Showing papers on "Catalysis published in 1991"

Computer Modeling of Chemical Reactions in Enzymes and Solutions

Abstract: Basic Principles of Chemical Bonding. Chemical Reactions in the Gas Phase and in Simple Solvent Models. Chemical Reaction in All--Atom Solvent Models. Potential Surfaces and Simulations of Macromolecules. Modeling Reactions in Enzymes: An Introduction. General Acid Catalysis and Electrostatic Stabilization in the Catalytic Reaction of Lysozyme. Serine Proteases and the Examination of Different Mechanistic Options. Simulating Metalloenzymes. How Do Enzymes Really Work? Index.

Catalyst system of enhanced productivity

Abstract: This invention relates to catalyst systems, and a method for using such system, for the enhanced production of homo and copolymer products of olefin, diolefin and/or acetylenically unsaturated monomers. This invention catalyst system comprises a Group III-A element compound for improving the productivity of an olefin polymerization catalyst which is the reaction product of a metallocene of a Group IV-B transition metal and an ionic activator compound comprising a cation capable of donating a proton and an anion which is bulky, labile and noncoordinateable with the Group IV transition metal cation produced upon reaction of the metallocene and activator compound to form the catalyst component of the catalyst system.

Removal of nitrogen monoxide through a novel catalytic process. 1. Decomposition on excessively copper-ion-exchanged ZSM-5 zeolites

Abstract: Repeated ion exchange of the ZSM-5 zeolite using aqueous copper(II) acetate solution was found to bring about excess loading of copper ions above an exchange level of 100%. The high activity of the resulting catalyst for NO decomposition was consistent for at least 30 h even at short contact time and low NO pressure. The number of copper ions that can adsorb NO molecules has been determined by a temperature-programmed desorption technique combined with IR measurement; 94% of Cu{sup 2+} ions in ZSM-5 were active for the adsorption. The activity of excessively copper ion exchanged ZSM-5 zeolite was slightly reduced by the oxygen in the feed gas while that of zeolite, of which the loading amount of copper was less than 100%, was greatly diminished under the same condition. SO{sub 2} completely poisons the activity at 673-923 K, but the activity can be regenerated at the higher temperature treatment.

Synthetic studies via the cross-coupling reaction of organoboron derivatives with organic halides

Abstract: Previously, we reported the palladium-catalyzed cross-coupling reaction of 1-alkenylboron compounds with various vinylic or aryl halides in the presence of base to provide corresponding coupling products in good yields, stereoand regioselectively. The recent progress of such reactions is discussed. Most recently, it has been found that B-alkylorganoboranes react readily with vinylic halides or haloarenes in the presence of special palladium catalyst and base. Furthermore, even the most difficult cross-coupling of B-alkyl-9-BBN with alkyl iodides has been demonstrated to proceed smoothly to give coupling alkane derivatives in moderate yields under special conditions. Finally, it will be discussed that B-alkyl-9-BBN derivatives react with iodoalkanes under carbon monoxide atmosphere in the presence of potassium phosphate and a catalytic amount of Pd(PPh,),, yielding unsymmetrical ketones in excellent yields. The reaction is extremely accelerated by irradiation of light. RECENT PROGRESS OF CROSS-COUPLING REACTION U S I N G 1 -ALKENYLBORANES Previously we reported a simple and versatile synthesis leading to conjugated (E,E)-, (E,Z)-, (Z,E)-, and (Z,Z)alkadienes (ref. 1) via a cross-coupling reaction of (E)or (Z)-1-alkenyldisiamylboranes or 2-[(E)-l-alkenyl1-1,3,2benzodioxaboroles (B-1-alkenylcatecholboranes) with either (E)or (Z)-1-alkenyl halides in the presence of a catalytic amount of palladium catalyst and base in benzene. The coupling with (E)-1-alkenylboronic acids or their esters prepared by hydroboration of alkynes with catecholborane always gives the expected dienes in 80-90% yields, while the coupling reactions with (Z)-1-alkenyldisiamyl(Ia) or (Z)-1-alkenyldicyclohexylboranes (Ib) give relatively poor yields of the coupling products (4), less than 50%. One of the major reasons for this difficulty appears to be due to the side reaction arising from the two alkyl groups on boron atom. In order to overcome this, we have attempted to use (Z)-1-alkenylboronates (3), f i t prepared by Brown and Imai (ref. 2). The reactions 1 a : R~ = siamyi 1 b : R2 cyclohexyl

Intrinsic kinetics of the Fischer-Tropsch synthesis on a cobalt catalyst

Abstract: The rate of synthesis gas consumption over a cobalt Fischer-Tropsch catalyst was measured in a well-mixed, continuous-flow, slurry reactor at 220-240 o C, 0.5-1.5 MPa, H 2 /CO feed ratios of 1.5-3.5, and conversions of 6-68% of hydrogen and 11-73% of carbon monoxide. The inhibiting effect of carbon monoxide was determined quantitatively and a Langmuir-Hinshelwood-type equation of the following form was found to best represent the results: −R H2+CO =aP CO P H2 /(1+bP CO ) 2 . The apparent activation energy was 93-95 kJ/mol. Data from previous studies on cobalt-based Fischer-Tropsch catalysts are also well correlated with this rate expression

Process for producing crystalline poly-alpha-olefins with a monocyclopentadienyl transition metal catalyst system

Abstract: The invention is a catalytic process using a Group IV B transition metal component and an alumoxane component to polymerize α-olefins to produce high crystallinity and high molecular weight poly-α-olefins.

Addition polymerization catalyst with oxidative activation

Abstract: Addition polymerization catalysts comprising a derivative of a Group 4 or Lanthanide metal compound prepared by oxidative activation, a process for preparation and an addition polymerization method utilizing such catalysts.

Improvements in the gaseous hydrogen-water equilibration technique for hydrogen isotope ratio analysis

Abstract: Improved precision in the H 2 -H 2 O equilibration method for δD analysis has been achieved in an automated system. Reduction in 1-δ standard deviation of a single mass-spectrometer analysis to 1.3‰ is achieved by (1) bonding catalyst to glass rods and assigning use to specific equilibration chambers to monitor performance of catalyst, (2) improving the apparatus design, and (3) reducing the H 3 + contribution of the mass-spectrometer ion source

Biological fuel cells with sulphide storage capacity

Abstract: Using bacteria that tolerate fairly high sodium sulphate concentrations and reduce sulphate and a coarse clay with buffering properties as solid electrolytes, biological fuel cells have been developed for providing electrical energy discontinuously. The biological active anodes, which accumulate fuel, contained a metal hydroxide catalyst that was converted during the biological process into a metal sulphide catalyst and functioned in a solidified aqueous electrolyte that contained sodium sulphate. The active carbon or titanium cathodes employed were activated with cobalt oxide spinels, molybdenum/vanadium compounds or metal chelates. When employed in continuous service for discontinuous energy consumption, fuel cells were capable of being operated with humus constituents or sugar waste as fuel over a period of 5 years without malfunction and maintenance. Positive results were achieved in the purification of waste-water with a modified type of fuel cell in which the production of energy was not dominant.

Improved methodology for photocyclization reactions

Abstract: To photocyclize stilbenes, a stoichiometric amount of iodine plus propylene oxide in the absence of air is superior to a catalytic amount of iodine in the air. The propylene oxide prevents HI from photoreducing double bonds. The absence of air prevents photooxidative side reactions, shown in one case to be caused by a photogenerated oxidant, possibly hydrogen peroxide