Navegando por Autor "Santos, João Henrique Zimnoch dos"

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Bentonites impregnated with TiO2 for photodegradation of methylene blue
(Elsevier, 2010-05) Rossetto, Enéderson; Petkowicz, Diego Ivan; Santos, João Henrique Zimnoch dos; Pergher, Sibele Berenice Castellã; Penha, Fábio Garcia
Four bentonites and one diatomite from Rio Negro (Argentina) were used as supports for titanium oxide (TiO2). The materials were characterized by X-ray diffraction, scanning electron microscopy, infrared spectroscopy, textural analysis by nitrogen adsorption, elemental analysis and diffuse reflectance spectroscopy. The specific surface areas calculated by the BET method were 76, 46, 80, and 31 for the bentonites and 153 m2/g for diatomite and were not changed by impregnation with TiO2. SEM analysis revealed agglomerates, probably due to titania domains on the surface. The properties of the lamellar materials were maintained after TiO2 impregnation, and all materials showed methylene blue photodegradation activity. The bentonites showed a higher activity than the commercial catalyst P25, likely due to the TiO2 distribution and better accessibility.
Catalytic photodegradation of dyes by in situ zeolite-supported titania
(Elsevier, 2010-04-15) Petkowicz, Diego Ivan; Pergher, Sibele Berenice Castellã; Silva, Carlos Daniel Silva da; Rocha, Zênis Novais da; Santos, João Henrique Zimnoch dos
The degradation of dyes (methylene blue, direct blue 71, direct yellow 8) by a series of titania-supported catalysts generated in situ via the impregnation of TiCl4 onto a series of zeolite, which was synthesized using rice husks as the silicon source, was individually evaluated. After calcination, the resulting supported catalysts were characterized by X-ray diffraction spectrometry, ultraviolet–visible diffuse reflectance spectroscopy, diffuse reflectance and transmittance infrared Fourier transform spectroscopy, energy dispersive X-ray scanning electron microscopy, small angle X-ray scattering and differential pulse voltammetry. The titania generated is present in the anatase phase, without affecting the zeolite framework. Catalyst activity was shown to be comparable to that of the commercial P-25 catalyst after 1 h of UV light exposition. Monitoring the catalyst performance of several batches of material showed that P-25 provided the highest photodecomposition until the third cycle. On the other hand, the activity of the in situ-supported titania catalyst, in spite of showing lower catalytic activity, remained roughly constant up to the fifth cycle. This suggests that the catalyst generated in situ is more suitable for both filtering and reuse.
Effect of textural characteristics of supported metallocenes on ethylene polymerization
(Springer, 2010-01-06) Silveira, Fernando; Brambilla, Rodrigo; Silveira, Nadya Pesce da; Alves, Maria do Carmo Martins; Stedile, Fernanda C.; Pergher, Sibele Berenice Castellã; Santos, João Henrique Zimnoch dos
Catalyst particle size is an important parameter in the polymer industry. A series of supports with different textural properties (silicas prepared by different routes), surface sites (alumino-silicate, silica-zirconia, magnesia-silica supports, and methylaluminoxane-modified silica) and crystallinity (amorphous, lamellar, and crystalline materials) were investigated in the sequential grafting reaction of two metallocene catalysts, Cp2ZrCl2 and (n-BuCp)2ZrCl2, in a 1:3 ratio. The catalyst systems were analyzed by Rutherford backscattering spectrometry, atomic force microscopy, small angle X-ray scattering, extended X-ray absorption fine structure spectroscopy, and nitrogen adsorption. All of the systems were shown to actively polymerize ethylene when methylaluminoxane was used as the cocatalyst. Experimental results are discussed in terms of the relationships between the radius of gyration of secondary particles and catalyst activity. A radius of gyration in the range of 8–9 nm was shown to be associated with higher catalyst activity.
Microporous and mesoporous supports and their effect on the performance of supported metallocene catalysts
(Elsevier, 2010-01-15) Silveira, Fernando Tobias; Alves, Maria do Carmo Martins; Stedile, Fernanda Chiarello; Pergher, Sibele Berenice Castellã; Santos, João Henrique Zimnoch dos
A series of hybrid-supported catalysts was prepared by sequentially grafting Cp2ZrCl2 and (nBuCp)2ZrCl2 (1:3 ratio) onto synthesized silica–zirconia xerogel, alumino-silicates, alumina, chrysotile and commercial MAO (methylaluminoxane)-modified silica. Supported catalysts were characterized by Rutherford backscattering spectrometry, atomic force microscopy, extended X-ray absorption fine structure spectroscopy, X-ray diffraction and nitrogen adsorption. The grafted metal content was between 0.21 and 1.00 wt.% Zr/SiO2 or Zr/Al2O3. All of the systems were shown to be active in ethylene polymerization with methylaluminoxane as the cocatalyst. The catalyst activity and polymer molecular weight depended on the effects of the textural characteristics of the supports on the structure of the generated supported catalyst species. The highest activity in ethylene polymerization (ca. 6560 kgPE molZr−1 h−1) was reached with the supported catalyst using commercial MAO-modified silica and also presented the lowest surface roughness. Correlation between EXAFS data and polymer characteristics was extracted: the production of polyethylenes with higher molecular weight was associated with the reduction in the interatomic Zr–O distance of the supported catalysts, which was shown to be dependent on the nature of the support.

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Navegando por Autor "Santos, João Henrique Zimnoch dos"