Polymer-Protected Palladium Nanoparticles and Their Use in Catalysis

Abstract

Stable palladium colloids were prepared by the in-situ reduction of palladium chloride (PdCl₂) in the presence of protective water-soluble polymers and cationic polyelectrolytes. The particle sizes, morphologies, and particle-size distributions were determined by transmission electron microscopy and found to be in the nanometer size range. The catalytic activity of these colloidal metal-polymer systems was tested by the hydrogenation of cyclohexene as a model reaction. Most of the polymer-protected palladium nanoparticles were found to be catalytically active, and final conversions up to 100% were obtained in many cases.     

双杂原子介孔材料的合成及催化应用

在强酸性条件下,采用沸石前驱体溶液与表面活性剂自组装的方法,合成双杂原子掺杂的介孔催化材料Sn/Ti-MS-1. 表征结果显示,Sn/Ti-MS-1具有典型的介孔结构,骨架中含有TS-1沸石的结构单元. 在苯酚和2,3,6-三甲基苯酚的双氧水氧化反应中,焙烧前后的Sn/Ti-MS-1均表现出了良好的催化反应活性,表明其钛物种具有良好的热稳定性,并且在大分子氧化反应应用中具有明显的优势. 同时,这种Sn/Ti双杂原子介孔材料显示了较快的催化反应速率.     

Selectivity Effects in Bimetallic Catalysis

An emerging area of homogeneous catalysis is the use of catalysts featuring two closely associated metal sites. This approach complements the traditional focus on single‐site catalysts and makes available new parameters with which to optimize catalytic behavior. Single‐site catalysts are optimized through changing 1) the identity of the metal, and 2) the steric and electronic properties of the ligands. Bimetallic catalysts introduce new optimization parameters such as 3) catalyst nuclearity (mononuclear vs. binuclear), and 4) bimetallic pairing (relative compatibility of two metal sites). In order to harness these new optimization parameters in developing systems, it is necessary to first understand the origin of bimetallic selectivity effects that already have been documented. This Concept article highlights bimetallic effects on the chemo‐, regio‐, and stereoselectivity of catalytic transformations, using selected case studies from the recent literature as illustrative examples.     

Preparation and Reaction of Naked Metal Clusters for Catalysis and Genetic Materials

Metal clusters that contain a small number of atoms usually present unique properties with dramatic dependence on their sizes, geometric structures, and compositions. The studies of naked metal clusters are devoted to develop new catalysts and functional materials of atomic precision, and enable to improve the fundamental theory of structure chemistry and to understand the basic reactions and properties bridging the gap between atoms and bulk materials. In particular, some interesting superatom clusters have received reasonable research interest indicative of materials gene of clusters. Here in this review, we simply summarize the preparation, stability, and reactivity of naked metal clusters with a few examples displayed. Hopefully it serves as a modest spur to stimulate more interest of related investigations in this field.     

手性原子簇合物与不对称催化反应

以骨架手性原子簇合物为催化剂的不对称催化反应一直认为是极富挑战性的课题，一旦实现，将是一种理想和概念上的突破，回顾原子簇合物的不对性及不对称催化反应的进展，阐述了我们的目标和一些相关的问题。     

A New Synthetic Methodology in the Preparation of Bimetallic Chalcogenide Clusters via Cluster-to-Cluster Transformations

A decanuclear silver chalcogenide cluster, [Ag₁₀(Se){Se₂P(OⁱPr)₂}₈] (2) was isolated from a hydride-encapsulated silver diisopropyl diselenophosphates, [Ag₇(H){Se₂P(OⁱPr)₂}₆], under thermal condition. The time-dependent NMR spectroscopy showed that 2 was generated at the first three hours and the hydrido silver cluster was completely consumed after thirty-six hours. This method illustrated as cluster-to-cluster transformations can be applied to prepare selenide-centered decanuclear bimetallic clusters, [Cu_xAg_10-x(Se){Se₂P(OⁱPr)₂}₈] (x = 0–7, 3), via heating [Cu_xAg_7−x(H){Se₂P(OⁱPr)₂}₆] (x = 1–6) at 60 °C. Compositions of 3 were accurately confirmed by the ESI mass spectrometry. While the crystal 2 revealed two un-identical [Ag₁₀(Se){Se₂P(OⁱPr)₂}₈] structures in the asymmetric unit, a co-crystal of [Cu₃Ag₇(Se){Se₂P(OⁱPr)₂}₈]_0.6[Cu₄Ag₆(Se){Se₂P(OⁱPr)₂}₈]_0.4 ([3a]_0.6[3b]_0.4) was eventually characterized by single-crystal X-ray diffraction. Even though compositions of 2, [3a]_0.6[3b]_0.4 and the previous published [Ag₁₀(Se){Se₂P(OEt)₂}₈] (1) are quite similar (10 metals, 1 Se²⁻, 8 ligands), their metal core arrangements are completely different. These results show that different synthetic methods by using different starting reagents can affect the structure of the resulting products, leading to polymorphism.     

多元多金属含氧簇合物在催化化学中的应用*

多金属含氧簇合物在催化化学中的重要性与日俱增,在原子经济反应和环境友好催化方面有着诱人的实用前景。这类物种的催化活性、理化性质、分子结构和固态体相结构以及制备方法均能在分子水平上给出详细信息,因而被视为混合金属氧化物催化剂的分子设计材料。本文拟对能够直观反映出这种信息的多元多金属含氧簇合物催化的研究作一评述。     

Catalysis by Molecular Metal Clusters

Molecular metal clusters form a very large and diverse family. They present the opportunity of modeling the intermediates involved in surface mediated catalytic reactions, of providing a source of very reactive mononuclear metal fragments, and of effecting catalytic cycles in which the cluster remains intact. The last mentioned aspect is the subject of this review article. The state-of-the-art of cluster catalysis is critically analyzed. The possibilities offered by molecular metal catalysts of performing catalytic reactions at multimetal atom sites are also discussed.     

负载型双金属催化剂的制备及其等离子体催化氨分解制氢性能

利用等体积浸渍法制备了Fe-Co、Fe-Ni、Mo-Co、Mo-Ni双金属催化剂(总金属含量均为10%(w,质量分数),双金属摩尔比均为1:1),考察了其在等离子体条件下氨分解活性,结果表明Fe-Ni双金属催化剂表现出较好的协同作用。在此基础上,进一步考察了Fe/Ni摩尔比对其活性的影响。结果表明:当Fe/Ni摩尔比为6/4时,氨分解活性最好,而且该双金属催化剂稳定性良好。采用N_2物理吸附、X射线衍射(XRD)、H_2-程序升温还原(H_2-TPR)和高分辨透射电子显微镜(HRTEM)对催化剂的物化性质、还原性能、微观形貌等进行了研究。结果表明:活性较好的Fe-Ni双金属催化剂中,Fe与Ni形成尖晶石结构NiFe_2O_4,该结构有利于Fe和Ni的还原,即活性组分易恢复金属态,这可能是其活性较高的原因。     

Polymerized Micelle-Protected Platinum Clusters. Preparation and Application to Catalyst for Visible Light-Induced Hydrogen Generation

Platinum clusters protected by polymerized micelles were prepared by radical polymerization of unsaturated surfactants which were involved in micelle-protected platinum clusters. The micelle-protected platinum clusters were successfully prepared by photoreduction of hexachloroplatinic acid in water in the presence of unsaturated surfactants. The platinum clusters thus obtained were characterized by electron microscopy and IR and ¹H-NMR spectroscopies. The average diameter of the platinum particles was about 1 nm by electron microscopy, and the polymerization was confirmed by IR and ¹H-NMR spectra. The platinum clusters thus obtained proved to be highly active catalysts for visible light-induced hydrogen generation in the system of EDTA/Ru(bpy)₃ ²⁺/MV²⁺. The polymerized micelle-protected platinum clusters showed higher catalytic activity than the linear polymer-protected one. The catalytic activity was affected by the electric charge of the surfactants in the polymerized micelle-protected platinum clusters. Nonionic polymers were superior to those having anionic and cationic hydrophilic groups from the viewpoint of catalytic activity. The nonionic polymerized micelle forms rigid hydrophobic cores which help charge separation and the formation of a sequential potential field.     

Polymer-Immobilized Clusters and Metal Nanoparticles in Catalysis

Kinetics and Catalysis - Recent advances in the synthesis of polymer-immobilized clusters and metal nanoparticles and their use in catalysis of many organic reactions were presented. The main types...     

Capped Bimetallic and Trimetallic Nanoparticles for Catalysis and Information Technology

Summary: Polymer-capped metal nanoparticles can be recognized as a kind of macromolecule-metal nanoparticle complexes. Here the preparations of the capped bimetallic and trimetallic nanoparticles, in which each particle contains two and three elements of metal, respectively, are presented. They may have a random alloy, a core/shell, or other kinds of structure depending on the preparation method and the combination of elements. The core/shell structure is advantageous to electronically control the activity of metal catalysts. The triple core/shell structured trimetallic nanoparticles were found to have higher catalytic activity than the corresponding monometallic and bimetallic nanoparticles in three cases. Capped metal nanoparticles were also used as a dopant to liquid crystals. Liquid crystal displays, fabricated by metal nanoparticle-doped liquid crystals, showed faster response than those without dopants. Bimetalization could increase the long-term stability in the doped liquid crystal displays. Thus, metal nanoparticles can improve the electronic display system, which occupies an important position in information technology. In addition, SmCo₅ nanomagnets were successfully prepared by a chemical method, possibly providing a new building block for information technology. The prepared SmCo₅ nanoparticles have a coercivity of 1500 Oe at room temperature. The bimetallic nanoparticles may open a new field in super-high-density magnetic memories.     

团簇动态相变催化

正识别和表征催化活性位点对于理解活性的起源至关重要。随着原位光谱,显微成像技术以及理论计算的发展使我们可以得到几个原子特殊排列组成的活性位的构效关系。然而,在探索更具挑战性的催化剂的活性位点方面研究进展甚微,对于这些催化剂来说,催化剂结构对环境极度敏感,在     

Application of Solid-State Molybdenum Sulfide Clusters with an Octahedral Metal Framework to Catalysis: Ring-Opening of Tetrahydrofuran to Butyraldehyde

Solid-state molybdenum sulfide clusters with an octahedral metal framework, the superconducting Chevrel phases, are applied to catalysis. The cluster of copper salt, Cu _x Mo₆S₈ (x = 2.94), stored in air is treated in a hydrogen stream above 300 °C. The activated cluster exhibits catalytic activity for the ring-opening of tetrahydrofuran, yielding butyraldehyde. Cyclic ethers such as trimethylene oxide and tetrahydropyran are also converted to the corresponding aldehydes. The cluster contains nonstoichiometric defects of sulfur atoms. Oxygen atoms are incorporated at the sulfur-deficient sites upon storage in air, but they are removed from the sites by the activation in a hydrogen stream. The resulting coordinatively unsaturated molybdenum atoms are catalytically active for the ring-opening reaction. The molybdenum atom in an intermediate oxidation state around 2+ is moderately coordinated by the oxygen of tetrahydrofuran and favorably releases the produced aldehyde. The neutral cluster Mo₆S₈, which has such sulfur-deficient sites, also catalyzes the reaction.     

Trinuclear Metal Clusters in Catalysis by Terpenoid Synthases

Terpenoid synthases are ubiquitous enzymes that catalyze the formation of structurally and stereochemically diverse isoprenoid natural products. Many isoprenoid coupling enzymes and terpenoid cyclases from bacteria, fungi, protists, plants, and animals share the class I terpenoid synthase fold. Despite generally low amino acid sequence identity among these examples, class I terpenoid synthases contain conserved metal binding motifs that coordinate to a trinuclear metal cluster. This cluster not only serves to bind and orient the flexible isoprenoid substrate in the precatalytic Michaelis complex, but it also triggers the departure of the diphosphate leaving group to generate a carbocation that initiates catalysis. Additional conserved hydrogen bond donors assist the metal cluster in this function. Crystal structure analysis reveals that the constellation of three metal ions required for terpenoid synthase catalysis is generally identical among all class I terpenoid synthases of known structure.     

Preparation, Characterization and Catalysis of Intrazeolite Molybdenum, Cobalt and Cobalt–Molybdenum Sulfide Clusters: A Molecular Approach to Hydrodesulfurization Catalysts

Better understandings of the nature of Co–Mo sulfide catalysts are of great importance to a rational design of highly active hydrodesulfurization catalysts on a molecular level. Synthesis of uniform binary sulfide clusters well-defined in structure and thermally stabilized on a support is desirable for such purposes. In the present study, successful preparations, using metal carbonyls as precursors, of Mo, Co and Co–Mo sulfide clusters encaged in zeolite are reported. The structure, location and catalytic properties of the clusters are described on the basis of XPS, XAFS, XRD, XRF, IR, HREM and adsorptions of benzene and NO. Implications for the generation of catalytic synergy between Co and Mo sulfides are presented in brief. It is suggested that the host–guest interactions between zeolite framework oxygens and precursor molecules and product clusters are crucial to the size and structure of the intrazeolite clusters.     

荧光银簇的制备、性能及应用研究进展

银簇是一类粒径为1-2 nm的银纳米材料,其除具有特殊的光、电、磁及催化等性能,还具有低毒、强荧光、生物相容性等特殊的物理、化学等特性。因此被广泛应用于生物检测、环境监测等领域。以银簇为研究对象,对银簇的制备、银簇的性能和银簇的应用进行综述。总结了荧光银簇的制备、性能和应用方面的最新研究进展。     

Subnanometer Bimetallic Platinum–Zinc Clusters in Zeolites for Propane Dehydrogenation

Propane dehydrogenation (PDH) has great potential to meet the increasing global demand for propylene, but the widely used Pt-based catalysts usually suffer from short-term stability and unsatisfactory propylene selectivity. Herein, we develop a ligand-protected direct hydrogen reduction method for encapsulating subnanometer bimetallic Pt–Zn clusters inside silicalite-1 (S-1) zeolite. The introduction of Zn species significantly improved the stability of the Pt clusters and gave a superhigh propylene selectivity of 99.3 % with a weight hourly space velocity (WHSV) of 3.6–54 h⁻¹ and specific activity of propylene formation of 65.5 mol g_Pt⁻¹ h⁻¹ (WHSV=108 h⁻¹) at 550 °C. Moreover, no obvious deactivation was observed over PtZn4@S-1-H catalyst even after 13000 min on stream (WHSV=3.6 h⁻¹), affording an extremely low deactivation constant of 0.001 h⁻¹, which is 200 times lower than that of the PtZn4/Al₂O₃ counterpart under the same conditions. We also show that the introduction of Cs⁺ ions into the zeolite can improve the regeneration stability of catalysts, and the catalytic activity kept unchanged after four continuous cycles.