G. Wendt

Perovskite-type oxides – catalysts for the total oxidation of chlorinated hydrocarbons

Abstract Chloromethane, dichloromethane and 1,2-dichloroethane were completely decomposed in air on perovskite-type catalysts (LaMnO3, LaCoO3, (La0.84,Sr0.16)(Mn0.67,Co0.33)O3) at reaction temperatures above 550°C. Besides the main reaction products (carbon dioxide, water and hydrochloric acid), by-products (higher chlorinated-, C–C coupling- and cracking products) were formed in the low temperature range. Depending on the reaction temperature, residence time and kind of chlorinated hydrocarbon a reversible catalyst deactivation takes place. In the case of LaCoO3 catalysts an irreversible deactivation was observed. X-ray diffraction (XRD) and electron probe microanalysis (EPMA) measurements with the perovskite-type catalysts after interaction of chlorinated hydrocarbons indicate the formation of chlorinated species on the catalyst surface and in the bulk.

Cordierite monolith supported perovskite-type oxides — catalysts for the total oxidation of chlorinated hydrocarbons

Abstract The catalytic behaviour of LaMnO 3 , LaCoO 3 and (La 0.84 Sr 0.16 )(Mn 0.67 Co 0.33 )O 3 perovskites supported on cordierite monoliths was studied in the total oxidation of chlorinated hydrocarbons (CHC). By-products (higher chlorinated hydrocarbons, lower molecular coupling and cracking products) were formed in the low temperature range depending on the kind and concentration of CHC in the feed and the reaction conditions. The preparation method (impregnation or coating) influences catalytic activity and by-product formation. Addition of water, methane or propane to the feed diminishes the by-product formation significantly. In the case of monolith supported LaCoO 3 perovskite, an irreversible catalyst deactivation was observed.

Perovskite-type oxide monolithic catalysts for combustion of chlorinated hydrocarbons

Abstract The catalytic activity of perovskite-coated and perovskite-extruded monolithic catalysts was studied in the total oxidation of several aliphatic chlorinated hydrocarbons. At low reaction temperatures a reversible catalyst deactivation takes place. The complete decomposition of the chlorinated hydrocarbons without formation of by-products depends on the reaction conditions, the kind of chlorinated hydrocarbon and the monolith preparation.

Propane dehydrogenation over supported platinum silicon nitride catalysts

Amorphous silicon nitrides were prepared by gas phase ammonolysis of tetrachlorosilane followed by thermal treatment in nitrogen or ammonia atmosphere. After deposition of platinum on the materials the obtained catalysts proved to be catalytically active and selective for propane dehydrogenation. Incorporation of boron, carbon and titanium in the supports influences significantly the catalytic properties. It is suggested that the comparable high catalytic activity, propene selectivity and stability of the catalysts are due to the basic properties of the catalyst surface.

Dimerization of n-butenes on amorphous NiO-Al2O3/ SiO2 catalysts

Abstract The conversion of different n-butenes on amorphous NiO-Al2O3/SiO2 catalysts has been studied in the liquid phase at 3.5 MPa and 370 K. The product distribution is consistent with a coordinative as well as carbenium ion dimerization mechanism, while the preferable conversion of but-1-ene points to the coordinative dimerization mechanism. Isomerization reactions of oligomers on acid sites take place, while the isomerization of the n-butenes is of minor importance. Catalyst deactivation by coke formation is caused by condensation products of Diels-Alder type reactions as well as multi-unsaturated oligomers. Transformation of cis-but-2-ene is accompanied by pronounced formation of coke precursors.

Influence of the preparation conditions on the properties of perovskite-type oxide catalysts

Abstract The effect of the precipitation conditions on the catalytic and structural properties of LaMnO 3+δ , LaCoO 3−δ and LaCo 1− y Mn y O 3±δ perovskites ( y = 0.33, 0.5, 0.67) has been studied by means of powder X-ray diffraction, temperature programmed oxygen desorption, textural measurements and catalytic activity measurements in methane total oxidation. Ageing time of the precipitate and H 2 O 2 content in the precipitant influences crystallinity and phase composition of the perovskite samples pretreated at 600 and 800 °C. The results of the catalytic activity are affected by the presence of oxide admixtures and crystallinity.

Dimerization of n-butenes on nickel and ammonium ion exchanges NaY zeolites

Nickel and ammonium ion exchanged NaY zeolites have been investigated in dimerization of n-butenes in the liquid phase. The dimerization reaction proceeds by a coordinative as well as carbenium ion reaction mechanism.AbstractЦеолиты NaY, ионообмененные на никель и аммоний, исследовали в димеризации н-бутенов в жидкой фазе. Рекция димеризации протекает как по координационоому механизму, так и при участии карбенийного нона.

Studies on nickel oxide mixed catalysts, V. Propene dimerization on Nio−Al2O3/SiO2 catalysts

The catalytic activity of various NiO−Al2O3/SiO2 catalysts has been investigated in a tubular fixed-bed reactor at high pressure. High selectivities to propene dimers were obtained on catalysts with a high Ni/Al ratio. The surface acidity of the catalysts influences strongly the selectivity and the product distribution.AbstractИзучена каталитическая активнось разных катализаторов типа NiO−Al2O3/SiO2 в интегральном реакторе при высоком давлении. Установлено, что катализаторы с большим соотношением Ni/Al обладают высокой селективностью по отношению к димерам. Кислотность поверхшости сильно влияет на селективность и распределение продуктов реакции.

TOTAL OXIDATION OF CHLORINATED HYDROCARBONS ON LaMnO3 PEROVSKITE TYPE CATALYST

The total oxidation of CH3Cl, CH2Cl2 and ClH2C-CH2Cl has been investigated on a LaMnO3 perovskite type catalyst. Depending on the reaction temperature, a reversible deactivation of the catalyst was observed. Small amounts of by-products were formed at low reaction temperatures.

Temperature programmed reduction studies on phase reconstruction of Na2O−MnOx-catalysts for the oxidative dehydrodimerization of methane

The change in phase composition and integral oxidation state of Na2O−MnOx-catalysts caused by simultaneous air and methane interaction was studied using Temperature Programmed Reduction. Sodium manganates (III, IV) continue to exist during catalytic reaction whereas sodium manganate (V) decomposes.AbstractИзменения в фазном составе и интегральном окисленном состоянии катализаторов Na2O−MnOx, вызванные одновременным взаимодействием с воздухом и метаном, были исследованы с помощью ТПВ. Натриевые манганаты (III, IV) продолжают существовать и в ходе каталитической реакции, в то время как натриевые манганаты(V) разлогаются.