Papers by Author: J.B.L. de Oliveira

Abstract: Because of the unique properties that the system TiO2-ZrO2 has, this system has attracted great interest in catalytic circles. In general, the TiO2-ZrO2 oxides composites have a greater surface area and a stronger acidity when compared to the single oxide and they are used as catalysts supports for many catalytic reactions. This work is to evaluate the effect of calcined temperature in structural and morphological characteristics of Ti_1-xZr_xO₂ nanopowders obtained by Pechini method. For this study, the doping value was 0.25 moles of Zr. The powders were calcined at temperature of 500 to 900°C for one hour. The powders were characterized by XRD, SEM and BET. The X-ray diffraction showed that the powders present a TiO₂ anatase phase and another of ZrO₂ tetragonal. The crystallite size ranged from 4.8 to 14.6 nm for the temperature of 500 to 900°C, respectively. The analysis of scanning electron microscopy showed soft homogeneous agglomerates with particles around 100 nm. The main particles sizes by BET were ranged from 10 to 20 nm, showing that the synthesis is effective to obtain nanometric powders.

Abstract: The aim of this work is to prepare and characterize Al2O3-ZrO2 powders by Pechine method and to evaluate them as supports for palladium catalysts in the selective reduction of NO with CH4. The effect of aluminum ion on the final characteristics of the zirconia powder is also investigated. The catalytic supports were characterized by X-ray diffraction (XDR), scanning electron microscopy (SEM) and catalytic activity. The XRD data showed the formation of tetragonal zirconia phase, with crystallite size of 6.3 and 6.1 nm for the supports prepared with 0.1 and 0.5 moles of Al3+, respectively. Both supports showed porous and homogeneous agglomerates. Pd/Al2O3-ZrO2 catalysts were active NO reduction by CH4.

Abstract: Conventional methods to obtain ceramic powders are inadequate for many technological applications because these powders react but slightly to sinterization, displaying weak reproducibility, nonhomogeneity and imprecise stoichiometric control of cations. Better results can be obtained by chemical synthesis because the powder retains its homogeneity on the atomic scale and may be calcined at low temperatures, yielding fine particulate oxides whose chemistry can be precisely controlled. Therefore, the objective of this work was to obtain the NiAl2O4 phase by the Pechini and combustion reaction methods, and comparatively analyze how these two synthesization methods affect the characteristics of the resulting powder, which was characterized by DRX, MEV and BET. The results revealed that both methods yield nanometric and crystalline NiAl2O4 powder having homogenous particle sizes and shapes. The powder obtained by the Pechini method exhibited agglomerate sizes 60% smaller than those obtained by combustion reaction.