TY - JOUR. T1 - Effects on general acid catalysis from mutations of the invariant tryptophan and arginine residues in the protein tyrosine phosphatase from Yersinia. AU - Hoff, Richard H.. AU - Hengge, Alvan C.. AU - Wu, Li. AU - Keng, Yen Fang. AU - Zhang, Zhong Yin. PY - 2000/1/11. Y1 - 2000/1/11. N2 - General acid catalysis in protein tyrosine phosphatases (PTPases) is accomplished by a conserved Asp residue, which is brought into position for catalysis by movement of a flexible loop that occurs upon binding of substrate. With the PTPase from Yersinia, we have examined the effect on general acid catalysis caused by mutations to two conserved residues that are integral to this conformation change. Residue Trp354 is at a hinge of the loop, and Arg409 forms hydrogen bonding and ionic interactions with the phosphoryl group of substrates. Trp354 was mutated to Phe and to Ala, and residue Arg409 was mutated to Lys and to Ala. The four mutant enzymes were studied using steady state kinetics and ...
TY - JOUR. T1 - Implication of substrate-assisted catalysis on improving lipase activity or enantioselectivity in organic solvents. AU - Tsai, Shau Wei. AU - Chen, Chun Chi. AU - Yang, Hung Shien. AU - Ng, I. Son. AU - Chen, Teh Liang. PY - 2006/8/1. Y1 - 2006/8/1. N2 - In comparison with the biocatalyst engineering and medium engineering approaches, very few examples have been reported on using the substrate engineering approach such as substrate-assisted catalysis (SAC) for naturally occurring or engineered lipases and serine proteases to improve the enzyme activity and enantioselectivity. By employing lipase-catalyzed hydrolysis of (R,S)-naproxen esters in water-saturated isooctane as the model system, we demonstrate the proton shuttle device to the leaving alcohol of the substrate as a new means of SAC to effectively improve the lipase activity or enantioselectivity. The result cannot only provide a strong evidence for the rate-limiting proton transfer for the bond-breaking of tetrahedron ...
A highly efficient and stable [email protected] catalyst was successfully prepared by immobilizing Pd onto diimine-functionalized mesoporous silica SBA-15. With the help of diimine functional groups grafted onto the SBA-15, Pd could be anchored on a support with high dispersion. [email protected] catalyst exhibited excellent catalytic performance for the Suzuki coupling reaction of electronically diverse aryl halides and phenylboronic acid under mild conditions with an ultralow amount of Pd (0.05 mol % Pd). When the catalyst amount was increased, it could catalyze the coupling reaction of chlorinated aromatics with phenylboronic acid. Compared with the catalytic performances of Pd/SBA-15 and [email protected] catalysts, the [email protected] catalyst exhibited higher hydrothermal stability and could be repeatedly used four times without a significant decrease of its catalytic activity.
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The full potential in catalyst development will only be realized if characterization techniques are available that can probe materials with subnanometer resolution. One of the most employed techniques to image heterogeneous catalysts at the nanometer and subnanometer scale is transmission electron microscopy (TEM). As suggested by the name, TEM uses ... read more electrons transmitted through the object for imaging. Since the interaction between electrons and matter is very strong, only thin parts, commonly much less than a micron in thickness, are imaged. Since heterogeneous catalysts are, in most cases, structured on a much smaller length scale, the sample thickness can be reduced to TEM requirements by appropriate preparation techniques and is, therefore, no limitation. show less ...
Deoxygenation of sulfoxides to their corresponding sulfides is an important reaction, and the development of efficient heterogeneous catalysts that can utilize molecular hydrogen (H2) as a reducing agent is highly desired. In this study, we successfully developed a new concept in heterogeneous catalysts, pla
Nanostructured single-site heterogeneous catalysts possess the advantages of classical solid catalysts, in terms of easy recovery and recycling, together with a defined tailored chemical and steric environment around the catalytically active metal site. The use of inorganic oxide supports with selected shape and porosity at a nanometric level may have a relevant impact on the regio- and stereochemistry of the catalytic reaction. Analogously, by choosing the optimal preparation techniques to obtain spatially isolated and well-characterised active sites, it is possible to achieve performances that are comparable to (or, in the most favourable cases, better than) those obtained with homogeneous systems. Such catalysts are therefore particularly suitable for the transformation of highly-functionalised fine chemicals and some relevant examples where high chemo-, regio- and stereoselectivity are crucial will be described.
A carbon-based solid acid catalyst was prepared by incomplete carbonization of H3PO4-impregnated pulp fibers followed by sulfonation. XRD, FT-IR, BET, TGA, and acid density test were employed to characterize the structure and performance of the catalyst. Results showed that the catalyst was amorphous carbon composed of aromatic carbon sheets with -COOH, -OH and -SO3H groups. Previous impregnation with H3PO4 could promote porosity formation of the catalyst. The optimized carbonization temperature and time for the catalyst were 250 °C and 1.5 h. The -SO3H density and specific surface area for the catalyst prepared under the optimized conditions were 1.1 mmol g−1 and 118 m2 g−1, respectively. Compared to HZSM-5, Amberlyst-15 and previous reported carbon catalysts, the catalyst showed higher catalytic activity for transesterification of methyl acetate with n-butanol as hydrophobic reaction. The catalyst had good thermal stability, which could bear 200 °C without decomposition. The catalyst ...
TY - JOUR. T1 - Optically active β-ketoiminato manganese(III) complexes as efficient catalysts in enantioselective aerobic epoxidation of unfunctionalized olefins. AU - Nagata, Takushi. AU - Imagawa, Kiyomi. AU - Yamada, Tohru. AU - Mukaiyama, Teruaki. PY - 1994/6/1. Y1 - 1994/6/1. N2 - A novel manganese(III) complex having an optically active N, N′-ethylenebis-β-ketoimine ligand was prepared and characterized crystallographically. The manganese(III) complexes behave as effective catalysts in enantioselective epoxidation of unfunctionalized olefins by combined use of molecular oxygen, an oxidant, and pivalaldehyde, a reductant. Dihydronaphthalene derivatives were converted into the corresponding optically active epoxides with good to high enantioselectivities.. AB - A novel manganese(III) complex having an optically active N, N′-ethylenebis-β-ketoimine ligand was prepared and characterized crystallographically. The manganese(III) complexes behave as effective catalysts in enantioselective ...
Novel Bi2S3/TiO2 Heterogeneous Catalyst: Photocatalytic Mechanism for Decolorization of Texbrite Dye and Evaluation of Oxygen Species - Heterogeneous;Sonochemical;Visible light;$Bi_2S_3$;DPCO;
Sie sind hier: Enhanced catalytic performance of immobilized Parvibaculum lavamentivorans alcohol dehydrogenase in a gas phase bioreactor using glycerol as an additive. ...
TY - JOUR. T1 - Synthesis and characterization of novel chiral sulfonato-salen-manganese(III) complex in a zinc-aluminium LDH host. AU - Bhattacharjee, Samiran. AU - Anderson, Jim. PY - 2004/3/7. Y1 - 2004/3/7. N2 - A novel heterogeneous catalyst, [Zn2.15Al0.86(OH)6.02] [Mn]0.19[C6H5COO]0.48·2H2O, where {[Mn] = chiral sulfonato-salen-manganese(III) complex, Na2MnC20H22N2S2O12Cl, intercalated into ZnII-AlIII layered double hydroxide host}, has been synthesized and found to be an effective heterogeneous catalyst for the stereoselective epoxidation of R-(+)-limonene using molecular oxygen. The catalyst could be recycled without loss of performance.. AB - A novel heterogeneous catalyst, [Zn2.15Al0.86(OH)6.02] [Mn]0.19[C6H5COO]0.48·2H2O, where {[Mn] = chiral sulfonato-salen-manganese(III) complex, Na2MnC20H22N2S2O12Cl, intercalated into ZnII-AlIII layered double hydroxide host}, has been synthesized and found to be an effective heterogeneous catalyst for the stereoselective epoxidation of ...
Catalysis is at the heart of chemical transformations; therefore, there are continuous efforts to develop new catalysts and increase catalytic performance for various applications. Metallic nanoparticles (NPs) have become essential tools for many chemical processes employed in industry and academia during recent decades.1-5 NPs possess high specific surface area, various shapes and sizes, and high reactivity, and they often exhibit activity different from that of the corresponding bulk materials, due to their distinctive quantum properties. Handling of NPs, however, is not easy, because NPs are often prone to self-aggregation, and it is difficult to separate them from reaction media because the classical, convenient filtration methods are not applicable. One economical way to overcome or minimise these limitations is to anchor NPs on supports, with the latter also serving as modifiers of catalytic properties. Nowadays, economic considerations and health issues are gaining more and more ...
We describe a new class of heterogeneous catalysts called supported molten metal catalysis (SMMC), in which molten metal catalysts are dispersed as nanodroplets on the surface of porous supports, allowing much larger active surface area than is possible in conventional contacting techniques for catalytic metals that are molten under reaction conditions, thus greatly enhancing their activity and potential utility. Specific examples of different types of reactions are provided to demonstrate the broad applicability of the technique in designing active, selective, and stable new catalysts. It is shown that dispersing the molten metal on a support in the suggested manner can enhance the rate of a reaction by three to four orders of magnitude as a result of the concomitant increase in the active surface area. New reaction examples include {gamma}-Al{sub 2}O{sub 3} supported molten Te (melting point 450 C) and Ga (MP 30 C) catalysts for bifunctional methylcyclohexane dehydrogenation. These catalysts provide
Introduction. Catalysis-catalysing for success Catalysing for success This presentation will discuss what catalysts are, their mechanisms of action and their significance to the chemical industry. Introduction Catalysis is a remarkable phenomenon. Quite apart from the scientific reality, the financial and environmental benefits of harnessing its power are very impressive. Catalysts in definition developed by scientists in the last century, are materials that change the rate of attainment of equilibrium without themselves being changed or consumed in the process. To illustrate the importance of catalysis, here are some of the many applications of it: Chemical and materials manufacturing, Fuel cells, Combustion devices, Pollution control systems, Laundry detergents. The mechanisms of catalytic action in some of the above applications will be discussed later. Types of Catalyst There are two types of catalyst: Industrial catalysts - These are non-biological catalysts, which include solid state, ...
2 Sheets-Sheet 1 w. L. HENDERSON I CATALYTIC OXIDATION UNIT FOR DOMESTIC OVEN EXHAUST Oct. 27,1970 Filed Feb WAYNE L. HENDERSON ms ATTORNEY Oct. 27 41970 w, HENDERSON 3,536,?!- CATALYTIC OXIDATION UNIT FOR DOMESTIC-OVENBXIIAUST Filed Feb. 21, 1968 2 shms snm a was I FIG.4 . l I I l I I I I I I I I I o 5 l 3o 4o so 6o INVENTOIL WAYNE L. neuoaasou HIS ATTORNEY United States Patent US. Cl. 23-288 2 Claims ABSTRACT OF THE DISCLOSURE A catalytic oxidation unit useful in eliminating smoke and odors issuing from the exhaust vent of a domestic cooking oven, particularly a high temperature, selfcleaning oven using a pyrolytic process for degrading food soils. The oxidation unit comprises a hollow housing supporting a plurality of catalyst coated gas burners of cellular ceramic construction and having a high surface-tovolume ratio. The housing has an intake port and an exhaust port and includes a partition which separates the housing into intake and afterburner compartments; with the gas flow being ...
кислотный катализ microheterogeneous catalysis микрогетерогенный катализ polyfunctional catalysis полифункциональный катализ photochemical catalysis фотохимический катализ fermentation catalysis ферментативный катализ acid base catalysis кислотно
The selective catalytic oxidation (SCO) of ammonia to N2 was studied by using a series of noble metal-V2O5-WO3 catalysts supported on titania-silica (TS) prepared by coprecipitation method. In the V2O5- WO3 catalyst system, the use of TS as a support was very effective to enhance catalytic activity compared with TiO2 or SiO2 alone. The addition of a slight amount of Pd and Ir to V2O5-WO3/TS catalyst caused also remarkable enhancement of the catalytic activity without decreasing the selectivity to N2. The present catalysts provide remarkably high catalytic performance for SCO of ammonia to N2 under the practical reaction conditions for an industrial application.
Enzyme catalysis can be regarded as a catalytic reaction between homogeneous and heterogeneous reactions. It can be seen as the reaction between the enzyme and the reaction for formation of intermediate compounds, and it can also be seen as the reaction after the surface of the enzyme adsorbs the reactant.. What are enzymes?. It is an organic colloidal substance composed of protein. It plays a catalytic role for biochemical reactions.. Fermentation also is finished by its role of protease enzyme.. Enzyme catalysis. Accelerating or slowing down a chemical reaction by enzymes is called enzyme catalysis. Hundreds of different reactions performing simultaneously in a living cell are accomplished by a considerable number of enzymes. In many cases, small structural changes in the substrate molecule will make the compound loss the ability to act as a substrate.. Features. Enzyme catalysis shows a characteristic which is not seen in non-enzymatic reaction. It can be saturated with substrate. When the ...
For a seminal work in HOMO activation via enamineintermediates, see: a) List B., Lerner R. A., Barbas III C. F. J.,Proline-Catalyzed Direct Asymmetric Aldol Reactions, J. Am.Chem. Soc., 2000, 122, 2395-2396. For a review in enamineactivation, see: b) Mukherjee S., Yang J. W., Hoffmann S.,List B., Asymmetric Enamine Catalysis, Chem. Rev. 2007,107, 5471-5569. For a seminal work in HOMO-activation viadienamine intermediates, see: c) Bertelsen S., Marigo M.,Brandes S., Dinér P., Jørgensen K. A., Dienamine Catalysis:Organocatalytic Asymmetric γ-Amination of α,β-UnsaturatedAldehydes, J. Am. Chem. Soc. 2006, 128, 12973-12980.For reviews in dienamine activation, see: d) Ramachary D. B.,Reddy Y. V., Dienamine Catalysis: An Emerging Technologyin Organic Synthesis, Eur. J. Org. Chem., 2012, 865-887. e)Parra A., Reboredo S., Alemán J., Asymmetric Synthesis ofCyclobutanes by a Formal [2+2] Cycloaddition Controlled byDienamine Catalysis, Angew. Chem. Int. Ed. 2012, 51, 9734-9735 ...
Winning commercial heterogeneous catalysts satisfy numerous key require- ments: as well as excessive catalytic task for the specified response, with excessive selectivity the place applicable, in addition they have a suitable advertisement existence and are rugged sufficient for transportation and charging into plant reactors. extra requisites contain the necessity to come on-line easily very quickly and reproducible production approaches that contain handy methods at appropriate expense. the advance of heterogeneous catalysts that meet those (often at the same time unique) calls for is much from basic, and likewise a lot of the particular production tech- nology is stored mystery for advertisement reasons-thus theres no smooth textual content that offers with the full of this significant topic. rules of Catalyst improvement, which offers comprehensively with the layout, improvement, and manufacture of functional heterogeneous catalysts, is for this reason specially helpful in assembly the ...
Research presented in this work describes investigations into the synthesis, structure, and reactivity of cooperative catalysts. Cooperative catalysis, the concept of actively involving ligands in catalytic transformations, is used extensively in enzymatic systems and has been shown to enable organometallic catalysts to realize improved enantioselectivity, chemoselectivity, or activation of otherwise unreactive bonds. Two types of cooperative catalysts are investigated in this work: non-innocent ligands and ligand-based directing groups. Initial investigations detailed in this work revolve around a catalyst of the first type: Shvos catalyst ({[Ph₄(η⁵-C₄CO)]₂H]}Ru₂(CO)₄(μ-H)) which is known for containing a non-innocent cyclopentadienone ligand. Shvos catalyst is shown to be a competent catalyst for alkylation of amines with alcohols and amines and is superior to other reported catalysts in some cases. Subsequent studies investigated the potential of Shvos catalyst to mediate ...
Fingerprint Dive into the research topics of Mechanism investigation on the formation of olefins and paraffin from the thermochemical catalytic conversion of triglycerides catalyzed by alkali metal catalysts. Together they form a unique fingerprint. ...
Development of oxygen evolution reaction (OER) catalysts with reduced precious metal content while enhancing catalytic performance has been of pivotal importance in cost-effective design of acid polymer electrolyte membrane water electrolyzers. Hollow multimetallic nanostructures with well-defined facets are ideally suited for saving the usage of expensive precious metals as well as boosting catalytic performances; however, Ir-based hollow nanocatalysts have rarely been reported. Here, a very simple synthetic scheme is reported for the preparation of hollow octahedral nanocages of Co-doped IrCu alloy with readily tunable morphology and size. The Co-doped IrCu octahedral nanocages show excellent electrocatalytic activity and long-term durability for OER in acidic media. Notably, their OER activity represents one of the best performances among Ir-based acidic OER catalysts.. ...
Homogeneous catalysts are in the same phase as the reactants while heterogeneous catalysts are not. As far as I understand, the phase matters in terms of effectivity depending on the phase that the reactants are in. For example, a solid catalyst in an aqueous solution or a liquid catalyst in an aqueous solution, versus a case where the reactants sit on the surface of the catalyst, which would be called adsorption ...
The role of carbonaceous deposits (coke) formed in dehydrogenation catalysis has been extensively investigated over the last few decades mainly with respect to the deactivation of metal-based and metal-free heterogeneous catalysts. Although much less emphasized, coke deposits grown on selected metal oxides have also been described as active and selective phases for alkene dehydrogenation under an oxidative or non-oxidative atmosphere. This work describes the straightforward preparation of coked γ-Al2O3 composites and their catalytic performance in the ethylbenzene (EB) direct dehydrogenation (DDH) to styrene (ST) under steam- and oxygen-free conditions. The study unveils the effective potentiality of a catalytic system already known to the scientific community but never employed for EB DDH under severe conditions, close to those commonly used in industrial plants (600 °C, 10 vol % EB/He, GHSV = 3000 h-1). Such a simple catalytic system has revealed a significant stability on long-term trials ...
Acid catalysis plays an important role in biomass conversion processes for producing chemicals and fuels. We report a relatively simple procedure for synthesizing versatile, strong acid catalysts based on carbon and carbon-silica composites with sulfonic acid groups. The process involves chemical activation of a sulfonic acid organic precursor at low temperature. The synthesis conditions can be modified to tune the surface composition, texture, and the acid properties of the materials towards superior catalytic performances. Molecular level insights into the nature and strength of the acid sites were gained by combining high resolution XPS and 1H-decoupled 31P MAS NMR spectroscopy of adsorbed triethylphosphine oxide. These materials are effective acid catalysts for the conversion of different biomass-derived chemicals to useful bio products such as furanic ethers and levulinate esters ...
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CANCELED | Terri Bright Hettinger, PhD will be joining us for Science Workshop to give a talk about industry careers and chemical catalysis.
Single-site catalysts can demonstrate high activity and selectivity in many catalytic reactions. The synthesis of these materials by impregnation from strongly oxidizing aqueous solutions or pH-controlled deposition often leads to low metal loadings or a range of metal species. Here, we demonstrate that simple impregnation of the metal precursors onto activated carbon from a low-boiling-point, low-polarity solvent, such as acetone, results in catalysts with an atomic dispersion of cationic metal species. We show the generality of this method by producing single-site Au, Pd, Ru and Pt catalysts supported on carbon in a facile manner. Single-site Au/C catalysts have previously been validated commercially to produce vinyl chloride, and here we show that this facile synthesis method can produce effective catalysts for acetylene hydrochlorination in the absence of the highly oxidizing acidic solvents previously used.
SLAC and Stanford researchers have shown for the first time that a cheap catalyst can split water and generate hydrogen gas for hours on end in the harsh environment of a commercial electrolyzer -- a step toward clean, large-scale hydrogen production for fuel, fertilizer and industry.
The reduction of automotive exhaust emissions has been one of the hottest topics in catalysis community since 1970s. Thanks to the development of three-way catalysts, main auto-exhaust pollutants, such as carbon monoxide, nitrogen oxides and unburned hydrocarbons, can be removed simultaneously. Nowadays, diesel engines and lean-engines become more and more popular due to their high fuel-efficiency and low CO2 emissions. Unfortunately, conventional three-way catalysts are not effective at reducing the NOx emissions from these engines due to the excess oxygen in the exhaust stream. Platinum catalysts were found to be highly active for selective NO reduction with hydrocarbons in excess oxygen and has good thermal stability and sulfur resistance. However, discrepancies still exist in the reaction mechanism of NO reduction with hydrocarbons on platinum catalysts. In this thesis, fundamental surface science studies were performed with in situ IR spectroscopic techniques combined with mass spectrometry, aiming
Researchers at the Department of Energys SLAC National Accelerator Laboratory and Stanford University have shown for the first time that a cheap catalyst can split water and generate hydrogen gas for hours on end in the ...
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This work was supported by the Spanish Government (contract MICINN-12-CTQ2011-29272-C04-02). M. León and L. Faba thank the Government of the Principality of Asturias for the Ph.D. fellow-ships (Severo Ochoa Program). ...
Dr. Sievers research interests are in heterogeneous catalysis, reactor design, applied spectroscopy, and characterization and synthesis of solid materials. Combining these interests he seeks to develop processes for the production of fuels and chemicals. His research program combines fundamental and applied research.. In fundamental studies, a suite of analytical and spectroscopic techniques (e.g. IR, NMR, XAS, Raman) is used to gain knowledge on structure-reactivity relationships of heterogeneous catalysts. Moreover, surface reactions are studied on a molecular level so that mechanisms and reaction pathways can be derived. Information obtained from these studies provides the foundation for intelligent catalyst design.. Applied studies focus specific catalytic processes. For these projects, continuously operated flow reactor systems are designed. Different catalysts are tested for reactivity, selectivity and stability and the influence of the operating conditions is investigated. Catalyst ...
A catalyst has been imaged with lattice resolution whilst surrounded by flowing gas, using a specially constructed in-situ cell for an electron microscope. This advancement demonstrates the...
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Traditionally, both processes have worked with vegetable refined. With a RBD refined is enough to obtain a quality product preserving installations and heterogeneous catalysts.. Biofuels based on vegetable oils are in extinction, with the incorporation of advanced raw materials being the reality and the growing trend today.. Advanced raw materials are generally waste materials. The residual materials have much higher refining needs than a first-use vegetable oil. The most abundant materials of this type today are recovered frying oils (UCO), cat1 & cat2 animal fats, tall oil, high acidity products, etc.. These raw materials cannot in any way be used directly in the manufacture of HVO. Since they would be a serious risk to the installation, in addition to poisoning the heterogeneous catalyst used, shortening the life of this expensive supply.. The elements and their repercussions are detailed below:. ...
Stringent new emission regulations pose challenges for the development of diesel catalyst technology. Future 4-way catalyst technology must provide for the simultaneous control of CO, HC, NOx and particulate matter (PM). Since NOx abatement is a reduction process while control of CO, HC and PM emissions requires catalytic oxidation, it is difficult to simultaneously control all four regulated pollutants under the oxidizing conditions found in diesel exhaust. New catalysts for lean NOx control have been developed for systems that operate with injection of reductant (active systems) and without injection of reductant (passive systems).In this study, two experimental catalysts which have potential as lean NOx catalysts, Pt/ZSM-5 and an Ir catalyst, were evaluated under both passive and active conditions. Conditions required for simultaneous PM and NOx abatement are discussed for a lean NOx + a conventional diesel oxidation catalyst (DOC) system. It was found that a Pt/ZSM-5 catalyst with mild HC ...
Oxidation of NO to NO₂ over a Diesel Oxidation Catalyst (DOC) plays an important role in different types of aftertreatment systems, by enhancing NOx storage on adsorber catalysts, improving the NOx reduction efficiency of SCR catalysts, and enabling the passive regeneration of Diesel Particulate Fil
Nanoparticles, specially metallic nanoparticles finely dispersed onto high surface area supports, play an important role in heterogeneous catalysis because the performance of a supported metal catalyst can be related to design, which is most crucial for the development of novel catalytic processes. It requires some understanding of the mechanism of the catalytic reaction, and knowledge of the crucial properties which determine the activity, selectivity and lifetime of the catalyst. Studies of the interrelationship between structural and chemical properties of solid materials and their catalytic properties. These studies are frequently carried out using specially prepared model catalysts which are amenable to analysis with modern surface analytical methods providing structural and chemical information on molecular scale, as TEM attach with X-EDS. Various techniques and concepts of solid state and surface chemistry are applied for modifying and synthesizing catalyst materials with the required structural
TY - JOUR. T1 - Recent developments in olefin polymerizations with transition metal catalysts. AU - Imanishi, Yukio. AU - Naga, Naofumi. PY - 2001/10. Y1 - 2001/10. N2 - Discovery of effective homogeneous transition metal catalysts for olefin polymerization must be one of the most dramatic technologies for polymer synthesis in the 1980s. Especially, development of group 4-metallocene catalysts not only improved the property of manufactured polyolefins but also made us possible to synthesize new type polyolefins. A large number of studies have also been made on structure and property of the resultant polyolefins with the advance of catalyst technology. Over the past few years, trend in catalyst development has moved from modification of group 4-metallocene catalysts to search for new generation catalysts, such as non-metallocene catalysts and late transition-metal catalysts. Some of the new catalysts can proceed specific polymerizations, which are not achieved with existent olefin polymerization ...
In a transition metal catalyst system, the improvement comprising including in the catalyst system an autoacceleration inhibitor, which (i) at about the temperature at which the catalyst system autoaccelerates, decomposes into a poison for the catalyst system; (ii) is present in the catalyst system in an amount sufficient to provide the quantity of poison required to inhibit the autoacceleration of the catalyst system at the autoacceleration temperature; and (iii) is either essentially inert at the normal operating temperature of the catalyst system or will cause substantially less inhibition of the catalyst system at the normal operating temperature than at the autoacceleration temperature.
TY - CONF. T1 - Conversion of methanol to olefins over zeolites with DDR topology: the role of template on catalytic performance. AU - Prokopyeva, I. AU - Gucuyener, C. AU - Gascon, J. AU - Kapteijn, F. PY - 2014. Y1 - 2014. M3 - Abstract. SP - 66. EP - 66. T2 - DPTI Annual Event 2014. Y2 - 6 November 2014 through 7 November 2014. ER - ...
A composite with well-dispersed metal nanoparticles at a ceramic surface was produced by partial reduction of solid solution. It was found that a small amount of dopant, such as Al2O3, Cr2O3, or Sc2O3, accelerated the precipitation of the metal nanoparticles during the reduction. Catalytic performance of the composite for methanol reforming was evaluated. In the Ni-based catalysts, the dopant decreased the CO production by promoting a methanation reaction, while in the Co-based catalysts, the dopant did it by inducing a water-gas shift reaction. Co/MgO with Sc2O3 doping showed the most preferable reforming performance, high H2 production, and CO2 selectivity. ...
Disclosed is a method for producing a biofuel. It comprises hydrolyzing an extract from a seaweed selected from a group consisting of red algae, brown algae, green algae or a combination therof in a presence of a heterogeneous catalyst; and converting the hydrolysate through enzymatic fermentation or chemical reaction into the biofuel. The heterogeneous catalyst can be recycled without a load of wastewater treatment and make the process simpler, thus enjoying a comparative advantage in terms of production cost and by-product treatment expense. In addition, the heterogeneous catalyst can be applied to a fixed bed reactor, allowing the process to be performed in a continuous manner. As a result, a smaller reactor can be employed at higher efficiency and productivity ...
A series of bifunctional organic catalysts containing acid and basic sites with ionic liquid characteristics have been prepared and their catalytic activity and reaction coordinate for aldol and Knoevenagel condensations have been compared. While the only factor controlling catalyst activity for the Knoevenagel condensation was the distance between the acid and base sites, the spatial orientation of the organocatalyst is also key to achieve high activity and selectivity in the Claisen-Schmidt condensation. Mechanistic studies based on theoretical DFT calculations show that the acid-base bifunctional organocatalyst follows a mechanism inspired in natural aldolases for the synthesis of trans-chalcones, being able to produce a large variety of these compounds of industrial interest. The combination of the acid-base pairs within the proper geometry and the ionic liquid nature makes this catalyst active, selective and recyclable.
TY - JOUR. T1 - Cooperative catalysis. T2 - A new development in heterogeneous catalysis. AU - Lee, Jeong Kyu. AU - Kung, Mayfair C.. AU - Kung, Harold H.. PY - 2008/8/1. Y1 - 2008/8/1. N2 - Whereas cooperative effect in catalysis, in which multiple chemical interactions participate cooperatively to achieve significant enhancement in catalytic activity and/or selectivity, is common in enzymatic reactions, it has been sparingly employed in heterogeneous catalytic systems. Here, some recent literature examples of abiotic catalysis, with emphasis on heterogeneous systems, that employ cooperation between acid and base and two metal centers are briefly described to demonstrate the principles involved. Since effective cooperation places strict demand on the positions of the different functional groups, new synthetic methods and strategies are needed to design and construct structures useful for cooperative catalysis. Recent progress in our laboratory in synthesizing new nanocage structures that ...
This thesis describes the use of rational redesign to modify the properties of the enzyme Candida antarctica lipase B. Through carefully selected single-point mutations, we were able to introduce substrate-assisted catalysis and to alter the reaction specificity. Other single-point mutations afforded variants with greatly changed substrate selectivity and enantioselectivity.. Mutation of the catalytic serine changed the hydrolase activity into an aldolase activity. The mutation decreased the activation energy for aldol addition by 4 kJ×mol-1, while the activation energy increased so much for hydrolysis that no hydrolysis activity could be detected. This mutant can catalyze aldol additions that no natural aldolases can catalyze.. Mutation of the threonine in the oxyanion hole proved the great importance of its hydroxyl group in the transition-state stabilization. The lost transition-state stabilization was partly replaced through substrate-assisted catalysis with substrates carrying a hydroxyl ...
A facile strategy for the synthesis of acidic ionic liquid based UiO-67 type MOFs was developed in this study. Bronsted acids (H2SO4, CF3SO3H and hifpOSO(3)H (hexafluoroisopropyl sulfuric acid)) were introduced into UiO-67-bpy (bpy = 2,2-bipyridine-5,5-dicarboxylic acid) frameworks by reacting with bipyridyl nitrogen to introduce the properties of an acidic ionic liquid into the frameworks. The prepared catalysts, denoted as UiO-67-HSO4, UiO-67-CF3SO3 and UiO-67-hifpOSO(3), were characterized by XRD, SEM, FT-IR, EA, TGA and N-2 adsorption-desorption studies. The relatively high surface area was still maintained and acidic active groups were uniformly dispersed in the frameworks. The catalytic performance of UiO-67-HSO4, UiO-67-CF3SO3 and UiO-67-hifpOSO(3) was evaluated by the esterification of acetic acid with isooctyl alcohol. The prepared catalysts showed good catalytic activities in the esterification, of which UiO-67-CF3SO3 gave the maximum isooctyl alcohol conversion of 98.6% under ...
According to Prof Song Jin, who led the research team, the new catalyst is almost as efficient as platinum and appears to show the highest catalytic performance among the non-noble metal catalysts reported so far.. The advance emerges from a long line of research in Jins lab that has focused on the use of iron pyrite and other inexpensive, abundant materials for energy transformation. Jin and his students discovered the new catalyst by replacing iron to make cobalt pyrite, and then added phosphorus.. Whats more, although electricity is the usual energy source for splitting water into hydrogen and oxygen, Jin said that the new catalyst can also work with energy from sunlight. We have demonstrated a proof-of-concept device for using this cobalt catalyst and solar energy to drive hydrogen generation, he claimed. ...
TY - JOUR. T1 - Catalytic conversion of pure glycerol over an un-modified H-ZSM-5 zeolite to bio-based aromatics. AU - He, Songbo. AU - Zuur, Kenny. AU - Santosa, Dian Sukmayanda. AU - Heeres, Andre. AU - Liu, Chuncheng. AU - Pidko, Evgeny. AU - Heeres, Hero Jan. PY - 2021/2. Y1 - 2021/2. N2 - The catalytic conversion of pure glycerol to bio-aromatics (bio-BTX) over an un-modified H-ZSM-5 (SiO2/Al2O3 molar ratio of 23) via an ex-situ catalytic pyrolysis approach in a continuous tandem-micro reactor at a scale of 1 g glycerol h−1 was investigated. A BTX peak carbon yield of 28.1 ± 0.2 % was obtained at a pyrolysis temperature of 400 °C, catalytic upgrading temperature of 500 °C, atmospheric pressure and a WHSV of 1 h−1. About 70 % of the bound oxygen in glycerol was converted to water. The latter was mainly formed in the catalytic upgrading unit (70 %), though conversion of glycerol to other oxygenates with water formation was also observed in the pyrolysis unit. Catalyst deactivation ...
The results of the studies on the influence of the phase transfer catalyst on the epoxidation of (Z,E,E)-1,5,9-cyclododecatriene (CDT) to 1,2-epoxy-5,9-cyclododecadiene (ECDD) in the H2O2/H3PW12O40 system by a method of phase transfer catalysis (PTC) were presented. The following quaternary ammonium salts were used as phase transfer catalysts: methyltributylammonium chloride, (cetyl)pyridinium bromide, methyltrioctylammonium chloride, (cetyl)pyridinium chloride, dimethyl[dioctadecyl(76%)+dihexadecyl(24%)] ammonium chloride, tetrabutylammonium hydrogensulfate, didodecyldimethylammonium bromide and methyltrioctylammonium bromide. Their catalytic activity was evaluated on the basis of the degree of CDT and hydrogen peroxide conversion and the selectivities of transformation to ECDD in relation to consumed CDT and hydrogen peroxide. The most effective PT catalysts were selected based on the obtained results. Among the onium salts under study, the epoxidation of CDT with hydrogen peroxide proceeds ...
A series of C2 symmetrical 1:2 Ni:L complexes derived from α-amino amides were studied for the enantioselective addition of dialkylzinc reagents to aldehydes. Different structural elements on the ligands seem to play an important role in determining the observed enantioselectivity. Through optimization of structure and reaction conditions, the best ligand provided secondary alcohols in excellent yields (up to 98%) and enantioselectivity of up to 99% ee for (R)-enantiomer. A transition state model has been proposed to explain the observed enantioselectivities based on computational calculations at the DFT level. Very interestingly, calculations suggest a coordination model of the aldehyde to the metal complex through association of a lone pair of the carbonyl oxygen to the hydrogen atom of an amino group ...
ABSTRACT. Electrophilic substitution reaction of indole with various aldehydes and cyclohexanone were carried out in the presence of electron-transfer (K5CoW12O40.3H2O) and green Lewis acid ([(n-C4H9)4N]3PMo2W9(Sn4+.H2O)O39) catalysts. These catalysts were characterized by N2-adsorption measurements, FT-IR, UV-Vis, 31P NMR, TGA, cyclic voltammetry and elemental analysis. Mechanisms for their catalytic activity are proposed. Both of these catalysts can be recovered and reused.. Keywords: Dodecatungstocobaltate, Sn (IV)-substituted polyoxometalate, bis(indolyl)methanes, electrophilic substitution, solvent-free conditions. ...
TY - JOUR. T1 - Chiral Co(II) metal-organic framework in the heterogeneous catalytic oxidation of alkenes under aerobic and anaerobic conditions. AU - Tuci, Giulia. AU - Giambastiani, Giuliano. AU - Kwon, Stephanie. AU - Stair, Peter C.. AU - Snurr, Randall Q.. AU - Rossin, Andrea. PY - 2014/3/7. Y1 - 2014/3/7. N2 - The chiral Co(II) MOF [Co(l-RR)(H2O)·H2O] ∞ [1; l-RR = (R,R)-thiazolidine-2,4-dicarboxylate] has been exploited in the catalytic oxidation of different alkenes (cyclohexene, (Z)-cyclooctene, 1-octene) using either tert-butyl hydroperoxide ( tBuOOH) or molecular oxygen (O2) as oxidants. Different chemoselectivities are observed, both substrate- and oxidant-dependent. A moderate enantioselectivity is also obtained in the case of prochiral precursors, revealing the chiral induction ability of the optically pure metal environment. The interaction of O2 with the exposed metal sites in 1 (after material preactivation and consequent removal of the coordinated aquo ligand) has been ...
The pH-responsive core-shell microspheres of poly(styrene-co-methylacrylic acid) (PS-co-PMAA) containing a polystyrene (PS) core and a poly(methylacrylic acid) (PMAA) shell are synthesized by one-stage soap-free copolymerization and the catalyst system palladium-iminodiacetic acid (IDA-Pd) is immobilized on the outer shell-layer of the core-shell microspheres to form the quasi-homogeneous and easily accessible catalyst PS-co-PMAA-IDA-Pd. This quasi-homogeneous PS-co-PMAA-IDA-Pd catalyst is highly dispersed in the reaction medium just like a homogeneous one and can be separated like a heterogeneous catalyst by adjusting the pH of the reaction medium. Suzuki reactions employing the quasi-homogeneous PS-co-PMAA-IDA-Pd catalyst are efficiently performed in water as the sole solvent under mild conditions such as room temperature. The PS-co-PMAA-IDA-Pd catalyst is also used in Heck reactions of a wide range of aryl halides with styrene and proves to be efficient in aqueous solution. The ...
Angewandte Chemie Kinetic Resolution DOI: 10.1002/anie.200503291 Self-Assembled Nanoreactors as Highly Active Catalysts in the Hydrolytic Kinetic Resolution (HKR) of Epoxides in Water Benjamin M. Rossbach, Kerstin Leopold, and Ralf Weberskirch* The synthesis of optically active organic compounds is a central research topic in chemistry because of their widespread use in the pharmaceutical industry as well as in the production of fine chemicals.[1] Catalytic enantioselective organic reactions can be achieved by metal catalysis,[2] by biocatalysis,[3] and more recently also by organocatalysis.[4] Despite the increased industrial demand for enantiomerically pure compounds, to date only a few catalytic asymmetric processes have found commercial application.[5] One rare exception is the hydrolytic kinetic resolution (HKR) of terminal epoxides, which allows the production of enantiopure epoxides and diols from the racemic stating materials.[6] These chiral compounds play a key role as intermediates in ...
Abstract: With the development of synthetic chemistry, more and more efficient catalysts are exploited to activate inert chemical bonds and organic molecules. In the synthetic chemistry, catalysts play an important role, scientists are paying more and more attention to the design and synthesis of catalysts. The majority of catalysts in homogeneous catalytic systems belong to mononuclear active species. In addition to the development of catalysis science, major research is also being conducted on the development of the coordination environment for metal centers to increase their catalytic ability and thereby create enhanced catalytic processes. The catalytic activity of dinuclear catalysts varies from those of mononuclear catalysts. Due to the synergistic effect between the two metal centers, the catalytic activity of dinuclear catalytic systems exhibits particular performance characteristics. The first row of elements in group Ⅷ of the periodic table, Fe, Co, and Ni, are also known as the ...
TY - JOUR. T1 - The comparative effect of particle size and support acidity on hydrogenation of aromatic ketones. AU - Kim, Kyung Duk. AU - Wang, Zichun. AU - Tao, Yongwen. AU - Ling, Huajuan. AU - Yuan, Yuan. AU - Zhou, Cuifeng. AU - Liu, Zongwen. AU - Gaborieau, Marianne. AU - Huang, Jun. AU - Yu, Aibing. PY - 2019/10/7. Y1 - 2019/10/7. N2 - A comparative study was reported for both the effects of shape-confined cubic Pd particle size (8, 13, and 21 nm) and surface property of most commonly used supports (SiO2, Al2O3, and silica-alumina) on catalytic performance in the chemoselective hydrogenation of three model bio-oil chemicals (benzaldehyde, acetophenone, and butyrophenone). The results showed that the size of Pd particles could be more associated with the hydrogenation reaction than acidities of the supports. Smaller size of Pd particles, regardless of the type of the support, provided the higher catalytic performance. XPS data showed that the electronic properties of Pd particles were ...
EDX analysis showed that the residual Mn composition of the 0 °C dealloyed sample (cat-4) is &4 at. 2 Results and Discussion 21 Fig. 7 (cat-10) Fig. 01 M MnSO4; B: HCl solution b 1 H NMR yield determined using CH2Br2 as an internal standard c Isolated yield remains approximately constant at &2 at. % for cat-5 to cat-7 (Fig. 4). Dealloying of the 200 lm thickness Cu30Mn70 alloy in HCl solution resulted in large ligaments with an average diameter of 60-70 nm (Fig. 3a, b, cat-8 and cat-9); in the reduced concentration, a non-nanopore structure was observed (Fig. 1314. 0793. 0845. 1158. 0900. 1266. 0885. 1764. 2233. 1451. 4 Experimental Section 49 50 2 Nanoporous Copper Metal Catalyst in Click Chemistry References 51 References 1. Zielasek V, Jürgens B, Schulz C et al (2006) Gold catalysts: nanoporous gold foams. Angew Chem Int Ed 45:8241-8244 2. Xu C, Su J, Xu X et al (2007) Low temperature CO oxidation over unsupported nanoporous gold. J Am Chem Soc 129:42-43 3. Xu C, Xu X, Su J et al (2007) ...
TY - JOUR. T1 - Hydrogenation of Lactic Acid to 1,2-Propanediol over Ru-Based Catalysts. AU - Liu, Kaituo. AU - Huang, Xiaoming. AU - Pidko, Evgeny A.. AU - Hensen, Emiel J.M.. PY - 2018. Y1 - 2018. N2 - The catalytic hydrogenation of lactic acid to 1,2-propanediol with supported Ru catalysts in water was investigated. The influence of catalyst support (activated carbon, γ-Al2O3, SiO2, TiO2, and CeO2) and promoters (Pd, Au, Mo, Re, Sn) on the catalytic performance was evaluated. Catalytic tests revealed that TiO2 yields the best Ru catalysts. With a monometallic Ru/TiO2 catalyst, a 1,2-propanediol yield of 70 % at 79 % lactic acid conversion was achieved at 130 °C after 20 h reaction. Minor byproducts of the hydrogenation reaction were propionic acid, ethanol, 1-propanol, and 2-propanol. For the bimetallic catalysts, the addition of Pd and Au slightly enhanced the performance of Ru/TiO2, whereas the addition of common hydrogenation promoters such as Re, Mo, and Sn impaired the activity.. AB - ...
Read Palladium-catalyzed synthesis of diarylbenzenes from coupling reactions between equal amount of diiodoarenes and arylboronic acids, Russian Journal of Applied Chemistry on DeepDyve, the largest online rental service for scholarly research with thousands of academic publications available at your fingertips.
Read Direct catalytic oxidation of cyclohexene to 1, 2-cyclohexanediol by aqueous hydrogen peroxide under solvent-free condition, Research on Chemical Intermediates on DeepDyve, the largest online rental service for scholarly research with thousands of academic publications available at your fingertips.
The catalytic performances of different commercial cobalt oxides(CoxOy, i.e., Co2O3, Co3O4, and CoO) for peroxymonosulfate(PMS) activation in dye degradation were compared in this study. The CoO/PMS system exhibited the highest catalytic oxidation performances with more than 96% methylene blue(MB) removal at 90 min. The concentration of dissolved cobalt ions from CoO was 1.474 mg/L at neutral pH and 5.231 mg/L at acidic pH at 90 min which accounted for the high MB removal and CoO activated PMS homogeneously compared to the associated CoSO4/PMS. Co3O4 and Co2O3 exhibited similar catalytic performances and characteristics. The MB removal in Co3O4/PMS and Co2O3/PMS system were more than 88% at neutral pH and over 64% at acidic pH, respectively, in 90 min. The concentration of dissolved cobalt ions from Co3O4 and Co2O3 was less than 0.018 mg/L at neutral pH and 0.036 mg/L at acidic pH at 90 min. The MB removal achieved by Co3O4/PMS and Co2O3/PMS were approximately three times higher than that ...
We explore RNA catalysis to learn about the catalytic potential of RNA and to decipher what is fundamental to all biological catalysts through comparison with protein enzyme catalysis. These studies also define the unique properties of RNA and proteins lead to catalytic and behavioral distinctions. The fundamental properties and behaviors of RNA molecules that we uncover teach us about how the potential function of RNA early in evolution and about the function of RNA molecules in modern-day biology. This knowledge may also be applied as RNA is co-opted for medical, technological and industrial applications.. Energy from binding interactions can be used to facilitate reactions of bond substrates, a fundamental precept of enzymology posited by Jencks for protein enzymes and demonstrated in our studies of RNA enzymes.. We currently focus on the group I ribozyme, the most well-studied catalytic RNA in both structure and function. We harness previous studies, including multiple crystal structures, a ...
We explore RNA catalysis to learn about the catalytic potential of RNA and to decipher what is fundamental to all biological catalysts through comparison with protein enzyme catalysis. These studies also define the unique properties of RNA and proteins lead to catalytic and behavioral distinctions. The fundamental properties and behaviors of RNA molecules that we uncover teach us about how the potential function of RNA early in evolution and about the function of RNA molecules in modern-day biology. This knowledge may also be applied as RNA is co-opted for medical, technological and industrial applications.. Energy from binding interactions can be used to facilitate reactions of bond substrates, a fundamental precept of enzymology posited by Jencks for protein enzymes and demonstrated in our studies of RNA enzymes.. We currently focus on the group I ribozyme, the most well-studied catalytic RNA in both structure and function. We harness previous studies, including multiple crystal structures, a ...
Ju, Y.-D., Xu, L.-W., Li, L., Lai, G.-Q., Qiu, H.-Y., Jiang, J.-X., Lu, Y. (2009-01-07). Erratum to Noyoris Ts-DPEN ligand: an efficient bifunctional primary amine-based organocatalyst in enantio- and diastereoselective Michael addition of 1,3-dicarbonyl indane compounds to nitroolefins [Tetrahedron Lett. 49 (2008) 6773] (DOI:10.1016/j.tetlet.2008.09.025). Tetrahedron Letters 50 (1) : 135-. [email protected] Repository. https://doi.org/10.1016/j.tetlet.2008.10. ...
View Cell Theory from BIOLOGY MCB2010 at Broward College. • Genetic material -> catalyst (RNA catalyst not regulated. Protein catalyst can be regulated.) • Metabolism (get energy -> grow
Again, if a pathway, even a prebiotic one, is making nonracemic chiral amino acids, it is catalyzed by a nonracemic chiral catalyst.* Setting aside the issue of how active and selective such prebiotic catalysts could be, a nonracemic chiral catalyst can arise either by chance due to low total number (if you only have 1 molecule, it can either be L- or D-, not racemic) or by specific synthesis by some other pathway. In the former case, that randomly synthesized catalyst will be destroyed or diluted away rather quickly - it must be amplified to remain effective, which means that its activity must feed back into its production, or in this case, amino acid synthesis must increase specific production of the catalyst, which is not all that plausible for reasons Ive discussed above. In the latter case, the specific synthesis of a chiral catalyst must again use another chiral catalyst - the origin of homochirality has just been displaced to an earlier event ...
Hydrogen could be an important source of clean energy, and the cleanest way to produce hydrogen gas is to split water into hydrogen and oxygen. But the catalyst currently used to facilitate this water-splitting reaction is platinum. And thats a problem.. When an electric current is run through water, it can split some of the water molecules. A catalyst lowers the amount of energy needed to split those molecules, and platinum is really, really good at this.. But platinum is also really, really expensive - much too expensive for widespread use in hydrogen production.. So, researchers have long viewed molybdenum sulfide (MoS2) as a promising, much cheaper alternative to platinum. The drawback is that MoS2s catalytic performance is far worse than platinums. To get around that problem, researchers have been trying to find ways to improve MoS2s catalytic performance. And now they may be on to something.. The biggest stumbling block to improving MoS2s performance has been a lack of understanding ...
A series of Ni/SBA-16 and NiMo/S16 catalysts were prepared by the impregnation methods and their performance on synthetic natural gas (SNG) production were systematically investigated in a continuous flow fixed-bed reactor. Coexistence of MoO3 in Ni-catalysts resulted in forming uniformly sized Ni particles and better heat-resistant performance because of the large surface area of SBA-16 supports and the strong interaction between Ni and SBA-16, while high MoO3(,3%) content will reduce the activity because of the partial coverage of nickel. Adopting the Mo-Ni impregnation sequence can significantly improve the activity of catalyst due to the moderate interaction between nickel and support and the electron transfer from MoO3 to Ni species. Ni-Mo/S16(1%) achieves the best activity with 100% CO conversion and 97% CH4 selectivity and yield at 350°C, 0.1MPa, and15000mL/g/h. The activity of Ni-Mo/S16(1%) remain stable after calcination in reactant gases at 700°C and during a 100 h reaction period. ...
Jointly promoting catalysis research. Researchers from Germany and Austria met for the first interdisciplinary conference of the CataLysis CRC-network Catalysis initiates central processes of our entire life on earth - from enzyme catalysis in metabolic processes in all organisms to natural photosynthesis and the production of synthetics and environmentally friendly energy sources. Scientists in four Collaborative Research Centres (CRCs) of the German Research Foundation (Deutsche Forschungsgemeinschaft, DFG) are currently investigating how these fundamental and at the same time diverse processes of chemical catalysis work exactly and how their principles can be used for sustainable value creation.. In order to set new research impulses and create synergies in the field, the four DFG-funded Collaborative Research Centres have now organised the first joint CataLysis conference. Around 170 researchers from Germany and Austria presented their latest research findings in a joint online conference ...
Y2Ce2O7 nano powders were synthesized via sol-gel reactions at 900 (S1), 1000 (S2) and 1100 (S3) ˚C for 4 h using yttrium acetate (C6H9O6Y.xH2O), ammonium cerium nitrate ((NH4)2Ce(NO3)6) and stearic acid (C18H36O2) as raw materials at stoichiometric 1:1 Y:Ce molar ratio. The synthesized materials were characterized by powder X-ray diffraction (PXRD) technique and Fourier transforms infrared (FTIR) spectroscopy. Structural analysis was performed by the FullProf program employing profile matching with constant scale factors. The results showed that the patterns had a main cubic Y2Ce2O7 structure with space group of Fm3m. The data showed that the lattice parameters were increased with increasing the reaction temperature. FESEM images showed that the synthesized Y2Ce2O7 particles had mono-shaped sphere morphologies. However, with increasing the reaction temperature to 1100 ˚C, the particle size scale was in micrometre range. Ultraviolet-visible spectra analysis showed that the nanostructured Y2Ce2O7
June 19, 1945- s. B. BECKER CATALYTIC CONVERSION OF RESIDUAL HYDROCARBON OILS Filed Sept. 30, 1941 Pstented June 19, 194s cArALYrIo CONVERSION oF RESIDUALv mnocARoN oms Sam B. Becker, Chicago, Ill., assignor to Standard Oil Company, Chicago, Ill., a corporation of Indiana Application September30, 1941, Serial No. 412,942 7 Claims. v (Cl. 196-52) Ihis invention relates to the conversion oi hydrocarbon oils and particularly heavy oils, such as petroleum residuums and heavy gas oils, into gasoline. The invention also relates to an ap- .paratus for carrying out the desired conversion. More specifically the invention relates to improvements in the process of converting unvaporizable residual oils by the action of subdivided, solid catalysts at high temperature. - One object of the invention is to increase the life of the catalyst in such a conversion process. Another object of the invention is to treat the heavy oil preliminarily immediately before contacting with the catalyst, thereby removing ...
Using cyclopropanation reactions catalyzed by dendrimer-encapsulated gold and other metal nanoclusters, including platinum, palladium and rhodium, we have demonstrated that changing the dendrimer properties allows catalytic reactivity in a heterogeneous catalyst to be tuned in a similar fashion to ligand modification in a homogeneous catalyst, says world renowned catalysis chemist Gabor Somorjai, one of the leaders of this research. Furthermore, we have shown that these heterogeneous catalysts employed in a fixed-bed flow reactor allow fine control over the residence time of the reactants and thus enable control over product distribution in a way that is not easily available for homogeneous catalysts ...
Active and stable metal-free heterogeneous catalysts for CO2 fixation are required to reduce the current high level of carbon dioxide in the atmosphere, which is driving climate change. In this work, we show that defects in nanosilica (E′ centers, oxygen vacancies, and nonbridging oxygen hole centers) convert CO2 to methane with excellent productivity and selectivity. Neither metal nor complex organic ligands were required, and the defect alone acted as catalytic sites for carbon dioxide activation and hydrogen dissociation and their cooperative action converted CO2 to methane. Unlike metal catalysts, which become deactivated with time, the defect-containing nanosilica showed significantly better stability. Notably, the catalyst can be regenerated by simple heating in the air without the need for hydrogen gas. Surprisingly, the catalytic activity for methane production increased significantly after every regeneration cycle, reaching more than double the methane production rate after eight ...
A system for controlled heat generation in exhaust pipeline is studied, consisting of fuel injector and oxidation catalyst (plus connecting pipes). A 3D-CFD software (StarCD) coupled with a tailored 1D model of catalytic monolith channel (XMR) are employed for simulations of realistic, fully 3D system geometry. Exhaust gas flow, fuel injection, and distribution at the catalyst inlet is solved by 3D-CFD, while the processes inside individual representative channels are simulated by the effective 1D model. The 3D-CFD software calls iteratively the 1D channel model with proper boundary conditions and solves 3D temperature profile over the monolith, utilizing local enthalpy fluxes (including gas-solid heat transfer and reaction enthalpy) calculated by the 1D channel model.Seven representative hydrocarbons are used for characterisation of Diesel fuel composition with respect to catalytic oxidation kinetics. Each representative component possesses its own light-off behaviour (described by a global ...
The objective of this project is to develop novel non-precious metal electrocatalysts for oxygen reduction reaction (ORR), and demonstrate the potential of the catalysts to perform at least as good as conventional Pt catalysts currently in use in polymer electrolyte membrane fuel cell (PEMFC) with a cost at least 50 % less than a target of 0.2 g (Pt loading)/peak kW and with durability | 2,000 h operation with less than 10 % power degradation. A novel nitrogen-modified carbon-based catalyst was obtained by modifying carbon black with nitrogen-containing organic precursor in the absence of transition metal precursor. The catalyst shows the onset potential of approximately 0.76 V (NHE) for ORR and the amount of H2O2 of approximately 3% at 0.5 V (NHE). Furthermore, a carbon composite catalyst was achieved through the high-temperature pyrolysis of the precursors of transition metal (Co and Fe) and nitrogen supported on the nitrogen-modified carbon-based catalyst, followed by chemical post-treatment. This
In the last decade, chemists have increasingly focused on the development of new and more efficient methods for the catalytic conversion of carbon dioxide into value-added organic molecules. Homogeneous catalysis has proved to be a key technology for the conversion of carbon dioxide under particularly mild reaction conditions that meet the increasing societal demands for sustainable chemical processing. In this account article, we focus on the most effective routes developed for ring expansion-addition reaction of carbon dioxide to epoxides mediated by either metal catalysts or organocatalyst systems to give cyclic organic carbonates.. ...
Hydr-) oxidic PdOxHy colloids were prepared by H2PdCl4 hydrolysis in presence of poly(vinylpyrrolidone) under pH control. After immobilization, the resulting catalysts show a high chemo- and stereo selectivity in the hydrogenation of C-C triple bonds. Systematic investigations of the preparation parameters indicate that the hydrolysis pH, the PVP amount and chainlength as well as the colloid aging time are of major importance for catalytic performance.. ...
Abstract (EN): A large number of studies can be found in the literature regarding the production of new catalysts for methanol steam reforming. This work summarizes the latest developments on catalysts for this application and is divided in two main groups: copper-based and group 8-10 metal-based catalysts. In each section, the strategies proposed by several authors to enhance the performance of the catalysts are described. An overall comparison between the two groups shows that copper-based catalysts are the most active ones, while the 8-10 group catalysts present better results in terms of thermal stability and long-term stability. Very promising results were reported for both groups, enhancing the value of methanol as a hydrogen carrier for fuel cell applications ...
TY - JOUR. T1 - Review of Enantioselective Homogeneous Supported Catalysis edited by Radovan Šebesta.. AU - Notestein, Justin M.. PY - 2012. Y1 - 2012. N2 - Enantioselective Homogeneous Supported Catalysis: RSC (Green Chemistry Series) edited by Radovan Sebesta, UK: Royal Society of Chemistry, 2011, 300pp. ISBN: 9781849731768.. AB - Enantioselective Homogeneous Supported Catalysis: RSC (Green Chemistry Series) edited by Radovan Sebesta, UK: Royal Society of Chemistry, 2011, 300pp. ISBN: 9781849731768.. U2 - 10.1007/s10562-012-0851-z. DO - 10.1007/s10562-012-0851-z. M3 - Book/Film/Article review. VL - 142. SP - 1150. EP - 1151. JO - Catalysis Letters. JF - Catalysis Letters. SN - 1011-372X. ER - ...
The side-chain of the nucleophilic residue performs covalent catalysis on the substrate. The lone pair of electrons present on the oxygen or sulfur attacks the electropositive carbonyl carbon.[3] The 20 naturally occurring biological amino acids do not contain any sufficiently nucleophilic functional groups for many difficult catalytic reactions. Embedding the nucleophile in a triad increases its reactivity for efficient catalysis. The most commonly used nucleophiles are the hydroxyl (OH) of serine and the thiol/thiolate ion (SH/S−) of cysteine.[2] Alternatively, threonine proteases use the secondary hydroxyl of threonine, however due to steric hindrance of the side chains extra methyl group such proteases use their N-terminal amide as the base, rather than a separate amino acid.[1][24]. Use of oxygen or sulfur as the nucleophilic atom causes minor differences in catalysis. Compared to oxygen, sulfurs extra d orbital makes it larger (by 0.4 Å)[25] and softer, allows it to form longer bonds ...
Development of sustainable catalytic systems for fundamentally important synthetic transformations and energy storage applications is an intellectually stimulating challenge. Catalytic dehydrogenation of feedstock chemicals, such as alcohols and amines to value-added products with the concomitant generation of dihydrogen is of much interest in the context of hydrogen economy and is an effective alternative to the classical oxidation reactions. Despite a number of homogeneous catalysts being identified for the acceptorless dehydrogenation, the use of high price and limited availability of precious metals and poor recovery of the catalyst have spurred interest in catalysis with more earth-abundant alternatives, especially iron. However, no report has described a reusable iron-based heterogeneous catalyst for oxidant-free and acceptorless dehydrogenation reactions. Here we replace expensive noble metal catalysts with an inexpensive, benign, and sustainable nanoscale iron catalyst for the efficient