Showing papers on "Catalysis published in 1986"
TL;DR: In this article, the effects of the type of alcohol, 1-butanol or methanol (MeOH), molar ratio of alcohol to SBO, type and amount of catalyst, and reaction temperature on rate constants and kinetic order were examined.
Abstract: Transesterification of soybean oil (SBO) and other triglycerides with alcohols, in the presence of a catalyst, yields fatty esters and glycerol. Di- and monoglycerides are intermediates. Reactions are consecutive and reversible. Rate constants have been determined for each reaction with a computerized kinetic program. The effects of the type of alcohol, 1-butanol or methanol (MeOH); molar ratio of alcohol to SBO; type and amount of catalyst; and reaction temperature on rate constants and kinetic order were examined. Forward reactions appear to be pseudo-first order or second order depending upon conditions used. Reverse reactions appear to be second order. At a molar ratio of MeOH/SBO of 6:1, a shunt reaction was observed. Energy of activation was determined for all forward and reverse reactions under a variety of experimental conditions from plots of log k vs 1/T. Values ranged from 8–20 kcal/mol.
1,215 citations
Patent•
14 Nov 1986TL;DR: An olefin polymerization catalyst comprising (a) a supported transition metal containing component, (b) a cocatalyst comprising an alumoxane and an organometallic compound of a metal of Groups IA, IIA, IIB, or IIIA of the Periodic Table.
Abstract: An olefin polymerization catalyst comprising (a) a supported transition metal containing component comprising the support treated with at least one metallocene and at least one non-metallocene transition metal compound, and a cocatalyst comprising an alumoxane and an organometallic compound of a metal of Groups IA, IIA, IIB, or IIIA of the Periodic Table.
829 citations
TL;DR: In this paper, an irreversible kinetic surface-reaction model based on the reaction of carbon monoxide and oxygen on a catalyst surface was presented, and it was found by computer simulation that the adsorbed molecules on the surface undergo both first-and second-order kinetic phase transitions.
Abstract: An irreversible kinetic surface-reaction model, based upon the reaction of carbon monoxide and oxygen on a catalyst surface, is presented. It is found by computer simulation that the adsorbed molecules on the surface undergo both first- and second-order kinetic phase transitions. These transitions correspond to the "poisoning" phenomenon seen on catalysts. Interesting transient and periodic behavior is also seen.
784 citations
TL;DR: Augmentation d'activite avec des substituants attracteurs d'electrons (dichloro ou dinitro)
Abstract: Augmentation d'activite avec des substituants attracteurs d'electrons (dichloro ou dinitro)
746 citations
663 citations
TL;DR: Hydroxyl radical Lipid peroxidation Transferrin iron binding Heme‐protein iron release Hemoglobin Fenton catalyst Desferrioxamine Bleomycin‐detectable iron.
626 citations
TL;DR: The immunoglobulin MOPC167, which binds the transition state analog p-nitrophenylphosphorylcholine with high affinity, catalyzed the hydrolysis of the corresponding carbonate 1 with first order in hydroxide ion concentration between pH 6.0 and 8.0.
Abstract: The immunoglobulin MOPC167, which binds the transition state analog p-nitrophenylphosphorylcholine with high affinity, catalyzed the hydrolysis of the corresponding carbonate 1. MOPC167 catalysis displayed saturation kinetics with catalytic constant (kcat) = 0.4 min-1 and Michaelis constant (Km) = 208 microM, showed substrate specificity, and was inhibited by p-nitrophenylphosphorylcholine. The rate of the reaction was first order in hydroxide ion concentration between pH 6.0 and 8.0. The lower limit for the rate of acceleration of hydrolysis by the antibody above the uncatalyzed reaction was 770. This study begins to define the rules for the generation of catalytic antibodies.
602 citations
TL;DR: In this article, a mechanism for the present CO2 photoreduction process is presented; it involves separate pathways for CO and formate generation, in which the [Re(bpy) (CO)3X] complex plays the role of both the photoactive and the catalytic center.
Abstract: [fac-Re(bpy) (CO)3Cl] (bpy = 2,2′-bipyridine) is an efficient homogeneous catalyst for the selective and sustained photochemical or electrochemical reduction of CO2 to CO. A quantum yield of 14% and a faradic efficiency of 98% were measured in the presence of excess Cl− ions. The photochemical process took place under visible-light irradiation and consumed a tertiary amine as electron donor. A formato-rhenium complex was isolated in the absence of excess Cl− ions. Substitution by Cl− ion generated free formate, but no CO was detected. Luminescence measurements showed that the tertiary amine quenches the metal-to-ligand charge-transfer excited state of the rhenium complex via a reductive mechanism, with a rate constant of 3.4 × 107M−1S−1. The 19e-complex [Re(bpy) (CO)3X]− produced either photochemically or electrochemically appears to be the active precursor in the CO-generation process. Detailed spectroscopic studies on 13C-enriched carbonyl-rhenium and formato-rhenium complexes derived from 13C-enriched CO2 were performed in order to confirm the origin of the products and to study the exchange of the ligands. A mechanism for the present CO2 photoreduction process is presented; it involves separate pathways for CO and formate generation, in which the [Re(bpy) (CO)3X] complex plays the role of both the photoactive and the catalytic center.
581 citations
TL;DR: A frontal chromatographic version of this technique has been developed which is very suitable for in situ measurements and this has enabled the apparent copper areas of various catalysts to be measured after exposures to methanol synthesis gases of different compositions at typical industrial conditions in microreactors commonly used for assessing the methenol synthesis activity of such catalysts as discussed by the authors.
510 citations
TL;DR: In this article, the effects of different types of catalysts on gelation time, porosity, bulk and apparent density, and volume shrinkage on drying were observed. And the authors proposed mechanisms for catalysis for the catalysts considered.
Abstract: In the sol-gel synthesis of silica, a silicon-containing raw material, a solvent, water, and a catalyst are utilized. By varying the catalyst, dramatic effects on gelation time, porosity, bulk and apparent density, and volume shrinkage on drying were observed. For example, porosities ranging from two to sixty-eight per cent can be obtained for dried and fired gels. Mechanisms for catalysis have been proposed for the catalysts considered.
497 citations
TL;DR: O/sub 2/ electrocatalysis is a particularly appropriate topic for the Berzelius lecture as discussed by the authors, in view of the interest in both catalysis and the element oxygen, and it is of critical importance to a number of applied aspects of electrochemistry.
TL;DR: In this paper, catalytic oxidation of methane was carried out over various perovskite-type oxides and compared with Pt/alumina catalyst at a conversion level below 80%.
TL;DR: The mechanistic investigation presently described points to the importance of molecular species adsorbed on the cathode surface and the size of the cyclam ligand and the presence of secondary amine groups (NH) might account for the very special properties of the electrocatalyst.
Abstract: The electrocatalytic properties of Ni cyclam/sup 2 +/ in CO/sub 2/ reduction have been studies. The influence of various experimental factors on the course of the reaction has been investigated. Under given conditions, Ni cyclam/sup 2 +/ is remarkably efficient and selective for electroreduction of CO/sub 2/ into CO, even in water. The stability of the system has been tested in long range electrolysis, showing that even after thousands of catalytic cycles no deactivation occurs. The mechanistic investigation presently described points to the importance of molecular species adsorbed on the cathode surface. The contribution of reduced species in the bulk is marginal. In addition, during the electrocatalytic process, a nickel(I) carbonyl complex is present: (Ni(cyclam)(CO))/sup +/. The latter complex may be involved in the catalytic reaction leading to CO evolution. Surprisingly, the behavior of Ni cyclam/sup 2 +/ as electrocatalyst is unique. Among the numerous complexes investigated, only Ni cyclam/sup 2 +/ shows such a large selectivity for the electroreduction of CO/sub 2/ over the electroreduction of water. The size of the cyclam ligand and the presence of secondary amine groups (NH) might account for the very special properties of the electrocatalyst.
TL;DR: In this paper, the kinetics of the CO-O2 and CO-NO reactions over single crystal Rh(111) and over alumina-supported Rh catalysts have been compared at realistic reactant pressures.
TL;DR: In this article, ZSM-5 zeolites containing Cu2+ ions showed unusually high and steady state activity for the catalytic decomposition of nitrogen monoxide; for example, the degrees of conversions of NO, and of conversion into N2 and O2 were 97, 85, and 70%, respectively, at 823 K with a contact time of 10.0 g s cm−3 over 73% exchanged Cu-ZSM−5.
Abstract: ZSM-5 zeolites containing Cu2+ ions showed unusually high and steady state activity for the catalytic decomposition of nitrogen monoxide; for example, the degrees of conversions of NO, and of conversion into N2 and O2 were 97, 85, and 70%, respectively, at 823 K with a contact time of 10.0 g s cm–3 over 73% exchanged Cu-ZSM-5.
TL;DR: It was found that these calix[6]arene derivatives efficiently accelerate acid-catalyzed hydration of I-benzyl1,4-dihydronicotinamide and the reaction proceeds according to the Michaelis-Menten kinetics, indicating that hexasulfonated calixarenes serve as a new class of catalysts, surfactants, and host molecules.
Abstract: Water-soluble hexasulfonated calix[6]arenes with various substituents (I-R) have been synthesized for the first time and applied as host molecules in an aqueous system. Dynamic ‘H NMR studies established that calb[6]arene-p-hexasulfonate (1-H) adopts a “winged” or “hinged” conformation in D20-Me2SO-d6 (2:l v/v) owing to hydrogen bonding among the OH groups, while 5,11,17,23,29,35-hexasulfonato-37,38,39,40,41,42-hexakis(hexyloxy)calix[6]arene (l-C6) adopts a similar conformation in D20 owing to hydrophobic bonding among the hexyl groups. The aggregation behavior in water was examined about I-C6 and I-C12. Physical (light-scattering, surface tension, and conductance) and spectral (fluorescence and absorption spectroscopies) studies established that 1-C, has a cmc at ca. 6 X IO4 M, as does sodium dodecyl sulfate (SDS), while I C l 2 has no detectable cmc and rather acts as a “unimolecular” micelle. In fact, l-C6 associated with small molecules (pyrene, 2-anilinonaphthalene, and Orange OT) according to the micelle-like biphasic concentration dependence, while 1-C12 formed host-guest-type 1: 1 complexes with these molecules. It was found that these calix[6]arene derivatives efficiently accelerate acid-catalyzed hydration of I-benzyl1,4-dihydronicotinamide and the reaction proceeds according to the Michaelis-Menten kinetics. In particular, the rate constants for 1-H and 1-CH2COOH, which both have acidic protons to catalyze the reaction and anionic sulfonates to stabilize the cationic intermediate at the two edges of the cavity, were greater by 426-1220-fold than those for noncyclic analogues. These findings indicate that hexasulfonated calix[6]arenes serve as a new class of catalysts, surfactants, and host molecules. This is the first example for the host-guest-type behavior of calixarenes observed in an aqueous system. The chemistry of cyclodextrins and cyclophanes has occupied a central interest in host-guest chemistry for the last two decades, and many functionalized host molecules which can mimic the in vivo action of enzymes by means of simple in vitro chemical systems have been exploited.2d Recently, Gutsche and coworker~’,~ have reported on a series of new cyclic molecules called “calixarenes” which are cyclic oligomers made up of benzene units as cyclodextrins are made up of glucose units. Since calixarenes possess a cylindrical architecture similar to cyclodextrins, they are expected to be useful to design enzyme mimics in totally synthetic systems.’.* Several groups have reported on the ionophoric properties of calixarenes which were obtained by introducing ether and/or ester groups into the edge of the cylindrical a rch i te~ture .~’~ In contrast, almost nothing is known with certainty as to the inclusion properties of calixarenes in solution, which should be more important in the design of the enzyme mimics. The data reported so far have been limited to only the solid and in fact, Gutsche stated in his recent review (1) Preliminary communications: (a) Shinkai, S.; Mori, S.; Tsubaki, T.; Sone, T.; Manabe, 0. Tetrahedron L e f f . 1984, 25, 5315. (b) Shinkai, S.; Koreishi, H.; Mori, S.; Sone, T.; Manabe, 0. Chem. Letf. 1985, 1033. (2) Breslow, R. Acc. Chem. Res. 1980, 13, 170. (3) Tabushi, I. Acc. Chem. Res. 1982, 15, 66. (4) Komiyama, M.; Hirai, H. J . Am. Chem. SOC. 1983, 105, 2018. (5) Bender, M. L.; Komiyama, M. In ‘Cyclodextrin Chemistry”; Spring(6) Murakami, Y. ‘Cyclophanes 11”; Springer-Verlag: Berlin, 1983; p 107. (7) Gutsche, C. D. Arc. Chem. Res. 1983, 16, 161. (8) Gutsche, C. D. In “Host Guest Complex Chemistry/Macrocycles”; (9) Chang, S.-K.; Cho, I. Chem. Lett. 1984, 477. (10) Ungaro, R.; Pochini, A.; Andreetti, G. D. J. Inclusion Phenom. 1984, er-Verlag: New York, 1977. Springer-Verlag: Berlin, 1985, p 375. 2. 199. -, . (1 1) Bocchi, V.; Foina, D.; Pochini, A,; Ungaro, R.; Andreetti, G. D. (12) McKervey, M. A.; Seward, E. M.; Ferguson, G.; Ruhl, B.; Harris, S. Tetrahedron 1982, 38, 373. J. J . Chem. SOC., Chem. Commun. 1985, 388. (1 3) Calixarenes can extract certain metal cations into the organic phase as their counterions: (a) Izatt, R. M.; Lamb, J. D.; Hawkins, R. T.; Brown, P. R.; Izatt, S. R.; Christensen, J. J. J. Am. Chem. Soc. 1983, 105, 1782. (b) Izatt, S. R.; Hawkins, R. T.; Christensen, J. J.; Zatt, R. M. Ibid. 1985, 107, 63. (14) Andreetti, G. D.; Ungaro, R.; Pochini, A. J. Chem. Soc., Chem. Commun. 1979, 1005. (15) (a) Coruzzi, M.; Andreetti, G. D.; Bocchi, V.; Pochini, A,; Ungaro, R. J . Chem. Soc., Perkin Trans. 2 1982, 1133. (b) Ungaro, R.; Pochini, A,; Andreetti, G. D.; Domiano, P. Ibid. 1985, 197. 0002-7863/86/ 1508-2409$01.50/0 article that there are no published data in support of solution complexes of calixarenes.8*16 This is in sharp contrast to cyclodextrins, which can form a variety of host-guest-type solution complexes. We noticed that the difference would stem mainly from the poor solubility of calixarenes; they are sparingly soluble in several organic solvents but insoluble in aqueous solutions. Therefore, the experimental efforts should be directed toward solubilization of calixarenes, which would eventually lead to tHe exploitation of calixarene-based host molecules and enzyme mimics. Here, we wish to report the synthesis and the solution properties of new water-soluble hexasulfonated calix[6]arenes (1-R). We have found that they serve not only as host molecules in an aqueous system but also as a new class of surfactants and acid catalysts.
TL;DR: In this paper, the ORTEP and activite pour l'hydrogenation de la cyclohexanone is described. Cycle d'hydgenation-deshydrogenation of butylcyclohexanol
Abstract: Structure ORTEP et activite pour l'hydrogenation de la cyclohexanone. Cycle d'hydrogenation-deshydrogenation de butylcyclohexanol
TL;DR: Partial oxidation is a widely used process to convert hydrocarbons and alcohols to valuable oxygen-containing chemicals as discussed by the authors, however, the direct utilization of these reactions for the manufacture of formaldehyde and methanol has remained extremely difficult.
Abstract: Partial oxidation is a widely used process to convert hydrocarbons and alcohols to valuable oxygen-containing chemicals. Although methane is the simplest hydrocarbon which gives formaldehyde and methanol as partial oxidation products, the direct utilization of these reactions for the manufacture of formaldehyde and methanol has remained extremely difficult. During the 1940s, two processes for the conversion of methane to formaldehyde were developed in Germany [l]. The first process used NO as a catalyst, and a commercial plant using this process was known to have been in operation in Copsa Mica in Romania. The second process used a combination of ozone and barium peroxide as the catalyst. In the current industrial practice, however, methane is converted to HCHO through a three-step process involving high temperature steam reforming, low pressure methanol synthesis, and oxidative dehydrogenation of methanol to formaldehyde, as shown by Unlike steam reforming, direct oxidation does not require ener...
TL;DR: In this paper, an investigation has been carried out of Fischer-Tropsch synthesis over potassium-promoted and unpromoted iron oxide catalysts, and the authors concluded that the phase of iron active for Fe2O3 Fischer-tropsch is a mixture of χ- and e′-iron carbides, and a small amount of α-iron.
TL;DR: In conclusion, pentadienyl ligand incorporation in 17-electron metal carbonyl complexes leads to a series of compounds for which much lower rates of substitution are observed and for which the substitutions also take place via dissociative means.
Abstract: philicities in these complexes, with vanadium in complexes 4 and 5 exhibiting greater electrophilicity. Given the inclination of other 17-electron metal carbonyl complexes to undergo associative ligand displacement reactions, it seems ironic that the incorporation of a pentadienyl ligand, which would be expected to promote associative attack via $ 73 coordination changes, should lead instead to a series of compounds for which much lower rates of substitution are observed and for which the substitutions also take place via dissociative means. Additional kinetic, EPR, and structural studies are under way in attempts to better understand the unexpected behavior of these 17-electron complexes.
TL;DR: The structure of NiO-SrTiO/sub 3/ powder has been studied by spectroscopic methods such as SEM, TEM, EXAFS, XANES, and XPS as mentioned in this paper.
Abstract: The structure of NiO-SrTiO/sub 3/ powder, which is a photocatalyst for the decomposition of water into H/sub 2/ and O/sub 2/, has been studied by spectroscopic methods such as SEM, TEM, EXAFS, XANES, and XPS. It has been clearly shown that the active catalyst has a peculiar structure; that is, nickel metal exists at the interface of NiO and SrTiO/sub 3/. The surface of NiO changes further into Ni(OH)/sub 2/ during the photocatalytic reaction in water. 31 references, 7 figures, 2 tables.
TL;DR: In this paper, the sulfur oxide species of a chelating organic sulfate structure, structure II, which is responsible for the generation of strong acidity, has been proposed, in which two covalent SO double bonds play an important role.
Abstract: When Fe/sub 2/O/sub 3/ was promoted by various sulfur compounds such as (NH/sub 4/)/sub 2/SO/sub 4/, SO/sub 3/, SO/sub 2/, or H/sub 2/S, strong acidity developed. Generation of this strong acidity was independent of the sulfur source provided that the oxidation state of sulfur was brought to +6. Structures of the sulfur-containing surface species were identified by infrared spectroscopy. The sulfur oxide species of a chelating organic sulfate structure, structure II, which is responsible for the generation of strong acidity, has been proposed, in which two covalent SO double bonds play an important role. The formation process of the species is discussed.
TL;DR: In this paper, a mechanism of reduction based on spectroscopic measurements of the surface phases before and after H2 treatment at 400 °C was proposed, where the authors showed that the cobalt in Magnesia-promoted CoO phases is reduced completely to the metal at much higher temperatures (500-700°C) but at 400°C the surface reduction is limited to 55% ± 5 after 1 h.
TL;DR: In this article, active and selective catalysts for oxidative coupling of methane were tested over many metal oxides (30 oxides) under the experimental conditions chosen (T = 973 K, PO2 = 0.4 kPa, PCH4 = 18.2 kPa and PHe = 82.7 kPa).
TL;DR: In this paper, the authors investigated the kinetics of hydrodechlorination of chlorobenzene over Pd Al 2 O 3 and Rh Al 2O 3 catalysts of varying dispersion and proposed a reaction scheme which is formally analogous to the Mars-van Krevelen mechanism for the oxidation of hydrocarbons.
Journal Article•
TL;DR: The mechanism of the epoxidation of ethylene with oxygen over silver catalysts has been examined in this article, where experiments were undertaken to determine whether adsorbed atomic oxygen is incorporated into ethylene to give epoxide, and to establish the relative rates of reaction of molecular oxygen impinging from the gas phase and of preadsorbed atoms.