Sol-Gel Preparation of Coating Films Containing Noble Metal Colloids

Coating films containing Au, Ag, Pt and Pd metal colloids have been prepared by sol-gel processing. It is shown that for oxide films the temperature where the metal particles are precipitated by heating in air depends on metal species: 200°C for Au, 600°C for Ag, 800°C for Pt and 1000°C for Pd. The use of reducing atmosphere lowers the temperature for formation of noble metal colloids. This procedure can be used for direct formation of metal colloids from metal ions in the film as well as reduction of oxide particles to metal particles in the film. For an organic-inorganic matrix, noble metal colloids are precipitated by thermal reduction or photo-reduction. Thermal reduction occurs as a result of reduction by decomposing organic matter. Photo-reduction occurs as a result of UV irradiation.     

贵金属芳烃饱和催化剂研究

近年来石油（尤其是柴油）馏分脱除芳烃的问题受到越来越多的重视。目前研究较多的脱芳烃催化剂有负载型金属硫化物催化剂及负载型贵金属催化剂。后者的脱芳烃深度明显优于前者,但后者对原料中硫化物极为敏感,提高其抗硫性是该催化剂的研究重点。本文着重对改善贵金属芳烃饱和催化剂抗硫性的最新研究进行了综述。     

贵金属芳烃饱和催化剂研究

近年来石油(尤其是柴油)馏分脱除芳烃的问题受到越来越多的重视。目前研究较多的脱芳烃催化剂有负载型金属硫化物催化剂及负载型贵金属催化剂。后者的脱芳烃深度明显优于前者,但后者对原料中硫化物极为敏感,提高其抗硫性是该催化剂的研究重点。本文着重对改善贵金属芳烃饱和催化剂抗硫性的最新研究进行了综述。     

多环芳烃在贵金属催化剂上竞争加氢反应的研究

采用水蒸汽脱铝获得了超稳Y载体, 并用离子交换法制备了金属含量约为0.8 wt%的双贵金属催化剂. 用NH₃程序升温脱附、X射线衍射、N₂吸附-脱附等方法表征了载体和催化剂. 以萘、蒽、芘加氢为模型反应, 在高压反应釜中研究了催化剂的加氢活性以及它们之间竞争加氢的反应. 结果表明, 催化剂具有深度加氢的能力. 萘与蒽竞争加氢的结果表明, 蒽的加氢活性高于萘加氢活性, 并且蒽抑制萘加氢, 萘抑制了八氢蒽向全氢蒽的转化. 说明对于分子动力学直径相当的混合体系中, 多环物质抑制少环物质的加氢. 分子动力学直径不同的萘与芘加氢结果表明, 萘的转化率始终高于芘的转化率, 并且单和混合体系中萘和芘的转化率变化程度不大, 说明分子能否扩散进入分子筛孔道内也是影响加氢活性的重要因素.     

两性高分子作为保护剂的贵金属胶体的制备及其催化氢化活性

在金属催化领域,近年来人们对于高分子保护金属胶体的研究表现出很大的兴趣。高分散、窄分布金属胶体的制备研究成为众多工作者努力的目标。这在沟通分子催化与凝聚相物质催化间的联系有着重要的理论意义和应用价值。人们作出了种种努力设法获得高分散、窄分布的金属胶体。如:Bradley等报导用金属蒸汽冷凝法,Schmid等用水溶性三苯膦磺酸钠小分子配位体作为稳定剂,Esumi等用在有机溶剂中热解金属化合物的方法,Toshima等利用表面活性剂形成胶束的方法,Nagy的工作也很相似。这些工作在一定程度上取得进展。     

Noble Metal Nanoparticles Stabilized by Hyper-Cross-Linked Polystyrene as Effective Catalysts in Hydrogenation of Arenes

This work is addressing the arenes’ hydrogenation—the processes of high importance for petrochemical, chemical and pharmaceutical industries. Noble metal (Pd, Pt, Ru) nanoparticles (NPs) stabilized in hyper-cross-linked polystyrene (HPS) were shown to be active and selective catalysts in hydrogenation of a wide range of arenes (monocyclic, condensed, substituted, etc.) in a batch mode. HPS effectively stabilized metal NPs during hydrogenation in different medium (water, organic solvents) and allowed multiple catalyst reuses.     

贵金属壳-胶球核纳米复合材料的研究进展

综述了贵金属纳米粒子修饰的核胶球材料的研究进展。 由于贵金属壳-胶球核复合材料具有高的稳定性和优异的光学、催化等性质,是当前材料科学研究领域的一个热点。 因此,发展简单的、大量的制备这种复合材料的方法,以及广泛深入地研究其性能和应用具有十分重要的意义。     

锚联膦,胺配体对胶体钯的配位俘获及其负载催化剂的催化性能

本文继采用含硫配体(-SH,-SR)对高分子保护金属胶体的配位俘获之后,采用锚联在SiO_2表面的较含硫配体配位能力弱的P,N配体分别与聚乙烯吡咯烷酮(PVP)保护的胶体钯在室温下反应,在P/Pd大于3.5,N/Pd大于7时,可以实施对保护金属胶体的配位俘获,证实了配位俘获法是一种具有普遍意义的方法,经原子吸收光谱分析,溶液中残留的金属钯的量小于0.36 ppm(P/Pd=3.5)。经电子能谱证实,锚联膦胺配体与金属钯之间存在配位作用,这是实施保护胶体负载化的关键。透射电镜分析表明,在整个配位俘获的过程中,无论是在载体上或是在溶液中,胶体钯的颗粒大小与分布均保持不变。因此,配位俘获法是一种能控制多相催化剂中金属颗粒大小与分布的有效方法。由此合成的钯催化剂具有很高的催化活性,良好的选择性和稳定性,在对Cis,Cis-1,3-环辛二烯的选择性加氢中,其活性仅比均相的PVP-Pd胶体催化剂稍低,选择性达100％。在周转数达12,000次/个钯原子后,其催化活性仍保持不变,随着P/Pd比的增大,催化活性迅速下降。     

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。     

贵金属固体催化剂的纳米结构及催化性能

 综述了贵金属催化剂纳米结构的形成和制备方法,以及催化活性与纳米粒子尺寸的关系. 还以负载型双金属催化剂为例,介绍了催化剂中的短程有序结构.     

Optical Properties of Noble Metal Clusters in Ultrathin Solid Films

We report on the optical properties (absorption, Raman response) of thin and ultrathin phthalocyanine and amorphous silicon films with incorporated noble metal clusters. The metal clusters cause the typical absorption features originating from their surface plasmon resonance. In ultrathin films, due to the spatially close interface, the plasmon absorption may be displaced from its resonance frequency in the bulk, and its average position may be controlled by the average thickness of the ultrathin optical film. For example, we observe a shift of the plasmon resonance of silver clusters in amorphous silicon films (on fused silica) from 440 nm to 740 nm, when the silicon thickness increases from zero up to 9 nm. The deposition experiments are accompanied by investigations of the film structure, particularly in order to estimate the silver cluster diameter, which is around 3 nm or less.     

贵金属助剂对费-托合成用钴基催化剂的促进作用

贵金属助剂促进的费-托合成用钴基催化剂具有高活性和长链烃(C₅⁺)选择性优越等特点,被广泛应用于由合成气制清洁燃料的合成反应中。 本文重点讨论了贵金属助剂对活性钴物种的结构（还原度、分散度、双金属颗粒或合金的构成）, 钴基催化剂稳定性以及其对费-托合成的反应速率和产物选择性的影响规律。     

贵金属纳米粒子/硅纳米线复合纳米材料的制备及其催化性能研究

以十二烷基硫酸钠(SDS)作为保护剂, 利用贵金属阳离子(Mⁿ⁺)与HF处理后的硅纳米线(SiNWs)之间的氧化还原反应, 在SiNWs表面负载了贵金属纳米粒子. 通过调控SDS/Mⁿ⁺物质的量比、反应物浓度、反应温度等实验参数, 制备出了金属纳米粒子粒径均一且负载密集的AuNPs/SiNWs, PtNPs/SiNWs复合材料. 将AuNPs/SiNWs复合材料应用在亚甲基蓝的还原反应, 实验结果显示, 60 min内AuNPs/SiNWs可以将55%的亚甲基蓝还原, 表明AuNPs/SiNWs具有良好的催化活性. 这种复合材料易于从反应溶液中分离出来, 可以实现纳米催化剂的循环使用.     

金属/金属氧化物纳米粒子在不对称氢化和氢转移反应中的应用研究进展

近年来,金属/金属氧化物纳米粒子催化的不对称氢化和氢转移反应已经成为催化领域的前沿和研究热点之一. 金属/金属氧化物纳米粒子的催化模式类似于“纳米反应器”,底物可以通过有机包覆层扩散至催化中心,局部的高催化剂浓度通常可以极大地提高催化反应转换数（TON）和转化频率（TOF）. 在以纳米金属为催化活性中心方面,Orito纳米铂体系获得最多的关注,科学家们从手性修饰剂的结构改造、催化剂载体的选择、不同的反应介质、纳米催化剂的形貌和催化反应机理等方面开展了较为系统的研究,并取得重要进展. 此外,纳米钯、铑、钌、铱和铁等金属纳米催化剂也在烯烃、酮和亚胺等化合物的不对称氢化和氢转移反应中表现出良好的催化性能,特别是纳米铱和铁催化剂已获得95%以上的对映选择性. 在金属/金氧化物纳米粒子为催化剂载体方面,其催化不对称氢化及氢转移反应的效率及对映选择性可与均相催化剂相媲美,同时还解决了均相催化剂难于回收再循环的缺陷. 本文简要介绍了近年来手性金属纳米催化剂在不对称氢化和氢转移反应领域的研究进展,讨论了相关反应的催化机理,并对该领域仍存在的问题和未来的发展方向进行了展望.     

高分子稳定的钌纳米金属簇选择性催化氢化巴豆醛

以聚乙烯吡咯烷酮稳定的钌纳米金属簇(PVP-Ru)为催化剂,进行了巴豆醛的选择性催化氢化。结果表明,反应体系中水和氢氧化钠的引入,可提高催化活性,但降低了选择性。某些金属阳离子对PVP-Ru的修饰作用使选择性有所提高,但降低了催化活性。尤其是经Co2 修饰后,巴豆醇的最高产率为5.5%,而催化活性由150.4 mol巴豆醛/mol Ru.h降至96.7 mol巴豆醛/mol Ru.h。     

镍族金属团簇在催化加氢过程中的应用

Nanoparticles of precious metals play an important role in many heterogeneous catalytic reactions due to their excellent catalytic performance. As an idealized model, gas phase metal clusters have been extensively utilized to understand catalytic mechanisms at a molecular level. Here we provide an overview of our recent studies on H₂ dissociative chemisorption on nickel family clusters. The structure evolution and the stability of the metal clusters were first compared. H₂ dissociation on the clusters was then carefully addressed to understand the capability of metal clusters to break the H-H bond. Two key parameters, the dissociative chemisorption energy (ΔE_CE) and the H sequential desorption energy (ΔE_DE), were employed to characterize the catalytic activity of metal clusters. Our results show that both ΔE_CE and ΔE_DE decline significantly as the H coverage increases. Since the catalyst is in general covered entirely by H atoms and H₂ molecules in a typical hydrogenation process, and maintained at a pre-determined pressure of H₂ gas, we can rationally use the calculated ΔE_CE and ΔE_DE values at full H saturation to address the activity of metal clusters. Our results suggest that at full H coverage, each Pt atom is essentially capable of adsorbing 4 H atoms, while each Ni or Pd atom can only accommodate 2 H atoms. Considering the similar values of H desorption energies on Pt and Pd clusters, the higher average H capacity per Pt atom could probably lead to a faster reaction rate because more active H atoms are produced on the Pt catalyst particles in the hydrogenation process. Finally, the charge sensitivity of the key catalytic properties of Pt clusters for hydrogenation was systematically evaluated. The results show that the dissociation of H₂ and H desorption are strongly correlated to the charge state of the Pt clusters at low H coverage. However, at high H-capacities, both ΔE_CE and ΔE_DE fall into a narrow range, suggesting that the charge can be readily dispersed and that the Pt-H bonds average the interaction between clusters and H atoms. As a result, the H-capacities on charged clusters were found to be similar as the cluster size increased; in case of sufficiently large clusters, the reactivity of a fully saturated cluster was no longer sensitive to its charge state.     

贵金属催化剂上氢气选择性催化还原NOx

NO_x的控制对于改善大气环境质量具有重要意义,而氢气选择性催化还原(H₂-SCR)NO_x作为一种高效环保的脱硝技术而备受关注。本文总结概述了近年来贵金属催化剂在H₂-SCR脱硝反应中的研究进展,首先介绍了H₂-SCR反应机理,在此基础上分别论述了影响贵金属催化剂性能的因素(如活性组分、载体类型、助剂添加及组分存在形式等)及催化剂结构与性能的构效关系。最后,针对目前存在的问题展望了H₂-SCR脱硝未来的发展方向。     

Electrodynamics of Noble Metal Nanoparticles and Nanoparticle Clusters

In this paper we examine the electrodynamics of silver nanoparticles and of clusters of nanoparticles, with an emphasis on extinction spectra and of electric fields near the particle surfaces that are important in determining surface-enhanced Raman (SER) intensities. The particles and clusters are chosen to be representative of what has been studied in recent work on colloids and with lithographically prepared particles. These include spheres, spheroids, truncated tetrahedrons, and clusters of two or three of these particles, with sizes that are too large to be described with simple electrostatic approximations but small compared to the wavelength of light. The electrodynamics calculations are mostly based on the discrete dipole approximation (DDA), which is a coupled-finite element approach which produces exact or nearly exact results for particles of arbitrary size and shape if fully converged. Mie theory results are used to study the validity of the DDA for spherical particles, and we also study the validity of the modified long wavelength approximation (MLWA), which is based on perturbative corrections to the electrostatic limit, and of the single dipole per particle approximation (SDA). The results show how the dipole plasmon resonance properties and the electric field contours around the particle vary with particle shape and size for isolated particles. For clusters of particles, we study the effect of interparticle spacing on plasmon resonance characteristics. We also show that the quadrupole resonance is much less sensitive to particle shape and interparticle interactions than the dipole plasmon resonance. These results provide benchmarks that will be used in future comparisons with experiment.     

手性Ru复合物催化剂的固载化及其不对称氢转移反应催化应用

Chiral Ru-BsDPEN, (1R,2R)-N-p-benzenesulfonyl-1,2-diphenylethylenediamine, catalyst has been immobilized on a mesoporous molecular sieve of MCM-41 type successfully. A hybrid mesoporous molecular sieve was synthesized using a precursor bearing benzene group, which in organosilica were sulfonylated and reacted with (1R,2R)-l,2-diphenylethylenediamine and [RuC1E(p-cymene)]2 successively to afford immobilized catalyst. The Brunauer-Emmett-Teller (BET) surface area and Barrett-Joyner-Halenda (BJH) pore size decreased after immobilization of catalyst onto the mesoporous material. Enantioselective transfer hydrogenation of ketones catalyzed by immobilized catalyst showed the highest yield of 22.36% and e.e. value of 31.47% by using acetophenone as substrate when reaction time was 48 and 16 h respectively.