物基聚酯单体的定向催化制备

有机二羧酸是重要的聚酯单体,广泛应用于化学纤维、轻工、电子等工业生产的各个方面.随着社会工业化的发展,以大量不可再生的石油资源为原料生产有机酸造成地球石油资源的匮乏和环境污染问题.通过生物质及其衍生物来制备高附加值化学品有机二羧酸,引起了化工应用领域的广泛关注.在合成生物质有机二羧酸的研究中,设计与制备具有高活性、高稳定性的催化剂具有重要意义.近年来,许多工作对催化剂的种类进行了探索,并取得了一定的研究进展.本文重点从生物质原料、催化剂性能评估、反应机理等方面对制备C₃～C₆二羧酸的催化体系进行了综述,包括丙二酸、丁二酸、2,5-呋喃二甲酸和己二酸,并对生物质有机二羧酸制备领域的发展进行了展望.     

氧化还原树脂的合成及其氧化还原性能

本文主要叙述了以国产717强碱性阴离子交换树脂为基体,采用甲醛与对苯二酚、邻苯二酚、连苯三酚和2,7-萘二酚等聚合生成氧化还原树脂,它们的氧化还原容量分别为5.3,5.4和5.2meq/g-干树脂.文中还介绍了本类树脂的氧化还原电位测定方法,并据此研究和测定了对苯二酚、邻苯二酚和连苯三酚型树脂的氧化还原电位,这些电位的测定结果与其氧化还原实验事实相符.也研究了多种氧化剂和还原剂与自制树脂的交换性能,讨论了这些树脂容量与交换性能的关系.应用所合成的新树脂进行了从硝酸银废液中回收银和对硫化氢试行氧化脱硫处理试验,效果良好.     

甲烷直接氧化制甲醇研究进展概述

目前,天然气转化为高附加值化工产品的应用越来越受到人们关注.甲烷作为天然气的主要成分,其转化和应用是天然气化工领域的重要研究方向.而甲烷直接氧化制甲醇长久以来一直是研究重点.甲烷直接氧化制甲醇与传统的甲烷二步法间接转化相比,有节能和工艺简化的突出特点.然而,甲醇直接氧化制甲醇过程所面临的主要问题有：(1)甲烷分子的活化能很高,需要苛刻的操作条件才能活化参与反应;(2)反应进行的程度难以控制,生成的甲醇会进一步被氧化生成较多副产物,大大降低甲醇收率.因此,高效活化甲烷分子和抑制甲醇深度氧化是促进该过程工业化的重要研究内容.本文主要论述了非均相、气相均相和液相体系中甲烷直接氧化制甲醇的研究进展.在甲烷非均相氧化过程中,采用过渡金属氧化物作为催化剂在高温条件下催化甲烷部分氧化反应,其中,钼系和铁系催化剂的研究最为广泛.研究表明, MoO3可作为催化剂的主要活性组分,尤以 MoO3/Ga2O3催化剂性能最好,得到甲醇收率最高.在铁系催化剂中, Fe-ZSM-5 催化反应的甲醇选择性和收率都相对较高;但是每次反应后催化剂都需要重新活化,这种间歇性操作会增加成本,不利于工业化应用.总之,甲烷的非均相氧化过程存在易形成金属聚集体、催化剂选择性低以及甲醇收率低(5%)等问题,需要深入系统地研究解决.然而,与非均相氧化过程相比,操作较为简单的甲烷气相均相氧化作为目前最有工业前景的过程受到越来越多关注.在此过程中,影响反应的主要因素有反应器、反应条件(反应压力、反应温度和反应时间等)以及添加的介质等.反应器的特殊设计需要考虑的方面有反应产物的分离与转移、反应热的移除以有效提高甲烷的转化率,比如膜反应器对物质的分离作用.反应压力对反应过程的影响较为复杂.基于动力学因素,提高反应压力可以较大幅度地增加甲醇收率,同时最佳反应温度降低,但是,当压力高于8.0 MPa时,设备成本消耗大幅增加.另外,研究表明,进料中加入 NOx作为添加介质可以提高甲烷转化率和甲醇选择性,同时降低初始反应温度.与前两个氧化体系相比,液相均匀氧化过程能够获得较高的甲烷转化率与甲醇选择性.但是液相体系中强腐蚀性介质的使用增加了设备成本,阻碍了该过程工业化的应用进程.因此,促进液相体系工业化的关键就是开发绿色高效的催化剂.     

La-Ba-Sn(Sm,Ce)体系催化剂上的甲烷氧化偶联

报道了La-Ba-Sn(sm,Ce)体系催化剂上甲烷氧化偶联反应(OCM)的催化性能.实验结果表明:第三组分Sn、Sm、Ce的添加显著提高了OCM催化活性和C₂烃选择性.不同催化剂制备方法对催化活性的影响不同,混浆法低温焙烧有利于低温OCM反应;干混法高温焙烧能在最佳OCM反应条件下获得较高的C₂烃收率和选择性.     

CexZr1—xO2复合氧化物负载PdO催化剂的CO和CH4氧化性能研究

以CexZr1-xO2复合氧化物为载体, 采用浸渍法配制了负载PdO催化剂,考察了催化剂对CO和CH4的氧化活性, 并对该催化剂的还原性能进行了表征. 结果表明,Ce/Zr比对催化剂的活性影响很大. 对于CO氧化, 当x=0.8时, 催化活性最高;而对于CH4氧化, x=0.5时,活性最高. 出现3个催化剂还原峰(α、β、γ), α峰归属于PdO还原,而β和γ峰归属于载体的还原. 我们认为α峰与CO氧化有关.     

基于催化氧化技术去除甲醛的研究进展

甲醛（HCHO）作为挥发性有机物（Volatile Organic Compounds,VOCs）,其催化氧化技术具有起燃温度低、设备简单、净化效率高等优点,被广泛采用,催化氧化催化剂主要为贵金属以及过渡金属氧化物.我们综述了近年来催化氧化甲醛的最新研究进展,尤其是甲醛催化氧化机理和提高催化活性的策略.最后,对催化氧化技术在甲醛催化氧化反应中的未来发展方向和趋势进行了展望.     

亚稳醌类分子的活性调控与仿生催化反应

醌及其亚胺类化合物是高亲电性、去芳构化的经典合成子,然而受限于易聚合、易水解等稳定性问题,其制备以及合成应用存在诸多挑战.我们利用仿生催化氧化策略,以易得的酚类化合物为原料,发展了金属催化剂/绿色终端氧化剂组合的催化体系,实现了高活性亚稳醌类分子的原位生成与活性调控,丰富了基于醌中间体的[3+2]、[3+3]、[4+2]等多个环加成反应并实现了区域选择性和立体选择性调控.对我们小组在亚稳醌的活性调控和仿生催化反应方面的研究成果做阶段性小节.     

Kinetics of the water-gas shift reaction in Fischer-Tropsch synthesis over a nano-structured iron catalyst

Based on formate and direct oxidation mechanisms, three Langmuir-Hinshelwood-Hougen-Watson (LHHW) kinetic models of the water-gasshift (WGS) reaction over a nano-structured iron catalyst under Fischer-Tropsch synthesis (FTS) reaction conditions were derived and compared with those over the conventional catalyst. The conventional and nanostructured Fe/Cu/La/Si catalysts were prepared by co-precipitation of Fe and Cu nitrates in aqueous media and water-oil micro-emulsion, respectively. The WGS kinetic data were measured by experiments over a wide range of reaction conditions and comparisons were also made for various rate equations. WGS rate expressions based on the formate mechanism with the assumption that the formation of formate is rate determining step were found to be the best.     

Active sites in working bifunctional GaH-TON aromatization catalysts: kinetic evaluation

The conversion of light alkanes to high value aromatics proceeds with a high selectivity over bifunctional, gallium (Ga) containing zeolite catalysts. It is generally agreed that Ga sites are involved in dehydrogenation reaction steps and that the zeolite acid sites catalyze cracking, oligomerization, and cyclization reactions. However, understanding of the precise roles of the acid and Ga sites in the reaction mechanisms is significantly hampered since the number of these sites in working catalysts is not known. This paper describes a kinetic approach to evaluation of the acid and Ga active sites in working Ga containing TON zeolite catalysts that relies on the analysis of the rates of formation of the primary products of a n-butane aromatization reaction. Our results show that the rate of ethane formation at low n-butane conversions can be used as a quantitative estimate of acidity in working bifunctional zeolite catalysts and demonstrate, for the first time, a significant decrease in the number of Br?nsted acid sites in the Ga containing catalysts under reaction conditions: around 47 and 79% for the catalysts with Ga loading of 1.5 and 2.5 wt %, respectively. We conclude that the reduction in acidity is associated with the formation of catalytically active Ga(+) ions and obtain estimates for the number and steady-state turnover activity of the acid and Ga active sites in n-butane transformation. We anticipate that our work will facilitate understanding of the precise roles of the acid and Ga sites in the mechanisms of alkane aromatization and, as a far-reaching implication, will prompt wider use of detailed kinetic studies for the evaluation of active sites in working catalysts.     

Organocatalytic kinetic resolution cascade reactions: new mechanistic and stereochemical manifold in diphenyl prolinol silyl ether catalysis

A new cascade reaction involving an iminium-catalyzed intramolecular oxa-Michael addition followed by an enamine-catalyzed intermolecular Michael addition is reported herein. This cascade reaction generates enantiopure, highly functionalized tetrahydropyrans and tetrahydrofurans in a one-pot reaction and in up to 89?% combined yield and up to 99?% ee. This cascade reaction is catalyzed by diaryl prolinol silyl ethers, which are a privileged class of catalysts. The stereochemical outcome of these cascade reactions is unprecedented. Computational studies indicate that this stereochemical outcome arises from nonclassical hydrogen-bonding interactions between the electrophile and the substrate, and from entropic considerations of preorganization. The unprecedented configurations of the cascade products, combined with the computational models, reveal for the first time that asymmetric induction by diaryl prolinol silyl ether catalysts is not always exclusively reagent controlled. The stereochemical outcome also arises from a kinetic resolution or dynamic kinetic resolution of the β-stereocenter through an enamine-catalyzed intermolecular reaction. This unprecedented organocascade reaction mechanism may be adaptable to diaryl prolinol silyl ether-catalyzed cascade reactions, in which both the iminium- and enamine-catalyzed steps are intermolecular, an underdeveloped type of cascade reaction.     

A new kinetic model for direct CO_2 hydrogenation to higher hydrocarbons on a precipitated iron catalyst:Effect of catalyst particle size

The kinetic of the direct CO_2 hydrogenation to higher hydrocarbons via Fischer–Tropsch synthesis(FTS)and reverse water-gas shift reaction(RWGS) mechanisms over a series of precipitated Fe/Cu/K catalysts with various particle sizes was studied in a well mixed, continuous spinning basket reactor. The iron catalysts promoted with copper and potassium were prepared via precipitation technique in various alcohol/water mixtures to achieve a series of catalyst particle sizes between 38 and 14 nm. A new kinetic model for direct CO_2 hydrogenation was developed with combination of kinetic model for FTS reaction and RWGS equilibrium condition. For estimate of structure sensitivity of indirect CO_2 hydrogenation to higher hydrocarbons, the kinetic parameters of developed model are evaluated for a series of iron catalysts with various particle sizes. For kinetic study a wide range of syngas conversions have been obtained by varying experimental conditions. The results show that the new developed model fits favorably with experimental data. The values of activation energies for indirect CO_2 hydrogenation reaction are fall within the narrow range of 23–16 kJ/mol.     

Re/Pt/Ce0.8Zr0.2O2/蜂窝整体催化剂上低温水煤气变换反应动力学研究

采用微分反应器,研究了新型Re/Pt/Ce0.8Zr0.2O2/蜂窝催化剂上低温水煤气变换反应的动力学行为。利用非线性最小二乘法处理正交设计的实验数据,获得了动力学方程的模型参数。所得的结果符合幂函数型动力学方程,经F检验和相关指数检验,实验值和模拟计算值符合较好。在该催化剂上水煤气变换反应的活化能为70kJ/mol,与文献中报道的数值相吻合。该催化剂上反应速率对CO、H2O、H2和CO2的反应级数分别为0.09、0.88、-0.54和-0.11,与传统的Cu基低变催化剂上的反应级数相差较大。这表明,低温水煤气变换反应在两种催化剂上遵循不同的反应机理。     

Scale-up of batch kinetic models

The scale-up of batch kinetic models was studied by examining the kinetic fitting results of batch esterification reactions completed in 75 mL and 5 L reactors. Different temperatures, amounts of catalysts, and amounts of initial starting reagents were used to completely characterize the reaction. A custom written Matlab toolbox called GUIPRO was used to fit first-principles kinetic models directly to in-line NIR and Raman spectroscopic data. Second-order kinetic models provided calibration-free estimates of kinetic and thermodynamic reaction parameters, time dependent concentration profiles, and pure component spectra of reagents and product. The estimated kinetic and thermodynamic parameters showed good agreement between small-scale and large-scale reactions. The accuracy of pure component spectra estimates was validated by comparison to collected NIR and Raman pure component spectra. The model estimated product concentrations were also validated by comparison to concentrations measured by off-line GC analysis. Based on the good agreement between kinetic and thermodynamic parameters and comparison between actual and estimated concentration and spectral profiles, it was concluded that the scale-up of batch kinetic models was successful.     

贵金属甲烷燃烧催化剂*

贵金属催化剂具有较高的甲烷燃烧活性,但是其弱的稳定性抑制了其在VOC脱除以及低浓瓦斯治理等领域的应用,因此提高贵金属甲烷燃烧催化剂的稳定性是目前研究的热点。本文综述了活性组分、载体、助剂和前驱体对贵金属甲烷燃烧催化剂性能的影响;重点介绍了具有较高甲烷燃烧活性的Pd基催化剂受这些因素的影响;结合甲烷燃烧动力学分析了反应组分对催化剂性能的影响;讨论了催化剂失活的机理以及导致研究结论存在较大分歧的原因,提出了避免这些分歧的措施。     

Mechanism and Kinetics of Reactions of C1 Molecules on Cu-Based Catalysts

The mechanism and kinetics of reactions occurring in the course of natural gas processing into motor fuels and other chemical products are considered with emphasis on copper-based catalysts. The following reactions are considered: methanol and methyl formate syntheses, dimethyl ether synthesis from syngas and by methanol dehydration, water-gas shift reaction, steam reforming of methanol and its decomposition to produce syngas, and others. It is shown that a key role in the mechanisms of the above reactions belong to transformations of stable, strongly (irreversibly) chemisorbed species, and this fact determines the specific features of the schemes of their mechanisms and kinetic models. The use of the specific features of reaction mechanisms makes it possible to increase the process efficiency (methanol and dimethyl ether syntheses) and provide a high selectivity (methyl formate synthesis).     

A comparison of direct methods to determine n-th order kinetic parameters of solid thermal decomposition for use in fire models

Pyrolysis models for burning solids in fire simulations are sensitive to the values of the activation energy, frequency factor, and reaction order that characterize the thermal decomposition of the solid to gaseous fuel, so direct measurement of these kinetic parameters is recommended, and simple methods are preferred. Three direct methods were evaluated with regard to the ability of their kinetic parameters to reproduce the thermal decomposition of five polymers measured by differential thermogravimetric analysis using the reaction order model. It was found that the two multiple heating rate methods produced identical, physically based kinetic parameters, while the peak property method produced non-physical kinetic parameters. However, all of these kinetic parameters in a single-step reaction order model gave reasonably good conversion histories for non-charring and moderately charring polymers. For a highly charring polymer, the conversion histories were poorly described without a multiple step reaction. The temperature at the maximum rate of conversion was found to be essentially independent of the reaction order, which decouples the frequency factor from the reaction order in the direct kinetic methods. Any of the direct methods are sufficiently accurate to obtain kinetic parameters for pyrolysis models because of the inherent spatial and temporal averaging of reaction rates at the burning surface of a thick solid and the uncertainty in the heat transfer mechanisms and thermo-physical parameters used in the models.