Estudo das características morfológicas texturais e estruturais dos catalisadores automotivos, síntese e caracterização de filmes alternativos

Abstract

The structural, morphological and textural changes of new and used automotive catalysts heated at temperatures between 500 and 1000°C were investigated. The catalysts were thermally characterized on simultaneous thermogravimetric and differential thermal analysis (TG-DTA) equipment performed in air and N2. Morphological changes were observed by scanning electron microscopy images. The analysis of SEM images showed that the thermal stabilizing elements in the alumina film on the catalyst presented a dispersed and heterogeneous aspect. About the elementary composition, the spectroscopic analysis by energy dispersive (EDS) evidenced the presence of the rhodium metal (Rh), cerium and zirconium, but the presence of other expected noble metals (Pd and Pt) was not confirmed. The contamination of the used catalyst was confirmed due to the observation of carbon, sulphur, zinc and phosphorus elements. Other complementary techniques such as X-ray diffractometry, helium picnometry and gas adsorption were also used to analyze the structural and textural changes of the catalysts. A significant decrease in the specific surface area of the new catalyst was observed when temperature was increased, indicating a low thermal stability. When the used catalyst was regenerated by heat treatment, an increase on its surface area was observed. Aiming to improve the properties of commercial catalyst, the synthesis of alumina film by sol-gel process using cordierite support also was investigated. Various colloidal dispersions were prepared using as reagents boehmite, -alumina, -alumina and aluminum alkoxide. Only aluminum alkoxide and boehmite were adequate for the adjustment of viscosity and dispersion preparation. Using these dispersions, barium doped alumina films were obtained. Morphological and textural analyses indicated the viability of these films to use in automotive catalysts.