Estudo da desativação hidrotérmica de catalisadores automotivos comerciais

Abstract

Water vapor is present in vehicular exhaust in significant amounts and may promote a series of thermal phenomena in the operating conditions of the automotive catalyst, reducing its lifetime. Thus, this dissertation aims to study the effects of hydrothermal deactivation in physicochemical and structural properties, and in catalytic performance of three Pd/Rh-based commercial automotive catalysts nominated A, C and E. These systems were subjected to heat treatment at 1000 ° C for 12 hours under three types of gas streams with the following composition: N2, 14% H2O/N2 and 18% H2O/N2. The catalysts characterization consisted of the following techniques: XRF, ICP-OES, TGA-DTA, N2 physisorption, TPD-H2 and TPR. The results obtained for the aged samples showed various phenomena characteristic of thermal degradation like sintering of alumina and CeO2-ZrO2 mixed oxide, alumina phase transitions and mixed oxide demixing. The evaluation of the catalytic activity was based on the reduction of NO by CO and the oxidation of CO and C3H8. For catalysts C and E, the aging process resulted in loss of activity, and results of the catalytic evaluation showed a good correlation with the textural properties and reducibility of these catalysts. On the other hand, the heat treatments activated catalyst A for all reactions. Although the three systems showed good activity in the reduction of NO by CO, the undesirable formation of N2O in significant amounts was observed for all samples, indicating that they lacked selectivity in the examined temperature range