Heterogeneous metal catalysts rather than homogeneous ones are recommended for industrial applications after considering their performance in activity, separation, and recycling [1]. The recycling of metal catalysts is important from economic and environmental points of view. When supported and bulk metal catalysts are used in liquid-phase organic reactions, there is a possibility that active metal species are leaching away into the liquid phases [2,3]. The metal leaching would make it difficult for the catalysts to maintain their desired initial performance for repeated batch reactions and during continuous ones. The metal leaching would also cause some undesired contamination of products by the metal species dissolved in the reaction mixture, and the separation of the metal contaminants would be required to purify the products. Therefore, various novel methods have been proposed so far to immobilize/stabilize the active metal species and to separate/collect/reuse the dissolved metal species [4]. In

The C-H activation reaction is a key reaction for the functionalization of organic compounds, which can convert raw materials or low-valued materials into feedstock and practical chemicals.1 Among various strategies developed to achieve this challenging goal, C-H activation catalyzed by homogeneous metal complexes has become a hot research topic in modern synthetic chemistry. Enormous progress has been made on the design and synthesis of efficient homogeneous catalysts such as Fe,2 Ir,3 Rh,4 Pd,5 and Ag.6 Considering the future practical applications and cost reductions,7 immobilization of homogeneous metal complexes on solid supports is important for catalyst recovery and reuse.8-17 Moreover, heterogenization has the ability to improve the stability of the catalysts as it suppresses deactivation caused by intermolecular pathways. Molecular heterogeneous catalysts also provide the facility to understand the nature of the active species, which can help to carry out mechanistic studies and ...

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 ...

The novel N,N,O-tridentate phenanthroline ligand (BinThro) bearing an axially chiral binaphthyl backbone prepared from BINOL was found to be an effective chiral catalyst for enantioselective addition of diethylzinc to aromatic aldehydes with high enantioselectivity (up to 95% ee).

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 ...

This work deals with the development of a green and versatile synthesis of stable mono- and bi-metallic colloids by means of microwave heating and exploiting ecofriendly reagents: water as the solvent, glucose as a mild and non-toxic reducer and polyvinylpirrolidone (PVP) as the chelating agent. Particle size-control, total reaction yield and long-term stability of colloids were achieved with this method of preparation. All of the materials were tested as effective catalysts in the reduction of p-nitrophenol in the presence of NaBH4 as the probe reaction. A synergistic positive effect of the bimetallic phase was assessed for Au/Cu and Pd/Au alloy nanoparticles, the latter showing the highest catalytic performance. Moreover, monoand bi-metallic colloids were used to prepare TiO2- and CeO2-supported catalysts for the liquid phase oxidation of 5-hydroxymethylfufural (HMF) to 2,5-furandicarboxylic acid (FDCA). The use of Au/Cu and Au/Pd bimetallic catalysts led to an increase in FDCA selectivity. Finally,

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-. ScholarBank@NUS 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

Hydrogenation reactions are of great importance in scientific research and in industry productions. Herein, we designed a novel system to realize photocatalytic transfer hydrogenation by using solar light as the energy input and methanol as the hydrogen source. In this reaction, titania loaded with Pd-Pt bimetallic alloy nanocrystals as a cocatalyst exhibited photocatalytic performance that was remarkably superior to that exhibited by titania with Pd or Pt alone as the cocatalyst. This work has shed light on the rational design of multifunctional catalysts through selecting appropriate bimetallic alloys as efficient cocatalysts. Light up, as if you have a catalyst: Photocatalytic transfer hydrogenation is efficiently realized on Pd-Pt/TiO2 under mild reaction conditions with the use of light irradiation as the energy input and methanol as the hydrogen source at ambient temperature. The Pd-Pt alloy cocatalyst exhibits enhanced catalytic performance relative to that of the monometallic Pd or Pt ...

3-Tributylstannylsulfolene (1) undergoes palladium-catalyzed cross-coupling reactions with aryl and vinyl halides, cyclohex-1-enyl triflates and acyl chlorides in moderate to excellent yield, thereby allowing rapid entry to a diverse range of 3-substituted sulfolenes, species known to be reliable precursors to 3-substituted 1,3-dienes.. ...

Angewandte Chemie Amine Synthesis Asymmetric Synthesis of Diarylmethyl Amines by Rhodium-Catalyzed Asymmetric Addition of Aryl Titanium Reagents to Imines** Tamio Hayashi,* Masahiro Kawai, and Norihito Tokunaga Asymmetric synthesis of diarylmethyl amines has attracted growing attention owing to their importance in biological activity.[1] Among several methods for performing the asymmetric synthesis,[2, 3] catalytic asymmetric addition of aryl metal reagents to imine derivatives seems to be most promising, provided that both high enantioselectivity and high catalytic activity are realized.[4] After our publication on the rhodium-catalyzed asymmetric addition of aryl stannanes to N-sulfonylimines,[5] two reports appeared on catalytic asymmetric arylation: 1) Br%se, Bolm, and co-workers described the addition of a phenylzinc reagent to masked Nformylimines in the presence of a chiral ketimine catalyst,[6] and 2) Tomioka illustrated the rhodium-catalyzed addition of aryl boroxines to N-tosylimines ...

This review with 206 references covers the literature published until March 2004 on the development and applications of new efficient catalyst systems for the Suzuki palladium-catalysed cross-coupling reaction of organoboron compounds with organic electrophiles. Where possible, the relative advantages of the new catalyst systems in this synthetically very important carbon-carbon bond forming reaction have been compared. 1 Introduction 2 Palladacycle Complexes as Catalyst Precursors 3 Catalyst Systems Composed of Pd(0) or Pd(II) Derivatives and Electron-Rich and/or Bulky Phosphine Ligands 4 Catalyst Systems Composed of Pd(0) or Pd(II) Derivatives and N-Heterocyclic Carbene Ligands 5 Water-Soluble Catalyst Precursors 6 Ligandless Catalyst Precursors 7 Other Novel Pd Catalyst Precursors 8 Conclusions.. ...

In three steps to ruthenium-based heterogeneous catalysts: The central element of this novel and simple route is the immobilization of Ru0 nanoparticles on montmorillonite (see picture; the arrows indicate a Ru nanoparticle intercalated in the interlaminar space of montmorillonite) with the help of an ionic liquid. The resulting catalyst is highly efficient for the hydrogenation of benzene. ...

Descrizione libro Royal Society Of Chemistry, United Kingdom, 2014. Hardback. Condizione libro: New. Language: English . Brand New Book. Catalysis is a central topic in chemical transformation and energy conversion. Thanks to the spectacular achievements of colloidal chemistry and the synthesis of nanomaterials over the last two decades, there have also been significant advances in nanoparticle catalysis. Catalysis on different metal nanostructures with well-defined structures and composition has been extensively studied. Metal nanocrystals synthesized with colloidal chemistry exhibit different catalytic performances in contrast to metal nanoparticles prepared with impregnation or deposition precipitation. Additionally, theoretical approaches in predicting catalysis performance and understanding catalytic mechanism on these metal nanocatalysts have made significant progress. Metal Nanoparticles for Catalysis is a comprehensive text on catalysis on Nanoparticles, looking at both their synthesis ...

TY - JOUR. T1 - Catalytic Enantioselective Addition of Terminal Alkynes to Aldehydes: Preparation of (S)-(-)-1,3-Diphenyl-2-Propyn-1-ol and (S)-(-)-4-Methyl-1-Phenyl-2-Pentyn-1,4-Diol. AU - Takita, Ryo. AU - Harada, Shinji. AU - Ohshima, Takashi. AU - Matsunaga, Shigeki. AU - Shibasaki, Masakatsu. PY - 2008. Y1 - 2008. U2 - 10.1002/0471264229.os085.13. DO - 10.1002/0471264229.os085.13. M3 - Article. VL - 85. JO - Organic Syntheses. JF - Organic Syntheses. SN - 0078-6209. ER - ...

The olefin metathesis reaction has become a widely used method for the construction of new carbon-carbon double bonds. The development of well-defined, ruthenium-based catalysts with high air- and moisture-stability and functional group tolerance has allowed synthetic chemists to exploit this reaction in many areas. The main goal of this thesis was to better understand the impact of changes in catalyst and monomer structure on the olefin metathesis reaction. The introduction of chelating alkylidene ligands to olefin metathesis catalysts has resulted in systems with high activity and stability that, for the most part, are active at or below room temperature. However, for some applications, catalysts that react only at higher temperatures are desirable. Chapter 2 describes the synthesis of latent olefin metathesis catalysts with chelating alkylidenes with a range of donor ligands: including phosphines, pyridines, imines, amines, and thioethers. The nature of the donor ligand was found to have a ...

Catalysis is a technologically important field which determines the quality of life in future. Catalyst research in pharmaceutical industry,fine chemical synthesis and emission control demands supported catalysts in bulk quantities.In the present work it was observed that clay supported catalysts mentioned in various chapters could also be used for the synthesis of similar molecules. The K10Ti catalyst can be used for the synthesis similar substituted imidazole derivatives under solvent free conditions and synthetically important Mannich bases of substrates containing various substitutes.Al-pillared saponite can be used for acetalation of other polyhydroxy compounds like glycerol,mannitol etc.Cu-Pd KSF catalyst has found application in C-C bond forming reactions which can be applied to other reactions and similar methods can be adopted for the synthesis of other catalyst by changing the transition metals. Montmorillonite K10 catalysed synthesis of triarylpyridines can be extended to the ...

Abstract. The use of the Xantphos ligand in a mild palladium-catalyzed Kumada-Corriu reaction of secondary benzylic bromides with aryl and alkenyl Grignard reagents minimizes the undesired β-elimination pathway. The corresponding cross-coupling products can be isolated in good yields with inversion of the configuration.. ...

0058]The seventh step of the aforementioned production method consists of deprotecting 2-propenyl groups of the compound of formula (8) to produce the compound of formula (II). Removal of the 2-propenyl groups can be carried out by a method described in the references, such as hydrolysis using an acid or base, or a deallylation reaction using a metal catalyst such as a palladium catalyst. In particular, a deallylation reaction using a metal catalyst such as a palladium catalyst is preferable, while the use of a zero valence palladium catalyst, such as tetrakis(triphenylphosphine) palladium, is particularly preferable. Although a commercially available reagent can also be used for the zero valence palladium catalyst such as tetrakis(triphenylphosphine) palladium, a method in which the catalyst is generated within the reaction system is preferable in consideration of reagent stability, and for example, a combination of a divalent palladium reagent and a ligand such as triphenylphosphine is ...

According to the Xinhua news, carbon dioxide that produced by the burning of fossil fuels is considered as the culprit of global warming. However, German researchers found that with the help of a metal catalyst, carbon dioxide and hydrogen can be generate methanol with industrial use under a mild condition. At present, the industrial production of methanol from hydrogen and carbon monoxide under high temperature and pressure and heterogeneous catalysis.. The researchers of Germany RWTH Aachen University reported on a German journal Applied Chemistry, in their experiments, they found that due to a homogeneous catalytic effect of a metal catalyst ruthenium (CAS No. is 7440-18-8) - phosphine complexes, carbon dioxide and hydrogen generated methanol in the pressurized solution. A carbon dioxide molecule and three hydrogen molecules can generate methanol (CH4O, CAS number is 67-56-1 )and water after their reaction. The researchers said that using this method that converting carbon dioxide and ...

A catalyst is a substance added to change the rate of a chemical reaction, generally to make it faster. Many different catalysts can be used for the Fischer-Tropsch process. The most common catalysts are the metals cobalt, iron, and ruthenium. These metals are all transition metals. The metal nickel can also be used, but generally with unwanted results. A nickel catalyst in the reaction usually produces a lot of methane, which is undesirable. Cobalt seems to be the most active catalyst (it has the greatest and fastest effect on the process). When the input is a natural gas, cobalt catalysts are very good for the Fischer-Tropsch process. Iron catalysts are better when the input gas is of lower quality (less pure) such as coal or biomass.[2] Most metals used for this process (like cobalt, nickel, and ruthenium) remain in their metal form when added to the process. However, iron catalysts behave very differently. Often, iron catalysts change form and chemical phase, like converting into various ...

The rate of aminolysis of benzylpenicillin and cephaloridine by hydroxylamine, unlike other amines, shows only a first order dependence on amine concentration. The rate enhancement compared with that predicted from a Bronsted plot for other primary amines with benzylpenicillin is greater than 106. This is much more than an -effect and is compatible with rate-limiting formation of the tetrahedral intermediate due to a rapid intramolecular general acid catalysed breakdown of the intermediate. For cephaloridine, the rate enhancement is greater than 104 which demonstrates that -lactam C-N bond fission and expulsion of the leaving group at C3 are not concerted.. ...

wp-content/uploads/2017/10/blank-box.png 0 0 admin /wp-content/uploads/2017/10/blank-box.png admin2015-01-16 20:47:322015-02-17 21:23:51Quantum mechanical/molecular mechanical study of the HDV ribozyme: Impact of the catalytic metal ion on the mechanism ...

Nitrogen doping in carbon nanotubes (CNTs) is of great interest because it endows the inherently inert surface of CNTs with a variety of chemical functionalities. For instance, nitrogen-doped carbon nanotubes (NxCNTs) have been shown a promising electrode catalyst support for polymer electrolyte membrane fuel cells because the doped nitrogen atoms can promote a high dispersion of the metal catalyst nanoparticles on the NxCNT surface, which is essential for achieving a high utilization and thus high catalytic performance. However, beyond the role in nanoparticle dispersion, how nitrogen doping affects the catalytic performance in the anode and in the cathode of a realistic membrane-electrode-assembly (MEA), still remains elusive. In this report, we performed a comparative study of NxCNTs at three different N doping levels as the anode and cathode catalyst support in both rotating disk electrode (RDE) and realistic direct methanol fuel cell (DMFC) test. Our results show that nitrogen doping can ...

This thesis deals with the copper-catalyzed substitution of allylic substrates.. In the first part of this thesis, the synthesis of a series of metallocenethiolates is described. The thiolates were examined as ligands in the enantioselective copper(I)-catalyzed γ-substitution of allylic acetates.. The second part describes a study on copper-catalyzed α-substitution of enantiomerically pure secondary allylic esters. It was observed that the degree of chirality transfer is strongly dependent on the reaction temperature. The loss of chiral information is consistent with an equilibration of the allylCu(III) intermediates prior to product formation, which is essential in order to realize a copper-catalyzed dynamic kinetic asymmetric transformation process.. The third part describes a study on copper-catalyzed stereoselective α-substitution of enantiopure acyclic allylic esters. This method, when combined, with ruthenium and enzyme catalyzed dynamic kinetic resolution of allylic alcohols, provides ...

A curable composition comprising (A) a compound having in the molecule two or more specific blocked carboxyl groups: (B) a compound having in the molecule two or more reactive functional groups which can form chemical bonds with the blocked carboxyl groups, and (C) a catalytic component selected from the following: (a) a thermal latent acid catalyst which comprises a compound having a epoxy group, a specific compound having a sulfur atom and a specific Lewis acid; (b) a thermal latent acid catalyst which comprises a specific compound, having at least one of a nitrogen atom, an oxygen atom, a phosphorus atom or a sulfur atom, a specific compound having a halogen atom and a specific Lewis acid having at least one of an aluminum atom, a zinc atom or a tin atom; or a mixture which comprises (c) a metallic chelate compound and a specific organic silicon compound or a condensate thereof. A two component curable composition is prepared by mixing (I) a main material composition or a solution thereof comprising

The front cover picture, provided by Shū Kobayashi and co-workers, illustrates a polymer immobilized chiral 2-oxopyrimidinium salt for asymmetric Michael addition of glycine-derived imines to α,β-unsaturated ketones. The reaction proceeded smoothly with 5 mol % of the heterogeneous catalyst and the products were obtained with good to excellent enantioselectivities. Interestingly, the addition of polydimethylsilane to the chiral heterogeneous catalyst greatly improved the ease of handling of the

A versatile palladium catalyst system was developed to effect the decarboxylative Heck coupling of a variety of arenecarboxylic acids with a wide range of olefins. The key to obtaining the efficient catalyst system is the use of 1-adamatanecarboxylic

Catalytic reductive coupling of two electrophiles and one unsaturated bond represents an economic and efficient way to construct complex skeletons, which is dominated by transition-metal catalysis via two electron transfer. Herein, we report a strategy of visible-light photoredox-catalyzed successive single electron transfer, realizing dearomative arylcarboxylation of indoles with CO2. This strategy avoids common side reactions in transition-metal catalysis, including ipso-carboxylation of aryl halides and β-hydride elimination. This visible-light photoredox catalysis shows high chemoselectivity, low loading of photocatalyst, mild reaction conditions (room temperature, 1 atm) and good functional group tolerance, providing great potential for the synthesis of valuable but difficultly accessible indoline-3-carboxylic acids. Mechanistic studies indicate that the benzylic radicals and anions might be generated as the key intermediates, thus providing a direction for reductive couplings with other

TY - JOUR. T1 - Enantioselective synthesis of substituted 3-quinolyl alkanols and their application to asymmetric autocatalysis. AU - Sato, Itaru. AU - Nakao, Tomohiko. AU - Sugie, Rie. AU - Kawasaki, Tsuneomi. AU - Soai, Kenso. PY - 2004/6/18. Y1 - 2004/6/18. N2 - Enantioenriched 3-quinolyl alkanols act as asymmetric autocatalysts in the addition of diisopropylzinc to the corresponding substituted quinoline-3-carbaldehydes, to afford themselves with an amplified enantiomeric excess (ee) of up to 97%.. AB - Enantioenriched 3-quinolyl alkanols act as asymmetric autocatalysts in the addition of diisopropylzinc to the corresponding substituted quinoline-3-carbaldehydes, to afford themselves with an amplified enantiomeric excess (ee) of up to 97%.. KW - Asymmetric amplification. KW - Asymmetric catalysis. KW - Autocatalysis. KW - Chirality. KW - Quinoline. UR - http://www.scopus.com/inward/record.url?scp=3042714314&partnerID=8YFLogxK. UR - ...

We report herein the highly enantioselective synthesis of 2-substituted tetrahydroquinolines through borrowing hydrogen, a process recognized for its environmentally benign and atom-economical nature. The use of an achiral iridacycle complex in combination with a chiral phosphoric acid as catalysts was the key to the development of this highly efficient and enantioselective transformation. Waste not, want not: A highly enantioselective synthesis of tetrahydroquinolines was made possible by hydro

A new type of supported rhodium nanoparticles were reproducibly prepared from N(2)H(4)BH(3) reduction of [Rh(mu-Cl)(1,5-cod)](2) without using any solid support and pre-treatment technique. Their characterization shows the formation of well dispersed rhodium(0) nanoparticles within the framework of a polyaminoborane based polymeric support. These new rhodium(0) nanoparticles were found to be the most active supported catalyst in the catalytic dehydrogenation of ammonia-borane in water at room temperature. ...

Abstract. A tandem sequential one-pot reaction employing both hydroamination and asymmetric transfer hydrogenation reactions enables an efficient and practical enantioselective synthesis of 3-substituted morpholines from aminoalkyne substrates. A wide range of functional groups is tolerated. Hydrogen-bonding interactions between the oxygen and the [(S,S)-Ts-DPEN] ligand of the Ru catalyst are crucial for obtaining high ees.. ...

The development of methodologies for C-N bond formation reactions is an important scientific challenge because of many academic and industrial applications. This work will focus particularly on palladium-catalyzed cross-couplings of amine-containing compounds with aryl halides. The scope of the BrettPhos precatalyst for the cross-coupling of ortho-substituted aryl iodides with amides is studied using substrates with a variety of functional groups. Due to potential metal-chelating issues with some of the substrates used in this study, a proposed ligand synthesis is discussed in which one of the methoxy groups of BrettPhos is replaced with a morpholine capable of occupying palladiums open coordination site during its catalytic cycle. A final C-N bond formation study focuses on the cross-coupling of aryl halides with amidine salts. For this cross-coupling, a methodology has been developed that can be applied to various electron-rich, electron-poor, and electron-neutral substrates. Furthermore, the ...

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Methodologies in Asymmetric Catalysis brings together leading scientists who have made major contributions to the field of asymmetric catalysis. This book assembles several new methodologies that are interdisciplinary by nature, incorporating organic synthesis, coordination chemistry, auto-catalysis, homogeneous and heterogeneous catalysis, kinetics and mechanism, etc. Thirteen chapters are included.

A new organocatalytic system was tested as a promoter for the asymmetric addition of Chans diene to aldehydes under solvent-free conditions. This new organocatalyst generated in situ by mixing 1-naphthyl-TADDOL derivative and Emim BF4 was able to give enantioenriched vinylogous aldols and hetero-Diels-Alder cycloadducts. A mechanistic investigation through the detection of nonlinear effects confirmed the involvement of the ionic liquid in the formation of a new catalytic supramolecular species ...

TY - JOUR. T1 - Transition-Metal-Free Catalysts for the Sustainable Epoxidation of Alkenes. T2 - From Discovery to Optimisation by Means of High Throughput Experimentation. AU - Lueangchaichaweng, Warunee. AU - Geukens, Inge. AU - Peeters, Annelies. AU - Jarry, Benjamin. AU - Launay, Franck. AU - Bonardet, Jean-Luc. AU - Jacobs, Pierre A.. AU - Pescarmona, Paolo P.. PY - 2012/2. Y1 - 2012/2. N2 - Transition-metal-free oxides were studied as heterogeneous catalysts for the sustainable epoxidation of alkenes with aqueous H2O2 by means of high throughput experimentation (HTE) techniques. A full-factorial HTE approach was applied in the various stages of the development of the catalysts: the synthesis of the materials, their screening as heterogeneous catalysts in liquid-phase epoxidation and the optimisation of the reaction conditions. Initially, the chemical composition of transition-metal-free oxides was screened, leading to the discovery of gallium oxide as a novel, active and selective ...

Close The Infona portal uses cookies, i.e. strings of text saved by a browser on the users device. The portal can access those files and use them to remember the users data, such as their chosen settings (screen view, interface language, etc.), or their login data. By using the Infona portal the user accepts automatic saving and using this information for portal operation purposes. More information on the subject can be found in the Privacy Policy and Terms of Service. By closing this window the user confirms that they have read the information on cookie usage, and they accept the privacy policy and the way cookies are used by the portal. You can change the cookie settings in your browser. ...

The production of clean and sustainable energy is considered as one of the most urgent issues for our society. Mastering the oxidation of water to dioxygen is essential for the production of solar fuels. A study of the influence of the substituents on the catalytic activity of a series of mononuclear Ru complexes (2a-e) based on a tetradentate ligand framework is presented. At neutral pH, using [Ru(bpy)(3)](PF6)(3) (bpy=2,2-bipyridine) as the terminal oxidant, a good correlation between the turnover frequency (TOF) and the Hammett sigma(meta) parameters was obtained. Additionally, a general pathway for the deactivation of Ru-based catalysts 2a-e during the catalytic oxidation of water through poisoning by carbon monoxide was demonstrated. These results highlight the importance of ligand design for fine-tuning the catalytic activity of water oxidation catalysts.. ...

Ternary Cu/ZnO/metal oxide catalysts are prepared through the co-precipitation method under strict control of parameters like pH, calcination conditions, and precipitation temperature in a systematic manner. The metal oxides applied in this study consist of Al2O3, ZrO2, La2O3 and Ce2O3. The distinction of this work in comparison with similar research is a comprehensive investigatation of the catalytic properties of metal oxides (including conversion, selectivity and stability) which have the potential for use in the methanol steam reforming process. The catalysts are characterized through XRD, SEM and BET. The prepared catalysts are applied in methanol steam reforming in a fixed bed reactor. A TGA analysis performed for all four catalysts determined that the Ce2O3 and ZrO2 metal oxide catalysts showed the best results in terms of stability with a coke formation of 0.7wt% and 0.8wt%, respectively; and maximum surface area is related to Cu/ZnO/Ce2O3, which can result in excellent stability and Cu

Ternary Cu/ZnO/metal oxide catalysts are prepared through the co-precipitation method under strict control of parameters like pH, calcination conditions, and precipitation temperature in a systematic manner. The metal oxides applied in this study consist of Al2O3, ZrO2, La2O3 and Ce2O3. The distinction of this work in comparison with similar research is a comprehensive investigatation of the catalytic properties of metal oxides (including conversion, selectivity and stability) which have the potential for use in the methanol steam reforming process. The catalysts are characterized through XRD, SEM and BET. The prepared catalysts are applied in methanol steam reforming in a fixed bed reactor. A TGA analysis performed for all four catalysts determined that the Ce2O3 and ZrO2 metal oxide catalysts showed the best results in terms of stability with a coke formation of 0.7wt% and 0.8wt%, respectively; and maximum surface area is related to Cu/ZnO/Ce2O3, which can result in excellent stability and Cu

Pd/Al2O3 catalysts oscillate between ignition and extinction of the catalytic partial oxidation of methane when they are exposed to a 2:1 reaction mixture of methane and oxygen. The oscillations of the catalytic performance and the structure of Pd/Al2O3 catalysts in a fixed-bed reactor were investigated using spatially and time-resolved in situ quick scanning X-ray absorption spectroscopy with online mass spectrometry. The dynamic methane conversion oscillated between an inactive state, where only combustion occurred, and an active state, after ignition, where partial oxidation of methane as a combination of total oxidation and reforming in the catalytic capillary reactor was observed. This change in catalytic performance was directly linked to changes in the oxidation state of the Pd/Al2O3 catalysts at different positions along the catalytic reactor. During the ignition of the catalytic partial oxidation of methane, the catalyst reduced from the end to the beginning of the catalyst bed and ...

Ribozymes enhance chemical reaction rates using many of the same catalytic strategies as protein enzymes. In the hepatitis delta virus (HDV) ribozyme, site-specific self-cleavage of the viral RNA phosphodiester backbone requires both divalent cations and a cytidine nucleotide. General acid-base catalysis, substrate destabilization and global and local conformational changes have all been proposed to contribute to the ribozyme catalytic mechanism. Here we report ten crystal structures of the HDV ribozyme in its pre-cleaved state, showing that cytidine is positioned to activate the 2-OH nucleophile in the precursor structure. This observation supports its proposed role as a general base in the reaction mechanism. Comparison of crystal structures of the ribozyme in the pre- and post-cleavage states reveals a significant conformational change in the RNA after cleavage and that a catalytically critical divalent metal ion from the active site is ejected. The HDV ribozyme has remarkable chemical ...

This thesis focuses on the development of methods for the activation of the hydroxyl group in non-derivatized alcohols in substitution reactions. The thesis is divided into two parts, describing three different catalytic systems.. The first part of the thesis (Chapter 2) describes nucleophilic allylation of amines with allylic alcohols, using a palladium catalyst to generate unsymmetrical diallylated amines. The corresponding amines were further transformed by a one-pot ring-closing metathesis and aromatization reaction to afford β-substituted pyrroles with linear and branched alkyl, benzyl, and aryl groups in overall moderate to good yields.. The second part (Chapters 3 and 4) describes the direct intramolecular stereospecific nucleophilic substitution of the hydroxyl group in enantioenriched alcohols by Lewis acid and Brønsted acid/base catalysis.. In Chapter 3, the direct intramolecular substitution of non-derivatized alcohols has been developed using Fe(OTf)3 as catalyst. The hydroxyl ...

Tom Simonite, www.newscientist.com A new catalyst that can split carbon dioxide gas could allow us to use carbon from the atmosphere as a fuel source in a

One of the most important inventions in heterocyclic chemistry is to identify and develop suitable methods in an eco-friendly and sustainable way. Recently, important discoveries were made in regards with L-proline and its derivative catalyzed asymmetric aldol product more efficiently with excellent enantioselectivity using additives. However, these approaches are more useful for avoiding the tedious methods for direct aldol asymmetric synthesis, but still considerable importance for investigation into novel organocatalyst approach. On other hand increasing interest associated with toxicity while modifying catalyst, cost and easily availability also more considerable. Keeping in mind all these disadvantages, water is the best choice as a reaction media and also eco-friendly approach, in this selection unmodified L-proline is an excellent organocatalyst due to tremendous applications including non toxic, hazards free, waste free, inexpensive, non flammable and easy availability. This book will be useful

This thesis embraces three main sections: the development of new molecular scaffolds for the organocatalytic Diels-Alder reaction, extension of the studies upon the a-effect and ji-stacking interactions to acyl-ammonium catalysis and development of novel molecular structures for the aminocatalysed Baylis-Hillman reaction. Chapter 1 describes some of the recent advances made in metal-free asymmetric catalysis and sets the work involved within this thesis into context. Chapter 2 describes the investigation of the a-effect and the modulation of face-face ji-jt interactions as a platform for the development of a novel family of catalyst for the aminocatalysed Diels-Alder reaction. After initial investigation on the effect of different counter anions and alternative electron withdrawing groups within achiral catalysts, the a-effect and the face-face ji-jt interactions design concepts were combined within the structure of a series of arenes based on the 8-aryl menthamine scaffold. Experiments ...