D. Kießling

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.

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.

Total Oxidation of Chlorinated Hydrocarbons on A1–xSrxMnO3 Perovskite‐Type Oxide Catalysts – Part I: Catalyst Characterization

Thermoanalytical measurements (DTG-DTA-MS), X-ray diffraction (XRD), temperature-programmed reduction (TPR), redox titration and X-ray photoelectron spectroscopy (XPS) were used to characterize A 1-x Sr x MnO 3 perovskite catalysts (A=La, Nd, Pr, Di (didymium)). The catalyst samples were investigated before and after interaction with chloromethane in the temperature range between 300 and 650°C. XRD and TPR measurements revealed the presence of oxide admixtures in samples calcined at 600 and 800°C, resp., in air. Crystallinity of the samples and the amount of oxide admixtures depend on the kind of A-site cations. Interaction of the perovskite samples with chlorinated hydrocarbons at reaction temperatures leads to a decrease of the specific surface areas; the perovskite structure is preserved. Redox titration and TPR measurements showed that the Mn(IV) content in the perovskites increases by partial substitution of La by Sr and decreases after interaction with chloromethane.

Total oxidation of chlorinated hydrocarbons on A1-xSrxMnO3 perovskite-type oxide catalysts. Part II: Catalytic activity

The influence of the kind of A-site cation in A 1-x Sr x MnO 3 perovskites (A=La, Pr, Nd, Di (didymium)) on the catalytic activity in the total oxidation of methane, chloromethane, dichloromethane, and trichloroethylene has been studied. In contrast to methane, the total oxidation of chlorinated hydrocarbons (CHC) is connected with a reversible catalyst deactivation and the formation of byproducts at low reaction temperatures. For the catalysts calcined at 600 and 800°C, resp., the catalytic activity is determined mainly by specific surface area, amount of oxide admixtures and crystallinity of the perovskite. DiMnO 3 showed the highest and PrMnO 3 catalysts the lowest catalytic activity in the total oxidation of methane and CHC. Partial substitution of A by Sr leads to an enhancement of the catalytic activity in the total oxidation of methane, but not in the total oxidation of CHC.