Showing papers on "Catalysis published in 1985"

Enzyme-catalyzed processes in organic solvents.

Abstract: Three different lipases (porcine pancreatic, yeast, and mold) can vigorously act as catalysts in a number of nearly anhydrous organic solvents Various transesterification reactions catalyzed by porcine pancreatic lipase in hexane obey Michaelis-Menten kinetics The dependence of the catalytic activity of the enzyme in organic media on the pH of the aqueous solution from which it was recovered is bell-shaped, with the maximum coinciding with the pH optimum of the enzymatic activity in water The catalytic power exhibited by the lipases in organic solvents is comparable to that displayed in water In addition to transesterification, lipases can catalyze several other processes in organic media including esterification, aminolysis, acyl exchange, thiotransesterification, and oximolysis; some of these reactions proceed to an appreciable extent only in nonaqueous solvents

Formation of gas-phase methyl radicals over magnesium oxide

Abstract: When methane was passed over MgO at temperatures of approximately 500/sup 0/C, methyl radicals were produced on the surface, released into the gas phase, and trapped downstream in a solid argon matrix where they were analyzed by EPR spectroscopy. Significant differences in initial activity were observed, depending on whether the MgO was pretreated under vacuum or a flow of oxygen. Vacuum conditioning led to essentially no activity while oxygen conditioning resulted in substantial radical production. The oxidant of choice was also critical. Nitrous oxide resulted in a continuous decline of activity while in the presence of oxygen the formation of radicals was at a steady state. Doping of MgO with lithium, sodium, or iron was also examined. Lithium was found to greatly increase the activity up to a doping level of approximately 15.0 wt%. Two pathways are believed to be responsible for the radical formation. Over pure MgO, intrinsic cattion vacancies react with molecular oxygen to given an O/sup -/ center which can abstract a hydrogen atom from methane to produce the methyl radical. For the lithium-doped samples, substitutional Li/sup +/ ions react with molecular oxygen to form a (Li/sup +/O/sup -/) center which is also capable of abstracting amore » hydrogen atom from methane. 28 references, 5 figures, 3 tables.« less

Synthesis of ethylene and ethane by partial oxidation of methane over lithium-doped magnesium oxide

Abstract: The partial oxidation of methane into more useful chemicals such as methanol, ethylene and benzene has been investigated extensively, although yields for these products have been poor1–4. Moreover, in several of these processes the required oxidant is N2O rather than O2. Recent work5 in our laboratory has demonstrated that lithium-doped magnesium oxide (Li/MgO) in the presence of O2 has high activity for abstracting H from CH4 to form ·CH3 radicals. This suggests that C2H6 and C2H4 (C2 compounds) are produced by a coupling between two gaseous ·CH3 radicals formed on this catalyst. We report here our success in converting CH4 to C2 compounds in high yields in conventional catalytic conditions.

Process for the preparation of hydrocarbons

Abstract: The present invention relates to a process for the preparation of hydrocarbons by catalytic reaction of carbon monoxide with hydrogen in which reaction a feed comprising hydrogen and carbon monoxide is contacted at elevated temperature and pressure with a catalyst comprising cobalt and manganese in which catalyst the cobalt/manganese molar ratio is between 14:1 and 7:1 and the GHSV is at least 1600 N1/1/h. Preferably the cobalt/manganese molar ratio is between 13:1 and 9:1 and the GHSV is between 2700 and 25,000 N1/1/h. The reaction is especially carried out in a slurry phase regime.

Aerobic epoxidation of olefins with ruthenium porphyrin catalysts

Abstract: Le dioxo(tetramesitylporphyrinato) ruthenium(VI) catalyse l'epoxydation des olefines (cyclooctene, cis- et trans-β-methylstyrene, norbornene) a temperature et pression ambiantes

Methanol carbonylation process

Abstract: An alcohol such as methanol is reacted with carbon monoxide in a liquid reaction medium containing a rhodium catalyst stabilized with an iodide salt, especially lithium iodide, along with alkyl iodide such as methyl iodide and alkyl acetate such as methyl acetate in specified proportions. With a finite concentration of water in the reaction medium the product is the carboxylic acid instead of, for example, the anhydride. The present reaction system not only provides an acid product of unusually low water content at unexpectedly favorable reaction rates but also, whether the water content is low or, as in the case of prior-art acetic acid technology, relatively high, is characterized by unexpectedly high catalyst stability; i.e., it is resistant to catalyst precipitation out of the reaction medium.

Palladium catalyzed coupling of organotin reagents with organic electrophiles

Abstract: A novel, synthetically useful palladium catalyzed cross-coupling reaction of organotin reagents with a variety of organic electrophiles that generates a new carbon—carbon bond has been discovered recently. Because this mild, versatile reaction is tolerant of a wide variety of organic functionality on either coupling partner, is stereospecific, and gives high yields, it is ideal for use in the synthesis of complicated organic molecules. In the presence of carbon monoxide, instead of a direct coupling reaction, carbon monoxide insertion takes place, stitching the coupling partners together and generating a ketone. The utility of this coupling reaction has been demonstrated by the synthesis of a macrodiolide antibiotic, marine sesquiterpenes, insect pheremones and a number of key synthetic intermediates.

Vanadium-phosphorus Oxide Catalysts for the Selective Oxidation of C-4 Hydrocarbons To Maleic-anhydride

Abstract: Maleic anhydride (MA) is an important intermediate in a large number of chemtcal processes. World capacity is of the order of 700,000 tonnes/yr, and its major use is in the manufacture of unstaurated polyester resins, which accounts for 60–70% of production [1,2]. Other uses are summarized in Table 1

Structure of rhodium in an ultradispersed Rh/Al2O3 catalyst as studied by EXAFS and other techniques

Abstract: The structure of rhodium in an ultradispersed 0.57 wt % Rh/y-Al,O, catalyst before and after CO adsorption was studied with extended X-ray absorption fine structure (EXAFS), X-ray photoelectron spectroscopy (XPS), electron spin resonance (ESR), temperature programmed reduction (TPR), CO infrared spectroscopy, and H2 and CO chemisorption. With the aid of these complementary techniques, it could be established that the structure of the rhodium catalyst was completely different before and after CO adsorption. Before CO adsorption and after reduction of the catalyst at 593 K, all the rhodium was reduced and in the form of three-dimensional metallic crystallites. CO adsorption disrupted the metal-metal bonds in the crystallites, leading to isolated rhodium geminal dicarbonyl species in which the rhodium was present as Rh'. Each rhodium ion was surrounded by two carbon monoxide molecules and three oxygen anions of the support.

Surface Characterization of Supported and Nonsupported Hydrogenation Catalysts

Abstract: Etude par chimisorption: Cu, Rh, Pt, Pd, Ni, Ru. Etude par chromatographie. Etude par desorption a temperature programmee de H 2 (pour Ni, Ir, Pt). Etude par XPS

Anodic Oxidation of Reductants in Electroless Plating

Abstract: The anodic oxidation of reductants (hypophosphite, formaldehyde, borohydride, dimethylamine borane, and hydrazine) was studied on different metal electrodes (Au, Pt, Pd, Ag, Cu, Ni, and Co) at various temperatures, with special interest in the catalytic aspect of electroless plating. The rate of the anodic oxidation strongly depended on the pH value, the concentration of reductants, and the nature of the metal electrode. The catalytic activities of the metals for the anodic oxidation of different reductants were evaluated by the potentials at a reference current density. The order of the catalytic activity with metal varied depending on the nature of the reductants. The catalytic activity series thus obtained can be utilized for choosing the reductant suitable for the metal to be deposited. Arrhenius plots of the anodic currents on different metals at a reference potential yielded their respective straight lines. Some correlations were observed between the catalytic activity and the activation energy. The catalytic activity series was discussed in connection with that for hydrogen electrode reaction.

Supported Chromium Catalysts for Ethylene Polymerization

Abstract: Publisher Summary This chapter discusses supported chromium (Cr) catalysts for ethylene polymerization. The Phillips Cr/silica polymerization catalyst is prepared by impregnating a Cr compound onto wide pore silica and then calcining in oxygen to activate the catalyst. This leaves Cr in the hexavalent state, monodispersed on the silica surface. Chromium trioxide (CrO3) has been impregnated most commonly, but even a trivalent Cr salt can be used because oxidation to Cr(VI) occurs during calcining. Dichromate is the main species in CrO3 solutions. Trivalent Cr salts, notably CrCl3, impregnated onto silica and calcined under vacuum, are found to polymerize ethylene. Three processes are used commercially to make linear polyethylene—namely, solution, slurry, and gas phase. All these processes are called “low-pressure processes” to distinguish them from the free radical or high-pressure process that makes highly branched polyethylene. The slurry process is very convenient for batch polymerization studies. The diluent permits precise control of the temperature and serves to dissolve ethylene and other reactants that must contact the catalyst during polymerization.

Correlation between catalytic activity and bonding and coordination number of atoms and molecules on transition metal surfaces: Theory and experimental evidence.

Abstract: Correlation between catalytic activity and low-energy local electronic fluctuations in transition metals is proposed. A theory and calculations are presented which indicate that maximum electronic fluctuations take place at high-coordination metal sites. Either (i) atomically rough surfaces that expose to the reactant molecules atoms with large numbers of nonmagnetic or weakly magnetic neighbors in the first or second layer at the surface or (ii) stepped and kinked surfaces are the most active in carrying out structure-sensitive catalytic reactions. The synthesis of ammonia from N2 and H2 over iron and rhenium surfaces, 1H2/2H2 exchange over stepped platinum crystal surfaces at low pressures, and the hydrogenolysis (C—C bond breaking) of isobutane at kinked platinum crystal surfaces are presented as experimental evidence in support of the theory.