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Abstract  

Different preparation routes derived both from the usual high-temperature solid state synthesis and the sol-gel process were applied for the synthesis of crystalline La1-xSrxMnO3+ phases with 0x 0.2. They were investigated by means of temperature programmed isotope exchange (TPIE) under various conditions. The 18O isotope exchange experiments yielded information on the dependence of the oxygen mobility on temperature and the Mn4+/Mn3+ratio. Both are related to the defect structure of the solid. TPIE was applied for studying the interaction between 18O2 and CH4 under static conditions and was compared with results obtained from catalytic investigations, i.e. the behavior of La1-xSrxMnO3+ (0x0.2) in both CO and CH4 oxidation with normal oxygen 16O2 under steady flow conditions.

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Abstract

Platinum catalysts supported on silicas with various physicochemical properties were prepared in order to investigate the effect of silica characteristics on their platinum dispersion and catalytic activity in the oxidation of carbon monoxide. Although titania-incorporation into silica and further treatment of the impregnated platinum precursor with hydrogen peroxide were effective for improving the dispersion and stability of platinum catalysts supported on silicas, regardless of the characteristic of the silicas, the platinum catalysts supported on fumed silica with a medium level of surface hydroxyl group concentration exhibited the highest catalytic activity among those supported on mesoporous silica, silica gel, and precipitated silica. The required properties of the highly active platinum catalyst seemed to be a high dispersion of platinum, the formation of a stable titania layer, and the generation of strong acid sites. By contrast, the precipitated silica with a small surface area and high concentration of surface hydroxyl groups was not appropriate for a catalytic support for platinum catalysts.

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oxidation completely. As the free energies of CO and H 2 oxidation reactions are very close (−281.4 kJ mol −1 for CO oxidation and −243.6 kJ mol −1 for H 2 oxidation), the catalyst used for this process has to preferentially oxidize CO in the presence of

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Abstract  

A copper, zinc and aluminium mixed oxides sample having the nominal composition 0.25 CuO/0.03 ZnO/Al2O3 was prepared by impregnating Al(OH)3 with copper and zinc nitrate solutions, drying at 100 °C then heating in air at 600 °C. The obtained solid was exposed to different doses of -rays (20–160 Mrad). The surface characteristics namelyS BETVP andr of different treated adsorbents were determined from N2 adsorption isothems measured at –196 °C. The catalytic activity of various irradiated solids was determined by following up the kinetics of CO-oxidation by O2 at 150–200 °C. The results showed that the doses up to 80 Mrad resulted in no significant change in theS BET but increased slightly theV P (20%) of the treated adsorbents. The irradiation at 160 Mrad caused an increase of 20% in theS BET of the irradiated solid sample. The catalytic activity increased progressively by increasing the dose, a dose of 160 Mrad brought about an increase of 140% in the catalyst's activity. The apparent activation energy of the catalytic reaction decreased monotonically by increasing the absorbed dose of -rays which was attributed to a parallel induced decrease in the value of pre-exponential term of the Arrhenius equation. The observed increase in the catalytic activity due to -irradiation has been interpreted as a result of increasing the concentration of catalytically-active sites contributing in chemisorption and catalysis of CO-oxidation via a possible fragmentation of CuO crystallites.

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Abstract  

The effects of -irradiation (20–160 Mrad) and lithium oxide doping (0.75–6 mol%) on the surface and catalytic properties of unloaded Co3O4 solid have been investigated. The surface characteristics of various solids were determined from nitrogen adsorption isothems taken at –196 °C and their catalytic activities were measured by following the kinetics of CO-oxidation by O2 at 100–150 °C using a static method. The results showed that -rays brough about a decrease of 21% inS BET of Co3O4 due to widening of its pores and led also to a considerable increase in its catalytic activity. A maximum increase of 91% was observed upon exposure to a dose of 80 Mrad. Lithium oxide-doping at at 500 °C resulted in an increase of 150% inS BET of treated solid without changing its mean pore radius. This treatment was also accompanied by an increase of about 50% in its catalytic activity measured at 150 °C. Gamma-irradiation and Li2O-doping of unloaded Co3O4 did not change the magnitude of apparent activation energy of catalysis of CO-oxidation by O2 but increased the concentration of catalytically active sites contributing in the catalytic process. In other words, -rays and lithium oxide doping did not alter the mechanism of catalytic oxidation of CO by O2 over unloaded cobaltic oxide solid.

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Abstract  

Gold (~1%) has been supported on the mixed oxides Al2O3–CuO–Mn2O3 with molar compositions 1:1:1, 1:0.7:0.3, 1:0.3:0.7, prepared by spray pyrolysis method. The supports and catalysts have been characterized by TG, DTA, N2 physisorption, XRD, SEM, and TEM methods and tested for CO oxidation (25–300 °C). The catalysts revealed high specific surface area and amorphous form for compositions 1:0.7:0.3 and 1:0.3:0.7. Gold deposited on the supports lowered the T 50 values by 50–80 °C. The highest CO conversion was obtained for 1:1:1 composition.

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Introduction Ferrite spinels are important catalysts for various chemical reactions like the water gas shift reaction, carbon monoxide (CO) oxidation, alkylation reactions etc. [ 1 – 3 ] due to their structural and redox

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Reaction Kinetics, Mechanisms and Catalysis
Authors: Viorel Chihaia, Karl Sohlberg, B. Grzybowska-Świerkosz, M. Ruszel, R. Grabowski, L. Kępiński, M. A. Małecka, and J. Sobczak

Introduction Numerous studies on catalytic performance in various reactions of nanogold particles dispersed on supports [ 1 – 3 ], which followed Haruta's discovery of high activity of nano Au/TiO 2 in CO oxidation [ 4 , 5

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decreases in the following order: Cs 3 HPVMo > (NH 4 ) 3 PMo ≈ (NH 4 ) 3 HPVMo > (NH 4 ) 1,5 CsH 1,5 PVMo > (NH 4 ) 2 KHPVMo > HPMo ≈ HPVMo (2) [ 18 ]. This correspondence between two series was expected as the CO oxidation is a surface-type reaction as it

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-010-0025-5 . 2. Wang X , Lu G , Guo Yu , Zhang Z , Guo Ya . Role of Rh promoter on increasing stability of Au/Al 2 O 3 catalyst for CO oxidation at low temperature . Environ Chem Lett. 2009 . doi: 10

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