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Investigação de processos colisionais e reacionais para cromo e vanádio em interface de espectrômetro de massa com plasma indutivamente acoplado
(Universidade Federal de São Carlos, 2013-03-14) Salazar, Rodrigo Fernando dos Santos; Nóbrega, Joaquim de Araújo; https://lattes.cnpq.br/8833989058164529; https://lattes.cnpq.br/9370462066771109
The analytical capability of inductively coupled plasma mass spectrometers (ICPMSs) and their wide use in different fields of science are well known. However some drawbacks, such as the occurrence of isobaric and polyatomic interferences and ionic suppression effects are commonly related to this method, mainly for ICP-MSs with quadrupole analyzers (ICP-QMS). Consequently, some elements as Cr and V are negatively affected due to polyatomic interferences caused by Ar, C, Cl, N, O and S species. Along the development of this method, different strategies were proposed such as dynamic reaction cell technologies (DRC) and collision-reaction interface (CRI) in order to correct for these effects. The aim of this thesis was to evaluate the application of CRI and DRC interfaces for polyatomic interferences correction affecting Cr and V determination. Solutions containing from 1000 up to 10000 mg L-1 of C, Cl, N and S were employed in order to evaluate polyatomic formation and correction of their effects with both devices. Helium and H2 were used as collision reaction gases through the skimmer cone in the ICP-QMS-CRI whereas NH3 was introduced into the DRC-ICP-QMS. These solutions contained 5 Sg L-1 of Cr and V. The figures of merit evaluated were: limits of detection (LOD, ng L-1), background equivalent concentration (BEC, ng L-1) and signal-to-background ratio (SBR) for instrument optimization and sample preparation based on microwave-assisted digestion (MAD), microwave induced combustion (MIC) and sample dilution with internal standardization for different samples were investigated. It was observed that the collision and reaction devices employed led to improvements of SBR, BEC and LOD values for Cr and V from 5 to 100-fold when compared with measurements without using either CRI or DRC. However, signal intensities for Cr and V with both devices decreased when compared with signal intensities obtained with pure analytical solutions. Losses of signal intensities were more critical in ICP-QMS-CRI, independently on the gas (20 mL min-1 He or H2), than in DRC-ICP-QMS (0.5 mL min-1 NH3). Consequently, better LOD and BEC values were achieved for DRC than CRI for Cr and V determinations in crude oil samples from three different sources and lubricant oil. Finally, it could be pointed out that both systems presented advantages and disadvantages that will depend on the analytical task but spectral interferences caused by concomitants could be solved using both devices.
Catalisadores de Cu/CeO2 modificados com La aplicados à reação de deslocamento gás-água
(Universidade Federal de São Carlos, 2013-03-14) Silva, Tatiana de Freitas; Assaf, José Mansur; https://lattes.cnpq.br/9563312407691130; https://lattes.cnpq.br/4435205814755218
The water gas shift reaction (WGSR) is often used in industrial processes in order to increase hydrogen production, as well as to remove quantities of CO in the chains produced by steam reforming of hydrocarbons. In this work, CuO/CeO2 and CuO/CeO2-La2O3 catalysts were prepared for application in the watergas shift reaction. The CeO2-La2O3 and CeO2 supports were prepared by three different methods: Hydrothermal (CeO2-La2O3(H) and CeO2 (H)), Co-precipitation (CeO2-La2O3(CP) and CeO2 (CP)) and Sol-gel ( CeO2(SG) and CeO2- La2O3(SG)). The La2O3-CeO2 supports were prepared according to the following molar ratios: 2:1, 1:1 and 1:2 (CeO2-La2O3). The activated catalysts were tested in the water gas shift reaction at temperatures between 150°C and 350°C and the formed products were analyzed by gas chromatography. The CO:H2O molar ratio used in all catalytic tests was 1:5. The catalysts Cu/CeO2(H), CuO/1CeO2-1La2O3(H), CuO/CeO2(CP), CuO/1CeO2-2La2O3(CP) and CuO/CeO2(SG) were also tested at 350°C for 24 hours in the shift reaction under the ideal situation (Reactor Feed: CO, N2 and H2O) to verify their stability. The catalysts CuO/CeO2 (H) and CuO/1CeO2-1La2O3(H) were also tested in the shift reaction under the real situation (Reactor Feed: CO, H2O, N2, H2 and CO2) for performance evaluation in a situation closer to the actual composition of the products observed at the output of industrial reformers. From the results it was observed that the addition of La to the CuO/CeO2 catalyst led to its structural stabilization by preventing the specific area decrease. The addition of La2O3 to the CuO/CeO2 catalysts caused a higher interaction of CuO with the supports, thereby preventing sintering of CuO, even during the reactions. XANES measurements in situ at the Cu edge confirmed the presence of Cu reduced during the course of the reaction, suggesting the presence of Cu sites with similar electron density. XANES spectra at the Ce edge confirmed that there were small changes in the oxidation state of Ce and that Ce species are more oxidized in the catalyst in which La is present. The presence of La probably contributed to higher stabilization of ceria and increased the mobility of oxygen due to vacancy formation in the CeO2 network. Catalysts whose supports were prepared by the hydrothermal method resulted in materials with higher specific area and higher catalytic activities and were more stable with respect to those obtained by the two other methods, during the 24 hours of reaction at 350°C. Therefore, the Cu/CeO2 (H) and Cu/1CeO2-1La2O3(H) catalysts show to be promising as catalysts for the shift reaction. We also observed that the support preparation process affected some properties of the material, such as phase formed, particle size, metallic area, dispersion, surface area and catalytic performance.
Continuidade de atratores para problemas parabólicos semilineares sob perturbações do domínio
(Universidade Federal de São Carlos, 2013-03-14) Samprogna, Rodrigo Antonio; Silva, Karina Schiabel; https://lattes.cnpq.br/2677541143976758; https://lattes.cnpq.br/4957079152385362
In this work we will obtain the continuity of attractors for semilinear parabolic problems with Neumann boundary conditions relatively to perturbations of the domain. We will show that, if the perturbations on the domain are such that the convergence of eingenvalues and eingenfunctions of the Neumann Laplacian is granted then we obtain the upper semicontinuity of the attractors. If, moreover, every equilibrium of the unperturbed problem is hyperbolic we also obtain the continuity of attractors