纤维素负载金属催化剂研究进展

高分子负载金属催化剂由于催化活性好、稳定性高、反应后容易和产物分离、易于从反应体系中分离回收和重复使用等原因,近年来成为了人们的研究热点之一。纤维素是自然界中储量最丰富的天然高分子,其在大多数有机溶剂中稳定,且其比表面积大,结构中含有大量羟基,可参与许多反应。本文以自然界中储量丰富、无毒、可降解、可再生的天然高分子纤维素为载体,按照纤维素负载金属催化剂制备方式的不同,综述了纤维素负载Pd、Ag、Au、Cu等金属催化剂的制备及其在有机反应中的应用。     

负载型过渡金属氧化物催化剂上SO_2的还原

研究了γ Al2 O3负载过渡金属氧化物催化剂上CO还原SO2 的反应 ,考察了系列过渡金属对该反应的催化活性 ,发现Fe系催化剂的性能最好。同时对还原反应的条件进行了选择 ,发现在较低温度下 ,大空速不利于SO2 的还原 ,而在较高温度下 ,气体空速对反应影响不大 ,不同的物料配比对反应结果有很大影响 ,当CO∶SO2 =2时 ,最有利于单质硫生成。研究证明 ,金属硫化物是催化SO2 还原反应的活性相 ,该活性相的形成与催化剂的氧化还原能力有关 ,整个还原反应的机理应为中间产物机理     

过渡金属基MOF材料在选择性催化还原氮氧化物中的应用

选择性催化还原(SCR)技术是目前应用最广泛的工业脱硝技术,研发具有优良活性和抗毒化性能的催化剂体系是研究学者关注的重点。过渡金属氧化物和金属有机骨架(MOF)材料因其优良的氧化还原性能在脱硝领域受到了广泛关注和研究,且研究学者发现将过渡金属氧化物与MOF材料结合能够进一步提高催化剂的脱硝活性。本文综述了近年来主要应用于NH₃-SCR反应的系列单过渡金属基MOF脱硝催化剂和复合过渡金属基MOF脱硝催化剂的研究进展,阐述了过渡金属基MOF脱硝催化剂抗水抗硫中毒性能和热稳定性的强化方法,并展望了未来过渡金属基MOF脱硝催化剂的主要研究方向：综合利用不同过渡金属氧化物的特点并结合金属氧化物间的强相互作用,制备得到具有优良脱硝活性、抗水抗硫性能和热稳定性的新型过渡金属基MOF脱硝催化剂,进一步通过实验和仿真模拟相结合制备高效过渡金属基MOF脱硝催化剂以满足工业化需求。     

室温离子液体在过渡金属催化反应中的应用研究进展

室温离子液体(RTILs)是在室温或近于室温下呈液态的由离子构成的盐类．如图1所示，RTILs按阳离子类型可以分为4类：烷基季铵盐离子；烷基季鳞盐离子；N，N-二烷基咪唑离子和N-烷基吡啶离子．按阴离子可分为：氯化盐 AlX3(X=卤素)和含有RF1^-,PF6^-等阴离子的离子液体．     

过渡金属催化苯并咪唑衍生物的合成研究进展

苯并咪唑衍生物具有多种生物活性,在医药、农药等领域有着广泛的应用,该类化合物的合成也是当前的研究热点之一.过渡金属催化苯并咪唑的合成方法具有简单、直接、高效等优点,近年来发展迅速,寻找更简单、高效、廉价、环保的催化体系,一直是化学工作者研究的目标.本文综述了当前报道较多的几种过渡金属催化合成苯并咪唑新方法的研究进展,并简要介绍了各类催化体系的优缺点.     

电解海水析氢反应过渡金属基催化剂的研究进展

海水作为地球上最丰富的自然资源之一,在实现大规模的电解水制氢方面具有得天独厚的优势。然而,海水中的Cl^-、Ca²⁺和Mg²⁺等使催化剂在阴极发生腐蚀、毒化或降解,导致其稳定性、活性以及使用寿命显著降低。近年来,为了解决上述问题,人们致力于设计开发廉价的高效稳定析氢反应（HER）催化剂,进而提高电解海水制氢效率。本文首先介绍了电解海水的优势及其HER所面临的挑战,其次从活性和稳定性等方面重点论述了硒化物、硫化物、氮化物以及磷化物等过渡金属基催化剂在电解海水HER中的研究进展,最后总结和展望了电解海水HER催化剂未来的发展前景。     

后过渡金属烯烃聚合催化剂的研究进展

综述了近两年来后过渡金属(VIII族)催化剂在乙烯、丙烯和α-烯烃聚合,α-烯烃和极性单体共聚,α-烯烃活性聚合,以及乙烯齐聚等方面的最新进展.     

过渡金属乙烯齐聚与聚合催化剂研究进展

综述了近年来过渡金属配合物催化乙烯齐聚与聚合的最新进展;介绍了乙烯齐聚或聚合的反应时间、反应温度、乙烯压力、助催化剂用量等反应条件及配体上不同取代基对前过渡金属(铬,锆,钛,钒)和后过渡金属(铁,钴,镍,铜)配合物的催化活性和齐聚或聚合产物的影响;分别以钛和镍配合物催化剂为例,介绍了前过渡金属和后过渡金属催化乙烯齐聚或聚合的机理。     

电容去离子过渡金属基电极设计及应用研究进展北大核心CSCD

电容去离子(Capacitive deionization,CDI)作为一种新兴的水淡化和离子分离方法,由于其离子选择性高、水回收率高和能耗低等优点受到广泛关注。与传统的基于碳电极的CDI相比,新兴的法拉第电极通过离子捕获的法拉第反应,提供了使得CDI的脱盐性能大幅提升的独特机会。而过渡金属基电极由于其高度可逆的法拉第响应,相对较高的导电性以及出色的理论赝电容值等优势,在CDI电极设计领域受到广泛关注。本文系统地归纳和梳理了过渡金属基电极在CDI应用中的材料分类,总结了针对其本征缺陷所进行改性工程,主要包括导电材料耦合、功能结构工程和缺陷工程等,并对其在海水淡化中的性能进行了总结;此外,从离子选择性分离、金属离子去除和营养元素回收等方面介绍了过渡金属基电极在CDI中的特定应用。最后,概述了剩余的挑战和研究方向,为未来的过渡金属基电极的开发与研究提供指导。     

Cyclooligomerization with Transition Metal Catalysts

This report is concerned not only with the syntheses of new ring systems and the preparation of derivatives of known rings but also with new types of catalysts based upon, e. g., nickel, iron, molybdenum, manganese, and palladium. The broad applicability of the methylene insertion reaction as a method for identifying mono- and di-methyl-substituted eight-, ten-, and twelve-membered rings is also demonstrated. A further section is concerned with the possible mechanism of C? C bond formation in transition metal complexes; several earlier suggestions have been revised in the light of new experimental data. In addition, experimental results are discussed which indicate that the reactivity and selectivity of the complexes formed by the nickel-ligand catalyst and olefins or alkynes depend upon the structure of the ligands.     

Influence of Ligands on the Activity and Specificity of Soluble Transition Metal Catalysts

The reaction of a covalently σ-bonded ligand (alkyl group, hydrogen) with a molecule (olefin, CO) attached to the transition metal by a coordinate bond is the essence of many catalytic processes. The influence of the other ligands in the complex on this reaction is discussed in the present article. Various ways in which the ligands can act, e.g. by electronic effects via the σ and π electron systems of the complex and by steric effects, are first described separately and then illustrated by examples.     

Cracking of Cellulose over Supported Metal Catalysts

Cellulose is cracked over supported Pt or Ru catalysts under hydrogenolysis conditions in water to give sorbitol as a main product. Among the catalysts tested, Pt/γ-Al₂O₃ gave the highest yield and selectivity, and this catalyst was recyclable in repeated runs. It is proposed that cellulose is hydrolyzed by in situ generated acid sites to form glucose, and glucose is immediately reduced to sorbitol over the metal catalyst.     

Recent Advances in Transition Metal-Based Catalysts for Ethylene Copolymerization with Polar Comonomer

The synthesis of polar functionalized polyolefin (PFP) offers improvement in mixing properties, polymer surface, and rheological properties with the potential of upgraded polyolefins for modern and ingenious applications. The synthesis of PFP from metal-based catalyzed olefin (non-polar in nature) copolymerization with polar comonomers embodies energy-efficient, atom-efficient, and apparently an upfront methodology. Despite their outstanding success during conventional polymerization of olefin, 3^rd and 4^th group (early transition metal)-based catalysts, owing to their electrophilic nature, face challenges mainly due to Lewis basic sites of the polar monomers. On the contrary, late transition metal-based catalysts have also made progress, in recent years, for PFP synthesis. The recent past has also witnessed several advancements in the development of dominating palladium-based catalysts while their lower resistance towards ligand functional groups has limited the practical application of abundant and cheaper nickel-based catalysts. However, the relentless efforts of the scientific community, during the past half-decade, have indicated rigorous progress in the development of nickel-based catalysts for PFP synthesis. In this review, we have abridged the recent research trends in both early as well as late transition metal-based catalyst development. Furthermore, we have highlighted the role of transition metal-based catalysts in influencing the polymer properties.     

新型烯烃聚合催化剂研究进展

由于过渡金属催化剂在烯烃聚合方面具有高活性和良好的分子剪裁性,通过调节催化剂的微结构或温度、压力等聚合环境的变化,可以在分子层次上实现烯烃聚合物的分子设计与组装,实现聚合物物理性质的调控,最近引起了人们的广泛关注。本文介绍了过渡金属催化剂的合成及其负载化,水相烯烃聚合及活性聚合等方面的研究进展。     

Asymmetric Syntheses with the Aid of Homogeneous Transition Metal Catalysts

The progress made in the field of homogeneous catalysis during the last five to six years has led, inter alia, to the development of highly selective catalysts for asymmetric syntheses. Homogeneous asymmetric hydrogenation, using well defined transition metal catalysts, may be achieved with optical yields of 85 to 90% or more. Catalytic reactions, in which the chiral centers are generated by C? C bond formation, can result in optical yields of 70 to 80%. The hydrogenation catalysts consist primarily of rhodium(I) complexes containing “Homer phosphanes”, phosphanes with chiral C atoms, or optically active amides. Catalysts which induce optical activity through the formation of C? C bonds have been developed from π-allylnickel halides, Lewis acids, and phosphanes containing chiral C atoms. The results obtained signify a breakthrough in an area of catalysis previously restricted to syntheses involving enzymes.     

Effect of Adsorption of ZrO2 in Catalysts on the Efficiency of Hydrolysisof Cellulose to Sugar in Aqueous System under Microwave Radiation

Five types of ZrO₂ are used to simply establish an effective aqueous catalytic system with sulfuric acid for the hydrolysis of cellulose to sugar, respectively. By adjusting surface roughness and particle size of ZrO₂, different adsorption is produced. Accordingly, following the thought to inhibit the self‐aggregation nature of cellulose, after the introduction of ZrO₂ with adsorption in catalysts, the efficiency of the hydrolysis of cellulose to sugar is improved. The results show different ZrO₂ can produce different effects during the hydrolysis of the cellulose with relatively low crystallinity. Under the optimal conditions, the conversion of cellulose and TRS yield reaches 95.5% and 93.6%, respectively. Through this research, it reveals the critical point to organize a feasible and useful way for the hydrolysis of cellulose to sugar with high efficiency in an aqueous system. An important theoretical and technical support is also provided for the conversion and utilization of cellulose in the future.     

Polymerization of 4-Dimethylamino-N-propargylpyridinium Bromide by Transition Metal Catalysts

The polymerization of an ionic propargyl derivative, 4-dimethylamino-N-propargylpyridinium bromide (DMAPPB), was carried out by palladium, platinum, and ruthenium chlorides. The polymerization of DMAPPB by these transition metal catalysts proceeded well to give a relatively high polymer yield. The chemical structure of the resulting polymer was characterized by such instrumental methods as elemental analysis, infrared, NMR, UV–visible spectroscopies to have conjugated polymer backbone system bearing 4-dimethylamino-N-methylenepyridinium bromide. The polymer was soluble in DMF, DMSO, and formic acid, and found to be less hygroscopic than those of similar homologues having more smaller substituents. The resulting polymers were mostly black powders and showed the amorphous morphology.     

磁性碳基磺酸化固体酸催化剂的制备及其催化水解纤维素

以纤维素和硝酸铁为原料,发烟硫酸为磺酸化试剂,采用热解法合成了磁性碳基磺酸化固体酸催化剂(Fe/C-SO3H).利用扫描电镜(SEM)、透射电镜(TEM)、X射线衍射(XRD)、X射线光电子能谱(XPS)、傅里叶变换红外(FT-IR)光谱仪和振动样品磁强计(VSM)等手段对催化剂进行了表征,评价了催化剂在纤维素水解反应中的催化活性.结果表明,Fe是以γ-Fe2O3的形式存在于碳本体中,催化剂呈现超顺磁性.对于纤维素的水解反应,在优化条件下,纤维素的转化率可达40.6%.此外,催化剂可稳定分散于反应体系中,并在外加磁场作用下可快速与反应体系分离.但催化剂重复使用时催化活性有所下降,其失活原因经初步认定是由于表面部分磺酸基团在反应过程中脱落.     

静电纺丝法制备纤维素纳米纤维的研究进展

纤维素纳米纤维很好的结合了纤维素的重要属性和纳米材料的各项特性,但纤维素大分子之间存在大量氢键,使得纤维素较难溶于普通溶剂,导致通过静电纺丝法直接制备纤维素纳米纤维具有一定的难度.而先采用静电纺丝法制备纤维素衍生物纳米纤维,再对纤维素衍生物纳米纤维进行水解也是制备纤维素纳米纤维的一种有效方法.本文对近年来这两种纤维素纳米纤维制备方法的研究进行了综述,并对静电纺制备纤维素纳米纤维的发展前景做出了展望.