Antoninho Valentini

Application of silica gel organofunctionalized with 3(1-imidazolyl)propyl in an on-line preconcentration system for the determination of copper by FAAS.

This study presents a new procedure for the determination of trace levels of copper(II) in an aqueous matrix, through flow injection (FI) on-line preconcentration with a minicolumn packed with silica gel modified with 3(1-imidazolyl)propyl groups. After the preconcentration stage, the analyte was eluted with a HNO(3) solution and determined by flame atomic absorption spectrometry (FAAS). The measurements of the analytical signals were carried out as peak area and peak height with the objective of evaluating the most appropriate absorption measurement for the proposed method. Four procedures to calculate the experimental enrichment factor (EF) were also studied. For a preconcentration time of 90s the enrichment factors found in this study varied between 19.5-25.8 and 36.2-42.2 for peak area and peak height, respectively. The precision of the proposed method was calculated for a solution containing 20mugl(-1) of Cu(II), when 11.2ml of solution was preconcentrated (n=7), and their respective relative standard deviation (R.S.D.) values were 1.2 and 1.4% for peak area and peak height, respectively. The detection limits obtained were 0.4 and 0.2mugl(-1) of Cu(II) for peak area and peak height, respectively, with a preconcentration time of 90s. The on-line preconcentration system accuracy was evaluated through a recovery test on the aqueous samples and analysis of a certified material.

The influence of cation segregation on the methanol decomposition on nanostructured SnO2

Abstract Here we describe a new route to synthesize ultrafine rare earth doped and undoped tin oxide particles for catalytic applications. The catalytic behavior observed in SnO2 samples suggests the control of the catalytic activity and the selectivity of the products by the segregation of a layer of a rare earth compound with the increase of the heat-treatment temperature. The ultrafine particles were characterized by means of BET, XPS, TEM, XRD and Rietveld refinement. It was demonstrated that the effects of the dopant on the methanol decomposition reaction and on the H2 selectivity were correlated with the segregation of a rare earth layer on the tin oxide samples.

Selective synthesis of vinyl ketone over SnO2 nanoparticle catalysts doped with rare earths

Ultrafine particles of tin oxide, doped with the rare earths Ce, Y and La respectively, were prepared using the polymeric precursor method. The novel application of nanostructured tin oxide, undoped and doped, to the CC bond formation of an α,β-unsaturated compound (methyl vinyl ketone; MVK) is presented. The promotion of SnO2 by rare earths results in a large increase in the catalytic activity and basicity (total basic sites). The catalytic behavior observed in SnO2 samples suggests that the control of the catalytic activity and the selectivity of the products takes place by the segregation of a layer of a rare earth compound, with the increase of the heat-treatment temperature. The structural variations of the ultrafine particles were characterized by means of BET, XRD, CO2 chemisorption and Raman.

Influence of Rare Earth Doping on the Structural and Catalytic Properties of Nanostructured Tin Oxide

Nanoparticles of tin oxide, doped with Ce and Y, were prepared using the polymeric precursor method. The structural variations of the tin oxide nanoparticles were characterized by means of nitrogen physisorption, carbon dioxide chemisorption, X-ray diffraction, and X-ray photoelectron spectroscopy. The synthesized samples, undoped and doped with the rare earths, were used to promote the ethanol steam reforming reaction. The SnO2-based nanoparticles were shown to be active catalysts for the ethanol steam reforming. The surface properties, such as surface area, basicity/base strength distribution, and catalytic activity/selectivity, were influenced by the rare earth doping of SnO2and also by the annealing temperatures. Doping led to chemical and micro-structural variations at the surface of the SnO2particles. Changes in the catalytic properties of the samples, such as selectivity toward ethylene, may be ascribed to different dopings and annealing temperatures.

Síntese, caracterização e estudo das propriedades catalíticas e magnéticas de nanopartículas de Ni dispersas em matriz mesoporosa de SiO2

Nickel nanoparticles supported on amorphous silica ceramic matrix were synthesized by the polymeric precursor method. The nanostructure was characterized by NMR, BET, XRD, SEM, TEM, and flame atomic absorption spectrometry techniques. It was observed a dependence of the crystallite size on the thermal annealing, under a N2 atmosphere. The materials presented a high catalytic activity and selectivity upon the b-pinene hydrogenation reaction. The magnetic hystereses were also correlated with the morphology of the processed material.

CO2 mitigation by carbon nanotube formation during dry reforming of methane analyzed by factorial design combined with response surface methodology

Abstract A factorial experimental design was combined with response surface methodology (RSM) to optimize the catalyzed CO2 consumption by coke deposition and syngas production during the dry reforming of CH4. The CH4/CO2 feed ratio and the reaction temperature were chosen as the variables, and the selected responses were CH4 and CO2 conversion, the H2/CO ratio, and coke deposition. The optimal reaction conditions were found to be a CH4/CO2 feed ratio of approximately 3 at 700 °C, producing a large quantity of coke and realizing high CO2 conversion. Furthermore, Raman results showed that the CH4/CO2 ratio and reaction temperature affect the systems response, particularly the characteristics of the coke produced, which indicates the formation of carbon nanotubes and amorphous carbon.

Cu, Fe, or Ni doped molybdenum oxide supported on Al2O3 for the oxidative dehydrogenation of ethylbenzene

Abstract Molybdenum-based catalysts supported on Al 2 O 3 doped with Ni, Cu, or Fe oxide were synthesized and used in ethylbenzene dehydrogenation to produce styrene. The molybdenum oxide was supported using an unconventional route that combined the polymeric precursor method (Pechini) and wet impregnation on commercial alumina. The samples were characterized by X-ray diffraction (XRD), N 2 adsorption-desorption isotherms, temperature-programmed reduction of H 2 (H 2 -TPR), and thermogravimetric (TG) analysis. XRD results showed that the added metals were well dispersed on the alumina support. The addition of the metal oxide (Ni, Cu, or Fe) of 2 wt% by wet impregnation did not affect the texture of the support. TPR results indicated a synergistic effect between the dopant and molybdenum oxide. The catalytic tests showed ethylbenzene conversion of 28%–53% and styrene selectivity of 94%–97%, indicating that the addition of the dopant improved the catalytic performance, which was related to the redox mechanism. Molybdenum oxides play a fundamental role in the oxidative dehydrogenation of ethylbenzene to styrene by its redox and acid–base properties. The sample containing Cu showed an atypical result with increasing conversion during the reaction, which was due to metal reduction. The Ni-containing solid exhibited the highest amount of carbon deposited, shown by TG analysis after the catalytic test, which explained its lower catalytic stability and selectivity.

Catalytic properties of cobalt and nickel ferrites dispersed in mesoporous silicon oxide for ethylbenzene dehydrogenation with CO2

A polymeric precursor method was applied to synthesize catalysts of the general formula MFe2O4 (M = Co and Ni) in order to contribute to studies on ethylbenzene dehydrogenation in the presence of CO2. The catalysts were characterized by TG, H2-TPR, XRD, Mossbauer spectroscopy (MS), N2 adsorption/desorption isotherms and TPD-CO2. Investigations using XRD and MS revealed that the spinel structures of CoFe2O4 and NiFe2O4 phases were formed. The catalytic results suggested that materials with a spinel structure are particularly interesting for ethylbenzene dehydrogenation. Compared to the other catalysts synthesized the sample containing cobalt ferrite showed higher conversion and good styrene selectivity. The analysis of the spent catalyst (DRX) showed that the CoFe2O4 phase was stable under the reaction conditions and that a coke (TG) deposit was more pronounced for the NiFeSi.

ESTUDO MICROESTRUTURAL DO CATALISADOR Ni/γ-Al 2 O 3 - EFEITO DA ADIÇÃO DE CeO 2 NA REFORMA DO METANO COM DIÓXIDO DE CARBONO

The carbon dioxide reforming of methane was carried out over nickel catalysts supported on the g-Al2O3/CeO2 system prepared by wet impregnation. With the increase of the CeO2 weight in the catalyst, a higher stability was observed in the catalytic activity, together with an excellent resistance to carbon deposition and a better Ni dispersion. The catalysts were characterized by means of surface area measurements, TPR, H2 chemisorption, XRD, SEM, EDX, XPS and TEM. An interaction between Ni and CeO2 was observed to the Ni/CeO2 sample after activation in a H2 atmosphere above 300 oC. Such behavior has a significantly influence on the catalytic activity.

Application of Ni:SiO2 nanocomposite to control the carbon deposition on the carbon dioxide reforming of methane.

Stable Ni nanoparticles embedded in a mesoporous silica material were used as catalysts for the conversion of methane into synthesis gas. This catalyst has the singular properties of controlling the carbon deposition and deactivation of active sites. A comparative study of our nanocomposites with conventional catalysts showed that impregnation material presented a preferential encapsulation and growth of carbon nanotubes on the metal surface. The impregnated catalyst showed a higher tendency for carbon nanotube and whiskers formation.