甲醛催化氧化反应机理的研究进展

催化氧化技术具有环境友好、节省能源、操作简单等优点,在治理室内甲醛污染方面显示出非常有潜力的应用前景。本文综述了近年来甲醛催化氧化反应机理的研究进展,阐述了在甲醛催化氧化过程中,氧的活化、可能产生的反应中间体以及反应路径。重点介绍了贵金属催化剂（Au、Pt、Pd 和Ag）和过渡金属（Mn、Co和Ce等）氧化物催化剂在甲醛氧化反应过程中,不同金属种类、载体性质和添加剂等对反应机理的影响。介绍了已经商业化的除甲醛产品所采用的反应机理。最后,指出了甲醛催化氧化反应机理存在的问题并对其未来研究发展方向进行了展望。     

Cooperative Catalysis with Aldehydes and Copper: Development and Application in Aerobic Oxidative C?H Amination at Room Temperature

A conceptually new cooperative catalytic system via a synergistic combination of aldehyde and copper catalysis has been established based on systemic mechanistic studies. This new cooperative catalysis has been successfully applied in the direct aerobic oxidative C H amination of azoles at room temperature, which was previously realized under harsh conditions. Mechanistic studies including isotopic labeling experiments and kinetic isotope effect (KIE) experiments support a reaction pathway that involves formation of an aminal, hydrolysis of the aminal to generate the copper‐amide species, subsequent C H amination and re‐oxidation of copper(I) to copper(II) by oxygen. It not only provides an efficient method to realize the oxidative C H amination of benzoxazoles with free amines at room temperature, but also paves the way for establishing new C N bond formation reactions by using this efficient cooperative catalysis.     

Solid-state NMR for metal-containing zeolites: from active sites to reaction mechanism

Metal-containing zeolite catalysts have found a wide range of applications in heterogeneous catalysis. To understand the nature of metal active sites and the reaction mechanism over such catalysts is of great importance for the establishment of structure-activity relationship. The advanced solid-state NMR (SSNMR) spectroscopy is robust in the study of zeolites and zeolite-catalyzed reactions. In this review, we summarize recent developments and applications of SSNMR for exploring the structure and property of active sites in metal-containing zeolites. Moreover, detailed information on host-guest interactions in the relevant zeolite catalysis obtained by SSNMR is also discussed. Finally, we highlight the mechanistic understanding of catalytic reactions on metal-containing zeolites based on the observation of key surface species and active intermediates.     

Fast pyrolysis of glucose‐based carbohydrates with added NaCl part 1: Experiments and development of a mechanistic model

Sodium ions, one of the natural inorganic constituents in lignocellulosic biomass, significantly alter pyrolysis behavior and resulting chemical speciation. Here, experiments were conducted using a micropyrolyzer to investigate the catalytic effects of NaCl on fast pyrolysis of glucose‐based carbohydrates (glucose, cellobiose, maltohexaose, and cellulose), and on a major product of cellulose pyrolysis, levoglucosan (LVG). A mechanistic model that addressed the significant catalytic effects of NaCl on the product distribution was developed. The model incorporated interactions of Na⁺ with cellulosic chains and low molecular weight species, reactions mediated by Na⁺ including dehydration, cyclic/Grob fragmentation, ring‐opening/closing, isomerization, and char formation, and a degradation network of LVG in the presence of Na⁺. Rate coefficients of elementary steps were specified based on Arrhenius parameters. The mechanistic model for cellulose included 768 reactions of 222 species, which included 252 reactions of 150 species comprising the mechanistic model of glucose decomposition in the presence of NaCl. © 2015 American Institute of Chemical Engineers AIChE J, 62: 766–777, 2016     

FePO Catalysts for the Selective Oxidative Dehydrogenation of Isobutyric Acid into Methacrylic Acid

This review presents the iron phosphorus oxides used as catalysts for isobutyric acid oxidative dehydrogenation. Research on this catalytic system has been developed in the last decade and many publications have been devoted to this reaction, as it can be a step in a new process of production of methyl methacrylate. We emphasize particularly the nature of the active phase, the active centers, and the role of water and promoters. The mechanistic aspects of the reaction, which corresponds to an extension of the Mars and van Krevelen mechanism with a special role of water partial pressure, are discussed.     

中孔材料在碱催化与氧化催化反应中的应用

中孔材料表面存在大量硅羟基,可稳定地与有机物或有机金属复合物基团相结合,可作为高度分散金属或氧化物载体,也可作为碱催化或氧化催化反应的催化剂。近年来,中孔材料在碱催化或氧化催化反应过程中的应用潜在价值备受关注,对中孔材料的研究成果进行分析,指出中孔材料在新催化体系中制备及应用的发展方向。     

Mechanistic Modelling of the Catalytic Pyrolysis of Methylcyclohexane

A detailed chemical kinetic mechanism describing the thermal and catalytic cracking of methylcyclohexane over a 12CaO.7Al₂O₃ catalyst is presented. The model is based on balanced equations for both molecular and radical species describing an experimental fixed‐bed reactor system. The mechanistic model is based on overall first‐order decomposition kinetics, which satisfactorily describes experimental data. The simulated product distributions show a reasonably good agreement with the experimental results and confirm the hypothesis that the catalyst does not affect the pyrolysis mechanism and only increases the rate of the initiation steps.     

Evidence for the Formation of a Radical‐Mediated Flavin‐N5 Covalent Intermediate

The redox‐neutral reaction catalyzed by 2‐haloacrylate hydratase (2‐HAH) leads to the conversion of 2‐chloroacrylate to pyruvate. Previous mechanistic studies demonstrated the formation of a flavin‐iminium ion as an important intermediate in the 2‐HAH catalytic cycle. Time‐resolved flavin absorbance studies were performed in this study, and the data showed that the enzyme is capable of stabilizing both anionic and neutral flavin semiquinone species. The presence of a radical scavenger decreases the activity in a concentration‐dependent manner. These data are consistent with the flavin iminium intermediate occurring by radical recombination.     

New Challenges in Heterogeneous Catalysis for the 21st Century

Abstract  

Heterogeneous catalysis has been around for a long time, but has still much room to grow. The empirical trial-and-error mode used to develop catalysts in early times has progressively made way for a more molecularly driven approach to their design. Modern surface-sensitive techniques have opened the way to a better understanding of the mechanisms of catalytic reactions and the demands imposed on catalytic sites. Computational studies have added insights into the structural and energetic details of surface species and the kinetic driving forces for specific surface reactions. Novel nanotechnology and synthetic advances have provided new methods to manufacture better-defined catalysts, with high concentrations of the active sites identified by fundamental mechanistic studies. All combined, these advances have led to the design of new catalysts by taking advantage of the size and shape of the nanoparticles used as active phases and of specific structures and the nature of the support. New research has also been directed to the development of more sophisticated nanostructures, to add new functionalities to simpler catalysts or to combine two or more primary functions into one single catalyst. Much progress has been made in these directions, but the new tools are yet to be fully exploited to resolve present limitations in a myriad of catalytic systems of industrial importance, for energy production and consumption, environmental remediation, and the synthesis of both commodity and fine chemicals.     

A highly efficient polymer‐anchored palladium(II) complex catalyst for hydrogenation,Heck cross‐coupling and cyanation reactions

BACKGROUND: Precise architectures of steric and electronic properties of palladium species play a crucial role in designing highly functionalized catalyst systems responsible for target organic transformations. Pd catalysts supported on polymer materials have been employed extensively as catalysts not only for hydrogenation but also for coupling reactions in the production of fine chemicals. RESULTS: A new polymer‐anchored Pd(II) complex has been synthesized and characterized. The catalyst shows high catalytic activity in the hydrogenation of styrene oxide, Heck cross‐coupling and cyanation reactions of aryl halides. The effect of various reaction parameters were investigated to optimize reaction conditions. The catalytic system shows good activity in the hydrogenation of styrene oxide (conversion 98%) with a selectivity to 2‐phenylethanol (93%) which is higher than its homogeneous analogues. The catalyst also exhibits excellent catalytic activity for the Heck cross‐coupling and cyanation reactions of various substituted and non‐substituted aryl halides. CONCLUSIONS: Results demonstrate that the catalyst is robust and stable and can be recovered quantitatively by simple filtration and reused several times without loss of activity. Copyright © 2010 Society of Chemical Industry     

New Ruthenium Catalysts for Asymmetric Transfer Hydrogenation of Prochiral Ketones

Tridentate N,N,N‐pyridinebisimidazolines have been studied as new ligands for the enantioselective transfer hydrogenation of prochiral ketones. High yields and excellent enantioselectivity up to >99 % ee have been achieved with an in situ generated catalytic system containing dichlorotris(triphenylphosphine)ruthenium and 2,6‐bis‐([4R,5R]‐4,5‐diphenyl‐4,5‐dihydro‐1H‐imidazol‐2‐yl)‐pyridine ( 3a ) in the presence of sodium isopropoxide.     

Palladium-Catalyzed Arylation Reactions: A Mechanistic Perspective

After being restricted for the intramolecular formation of C–C bonds, the palladium catalyzed arylation reaction has been extended for the intermolecular synthesis of biaryls systems. Many of these reactions have been demonstrated to proceed by mechanisms that involve a concerted metalation–deprotonation, in which the base plays an important role in the proton abstraction. Other mechanisms based on electrophilic aromatic substitution and on Pd^II/Pd^IV or Pd^II/Pd^III catalytic cycles have also been proposed. This review summarizes the most important recent advancements on the mechanistic understanding of the different types of palladium-catalyzed arylations reactions.     

Assessing the Recyclability of Supramolecularly Assembled Organocatalytic Species: A Theoretical Insight

Asymmetric organocatalytic synthesis is a powerful tool in organic chemistry to achieve desired stereoisomers in high purity via mild catalytic routes. The immobilization of homogeneous catalytic species onto heterogeneous phases embodies the evolution of asymmetric catalysis, since it allows the recycling of the catalyst for several runs until degradation. Previously reported non-covalent immobilization of proline-based catalysts for aldol reaction onto magnetic nanoparticles functionalized with β-cyclodextrin (MNP-β-CB) demonstrated the viability of the methodology. This paper proposes two new catalyst recycling strategies based on Cucurbit[7]uril (CB[7]) for the aldol reaction and the Robinson annulation. These recycling methodologies are conceptually different. The former relies on the homogeneous encapsulation of the catalyst in cucurbituril, CB[7] ⋅ Cat, and its recycling in the aqueous phase by extraction of the aldol product with organic solvents. The latter relies on the heterogeneous encapsulation of the catalyst as MNP-CB[7] ⋅ Cat2 system and its recycling by magnetic harvesting. Density functional theory (DFT) calculations have been employed to rationalize the thermodynamics of experimental results, and to suggest caveats and plausible improvements in view of a future catalytic design.     

等离子体技术在天然气化工中的应用

论述了热等离子体裂解天然气制乙炔和冷等离子体促进天然气转化的研究概况 ,着重从反应过程、反应器、等离子体与催化剂的协同效应、反应机理和动力学方面评述了国内外等离子体技术在天然气化工中利用的研究进展和发展趋势 .     

Facilitation of cascade biocatalysis by artificial multi-enzyme complexes — A review

Multi-enzyme complexes are the results of natural evolution to facilitate cascade biocatalysis. Through enzyme colocalization within a complex, the transfer efficiency of reaction intermediates between adjacent cascade enzymes can be promoted, resulting in enhanced overall reaction efficiency. Inspired by nature, a variety of approaches have been developed for the assembly of artificial multi-enzyme complexes with different spatial organizations, aiming at improving the catalytic efficiency of enzyme cascade. A recent trend of this research area is the creation of enzyme complexes with a controllable spatial organization which helps with the mechanistic studies and bears the potential to further increase metabolic productivity. In this review, we summarize versatile strategies for the assembly of artificial multi-enzyme complexes, followed by an inspection of the mechanistic studies of artificial multi-enzyme complexes for their enhancement of catalytic efficiency. Furthermore, we provide some highlighted in vivo, ex vivo, and in vitro examples that demonstrate the ability of artificial multi-enzyme complexes for enhancing the overall production efficiency of value-added compounds. Recent research progress has revealed the great biotechnological potential of artificial multi-enzyme complexes as a powerful tool for biomanufacturing.     

Transient Studies of Direct N2O Decomposition over Pt–Rh Gauze Catalyst. Mechanistic and Kinetic Aspects of Oxygen Formation

For elucidating the mechanistic aspects of oxygen formation during N₂O decomposition over commercial woven Pt–Rh gauze, transient experiments were carried out in the temporal analysis of products (TAP) reactor by pulsing N₂ ¹⁶O over ¹⁸O-pretreated gauze catalyst at temperatures typical of industrial ammonia burners (1073–1273 K). The transient responses of N₂O and the products of its decomposition (O₂ and N₂) were fitted to two different mechanistic models. From the isotopic studies and the fitting of transient experiments, two separate routes of oxygen formation during catalytic N₂O decomposition have been identified. Oxygen is produced via both (i) interaction of N₂O with adsorbed oxygen species formed from N₂O and (ii) recombination of adsorbed oxygen species on the catalyst surface. The relative contribution of these reaction pathways depends on the reaction temperature.     

A kinetic study of methanol decomposition catalyzed over plate-type palladium catalyst

A kinetic study of the catalytic methanol decomposition to carbon monoxide and hydrogen has been carried out in the pressure range of methanol up to 8 atm at 200 and 250°C over a palladium catalyst supported on an oxidized aluminum plate. The reaction pathway can be proposed as (i) dissociative adsorption of methanol to methoxyl groups and hydrogen adsorbed on palladium sites, (ii) decomposition of the methoxyl groups to carbon monoxide and hydrogen adsorbed, and (iii) desorption of the surface carbon monoxide and hydrogen species. It is suggested that the second step is rate-determining and the surface hydrogen species enhance the decomposition of the methoxyl groups. This revised version was published online in July 2006 with corrections to the Cover Date.     

Molecular Aspects of Catalytic Reactivity. Application of EPR Spectroscopy to Stuies of the Mechanism of Heterogeneous Catalytic Reactions

The basic objective of mechanistic studies of real catalytic processes is to dissect the course of the reaction into individual steps; ascertain their sequence; and determine the stoichiometry, structure, and electronic states of active sites and intermediates. The electron paramagnetic resonance (EPR) technique is at present widely used to explore many of these principal aspects of heterogeneous catalysis and surface chemistry. The extreme sensitivity compared to the usual spectroscopic methods is perhaps its most acknowledged advantage and makes EPR best suited to investigate and characterize low-abundance active sites and intermediates appearing during catalytic reaction. Additional information can be drawn from the theoretical analysis of the experimental spin Hamiltonian parameters within the ligand field and from angular overlap or Newman's superposition models as well as by more sophisticated quantum chemical calculations. The purpose of this paper is to show how catalysis benefits from EPR spectroscopy and to identify the issues and areas explored by this method. A comprehensive literature review is not attempted in this article; instead, attention is directed toward application of EPR for elucidation of the molecular reaction mechanism that can provide a scientific background for understanding many fundamental aspects of catalytic activity. The major events of mechanistic studies which involve the identification of active sites, activation of reagents, and determination of the reaction pathways are illustrated by selected examples and discussed. An approach that is complementary to mechanistic catalytic test studies is also presented. It consists of spectroscopic investigations of a set of partial reactions, driven by external creation of the supposed active sites and intermediates, with the aim of reproducing and verifying the feasibility of the postulated catalytic cycle. Moreover, to assure some consistency of the subject, basic characteristics of EPR spectroscopy related to surface studies and chemical theories of reactivity are concisely reviewed.     

Sharpless Asymmetric Dihydroxylation of Olefins in WaterSurfactant Media with Recycling of the Catalytic System by Membrane Nanofiltration

This paper presents a new and more sustainable alternative approach for the Sharpless catalytic asymmetric dihydroxylation (AD) of olefins using a water/surfactant system as reaction media. The AD reaction was performed using several cationic and anionic surfactants allowing yields and enantiomeric excesses higher or comparable with the conventional systems (using organic mixtures). The use of this water/surfactant medium offers the additional advantage of performing the reactions without the need of a slow addition of olefins. Asymmetric dihydroxylation of 1‐hexene in a 1.5 mM sodium cholate aqueous solution, using N‐methylmorpholine N‐oxide (NMO) as co‐oxidant was selected as model system to evaluate the feasibility of recycling the Sharpless catalytic system by nanofiltration. The reaction media was processed by nanofiltration, the product was isolated in the permeate, whereas the catalytic system and surfactant were retained by the membrane and recycled through six successive reactions, improving the catalyst turn‐over number. The experimental results were compared with the ones calculated on the basis of mass balances, membrane rejections to product and reaction yields.