Rosa Fenoglio

Catalytic wet peroxide oxidation of phenol solutions over CuO/CeO2 systems.

Three 5% CuO/CeO(2) catalysts were synthesized by sol-gel, precipitation and combustion methods, followed by incipient wetness impregnation with copper nitrate. The samples were characterized by XRD, TPR, BET and tested for the catalytic wet peroxide oxidation of a phenol solution (5 g/L). The reaction took place in a batch reactor at atmospheric pressure, in a temperature range of 60-80°C, during 4h. Phenol conversion, H(2)O(2) consumption, pH and chemical oxygen demand were determined. The reaction temperature and the catalyst loading did improve the phenol and the H(2)O(2) conversions. The effect on the selectivity towards complete mineralization was less marked, with levels among 60-70%. Stepwise addition of H(2)O(2) was also tested.

Effects of oxidation and reduction treatments on methylcyclopentane hydrogenolysis over Rh/TiO2 and Rh/SiO2 catalysts

Abstract We have studied the effects of oxidation and reduction treatments of supported rhodium on its catalytic activity. In particular, we have studied the hydrogenolysis of methylcyclopentane over Rh/SiO 2 and Rh/TiO 2 catalysts with different metal dispersions. It has been observed that following oxidation at 673 K, a subsequent reduction at increasing temperatures causes a gradual increase in activity. When the reduction temperature reaches about 550 K a maximum in activity is observed, while a further increase in reduction temperature causes a decrease in activity. The same trend is observed on both SiO 2 - and TiO 2 -supported catalysts. However, the activity variations are most pronounced when the metal dispersion is high and the support is TiO 2 . The changes in overall activity are accompanied by changes in selectivity. It is observed that the selectivity toward n -hexane follows the pattern opposite that of the activity, showing a minimum at reduction temperatures of about 550 K. Again, these selectivity variations are most pronounced for the titania-supported catalyst. We interpret these variations in terms of morphology changes occurring in the metal particles during the oxidation/reduction cycles. The reduction following the oxidation treatment initially renders the metal particles with a very open structure. Under these conditions the catalytic activity is relatively low. An increase in the reduction temperature causes an annealing of the metal particles, reaching an optimal configuration at about 550 K for which the catalytic activity shows a maximum. A further annealing of the metal particle caused by an increase in reduction temperature causes the activity to decrease. In the case of TiO 2 , these changes are enhanced by an interaction occurring under high-temperature oxidation conditions between the oxidized Rh particles and the support. The behavior of the TiO 2 -supported catalysts is also different at high reduction temperatures due to the well known SMSI effect.

Selectivity changes in the ring-opening reaction of methylcyclopentane over rhodium catalysts caused by the addition of silver and metal—support interactions

Abstract The hydrogenolysis of methylcyclopentane (MCP) was studied over Rh-Ag/TiO 2 catalysts after various reduction/oxidation treatments. It was observed that the addition of silver causes a decrease in activity, accompanied by an increase in the selectivity toward n-hexane (n-Hx). The decrease in activity and changes in selectivity are interpreted in terms of a shift in the ring-opening mechanism. When the rhodium surface is free from silver or support species, the reaction mainly proceeds via multi-site complexes and preferentially leads to 2-methylpentane (2MP) and 3-methylpentane (3MP). On these surfaces the 2MP-to-3MP ratio is much higher than the expected statistical value of 2. On the other hand, when silver, or TiO x species from the support, or both, are present on the rhodium surface the large ensembles are blocked. This site blockage causes a shift to a single-site mechanism which yields a product distribution closer to the statistical distribution, i.e., the percentage of n-Hx increases and the 2MP-to-3MP ratio decreases. The selectivity changes are much greater in the case of co-impregnated Rh-Ag catalysts reduced at 773 K. The enhanced effects observed on this catalyst are explained in terms of an interaction between silver and the TiO x species which causes a better spreading of silver over rhodium than that obtained with lower reduction temperatures. These results provide further evidence for a previously proposed “indirect SMSI effect” of TiO 2 in bimetallic catalysts.

Interactions of the Impregnating Solution With the Support During the Preparation of Rh/Tio2 Catalysts

Summary We have analyzed the different phenomena occurring during the impregnation of titania with aqueous solutions of rhodium chloride. Our results demonstrate that the deposition of the Rh precursors on titania, at low pH values (about 3), involves three different processes: a) adsorption of anionic species, b) ligand exchange reaction and c) acid attack of the support.

Oxidation of hazardous compounds by heterogeneous catalysis based on Cu/Al2O3 system in Fenton-type reactions

ABSTRACT This review examines in detail all components involved in heterogeneous Fenton-type reactions, with special focus on copper species supported on alumina for H2O2 decomposition, their redox chemistry, and their practical advantages over traditional Fenton for the degradation of recalcitrant organic compounds. Several aspects for a deeper comprehension of the properties of γ-Al2O3 as support for catalytic applications are discussed. Iron-free systems stability after calcination and catalyst performance during the oxidation reaction are evaluated to solve the disadvantages of iron-based system. Copper species supported on alumina for H2O2 decomposition in Fenton-like reactions are examined, with special focus on their redox chemistry and practical advantages over traditional Fenton system for recalcitrant compounds degradation. Characterization techniques for the elucidation of the structures, compositions, and chemical properties of both the solids used in heterogeneous catalysis, and the adsorbates and intermediates present on the surfaces of the catalysts during reaction are explained. Global indicators for chemical characterization of wastewaters and measurement of catalytic efficiency are described.

Enhanced methane production from methanol decomposition over Pt/TiO2 catalysts

The promoting effect of TiO2 on CH4 formation from CH3OH decomposition has been investigated. Hydrogen and CO are products of CH3OH decomposition which can subsequently react to produce CH4. We observe an enhancement in this secondary reaction when the support is TiO2. This enhancement is lost after a high temperature reduction.AbstractИсследовали промотирующее влияние TiO2 на образование CH4 при разложении CH3OH. Продуктами разложения CH3OH являются водород и CO, которые далее могут реагировать, давая CH4. Наблюдали ускорение этой вторичной реакции при использовании TiO2 в качестве носителя. Это ускорение, однако, исчезает после восстановления катализатора при высокой температуре.

Improved Fe 2 O 3 /Al 2 O 3 Systems for the Oxidation of a Model Organic Pollutant Using H 2 O 2 as Oxidant

Fil: Di Luca, Carla. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Centro Cientifico Tecnologico Conicet - Mar del Plata. Instituto de Investigaciones en Ciencia y Tecnologia de Materiales. Universidad Nacional de Mar del Plata. Facultad de Ingenieria. Instituto de Investigaciones en Ciencia y Tecnologia de Materiales; Argentina

Morphology Changes of Supported Rh Particles During Thermal Treatments as Probed by Catalytic Measurements

Summary The effects of oxidation - reduction cycles on the activity and selectivity of supported Rh catalysts were investigated using the hydrogenolysis of methylcyclopentane (MCP) as a test reaction. From the analysis of catalytic properties and reduction profiles it is concluded that, on silica-supported catalysts, following the initial oxidation at 400°C, successive reduction treatments at increasing temperatures cause a progressive reconstruction of the Rh particles. On γ-alumina-supported catalysts the situation is more complex. The interaction of Rh with the support during the initial oxidation makes a fraction of the Rh inaccessible to the gas phase. Only after subsequent oxidation - reduction cycles do they behave like the silica-supported catalysts

Characterization of strong metal-support interaction in Pt/TiO2 catalysts by thermal programmed desorption of benzene

The Pt−TiO2 interaction after HTR was studied by the TPD of benzene. Shifts in desorption temperatures are detected after HTR. They may be ascribed to electronic and morphologic changes.AbstractВзаимодействия на Pt/TiO2 после ВТВ были изучены на примере ТПД бензола. Детектировали смещения температур десорбции после ВТВ. Они приписываются электронным и морфологическим изменениям.