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  • Author or Editor: M. Caldararu x
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Abstract  

The surface properties of supported gallium oxide catalysts prepared by impregnation of various supports (γ-Al2O3, SiO2, TiO2, ZrO2) were investigated by adsorption microcalorimetry, using ammonia and water as probe molecules. In the case of acidic supports (γ-Al2O3, ZrO2, TiO2), the acidic character of supported gallium catalysts always decreased in comparison with gallium-free supports; on very weakly acidic SiO2, new acidic centers were created when depositing Ga2O3. The addition of gallium oxide decreased the hydrophilic properties of alumina, titania and zirconia, but increased the amount of water adsorbed on silica. The catalytic performances in the selective catalytic reduction of NO by C2H4 in excess oxygenwere in the order Ga/Al2O3>Ga/TiO2>Ga/ZrO2>>Ga/SiO2. This order is more related to the quality of the dispersion of Ga2O3 on the support than to the global acidity of the solids.

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Abstract  

Samples with various amounts of tin oxide were prepared by impregnating γ-Al2O3, TiO2(anatase), SiO2, ZrO2 and MgO with tin tetrachloride or tributyltin acetate solutions. After drying and calcination, the samples were characterized by chemical analysis, XRD and BET measurements. Ammonia adsorption microcalorimetry was used in order to determine the number, strength and strength distribution of surface acid sites. The influence of the adsorption temperature, evacuation temperature, amount of SnO2 deposited and of the nature of the support on the adsorption properties were studied.

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Reaction Kinetics, Mechanisms and Catalysis
Authors: Viorel Chihaia, Karl Sohlberg, M. Scurtu, S. Mihaiu, M. Caldararu, and M. Zaharescu

Abstract

Tin and cerium based oxide ceramics, due to their peculiar properties, are good candidates for using as sensors, solid electrolytes in fuel cells, and catalysts. In the present work, Sn–Ce–O powders with the composition of interest for catalysis applications were obtained by solid state reactions and by thermal decomposition of the different tin and cerium precursors. The structural characterization of the resulted samples was performed by X-ray diffraction. Morphological characteristics were evaluated from X-ray microstructural parameters and BET surface areas measurements. Surface evolution of the studied powders was investigated by electrical measurements in various atmospheres in the 25–400 °C temperature range. The samples studied behave as a n-type semiconductor. The catalytic activity for CO oxidation was measured in gas flow between 25 and 400 °C. The conversion degree depends on the preparation method of the samples. Magnetic susceptibility measurements at room temperature of the samples before and after catalytic test indicated a paramagnetic behavior. Higher values of magnetic susceptibility of the samples after catalytic test compared to initial ones could indicate the influence of CeO2 on the catalytic activity.

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Abstract

The in situ electrical properties and the catalytic activity of copper ferrite obtained by co-precipitation and thermal decomposition of polynuclear coordination compounds were studied in the propane oxidation reaction. The sample prepared by complexation had a better catalytic activity. Based on the conductivity data and the relative phase distribution in fresh and used compounds, the results are discussed in terms of the redox-type mechanism.

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Abstract

The electrical conductivity and the catalytic activity of SnO2 loaded TiO2 (anatase) particles were investigated in operando conditions. SnO2 depositions over commercial TiO2 samples (Sigma Aldrich and Rhone Poulenc) were obtained by the impregnation method. The samples were characterized by XRD, SEM/EDX and BET–N2 adsorption techniques. The AC electrical conductivity of the samples were measured between 25 and 400 °C under various atmospheres. The effect of the reactant mixture on the electrical conductivity and the catalytic performances of the samples were tested in propene oxidation. The results showed that the conductivity of SnO2/TiO2 samples depends strongly on the surface area of TiO2 support. The reducing effect of propene is more evident for higher surface area catalysts, these one showing also higher activity. On the other hand, the SnO2 deposition results in an increase of catalytic performances.

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Reaction Kinetics, Mechanisms and Catalysis
Authors: Viorel Chihaia, Karl Sohlberg, M. Scurtu, C. Hornoiu, M. Caldararu, C. Munteanu, G. Postole, N. I. Ionescu, T. Yuzhakova, and A. Redey

Abstract

The surface dynamics of SnO2/γ-Al2O3 catalysts with different tin dioxide loadings (3 and 20 wt%) prepared by the impregnation method were investigated by using in situ electrical/dielectric measurements. The samples were characterized by BET, inductively coupled plasma atomic emission spectroscopy and X-ray diffraction methods. The propylene oxidation reaction, in the temperature range of 30–400 °C, was used to identify the catalytic activity of SnO2 based catalysts. Results are discussed on the bases of the electrical changes accompanying variation of the active phase content. The conductance/capacitance of supported samples evidenced the reciprocal influence of the support and of the guest oxide.

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