Showing papers on "Catalysis published in 1973"

Platinum-Like Behavior of Tungsten Carbide in Surface Catalysis

Abstract: Tungsten carbide catalyzes the formation of water from hydrogen and oxygen at room temperature, the reduction of tungsten trioxide by hydrogen in the presence of water, and the isomerization of 2,2-dimethylpropane to 2-methylbutane. This catalytic behavior, which is typical of platinum, is not exhibited at all by tungsten. The surface electronic properties of the latter are therefore modified by carbon in such a way that they resemble those of platinum.

Enzymatic Catalysis and Transition-State Theory

Abstract: The application of transition-state theory to enzymatic catalysis provides an approach to understanding enzymatic catalysis in terms of the factors that determine the strength of binding of ligands to proteins. The prediction that the transition state should bind to the enzyme much more tightly than the substrate is supported by the experimental results with stable analogs of transition states. Transition-state analogs have great potential for use in understanding enzymatic catalysis and in inhibiting enzymes. Because of their potency and specificity as enzyme inhibitors, some of them may become very useful chemotherapeutic agents.

Restricted diffusion in liquids within fine pores

Abstract: The effect on the liquid-phase effective diffusivity in fine pores of the ratio of solute molecular diameter to pore diameter and of preferential solute adsorption was studied by measurements on homogeneous silicaalumina bead catalyst (pore diameter = 3.2 nm). A proposed empirical correlation is based on the investigation of a variety of binary systems of paraffins and aromatic hydrocarbons and of aqueous solutions of sugars.

Studies on Horseradish Peroxidase. XI. On the Nature of Compounds I and II as Determined from the Kinetics of the Oxidation of Ferrocyanide

Abstract: In order to investigate the nature of compounds I and II of horseradish peroxidase, the kinetics were studied of ferrocyanide oxidation catalyzed by these compounds which were prepared from three d...

Hydrogenation over supported gold catalysts

Abstract: Gold on silica, or on γ-alumina, or on boehmite, prepared by thermal decomposition of impregnated chloroauric acid at 383–403 K, and by other methods, activates molecular hydrogen and catalyses the hydrogenation of mono-olefins, buta-1,3-diene, and but-2-yne.

Organic Compounds in Meteorites: They may have formed in the solar nebula, by catalytic reactions of carbon monoxide, hydrogen, and ammonia

Abstract: Organic compounds in meteorites seem to have formed by catalytic reactions of CO, H2, and NH3 in the solar nebula, at 360 degrees to 400 degrees K and (4 to 10) x 10-6 atm. The onset of these reactions was triggered by the formation of suitable catalysts (magnetite, hydrated silicates) at these temperatures. These reactions may be a source of prebiotic carbon compounds on the inner planets, and interstellar molecules.

Specificity in Catalytic Hydrogenolysis by Metals

Abstract: Publisher Summary Hydrogenolysis reactions of hydrocarbons involve the rupture of carbon–carbon bonds and the formation of carbon–hydrogen bonds. The reactions are exothermic and are catalyzed by various transition metals. This chapter discusses the catalytic hydrogenolysis on metals. At temperatures much lower than are required for hydrogenolysis, the chemisorption of hydrocarbons on metals is accompanied by evolution of hydrogen. Exchange reactions between paraffins and deuterium to yield deuteroparaffins occur at similar temperatures. These results indicate that carbon–hydrogen bonds are activated more readily than carbon–carbon bonds and that dehydrogenative chemisorption of the hydrocarbon is the initial step in hydrogenolysis. The hydrogen deficient surface species formed from the hydrocarbon then undergoes carbon–carbon bond scission, followed by hydrogenation and desorption to complete the reaction. The chapter describes the specificity of metal catalysts for hydrogenolysis reactions. This includes an extensive comparison of the catalytic activities of various metals and an attempt to relate the resulting “activity patterns” to properties of the metallic state.

Steam reforming catalysts

Abstract: A catalyst for steam reforming of hydrocarbons comprises a refractory support, a catalytic metal or compound thereof reducible upon heating to the metal, and alkali or alkaline earth metal compound, wherein the refractory support which contains one or more acidic or amphotoic constituents is reacted at above 500 DEG C. with an alkaline compound to form a less water soluble or less easily water leachable compound and the so-treated support material is mixed with the catalyst metal constituent. The refractory support is preferably Al2O3 or SiO2 or mixtures thereof e.g. china clay but TiO2, ZrO2, V2O5, WO3, or mixtures of chromia with Al2O3 or SiO2 may also be used. The alkali or alkaline earth metal compound is one which at least when heated is basic and is preferably alkaline aqueous solution or convertible to the carbonate or oxide on heating. It may be an oxide, hydroxide, carbonate, bicarbonate, nitrite, nitrate, or aluminate, silicate or carboxylate e.g. acetate. If SiO2 forms the support and a alkali metal compound is present then an oxide which can form complex i.e. insoluble silicates should be added e.g. G2O3 or Al2O3. The support and the alkaline compound may be heat treated at 600-900 DEG C The catalytic metal may be Ni, Co, Ru, Rh, Pd, Os, Ir, Pt or mixtures thereof e.g. Ni + 0.001%-0.1% Rh, Ru or Pt. The preferred Ni or Co p content is 12-31% as NiO. In specific embodiments, china clay is mixed with (a) KOH solution or (b) Ca(NO3)2 solution to form a paste, the mass dried and then heated to 700 DEG C1. Basic nickel carbonate is then mixed with a slurry of the treated china clay together with (a) MgO or (b) soda ash and an aluminous cement and graphite added to the composition. The composition can be modified after manufacture by adding chloroplatinic acid solution and heating. Uncombined alkaline compound may be washed from the composition.

Carboxylato-triphenylphosphine complexes of ruthenium, cationic triphenylphosphine complexes derived from them, and their behaviour as homogeneous hydrogenation catalysts for alkenes

Abstract: The two-electron reduction of the oxo-centred triangular acetato-complex, Ru3O(CO2Me)6(PPh3)3, in which the metal has mean oxidation state 2⅔, gives a yellow ruthenium(II) species, probably Ru(CO2Me)2PPh3. In methanol containing a non-complexing strong acid and additional triphenylphosphine to give a minimum PPh3 : Ru ratio of 2 : 1, the complex acts as a catalyst for the hydrogenation of alkenes. Similar catalyst solutions in methanol are obtained by the action of acids on the hydrido-acetate, RuH(CO2Me)(PPh3)3, or the dihydride, Ru(H)2(PPh3)4; aqueous fluoroboric acid, p-toluenesulphonic acid hydrate or trifluoromethylsulphonic acid have been used. The initial product is evidently the (solvated) cation [Ru(PPh3)3]2+, but in presence of alkene a bis species, such as [Ru(PPh3)2(alkene)]2+ is formed. On standing, or on treatment with H2 or CO in absence of alkene, the orange-red tris species are converted to catalytically inactive yellow species, this reaction being faster in presence of water. From aged solutions the salt [(Ph3P)2Ru(OH)2Ru(PPh3)2](BF4)2 has been isolated. The yellow solutions of Ru(CO2Me)2PPh3 are oxidised by air to a new type of oxo-bridged ruthenium(III) complex, Ru2O(CO2Me)4(PPh3)2, which is shown to be an intermediate in the preparation of RuH(CO2Me)(PPh3)3 from commercial hydrated ruthenium chloride. The diacetate, Ru(CO2Me)2(PPh3)2 has also been prepared and the reduction of the tetra-µ-acetato-complex [Ru2(CO2Me)4]Cl investigated. Analogues of some of the compounds with other carboxylate groups are described.

The “Nickel Effect”

Abstract: Whereas the reaction of ethylene and triethylaluminum under pressure at 100°C yields trialkylaluminum compounds having long alkyl chains, the presence of small amounts of nickel salts induces the formation of butene. The discovery of this “nickel effect” represents the starting point for the development of the Ziegler catalysts. Comparatively little was formerly known about the nature and the mode of action of the catalytically active nickel species. A basis for the elucidation of the effect was provided by studies on the reduction of nickel compounds by organoaluminum compounds, on the occurrence and existence of nickel hydrides, and on interactions between nickel(0) and Lewis acids as well as organic compounds of main group metals. The most significant result of these studies is the recognition that multicenter bonding systems involving trialkylaluminum compounds and nickel atoms are involved. These react further with complex bonded ethylene in what is probably a concerted manner.

Gold catalysts for olefin hydrogenation

Abstract: Gold catalysts active for the hydrogenation and isomerisation of olefins have been prepared by the thermal decomposition of chloroauric acid supported on silica and alumina. The activity depends critically on the concentration of gold in the catalyst. This article considers the implications of these results and their possible industrial applications.