Alcineia C. Oliveira

Structural characterization of highly stable Pt−Ni supported zeolites and its catalytic performance for methane reforming with CO2

Abstract A series of metal supported on dealuminated zeolites were synthesized. XRD, N 2 -adsorption isotherms, acidity measurements and XPS spectroscopy as well as the catalytic activity in CO 2 reforming of methane were used to characterize the solids. The performance measured with the bimetallic nickel and platinum catalysts dispersed on beta zeolite indicate a major improvement in efficient application for dry reforming of methane. It was due to the accessibility and acidity considerably improved upon dealumination. Besides, a high stability of the supports was provided towards hydrogen production due to the physico-chemical properties of the solids.

Nanosized Pt-containing Al2O3 as an efficient catalyst to avoid coking and sintering in steam reforming of glycerol

The action of nanosized Pt-containing Al2O3 catalysts to avoid coking and sintering was studied in steam reforming of glycerol. The solids exhibited almost 100% conversion toward syngas produced at a suitable water to glycerol ratio. Depending on the promoter, a drastic drop in hydrogen yield was observed due to coking and sintering effects. Spent catalyst characterizations by Raman, HRTEM, XRD, TG and SEM-EDS as well as textural property techniques showed that coking, rather than sintering, was the main cause that determined the low hydrogen selectivity of nanosized Pt-containing Al2O3 with La2O3 or ZrO2. In contrast, coking did not cover the active sites of Pt-containing Al2O3 with MgO or CeO2. Thus, steam suppressed carbon deposition and improved the nanosized Pt/MgO–Al2O3 catalyst stability in the steam reforming of glycerol.

Acidic, physico-chemical and catalytic properties of MCM-41 containing transitions metals

In order to explain the acidity of MCM-41 containing transitions metals, chromium and iron were tentatively introduced in MCM-41. The structural features, surface properties as well as the catalytic activity in the isobutane production were evaluated. Chromium or iron were partially introduced in MCM-41 by increasing the acidity of the solid. Both Cr-and Fe-MCM-41 possess relatively weak Bronsted and Lewis acid sites, however, the strength of the acid sites on the Fe or Cr modified sample was significantly increased, indicating that the presence of metals greatly enhances the acidity of the material. The activity of the metals MCM-41 to the isobutane production can be related to the acidity generated by the metals presence.

Temperature and high pressure effects on the structural features of catalytic nanocomposites oxides by Raman spectroscopy.

Structural characterizations of nanostructured oxides were studied by X-ray diffraction (XRD), Raman and infrared spectroscopy. The oxides catalysts namely, SnO2, ZrO2, CeO2, MnOx, Al2O3 and TiO2 were prepared by a nanocasting route and the effect of the temperature and pressure on the stability of the solids was evaluated. Raman spectra showed that ZrO2 and TiO2 exhibited phase transitions at moderate temperatures whereas CeO2, SnO2 and MnOx had an effective creation of defects in their structures upon annealing at elevated temperatures. The results suggested also that the effect of the temperature on the particles growth is related to the type of oxide. In this regard, phase transition by up to 600°C accelerated the sintering of ZrO2 and CeO2 grains compared to TiO2, SnO2 and MnOx counterparts. Under hydrostatic pressures lower than 10GPa, rutile TiO2 and tetragonal ZrO2 exhibited pressure induced phase transition whereas CeO2 and SnO2 were stable at pressures close to 15GPa. The experiments revealed that the nanostructured SnO2 oxide exhibited stable performance at relatively high temperatures without phase transition or sintering, being suitable to be used as catalysts in the range of temperature and pressure studied.

Porous ternary Fe-based catalysts for the oxidative dehydrogenation of ethylbenzene in the presence (absence) of carbon dioxide

Porous ternary Fe-based catalysts were characterized and their catalytic properties through the oxidative dehydrogenation of ethylbenzene in the presence (ODH) or absence (DH) of carbon dioxide were investigated. The catalysts were characterized by X-ray diffraction (XRD), chemical analyses, thermoprogrammed reduction (TPR), physisorption measurements, Raman spectroscopy and scanning electron microscopy coupled to energy-dispersive X-ray spectrometry (SEM-EDX). The kinetic modeling of reverse water gas shift reaction (RWGS) and the effects of reaction parameters, such as reaction temperature and CO2/H2 ratio on the catalytic activity, were also investigated. The addition of Zn, La, Mg or Ni promoters to a porous Fe-based solid greatly enhanced the ODH reaction, whereas that of the RWGS is favoured by Ni promotion. The CO2/H2 = 1 ratio and temperature of 850 K were the best conditions for RWGS occurrence. The implications of these conditions on catalyst application for ODH and DH reactions were discussed. Ethylbenzene conversions were too low due to the decreased textural properties of some catalysts as well as the selectivity to styrene is inhibited. A porous FeAlZn catalyst exhibited higher catalytic performance than the other ternary solids in terms of the ethylbenzene dehydrogenation and resistance against deactivation, whereas low RGWS conversions were observed under the abovementioned conditions.

Influence of the starting materials on the catalytic properties of iron oxides

The effect of iron nitrate, sulfate and chloride on the catalytic properties of hematite toward ethylbenzene dehydrogenation has been studied. Iron nitrate has been the best precursor to prepare the catalysts.

Estudo de casos na formação de professores de química

Case studies were used as teaching methodology in Chemistry teacher education. The reffered methodology consists of teaching principles of Physical Chemistry associated to biodiesel theme in an undergraduate chemistry course with pre-service teachers, who are temporary teachers in high schools in Fortaleza, Ceara, Brazil. The results showed that the methodology was well accepted by the pre-service teachers. The concepts related to Chemistry, by means of multidisciplinary science, technological and social approaches make it able to overcome and improve the present situation in public schools and provided the learning of the chemistry concepts by high school students.

Raman studies of nanocomposites catalysts: temperature and pressure effects of CeAl, CeMn and NiAl oxides

High temperature and pressure effects on the physicochemical properties of binary oxides catalysts were investigated. The nanocomposites catalysts comprising of CeAl, CeMn and NiAl were characterized through various physicochemical techniques. A study of the temperature and pressure induced phenomena monitored by Raman spectroscopy was proposed and discussed. Spectral modifications of the Raman modes belonging to the CeMn suggest structural changes in the solid due to the MnO2 phase oxidation with increasing temperature. The thermal expansion and lattice anharmonicity effects were observed on CeMn due to lack of stability of the lattice vacancies. The CeAl and NiAl composites presented crystallographic stability at low temperatures however, undertake a phase transformation of NiO/Al2O3 into NiAl2O4, mostly without any deformation in its structure with increasing the temperature. It was also inferred that the binary oxides are more stables in comparison with monoxides. Detailed pressure-dependent Raman measurements of the T2g phonon mode of CeMn and NiAl revealed that the pressure contributes to modify bonds length and reduces the particles sizes of the solids. On the contrary, high pressure on CeAl sample improved the stability with addition of Al2O3 in the CeO2 lattice. The results then suggest a good stability of CeAl and NiAl composite catalysts at high pressure and low temperature and show how to prospect of tuning the catalysis for surface reactions entirely through in situ spectroscopic investigations means.

Avaliação de uma proposta contextualizada sobre o ensino de polarimetria nos cursos de farmácia e engenharia de alimentos, na Universidade Federal do Ceará

This work deals with an evaluation of an experimental application about polarimetry for pharmacy and food engineering courses. Foods obtained from the undergraduate students were used for demonstrating multidisciplinary concepts and these concepts were associated to the teaching of polarimetry. According to the results, the benefits of the contextualization are beyond the class and the undergraduating students became interested in control of quality of foods. From these results, it can be concluded that the experimental emphasis given is valid and creates motivation and interest for learning physico-chemistry, in comparison with the traditional methodology applied to teach polarimetry.