Characteristics of metallic iron in Y-zeolite catalysts reduced by hydrogen atom beams

Hydrogen atom beams were used to reduce the ionic species of iron-Fe(II) and Fe(III) in Y-zeolite. Reduction to metallic states was confirmed by ferromagnetic resonance (FMR) spectroscopy, and the catalytic activity in CO hydrogenation showed high selectivity towards ethylene and butene.     

Determination of iron by catalytic oxidation of p-aminophenol by hydrogen peroxide

The oxidation reaction of p-aminophenol by hydrogen peroxide was studied in the presence of ferric ions, which catalyzes it. The corresponding rate constants were calculated and the activation energy was determined. A method for ultramicrodetermination of ferric ion was developed using the method of tangents. Determination of ferric ions from 0.5 × 10^?1 up to 4.5 × 10^?2 μg/ml is possible with a relative mean error of ± 1.55%. The influence of several ions was also investigated.     

Changes in surface composition of Fe-Si-Cr-K oxide alkylation catalyst: the marked role of potassium ferrites

The influence of gas-phase methylation of phenol on the state of the Fe-Si-Cr-K oxide catalyst surface was investigated by thermodesorption of K atoms and ions. Changes in potassium desorption energies, as determined from Arrhenius-like plots, varied from 3.07 eV to 1.21 eV for the atoms and from 2.59 eV to 2.89 eV for ion desorption from the active and deactivated samples, respectively. The results were discussed in terms of transformation of the catalyst surface and formation of β-ferrite.     

Air-stable iron catalyst for the Oppenauer-type oxidation of alcohols

An alcohol oxidation process using an air-stable iron tricarbonyl compound structurally similar to Shvo’s diruthenium bridging hydride was developed. Secondary benzylic and allylic alcohols are oxidized in high yields, and evidence for an Oppenauer-type mechanism is presented.     

Moderate-temperature reduction of copper chromite by hydrogen and hydrogen desorption from the surface of reduced chromite

The reduction of copper chromite CuCr₂O₄ by hydrogen at 300–573 K and a hydrogen pressure of 4×10⁴-8 × 10⁴ 10⁴ Pa and hydrogen desorption from the surface of a reduced sample are studied. The rate of copper chromite reduction becomes high at temperatures above 473 K. Hydrogen desorbs from the surface of metallic copper covering the surface of chromite during its reduction. The heat of hydrogen adsorption on the metallic copper is almost independent of the surface coverage, 70–80 kJ/mol.     

Changes in surface composition of Fe-Si-Cr-K oxide alkylation catalyst: the marked role of potassium ferrites

The influence of gas-phase methylation of phenol on the state of the Fe-Si-Cr-K oxide catalyst surface was investigated by thermodesorption of K atoms and ions. Changes in potassium desorption energies, as determined from Arrhenius-like plots, varied from 3.07 eV to 1.21 eV for the atoms and from 2.59 eV to 2.89 eV for ion desorption from the active and deactivated samples, respectively. The results were discussed in terms of transformation of the catalyst surface and formation of β-ferrite.     

Phase state of iron system colloidal catalyst in butadiene polymerization

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Clean fuel-oriented investigation of thiophene oxidation by hydrogen peroxide using polyoxometalate as catalyst

After catalyst screening for oxidative desulfurization of fuel oil within several polyoxometalates, H₃PW₆Mo₆O₄₀ was confirmed for the first time to be an effective and recoverable catalyst for the oxidative removal of thiophene, being also effective for the desulfurization of real diesel and gasoline.     

Direct comparison of the electrocatalytic oxidation of hydrogen by an enzyme and a platinum catalyst

It is shown that for molecules of Allochromatium vinosum [NiFe]-hydrogenase adsorbed on a pyrolytic graphite electrode the nickel-iron active site catalyzes hydrogen oxidation at a diffusion-controlled rate matching that achieved by platinum.     

Rapid potentiometric determination of the iron oxidation state in silicates

The rapid potentiometric determination of the oxidation state of iron in a wide range of silicates is described. A platinum/platinum—rhodium (20%) bimetallic electrode with a small constant applied current is used for end-point detection. Samples are decomposed in 10–60 min by boiling with hydrofluoric—sulphuric acid in special PTFE decomposition—titration vessels in an atmosphere of nitrogen. Total iron is reduced with mercury-treated zinc or nickel reductors. Sulphides or other constituents do not interfere significantly and the procedures are relatively insensitive to aerial oxidation. The average standard deviation is 0.35% for iron(II) and 0.22% for total iron. The accuracy compares well to the available data for international standard rocks.     

Efficient solvent-free iron (III) catalyzed oxidation of alcohols by hydrogen peroxide

Selective oxidation of secondary and benzylic alcohols was efficiently accomplished by H₂O₂ under solvent-free condition catalyzed by FeBr₃. Secondary alcohols are selectively oxidized even in the presence of primary ones. This method is high yielding, safe and operationally simple.     

The surface properties of iron catalyst for ammonia synthesis

The reduction process and the surface properties of industrial prereduced triply and doubly promoted iron catalyst for ammonia synthesis have been studied using thermogravimetry, thermal desorption of N₂ and X-ray diffraction. The properties of both catalysts have been discussed on the basis of the double layer model of iron catalyst. A concept of facet formation on the active surface of the catalysts has been proposed. This revised version was published online in June 2006 with corrections to the Cover Date.     

Investigations of changes in the oxidation state of the catalyst during the OsO4-catalysed decomposition of hydrogen peroxide

By using different methods, such as spectrophotometry, potentiometric titration, polarography and extraction, it was found that at pH 8.5 osmium (VIII) is reduced by hydrogen peroxide to osmium(VI) to various extents. At pH 10.6, where the rate of the OsO₄-catalysed decomposition of hydrogen peroxide reaches its maximum, the concentration ratio of osmium (VIII) and osmium (VI) was found to be nearly one. This favours the explanation that the maximum rate of hydrogen peroxide decomposition is found at the pH where the rate of reduction of osmium (VIII) by hydrogen peroxide just becomes equal to the rate of oxidation of osmium (VI) by hydrogen peroxide.     

Transition state modeling and catalyst design for hydrogen bond-stabilized enolate formation

[reaction: see text] A catalyst for enolate formation was designed that incorporates an amine base along with a thiourea to bind to the oxygen atom of the substrate and enolate through hydrogen bonding. A computational model of the transition state was developed in which the thiourea (modeled initially as a urea) and amine were separate molecules. This model and models incorporating one or two methanol molecules in place of the urea showed an out-of-plane hydrogen bond, apparently to the carbonyl pi-bond, in addition to an in-plane hydrogen bond to an unshared electron pair. In contrast, optimized complexes of the ketone and the fully formed enolate showed only in-plane hydrogen bonding. The transition state model with the urea and amine was used to define a database search with the computer program CAVEAT to identify structures suitable for linking the amine and urea/thiourea moieties in the transition state. On the basis of a group of structures identified from this search, a flexible but conformationally biased linker was designed to connect the two catalytic moieties. The molecule having the amine and thiourea moieties connected by this linker was synthesized and was shown to catalyze proton exchange between methanol and deuterated acetone. The catalyst was about 5-fold more efficient than the amine and thiourea as separate molecules and relative to a similar but less conformationally biased catalyst.     

Selective oxidation of CO under conditions of catalyst surface ignition

The oxidation of CO in the presence of an excess of hydrogen and to 20% CO₂ and H₂O in the starting mixture was studied in flow reactors with high and low rates of heat removal. The ignition of the catalyst surface was observed in the reactor with a low rate of heat removal; catalyst surface ignition initially occurred at a “hot” spot (section) of the catalyst bed and gradually propagated along the bed. Experimental data on the relaxation dynamics of residual CO concentration and temperature in a catalyst bed under conditions of small heater temperature disturbances near and at the critical temperature of ignition and the effect of oxygen concentration in the starting mixture on this process are reported. It was found exprimentally that the ignition regime in the tested cases was more favorable for the selective oxidation of CO in an excess of hydrogen than the reaction in an isothermal reactor; this was likely due to the more favorable temperature distribution over the length of the catalyst bed.     

Redox control of a polymerization catalyst by changing the oxidation state of the metal center

The activity of cerium alkoxide complexes supported by a Schiff base ligand was controlled using redox reagents during the ring-opening polymerization of L-lactide. The rate of L-lactide polymerization was modified by switching in situ between the cerium(III) and cerium(IV) species.