Catalytic and coordination facets of single-site non-metallocene organometallic catalysts with N-heterocyclic scaffolds employed in olefin polymerization

This review discusses the principles underlying mononucleating N-heterocyclic ligand design, selectivity of metal centers, preparation of organometallic catalysts with a N-heterocyclic backbone, and their catalytic activity in olefin oligo/polymerization. A vast number of N-heterocyclic organometallic compounds have been applied for the polymerization on account of their modest cost, low toxicity, and the large availability of transition metals in stable and variable oxidation states, which makes them versatile precursors for these reactions. The main points of focus in this review are the key advances made over more the past 25 years in the design and development of non-metallocene single-site organometallic catalysts bearing different N-heterocyclic scaffolds as a backbone. These catalysts are applied as precursors for the transformation of ethylene, higher α-olefins, and cyclic olefins into oligo/polymers. Emphasis is placed on the architecture of ligand peripheries for tuning the formed polymer properties and the consequences on product formation of different alkyl or aryl substituents directly attached to the metal center in a N-heterocyclic ligand system.     

Design, Synthesis, and In Situ Characterization of New Solid Catalysts

The precise atomic architecture of the catalytically active center is the central topic of the approach presented herein to the design of solid-state catalysts. A wide range of new catalysts may be designed that effect regioselective, shape-selective, and enantioselective conversions, as well as producing high-performance catalysts for the isomerization and hydrogenation of alkenes and the terminal oxidation of alkanes. All the new catalysts described are either microporous or mesoporous solids that have the dual advantages of possessing large specific surfaces and being amenable to delicate structural and compositional variation.     

纳米碳材料非金属催化的研究进展

纳米碳材料直接作为催化剂的非金属碳催化是目前材料科学与催化领域的前沿方向之一.相对于传统金属催化剂,纳米碳材料催化剂具有高效环保、低能耗、耐腐蚀等优点.在烃类转化、化学品合成、能源催化等领域表现出优异的催化性能和发展潜力.综述了近年来纳米碳非金属催化研究的最新进展,主要包括新型纳米碳材料的表面性质、催化特性、反应机理和宏观制备等关键问题,并对纳米碳催化存在的挑战和前景进行了展望.     

Progress in design and architecture of metal nanoparticles for catalytic applications

Over the past few years, nanometer-sized transition metal particles have been intensively pursued as potentially advanced catalysts because their special properties lie between those of single metal atoms and bulk metal. Achieving the accurate control of particle size and overall particle size distribution is one of the most crucial challenges to provide unique chemical and physical properties. We highlight herein our recent progress in the exploitation of promising nanoparticle (NP)-based catalysts designed by precise architecture that enable efficient and selective chemical transformations and can be completely separated and are recyclable. This perspective article consists of the following two specific topics: (i) multifunctional catalysts based on magnetic NPs and (ii) new routes for the preparation of supported metal NPs catalysts. The synthetic strategies described here are simple and general for practical catalyst design, thus allowing a strong protocol for creating various nanostructured catalysts.     

Importance of catalyst–photoabsorber interface design configuration on the performance of Mo-doped BiVO4 water splitting photoanodes

Photoelectrochemical water splitting is mostly impeded by the slow kinetics of the oxygen evolution reaction. The construction of photoanodes that appreciably enhance the efficiency of this process is of vital technological importance towards solar fuel synthesis. In this work, Mo-modified BiVO₄ (Mo:BiVO₄), a promising water splitting photoanode, was modified with various oxygen evolution catalysts in two distinct configurations, with the catalysts either deposited on the surface of Mo:BiVO₄ or embedded inside a Mo:BiVO₄ film. The investigated catalysts included monometallic, bimetallic, and trimetallic oxides with spinel and layered structures, and nickel boride (Ni_xB). In order to follow the influence of the incorporated catalysts and their respective properties, as well as the photoanode architecture on photoelectrochemical water oxidation, the fabricated photoanodes were characterised for their optical, morphological, and structural properties, photoelectrocatalytic activity with respect to evolved oxygen, and recombination rates of the photogenerated charge carriers. The architecture of the catalyst-modified Mo:BiVO₄ photoanode was found to play a more decisive role than the nature of the catalyst on the performance of the photoanode in photoelectrocatalytic water oxidation. Differences in the photoelectrocatalytic activity of the various catalyst-modified Mo:BiVO₄ photoanodes are attributed to the electronic structure of the materials revealed through differences in the Fermi energy levels. This work thus expands on the current knowledge towards the design of future practical photoanodes for photoelectrocatalytic water oxidation.

     

A convenient synthesis of a porphyrin cross-linked polymer,its application as a size selective heterogeneous catalyst and a comparison with a porphyrin-cored hyperbranched polymer

This paper describes how the polymeric structure and environment surrounding supported catalysts can be used to affect the product outcome from a reaction. As well as reporting a size/shape selectivity, we also describe a significant effect on product distribution. Specifically, how the polymeric environment can favour or disfavour particular products. As such, these results illustrate how it may be possible to target more or less of a specific compound (from a possible mix) by careful choice of the polymer architecture surrounding a catalyst.     

Structured catalysts for methanol-to-olefins conversion: a review

Conversion of methanol to light olefins is a promising alternative for the conversion of new feed-stocks such as gas, coal or biomass to ethylene and propylene via the methanol-to-olefins (MTO) process. During the last decade, the use of structured catalysts in this reaction has received increasing attention. The effect of such structured catalysts on the stability and selectivity is discussed in this review. The reaction and coking mechanism show the importance of good mass transfer properties of the catalyst in the MTO reaction. Important aspects such as thickness of the coating, crystal size of the zeolite and architecture of the support on the mass transfer properties of the final catalyst are highlighted. An overview of the results of structured catalysts used in the MTO reaction is presented.     

功能化金属有机框架材料催化二氧化碳转化研究进展

作为主要温室气体,二氧化碳(CO_2)导致了全球变暖与海洋酸化,同时CO_2也是重要的C1资源。在温和条件下,利用催化剂将CO_2高效、高选择性地转化为具有高附加值的化学品,对缓解CO_2给气候变化带来的负面影响和减少对化石能源的依赖具有重要意义。作为一类新兴的多孔晶态材料,金属-有机框架(metal-organic frameworks,MOFs)同时具备多相催化剂的可分离回收再利用以及均相催化剂的高选择性和高活性等性质,是优良的多相催化剂。本文主要聚焦功能化MOFs催化剂的结构特性及其在催化转化CO_2方面的应用,着重介绍该领域近期的研究进展,并对今后该领域的研究趋势及应用前景进行了展望。     

Multivalency as a Key Factor for High Activity of Selective Supported Organocatalysts for the Baylis–Hillman Reaction

The polystyrene‐supported N‐alkylimidazole‐based dendritic catalysts for the Baylis–Hillman reaction exhibit one of the strongest beneficial effects of multivalent architecture ever reported for an organocatalyst. The yields in the model reaction of methyl vinyl ketone with p‐nitrobenzaldehyde are more than tripled when a non‐dendritic catalyst is replaced by a second‐ or third‐generation analogue. Moreover, the reaction of the less active substrates will not occur with the non‐dendritic catalyst and will proceed to a significant extent only with the analogous catalysts of higher generations. A substantial additional enhancement of the reaction yield could be achieved by increasing the content of water in the reaction solvent. The plausible cause of the dendritic effect is the assistance of the second, nearby imidazole moiety in the presumably rate‐determining proton transfer in the intermediate adduct, after the first imidazole unit induced the formation of the new carbon–carbon bond.     

离子液体中手性催化剂回收研究

近年来,贵重的手性催化剂的回收与再利用越来越引起化学工作者的关注,而离子液体在催化剂回收方面有其独特的优势.本文综述了离子液体在手性催化反应中的应用,在回收催化剂的同时,也能一定程度上提高催化剂的催化效率:着重介绍了新型含咪唑盐手性催化剂及其在不对称催化中的应用,由于它在离子液体和有机溶剂的显著差异可以很容易地得到回收,并且能一定程度地稳定催化剂,提高催化效率,这对我们设计合成新型可回收的催化剂具有重要的借鉴意义.     

Supramolecular chemistry

The article discusses molecular recognition and overviews the key concepts -storage and retrieval of chemical information by molecular structures, supramolecular reagents and catalysts, molecular transport, semiochemistry and self assembly. The prospects of controlling supramolecular architecture through engineered molecular recognition and design of ‘programmed systems’ controlled by molecular information are also discussed.     

Enhanced CO tolerance for hydrogen activation in Au-Pt dendritic heteroaggregate nanostructures

Au-Pt heteroaggregate nanostructures were prepared by sequential reduction methods. The structures have approximately 11 nm Au cores with Pt "tendrils" attached to the Au surface. The heteroaggregates are active H2 oxidation catalysts and show high activity at 90 degrees C in the presence of 1000 ppm CO. The surprising CO-tolerant behavior arises from the composition and unusual architecture of the particles.     

单原子催化剂在电化学中的研究进展

目前单原子催化剂的研究呈现爆发式增长, 已然成为材料科学和催化领域的明星材料和研究热点. 前期报道的单原子催化剂研究主要针对某一个应用方向进行探讨, 较少研究催化剂的双功能或多功能应用. 近年来, 为了拓展单原子催化剂在更多领域和方向的应用, 具有双功能甚至多功能的单原子催化剂的设计开发备受关注. 本文综合评述了近年来具有双功能活性的单原子催化剂的研究进展, 重点介绍了其在电化学领域中的最新应用研究. 最后, 对具有双功能活性的单原子催化剂发展研究中存在的问题进行了简要分析, 并对未来发展前景进行了展望.     

担载型钴镍金属氧化物催化剂上CH4还原NO反应研究

ＮＯｘ是大气的主要污染物之一,近年来,利用甲烷选择还原ＮＯｘ引起了广泛关注,研究发现,Ｃｏ、Ｍｎ和Ｎｉ离子交换的ＺＳＭ－５分子筛具有较高的活性［１～３］．但金属离子交换的分子筛催化剂有热稳定性差、易失活等缺点．最近已有金属氧化物用作甲烷还原ＮＯｘ反应...     

负载型钼系超细催化剂的合成,结构与反应性能研究

负载型钼系催化剂广泛用于加氢脱硫、抗硫甲烷化及部分氧化等,其加氢脱硫活性与低温氧的表面吸附量成正比,活性组分受载体性质的影响。超细粒子是近年来兴起的新型催化材料,由于其表面及体积效应,导致其特殊的表面吸附性能。以超临界法合成NiO/Al_2O_3、Fe_2O_3/SiO_2等超细催化剂已有报道,但该法对MoO_3/Al_2O_3的合成尚未见报道。本文以MoO_3/Al_2O_3超临界法合成超细粒子催化剂,根据超细催化剂分散性与粒径的关系选择了活性与钼表面分散性有依赖关系的临氢重整反应为探针,研究了超细MoO_3/Al_2O_3催化剂的性质。     

Catalytic systems based on fiberglass woven matrices doped with metals in reaction of nitrogen oxide reduction

The results of a study of the reactions catalyzed by nontraditional fiberglass woven catalysts activated by metals or oxides, are presented. The catalytic activity of such catalysts, activated by implanting Pt, Pd, Co, or Cr, in NO reduction with carbon monoxide and propane is studied. Fiberglass catalysts containing Pt and Pd are more active than traditional catalysts. The catalysts are studied by temperature-programmed reduction (TPR), IR spectroscopy, and diffuse-reflectance electronic spectroscopy. Active sites of two kinds act on the platinum catalysts. One of them is platinum encapsulated in the glass matrix of the support. Active sites are assumed to be at the metal-support interface     

A Hierarchical Structural Model for the Interpretation of Mercury Porosimetry and Nitrogen Sorption

A new model of interpretation for the mercury porosimetry experiment has been presented. The void space of a porous solid is modeled by separate representations of both the macroscopic (>10 μm) and the mesoscopic (<10 μm) length scale properties of the material. Complementary information from nitrogen adsorption, on the mesoscopic scale, and NMR imaging, on the macroscopic scale, is used in conjunction with the mercury porosimetry data to provide a more accurate structural representation of a porous medium. The model is therefore able to probe spatial geometric changes in pellet structural architecture over many length scales during processes such as catalyst manufacture and the deactivation of catalysts by coke deposition. Copyright 2000 Academic Press.     

From zirconium to titanium: the effect of the metal in propylene polymerisation using fluxional unbridged bicyclic catalysts

Catalytic systems based on unbridged substituted indenyl systems are becoming of interest in the production of elastomeric polypropylene. A full understanding of the structural features necessary to control this kind of behaviour has not yet been achieved, since relatively slight changes in the molecular architecture can lead to polymers with remarkably different properties. We report here our recent findings regarding the study of bicyclic zirconium and titanium complexes as fluxional catalysts in propylene polymerisation. Most of them have been synthesised according to a synthetic procedure that allowed us to prepare a series of complexes in which the ring fused to the cyclopentadienyl moiety is saturated and of different sizes, thus introducing a flexibility parameter that can be finely tuned. The results obtained show that the stereoselectivity induced by this class of catalysts strongly depends both on the structure of the ligand and on the nature of metal atom (Zr vs. Ti). The titanium-based catalysts yield polypropylenes with new and interesting microstructures, in particular when an higher stability is achieved through a careful choice of the substitution pattern of the ligands.     

Enhanced cooperativity through design: pendant Co(III)--salen polymer brush catalysts for the hydrolytic kinetic resolution of epichlorohydrin (salen=N,N'-bis(salicylidene)ethylenediamine dianion)

The Co(III)--salen-catalyzed (salen=N,N'-bis(salicylidene)ethylenediamine dianion) hydrolytic kinetic resolution (HKR) of racemic epoxides has emerged as a highly attractive and efficient method of synthesizing chiral C(3) building blocks for intermediates in larger, more complex molecules. HKR reaction rates have displayed a second order dependency on the concentration of active sites, and thus researchers have proposed a bimetallic transition state for the HKR mechanism. Here we report the utilization of pendant Co(III)--salen catalysts on silica supported polymer brushes as a catalyst for the HKR of epichlorohydrin. The novel polymer brush architecture provided a unique framework for promoting site-site interactions as required in the proposed bimetallic transition state of the HKR mechanism. Furthermore, the polymer brushes mimic the environment of soluble polymer-based catalysts, whereas the silica support permitted facile recovery and reuse of the catalyst. The polymer brush catalyst displayed increased activities over the soluble Jacobsen Co--salen catalyst and was observed to retain its high enantioselectivities (>99 %) after each of five reactions despite decreasing activities. Analysis indicated decomposition of the salen ligand as an underlying cause of catalyst deactivation.     

Hierarchically Structured Nanomaterials for Electrochemical Energy Conversion

Hierarchical nanomaterials are highly suitable as electrocatalysts and electrocatalyst supports in electrochemical energy conversion devices. The intrinsic kinetics of an electrocatalyst are associated with the nanostructure of the active phase and the support, while the overall properties are also affected by the mesostructure. Therefore, both structures need to be controlled. A comparative state‐of‐the‐art review of catalysts and supports is provided along with detailed synthesis methods. To further improve the design of these hierarchical nanomaterials, in‐depth research on the effect of materials architecture on reaction and transport kinetics is necessary. Inspiration can be derived from nature, which is full of very effective hierarchical structures. Developing fundamental understanding of how desired properties of biological systems are related to their hierarchical architecture can guide the development of novel catalytic nanomaterials and nature‐inspired electrochemical devices.