Optimization of MoVSb oxide catalyst for partial oxidation of isobutane by combinatorial approaches

Optimization of the Mo-V-Sb mixed-oxide system for the selective oxidation of isobutane to methacrolein by true combinatorial methods primarily is intended to reduce the number of experiments in a broad parameter space. Therefore, an evolutionary approach based on a genetic algorithm has been chosen to screen three generations of 30 catalysts. With the help of automated sol-gel synthesis techniques, a high-throughput continuous flow reactor (16UPCFR), and appropriate software for experimental design, a new catalyst composition with improved performance has been obtained. Finally, the best catalysts were scaled-up to gram quantities and tested in a continuous-flow reactor unit that was equipped with four parallel reactors (4UPCFR). The final catalyst showed a significantly higher selectivity toward methacrolein at the same isobutane conversion, compared to the initial Mo8V2Sb90O(x) catalyst.     

Flow fine synthesis with heterogeneous catalysts

In the past few decades, organic reactions under flow conditions have attracted increasing attention. Flow reactions have a number of advantages over batch reactions in terms of environmental compatibility, efficiency, and safety. In particular, flow reactions with heterogeneous catalysts that yield desired products without significant levels of by-product formation can enable purification processes to be avoided. This feature can allow flow reactions to be assembled in a multi-step and continuous manner for the synthesis of complex molecules. These new techniques have opened up new approaches to the synthesis of fine chemicals and are expected to play a prominent role in future chemical manufacturing processes. In this context, this review aims to summarize recent developments in continuous-flow reactions with heterogeneous catalysts for synthesis of fine chemicals.     

Preparation and activity measurement of some low pressure methanol synthesis catalysts

Summary In the present study, twenty four catalysts for low pressure methanol synthesis were prepared according to a pre-designed research program consisting of three stages. In each stage, applying the experimental design techniques, a number of catalysts were synthesized by the co-precipitation method, using different proportions of metal salts solutions. The activities of the catalysts were determined applying a laboratory scale continuous packed bed reactor. It was noted that the calcinations temperature, ageing time and molar ratio of metal nitrates to precipitant, had the highest effects on the activity of the catalysts.     

Solid-phase synthesis of homogeneous ruthenium catalysts on silica for the continuous asymmetric transfer hydrogenation reaction

The solid-phase synthesis of new asymmetric transfer hydrogenation catalysts as well as the use of these silica supported systems in batch and flow reactors is reported. The ruthenium complex of NH-benzyl-(1R,2S)-(-)-norephedrine covalently tethered to silica showed a high activity and enantioselectivity in the reduction of acetophenone. In three consecutive batchwise catalytic runs, we obtained ee values of 88%. In a continuous flow reactor, a very constant catalytic activity was observed; no catalyst deactivation occurred over a period of one week. This has been ascribed to successful site isolation. Using optimized conditions in this flow reactor, the ee was as high as 90% at 95% conversion. The supported catalysts generally show the same trend in catalyst performance as in solution. The viability of our approach was further shown in one example, the ruthenium(II) complex of (1S,2R)-(+)-2-amino-1,2-diphenylethanol, for which an enantiomeric excess of 58% was observed, which is nearly three times higher than its homogeneous analogue.     

Supramolecular Strategies for the Recycling of Homogeneous Catalysts

Supramolecular approaches are increasingly used in the development of homogeneous catalysts and they also provide interesting new tools for the recycling of metal-based catalysts. Various non-covalent interactions have been utilized for the immobilization homogeneous catalysts on soluble and insoluble support. By non-covalent anchoring the supported catalysts obtained can be recovered via (nano-) filtration or such catalytic materials can be used in continuous flow reactors. Specific benefits from the reversibility of catalyst immobilization by non-covalent interactions include the possibility to re-functionalize the support material and the use as “boomerang” type catalyst systems in which the catalyst is captured after a homogeneous reaction. In addition, new reactor design with implemented recycling strategies becomes possible, such as a reverse-flow adsorption reactor (RFA) that combines a homogeneous reactor with selective catalyst adsorption/desorpion. Next to these non-covalent immobilization strategies, supramolecular chemistry can also be used to generate the support, for example by generation of self-assembled gels with catalytic function. Although the stability is a challenging issue, some self-assembled gel materials have been successfully utilized as reusable heterogeneous catalysts. In addition, catalytically active coordination cages, which are frequently used to achieve specific activity or selectivity, can be bound to support by ionic interactions or can be prepared in structured solid materials. These new heterogenized cage materials also have been used successfully as recyclable catalysts.     

High throughput development of selective oxidation catalysts at Süd-Chemie

The Temkin reactor concept was successfully extended to the high throughput operation mode and it could be considerably improved as compared to the original design with respect to an optimized gas flow pattern over the full size beads. This improved parallel reactor design was successfully used for the high throughput optimization of an innovative new class of physically coated VAM shell catalysts. Exploiting this novel, improved Temkin reactor concept allowed Süd-Chemie not only to optimize the multiparameter compositional space of noble metal and promoter loadings on the support spheres but for the first time to combine this "chemical optimization" with the high throughput improvement of catalytically decisive parameters as the active shell thickness, the metal distribution cross the shell, the pore diameters, and the pore volumes. This new class of physically impregnated VA catalysts, called VAM2ax, impress by its exceptionally high VA selectivity of above 94% at 50% oxygen conversion and the very high space time yields of > 1000 g VAM/l*h which easily can be reached over these shell catalysts with optimized mass and heat transport properties.     

Conversion of cellulose to glucose and levulinic acid via solid-supported acid catalysis

Cellulose is hydrolyzed to glucose, which is further converted to levulinic acid in the presence of surface-supported Brønsted and Lewis acid catalysts. Nafion catalysts, in particular, have the potential to be recycled or applied to a continuous flow reactor for the synthesis of these biofuel precursors.     

Recent Advances in Multifunctional Capsule Catalysts in Heterogeneous Catalysis?

Capsule catalysts composed of pre-shaped core catalysts and layer zeolites have been widely used in the tandem reactions where multiple continuous reactions are combined into one process. They show excellent catalytic performance in heterogeneous catalysis, including the direct synthesis of middle isoparaffins or dimethyl ether from syngas, as compared to the conventional hybrid catalysts. The present review highlights the recent development in the design of capsule catalysts and their catalytic applications in heterogeneous catalysis. The capsule catalyst preparation methods are introduced in detail, such as hydrothermal synthesis method, dual-layer method, physically adhesive method and single crystal crystallization method. Furthermore, several new applications of capsule catalysts in heterogeneous catalytic processes are presented such as in the direct synthesis of liquefied petroleum gas from syngas, the direct synthesis of para-xylene from syngas and methane dehydroaromatization. In addition, the development in the design of multifunctional capsule catalysts is discussed, which makes the capsule catalyst not just a simple combination of two different catalysts, but has some special functions such as changing the surface hydrophobic or acid properties of the core catalysts. Finally, the future perspectives of the design and applications of capsule catalysts in heterogeneous catalysis are provided.     

An Immobilized‐Dirhodium Hollow‐Fiber Flow Reactor for Scalable and Sustainable C−H Functionalization in Continuous Flow

A scalable flow reactor is demonstrated for enantioselective and regioselective rhodium carbene reactions (cyclopropanation and C?H functionalization) by developing cascade reaction methods employing a microfluidic flow reactor system containing immobilized dirhodium catalysts in conjunction with the flow synthesis of diazo compounds. This allows the utilization of the energetic diazo compounds in a safe manner and the recycling of the dirhodium catalysts multiple times. This approach is amenable to application in a bulk‐scale synthesis employing asymmetric C?H functionalization by stacking multiple fibers in one reactor module. The products from this sequential flow–flow reactor are compared with a conventional batch reactor or flow–batch reactor in terms of yield, regioselectivity, and enantioselectivity.     

Microwave Irradiation in Micro‐ Meso‐Fluidic Systems; Hybrid Technology has Issued the Challenge

A combination of microwave irradiation and flow chemistry has been described as a promising smart and hyphenated technology that can fuse and synergize the benefits of the techniques. The cells and tissues of all living organisms promote a huge number of bioorganic reactions that occur as flow systems and not the batch‐type conditions typically used by chemists and biotechnologists. Microwave‐assisted chemical conversion carried out in continuous flow mode with micro‐ or meso‐channel reactors can offer significant processing advantages, including improved thermal exchange, energy efficiency, safety, mixing control, a wider range of reaction conditions, repeatability and scalability as well as dramatic reductions in side‐reactions and degradations. This review will discuss relevant examples of organic synthesis and nanoparticles production performed in continuous flow mode with integrated microwave irradiation in micro‐ or mesofluidic systems.     

Diverse Supports for Immobilization of Catalysts in Continuous Flow Reactors

The rapid development of continuous flow processes is driving innovations in various chemical syntheses and industrial productions. Immobilizing catalysts in flow reactors allows transformations with high-efficiency and excludes the subsequent separation procedures. This concept outlines the approaches to incorporate catalysts within flow reactors, with particular focus on the application of additional supports including inorganic materials like silica, zeolite and reduced graphene oxide, polymeric materials like polymer packings, monoliths, cross-linked gels and polymer brushes, and other materials for specific conditions like transparent glass fibers and glass beads. Furthermore, advanced methods to develop ordered micro-/nanoarrays from internal walls of flow channels for immobilization of catalysts as well as application of innovative vortex fluidic devices are discussed to inspire new designs of supports for novel fluidic reactors with broad applications.     

Chemical aerosol flow synthesis of semiconductor nanoparticles

Nanometer-sized semiconductor particles (quantum dots) have been the subject of intense research during the past decade owing to their novel electronic, catalytic, and optical properties. Fundamental properties of these nanoparticles (1-20 nm diameter) can be systematically changed simply by controlling the size of the crystals while holding their chemical composition constant. We describe here a new methodology for the continuous production of fluorescent CdS, CdSe, and CdTe nanoparticles using ultrasonically generated aerosols of high boiling point solvents. Each submicron droplet serves as a separate nanoscale chemical reactor, with reactions proceeding as the liquid droplets (which hold both reactants and surface stabilizers) are heated in a gas stream. The method is inexpensive, scalable, and allows for the synthesis of high quality nanocrystals. This chemical aerosol flow synthesis (CAFS) can be extended to the synthesis of nanostructured metals, oxides, and other materials.     

A novel 3D Tesla valve micromixer for efficient mixing and chitosan nanoparticle production

Current three-dimensional micromixers for continuous flow reactions and nanoparticle synthesis are complex in structure and difficult to fabricate. This paper investigates the design, fabrication, and characterization of a novel micromixer that uses a simple spatial Tesla valve design to achieve efficient mixing of multiple solutions. The flow characteristics and mixing efficiencies of our Tesla valve micromixer are investigated using a combination of numerical simulations and experiments. The results show that in a wide range of flow rates, viscoelastic solutions with different concentrations can be well mixed in our micromixer. Finally, experiments on the synthesis of chitosan nanoparticles are conducted to verify the practicability of our micromixer. Compared with nanoparticles prepared by conventional magnetic stirring, the size of nanoparticles prepared by micromixing is smaller and the distribution is more uniform. Therefore, our Tesla valve micromixer has significant advantages and implications for mixing chemical and biological reactions.     

CO气相合成草酸二乙酯催化剂性能评价

考察了Al2O3载体的类型和形状、活性组分Pd的负载量、活性组分Pd和助催化剂Fe之比对工业原料CO气相催化合成草酸二乙酯(DEO)反应的影响。结果表明,当Pd的负载量为1%～5%、Pd/Fe为0.2～2.0(mol比)、条状α-Al2O3为载体时,催化剂的性能优良,在此条件下,草酸二乙酯的最大收率可达60%, CO转化率可达63%,草酸二乙酯选择性可达98%。     

Highly Catalytic Enantioselective Addition of Diethyl Zinc to Aldehydes and Chalcone in the Presence of Chiral Ligands

Catalytic asymmetric carbon-carbon bond formation is one of the most important reactions and have attracted much attention to develop more efficient enantioselective C-C formation methods in organic synthesis. In this field, asymmetric addition of diethylzinc to aldehydes[1] and conjugate addition to enones[2] have drawn special interests and have been greatly developed. Regardless of it, much spaces in these areas still exist, so it needs more extensive and intensive researches for the purpose of as follows: (1) attaching ligands to a polymer for the easy separation of the catalysts so as to be able to allow very efficient recovery and reuse of the catalysts, and the possibility of carrying out the desired transfomation in continuous mode in a flow reactor, etc., (2) searching for novel chiral catalysts with such features as more suitable for more extensive substrates varieties, and more convenient and economical as well as possessing applicable prospect, and so on. Here we report some works in these areas done in our laboratory.     

High-throughput approaches for the discovery and optimization of new olefin polymerization catalysts

The discovery of new olefin polymerization catalysts is currently a time-intensive trial-and-error process with no guarantee of success. A fully integrated high-throughput screening workflow for the discovery of new catalysts for polyolefin production has been implemented at Symyx Technologies. The workflow includes the design of the metal-ligand libraries using custom-made computer software, automated delivery of metal precursors and ligands into the reactors using a liquid-handling robot, and a rapid primary screen that serves to assess the potential of each metalligand-activator combination as an olefin polymerization catalyst. "Hits" from the primary screen are subjected to secondary screens using a 48-cell parallel polymerization reactor. Individual polymerization reactions are monitored in real time under conditions that provide meaningful information about the performance capabilities of each catalyst. Rapid polymer characterization techniques support the primary and secondary screens. We have discovered many new and interesting catalyst classes using this technology.     

Methanation of syngas over coral reef-like Ni/Al_2O_3 catalysts

Coral reef-like Ni/Al2O3 catalysts were prepared by co-precipitation of nickel acetate and aluminium nitrate with sodium carbonate aqueous solution in the medium of ethylene glycolye.Methanation of syngas was carried out over coral reef-like Ni/Al2O3 catalysts in a continuous flow type fixed-bed reactor.The structure and properties of the fresh and used catalysts were studied by SEM,N2 adsorption-desorption,XRD,H2-TPR,O2-TPO,TG and ICP-AES techniques.The results showed that the coral reef-like Ni/Al2O3 catalysts exhibited better activity than the conventional Ni/Al2O3-H2O catalysts.The activities of coral reef-like catalysts were in the order of Ni/Al2O3-673>Ni/Al2O3-573>Ni/Al2O3- 473>Ni/Al2O3-773.Ni/Al2O3-673-EG catalyst showed not only good activity and improved stability but also superior resistance to carbon deposition,sintering,and Ni loss.Under the reaction conditions of CO/H2(molar ratio)=1:3,593 K,atmospheric pressure and a GHSV of 2500 h-1,CH4 selectivity was 84.7%,and the CO conversion reached 98.2%.     

非金属催化剂在催化环氧化物和CO2合成环状碳酸酯中的研究进展

随着科学技术的进步和工业化的发展,大量化石燃料被消耗,大气中二氧化碳浓度急剧增加,导致温室效应加剧,严重威胁到人类的生存和发展。基于可持续发展的思想,利用储量丰富且廉价的二氧化碳作为 C1资源替代有毒的气体(如一氧化碳和光气等)制备具有广泛应用的环状碳酸酯,不仅满足“绿色化学”的要求,而且符合“原子经济性”的原则。迄今为止,大量用于催化二氧化碳和环氧化物环加成反应合成环状碳酸酯的催化剂,包括均相催化剂(如金属卤化物、有机碱、离子液体和金属配合物),多相催化剂(如金属氧化物、负载型催化剂、有机聚合物、金属有机框架材料和碳材料等)被报道。其中金属催化剂占主导地位,大多表现出优异的催化活性。然而,目前可供开采的金属矿越来越少,大多数金属的回收再利用率较低,重金属污染日趋严重。因此,开发新型、廉价、绿色、高效、循环性和稳定性好的非金属催化剂具有重要意义。
　　本文主要介绍了近3年以来用于催化二氧化碳和环氧化物环加成反应合成环状碳酸酯的非金属催化剂,主要包括有机碱、离子液体、固载型催化剂、有机聚合物和碳材料等。概括了不同种类催化剂的设计思想及其催化反应机理,重点阐述了分子内以及分子间各种功能基团的协同作用对环加成反应的影响。通过比较发现,具有“C–N=C”结构的有机碱活性相对较高,氢键给体和亲核物质都能与有机碱协同作用提高其催化活性;传统离子液体的活性一般不理想,氢键给体如羟基和羧基的引入有利于促进环加成反应,且多阳离子和多氢键给体功能化的离子液体表现出更高的催化活性;负载型催化剂中,载体和活性组分之间的协同作用有利于加速环加成反应的进行,多种功能基团负载和以共价键方式多层固载能更好地提高催化剂稳定性和催化活性;利用非烯烃化合物制得的活性组分位于主链的多孔有机聚合物,催化活性和稳定性大多高于活性组分位于侧链的烯烃聚合物;碳材料催化剂中,引入不饱和的 N物种(如伯胺和吡啶氮),有利于 CO2的吸附和活化,能促进环加成反应。此外,利用密度泛函的方法,计算模拟催化反应过程,能更好地揭示反应机理,并为设计和制备高效的催化剂提供理论指导。
　　该领域目前面临的重要挑战是研发可以同时实现二氧化碳捕获和转化的新型、环保和高效非金属催化剂,终极目标是利用多孔催化材料在常温和常压下直接捕获工业废气中的二氧化碳,并利用捕获的二氧化碳实现环状碳酸酯的连续生产。基于协同催化的设计思想,利用多种基团功能化的策略合成高效吸附和活化二氧化碳以及开环活化环氧化物的非金属催化剂,有望实现上述目标。     

Synthesis of substituted indoles using continuous flow micro reactors

Continuous flow micro fluidic devices for organic synthesis (‘micro reactors’) are becoming established in a number of facets of modern applied chemistry. As part of a concurrent research project with a pharmaceutical company for generation of materials of pharmaceutical interest within continuous flow environments, we present here, for the first time a series of indoles that have been produced within micro reactor systems. We have developed three different approaches to the synthesis, which are compared with traditional batch synthesis as well as each other in terms of ease of optimization, chemical suitability and versatility, and implications as to throughput. Typical throughputs of approach 1 (simulated classical synthesis) were in the region of 2 mgh⁻¹ of indoles such as tetrahydrocarbazole and cyclopentaindole. The second approach (based on Elk's modification of Fischer indole synthesis) gave throughputs of 5.7-8.9 mgh⁻¹ and the final approach (using heterocatalytic flow reactors) gave the highest throughputs of 12.7-20.1 mgh⁻¹. All throughputs are per single channel reactor system (i.e., one single reactor set up), and the latter two approaches produce viable output quantities for the syntheses of radiolabelled materials (where typically minute amounts of high purity materials are required from a rapid and safe production environment).