Asymmetric heterogeneous catalysis

Limited natural resources and an increasing demand for enantiomerically pure compounds render catalysis and especially heterogeneous asymmetric catalysis a key technology. The field has rapidly advanced from the initial use of chiral biopolymers, such as silk, as a support for metal catalysts to the modern research areas. Mesoporous supports, noncovalent immobilization, metal-organic catalysts, chiral modifiers: many areas are rapidly evolving. This Review shows that these catalysts have more to them than facile separation or recycling. Better activities and selectivities can be obtained than with the homogeneous catalyst and novel, efficient reaction mechanisms can be employed. Especially fascinating is the outlook for highly ordered metal-organic catalysts that might allow a rational design, synthesis, and the unequivocal structural characterization to give tailor-made catalysts.     

Mechanochemistry in heterogeneous catalysis

Heterogeneous-catalytic reactions on solid-phase catalysts activated by mechanical treatment are discussed. Attention is mainly focused on investigations into the nature of the active centers of the catalysts-nonequilibrium states-formed by mechanical activation of the solids. __________ Translated from Teoreticheskaya i éksperimental’naya Khimiya, Vol. 43, No. 4, pp. 199–214, July–August, 2007.     

An approach to describe relaxation rates in heterogeneous catalytic reactions

A system of equations allowing for the most essential properties of catalytic surfaces is suggested to describe the rate of chemical conversion.

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单原子催化:沟通均相催化与多相催化的桥梁（英文）

催化在现代化学工业中占据着极为重要的地位.催化剂是催化过程的核心.均相催化剂由于具有均一、孤立的活性位点,往往具有高活性与高选择性;但是分离困难限制了其实际应用.多相催化剂由于金属原子利用效率低、活性组分不均匀,活性与选择性相对较低;但其稳定易分离的特点使得目前大多数工业催化过程都是多相催化过程.近年来,单原子催化逐渐成为催化领域新的研究热点与前沿,受到相关研究人员的广泛关注.作为一种多相催化剂,单原子催化剂具有稳定易分离的优势.此外,单原子催化剂具有类似均相催化剂的孤立活性位点,可能具有高活性与高选择.因此单原子催化的概念一经提出,便被认为有望成为架起多相催化与均相催化的桥梁;但几年来并未从实验上得到证实.2016年开始,逐渐有单原子催化剂在经典均相催化反应过程中的应用报道,为该观点提供了实验上的证据.本综述概述了2016至2017年单原子催化剂在典型均相催化反应中的成功应用,包括:1)氢甲酰化反应.以烯烃和合成气为原料合成精细化学品醛类化合物的氢甲酰化反应是目前化工生产中典型的均相催化反应之一.2016年,张涛课题组和曾杰课题组先后报道了Rh/ZnO和Rh/CoO单原子催化剂在该反应中的成功应用.催化剂都表现出优异的催化性能,活性与经典均相Wilkinson’s催化剂相当;2)氢硅加成反应.作为合成有机硅产品的重要反应之一,工业上硅氢加成反应主要由Pt基均相催化剂催化.2016年Beller课题组首次报道了将Pt/Al_2O_3单原子催化剂用于烯烃硅氢加成反应中.该催化剂除表现出良好的催化活性和区域选择性外,还具有较高的稳定性和底物普适性;3)C–H键选择性氧化.烷烃部分氧化反应在学术研究和工业应用方面都有重要意义.刘文刚等将M-N-C单原子催化剂(其中M为Fe,Co等金属)成功应用于C–H键的活化反应中,并对催化剂的结构进行了深入剖析.以上实例表明通过调控金属与载体组合、设计开发合适的单原子催化剂,可以达到结合均相催化高活性、高选择性与多相催化稳定易分离的目的,为均相催化多相化提供了一条新途径,也证明单原子催化可望成为沟通均相催化与多相催化的桥梁.     

Applying structural transition theory to describe enzyme kinetics in heterogeneous systems

Enzyme action was investigated by assuming the occurrence of different states of enzyme-substrate affinities. These states were considered to involve enzyme species with distinct abilities to form reaction product. The results obtained showed strong agreement with the experimental data for the action of peroxidase. This approach provides a powerful tool for predicting the kinetic behavior of other enzymatic processes in conditions not described before. An additional feature of this approach is the ability to characterize processes at any enzyme-substrate concentration ratio, including high enzyme-substrate ratios and enzyme inhibition by substrate or product. This proposal can also be used in systems with heterogeneity concerning the investigated enzyme.     

Reaction selectivity in heterogeneous catalysis

The understanding of selectivity in heterogeneous catalysis is of paramount importance to our society today. In this review we outline the current state of the art in research on selectivity in heterogeneous catalysis. Current in-situ surface science techniques have revealed several important features of catalytic selectivity. Sum frequency generation vibrational spectroscopy has shown us the importance of understanding the reaction intermediates and mechanism of a heterogeneous reaction, and can readily yield information as to the effect of temperature, pressure, catalyst geometry, surface promoters, and catalyst composition on the reaction mechanism. DFT calculations are quickly approaching the ability to assist in the interpretation of observed surface spectra, thereby making surface spectroscopy an even more powerful tool. HP-STM has revealed three vitally important parameters in heterogeneous selectivity: adsorbate mobility, catalyst mobility and selective site-blocking. The development of size controlled nanoparticles from 0.8 to 10 nm, of controlled shape, and of controlled bimetallic composition has revealed several important variables for catalytic selectivity. Lastly, DFT calculations may be paving the way to guiding the composition choice for multi-metallic heterogeneous catalysis for the intelligent design of catalysts incorporating the many factors of selectivity we have learned.     

Bridging electrochemistry and heterogeneous catalysis

The discovery of the effect of the electrochemical promotion of catalysis (EPOC) or non-Faradaic electrochemical modification of catalytic activity (NEMCA effect) is described together with the key steps of its exploration at high pressure and high vacuum and its rationalization via electrochemical and surface science techniques. Recent attempts for its practical utilization are also surveyed.     

The theoretical approach to surface chemistry and heterogeneous catalysis

Transition metals are the most interesting items among heavy atoms due to their extensive use in catalysis. Present understanding of heterogeneous catalytic reactions is still very poor, and new experimental and theoretical techniques have been developed in recent years with the aim of elucidating the mechanism of adsorption and reaction of simple molecules over metal surfaces or clusters. Empirical, semiempirical, and ab initio methods of calculations are briefly reviewed: results and perspectives are presented.     

Monolithic systems: from separation science to heterogeneous catalysis

Recent results that have been obtained in the ring-opening metathesis polymerization (ROMP)-based synthesis of monolithic supports are summarized. We have elaborated a synthetic concept that allows modifying monolithic supports in a way that they can be used both for applications in separation science, for SEC and as supports for catalytically active systems. In all cases, a tailor-made microstructure was accessible due to the controlled character of the transition-metal catalyzed polymerization. Taking advantage of the “living” catalytic sites, an “in situ” functionalization was accomplished by subsequently grafting a variety of functional monomers and catalyst precursors onto the rod. Their design and use as supports for high-performance separation devices (e.g. for ds-DNA) and catalytic supports (e.g. supported Grubbs-type catalysts) is summarized.     

Surface chemistry connecting heterogeneous catalysis,photocatalysis and plasmonic catalysis

正Chemical reactions catalyzed by solid catalysts have recently expanded rapidly from traditional heterogeneous catalytic reactions to photocatalytic reactions and further to plasmonic-catalytic reactions,however,the fundamental understanding of the commonalities and differences among heterogeneous catalysis,     

In situ electron paramagnetic resonance: a unique tool for analyzing structure-reactivity relationships in heterogeneous catalysis

Electron Paramagnetic Resonance (EPR) offers widespread opportunities for monitoring catalytically relevant species that contain unpaired electrons under conditions close to those of heterogeneous catalytic gas and liquid phase reactions. In this tutorial review, after introducing basic theoretical and experimental principles of the technique, selected examples of typical applications are discussed that comprise (1) transition metal ions in paramagnetic valence states such as vanadium, (2) radical anions such as O˙(-) formed on oxide surfaces and (3) electrons in ferromagnetic particles such as nickel as well as in conduction bands of organic conductors such as polyaniline.     

Advanced synthesis for advancing heterogeneous catalysis

There are tremendous needs and opportunities for the understanding and application of heterogeneous catalysis in the solution of vexing technological problems. Nanoscale, catalytically active phases, particularly metal nanoparticles and metal oxide clusters, supported on high surface area oxides (supported catalysts) are one of the most important classes of heterogeneous catalysts. The problem of inhomogeneity and the limits it places on the understanding of catalytic chemistry has led to substantial efforts to produce more uniform catalyst systems via more synthetic control. This article highlights an approach adopted at Argonne National Laboratory for the synthesis of uniform supported metal and oxide particles.     

Plasmonic heterogeneous catalysis for organic transformations

Plasmonic catalysis has been recognised as a promising alternative to many conventional thermal catalytic processes in organic synthesis. In addition to their high activity in fine chemical synthesis, plasmonic photocatalysts are also able to maintain control of selectivity under mild conditions by utilising visible-light as an energy source. This review provides an overview of the recent advances in organic transformations with plasmonic metal nanostructures, including selective reduction, selective oxidation, cross-coupling and addition reactions. We also summarize the photocatalysts and catalytic mechanisms involving surface plasmon resonance. Finally, control of reaction pathway and strategies for tailoring product selectivity in fine chemical synthesis are discussed.     

Microfabricated reactors for on-chip heterogeneous catalysis

Microfabricated devices constructed from glass and polydimethylsiloxane with integral heaters are described, which can be used for heterogeneous catalysis reactions. Sulfated zirconia is used as the catalyst in an open channel reactor, with either a syringe pump or electroosmotic flow being used to deliver the reactants. The results clearly demonstrate that very high conversion efficiencies are possible, however, the thermodynamics of the reactions are the same as in bulk systems. Ethanol and hexanol are dehydrated to ethene and hexene, respectively, with conversion efficiencies approaching 100%, and the esterification of ethanol is investigated. Yields of approximately 30% ethyl acetate are obtained by gas chromatographic analysis. This is the first time such a method for fabricating a catalyst micro reactor has been reported, yet it demonstrates sufficient robustness and resistance to leakage. The use of electroosmotic flow in a heated catalyst reactor is a significant advancement in reactor design.