1,721,065 research outputs found
NOx photodegradation by nano-TiO2. The role of the structural and morphological features of the material
No full textCatalizzatori di zirconia solfatata (SZ) drogati con Fe e Mn per la reazione di esterificazione dell’acido benzoico
No full textChoosing the best diluent for a fixed catalytic bed : The case of CO hydrogenation
Full text linkFixed bed reactors are frequently used for many catalytic reactions, but the difficult to remove the reaction heat in highly exothermic
reactions can bring to a bad performance of the catalyst or to its fast deactivation. A possible solution is to use diluents, i.e., inactive
ceramic bodies, tailored to mix intimately with the catalyst without affecting the fluid flow through the catalyst bed. The influence of the
use of diluent materials on Fischer–Tropsch synthesis catalyst activity is here fully discussed
Mn3O4 and γ-MnOOH powders, preparation, phase composition and XPS characterisation
No full textThe paper reports data relative to the preparation of Mn3O4 and γ- MnOOH powders by following hydrothermal procedures. The mixed valence spinel was prepared starting either from manganous sulphate or chloride and oxidising in suspension (by either air or oxygen) the alkaline precipitate. Manganite was obtained by oxidising manganous sulphate solutions with H2O2, subsequent alkalisation and refluxing. The samples were characterised for phase composition by X-ray diffraction. Pure phase oxides were obtained in the case of both Mn3O4 and γ-MnOOH when Mn(II) sulphate was used as the precursor. The pure phase samples were submitted to X-ray photoelectron spectroscopy (XPS) investigation, in the case of manganese, for both 2p and 3s spectral regions. The binding energies of the un-fitted experimental Mn peaks compare well with the relative values reported in the literature for the compounds. With the aim of assessing the actual Mn speciation, in the external layers, the fitting procedure of the experimental XPS peaks has been performed by modulating the relative intensities of the spectral components on the grounds of distinct hypotheses consistent with the oxide formulas. The possibility of extending the outcome of this elaboration to the bulk composition of the samples is also discussed.
The paper reports data relative to the preparation of Mn3O4 and γ-MnOOH powders by following hydrothermal procedures. The mixed valence spinel was prepared starting either from manganous sulphate or chloride and oxidizing in suspension (by either air or oxygen) the alkaline precipitate. Manganite was obtained by oxidizing manganous sulphate solutions with H2O2, subsequent alkalization and refluxing. The samples were characterized for phase composition by X-ray diffraction. Pure phase oxides were obtained in the case of both Mn3O4 and γ-MnOOH when Mn(II) sulphate was used as the precursor. The pure phase samples were submitted to X-ray photoelectron spectroscopy (XPS) investigation, in the case of manganese, for both 2p and 3s spectral regions. The binding energies of the un-fitted experimental Mn peaks compare well with the relative values reported in the literature for the compounds. With the aim of assessing the actual Mn speciation, in the external layers, the fitting procedure of the experimental XPS peaks has been performed by modulating the relative intensities of the spectral components on the grounds of distinct hypotheses consistent with the oxide formulas. The possibility of extending the outcome of this elaboration to the bulk composition of the samples is also discussed
Nano-titania assisted photoreduction of Cr (VI) : the role of different TiO2 polymorphs
No full textNanocrystalline TiO2 samples, with controlled phase composition, were obtained by combining reactions in solution with mild hydrothermal or thermal treatments. By using as the starting salt TiCl3, pure phase rutile with crystallite sizes of 6 nm and a BET surface area of 130 m(2) g(-1) was obtained. The photocatalytic activity of the synthesized samples along with that of several commercially available TiO2 samples, was tested for the photoreduction of Cr(VI). The reaction was performed in TiO2 aqueous slurry in the presence of different sacrificial molecules (formic acid (FA), isopropyl alcohol (IPA) and sodium sulphite (SS)). The pH of the reaction (2.5) was defined on the grounds of the energy level of the TiO2 conduction band and of the reduction potential of the Cr(VI)/Cr(III) couple. The reaction kinetics could be described, for all samples, by a pseudo-first order rate equation.
The photocatalytic activity of the anatase-brookite synthesized composite and of the anatase-rutile commercial P25 were found to be the highest (94% at 90 min reaction time). Rutile samples, both synthesized ( = 6 nm) and commercial ( = 93 nm), showed a lower activity with respect to the other samples (around 80% at 90 min reaction time). This occurrence is discussed also on the grounds of diffuse reflectance spectra.
Cr(O) was observed at the surface of TiO2 samples by XPS analyses. Since thermodynamic analysis shows that TiO2 cannot photoreduce Cr(III) to Cr(O), the formation of Cr(O) is attributed to the reducing action of the produced IPA radicals
Ultrasonic activation of TiO2 : physico-chemical properties and photocatalytic activity in the degradation of organic pollutants
No full textTailored nanosized TiO2 for photocatalytic applications and the liquid and in the gas phase
No full textUse of perfluoropolyether coatings to prevent fouling on heat exchanger metal surfaces
No full textFouling on heat-transfer surface in heat exchanger is a hard problem to solve and several methods have been suggested to inhibit the deposition of scale on heat exchangers surfaces ( Malayeri et al., 2009; Müller-Steinhagen et al., 2011). One possibility to reduce or to avoid fouling is the modification of the heat transfer solid surface properties.
The scope of this work is to create a coating on metallic surface in order to avoid any interaction of the metallic surface with harmful precipitates, thus preventing the fouling in heat exchangers. Perfluoropolyethers are used to obtain thin fluorinated layer able to preserve the properties of heat exchanger and, at the same time, make metallic surface hydrophobic. To demonstrate the ability of the hydrophobic coating to prevent fouling, a pilot plant with two identical heat exchangers AEW TEMA TYPE working in parallel at the same operating condition was built. One of them was characterized by the polymeric coating either on internal and external tubes surfaces. A simultaneously monitoring of the heat exchangers made possible to compare the performance of the coated heat exchanger respect to the not coated one. After a six months operation period , obtained experimental results demonstrate a significant increase of heat transfer resistance due to the fouling on the uncoated heat exchanger, respect to the coated one
Ultrasonidos y microondas en la preparacion de catalizadores soportados a base de hierro para la sintesis de Fischer-Tropsch
No full textCatalizadores con un contenido de hierro del 30% en peso, promovidos con K (2,0% en peso) y Cu (3,75% en peso), fueron sintetizados utilizando tres métodos: 1) el método de impregnación tradicional (TR); 2) El método de impregnación tradicional asistido por ultrasonido (US) y 3) El método de impregnación tradicional asistido por microondas (MW). Todas las muestras fueron caracterizadas por BET, XRPD, TG-DTA, FT-IR, TPR, SEM y TEM y evaluadas en una planta de laboratorio para la síntesis de Fischer-Tropsch bajo condiciones de operación de 220oC y 20 bar. Los resultados de la caracterización de los catalizadores indicaron que la morfología de las muestras depende en gran medida del método de preparación. Los mejores resultados en términos de rendimiento (41%) y selectividad hacia los hidrocarburos pesados, fueron obtenidos utilizando las microondas; mientras que en términos de conversión de CO los mejores resultados fueron obtenidos utilizando ultrasonidos (58%). Las muestras preparadas con métodos no tradicionales arrojaron mejores resultados, probablemente debido a una distribución más amplia y uniforme del Fe en el medio durante la fase de síntesis
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