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The effect of the acidity (p K) of the source of protons on the rate and selectivity of acetylene reduction has been investigated in order to elucidate the mechanism of protonation of substrate molecules coordinated to the reduced FeMoco cluster. A number of compounds whose p K in DMF varies between 6 and 20 have been examined as protonating agents. The rate of the reaction is almost independent of the acidity of the proton donor in a wide p K range. This can be explained in terms of the specific features of substrate protonation catalyzed by iron-sulfur clusters. Active protonating agents in the system are those which react with the catalyst to form hydrogen-bonded association species or those which are ligands reversibly binding to the cluster and are capable of donating protons, likely with simultaneous electron transfer. [ABSTRACT FROM AUTHOR]

The activity of 0.25-5% Ag/AlO catalysts in the selective catalytic reduction of nitrogen oxides with n-hexane under the conditions of promotion with a small amount of H was studied. It was found that, upon the introduction of ∼1000 ppm of H into the reaction mixture, the Ag/AlO samples containing 1-2% Ag exhibited optimum activity and selectivity. It was established that, in the presence of 1000 ppm of H, the rate of the selective catalytic reduction of NO was higher by a factor of 10-13, and the onset temperature of the reaction was lower by approximately 100°C. It was found by X-ray photoelectron spectroscopy, temperature-programmed reduction, and UV spectroscopy that the high activity of 1-2% Ag/AlO catalysts was due to the presence of small Ag and Ag clusters on their surface. A decrease in the concentration of Ag below the optimum value resulted in the predominance of an inactive ionic form on the catalyst surfaces. As the concentration of Ag was increased (>2%), large particles of AgO and Ag, which facilitate the oxidation of n-CH, were formed to lead to a decrease in selectivity and in the degree of reduction of nitrogen oxides. [ABSTRACT FROM AUTHOR]

Tin and titanium dioxides and their compositions were studied as catalysts for the reaction of complete oxidation of methane. The catalytic activity of the test samples was compared in terms of first-order reaction rate constants with reference to the unit surface area of a catalyst. The crystal structures and specific surface areas of the obtained compositions were characterized. The thermal stability of SnO was investigated. Data on the temperature-programmed reduction of SnO and the composition SnTiO in hydrogen were given. [ABSTRACT FROM AUTHOR]

This paper is focused upon the influence of potassium on the reduction behavior and catalytic properties of Fe2O3, Ru/Fe2O3 and Ru/(K)Fe2O3 catalysts for the water gas shift (WGS) reaction. The effect of promotion by potassium is attributed to stabilization of a highly dispersed ruthenium phase on the iron oxide surface. The hydrogen reduction behavior of Fe2O3 catalysts is strongly influenced by time-pressure dependent processes and comprises two or three heavily overlapped TPR peaks which can be ascribed to the following stages of the iron(III) oxide reduction 3Fe2O3 ? 2Fe3O4 ? 6FeO ? 6Fe. The appearance of FeO as an intermediate phase was confirmed by XRD. The presence of ruthenium(IV) oxide substantially changes the kinetics of the reduction process. In the case of potassium-doped catalysts, the reduction of Fe2O3 is substantially different and is assigned to the reduction phase of KFeO2. Both ruthenium and potassium have a promoting effect on the catalytic activity for the WGS reaction. [ABSTRACT FROM AUTHOR]

The reductive dehydration of cyclic (C5, C6) and aliphatic (C2-C4) alcohols into polycycloalkanes and alkanes whose carbon skeleton has at least twice as many atoms as that of the original substrate is reported for the first time. This reaction takes place at 250-350°C and 7-50 atm in the presence of a polymetallic catalytic system based on an iron-containing fused catalyst or a hydrided iron- and titanium-containing intermetallide mixed with a small amount of Pt/Al2O3. The mechanism of this new reaction is discussed in terms of the mechanisms of known reactions of alcohols and aldehydes enlarging the carbon skeleton. [ABSTRACT FROM AUTHOR]