Mauri José Baldini Cardoso

Zirconia–alumina mixing in alumina-supported zirconia prepared by impregnation with solutions of zirconium acetylacetonate

Materials containing 2–20 wt% zirconia supported on γ-alumina were prepared by multiple step incipient wetness impregnation with solutions of zirconium acetylacetonate in benzene. The materials were calcined at 823 K and were characterised by X-ray diffraction, XPS, DRS in the UV-visible region and FTIR in the regions of OH stretching and skeletal vibrations of adsorbed pyridine. The results demonstrated that the zirconium is present as isolated species at the surface and in the bulk of a mixed zirconia–alumina phase formed by migration of the zirconium ions into the subsurface layers of the support. The presence of zirconia at the alumina surface caused the appearance of basic hydroxyl groups bonded to a single zirconium ion, of weak Lewis acidic sites, probably associated with zirconium sites, and a decrease in concentration of stronger Lewis sites associated with the alumina surface.

O efeito da desativação térmica nas propriedades oxirredutoras e na atividade catalítica de catalisadores CZ e Pd-CZ

Automotive catalyst, using in Brazil since 1992, is a essential technology for vehicular emissions control. Noble metals are the active phase of these catalysts, and cerium zirconium mixed oxides (CZ), responsibles for the oxygen storage capacity (OSC), one of the most important aspect for the operational performance of the catalyst. In this context, the oxireduction properties analysis of CZ and Pd/CZ (palladium supported in CZ) system are the objective of this study, as well as, the impact of the thermal aging in the OSC. Aging consisted of treatments at 900 or 1200 °C, for 12 or 36 h, in oxidizing condition.