Adeilton P. Maciel

Microstructural and morphological analysis of pure and Ce-doped tin dioxide nanoparticles

Structural and morphological studies in pure and Ce-doped tin dioxide nanoparticles with high stability against particle growth were performed in samples, obtained using the polymeric precursor method and prepared at different annealing temperatures. A Ce-rich surface layer was used to control the particle size and stabilize SnO2 against particle growth. The formation of this segregated layer can contribute to a decreased surface energy, acting in the driving force, or reducing the surface mobility. Only the cassiterite SnO2 phase was observed below 1000 � C and a secondary phase (CeO2) was observed for the Ce-doped SnO2 at temperatures higher than 1000 � C, when de-mixing process occurs. The evolution of crystallite size, microstrain and morphology of the nanoparticles with annealing temperatures was investigated by X-ray diffraction (XRD), associated to Rietveld refinements, X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM). # 2002 Elsevier Science Ltd. All rights reserved.

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 Cue5f8C 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.

Glass transition temperature of hard chairside reline materials after post-polymerisation treatments

OBJECTIVEnThis study evaluated the effect of post-polymerisation treatments on the glass transition temperature (T(g)) of five hard chairside reline materials (Duraliner II-D, Kooliner-K, New Truliner-N, Ufi Gel hard-U and Tokuso Rebase Fast-T).nnnMATERIALS AND METHODSnSpecimens (10 x 10 x 1 mm) were made following the manufacturers instructions and divided into three groups (n = 5). Control group specimens were left untreated. Specimens from the microwave group were irradiated with pre-determined power/time combinations, and specimens from the water-bath group were immersed in hot water at 55 degrees C for 10 min. Glass transition ( degrees C) was performed by differential scanning calorimetry. Data were analysed using anova, followed by post hoc Tukeys test (alpha = 0.05).nnnRESULTSnBoth post-polymerisation treatments promoted a significant (p < 0.05) increase in the T(g) of reline material K. Materials K, D and N showed the lowest T(g) (p < 0.05). No significant difference between T and U specimens was observed.nnnCONCLUSIONnPost-polymerisation treatments improved the glass transition of material Kooliner, with the effect being more pronounced for microwave irradiation.

Gas-phase selective conjugate addition of methanol to acetone for methyl vinyl ketone over SnO2 nanoparticle catalysts

Neste trabalho e apresentada a reacao de condensacao aldolica entre metanol e acetona promovida por nanoparticulas de dioxido de estanho, nao dopadas e dopadas com as terras raras Ce e Y. Diversas condicoes de relacao molar metanol/acetona foram avaliadas, objetivando a obtencao com elevada seletividade do composto a, b-insaturado, metil vinil cetona. As nanoparticulas foram preparadas empregando-se o metodo dos precursores polimericos. As amostras foram caracterizadas por meio de adsorcao de N2 para determinacao de area superficial especifica (BET), difracao de raios X (DRX), adsorcao quimica de CO2, espectroscopia de fotoeletrons (XPS) e microscopia eletronica de transmissao (MET). O comportamento catalitico observado para as amostras de SnO2 sugere que a relacao molar metanol/acetona e a dopagem com as terras raras desempenham um papel importante na atividade catalitica do material e na seletividade aos produtos reacionais. Os resultados de DRX e XPS apontam para a formacao de uma camada de segregacao, para as amostras dopadas, devido ao tratamento termico imposto. Essa camada de segregacao afeta diretamente o comportamento catalitico do material frente a reacao de condensacao.

Processing effects of nanometric rare earth-doped tin oxides on the synthesis of methyl vinyl ketone

Nanoparticle catalysts based on SnO2 were processed by two different methods, víz.the polymeric precursor and high-energy mechanical milling. The sample morphology and catalytic performance in the aldol condensation between methanol and acetone were modified by the processing and rare earth doping.

Nanopartículas catalisadoras suportadas por materiais cerâmicos

This work presents the procedures for preparing SiO2, SnO2 and Al2O3 ceramic materials and also their catalytic properties for the reforming reactions of methane and methanol. The analyses of the carbonaceous residues suggest that the structural modification of the catalyst can minimize the deactivation effect upon them.

FREE GLYCERIN DETERMINATION IN ETHANOL BIODIESEL UTILIZING SPECTROPHOTOMETRIC AND CHROMATOGRAPHIC (GC/FID) METHODS

According to the Resolution number 7 from the Brazilian National Agency of Oil, Natural Gas and Biofuels (ANP), the official methodologies for free glycerin determination in biodiesel are the ASTM D 6584, EN 14105 and EN 14106 methods. However, these procedures are limited to the analysis of free glycerin in methyl esters and they are not suitable for the analysis of esters from lauric oils. In the present work, a gas chromatographic method was developed for the determination of the amount of free glycerin in ethyl esters from lauric oils, aiming at overcoming the limitations present in the official methods. Moreover, the present method can also be used for ethanol and methanol biodiesel samples from other oily sources. Besides, a methodology that ascertains the content of free glycerin by UV-Vis spectrophotometry was also applied. Both methods were sensitive enough to determine the content of free glycerin in biodiesel, below the limit specified by the ANP, fixed at 0.02 % (200 mg/L), achieving the detection limits of 5.69 mg/L and 2.17 mg/L for the chromatographic and spectrophotometric methods, respectively.

Qualitative and Quantitative Chromatographic Methods for Analysis of Glyceroltert-Butylation Reaction Product

This study examined the glycerol tert-butylation reaction products by chromatography. Qualitative analysis by TLC and GC-MS were effective, especially because di-tert-butylglycerols (DTBG) and tri-tert-butylglycerol (TTBG) are not available commercially. In all mass spectra, the GTBE showed ions at m/z 57 and 117, relative to ions of groups tert-butyl [C4H9] + and tert-butoxy-methyl [M-CH3OC(CH3)3] , respectively. The GC-FID method was efficient in the separation of the compounds under study, and had good linearity (Ruf0b30.997), throughout the interval of 0.60 to 15.0mg.mL, 0.24 to 6.0mg.mL and 0.03 to 1.0mg.mL diisobutylene, glycerin and MTBE, respectively.